Special Interest Group on Aperiodic Crystals

Update: 31-Dec-2009
Title:: Effect of the "negative chemical" pressure on the temperatures of phase transitions in the TlInS2 layered crystal
Authors:: Seyidov, MHY; Suleymanov, RA; Salehli, F Author Full Names: Seyidov, M. - H. Yu.; Suleymanov, R. A.; Salehli, F.
Source:: PHYSICS OF THE SOLID STATE 51 (12): 2513-2519 DEC 2009
Abstract:: The temperature dependences of the permittivity of TlInS2(1 -x)Se2x solid solutions have been experimentally investigated in the temperature range including the points of structural phase transitions in the solid solutions. It has been established that the isovalent substitution of selenium for sulfur in the anion sublattice of the TlInS2(1 - x)Se2x solid solutions shifts the phase transition temperatures T (i) and T (c) toward the low-temperature range with a simultaneous decrease in the temperature interval of the existence of the incommensurate phase. The T-x phase diagram is constructed for the solid solutions under study and the coordinates are determined for a critical point (of the Lifshitz type) at which the lines T (i) (x) and T (c) (x) converge in the phase diagram. The pattern of the T-x phase diagram for the TlInS2(1 - x)Se2x solid solutions has been analyzed within the phenomenological model of a virtual crystal.
Update: 24-Dec-2009
Title:: Hydriding of Ti45Zr38Ni17-xFex nanocompounds
Authors:: Zywczak, A; Shinya, D; Gondek, L; Takasaki, A; Figiel, H Author Full Names: Zywczak, A.; Shinya, Daigo; Gondek, L.; Takasaki, Akito; Figiel, H.
Source:: SOLID STATE COMMUNICATIONS 150 (1-2): 1-4 JAN 2010
Abstract:: Ti-based quasicrystals belong to the second largest group of the stable quasicrystals, showing attractive properties as hydrogen storage materials. The Ti45Zr38Ni17 intermetallic compound forms an icosahedral (i-phase) structure, in which Ti and Zr atoms possess very good chemical affinity for hydrogen absorption. We modified the Ti45Zr38Ni17 compounds by substituting 3d metals (iron) for Ni to obtain amorphous phase. The samples were produced by mechanical alloying. The 3d metal atoms are located in the same positions as nickel. The structural characterization was made by means of XRD measurements. Thermodynamic properties were studied by differential scanning calorimetry (DSC) and thermal desorption spectroscopy (TDS). The obtained amorphous phases Ti45Zr38Ni(9,13)Fe(8,4) transform to the i-phase at the similar temperature range as Ti45Zr38Ni17. The final concentration of absorbed hydrogen depends on the amount of Fe. When increasing the amount of iron, the hydrogen release temperature becomes lower. After hydriding, the samples decompose into simple metal hydrides. (C) 2009 Elsevier Ltd. All rights reserved.
Title:: MODULATED MAGNETIC STATE OF A NONUNIFORMLY STRAINED IRON BORATE SINGLE CRYSTAL INDUCED BY A MAGNETIC FIELD
Authors:: Boidedaev, SR; Sokolov, BY Author Full Names: Boidedaev, S. R.; Sokolov, B. Yu.
Source:: RUSSIAN PHYSICS JOURNAL 52 (7): 759-762 JUL 2009
Abstract:: A remarkable feature of technical magnetization of a nonuniformly strained iron borate (FeBO3) crystal is long-period spatial modulation of the magnetic order parameter for this weak ferromagnet observed in external magnetic field H-1 <= H <= H-2 [1]. Investigations performed in [1] have demonstrated that the modulated magnetic structure (MMS) of nonuniformly strained FeBO3 arises when the vector. is oriented near a certain reference crystal direction of the easy magnetization (basal) crystal plane. During magnetization in this direction, rotation of the ferromagnetism vector m (or of the antiferromagnetism vector l perpendicular to m by definition) in the basal plane occurs somewhat specifically: after the termination of displacements of the domain boundaries, the single domain structure is first formed in the crystal, and the local vectors m appear oriented along the easy magnetization direction (the uniform low-field phase); then at H = H-1! , the magnetic structure of the crystal changes from the uniform to spatially modulated structure stable for H-1 <= H <= H-2 (the sinusoidal phase); then at H = H-2, the crystal passes once again to the uniform magnetic state with m parallel to H (the uniform high-field phase). The sinusoidal phase has the form of a static transverse spin wave linearly polarized in the basal plane in which the azimuth of the local vector m oscillates about the average magnetization direction. Since the MMS is not observed in FeBO3 without mechanical stresses, the specific feature of magnetization of the examined crystal established in [1] was attributed to the occurrence in its basal plane of additional spatially nonuniform (random) magnetic anisotropy caused by local deformations of the crystal lattice at mechanical stresses. According to models of crystal transition from the uniform to modulated magnetic state suggested in [1], the spatial orientation of the vector m (l) in the sinusoidal magnetic phase is determined by competition between the orienting action of the exchange forces on the local sublattice magnetic moments and the disorienting action of the nonuniform magnetic anisotropy forces. Experimental investigations performed in [1] demonstrated that the MMS was observed at temperatures. T < T-s approximate to 140 K; in the examined temperature interval (90 <= T <= 140 K), the spatial MMS period D remained virtually independent of., but significantly decreased with increasing.. In this case, the direction along which modulation of the azimuth of the vector m (l) is observed is independent of. and.; the amplitude of deviation of the local vector m from the average crystal magnetization direction decreases with increasing. and/or.; the field strengths at which the MMS is observed Delta H = (H-2 - H-1) -> 0 when T -> T-s; transitions low-field uniform phase <-> sinusoidal phase <-> high-field uniform phase are the first-order magnetic phase transitions. The present work analyzes the above-listed main properties and conditions of existence of the MMS in a nonuniformly strained FeBO3 crystal using the model suggested in [1].
Update: 17-Dec-2009
Title:: Origin of the long-wavelength magnetic modulation in Ca3Co2O6
Authors:: Chapon, LC Author Full Names: Chapon, L. C.
Source:: PHYSICAL REVIEW B 80 (17): Art. No. 172405 NOV 2009
Abstract:: The origin of the long-wavelength incommensurate magnetic structure of Ca3Co2O6 is discussed considering possible interchains super-superexchange paths. The experimental value of the propagation vector k=(0,0,Delta) with Delta>1 can be reproduced only if one considers the next-nearest super-superexchange interaction. A spin-dimer analysis using the extended Huckel tight-binding method confirms that, despite longer interatomic Co-Co distances, the latter interaction is indeed much stronger. The stability of the observed structure with respect to certain commensurate states is discussed.
Title:: Magnetic and electronic properties of Eu1-xSrxMnO3 (0.3 < x < 0.7) single crystals
Authors:: Tomioka, Y; Kumai, R; Ito, T; Tokura, Y Author Full Names: Tomioka, Y.; Kumai, R.; Ito, T.; Tokura, Y.
Source:: PHYSICAL REVIEW B 80 (17): Art. No. 174414 NOV 2009
Abstract:: Among versatile perovskite manganites showing colossal magnetoresistance (CMR), Eu1-xSrxMnO3 around x similar to 0.4 shows the ferromagnetic metal with the lowest transition temperature (similar to 40 K) due to the narrowest one-electron bandwidth and hence is readily subject to the drastic phase changes with variations in temperature, magnetic field, and hole doping (x). We have investigated the variation in the electronic state with x with use of single crystals. As x increases, the ferromagnetic metal at 0.38 < x < 0.47 changes to a spin-glasslike insulator at 0.48 < x < 0.5, the layered antiferromagnetic (A-type) state at 0.51 < x < 0.6, and the chained antiferromagnetic (C-type) state at 0.6 < x, respectively. Due to the increased disorder upon alloying of Eu/Sr, the charge/orbital ordering with the modulation vector (0, q, 0) with q=1/2 in the orthorhombic Pbnm setting (a(0)similar to b(0)similar to c(0)/root 2 similar to root 2a(p), a(p) being the lattice parameter of the pseudocubic lattice) cannot be formed in a long range but remains short ranged. In the vicinity of x=0.5, an application of an external magnetic field removes such short-range charge/orbital ordering (q=1/2) to cause an insulator to metal transition or CMR. In a broad range of x (0.55 < x < 0.59), the critical temperature for the layered antiferromagnetic state is relatively lowered and alternatively the charge/orbital ordering with q similar to 1/3 becomes to be visible. It has also been found that the modulation is temperature dependent; commensurate with q similar to 1/3 upon the transition while incommensurate with q>1/3 at low temperatures.
Title:: Transition from spin-density-wave to layered antiferromagnetic state induced by hydrogen as a test for the origin of spin-density waves in chromium
Authors:: Uzdin, VM; Zabel, H; Remhof, A; Hjorvarsson, B Author Full Names: Uzdin, V. M.; Zabel, H.; Remhof, A.; Hjorvarsson, B.
Source:: PHYSICAL REVIEW B 80 (17): Art. No. 174418 NOV 2009
Abstract:: Neutron scattering experiments of Cr/V(001) superlattices are discussed, which show that the incommensurate spin-density-wave (SDW) in thick Cr layers becomes suppressed when the V spacer layers are loaded with hydrogen. The hydrogen loading triggers a transition from the incommensurate SDW state to a commensurate antiferromagnetic state. Model Hamiltonian calculations are presented, which show that this transition is not connected with the nesting property of the Cr Fermi surface. Instead, the transition is a manifestation of the antiferromagnetic ground state of Cr, which is separated from the incommensurate SDW state by an energy barrier. Hydrogen is identified as an effective trigger for reducing the activation barrier, enabling the system to relax to the ground state.
Title:: Mutual enhancement of magnetism and Fulde-Ferrell-Larkin-Ovchinnikov superconductivity in CeCoIn5
Authors:: Mierzejewski, M; Ptok, A; Maska, MM Author Full Names: Mierzejewski, Marcin; Ptok, Andrzej; Maska, Maciej M.
Source:: PHYSICAL REVIEW B 80 (17): Art. No. 174525 NOV 2009
Abstract:: Recent experiments on CeCoIn5 suggest an unusual interplay between superconducting and magnetic orders that gives rise to a multicomponent (magnetosuperconducting) phase. We demonstrate that characteristics of CeCoIn5 make this system particularly well suited for the onset of such a phase. Based on general considerations, we show that superconductivity with nonzero Cooper-pair momentum may lead to an enhancement of the spin-spin response function and, simultaneously, incommensurate spin-density wave may enhance the Cooper-pair susceptibility.
Title:: Incommensurate spin correlation driven by frustration in BiCu2PO6
Authors:: Mentre, O; Janod, E; Rabu, P; Hennion, M; Leclercq-Hugeux, F; Kang, J; Lee, C; Whangbo, MH; Petit, S Author Full Names: Mentre, O.; Janod, E.; Rabu, P.; Hennion, M.; Leclercq-Hugeux, F.; Kang, J.; Lee, C.; Whangbo, M. -H.; Petit, S.
Source:: PHYSICAL REVIEW B 80 (18): Art. No. 180413 NOV 2009
Abstract:: The magnetic properties of BiCu2PO6 have been analyzed by means of magnetic-susceptibility and inelastic neutron-scattering measurements on powder samples by evaluating the spin-exchange interactions on the basis of density-functional calculations and by simulating the inelastic neutron scattering in terms of spin-exchange parameters. BiCu2PO6 exhibits magnetic properties described by the two-leg spin ladder with strong spin frustration along each leg chain and has a gapped quantum singlet ground state with excited magnetic states, showing an incommensurate dispersion arising from frustration.
Title:: Basic Co-rich decagonal Al-Co-Ni: Average structure
Authors:: Strutz, A; Yamamoto, A; Steurer, W Author Full Names: Strutz, Angelica; Yamamoto, Akiji; Steurer, Walter
Source:: PHYSICAL REVIEW B 80 (18): Art. No. 184102 NOV 2009
Abstract:: The two-layer average structure of the high-temperature phase basic Co-rich decagonal Al72.5Co18.5Ni9 was determined based on single-crystal x-ray diffraction data. The five-dimensional (5D) structure model was refined in the noncentrosymmetric 5D space group P10m2 (112 parameters, wR=0.123 and R=0.156 for 957 reflections). The close relationship of the model structure with that of W-Al-Co-Ni, a << 3/2,2/1 >> approximant, is shown.
Title:: Magnetism in CeFeAsO1-xFx and LaFeAsO1-xFx from first principles
Authors:: Sharma, S; Shallcross, S; Dewhurst, JK; Sanna, A; Bersier, C; Massidda, S; Gross, EKU Author Full Names: Sharma, S.; Shallcross, S.; Dewhurst, J. K.; Sanna, A.; Bersier, C.; Massidda, S.; Gross, E. K. U.
Source:: PHYSICAL REVIEW B 80 (18): Art. No. 184502 NOV 2009
Abstract:: Using state-of-the-art first-principles calculations we study the magnetic behavior of CeOFeAs. We find the Ce layer moments oriented perpendicular to those of the Fe layers. An analysis of incommensurate magnetic structures reveals that the Ce-Ce magnetic coupling is rather weak with, however, a strong Fe-Fe and Fe-Ce coupling. Comparison of the origin of the tetragonal to orthorhombic structural distortion in CeOFeAs and LaOFeAs shows marked differences; in CeOFeAs the distortion is stabilized by a lowering of spectral weight at the Fermi level, while in LaOFeAs by increase in Fe spin moment. Finally, we investigate the impact of electron doping upon CeOFeAs and LaOFeAs and show that (a) while in CeOFeAs the ground-state Fe moment remains largely unchanged by doping, the stability of magnetic order goes to zero at a doping that corresponds well to the vanishing of the Neacuteel temperature and, (b) in contrast the LaOFeAs system remains magnetic wit! h a slowly vanishing moment as a function of doping.
Title:: Optimizing the thermoelectric efficiency of icosahedral quasicrystals and related complex alloys
Authors:: Macia, E Author Full Names: Macia, Enrique
Source:: PHYSICAL REVIEW B 80 (20): Art. No. 205103 NOV 2009
Abstract:: In this work we analyze the potential role of quasicrystals and related alloys in thermoelectric material research. Relatively large figure of merit values are expected for those samples exhibiting two properly located narrow features in the density of states close to the Fermi level. It is expected that optimized quasicrystals will perform better at relatively low temperatures, whereas the ZT curve of complex metallic alloys reaches its maximum at high temperatures. Among state-of-the-art quasicrystals most promising samples for thermoelectric applications are found in the AlPd (Mn,Re) system. Quasicrystalline and related approximants in the ScMgCuGa and CaAuIn systems, synthesized on the basis of pseudogap tuning concepts, appear as promising candidates as well.
Title:: Disordered, quasicrystalline and crystalline phases of densely packed tetrahedra
Authors:: Haji-Akbari, A; Engel, M; Keys, AS; Zheng, XY; Petschek, RG; Palffy-Muhoray, P; Glotzer, SC Author Full Names: Haji-Akbari, Amir; Engel, Michael; Keys, Aaron S.; Zheng, Xiaoyu; Petschek, Rolfe G.; Palffy-Muhoray, Peter; Glotzer, Sharon C.
Source:: NATURE 462 (7274): 773-U91 DEC 10 2009
Abstract:: All hard, convex shapes are conjectured by Ulam to pack more densely than spheres(1), which have a maximum packing fraction of phi = pi/root 18 approximate to 0.7405. Simple lattice packings of many shapes easily surpass this packing fraction(2,3). For regular tetrahedra, this conjecture was shown to be true only very recently; an ordered arrangement was obtained via geometric construction with phi = 0.7786 (ref. 4), which was subsequently compressed numerically to phi = 0.7820 (ref. 5), while compressing with different initial conditions led to phi = 0.8230 ( ref. 6). Here we show that tetrahedra pack even more densely, and in a completely unexpected way. Following a conceptually different approach, using thermodynamic computer simulations that allow the system to evolve naturally towards high-density states, we observe that a fluid of hard tetrahedra undergoes a first-order phase transition to a dodecagonal quasicrystal (7-10), which can be compressed to a packing fraction of phi = 0.8324. By compressing a crystalline approximant of the quasicrystal, the highest packing fraction we obtain is phi = 0.8503. If quasicrystal formation is suppressed, the system remains disordered, jams and compresses to phi = 0.7858. Jamming and crystallization are both preceded by an entropy-driven transition from a simple fluid of independent tetrahedra to a complex fluid characterized by tetrahedra arranged in densely packed local motifs of pentagonal dipyramids that form a percolating network at the transition. The quasicrystal that we report represents the first example of a quasicrystal formed from hard or non-spherical particles. Our results demonstrate that particle shape and entropy can produce highly complex, ordered structures.
Title:: Effects of the fourth component and undercooling on morphology of primary Mg-Zn-Y icosahedral quasicrystal phase under normal casting conditions
Authors:: Wang, ZF; Zhao, WM; Hur, BY; Huang, CY; Yu, CQ Author Full Names: Wang Zhifeng; Zhao Weimin; Hur, Bo-Young; Huang Chunying; Yu Chengquan
Source:: CHINA FOUNDRY 6 (4): 293-299 NOV 2009
Abstract:: The paper presents some results of the investigation on effects of the fourth component (Ti, C, Sb or Cu) and undercooling on the morphology, size and forming process of primary Mg-Zn-Y icosahedral quasicrystal phase (I-phase) under normal casting conditions. The result shows that the addition of certain amount of fourth component can transform I-phase morphology from petal-like to spherical. However, I-phase will grow up to petal-like if superfluous addition of the fourth component applied. It is also found that the solidified morphology of I-phase depends on the stability of spherical I-phase during the subsequent growth, and critical radius of maintaining the spherical I-phase interface relatively stable. Further, mini-sized spherical I-phase can be produced with high content of the fourth component by undercooling. Such findings are benefical for industrializing Mg-based quasicrystals.
Update: 11-Dec-2009
Title:: Influence of Boron Additions on Dissipative Properties of Quasicrystalline Al-Cu-Fe Coatings
Authors:: Ustinov, AI; Polishchuk, SS; Telychko, VA; Melnychenko, TV Author Full Names: Ustinov, A. I.; Polishchuk, S. S.; Telychko, V. A.; Melnychenko, T. V.
Source:: METALLOFIZIKA I NOVEISHIE TEKHNOLOGII 31 (6): 847-854 JUN 2009
Abstract:: Influence of boron on mechanical and dissipative properties of quasicrystalline Al-Cu-Fe coatings is studied. As shown, the hardness of coatings based on quasicrystalline Al-Cu-Fe phase under alloying with boron remains practically unchanged, while their fracture toughness slightly increases. At the same time, damping capacity of nanoquasicrystalline coating Al-Cu-Fe-B is found to be essentially lower as compared with that of similar coating without boron. Possible mechanisms of the change in dissipative properties are discussed.
Title:: The commensurate modulated structure of the metastable state in spin crossover complex [Fe(abpt)(2)(NCS)(2)]
Authors:: Sheu, CF; Chen, SM; Wang, SC; Lee, GH; Liu, YH; Wang, Y Author Full Names: Sheu, Chou-Fu; Chen, Szu-Miao; Wang, Shih-Chi; Lee, Gene-Hsiang; Liu, Yi-Hung; Wang, Yu
Source:: CHEMICAL COMMUNICATIONS (48): 7512-7514 2009
Abstract:: Two new polymorphs (C and D) of [t-Fe(abpt)(2)(NCS)(2)] are characterized, a commensurate modulated structure with the c axis tripled in the thermally quenched metastable high spin state at 25 K is found in polymorph C.
Title:: Superplastic Behavior in Mg-Zn-Y Alloy with Dispersed Quasicrystal Phase Particles
Authors:: Somekawa, H; Singh, A; Mukai, T Author Full Names: Somekawa, Hidetoshi; Singh, Alok; Mukai, Toshiji
Source:: ADVANCED ENGINEERING MATERIALS 11 (10): 782-787 OCT 2009
Update: 4-Dec-2009
Title:: Influence of polytypism on structural phase transformations in TlGaSe2 crystals
Authors:: Borovoi, NA; Gololobov, YP; Isaenko, GL; Stepanishchev, NB Author Full Names: Borovoi, N. A.; Gololobov, Yu. P.; Isaenko, G. L.; Stepanishchev, N. B.
Source:: PHYSICS OF THE SOLID STATE 51 (11): 2367-2370 NOV 2009
Abstract:: The polytypism is found to have a significant influence on the structural transformation of the crystal lattice of the TlGaSe2 ferroelectric with variations in temperature. In the 2C-polytype, unlike the C-polytype, a first-order structural phase transition, which leads to a change in the translational symmetry along the C axis, is not observed in the temperature range T = 90-300 K and a second-order phase transition due to the formation of an incommensurate phase occurs at a higher temperature.
Title:: Crossover Induced by Spin-Density-Wave Interference in the Coherence of Singlet Electron Pairs in Cr
Authors:: Robinson, JWA; Halasz, GB; Blamire, MG Author Full Names: Robinson, J. W. A.; Halasz, Gabor B.; Blamire, M. G.
Source:: PHYSICAL REVIEW LETTERS 103 (20): Art. No. 207002 NOV 13 2009
Abstract:: To study the interaction of s-wave superconductivity with spin-density waves (SDWs), we have measured a series of Nb/Cr/Nb Josephson junctions and determined the coherence length xi describing the decay of the critical current with Cr thickness, L. We observe a crossover in xi from approximately 14 nm to 4 nm as L increases to 10 nm, which is consistent with a transition from commensurate to incommensurate SDWs expected for this thickness range.
Title:: Ferroelastic crystals and their nonlinear elastic properties observed in frequency range from gigahertz to milihertz
Authors:: Wiesner, M Author Full Names: Wiesner, Maciej
Source:: PHASE TRANSITIONS 82 (10): 699-754 2009
Abstract:: The experiments reported in this article have been performed to unify the results of earlier and recent determinations of parameters describing the elastic properties of Rb4LiH3(SO4)4, LiCsSO4 (LCS) and KH2PO4 crystals measured by different experimental methods. The above crystals undergo a second-order phase transition, incommensurate phase transition (PT) and a first-order but close to second-order phase transition, respectively. To investigate the elastic properties of the crystals in the frequency range from 10-1 to 1010 Hz, five experimental methods were applied: dynamic mechanical analysis, piezoelectric resonance, composite oscillator bar, ultrasonic wave propagation and Brillouin light scattering. The results of the experiments allowed identification of the processes contributing to the elastic response of the crystals investigated. Moreover, for the LCS crystal a model of the incommensurate PT was presented.
Title:: Quasicrystalline phase formation in the conventionally solidified Al-Cu-Fe system
Authors:: Gogebakan, M; Avar, B; Uzun, O Author Full Names: Gogebakan, M.; Avar, B.; Uzun, O.
Source:: MATERIALS SCIENCE-POLAND 27 (3): 919-926 2009
Abstract:: Structural characteristics and thermal behaviour of the conventionally solidified Al-Cu-Fe alloys with nominal compositions of Al70Cu20Fe10, Al65Cu20Fe15 and Al63Cu25Fe12 were investigated by X-ray diffraction, scanning electron microscopy, and differential thermal analysis techniques. Results show that a single quasicrystalline phase forms in a conventionally solidified Al65Cu20Fe15 alloy, being thermodynamically stable without phase transition up to the melting point. A cubic AlFe(Cu) solid solution, identified as beta phase, and a cubic AlCu(Fe) solid solution, identified as tau phase, were observed with quasicrystalline phase for Al63Cu25Fe12 alloy. Conventional solidification of Al70Cu20Fe10 alloy does not result in quasicrystalline phase formation. However, the formation of quasicrystalline phase in conventionally solidified Al70Cu20Fe10 alloy was observed after additional annealing at elevated temperature. SEM micrographs for Al70Cu20Fe10 and Al63Cu25Fe12 alloys after annealing at 700 degrees C for 4 h revealed the formation of pentagonal dodecahedrons in the quasicrystalline phase, with an edge size of about 30 mu m.
Title:: Monte-Carlo investigation of an anisotropic Ising model
Authors:: Murtazaev, AK; Ibaev, ZG Author Full Names: Murtazaev, A. K.; Ibaev, Zh. G.
Source:: LOW TEMPERATURE PHYSICS 35 (10): 792-796 OCT 2009
Abstract:: The Monte Carlo method is used to study long-period modulated structures in an anisotropic Ising model with competing interactions (ANNNI model). The character, particularities, and dependence of the modulated structures on the temperature and ratio of the exchange interaction constants between the nearest and next-to-nearest neighbors are determined. The phase diagram is constructed. (C) 2009 American Institute of Physics. [doi: 10.1063/1.3253402]
Title:: Lattice Distortion Coupled with Magnetic Ordering in a Triangular Lattice Antiferromagnet CuCrO2
Authors:: Kimura, K; Otani, T; Nakamura, H; Wakabayashi, Y; Kimura, T Author Full Names: Kimura, Kenta; Otani, Tsuyoshi; Nakamura, Hiroyuki; Wakabayashi, Yusuke; Kimura, Tsuyoshi
Source:: JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 78 (11): Art. No. 113710 NOV 2009
Abstract:: We investigated magnetostrictive properties of a triangular lattice antiferromagnet CuCrO2 showing an incommensurate proper-screw spin order by means of x-ray diffraction and strain gauge measurements. A deformation of the triangular lattice plane leading to a lowered crystallographic symmetry was found upon the magnetic ordering, which demonstrates a strong spin-lattice coupling in this system. The resultant multiple structural domains can be successfully arranged by magnetic field cooling procedures. We discuss the relationship between the lattice distortion and incommensurability in CuCrO2.
Title:: Renormalization of Commensurate Magnetic Peak in Ni-Doped La1.85Sr0.15CuO4
Authors:: Matsuura, M; Kofu, M; Kimura, H; Hirota, K Author Full Names: Matsuura, Masato; Kofu, Maiko; Kimura, Hiroyuki; Hirota, Kazuma
Source:: JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 78 (11): Art. No. 114703 NOV 2009
Abstract:: We have studied magnetic excitations in impurity-doped La(1.85)Sr(0.15)Cu(1-y)A(y)O(4) (A = Ni or Zn) by neutron scattering. The dispersion for Zn:y = 0.017 is similar to that for the impurity-free sample: incommensurate peaks with incommensurability delta = 0.12 +/- 0.01 (rlu) do not change their positions up to 21 meV. On the other hand, for Ni:y = 0.029, two incommensurate peaks observed at low energies suddenly change into a single broad commensurate peak at E-cross = 15 meV. Compared with that for the impurity-free sample with a similar Sr concentration of x = 0.16, E-cross for Ni:y = 0.029 is decreased by nearly the same factor as the reduction in T-c. This is very similar to the shift of resonance energy (E-res) in Ni-doped YBa2Cu3O7. These common impurity effects on the shifts of E-cross and E-res suggest the same magnetic origin of the resonance peak in YBa2Cu3O6+x and that of the crossing point of upward and downward dispersions in La2-xSrxCuO4. We propose that the sudden change in the dispersions is better described by a crossover from incommensurate spin fluctuations to a gapped spin wave rather than an hourglass-like dispersion.
Title:: Antiferromagnetic Order and pi-Triplet Pairing in the Fulde-Ferrell-Larkin-Ovchinnikov State
Authors:: Yanase, Y; Sigrist, M Author Full Names: Yanase, Youichi; Sigrist, Manfred
Source:: JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 78 (11): Art. No. 114715 NOV 2009
Abstract:: The anti ferromagnetic Fulde-Ferrell-Larkin-Ovchinnikov (AFM-FFLO) state of coexisting d-wave FFLO superconductivity and incommensurate AFM order is studied on the basis of Bogoliubov-de Gennes (BdG) equations. We show that the incommensurate AFM order is stabilized in the FFLO state by the appearance of the Andreev bound state localized around the zeros of the FFLO order parameter. The AFM-FFLO state is further enhanced by the induced pi-triplet superconductivity (pair density wave). The AFM order occurs in the FFLO state even when it is neither stable in the normal state nor in the BCS state. The order parameters of the AFM order, d-wave superconductivity, and pi-triplet pairing are investigated by focusing on their spatial structures. Roles of the spin fluctuations beyond the BdG equations are discussed. Their relevance to the high-field superconducting phase of CeCoIn5 is discussed.
Title:: Atomic dynamics of a d-AlNiFe decagonal quasicrystal
Authors:: Parshin, PP; Zemlyanov, MG; Panova, GK; Shikov, AA; Brand, RA; Grushko, B Author Full Names: Parshin, P. P.; Zemlyanov, M. G.; Panova, G. Kh.; Shikov, A. A.; Brand, R. A.; Grushko, B.
Source:: JOURNAL OF EXPERIMENTAL AND THEORETICAL PHYSICS 109 (4): 645-651 OCT 2009
Abstract:: The atomic dynamics of an Al71.3Ni24Fe4.7 decagonal quasicrystal has been investigated using the isotopic contrast method for inelastic neutron scattering. The partial vibrational spectra of the Ni, Fe, and Al atoms and the spectrum of the thermal vibrations of the alloy have been reconstructed directly from the experimental data without any model assumptions. The cutoff energies and the positions of the main features of the spectra have been determined. It has been revealed that the average binding energy of the nickel atoms in the quasicrystal under investigation is lower than that of the iron atoms and the vibrational spectrum of the aluminum atoms is noticeably harder than the spectrum of the pure metal. The results obtained for the d-AlNiFe decagonal quasicrystal have been compared with the previously published data for an i-AlCuFe icosahedral quasicrystal.
Update: 26-Nov-2009
Title:: Long-period states of a crystal finite-size-particle system
Authors:: Dmitriev, SV; Potekaev, AI; Samsonov, AV Author Full Names: Dmitriev, S. V.; Potekaev, A. I.; Samsonov, A. V.
Source:: RUSSIAN PHYSICS JOURNAL 52 (6): 622-639 JUN 2009
Abstract:: A one-dimensional model is proposed, which ensures description of origination and main properties of longperiod and incommensurate phases of crystal having complex structure and consists of comparatively rigid "atomic clusters". In the case where reciprocal rotations of theses clusters are considerably large, not only translational but also rotational degrees of freedom have to be taken into account for the clusters. It is consideration of the rotational degrees of freedom which might provide for formation of long-period states and development of a number of physical effects, such as a variety of soliton solutions (of domain walls) and their non-trivial dynamics.
Title:: High-resolution electron microscopy for incommensurate structure of KxRhO2 crystal
Authors:: Yubuta, K; Shibasaki, S; Terasaki, I; Kajitani, T Author Full Names: Yubuta, Kunio; Shibasaki, Soichiro; Terasaki, Ichiro; Kajitani, Tsuyoshi
Source:: PHILOSOPHICAL MAGAZINE 89 (31): 2813-2822 2009
Abstract:: An incommensurate, (3 + 2)- dimensional structure is locally observed in a K0.49RhO2 crystal synthesized by the flux growth method. The averaged potassium to rhodium ratio of the grown crystals was determined as 0.49 using an electron probe microanalyzer operated in the wave dispersive spectroscopy mode. The potassium content of the incommensurate phase was determined as 0.25 by the transmission electron microscopy-energy dispersive spectroscopy method. Satellite reflections of an incommensurate phase having two modulation vectors, q(1)* = 0.15a(o)* + 0.21b(o)* and q(2)* = -0.21a(o)* + 0.36b(o)* (a(o) is the unit cell for a gamma-NaxCoO2-type structure), are indexed successfully. High-resolution electron microscopy (HREM) images show dark streaks running parallel in the a-b plane. The separations and directions of the dark streaks have a close relationship between the q-vector of satellite spots. A HREM image taken with the electron beam parallel to [100] direction shows planer clusters between CdI2-type RhO2 layers. These clusters correspond to the intercalated potassium ions.
Title:: Plastic analysis of crack problems in three-dimensional icosahedral quasicrystalline material
Authors:: Li, W; Fan, TY; Wu, YL Author Full Names: Li, Wu; Fan, Tian You; Wu, Yun Long
Source:: PHILOSOPHICAL MAGAZINE 89 (31): 2823-2831 2009
Abstract:: Due to their complexity, the basic plastic properties of all quasicrystalline materials are essentially unknown [M. Feuerbacher, C. Thomas, K. Urban, Plastic behaviour of quasicrystalline materials, in Quasicrystals: Structure and Physical Properties, H.R. Trebin, ed., Wiley/VCH, Berlin, 2003]. Plastic deformation of cracks in icosahedral quasicrystals have been analyzed in a strict and systematic form and the crack tip opening displacement (CTOD) and size of the plastic zone around the crack tip was determined exactly. CTOD is suggested as a parameter of plastic fracture for quasicrystalline materials. The present work may also provide a novel methodology for plastic analysis of quasicrystals.
Title:: Octahedral tilt twinning and compositional modulation in NaLaMgWO6
Authors:: King, G; Garcia-Martin, S; Woodward, PM Author Full Names: King, Graham; Garcia-Martin, Susana; Woodward, Patrick M.
Source:: ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 65: 676-683 Part 6 DEC 2009
Abstract:: A combination of selected-area electron diffraction (SAED), neutron powder diffraction (NPD) and high-resolution transmission electron microscopy (HRTEM) reveals a complex superstructure in the ordered perovskite NaLaMgWO6. Through indexing of SAED patterns the unit-cell dimensions are found to be 46.8 x 7.8 x 7.9 angstrom, which corresponds to a 12a(p) x 2a(p) x 2a(p) superstructure of the simple Pm (3) over barm perovskite unit cell. HRTEM images reveal the formation of an unmistakable stripe contrast that repeats with the same periodicity. Doubling of the b and c axes is brought about by a combination of layered ordering of Na and La, rock-salt ordering of Mg and W, and octahedral tilting. The a axis repeat distance results from a one-dimensional twinning of the octahedral tilts in combination with a compositional modulation. Modeling of the NPD pattern shows that the underlying tilt system is a(-)a(-)c(0) with tilt angles of similar to 8 degrees about the a and b axes. The octahedral tilt-twin boundaries run perpendicular to the a axis and are separated by 6a(p). Simulated HRTEM images show that octahedral tilt twinning alone cannot explain the stripes seen in the HRTEM images, rather a compositional modulation involving the A-site cations is necessary to explain the experimental images.
Update: 19-Nov-2009
Title:: A One-Dimensional Metal Embedded in Salt Matrices: Synthesis, Modulated Crystal Structures, Electrical Conductivity, and Chemical Bonding of (1)(infinity)[PdBi6][(Bi,Sn)(1-delta)Br5-delta,]
Authors:: Wahl, B; Kloo, L; Ruck, M Author Full Names: Wahl, Bernhard; Kloo, Lars; Ruck, Michael
Source:: ZEITSCHRIFT FUR ANORGANISCHE UND ALLGEMEINE CHEMIE 635 (12): 1979-1985 2009
Abstract:: The metal-rich compounds (1)(infinity)[PdBi6][(Bi,Sn)(1-delta)Br5-delta,] with delta(1) = 2/13, delta(1)' = 5/26, or delta(2) = delta(2)' = 2/12 were synthesized from Bi2Pd, BiBr3, and Sn at 300 degrees C. The crystal structures contain intermetallic rods (1)(infinity)[Pd@Bi2/1Bi8/2](2.5+) embedded in salt-like matrices, which consist of groups of bromido-bismuthate(III)-stannate(II) octahedra [(Bi,Sn)(n)Br4n+2](m-) (n = 2, 3) and isolated Br- ions. Metrical incompatibilities of the two subsystems in the crystalline metal-salt hybrid result in non-stoichiometry of the salt pan associated with complex superstructures. The average structure is described in the orthorhombic space group Pmmm with a approximate to 408 pm, b approximate to 2263 pm, c approximate to 849 pm. It feigns statistical distribution of vacancies and orientational disorder of the concatenated octahedra. By choosing the modulation vectors q(i) = 2/ta* + 1/2b* + 1/2c* with t(1) = 13 or t(2) = 12, the additional weak reflections of the diffraction patterns are indexed. Ordered structure models are achieved in the [3+1]-dimensional superspace group Pmmm(alpha 1/21/2)000. Metallic conductivity along [100], i.e. the direction of the (1)(infinity)[Pd@Bi2/1Bi8/2](2.5+) rods, was determined for a single-crystal. One-dimensional band structure calculations reveal Bi p-bands crossing the Fermi level for formula charges higher than 2+. The electron localization indicator (ELI) indicates two-center Bi-Bi bonds as well as multi-center bonds inside the metallic part, whereas the bismuth l one-pairs point towards the non-conducting part of the structure.
Title:: Quasiparticles of Spatially Anisotropic Triangular Antiferromagnets in a Magnetic Field
Authors:: Kohno, M Author Full Names: Kohno, Masanori
Source:: PHYSICAL REVIEW LETTERS 103 (19): Art. No. 197203 NOV 6 2009
Abstract:: The spectral properties of the spin-1/2 Heisenberg antiferromagnet on an anisotropic triangular lattice in a magnetic field are investigated using a weak-interchain-coupling approach combined with exact solutions of a chain. Dominant modes induced by interchain interactions in a magnetic field behave as quasiparticles which show distinctive features such as anomalous incommensurate ordering and high-energy modes. In terms of them, various unusual features observed in the anisotropic triangular antiferromagnet Cs2CuCl4 in a magnetic field are quantitatively explained in a unified manner.
Title:: The uniaxially aperiodic structure of a thin Cu film on fivefold i-Al-Pd-Mn
Authors:: Pussi, K; Gierer, M; Diehl, RD Author Full Names: Pussi, K.; Gierer, M.; Diehl, R. D.
Source:: JOURNAL OF PHYSICS-CONDENSED MATTER 21 (47): Art. No. 474213 NOV 25 2009
Abstract:: A thin film of copper on the fivefold surface of Al-Pd-Mn forms a structure that is uniaxially commensurate with the aperiodic structure of the substrate. This structure has been analyzed using low-energy electron diffraction and is found to consist of a vicinal surface of a body-centered tetragonal (bct) (100) structure. This bct(100) structure has lattice parameters of a = 2.88 angstrom, b = 2.55 angstrom and c = 2.88 angstrom, with the vicinal surface making an angle alpha of 13.28 degrees relative to the a-b plane. This structure provides an explanation for the delayed ordering observed during the growth of the film. Simple conditions are derived for which the growth of ordered one-dimensionally quasiperiodic thin films on quasicrystals may be favorable. This finding is relevant to the use of quasicrystals as a means of matching interfaces in thin film systems.
Title:: Synthesis of the quasi-crystalline phase in Al63Cu25Fe12 powders prepared by mechanical alloying
Authors:: Avar, B; Gogebakan, M Author Full Names: Avar, B.; Gogebakan, M.
Source:: JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS 11 (10): 1460-1463 OCT 2009
Abstract:: This work investigated the quasicrystalline phase formation during heat treatment in the Al63Cu25Fe12 alloy prepared via mechanical alloying, starting from pure elemental powders. The mechanical alloying process was performed at a speed of 300 rpm for times up to 70 hours. The structural evolution of the mechanically alloyed Al63Cu25Fe12 powders at different stages of milling was examined by X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. The present results showed that mechanical alloying of the Al63Cu25Fe12 alloy did not result in the quasicrystalline icosahedral phase (i-phase). The long time milling resulted in the formation of an AlFe(Cu) solid solution identified as the beta-phase. In order to examine the structural changes with annealing temperature, the mechanically alloyed powders were heat treated at 600, 700 and 800 degrees C for 4 hours under vacuum. However, the formation of a quasicrystalline phase in the Al63Cu25Fe12 alloy was observed after additional annealing at elevated temperature. In the present work, quasicrystalline phase formation in both the as-milled and heat-treated powders is discussed in detail.
Title:: Minerals as advanced materials
Authors:: Depmeier, W Author Full Names: Depmeier, W.
Source:: CRYSTAL RESEARCH AND TECHNOLOGY 44 (10): 1122-1130 Sp. Iss. SI OCT 2009
Abstract:: A resume is given on relationships between minerals and materials. It is shown that Nature has many advantages over technology which can be profitably exploited for finding new materials with useful properties. However, Nature has also inherent limitations. Therefore, it seems advisable to use the knowledge of minerals as a treasure which can be tapped for getting inspired on the way to finding new materials. Several examples are given, including those of zorite/ETS-4/ETS-10, boracites, zircon, kesterite, a natural quasicrystal, opals, ultramarine and mayenite.
Update: 13-Nov-2009
Title:: AlCoNi quasicrystal sphere growth experiment from a metallic solution
Authors:: Meisterernst, G; Bauer, B; Gille, P Author Full Names: Meisterernst, Goetz; Bauer, Birgitta; Gille, Peter
Source:: ZEITSCHRIFT FUR KRISTALLOGRAPHIE 224 (10): 471-477 2009
Abstract:: Crystal growth studies starting from spherical surfaces of single crystals can reveal morphological features that cannot be obtained in usual growth experiments. Especially, facets of a greater variety of crystallographic forms may occur that are otherwise hidden by the slowest growing faces which dominate the crystal's morphology. We did a sphere growth experiment with a decagonal Al72Co9Ni19 quasicrystal prepared from a large single-grain sample formerly grown using the Czochralski method from an off-stoichiometric melt. By heating the polished crystalline half-sphere to a temperature slightly higher than its own growth temperature a thin liquid layer of self-flux formed. A partial evaporation of Al being the solvent of this system caused re-crystallisation at the surface of the quasicrystalline sphere. After several times repeating this process at further increasing temperatures, tiny faces of four different crystallographic forms developed. By using an optical goniometer and electron scanning microscopy indexing of these facets was possible. With the only exception of the decagonal prism {10000} they had not been observed so far in contact to the melt. The results are discussed with respect to the inclined net plane concept established by Steurer and Cervellino [Acta Cryst. A57 (2001) 333-340]. The experimental approach is not specific to sphere growth studies of quasicrystals but can be applied to other high-temperature solution growth systems as well.
Title:: Atomic coexistence of superconductivity and incommensurate magnetic order in the pnictide Ba(Fe(1-x)Cox)(2)As-2
Authors:: Laplace, Y; Bobroff, J; Rullier-Albenque, F; Colson, D; Forget, A Author Full Names: Laplace, Y.; Bobroff, J.; Rullier-Albenque, F.; Colson, D.; Forget, A.
Source:: PHYSICAL REVIEW B 80 (14): Art. No. 140501 OCT 2009
Abstract:: As-75 nuclear magnetic resonance (NMR) and susceptiblity were measured in a Ba(Fe1-xCox)(2)As-2 single crystal for x=6%. NMR spectra and relaxation rates allow to show that all Fe sites experience an incommensurate magnetic ordering below T=31 K. Comparison with undoped compound allows to estimate a typical moment of 0.05 mu(B). Anisotropy of the NMR widths can be interpreted using a model of incommensurability with a wave vector (1/2-epsilon,0, l) with epsilon of the order of 0.04. Below T-C=21.8 K, a full volume superconductivity develops as shown by susceptibility and relaxation rate, and magnetic order remains unaffected, demonstrating coexistence of both states on each Fe site.
Title:: Coexistence of incommensurate magnetism and superconductivity in Fe(1+y)SexTe(1-x)
Authors:: Khasanov, R; Bendele, M; Amato, A; Babkevich, P; Boothroyd, AT; Cervellino, A; Conder, K; Gvasaliya, SN; Keller, H; Klauss, HH; Luetkens, H; Pomjakushin, V; Pomjakushina, E; Roessli, B Author Full Names: Khasanov, R.; Bendele, M.; Amato, A.; Babkevich, P.; Boothroyd, A. T.; Cervellino, A.; Conder, K.; Gvasaliya, S. N.; Keller, H.; Klauss, H. -H.; Luetkens, H.; Pomjakushin, V.; Pomjakushina, E.; Roessli, B.
Source:: PHYSICAL REVIEW B 80 (14): Art. No. 140511 OCT 2009
Abstract:: We have studied the superconducting and magnetic properties of Fe1+ySexTe1-x single crystals (0 <= x <= 0.5) by magnetic susceptibility, muon-spin rotation, and neutron diffraction. We find three regimes of behavior: (i) commensurate magnetic order for x less than or similar to 0.1, (ii) bulk superconductivity for x similar to 0.5, and (iii) a range x approximate to 0.25-0.45 in which superconductivity coexists with incommensurate magnetic order. The results are qualitatively consistent with two-band mean-field models in which itinerant magnetism and extended s-wave superconductivity are competing order parameters.
Title:: Transition from turbulent to nearly laminar vortex flow in superconductors with periodic pinning
Authors:: Gutierrez, J; Silhanek, AV; Van de Vondel, J; Gillijns, W; Moshchalkov, VV Author Full Names: Gutierrez, J.; Silhanek, A. V.; Van de Vondel, J.; Gillijns, W.; Moshchalkov, V. V.
Source:: PHYSICAL REVIEW B 80 (14): Art. No. 140514 OCT 2009
Abstract:: We revisit the vortex dynamics in Al thin films containing an artificial periodic array of antidots by means of electrical transport measurements. We clearly identify a turbulent to laminarlike vortex flow transition which manifests itself as a negative differential resistivity. This transition is accompanied by a strong irreversibility in the voltage-current characteristics. The dynamical phase diagrams obtained as a function of commensurability, temperature, and driving force are in good agreement with the early predictions by Reichhardt et al. [Phys. Rev. Lett. 78, 2648 (1997)] based on molecular dynamic simulations.
Title:: Lattice dynamics and external magnetic-field effects in Ni-Fe-Ga alloys
Authors:: Perez-Landazabal, JI; Recarte, V; Sanchez-Alarcos, V; Rodriguez-Velamazan, JA; Jimenez-Ruiz, M; Link, P; Cesari, E; Chumlyakov, YI Author Full Names: Perez-Landazabal, J. I.; Recarte, V.; Sanchez-Alarcos, V.; Rodriguez-Velamazan, J. A.; Jimenez-Ruiz, M.; Link, P.; Cesari, E.; Chumlyakov, Y. I.
Source:: PHYSICAL REVIEW B 80 (14): Art. No. 144301 OCT 2009
Abstract:: Precursor phenomena were investigated in a Ni-Fe-Ga alloy close to the stoichiometric Heusler composition Ni2FeGa. In particular, the phonon-dispersion curves, the diffuse scattering and the magnetic properties of a single crystalline Ni51.5Fe21.5Ga27 alloy were measured as a function of temperature. The TA(2) branch along the [110] direction of the L2(1) phase shows a significant phonon softening around xi = 0.35 resulting in a marked dip which becomes more pronounced as the temperature decreases. Diffuse neutron-scattering measurements performed along [(xi) over bar xi 0] direction around Bragg reflections also reveal the presence of small satellite peaks at xi = 0.33 whose intensity increases on approaching the martensitic transformation temperature. Both elastic and inelastic-scattering anomalies confirm the occurrence of premartensitic phenomena in Ni-Fe-Ga alloys. The influence of an external magnetic field (6 T) on the anomalous phonon is shown to be negli! gible and just a small shift of the transformation temperature takes place because of the magnetic field.
Title:: Thermal entanglement of spin chains with quantum critical behavior
Authors:: Zvyagin, AA Author Full Names: Zvyagin, A. A.
Source:: PHYSICAL REVIEW B 80 (14): Art. No. 144408 OCT 2009
Abstract:: Results for the characteristics of the macroscopic thermal entanglement for integrable spin-1/2 antiferro-magnetic chain models with multispin interactions in the thermodynamic limit are presented. Such interactions cause quantum-phase transitions to incommensurate phases with partial spontaneous magnetization. We have derived exact equations, which determine the thermal and magnetic field behavior of the concurrence of spin chains. The analysis of these equations shows that there exists a critical temperature, below which the thermal entanglement of considered spin chains is nonzero. We have shown that at those quantum-phase transitions, caused by multispin interactions, the thermal entanglement is reduced. Also, we have shown that the thermal entanglement is reduced due to nonzero magnetization of spin chains in the ground state, caused by multispin interactions.
Title:: Observation of strong magnetoelastic coupling in a first-order phase transition of CrOCl
Authors:: Angelkort, J; Wolfel, A; Schonleber, A; van Smaalen, S; Kremer, RK Author Full Names: Angelkort, Joachim; Woelfel, Alexander; Schoenleber, Andreas; van Smaalen, Sander; Kremer, Reinhard K.
Source:: PHYSICAL REVIEW B 80 (14): Art. No. 144416 OCT 2009
Abstract:: The phase transition of CrOCl toward a state of antiferromagnetic order below T-N=13.5 K has been identified as a first-order phase transition. The transition is accompanied by a lattice and structural distortion toward a twofold, 2b nuclear superstructure with a-axis unique monoclinic symmetry, as evidenced by temperature-dependent x-ray diffraction experiments. Magnetic-susceptibility and magnetization measurements indicate a transition with strong magnetoelastic coupling to a uniaxial antiferromagnet with ordered moments along c. A second transition is discovered at T-c approximate to 27.2 K that is presumably of purely magnetic origin and might indicate the formation of an incommensurate magnetic superstructure. The different behaviors of TiOCl, VOCl, and CrOCl are the result of the different symmetries of the filled 3d orbitals, which lead to different exchange interactions on the MO double layers of these isostructural compounds.
Title:: Formation of a well ordered ultrathin aluminum oxide film on icosahedral AlPdMn quasicrystal (vol 76, 094203, 2007)
Authors:: Longchamp, JN; Burkardt, S; Erbudak, M; Weisskopf, Y Author Full Names: Longchamp, J. -N.; Burkardt, S.; Erbudak, M.; Weisskopf, Y.
Source:: PHYSICAL REVIEW B 80 (14): Art. No. 149901 OCT 2009
Title:: Field suppression of the modulated phase of Ce2Pd2Sn
Authors:: Berisso, MG; Sereni, JG; Braghta, A; Schmerber, G; Chevalier, B; Kappler, JP Author Full Names: Gomez Berisso, M.; Sereni, J. G.; Braghta, A.; Schmerber, G.; Chevalier, B.; Kappler, J. P.
Source:: PHYSICA B-CONDENSED MATTER 404 (19): 2930-2933 OCT 15 2009
Abstract:: Low temperature magnetic (M) and thermal (C-p) properties of the intermetallic compound Ce2Pd2Sn have been investigated at zero and different magnetic fields. Two transitions were recognized at T-C = 2.1 K and T-M = 4.8 K, with latter nearly coinciding with the extrapolated Curie-Weiss temperature theta(p) = 4.5 K. The Curie factor evaluated from T >= T-M, is approximate to 2 mu(B) The positive value of theta(p), the triangular coordination of the magnetic (Ce) atoms and the weak effect of applied magnetic field, reveal that T-M cannot be considered as a canonic antiferromagnetic transition like claimed in the literature. M(T) measurements under moderate magnetic fields (0 <= B <= 2.5 kOe) show T-C(B) increasing while T-M(B) is practically not affected. Both transition merge in a critical point at T-cr = (4.3 +/- 0.3)K for B-cr = (2.1 +/- 0.3)kOe, where the intermediate phase is suppressed. At T-C = 2.2 K, the cusp of a first order transition is observed in C-p(T). According to the proposed ferromagnetic ground state, it is followed by a C-p(T)alpha T(3/2)exp(-E-g/T) dependence, with a gap of anisotropy E-g approximate to 7 K. (C) 2009 Elsevier B.V. All rights reserved.
Title:: Antiferromagnetic structure in UNiAl at dilution temperatures
Authors:: Prokes, K; Bruck, E; Sechovsky, V Author Full Names: Prokes, K.; Bruck, E.; Sechovsky, V.
Source:: PHYSICA B-CONDENSED MATTER 404 (19): 3025-3027 OCT 15 2009
Abstract:: Neutron diffraction experiments in zero field reveals that the originally sine-wave-modulated antiferromagnetic structure in UNiAl starts to square-up at low temperatures. The squaring-up is, however, not completed even at 150 mK, most probably due to competing magnetic interactions. The fact that the magnetic moments are not equal at all the uranium atomic sites is responsible at least partially for the enhanced low-temperature-specific heat coefficient observed in UNiAl at low temperatures. (C) 2009 Elsevier B.V. All rights reserved.
Title:: Resonant X-ray scattering study of Ca3Co2O6 ground state: Preliminary results of magnetic field effects
Authors:: Mazzoli, C; Bombardi, A; Agrestini, S; Lees, MR Author Full Names: Mazzoli, C.; Bombardi, A.; Agrestini, S.; Lees, M. R.
Source:: PHYSICA B-CONDENSED MATTER 404 (19): 3042-3044 OCT 15 2009
Abstract:: We present resonant magnetic X-ray scattering (RMXS) measurements in an applied magnetic field on a single crystal of Ca3Co2O6. We focus our attention on the transition from an incommensurate partially disordered antiferromagnetic state to a ferrimagnetic state: a lock-in and a divergence of the magnetic correlation length at the transition shed light on the nature of the ground state and on the c-axis vs. in-plane exchange couplings in this system. (C) 2009 Elsevier B.V. All rights reserved.
Title:: Magnetic properties of the t-J model at low doping
Authors:: Falb, J; Neto, MBS; Muramatsu, A Author Full Names: Falb, J.; Silva Neto, M. B.; Muramatsu, A.
Source:: PHYSICA B-CONDENSED MATTER 404 (19): 3075-3078 OCT 15 2009
Abstract:: A path-integral for the t-J model in two dimensions is constructed based on Dirac quantization, with an action found originally by Wiegmann [Phys. Rev. Lett. 60 (1988) 821; Nucl. Phys. B 323 (1989) 311]. Concentrating on the low doping limit, we assume short range anti ferromagnetic order of the spin degrees of freedom. Going over to a local spin quantization axis of the dopant fermions that follows the spin degree of freedom, staggered CP1 fields result and the constraint against double occupancy can be resolved. The staggered CP1 fields are split into slow and fast modes, such that after a gradient expansion, and after integrating out the fast modes and the dopant fermions, a CP1 field-theory with a massive gauge field is obtained that describes generically incommensurate coplanar magnetic structures, as discussed previously in the context of frustrated quantum anti ferromagnets. The analysis of Landau damping shows that in this case, even in the presence of doping, the dynamical critical exponent z = 1. as a consequence of coupling of the dopant holes to a spin current, as opposed to a spin density. This result agrees with experimental observations in the underdoped region of high temperature superconductors, and departs from the one obtained by Hertz and Millis (z = 2) in the case of spin density waves in the Hubbard model. (C) 2009 Elsevier B.V. All rights reserved.
Title:: X-ray resonant scattering study of the magnetic phase diagram of multiferroic TbMnO3
Authors:: Walker, HC; Ewings, RA; Fabrizi, F; Mannix, D; Mazzoli, C; Wilkins, SB; Paolasini, L; Prabhakaran, D; Boothroyd, AT; McMorrow, DF Author Full Names: Walker, H. C.; Ewings, R. A.; Fabrizi, F.; Mannix, D.; Mazzoli, C.; Wilkins, S. B.; Paolasini, L.; Prabhakaran, D.; Boothroyd, A. T.; McMorrow, D. F.
Source:: PHYSICA B-CONDENSED MATTER 404 (19): 3264-3266 OCT 15 2009
Abstract:: We present the magnetic phase diagram of multiferroic TbMnO3 for H parallel to b determined using X-ray resonant scattering at the Tb L-3-edge. Investigations of two different magnetic domains, C-type and F-type, demonstrate very similar behaviour in high applied magnetic fields, with a low temperature incommensurate to commensurate transition at H similar or equal to 4.5T, concurrent with the polarisation flop observed in bulk magnetoelectric measurements. (C) 2009 Elsevier B.V. All rights reserved.
Title:: Effect of Nonmagnetic Substituents Mg and Zn on the Phase Competition in the Multiferroic Antiferromagnet MnWO4
Authors:: Meddar, L; Josse, M; Deniard, P; La, C; Andre, G; Damay, F; Petricek, V; Jobic, S; Whangbo, MH; Maglione, M; Payen, C Author Full Names: Meddar, Lynda; Josse, Michael; Deniard, Philippe; La, Carole; Andre, Gilles; Damay, Francoise; Petricek, Vaclav; Jobic, Stephane; Whangbo, Myung-Hwan; Maglione, Mario; Payen, Christophe
Source:: CHEMISTRY OF MATERIALS 21 (21): 5203-5214 NOV 10 2009
Abstract:: The effects of substituting nonmagnetic Ma(2+) and Zn2+ ions for the Mn2+ (S = 5/2) ions oil the structural, magnetic, and dielectric properties of the multiferroic frustrated antiferromagnet MnWO4 were investigated Polycrystalline samples of Mn1-xMgxWO4 and Mn1-xZnxWO4 (0 <= x <= 0.3) solid Solutions were prepared via a solid-state route and characterized via X-ray and neutron diffraction, magnetization, and dielectric permittivity measurements. Mg and Zn substitutions result in very similar effects The Neel temperature (T-N), the AF3-to-AF2 magnetic phase-transition temperature (T-2), and the critical ferroelectric temperature (T-c = T-2) of MnWO4 are reduced upon nonmagnetic doping. At the lowest temperature (T = 1.5 K), the incommensurate magnetic Structure for x(Mg) = 0 15 and v(Zn) = 0.15 corresponds to either a sinusoidal spin arrangement or an elliptical spin-spiral phase similar to the polar AF2 structure observed in MnWO4 These findings were discussed by considering the effects of the Mg and Zn Substitutions oil the crystal lattice and on the spin exchange network of MnWO4.
Update: 5-Nov-2009
Title:: Crossover from incommensurate to commensurate magnetic orderings in CoCr2O4
Authors:: Chang, LJ; Huang, DJ; Li, WH; Cheong, SW; Ratcliff, W; Lynn, JW Author Full Names: Chang, L. J.; Huang, D. J.; Li, W-H; Cheong, S-W; Ratcliff, W.; Lynn, J. W.
Source:: JOURNAL OF PHYSICS-CONDENSED MATTER 21 (45): Art. No. 456008 NOV 11 2009
Abstract:: The conical spin order of multiferroic CoCr2O4 has been studied by a neutron diffraction to investigate its magnetic phase transitions at temperatures below 40 K. Magnetic order of a spiral spin component with an incommensurate propagation vector of (0.63, 0.63, 0) was observed at 26 K, while at 14.5 K, the incommensurate conical spin order showed a transition into the fixed commensurate propagation vector of (2/3, 2/3, 0). In addition, two satellite peaks with propagation vectors of (0.035, 0, 0) and (0, 0.035, 0) from the commensurate vector were observed. The widths of these peaks indicate a long-range magnetic order. This new magnetic configuration below 14.5 K may lead to a new model of multiferroic behavior differing from the well-known spin-current model for magnetic ferroelectricity.
Update: 29-Oct-2009
Title:: Electronic Self-Organization in the Single-Layer Manganite Pr1-xCa1+xMnO4
Authors:: Ye, F; Chi, SX; Fernandez-Baca, JA; Moreo, A; Dagotto, E; Lynn, JW; Mathieu, R; Kaneko, Y; Tokura, Y; Dai, PC Author Full Names: Ye, F.; Chi, Songxue; Fernandez-Baca, J. A.; Moreo, A.; Dagotto, E.; Lynn, J. W.; Mathieu, R.; Kaneko, Y.; Tokura, Y.; Dai, Pengcheng
Source:: PHYSICAL REVIEW LETTERS 103 (16): Art. No. 167202 OCT 16 2009
Abstract:: We use neutron scattering to investigate the doping evolution of the magnetic correlations in the single-layer manganite Pr1-xCa1-xMnO4, away from the x = 0.5 composition where the CE-type commensurate antiferromagnetic (AF) structure is stable. We find that short-range incommensurate spin correlations develop as the system is electron doped (x < 0.5), which coexist with the CE-type AF order. This suggests that electron doping in this system induces an inhomogeneous electronic self-organization, where commensurate AF patches with x = 0.5 are separated by electron-rich domain walls with short-range magnetic correlations. This behavior is strikingly different than for the perovskite Pr1-xCaxMnO3, where the long-range CE-type commensurate AF structure is stable over a wide range of electron or hole doping around x = 0.5.
Title:: Low temperature thermodynamical properties of ErCu2Si2
Authors:: Baran, S; Gondek, L; Szytula, A; Kaczorowski, D; Pikul, A; Penc, B; Piekarz, P; Hoser, A; Gerischer, S Author Full Names: Baran, S.; Gondek, L.; Szytula, A.; Kaczorowski, D.; Pikul, A.; Penc, B.; Piekarz, P.; Hoser, A.; Gerischer, S.
Source:: JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 322 (1): 12-18 JAN 2010
Abstract:: ErCu2Si2 crystallises in the tetragonal ThCr2Si2-type crystal structure. In this paper results of magnetometric, electrical transport, specific heat as well as neutron diffraction are reported. Results of electrical resistivity and specific heat measurements performed at low temperature yield existence of magnetic ordering roughly at 1.3 K. These results are in concert with neutron diffraction measurements, which reveal simple antiferromagnetic ordering between 0.47 and 1.00 K. At temperatures ranging from 1.00 up to 1.50K an additional incommensurate magnetic structure was observed. The propagation vector kappa = (0;0;0.074) was proposed to describe magnetic reflections within the amplitude modulated magnetic structure. Basing on specific heat studies the crystal field levels splitting scheme and magnetic entropy were calculated. (C) 2009 Elsevier B.V. All rights reserved.
Title:: Competing magnetic structures in the DySi FeB-type phase diagram
Authors:: Schobinger-Papamantellos, P; Rodriguez-Carvajal, J; Ritter, C; Buschow, KHJ Author Full Names: Schobinger-Papamantellos, P.; Rodriguez-Carvajal, J.; Ritter, C.; Buschow, K. H. J.
Source:: JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 322 (1): 119-132 JAN 2010
Abstract:: The temperature magnetic phase diagrams, of the dimorphic DySi compound, have been studied in terms of wave vectors in the range 1.5-45 K, by neutron diffraction. The polycrystalline sample consists of 26% of CrB-type (Cmcm no. 63, all atoms at 4c site: (0, y, 1/4)) and of 74% of FeB-type (Pnma no. 62, all atoms at 4c site: (x, 1/4, z)). The CrB-ordering is described by the wave vector: q(1) = (0, 0, 1/2) over the entire magnetically ordered regime with a uniaxial magnetic structure along the shortest axis c. The FeB-type magnetic phase diagram reveals three distinct regions of magnetic ordering below T-N and one first order transition at T-2=23.5K (on heating). The ordering is described by two symmetry independent magnetic vectors q(2)=(0, 1/2,1/6) and q(3)=(0, q(3y), q(3z)) with a temperature variable length. At 1.5 K q(3y) approximate to 1/2 and q(3z) approximate to 1/11. The two phases coexist in the form of domains. They differ in the moment orientation of the q(3) phase that deviates by similar to 22 degrees from the b-axis in the (0, 0, 1) plane. The low temperature range (LT) 1.5 K-T-2 subdivides into two regions: (i) LT-1, between 1.5 K-T-1 where the relative amount of the two phases remains unchanged and in (ii) LT-2: T-1-T-2 where the amount of the incommensurate q3 phase increases at the cost of the commensurate q(2) amplitude modulated structure which remains unchanged but fully disappears at the first order transition at T-2=23.5 K. The q(3) phase undergoes minor changes until 22 K and gets destabilised at T-2 where the q(3z) component jumps from the LT value q(3z) approximate to 1/11 to the HT value approximate to 1/7 and the q(3y) component increases from 0.484(1) to 0.495(1). (iii) The high temperature (HT) range T-2-T-N (T-N=40 +/- 1 K) is described by a single wave vector q(3). The disproportionation of the HT magnetic phase q(3) below T-2 into two coexisting distinct phases q(2), q(3) down to 1.5 K is an unusual phenomenon, to our knowledge observed for the first time. Various mechanisms are discussed. (C) 2009 Elsevier B.V. All rights reserved.
Title:: Self-similar transformation and quasi-unit cell construction of quasi-periodic structure with twelve-fold rotational symmetry
Authors:: Liao, LG; Fu, H; Fu, XJ Author Full Names: Liao Long-Guang; Fu Hong; Fu Xiu-Jun
Source:: ACTA PHYSICA SINICA 58 (10): 7088-7093 OCT 2009
Abstract:: The structural properties of a quasicrystal model with twelve-fold rotational symmetry are studied. We correct the errors in the self-similar transformation of the square-rhombus-hexagon tiling model proposed by Socolar. Based on the Stampfli-Gahler square-rhombus-triangle tiling model, the quasi-unit cell is successfully constructed, which can describe the dodecagonal quasiperiodic structure by the covering theory.
Title:: Measurement of anisotropy thermopower of decagonal AlCuCo quasicrystal
Authors:: Fan, ZJ; Geng, XW; Kong, WJ; Jin, YR Author Full Names: Fan Zhen-Jun; Geng Xue-Wen; Kong Wen-Jie; Jin Yi-Rong
Source:: ACTA PHYSICA SINICA 58 (10): 7119-7123 OCT 2009
Abstract:: The thermopower of decagonal AlCuCo quasicrystal was measured in the periodic and quasiperiodic direction by laser heating alternating current measurement method in the temperature range of from 300 K to 1200 K. We found that the thermopower is negative in the periodic direction and positive in the quasiperiodic direction. The thermopower hopps at 1123 K (850 degrees C) along the periodic direction. The change of the thermopower is not monotonic at high temperature. The measurement method we used is sensitive to the phase transition point.
Title:: Multiresolution of quasicrystal diffraction spectra
Authors:: Elkharrat, A; Gazeau, JP; Denoyer, F Author Full Names: Elkharrat, Avi; Gazeau, Jean-Pierre; Denoyer, Francoise
Source:: ACTA CRYSTALLOGRAPHICA SECTION A 65: 466-489 Part 6 NOV 2009
Abstract:: A method for analyzing and classifying two-dimensional pure point diffraction spectra (i.e. a set of Bragg peaks) of certain self-similar structures with scaling factor beta > 1, such as quasicrystals, is presented. The two-dimensional pure point diffraction spectrum Pi is viewed as a point set in the complex plane in which each point is assigned a positive number, its Bragg intensity. Then, by using a nested sequence of self-similar subsets called beta-lattices, we implement a multiresolution analysis of the spectrum Pi. This analysis yields a partition of Pi simultaneously in geometry, in scale and in intensity (the 'fingerprint' of the spectrum, not of the diffracting structure itself). The method is tested through numerical explorations of pure point diffraction spectra of various mathematical structures and also with the diffraction pattern of a realistic model of a quasicrystal.
Update: 22-Oct-2009
Title:: Magnetic Properties of Multiferroics Bi(1-x)A(x)FeO(3-x/2) (A = Ca, Sr, Pb, Ba)
Authors:: Troyanchuk, IO; Mantytskaya, OS; Chobot, AN; Tereshko, NV Author Full Names: Troyanchuk, I. O.; Mantytskaya, O. S.; Chobot, A. N.; Tereshko, N. V.
Source:: PHYSICS OF THE SOLID STATE 51 (10): 2105-2108 OCT 2009
Abstract:: The magnetic properties of Bi(1-x)A(x)FeO(3-x/2) (A is an alkaline-earth ion) solid solutions have been studied in magnetic fields of up to 140 kOe. The ferroelectric phase (space group R3c) transforms into the nonpolar pseudocubic phase at x approximate to 0.2. It is demonstrated that the substitution of alkaline-earth ions for bismuth ions (x >= 0.1) leads to a complete destruction of the modulated antiferromagnetic structure and the appearance of a weakly ferromagnetic state within the R3c state. In the pseudocubic phase, the spontaneous magnetization is absent; however, the field dependence of the magnetization is nonlinear and depends on the magnetic prehistory.
Title:: MATERIALS SCIENCE Quasicrystals from nanocrystals
Authors:: van Blaaderen, A Author Full Names: van Blaaderen, Alfons
Source:: NATURE 461 (7266): 892-893 OCT 15 2009
Title:: Quasicrystalline order in self-assembled binary nanoparticle superlattices
Authors:: Talapin, DV; Shevchenko, EV; Bodnarchuk, MI; Ye, XC; Chen, J; Murray, CB Author Full Names: Talapin, Dmitri V.; Shevchenko, Elena V.; Bodnarchuk, Maryna I.; Ye, Xingchen; Chen, Jun; Murray, Christopher B.
Source:: NATURE 461 (7266): 964-967 OCT 15 2009
Abstract:: The discovery of quasicrystals in 1984 changed our view of ordered solids as periodic structures (1,2) and introduced new long-range-ordered phases lacking any translational symmetry(3-5). Quasi-crystals permit symmetry operations forbidden in classical crystallography, for example five-, eight-, ten-and 12-fold rotations, yet have sharp diffraction peaks. Intermetallic compounds have been observed to form both metastable and energetically stabilized quasicrystals (1,3,5); quasicrystalline order has also been reported for the tantalum telluride phase with an approximate Ta1.6Te composition(6). Later, quasicrystals were discovered in soft matter, namely supramolecular structures of organic dendrimers(7) and tri-block copolymers(8), and micrometre-sized colloidal spheres have been arranged into quasicrystalline arrays by using intense laser beams that create quasi-periodic optical standing-wave patterns(9). Here we show that colloidal inorganic nanoparticles can self-assemble into binary aperiodic superlattices. We observe formation of assemblies with dodecagonal quasicrystalline order in different binary nanoparticle systems: 13.4-nm Fe2O3 and 5-nm Au nanocrystals, 12.6-nm Fe3O4 and 4.7-nm Au nanocrystals, and 9-nm PbS and 3-nm Pd nanocrystals. Such compositional flexibility indicates that the formation of quasicrystalline nanoparticle assemblies does not require a unique combination of interparticle interactions, but is a general sphere-packing phenomenon governed by the entropy and simple interparticle potentials. We also find that dodecagonal quasicrystalline superlattices can form low-defect interfaces with ordinary crystalline binary superlattices, using fragments of (3(3).4(2)) Archimedean tiling as the 'wetting layer' between the periodic and aperiodic phases.
Title:: Magnetic structures of quaternary intermetallic borocarbides RCo2B2C (R = Dy, Ho, Er)
Authors:: ElMassalami, M; Moreno, R; Takeya, H; Ouladdiaf, B; Lynn, JW; Freitas, RS Author Full Names: ElMassalami, M.; Moreno, R.; Takeya, H.; Ouladdiaf, B.; Lynn, J. W.; Freitas, R. S.
Source:: JOURNAL OF PHYSICS-CONDENSED MATTER 21 (43): Art. No. 436006 OCT 28 2009
Abstract:: The magnetic structures of the title compounds have been studied by neutron diffraction. In contrast to the isomorphous RNi2B2C compounds, wherein a variety of exotic incommensurate modulated structures has been observed, the magnetic structure of ErCo2B2C is found to be a collinear antiferromagnet with k = (12, 0, 12) while those of HoCo2B2C and DyCo2B2C are observed to be simple ferromagnets. For all studied compounds, the moments are found to be confined within the basal plane and their magnitudes are comparable to the values obtained from the low-temperature isothermal magnetization measurements. The absence of modulated magnetic structures in the RCo2B2C series (for ErCo2B2C, verified down to 50 mK) is attributed to the quenching of the Fermi surface nesting features.
Title:: A comparative study of the magnetic properties of the 1/1 approximant Ag50In36Gd14 and the icosahedral quasicrystal Ag50In36Gd14
Authors:: Wang, P; Stadnik, ZM; Al-Qadi, K; Przewoznik, J Author Full Names: Wang, P.; Stadnik, Z. M.; Al-Qadi, K.; Przewoznik, J.
Source:: JOURNAL OF PHYSICS-CONDENSED MATTER 21 (43): Art. No. 436007 OCT 28 2009
Abstract:: We report on measurements of the dc and ac magnetic susceptibility, Gd-155 Mossbauer spectra, and specific heat of the 1/1 approximant Ag50In36Gd14, and of the ac magnetic susceptibility of the icosahedral quasicrystal Ag50In36Gd14. These alloys are shown to be spin glasses. For the icosahedral quasicrystal Ag50In36Gd14, spin freezing occurs at T-f = 4.3 K, and the frequency dependence of T-f is well accounted for by the Vogel-Fulcher and power laws. Spin freezing in the 1/1 approximant Ag50In36Gd14 occurs in two stages: at T-f1 = 3.7 K, Gd spins develop short-range correlations but continue to fluctuate, and then long-range freezing is achieved at T-f2 = 2.4 K. The frequency dependences of T-f1 and T-f2 can be accounted for by means of the Vogel-Fulcher law and the critical slowing down dynamics. It is shown that the spin freezing in both alloys is a nonequilibrium phenomenon rather than a true equilibrium phase transition. The Gd-155 Mossbauer spectra of the 1/1 approximant Ag50In36Gd14 confirm that the Gd spins are frozen at 1.5 K and are fluctuating at 4.6 K. The magnetic specific heat exhibits a maximum at a temperature that is 30% larger than T-f1, but the temperature derivative of the magnetic entropy peaks at T-f1. The Debye temperature of the 1/1 approximant Ag50In36Gd14 is 199(1) K as determined from the Mossbauer data, and 205(2) K as determined from the specific heat data.
Title:: Processing and characterization of rapidly quenched Ti-based alloys: Influence of solidification rate on the as-quenched structures
Authors:: Lefaix, H; Vermaut, P; Janickovic, D; Svec, P; Portier, R; Prima, F Author Full Names: Lefaix, H.; Vermaut, P.; Janickovic, D.; Svec, P.; Portier, R.; Prima, F.
Source:: JOURNAL OF ALLOYS AND COMPOUNDS 483 (1-2): 168-172 AUG 26 2009
Abstract:: >From technological viewpoint. icosahedral Ti-Zr-Ni phase may give challenging opportunities as novel hydrogen storage and hydride battery. Nevertheless. from the structural standpoint, the phase selection criterion as function of solidification route remains unclear. A series of Ti45Zr38Ni17 alloys, known to provide stable and well-ordered quasicrystals, was produced by planar flow casting using different processing parameters. From structural characterization, it appears that, at high cooling rate, i.e. high wheel speeds, or for the highest temperature of the melt, the as-quenched sample exhibits a mixture of nanoscale P and amorphous phases. The icosahedral phase precipitates when decreasing the wheel speed, from lower temperatures of the melt or after annealing a crystallized amorphous matrix. The reproducible formation of quasicrystals, observed in the amorphous matrix containing P particles, corroborates the competition between icosahedral and body-centered cubic (bcc) phases during the solidification process. These results are promising since it could be possible to control volume fractions of these two phases by choosing well-fitted thermal treatments so that quasicrystals mechanical properties should be improved by dispersion of a stable bcc phase. (C) 2008 Elsevier B.V. All rights reserved.
Title:: Multi-scaled polymer-based composite materials synthesized by mechanical alloying
Authors:: Kaloshkin, SD; Vandi, LJ; Tcherdyntsev, VV; Shelekhov, EV; Danilov, VD Author Full Names: Kaloshkin, S. D.; Vandi, L. -J.; Tcherdyntsev, V. V.; Shelekhov, E. V.; Danilov, V. D.
Source:: JOURNAL OF ALLOYS AND COMPOUNDS 483 (1-2): 195-199 AUG 26 2009
Abstract:: Multi-scaled composite materials are of great importance, because they exhibit higher mechanical properties than those attained using conventional fillers or polymer blends. In this work, multi-scaled composite materials based on ultra-high-molecular weight polyethylene (UHMWPE), quasicrystals, polyimide and bronze are investigated for use in the moving parts of machines, gears, bearings, and sliding elements. The main object is to investigate the process of fabricating such composite materials, and to check if these materials are reproducible and reliable to an industrial extent. The specimens were prepared using a high-energy planetary mill. When milled with bronze, the quasicrystalline phase was dissolved into an intermetallic solid solution: milling with polymers showed to conserve the quasicrystalline phase, whereas the crystallization of UHMWPE was achieved during the milling process. Tribological study of consolidated samples showed an increase in the wear resistance for the bronze-containing composite materials. in comparison with pure UHMWPE, the polyimide-based specimen exhibited higher strength and hardness. This work has demonstrated the possibility of producing composite materials with acceptable and reliable properties using the mechanical alloying technology. (C) 2008 Elsevier B.V. All rights reserved.
Title:: Nanostructure controlling in Zr-based metallic glasses using icosahedral local structure
Authors:: Saida, J; Kato, H; Setyawan, AD; Yoshimi, K; Inoue, A Author Full Names: Saida, J.; Kato, H.; Setyawan, A. D.; Yoshimi, K.; Inoue, A.
Source:: JOURNAL OF ALLOYS AND COMPOUNDS 483 (1-2): 231-234 AUG 26 2009
Abstract:: Glass-nano(quasi)crystal composite materials based on Zr-Al-Ni-Cu metallic glasses have been synthesized by controlling the nucleation and growth rates of the precipitated phase correlated with a unique icosahedral local structure. It is well known that the Zr65Al7.5Ni10Cu17.5 metallic glass has a high glass-forming ability (GFA), which enables us to produce the glassy sample with a bulky shape. Controlling a substitution of QC-forming elements such as noble metals with Cu and annealing condition, the nanoscale icosahedral quasicrystalline phase (I-phase) with various grain sizes and nucleus densities can be formed. Moreover, we have succeeded to control the nano-QC phase nucleation by changing the atmosphere pressure during casting, which results in the formation of new bulk metallic glasses (BMGs). These nanoscale structure and nucleation controlling techniques in BMGs bring a significant improvement of mechanical properties such as high strength and good ductility. (C) 2008 Elsevier B.V. All rights reserved.
Title:: Characterization of phases in complex metallic alloys Al73Mn27-xFex (x=2, 4 and 6)
Authors:: Priputen, P; Kusy, M; Kriska, M; Lipka, R; Illekova, E; Svec, P; Bursik, J; Svoboda, M; Dolinsek, J; Janovec, J Author Full Names: Priputen, P.; Kusy, M.; Kriska, M.; Lipka, R.; Illekova, E.; Svec, P.; Bursik, J.; Svoboda, M.; Dolinsek, J.; Janovec, J.
Source:: INTERMETALLICS 17 (12): 1047-1051 DEC 2009
Abstract:: The characterization of phases in Al73Mn27-xFex (x = 2, 4 and 6) alloys was performed using X-ray diffraction, differential thermal analysis, and scanning electron microscopy enabling energy dispersive X-ray spectroscopy. Both the annealed and the thermally cycled states were studied. In the annealed states the occurrence of T-phase was expected, however it was confirmed for alloys Al73Mn25Fe2 and Al73Mn23Fe4 only. The annealing of the Al73Mn21Fe6 alloy probably led to the formation of decagonal quasicrystal (D). The T- and D-phases were found to be unstable at low temperatures. In the states after DTA the low temperature Al-11(Mn,Fe)(4) and gamma(2) phases were observed in the Al73Mn25Fe2 and Al73Mn21Fe6 alloys, while only the former phase was observed in the Al73Mn23Fe4 alloy. (C) 2009 Elsevier Ltd. All rights reserved.
Title:: Structure Determination of Two Modulated gamma-Brass Structures in the Zn-Pd System through a (3+1)-Dimensional Space Description
Authors:: Gourdon, O; Izaola, Z; Elcoro, L; Petricek, V; Miller, GJ Author Full Names: Gourdon, Olivier; Izaola, Zunbeltz; Elcoro, Luis; Petricek, Vaclav; Miller, Gordon J.
Source:: INORGANIC CHEMISTRY 48 (20): 9715-9722 OCT 19 2009
Abstract:: The structure determination of two composite compounds in the Zn-Pd system with close relationships to the cubic gamma-brass structure Zn11-delta Pd2+delta is reported. Their structures have been solved from single crystal X-ray diffraction data within a (3 + 1)-dimensional [(3 + 1)D] formalism. Zn75.7(7)Pd24.3 and Zn78.8(7)Pd21.2 crystallize with orthorhombic symmetry, superspace group Xmmm(00 gamma)0s0 (X [(1/2,1/2,0,0); (0,1/2,1/2,1/2); (1/2,0,1/2,1/2)]), with the following lattice parameters, respectively: a(s) = 12.929(3) angstrom, b(s) = 9.112(4) angstrom, c(s) = 2.5631(7) angstrom, q = 8/13 c* and V-s = 302.1(3) angstrom(3) and a(s) = 12.909(3) angstrom, b(s) = 9.115(3) angstrom, c(s) = 2.6052(6) angstrom, q = 11/18 c* and V-s = 306.4(2) angstrom(3). Their structures may be considered as commensurate because they can be refined in the conventional 3D space groups (Cmce and Cmcm, respectively) using supercells, but they also refined within the (3 + 1)D formalism to residual factors R = 3.14% for 139 parameters and 1184 independent reflections for Zn75.7(7)Pd24.3 and R = 3.16% for 175 parameters and 1804 independent reflections for Zn78.8(7)Pd21.2. The use of the (3 + 1)D formalism improves the results of the refinement and leads to a better understanding of the complexity of the atomic arrangement through the various modulations (occupation waves and displacive waves). Our refinements emphasize a unique Pd/Zn occupancy modulation at the center of distorted icosahedra, a modulation which correlates with the distortion of these polyhedra.
Title:: Nanoquasicrystalline Al-Fe-Cr-based alloys. Part I: Phase transformations
Authors:: Galano, M; Audebert, F; Stone, IC; Cantor, B Author Full Names: Galano, M.; Audebert, F.; Stone, I. C.; Cantor, B.
Source:: ACTA MATERIALIA 57 (17): 5107-5119 OCT 2009
Abstract:: Nanoquasicrystalline Al-Fe-Cr-based alloys composed of sub-micro-sized icosahedral quasicrystalline particles embedded in alpha-Al matrix have a higher strength at elevated temperature compared with commercial Al alloys. However, further improvement of the microstructural stability is desirable in order to maximize the elevated temperature strength. A detailed study of the effect on the microstructure and the phase transformations by the addition of Ti, V, Nb or Ta to a ternary Al-93(Fe3Cr2)(7) alloy was carried out using heat treatment and microstructural characterization. The addition of the fourth element leads to a refined microstructure and can stabilize the icosahedral topology, delaying the quasicrystalline icosahedral phase decomposition until a higher temperature is reached. The addition of Nb or Ta enabled a greater stabilization effect than the addition of Ti or V, retaining a microstructure similar to the as-spun state after heat treatment between 450 and 550 degrees C and even retaining icosahedral particles up to 550 degrees C. The outstanding microstructural stabilization obtained with addition of Nb or Ta leads to very promising applications in the automotive and aeronautic industries. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Update: 15-Oct-2009
Title:: Nonmetallic Nature of the Interrelation of Thermal, Magnetic, and Electrical Properties in Icosahedral Quasicrystals at High Temperatures
Authors:: Prekul, AF; Shchegolikhina, NI; Nazarova, SZ; Edagawa, K Author Full Names: Prekul, A. F.; Shchegolikhina, N. I.; Nazarova, S. Z.; Edagawa, K.
Source:: PHYSICS OF METALS AND METALLOGRAPHY 108 (2): 120-124 AUG 2009
Abstract:: In the icosahedral phase of Al-Cu-Fe alloys in the temperature range above 300 K there has been found an interrelation between the heat capacity, magnetic susceptibility, and conductivity not characteristic of typical metals. It is supposed that these phases are systems whose properties at finite temperatures are predominantly determined by excited electrons rather than by electrons with a Fermi energy E-F.
Title:: Spin Amplitude Modulation Driven Magnetoelectric Coupling in the New Multiferroic FeTe2O5Br
Authors:: Pregelj, M; Zaharko, O; Zorko, A; Kutnjak, Z; Jeglic, P; Brown, PJ; Jagodic, M; Jaglicic, Z; Berger, H; Arcon, D Author Full Names: Pregelj, M.; Zaharko, O.; Zorko, A.; Kutnjak, Z.; Jeglic, P.; Brown, P. J.; Jagodic, M.; Jaglicic, Z.; Berger, H.; Arcon, D.
Source:: PHYSICAL REVIEW LETTERS 103 (14): Art. No. 147202 OCT 2 2009
Abstract:: The magnetic and ferroelectric properties of the layered geometrically frustrated cluster compound FeTe2O5Br were investigated with single-crystal neutron diffraction and dielectric measurements. An incommensurate transverse amplitude modulated magnetic order with the wave vector q = (1/2, 0.463, 0) develops below T-N = 10.6(2) K. Simultaneously, a ferroelectric order due to exchange striction involving polarizable Te4+ lone-pair electrons develops perpendicular to q and to Fe3+ magnetic moments. The observed magnetoelectric coupling is proposed to originate from the temperature dependent phase difference between neighboring amplitude modulation waves.
Title:: Magnetic structure and ferroelectric polarization of MnWO4 investigated by density functional calculations and classical spin analysis
Authors:: Tian, C; Lee, CH; Xiang, HJ; Zhang, YM; Payen, C; Jobic, S; Whangbo, MH Author Full Names: Tian, Chuan; Lee, Changhoon; Xiang, Hongjun; Zhang, Yuemei; Payen, Christophe; Jobic, Stephane; Whangbo, Myung-Hwan
Source:: PHYSICAL REVIEW B 80 (10): Art. No. 104426 SEP 2009
Abstract:: The ordered magnetic states of MnWO4 at low temperatures were examined by evaluating the spin exchange interactions between the Mn2+ ions of MnWO4 on the basis of first principles density functional calculations and by performing classical spin analysis with the resulting spin exchange parameters. Our work shows that the spin exchange interactions are frustrated within each zigzag chain of Mn2+ ions along the c direction and between such chains of Mn2+ ions along the a direction. This explains the occurrence of a spiral-spin order along the c and a directions in the incommensurate magnetic state AF2, and that of a up arrow up arrow down arrow down arrow spin order along the c and a directions in the commensurate magnetic state AF1. The ferroelectric polarization of MnWO4 in the spiral-spin state AF2 was examined by performing Berry phase calculations for a model superstructure to find that the ferroelectric polarization occurs along the b direction,! in agreement with experiment.
Title:: Magnetic and crystal structure of Ho-5(SixGe(1-x))(4) studied by neutron diffraction
Authors:: Ritter, C; Magen, C; Morellon, L; Algarabel, PA; Ibarra, MR; Pereira, AM; Araujo, JP; Sousa, JB Author Full Names: Ritter, C.; Magen, C.; Morellon, L.; Algarabel, P. A.; Ibarra, M. R.; Pereira, A. M.; Araujo, J. P.; Sousa, J. B.
Source:: PHYSICAL REVIEW B 80 (10): Art. No. 104427 SEP 2009
Abstract:: The magnetic and crystal structures of the magnetocaloric Ho-5(SixGe1-x)(4) (x= 1, 0.75, 0.5 and 0) have been studied by neutron powder diffraction experiments. The room-temperature crystal phases of the compositions x= 1, 0.75, and 0.5 are preserved in the whole temperature range 2-300 K, i.e. the Gd5Si4-type Pnma O(I) structure for Ho5Si4, the Gd5Si2Ge2-type P112(1)/a M state in x= 0.75, and the Sm5Ge4-type Pnma O(II) phase in x= 0.5. Ho5Si4 undergoes a second order ferromagnetic (FM) transition at T-C= 77 K into a noncollinear FM structure with the magnetization oriented mainly along the a axis and weak antiferromagnetic (AFM) coupling along b and c (magnetic space group Pnm'a'). Ho5Si3Ge becomes FM at T-C= 50 K (magnetic space group P112(1)'/a). At T-C'similar to 16 K an incipient second incommensurate magnetic phase appears which becomes commensurate below 8 K with a propagation vector k=(0 0 1/4). The magnetic structure of the main phase at 30 and 2 K shows the dominance of a FM coupling along the a axis with an AFM canting along c. Ho5Si2Ge2 stands out for the complexity of its low-temperature magnetic structure. In addition to the Neel transition of the O(II) phase at T-N similar to 30 K (magnetic space group Pn'm'a'), two additional magnetic phases with propagation vectors k=(0 0 1/4) and k=(1/2 0 0) appear at 15 and 12 K, respectively. In Ho5Ge4 the main O(II) structure orders AFM with k=(0 0 0) at T-N similar to 30 K in the same magnetic space group Pn'm'a'. Below 25 K a complete structural transition from high temperature O(II)Pnma to P2(1)/m takes place within the AFM state. The magnetic structure of this new nuclear phase stays AFM with k=(0 0 0), but sees two out of six independent Ho sites non magnetic. A second magnetic transition takes place at about 18 K characterized by the appearance of a second propagation vector k=(0 0 1/2) which magnetically couples the formerly non magnetic Ho sites. Magnetic- field dependent neutron diffractograms demonstrate that FM sets in in Ho5Ge4. The onset of ferromagnetism is associated with the previously reported nucleation of a new high field O(II) Pnma phase. Contrary to the intensity of the magnetic coupling with the propagation vector k=(0 0 0), which disappears quickly with the onset of FM, a progressive decrease of the intensity associated with the state k=(0 0 1/2) suggests a possible relationship between the extent of the magnetic coupling k=(0 0 1/2) and the percentage of remnant P2(1)/m phase.
Title:: Short-range incommensurate magnetic order near the superconducting phase boundary in Fe(1+delta)Te(1-x)Sex
Authors:: Wen, JS; Xu, GY; Xu, ZJ; Lin, ZW; Li, Q; Ratcliff, W; Gu, G; Tranquada, JM Author Full Names: Wen, Jinsheng; Xu, Guangyong; Xu, Zhijun; Lin, Zhi Wei; Li, Qiang; Ratcliff, W.; Gu, Genda; Tranquada, J. M.
Source:: PHYSICAL REVIEW B 80 (10): Art. No. 104506 SEP 2009
Abstract:: We performed elastic neutron-scattering and magnetization measurements on Fe1.07Te0.75Se0.25 and FeTe0.7Se0.3. Short-range incommensurate magnetic order is observed in both samples. In the former sample with higher Fe content, a broad magnetic peak appears around (0.46,0,0.5) at low temperature, while in FeTe0.7Se0.3, the broad magnetic peak is found to be closer to the antiferromagnetic (AFM) wave vector (0.5,0,0.5). The incommensurate peaks are only observed on one side of the AFM wave vector for both samples, which can be modeled in terms of an imbalance of ferromagnetic/antiferromagnetic correlations between nearest-neighbor spins. We also find that with higher Se (and lower Fe) concentration, the magnetic order becomes weaker while the superconducting temperature and volume increase.
Title:: Stability of nodal quasiparticles in underdoped YBa2Cu3O6+y probed by penetration depth and microwave spectroscopy
Authors:: Huttema, WA; Bobowski, JS; Turner, PJ; Liang, RX; Hardy, WN; Bonn, DA; Broun, DM Author Full Names: Huttema, W. A.; Bobowski, J. S.; Turner, P. J.; Liang, Ruixing; Hardy, W. N.; Bonn, D. A.; Broun, D. M.
Source:: PHYSICAL REVIEW B 80 (10): Art. No. 104509 SEP 2009
Abstract:: High-resolution measurements of superfluid density rho(s)(T) and broadband quasiparticle conductivity sigma(1)(Omega) have been used to probe the low-energy excitation spectrum of nodal quasiparticles in underdoped YBa2Cu3O6+y. Penetration depth lambda(T) is measured to temperatures as low as 0.05 K. sigma 1(Omega) is measured from 0.1 to 20 GHz and is a direct probe of zero-energy quasiparticles. The data are compared with predictions for a number of theoretical scenarios that compete with or otherwise modify pure d(x2-y2) superconductivity, in particular, commensurate and incommensurate spin and charge-density waves; d(x2-y2) + is and d(x2-y2) + id(xy) superconductivity; circulating current phases; and the BCS-BEC crossover. We conclude that the data are consistent with a pure d(x2-y2) state in the presence of a small amount of strong scattering disorder, and are able to rule out most candidate competing states either completely or to a level set by the energy scale of the disorder, T-d similar to 4 K. Commensurate spin and charge-density orders, however, are not expected to alter the nodal spectrum and therefore cannot be excluded.
Title:: Structure of the fivefold surface of the Ag-In-Yb icosahedral quasicrystal
Authors:: Sharma, HR; Shimoda, M; Sagisaka, K; Takakura, H; Smerdon, JA; Nugent, PJ; McGrath, R; Fujita, D; Ohhashi, S; Tsai, AP Author Full Names: Sharma, H. R.; Shimoda, M.; Sagisaka, K.; Takakura, H.; Smerdon, J. A.; Nugent, P. J.; McGrath, R.; Fujita, D.; Ohhashi, S.; Tsai, A. P.
Source:: PHYSICAL REVIEW B 80 (12): Art. No. 121401 SEP 2009
Abstract:: The surface structural study of an icosahedral (i) quasicrystal of the Cd-Yb family is presented. Comparison of bias-dependent scanning tunneling microscopy data from the fivefold surface of i-Ag-In-Yb with the refined bulk model of isostructural i-Cd-Yb indicates that surfaces are formed at bulk planes intersecting the center of the rhombic triacontahedral clusters, the building blocks of the Cd-Yb family quasicrystals. These observations open up the possibility of the use of this material as a template for epitaxial structures.
Title:: Electronic structure of RNiC2 (R = Sm, Gd, and Nd) intermetallic compounds
Authors:: Laverock, J; Haynes, TD; Utfeld, C; Dugdale, SB Author Full Names: Laverock, J.; Haynes, T. D.; Utfeld, C.; Dugdale, S. B.
Source:: PHYSICAL REVIEW B 80 (12): Art. No. 125111 SEP 2009
Abstract:: First-principles calculations of the electronic structure of members of the RNiC2 series are presented and their Fermi surfaces investigated for nesting propensities, which might be linked to the charge-density waves exhibited by certain members of the series (R=Sm, Gd, and Nd). Calculations of the generalized susceptibility, chi(0)(q, omega), show strong peaks at the same q vector in both the real and imaginary parts for these compounds. Moreover, this peak occurs at a wave vector which is very close to that experimentally observed in SmNiC2. In contrast, for LaNiC2 (which is a superconductor below 2.7 K) as well as for ferromagnetic SmNiC2, there is no such sharp peak. This could explain the absence of a charge-density wave transition in the former, and the destruction of the charge-density wave that has been observed to accompany the onset of ferromagnetic order in the latter.
Title:: Theoretical study of the magnetism in the incommensurate phase of TiOCl
Authors:: Mastrogiuseppe, DM; Torio, ME; Gazza, CJ; Dobry, AO Author Full Names: Mastrogiuseppe, D. M.; Torio, M. E.; Gazza, C. J.; Dobry, A. O.
Source:: PHYSICA B-CONDENSED MATTER 404 (18): 2805-2808 OCT 1 2009
Abstract:: Going beyond a recently proposed microscopic model [D. Mastrogiuseppe. A. Dobry, arXiv:0810.3018v] for the incommensurate transition in the spin-Peierls TiOX (X = Cl, Br) compounds, in the present work we start by studying the thermodynamics of the model with XY spins and adiabatic phonons. We find that the system enters an incommensurate phase by a first order transition at a low temperature T-c1. At a higher temperature T-C2 a continuous transition to a uniform phase is found. Furthermore, we study the magnetism in the incommensurate phase by density matrix renormalization group (DMRG) calculations on a one-dimensional Heisenberg model where the exchange is modulated by the incommensurate atomic position pattern. When the wave vector q of the modulation is near pi, we find local magnetized zones (LMZ) in which spins abandon their singlets as a result of the domain walls induced by the modulated distortion. When q moves far away enough from pi, the LMZ disappear and the system develops incommensurate magnetic correlations induced by the structure. We discuss the relevance of this result regarding previous and future experiments in TiOCl (C) 2009 Elsevier B.V. All rights reserved.
Title:: Frustration of Magnetic and Ferroelectric Long-Range Order in Bi2Mn4/3Ni2/3O6
Authors:: Claridge, JB; Hughes, H; Bridges, CA; Allix, M; Suchomel, MR; Niu, H; Kuang, X; Rosseinsky, MJ; Bellido, N; Grebille, D; Perez, O; Simon, C; Pelloquin, D; Blundell, SJ; Lancaster, T; Baker, PJ; Pratt, FL; Halasyamani, PS Author Full Names: Claridge, John B.; Hughes, Helen; Bridges, Craig A.; Allix, Mathieu; Suchomel, Matthew R.; Niu, Hongjun; Kuang, Xiaojun; Rosseinsky, Matthew J.; Bellido, Natalia; Grebille, Dominique; Perez, Olivier; Simon, Charles; Pelloquin, Denis; Blundell, Stephen J.; Lancaster, Tom; Baker, Peter J.; Pratt, Francis L.; Halasyamani, P. Shiv
Source:: JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 131 (39): 14000-14017 OCT 7 2009
Abstract:: The slight incommensurate modulation of the structure of Bi2Mn4/3Ni2/3O6 is sufficient to suppress the electrical polarization which arises in commensurate treatments of the structure, due to antiferroelectric coupling of local polar units of over 900 angstrom(3). The incommensurate structure is produced by the competition between ferroelectric Bi lone pair-driven A site displacement, chemical order of Mn and Ni on the B site, and both charge and orbital order at these transition metals. The interplay between the frustrated polar Bi displacements and the frustrated spin order at the B site, induced by positional disorder, produces magnetodielectric coupling between the incommensurately modulated lattice and the spin-glass-like ground state with an unusual relationship between the magnetocapacitance and the applied field.
Title:: Molecular dewetting on insulators
Authors:: Burke, SA; Topple, JM; Grutter, P Author Full Names: Burke, S. A.; Topple, J. M.; Gruetter, P.
Source:: JOURNAL OF PHYSICS-CONDENSED MATTER 21 (42): Art. No. 423101 OCT 21 2009
Abstract:: Recent attention given to the growth and morphology of organic thin films with regard to organic electronics has led to the observation of dewetting (a transition from layer (s) to islands) of molecular deposits in many of these systems. Dewetting is a much studied phenomenon in the formation of polymer and liquid films, but its observation in thin films of the 'small' molecules typical of organic electronics requires additional consideration of the structure of the interface between the molecular film and the substrate. This review covers some key concepts related to dewetting and molecular film growth. In particular, the origins of different growth modes and the thickness dependent interactions which give rise to dewetting are discussed in terms of surface energies and the disjoining pressure. Characteristics of molecular systems which may lead to these conditions, including the formation of metastable interface structures and commensurate-incommensurate phase transitions, are also discussed. Brief descriptions of some experimental techniques which have been used to study molecular dewetting are given as well. Examples of molecule-on-insulator systems which undergo dewetting are described in some detail, specifically perylene derivatives on alkali halides, C-60 on alkali halides, and the technologically important system of pentacene on SiO2. These examples point to some possible predicting factors for the occurrence of dewetting, most importantly the formation of an interface layer which differs from the bulk crystal structure.
Update: 8-Oct-2009
Title:: Spin chirality and electric polarization in multiferroic compounds RMn2O5 (R = Ho, Er)
Authors:: Wakimoto, S; Kimura, H; Fukunaga, M; Nishihata, K; Takeda, M; Kakurai, K; Noda, Y; Tokura, Y Author Full Names: Wakimoto, Shuichi; Kimura, Hiroyuki; Fukunaga, Mamoru; Nishihata, Keisuke; Takeda, Masayasu; Kakurai, Kazuhisa; Noda, Yukio; Tokura, Yoshinori
Source:: PHYSICA B-CONDENSED MATTER 404 (17): 2513-2516 SEP 1 2009
Abstract:: Polarized neutron diffraction experiments have been performed on multiferroic materials RMn2O5 (R = Ho, Er) under electric fields in the ferroelectric commensurate (CM) and the low-temperature incommensurate (LT-ICM) phases, where the former has the highest electric polarization and the latter has reduced polarization. It is found that, after cooling in electric fields down to the CM phase, the magnetic chirality is proportional to the electric polarization. Also we confirmed that the magnetic chirality can be switched by the polarity of the electric polarization in both the CM and LT-ICM phases. These facts suggest an intimate coupling between the magnetic chirality and the electric polarization. However, upon the transition from the CM to LT-ICM phase, the reduction of the electric polarization is not accompanied by any reduction of the magnetic chirality, implying that the CM and LT-ICM phases contain different mechanisms of the magnetoelectric coupling. (C) 2009 Elsevier B.V. All rights reserved.
Title:: Solid State Polyselenides and Polytellurides: A Large Variety of Se-Se and Te-Te Interactions
Authors:: Graf, C; Assoud, A; Mayasree, O; Kleinke, H Author Full Names: Graf, Christian; Assoud, Abdeljalil; Mayasree, Oottil; Kleinke, Holger
Source:: MOLECULES 14 (9): 3115-3131 SEP 2009
Abstract:: A large variety of different interactions between the chalcogen atoms, Q, occur in the solid state structures of polyselenides and polytellurides, including both molecular and infinite units. The simplest motifs are classical Q(2)(2-) dumbbells and nonlinear Qn(2-) chains (n = 3, 4, 5,..), e. g. found in alkali metal polychalcogenides. In addition, nonclassical so-called hypervalent motifs exist in the form of linear Q(3)(4-) units or within larger units such as Q(4)(4-) and Q(5)(4-). Infinitely extended Q units include zigzag, cis/trans and linear chains, as well as planar and slightly puckered layers. Several of those are susceptible to Peierls distortions, leading to the formation of both commensurate and incommensurate superstructures and anomalies in transport properties, including metal-nonmetal transitions.
Title:: Manganese adlayers on i-Al-Pd-Mn quasicrystal: growth and electronic structure
Authors:: Shukla, AK; Dhaka, RS; D'Souza, SW; Maniraj, M; Barman, SR; Horn, K; Ebert, P; Urban, K; Wu, D; Lograsso, TA Author Full Names: Shukla, A. K.; Dhaka, R. S.; D'Souza, S. W.; Maniraj, M.; Barman, S. R.; Horn, K.; Ebert, Ph; Urban, K.; Wu, D.; Lograsso, T. A.
Source:: JOURNAL OF PHYSICS-CONDENSED MATTER 21 (40): Art. No. 405005 OCT 7 2009
Abstract:: Pseudomorphic growth of thin elemental metal films is often observed on a variety of crystalline solids. On quasicrystalline surfaces with their complex structure and the absence of translational periodicity, the situation is different since elemental metals do not exhibit quasicrystalline order, and hence the specific interaction between overlayer and substrate is decisive. Here we study the growth of manganese films on an icosahedral i-Al-Pd-Mn alloy with a view to establishing the growth mode and electronic structure. Although we observe an exponential intensity variation of the adlayer and substrate related x-ray photoemission spectroscopy (XPS) peaks, low energy electron diffraction (LEED) shows that Mn adlayers do not exhibit quasicrystallinity. The detailed structure of the Mn 2p core level line reveals considerable electronic structure differences between the quasicrystalline and elemental metal environment. Evidence of a substantial local magnetic moment on the Mn atoms in the overlayer (about 2.8 mu(B)) is obtained from the Mn 3s exchange splitting.
Title:: Pressure-induced disorder in Rb2ZnCl4
Authors:: Machon, D; Grzechnik, A; Friese, K Author Full Names: Machon, Denis; Grzechnik, Andrzej; Friese, Karen
Source:: JOURNAL OF PHYSICS-CONDENSED MATTER 21 (40): Art. No. 405405 OCT 7 2009
Abstract:: Rb2ZnCl4 in the normal phase (T = 308-313 K) has been studied under pressure by means of single-crystal x-ray diffraction up to 3.84 GPa and Raman spectroscopy up to 5.9 GPa. No pressure-induced phase transition has been observed but an orientational disorder of the tetrahedra is enhanced with the pressure. At the same time a partial one-dimensional correlation of some chlorine atoms might be favoured at high pressures. Raman spectra in the incommensurate phase (T = 293 K) were collected to higher pressure (24.2 GPa) varying the pressure-transmitting medium. The hydrostaticity during the compression is shown to affect drastically the broadness of the Raman peaks, leading to an amorphous-like spectrum in the least hydrostatic case.
Title:: Crystallographic and electrochemical characteristics of Ti-Zr-Ni-Pd quasicrystalline alloys
Authors:: Liu, BZ; Zhang, YD; Mi, GF; Zhang, Z; Wang, LM Author Full Names: Liu, Baozhong; Zhang, Yude; Mi, Guofa; Zhang, Zhi; Wang, Limin
Source:: INTERNATIONAL JOURNAL OF HYDROGEN ENERGY 34 (16): 6925-6929 Sp. Iss. SI AUG 2009
Abstract:: Ti45Zr35Ni20-xPdx (x = 0, 1, 3, 5 and 7, at%) alloys were prepared by melt-spinning. The phase structure and electrochemical hydrogen storage performances of melt-spun alloys were investigated. The melt-spun alloys were icosahedral quasicrystalline phase, and the quasi-lattice constant increased with increasing x value. The maximum discharge capacity of alloy electrodes increased from 79 mAh/g (x = 0) to 148 mAh/g (x = 7). High-rate dis-chargeability and cycling stability were also enhanced with the increase of Pd content. The improvement in the electrochemical hydrogen storage characteristics may be ascribed to better electrochemical activity and oxidation resistance of Pd than that of Ni. (C) 2009 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.
Title:: Investigation of the New P ' 3-Na0.60VO2 Phase: Structural and Physical Properties
Authors:: Szajwaj, O; Gaudin, E; Weill, F; Darriet, J; Delmas, C Author Full Names: Szajwaj, Olivier; Gaudin, Etienne; Weill, Francois; Darriet, Jacques; Delmas, Claude
Source:: INORGANIC CHEMISTRY 48 (19): 9147-9154 OCT 5 2009
Abstract:: A new layered phase Na0.60VO2 was synthesized by chemical deintercalation of sodium from the pristine compound O3-NaVO2. The Na0.60VO2 compound exhibits a distorted P'3-type oxygen stacking (AABBCC) with an average monoclinic unit cell containing a = 4.9862(14) angstrom, b = 2.8708(8) angstrom, c = 5.917(2) angstrom, and beta = 104.36(3)degrees. A modulated structure was observed by transmission electron microscopy and X-ray diffraction (XRD) measurements. Indexation of the XRD pattern was achieved by using the q vector equal to 0.44b(star), and the 4D superspace group C2/m (0 beta 0) s0 was then deduced. The specific heat measurement showed a strong correlated system with a gamma value of around 20 mJ . mol(-1) . K-2. The electrical conductivity shows a semiconductor-like behavior with an activation energy of 0.52 eV. A paramagnetic behavior of the susceptibility is observed below room temperature with a Curie constant equal to C = 0.076 emu . K-1 . mol(-1) . Oe(-1). To explain this small value, a model of pseudotriangular clusters of vanadium with a random distribution of V3+ and V4+ was considered.
Title:: Phase formation and structures of quasicrystals and approximants in the Zn-Mg-(Ti, Zr, Hf) system
Authors:: Ohhashi, S; Abe, E; Tanaka, M; Tsai, AP Author Full Names: Ohhashi, S.; Abe, E.; Tanaka, M.; Tsai, A. P.
Source:: ACTA MATERIALIA 57 (16): 4727-4735 SEP 2009
Abstract:: The compositional regions for primitive (P) and face-centered (F) icosahedral quasicrystals (iQc) have been determined to be around Zn84Mg9Zr7 and Zn75Mg18Zr6, respectively. A 1/1 approximant of the F-type iQc was found to have a composition around Zn77Mg18Zr5. A similar tendency has been verified for the Zn-Mg-Hf system. No stable iQc was observed in the Zn-Mg-Ti system. High-resolution X-ray measurements performed with synchrotron radiation showed that the stable iQcs are highly ordered and contain less phason disorder. High-angle annular dark field (HAADF) scanning transmission electron microscopy observation of the 1/1 Zn-Mg-Hf approximant effectively revealed the Hf positions in the structure, whose local contrasts can be reasonably interpreted by a structural model where icosahedral and dodecahedral Hf clusters are mutually interpenetrated. Similar appearances of local contrasts were frequently observed in HAADF images of the F-type iQc, indicating that the iQc structure is also build up of icosahedral clusters that are almost identical to those in the 1/1 approximant. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Update: 1-Oct-2009
Title:: Tailoring Thermally Induced Nano-Quasicrystallization and Deformation-Assisted Nanocrystallization for Mechanical Property Improvement in Zr-Al-Ni-Cu-Pd Bulk Metallic Glasses
Authors:: Saida, J; Setyawan, AD; Kato, H; Matsushita, M; Inoue, A Author Full Names: Saida, Junji; Setyawan, Albertus D.; Kato, Hidemi; Matsushita, Mitsuhide; Inoue, Akihisa
Source:: MATERIALS TRANSACTIONS 50 (8): 2079-2086 AUG 2009
Abstract:: The material design tailoring of a synergistic effect of an in-situ nano secondary phase formation and defomation-induced nanocrystallization for improving the mechanical strength and ductility, has been investigated in Zr65Al7.5Ni10Cu17.5-xPdx bulk metallic glasses (BMGs). As-cast Zr65Al7.5Ni10Cu17.5-xPdx (x = 5-17.5) BMGs have significant ductility in compressive deformation, which is attributed to deformation-induced dynamic nanocrystallization. The 10at% Pd-containing BMG with a low volume fraction of the quasicrystalline (QC) phase of less than 6% exhibits increases in strength and Young's modulus, in addition to a remaining plasticity of similar to 5%, compared with the monolithic glassy alloy. Such improvements in the mechanical properties originate from the combination of two effects of in-situ homogenous nano-QC formation and deformation-induced inhomogeneous nanocrystallization. The present method should be regarded as a new technique for the production of BMGs with high strength and good ductility. [doi:10.2320/matertrans.M2009135]
Update: 24-Sep-2009
Title:: Microstructure, surface composition and chemical stability of partly ordered LaTiO2N
Authors:: Logvinovich, D; Bocher, L; Sheptyakov, D; Figi, R; Ebbinghaus, SG; Aguiar, R; Aguirre, MH; Reller, A; Weidenkaff, A Author Full Names: Logvinovich, Dmitry; Bocher, Laura; Sheptyakov, Denis; Figi, Renato; Ebbinghaus, Stefan G.; Aguiar, Rosiana; Aguirre, Myriam H.; Reller, Armin; Weidenkaff, Anke
Source:: SOLID STATE SCIENCES 11 (8): 1513-1519 AUG 2009
Abstract:: LaTiO2N was synthesized in a thermal ammonolysis process of crystalline La2Ti2O7 prepared by conventional solid state reaction or by ammonolysis of a homogeneous amorphous precursor obtained from a soft-chemistry approach. At room temperature slowly cooled LaTiO2N prepared from either precursor crystallizes in space group I (1) over bar and shows a partially ordered anionic arrangement in contrast to a quenched reference sample. The material possesses a complex microstructure represented by twin domains of different types and orientations, as well as incommensurately modulated fragments. The presence of minor C- and N-containing phases such as carbonates, cyanides and nitrates as well as a small amount of a reoxidation intermediate was detected by infrared and Raman spectroscopy. These small amounts of secondary phases can generally influence the results of the O/N content determination of oxynitride compounds when using thermal analysis methods. The formation of such unwanted secondary phases can be avoided by quenching the oxynitride sample or by cooling in inert atmosphere. (C) 2009 Elsevier Masson SAS. All rights reserved.
Title:: Detailed Phase Analysis and Crystal Structure Investigation of a Bi1-xCaxFeO3-x/2 Perovskite-Related Solid Solution Phase and Selected Property Measurements Thereof
Authors:: Schiemer, J; Withers, R; Noren, L; Liu, Y; Bourgeois, L; Stewart, G Author Full Names: Schiemer, Jason; Withers, Ray; Noren, Lasse; Liu, Yun; Bourgeois, Laure; Stewart, Glen
Source:: CHEMISTRY OF MATERIALS 21 (18): 4223-4232 SEP 22 2009
Abstract:: A well-ordered, perovskite-related, (Bi1-xCaxFeO3-x/2)-O-III solid solution phase is synthesized via a rapid liquid phase sintering technique and shown to exist over the composition range similar to 0.20 < x < similar to 0.49. Two phase regions are shown to separate this phase from compositionally narrow end-member (Bi1-xCaxFeO3-x/2)-O-III solid solutions based on rhombohedral BiFeO3 and brownmillerite, Ca2Fe2O5, respectively. The wide range, non-stoichiometric phase is characterized by a well ordered, (in general) incommensurately modulated structure that varies systematically with composition. Mossbauer spectroscopy is used to verify the oxidation state of iron as (III), as well as showing the existence of three separate iron environments across the solid solution field. HRTEM imaging is used to develop a structural model for the phase at one particular composition. The magnetic, dielectric, and impedance properties of this solid solution phase are reported. Magnetic measurements show antiferromagnetic behavior. There is no change in either susceptibility or antiferromagnetic behavior with composition. Attempts at obtaining saturated ferroelectric loops failed due to high intrinsic conductivity. The phase is found to exhibit a low frequency impedance relaxation that is likely due to correlated oxygen vacancy hopping.
Title:: Differential geometry: a natural tool for describing symmetry operations
Authors:: Kocian, P; Schenk, K; Chapuis, G Author Full Names: Kocian, Philippe; Schenk, Kurt; Chapuis, Gervais
Source:: ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 65: 329-341 Part 5 OCT 2009
Abstract:: Differential geometry provides a useful mathematical framework for describing the fundamental concepts in crystallography. The notions of point and associated vector spaces correspond to those of manifold and tangent space at a given point. A space-group operation is a one-to-one map acting on the manifold, whereas a point-group operation is a linear map acting between two tangent spaces of the manifold. Manifold theory proves particularly powerful as a unified formalism describing symmetry operations of conventional as well as modulated crystals without requiring a higher-dimensional space. We show, in particular, that a modulated structure recovers a three-dimensional periodicity in any tangent space and that its point group consists of linear applications. (C) 2009 International Union of Crystallography Printed in Singapore - all rights reserved
Title:: Point substitution processes for decagonal quasi-periodic tilings
Authors:: Fujita, N Author Full Names: Fujita, Nobuhisa
Source:: ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 65: 342-351 Part 5 OCT 2009
Abstract:: A general construction principle for the inflation rules for decagonal quasiperiodic tilings is proposed. The prototiles are confined to be polygons with unit edges. An inflation rule for a tiling is the combination of expansion and division of the tiles, where the expanded tiles can be divided arbitrarily as long as the set of prototiles is maintained. A certain kind of point decoration process turns out to be useful for the identification of possible division rules. The method is capable of generating a broad range of decagonal tilings, many of which are chiral and have atomic surfaces with fractal boundaries. Two new families of decagonal tilings are presented; one is quaternary and the other ternary. The properties of the ternary tilings with rhombic, pentagonal and hexagonal prototiles are investigated in detail. (C) 2009 International Union of Crystallography Printed in Singapore - all rights reserved
Update: 17-Sep-2009
Title:: Symmetry Breaking in Dense Solid Hydrogen: Mechanisms for the Transitions to Phase II and Phase III
Authors:: Toledano, P; Katzke, H; Goncharov, AF; Hemley, RJ Author Full Names: Toledano, Pierre; Katzke, Hannelore; Goncharov, Alexander F.; Hemley, Russell J.
Source:: PHYSICAL REVIEW LETTERS 103 (10): Art. No. 105301 SEP 4 2009
Abstract:: Spectroscopic data for the high-pressure phases of hydrogen together with the topology of the phase diagram provide new insight on the behavior of the material at megabar pressure. Structural mechanisms are proposed for the transitions to phases II and III. These mechanisms include a partially ordered structure (possibly incommensurate) and an ordered isotranslational structure for the two phases, respectively. The analysis supports the existence of an additional phase, isostructural to phase III, with boundary that meets to form a second triple point with phases I and III.
Title:: Aperiodicity, structure, and dynamics in Ni(CN)(2)
Authors:: Goodwin, AL; Dove, MT; Chippindale, AM; Hibble, SJ; Pohl, AH; Hannon, AC Author Full Names: Goodwin, Andrew L.; Dove, Martin T.; Chippindale, Ann M.; Hibble, Simon J.; Pohl, Alexander H.; Hannon, Alex C.
Source:: PHYSICAL REVIEW B 80 (5): Art. No. 054101 AUG 2009
Abstract:: By combining the results of both x-ray diffraction and neutron total-scattering experiments, we show that Ni(CN)(2) exhibits long-range structural order only in two dimensions, with no true periodicity perpendicular to its gridlike layers. Reverse Monte Carlo analysis gives an experimental distinction between M-C and M-N bond lengths in a homometallic cyanide framework and identifies the vibrational modes responsible for anomalous positive and negative thermal expansion in the title compound.
Title:: Origin of Moireacute structures in C-60 on Pb(111) and their effect on molecular energy levels
Authors:: Li, HI; Franke, KJ; Pascual, JI; Bruch, LW; Diehl, RD Author Full Names: Li, H. I.; Franke, K. J.; Pascual, J. I.; Bruch, L. W.; Diehl, R. D.
Source:: PHYSICAL REVIEW B 80 (8): Art. No. 085415 AUG 2009
Abstract:: Low-energy electron diffraction (LEED) indicates that the monolayer structure of C-60 on Pb(111) comprises two coexisting incommensurate structures with nonsymmetry epitaxial rotations near 20 degrees relative to the Pb(111) lattice. These structures are observed in scanning tunneling microscopy (STM) as Moireacute superstructures having periods of about 46 A degrees and 34 A degrees. The Moireacute images and LEED patterns are consistent with two higher-order commensurate (HOC) structures that were identified using the hexagonal number sequence method. These structures are close to predictions from the Novaco-McTague theory of epitaxial rotation, assuming a weakly corrugated substrate potential. As a consequence of the fullerenes within the Moireacute structures having different local environments, the energetic alignment of the molecular resonances is also modulated, with shifts measured by tunneling spectroscopy of up to 20 meV.
Title:: Commensurate lock-in and incommensurate supersolid phases of hard-core bosons on anisotropic triangular lattices
Authors:: Isakov, SV; Chien, HC; Wu, JJ; Chen, YC; Chung, CH; Sengupta, K; Kim, YB Author Full Names: Isakov, Sergei V.; Chien, Hong-Chi; Wu, Jian-Jheng; Chen, Yung-Chung; Chung, Chung-Hou; Sengupta, Krishnendu; Kim, Yong Baek
Source:: EPL 87 (3): Art. No. 36002 AUG 2009
Abstract:: We investigate the interplay between commensurate lock-in and incommensurate supersolid phases of the hard-core bosons at half-filling with anisotropic nearest-neighbor hopping and repulsive interactions on triangular lattice. We use numerical quantum and variational Monte Carlo as well as analytical Schwinger boson mean-field analysis to establish the ground states and phase diagram. It is shown that, for finite-size systems, there exist a series of jumps between different supersolid phases as the anisotropy parameter is changed. The density ordering wave vectors are locked to commensurate values and jump between adjacent supersolids. In the thermodynamic limit, however, the magnitude of these jumps vanishes leading to a continuous set of novel incommensurate supersolid phases. Copyright (C) EPLA, 2009
Update: 10-Sep-2009
Title:: Coupled Magnetic and Ferroelectric Domains in Multiferroic Ni3V2O8
Authors:: Cabrera, I; Kenzelmann, M; Lawes, G; Chen, Y; Chen, WC; Erwin, R; Gentile, TR; Leao, JB; Lynn, JW; Rogado, N; Cava, RJ; Broholm, C Author Full Names: Cabrera, I.; Kenzelmann, M.; Lawes, G.; Chen, Y.; Chen, W. C.; Erwin, R.; Gentile, T. R.; Leao, J. B.; Lynn, J. W.; Rogado, N.; Cava, R. J.; Broholm, C.
Source:: PHYSICAL REVIEW LETTERS 103 (8): Art. No. 087201 AUG 21 2009
Abstract:: Electric control of multiferroic domains is demonstrated through polarized magnetic neutron diffraction. Cooling to the cycloidal multiferroic phase of Ni3V2O8 in an electric field E causes the incommensurate Bragg reflections to become neutron spin polarizing, the sense of neutron polarization reversing with E. Quantitative analysis indicates the E-treated sample has a handedness that can be reversed by E. We further show a close association between cycloidal and ferroelectric domains through E-driven spin and electric polarization hysteresis. We suggest that a definite cycloidal handedness is achieved through magnetoelastically induced Dzyaloshinskii-Moriya interactions.
Title:: Structural transformations and magnetic properties of Bi(1-x)Ln(x)FeO(3) (Ln = La, Nd, Eu) multiferroics
Authors:: Troyanchuk, IO; Bushinsky, MV; Karpinsky, DV; Mantytskaya, OS; Fedotova, VV; Prochnenko, OI Author Full Names: Troyanchuk, I. O.; Bushinsky, M. V.; Karpinsky, D. V.; Mantytskaya, O. S.; Fedotova, V. V.; Prochnenko, O. I.
Source:: PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS 246 (8): 1901-1907 AUG 2009
Abstract:: Crystal structures of Bi(1-x)Ln(x)FeO(3) systems (Ln = La, Nd, Eu) are studied using X-ray and neutron diffraction, magnetization measurements as well as electron microscopy. It was shown that the unit cell of the Bi1-xLaxFeO3 system is described with the R3c space group in the concentration interval 0 < x < 0.15, with the space group Imma (0.4 < x < 0.5) and with the Puma at x > 0.5. The mixed-phase state was observed in the range 0.15 < x < 0.4 independent of synthesis conditions. A similar sequence of the phase transformations was observed for Bi1-xNdxFeO3 system, In the case of qBi(1-x)Eu(x)FeO(3) series the unit cell is rhombohedral (R3c) at x 0.08 and orthorhombic (Pnma) at x > 0.20, whereas no evidence for Imma phase was found. The magnetization study has revealed the spontaneous magnetization to be associated with Prima and Imma phases that do not allow conventional ferroelectricity, The ferroelectric R3c phase exhibits meta-magnetic behavior due to transition from an incommensurately modulated antiferromagnetic state to a weak ferromagnetic state. Substitution of Bi3+ with Ln(3+) leads to a strong decrease of external magnetic field inducing a metamagnetic transition. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Title:: Resonant Magnetic X-ray Diffraction Study on the Triangular Lattice Antiferromagnet GdPd2Al3
Authors:: Inami, T; Terada, N; Kitazawa, H; Sakai, O Author Full Names: Inami, Toshiya; Terada, Noriki; Kitazawa, Hideaki; Sakai, Osamu
Source:: JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 78 (8): Art. No. 084713 AUG 2009
Abstract:: Resonant magnetic x-ray diffraction experiments were carried out on the stacked triangular lattice antiferromagnet GdPd2Al3. The experiments revealed an expected initial collinear c-axis order at T-N1 followed by an additional in-plane order at T-N2, while at the same time we found that the ground state is a helically ordered state of a very long incommensurate period of approximately 700 angstrom. The distribution of K-domains was highly anisotropic, and the domain with the modulation vector normal to the surface of the crystal was ascendant. Low-field magnetization is discussed on the basis of the observed incommensurate magnetic structure.
Title:: Studies of Multiferroic System of LiCu2O2: II. Magnetic Structures of Two Ordered Phases with Incommensurate Modulations
Authors:: Kobayashi, Y; Sato, K; Yasui, Y; Moyoshi, T; Sato, M; Kakurai, K Author Full Names: Kobayashi, Yoshiaki; Sato, Kenji; Yasui, Yukio; Moyoshi, Taketo; Sato, Masatoshi; Kakurai, Kazuhisa
Source:: JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 78 (8): Art. No. 084721 AUG 2009
Abstract:: Neutron diffraction and Li-7-NMR have been applied to determine the three dimensional magnetic structures of the multiferroic system LiCu2O2, which has four chains (ribbon chains) of edge-sharing CuO4 square planes in a unit cell. First, we have confirmed that there are successive magnetic transitions at T-N1 = 24.5 K and T-N2 = 22.8 K. In the T region between T-N1 and T-N2, the quasi one-dimensional spins (S = 1/2) of Cu2+ ions within a chain have a collinear and sinusoidally modulated structure with Cu-moments parallel to the c-axis and with the modulation vector along the b-axis. At T < T-N2, an ellipsoidal helical spin structure with the incommensurate modulation has been found. We present detailed parameters, describing the modulation amplitudes, helical axis vectors as well as the relative phases of the modulations of four ribbon chains, which can well reproduce both the NMR and neutron results, in the two magnetically ordered phases. This finding of the rather precise magnetic structures enables us to discuss the relationship between the magnetic structure and the multiferroic nature of the present system in zero magnetic field, as presented in our companion paper (paper I), and open a way how to understand the reported electric polarization under the finite magnetic field.
Title:: Evaluation of the local environment for nanoscale quasicrystal formation in Zr80Pt20 glassy alloy using Voronoi analysis
Authors:: Saida, J; Itoh, K; Sato, S; Imafuku, M; Sanada, T; Inoue, A Author Full Names: Saida, Junji; Itoh, Keiji; Sato, Shigeo; Imafuku, Muneyuki; Sanada, Takashi; Inoue, Akihisa
Source:: JOURNAL OF PHYSICS-CONDENSED MATTER 21 (37): Art. No. 375104 SEP 16 2009
Abstract:: The local atomic structure of nano-quasicrystal-forming Zr80Pt20 binary glassy alloy was investigated by reverse Monte Carlo modeling based on the results of x-ray diffraction. A prepeak at Q similar to 17 nm(-1) originating from the unique bonding between the Pt-Pt pair is observed in the structure factor. Voronoi analysis indicates that an icosahedral-like polyhedron is formed around Pt. It is also found that icosahedral-like polyhedra exist around Zr; however, the fraction of perfect icosahedra is considerably lower than that in the nano-quasicrystal-forming Zr70Pd30 glassy alloy. A difference in the local environment between the two binary quasicrystal-forming glassy alloys is suggested.
Title:: Direct observation of double-k lattice modulation in double-k magnetic structures. The case of CeAl2
Authors:: Stunault, A; Schweizer, J; Givord, F; Vettier, C; Detlefs, C; Boucherle, JX; Lejay, P Author Full Names: Stunault, A.; Schweizer, J.; Givord, F.; Vettier, C.; Detlefs, C.; Boucherle, J-X; Lejay, P.
Source:: JOURNAL OF PHYSICS-CONDENSED MATTER 21 (37): Art. No. 376004 SEP 16 2009
Abstract:: Symmetry analysis is combined with x-ray scattering experiments to investigate the lattice modulation associated with the incommensurate magnetic structure in the case of a double-k structure. The expansion of the free energy shows that the components of the magnetic structure with propagation vectors k(1) and k(2) can couple via components of lattice modulations. It is shown that the classical diffraction peaks reflecting a 2k propagation vector, associated with magneto-elastic effects in single-k structures, will coexist with diffraction peaks with propagation vectors k(1) - k(2) or k(1) + k(2). The existence of these latter peaks can be considered as a signature of a double-k magnetic structure. In the case of the double-k modulated structure of CeAl2, group theory is applied directly to the study of the charge modulation. An x-ray scattering study of the 2k satellites shows that the lattice displacements of the two Ce sites of the structure are antiparallel to each other, and perpendicular to the direction of the magnetic modulation. We also confirm experimentally the existence of k(1) + k(2) satellites.
Title:: Formation of Nano-Quasicrystalline Decagonal Phase in the Al70Cu10Co5Ni15 System by High Energy Ball Milling
Authors:: Yadav, TP; Mukhopadhyay, NK; Shaz, MA; Tiwari, RS; Srivastava, ON Author Full Names: Yadav, T. P.; Mukhopadhyay, N. K.; Shaz, M. A.; Tiwari, R. S.; Srivastava, O. N.
Source:: JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY 9 (9): 5527-5532 SEP 2009
Abstract:: A nano decagonal quasicrystalline phase in the Al70Cu10Co5Ni15 alloy has been synthesized by mechanical alloying of a mixture of elemental powders followed by annealing. A high-energy ball milling of the elemental mixture of Al, Cu, Co and Ni leads to the formation of B2 type quaternary intermetallic alloys. The X-ray diffraction and transmission electron microscopy techniques have been employed for characterization of the samples. It was observed that the dissolution of the individual elements into an alloy led to the formation of a nano B2 phase. This phase was found to be quite stable against milling and no other crystalline or amorphous phases could be detected. Milled powder after annealing at 700 degrees C for 60 h was found to transform to nano-decagonal phase. Attempts have been made to understand the evolution of the complex intermetallic nano phases and their relative stability during milling.
Title:: Two Variants of the 1/2[110](p)(203)(p) Crystallographic Shear Structures: The Phasoid Sr0.61Pb0.18(Fe0.75Mn0.25)O-2.29
Authors:: Lepoittevin, C; Hadermann, J; Malo, S; Perez, O; Van Tendeloo, G; Hervieut, M Author Full Names: Lepoittevin, Christophe; Hadermann, Joke; Malo, Sylvie; Perez, Olivier; Van Tendeloo, Gustaaf; Hervieut, Maryvonne
Source:: INORGANIC CHEMISTRY 48 (17): 8257-8262 SEP 7 2009
Abstract:: For the composition (Sr0.61Pb0.18)(Fe0.75Mn0.25)O-2.29, a new modulated crystallographic shear structure, related to perovskite, has been synthesized and structurally characterized by transmission electron microscopy. The structure can be described using a monoclinic supercell with cell parameters a(m) = 27.595(2) angstrom, b(m) = 3.8786(2) angstrom, c(m) = 13.3453(9) angstrom, and beta(m) = 100.126(5)degrees, refined from powder X-ray diffraction data. The incommensurate crystallographic shear phases require an alternative approach using the superspace formalism. This allows a unified description of the incommensurate phases from a monoclinically distorted perovskite unit cell and a modulation wave vector. The structure deduced from the high-resolution transmission electron microscopy and high-angle annular dark-field-scanning transmission electron microscopy images is that of a 1/2[110](p)(203)(p) crystallographic shear structure. The structure follows the concept of a phasoid, with two coexisting variants with the same unit cell. The difference is situated at the translational interface, with the local formation of double (phase 2) or single (phase 1) tunnels, where the Pb cations are likely located.
Title:: Spin density wave dislocation in chromium probed by coherent X-ray diffraction
Authors:: Jacques, VLR; Le Bolloc'h, D; Ravy, S; Giles, C; Livet, F; Wilkins, SB Author Full Names: Jacques, V. L. R.; Le Bolloc'h, D.; Ravy, S.; Giles, C.; Livet, F.; Wilkins, S. B.
Source:: EUROPEAN PHYSICAL JOURNAL B 70 (3): 317-325 AUG 2009
Abstract:: We report on the study of a magnetic dislocation in pure chromium. Coherent X-ray diffraction profiles obtained on the incommensurate Spin Density Wave (SDW) reflection are consistent with the presence of a dislocation of the magnetic order, embedded at a few micrometers from the surface of the sample. Beyond the specific case of magnetic dislocations in chromium, this work may open up a new method for the study of magnetic defects embedded in the bulk.
Title:: Field-dependent competing magnetic ordering in multiferroic Ni3V2O8
Authors:: Singh, AK; Jain, D; Ganesan, V; Nigam, AK; Patnaik, S Author Full Names: Singh, A. K.; Jain, D.; Ganesan, V.; Nigam, A. K.; Patnaik, S.
Source:: EPL 86 (5): Art. No. 57001 JUN 2009
Abstract:: The geometrically frustrated magnet Ni3V2O8 undergoes a series of competing magnetic ordering at low temperatures. Most importantly, one of the incommensurate phases has been reported to develop a ferroelectric correlation caused by spin frustration. Here we report an extensive thermodynamic, dielectric and magnetic study on clean polycrystalline samples of this novel multiferroic compound. Our low-temperature specific heat data at high fields up to 14 Tesla clearly identify the development of a new magnetic-field-induced phase transition below 2 K that shows signatures of simultaneous electric ordering. We also report temperature-and field-dependent dielectric constant that enables us to quantitatively estimate the strength of magnetoelectric coupling in this improper ferroelectric material. Copyright (C) EPLA, 2009
Title:: Theory of magnetic order in Fe1+yTe1-xSex
Authors:: Fang, C; Bernevig, BA; Hu, JP Author Full Names: Fang, Chen; Bernevig, B. Andrei; Hu, Jiangping
Source:: EPL 86 (6): Art. No. 67005 JUN 2009
Abstract:: We develop a local spin model to explain the rich magnetic structures in the ironbased superconductors Fe1+yTe1-xSex. We show that our model exhibits both commensurate antiferromagnetic and incommensurate magnetic order along the crystal a-axis. The transition from the commensurate to the incommensurate phase is induced when the concentration of excess Fe atoms is larger than a critical value. Experimentally measurable spin-wave features are calculated, and the mean-field phase diagram of the model is obtained. Our model also suggests the existence of a large quantum critical region due to strong spin frustration upon increasing Se concentration. Copyright (C) EPLA, 2009
Title:: A "checkerboard" orbital-stripe phase and charge ordering transitions in Pr(SrxCa2-x)Mn2O7 (0 <= x <= 0.45)
Authors:: Li, ZA; Li, X; Wang, Z; Tian, HF; Ma, C; Zeng, LJ; Yang, HX Author Full Names: Li, Z. A.; Li, X.; Wang, Z.; Tian, H. F.; Ma, C.; Zeng, L. J.; Yang, H. X.
Source:: EPL 86 (6): Art. No. 67010 JUN 2009
Abstract:: The charge/orbital ordering (COO) behaviors in the double-layered Pr(SrxCa2-x)Mn2O7 have been investigated by in situ transmission electron microscopy (TEM) observations. The experimental results reveal that two charge ordering (CO) phase transitions, so-called T-co1 and T-co2, commonly exist in the orthorhombic Pr(SrxCa2-x)Mn2O7 (0 <= x <= 0.45) samples. Moreover, a "checkerboard" orbital-stripe phase characterized by two orthogonal COO modulations, q(a) and q(b), is observed between T-co1 and T-co2 in all samples. Detailed TEM investigations on the x=0.2 sample, in which a visible electric polarization was found (Tokunaga Y. et al., Nat. Mater., 5 (2006) 937) demonstrate that the q(b) modulation only survives between T-co1 and T-co2, and the "checkerboard" phase transforms into the conventional one-dimensional COO stripe phase below T-co2. The reversal of in-plane optical anisotropy across the T-co2 transition (Tokunaga Y. et al., Nat. Mater., 5 (2006) 937) is also explained based on TEM result. Copyright (C) EPLA, 2009
Title:: Polygrain icosahedral Al-Pd-Re quasicrystal as a granular electronic conductor
Authors:: Vekilov, YK; Chernikov, MA Author Full Names: Vekilov, Yu. Kh.; Chernikov, M. A.
Source:: EPL 87 (1): Art. No. 17010 JUL 2009
Abstract:: The mechanism of low-temperature electronic transport in polygrain samples of icosahedral Al-Pd-Re is analyzed by analogy with granular electronic systems. The intergranular tunneling and electrostatic energy (Coulomb blockade) are responsible for a specific behaviour of the electrical conductivity in polygrain samples of icosahedral Al-Pd-Re at low temperatures. Depending on the structural state of the sample, both factors may be important and the variable-range hopping regime, of Efros-Shklovskii's type, takes place. For the strong-coupling state the tunneling prevails, and the low-temperature variation of the electrical conductivity is dominated by the Coulomb-interaction and weak-localization corrections. Copyright (C) EPLA, 2009
Title:: Suppression of the current leakage in charge ordered Lu2Fe2Fe1-xMnxO7 (0 < x < 0.86)
Authors:: Qin, YB; Yang, HX; Zhang, Y; Tian, HF; Ma, C; Zeng, LJ; Li, JQ Author Full Names: Qin, Y. B.; Yang, H. X.; Zhang, Y.; Tian, H. F.; Ma, C.; Zeng, L. J.; Li, J. Q.
Source:: APPLIED PHYSICS LETTERS 95 (7): Art. No. 072901 AUG 17 2009
Abstract:: The ferroelectricity, magnetic properties, and charge-ordering modulations in the layered Lu2Fe2Fe1-xMnxO7 have been investigated for x ranging from 0 to 0.86. Experimental measurements reveal that substitution of Mn for Fe could evidently influence the low temperature magnetic transition. Moreover, ferroelectric analysis suggests that introduction of Mn ions in this layered system can efficiently suppress the conducting leakage and result in clear hysteresis loops in the polarization-electric field switching curves. The charge ordering states in Lu2Fe2Fe1-xMnxO7 characterized by two incommensurate modulations has been observed and discussed in association with the local spontaneous polarizations.
Update: 3-Sep-2009
Title:: Rare-earth free wrought-processed magnesium alloy with dispersion of quasicrystal phase
Authors:: Somekawa, H; Osawa, Y; Singh, A; Mukai, T Author Full Names: Somekawa, Hidetoshi; Osawa, Yoshiaki; Singh, Alok; Mukai, Toshiji
Source:: SCRIPTA MATERIALIA 61 (7): 705-708 OCT 2009
Abstract:: Quasicrystal and related phase particles were successfully dispersed in wrought-processed Mg-7.6 wt.% Zn-3.9 wt.% Al alloy with homogeneous and fine-grained structures. This rare-earth-free alloy showed high strength and ductility balance, which was superior to that of the well-known quasicrystal phase dispersed in Mg-Zn-RE alloys, with a weak texture and a reduction of mechanical asymmetry in yield strength. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:: Microstructural characterization of a laser remelted coating of Al91Fe4Cr3Ti2 quasicrystalline alloy
Authors:: Gargarella, P; Almeida, A; Vilar, R; Afonso, CRM; Rios, CT; Bolfarini, C; Botta, WJ; Kiminami, CS Author Full Names: Gargarella, P.; Almeida, A.; Vilar, R.; Afonso, C. R. M.; Rios, C. T.; Bolfarini, C.; Botta, W. J.; Kiminami, C. S.
Source:: SCRIPTA MATERIALIA 61 (7): 709-712 OCT 2009
Abstract:: A bulk sample of Al-Fe-Cr-Ti alloy with adequate composition to form quasicrystalline phases has been surface remelted, using laser processing techniques, to produce a quasicrystalline surface coating. After the laser treatment,
Update: 31-Dec-2008
Title:: Lattice dynamical calculation of negative thermal expansion in ZrV2O7 and HfV2O7
Authors:: Mittal, R; Chaplot, SL Author Full Names: Mittal, R.; Chaplot, S. L.
Source:: PHYSICAL REVIEW B 78 (17): Art. No. 174303 NOV 2008
Abstract:: We report lattice dynamics calculations of negative thermal-expansion (NTE) behavior of ZrV2O7 family, extending our previous work on the ZrW2O8 family. The two families of compounds differ in terms of the oxygen coordination around the V/W atoms leading to differences in the nature of soft phonons under compression that are responsible for the NTE. Our calculations quantitatively reproduce the negative expansion over a range of temperatures. We also discuss the relation of the soft phonons with the phase transitions observed in the ZrV2O7 family. Especially, the calculations show a soft-phonon mode at a wave vector of 0.31 < 1,1,0 >, which is in excellent agreement with the known incommensurate modulation in ZrV2O7 below 375 K.
Title:: Infrared-active excitations related to Ho3+ ligand-field splitting at the commensurate-incommensurate magnetic phase transition in HoMn2O5
Authors:: Sirenko, AA; O'Malley, SM; Ahn, KH; Park, S; Carr, GL; Cheong, SW Author Full Names: Sirenko, A. A.; O'Malley, S. M.; Ahn, K. H.; Park, S.; Carr, G. L.; Cheong, S-W.
Source:: PHYSICAL REVIEW B 78 (17): Art. No. 174405 NOV 2008
Abstract:: Linearly polarized spectra of far-infrared (IR) transmission in HoMn2O5 multiferroic single crystals have been studied in the frequency range between 8.5 and 105 cm(-1) and for temperatures between 5 and 300 K. Polarization of IR-active excitations depends on the crystallographic directions in HoMn2O5 and is sensitive to the magnetic phase transitions. We attribute some of the infrared-active excitations to electric-dipole transitions between ligand-field (LF) split states of Ho3+ ions. For light polarization along crystalline b axis, the oscillator strength of electric dipoles at low frequencies (10.5, 13, and 18 cm(-1)) changes significantly at the commensurate-incommensurate antiferromagnetic phase transition at T-3=19 K. This effect shows a strong correlation with the pronounced steps of the b-directional static dielectric function. We propose that the LF on Ho3+ connects the magnetism and dielectric properties of this compound through coupling with the Mn spin structure. We comment on the possibility for composite excitations of magnons and excited LF states.
Title:: Doping-dependent charge and spin superstructures in layered cobalt perovskites
Authors:: Sakiyama, N; Zaliznyak, A; Lee, SH; Mitsui, Y; Yoshizawa, H Author Full Names: Sakiyama, N.; Zaliznyak, A.; Lee, S. -H.; Mitsui, Y.; Yoshizawa, H.
Source:: PHYSICAL REVIEW B 78 (18): Art. No. 180406 NOV 2008
Abstract:: We have investigated cobaltite relatives of the layered perovskite cuprates and nickelates, Pr2-xCaxCoO4 (0.39 <= x <= 0.73) and La2-xSrxCoO4 (x=0.4, 0.61), using elastic neutron scattering. We have discovered doping-dependent incommensurate short-range ordering of charges and magnetic moments, which in cobaltites occur in the nonitinerant polaron phase, for 0.5 <= x <= 0.75. The charge order exists already at room temperature and shows no change on cooling. The incommensurability of its propagation vector, Q(c)=(epsilon(c), 0, l), roughly scales with the concentration of Co2+ ions, epsilon(c) similar to (1-x). Magnetic order follows at low T less than or similar to 40 K and has twice larger periodicity, indicating a dominant antiferromagnetic correlation between the nearest Co2+ spins.
Title:: Magnetic switching and phase competition in the multiferroic antiferromagnet Mn1-xFexWO4
Authors:: Ye, F; Ren, Y; Fernandez-Baca, JA; Mook, HA; Lynn, JW; Chaudhury, RP; Wang, YQ; Lorenz, B; Chu, CW Author Full Names: Ye, F.; Ren, Y.; Fernandez-Baca, J. A.; Mook, H. A.; Lynn, J. W.; Chaudhury, R. P.; Wang, Y. -Q.; Lorenz, B.; Chu, C. W.
Source:: PHYSICAL REVIEW B 78 (19): Art. No. 193101 NOV 2008
Abstract:: Elastic neutron scattering is used to study the spin correlations in the multiferroic Mn1-xFexWO4 with x=0.035, 0.05, and 0.10. The noncollinear incommensurate (ICM) magnetic structure associated with the ferroelectric (FE) phase in pure MnWO4 is suppressed at x=0.035 and completely absent at x=0.10. The ICM spin order and FE phase can be restored by applying a magnetic field along the spin easy axis. The low-T commensurate magnetic structure extends in both H/T with increasing Fe concentration. The systematic evolution of the magnetic and electric properties indicates that the noncollinear ICM spin order results from competing magnetic interactions and its stabilization can be tuned by the internal (x) or external (magnetic-field) perturbations.
Title:: Microscopic model for transitions from Mott to spin-Peierls insulator in TiOCl
Authors:: Zhang, YZ; Jeschke, HO; Valenti, R Author Full Names: Zhang, Yu-Zhong; Jeschke, Harald O.; Valenti, Roser
Source:: PHYSICAL REVIEW B 78 (20): Art. No. 205104 NOV 2008
Abstract:: On the basis of ab initio density-functional-theory calculations, we derive the underlying microscopic model Hamiltonian for TiOCl, a unique system that shows two consecutive phase transitions from a Mott insulator to a spin-Peierls insulator through a structurally incommensurate phase. We show with our model that the presence of magnetic frustration in TiOCl leads to a competition with the spin-Peierls distortion, which results in the unusual incommensurate phase. In addition, our calculations indicate that the spin-Peierls state is triggered by adiabatic phonons, which is essential for understanding the nature of the phase transition.
Title:: Chimie Douce Route to Sodium Hydroxo Titanate Nanowires with Modulated Structure and Conversion to Highly Photoactive Titanium Dioxides
Authors:: Peng, CW; Richard-Plouet, M; Ke, TY; Lee, CY; Chiu, HT; Marhic, C; Puzenat, E; Lemoigno, F; Brohan, L Author Full Names: Peng, Chih-Wei; Richard-Plouet, Mireille; Ke, Tsung-Yin; Lee, Chi-Young; Chiu, Hsin-Tien; Marhic, Christiane; Puzenat, Eric; Lemoigno, Frederic; Brohan, Luc
Source:: CHEMISTRY OF MATERIALS 20 (23): 7228-7236 DEC 9 2008
Abstract:: Sodium hydroxo titanate nanowires with NaTi2O4(OH) formulation are fabricated by chimie-douce from TiO2 powders in a hot concentrated base solution. In the present work, we investigate, in detail, the structure and morphology of the titanate, acid-exchanged materials, and phases formed during dehydration of these compounds; we then discuss the relationship between the initial titanate structure and TiO2 formation. XRD, ED, HRTEM, EDS, density measurements, and TG/MS results suggest that the titanate and acid-exchanged structures were closely related to the pseudolepidocrocite arrangement ("Cs2Ti6O12" type). The average structure of NaTi2O4(OH) nanowires consists of noncorrugated Ti2O3(OH) and NaO layers stacked along the [0 10] direction and an energy minimization was further conducted by theoretical methods. From TEM study, we demonstrated that NaTi2O4(OH) exhibits a modulated structure (q wave vector equals to 1/7 [001]*), which originates from the misfit between the NaO and Ti2O3(OH) sublattices. NaTi2O4(OH) structure has a monoclinic distortion (I2/m space group) with refined unit cell a = 0.37000(6) nm, b = 1.7816(4) nm, c = 2.2077(3) nm, beta = 92.70(1)degrees. Proton exchange followed by heat treatment convert the sodium hydroxo titanate into highly photoactive TiO2 nanowires. The activity is attributed to the presence of preferentially exposed (001) surface plane which is explained by the topotactic phase transformation of TiO2(B) into anatase.
Title:: Activation of magnetic shape memory effect in Ni-Mn-Ga alloys by mechanical and magnetic treatment
Authors:: Straka, L; Heczko, O; Hanninen, H Author Full Names: Straka, Ladislav; Heczko, Oleg; Haenninen, Hannu
Source:: ACTA MATERIALIA 56 (19): 5492-5499 NOV 2008
Abstract:: Mechanical and magnetic training decreased considerably the twinning stress of five-layered modulated, approximately tetragonal martensite (5M) oh Ni-Mn-Ga and Ni-Mn-Ga doped with Fe, and of seven-layered modulated, approximately orthorhombic Ni-Mn-Ga martensite (7M). Repeated compressions along two perpendicular directions of single crystal specimens of 5M and 7M reduced the twinning stress approximately threefold. Further reduction of twinning stress of 7M was achieved by the rotation of the specimen in I T magnetic field several times. The training resulted in the appearance of the magnetic shape memory effect or giant magnetic-field-induced strain in agreement with a simple energy-based model of the effect. The origin of the decrease in twinning stress is discussed. (c) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Update: 19-Dec-2008
Title:: High-temperature heat capacity of the Al63Cu25Fe12 quasicrystal
Authors:: Prekul, AF; Kazantsev, VA; Shchegolikhina, NI; Gulyaeva, RI; Edagawa, K Author Full Names: Prekul, A. F.; Kazantsev, V. A.; Shchegolikhina, N. I.; Gulyaeva, R. I.; Edagawa, K.
Source:: PHYSICS OF THE SOLID STATE 50 (11): 2013-2015 NOV 2008
Abstract:: The mechanisms of energy absorption by metallic alloys with long-range aperiodic lattice order and electronic properties of marginal metals are studied. The heat capacity and linear expansion coefficient of the Al63Cu25Fe12 icosahedral phase in the temperature range 300-1000 K are measured for the first time. Disagreement between the measured heat capacity and predictions made from the Debye model is found and analyzed. It is shown that the excess heat capacity observed at the temperatures of the experiment is fitted by Einstein's function in the approximation T
Title:: Longitudinal Spin Density Wave Order in a Quasi-1D Ising-like Quantum Antiferromagnet
Authors:: Kimura, S; Matsuda, M; Masuda, T; Hondo, S; Kaneko, K; Metoki, N; Hagiwara, M; Takeuchi, T; Okunishi, K; He, Z; Kindo, K; Taniyama, T; Itoh, M Author Full Names: Kimura, S.; Matsuda, M.; Masuda, T.; Hondo, S.; Kaneko, K.; Metoki, N.; Hagiwara, M.; Takeuchi, T.; Okunishi, K.; He, Z.; Kindo, K.; Taniyama, T.; Itoh, M.
Source:: PHYSICAL REVIEW LETTERS 101 (20): Art. No. 207201 NOV 14 2008
Abstract:: >From neutron diffraction measurements on a quasi-1D Ising-like Co2+ spin compound BaCo2V2O8, we observed an appearance of a novel type of incommensurate ordering in magnetic fields. This ordering is essentially different from the Neel-type ordering, which is expected for the classical system, and the peculiar spin structure is caused by quantum fluctuation inherent in the quantum spin chain. A Tomonaga-Luttinger liquid nature characteristic of the gapless quantum 1D system is responsible for the realization of the incommensurate ordering.
Title:: Charge Order in LuFe2O4: Antiferroelectric Ground State and Coupling to Magnetism
Authors:: Angst, M; Hermann, RP; Christianson, AD; Lumsden, MD; Lee, C; Whangbo, MH; Kim, JW; Ryan, PJ; Nagler, SE; Tian, W; Jin, R; Sales, BC; Mandrus, D Author Full Names: Angst, M.; Hermann, R. P.; Christianson, A. D.; Lumsden, M. D.; Lee, C.; Whangbo, M. -H.; Kim, J. -W.; Ryan, P. J.; Nagler, S. E.; Tian, W.; Jin, R.; Sales, B. C.; Mandrus, D.
Source:: PHYSICAL REVIEW LETTERS 101 (22): Art. No. 227601 NOV 28 2008
Abstract:: X- ray scattering by multiferroic LuFe2O4 is reported. Below 320 K, superstructure reflections indicate an incommensurate charge order with propagation close to (1/3 1/3 3/2). The corresponding charge configuration, also found by electronic structure calculations as most stable, contains polar Fe= O double layers with antiferroelectric stacking. Diffuse scattering at 360 K, with (1/3 1/3 0) propagation, indicates ferroelectric short- range correlations between neighboring double layers. The temperature dependence of the incommensuration indicates that charge order and magnetism are coupled.
Update: 12-Dec-2008
Title:: Influence of Rolling on the Precipitation of Icosahedral Quasicrystalline Phase in Zr-Al-Ni-Cu-Ag Amorphous Alloy
Authors:: Dang, SE; Wang, XH; Lian, PX; Hu, Y; Yan, ZJ; Liang, W; Zhang, GQ Author Full Names: Dang Shu'e; Wang Xianghui; Lian Peixia; Hu Yong; Yan Zhijie; Liang Wei; Zhang Guoqing
Source:: RARE METAL MATERIALS AND ENGINEERING 37 (10): 1800-1803 OCT 2008
Abstract:: Influence of rolling on the precipitation of icosahedral quasicrystalline phase (I-phase) in Zr65Al7.5Ni10Cu12.5Ag5 amorphous alloy is investigated by X-ray diffraction (XRD) and differential scanning calorimetry (DSC). The results show that more I-phase precipitate in the rolled alloys than that in the as-cast one, and that the amount becomes the maximum when the deformation degree epsilon reaches 70 %. Furthermore, the thermal stability of the I-phase increases with the deformation degree increasing. The thermal stability of I-phase shows the maximum at epsilon=70 %, but subsequently decreases. It is attributed to the change of atomic configuration in the alloy during plastic deformation.
Title:: Magnetic Dispersion of the Diagonal Incommensurate Phase in Lightly Doped La2-xSrxCuO4
Authors:: Matsuda, M; Fujita, M; Wakimoto, S; Fernandez-Baca, JA; Tranquada, JM; Yamada, K Author Full Names: Matsuda, M.; Fujita, M.; Wakimoto, S.; Fernandez-Baca, J. A.; Tranquada, J. M.; Yamada, K.
Source:: PHYSICAL REVIEW LETTERS 101 (19): Art. No. 197001 NOV 7 2008
Abstract:: We present inelastic neutron scattering experiments on a single-domain crystal of lightly doped La1.96Sr0.04CuO4. We find that the magnetic excitation spectrum in this insulating phase with a diagonal incommensurate spin modulation is remarkably similar to that in the superconducting regime, where the spin modulation is bond parallel. In particular, we find that the dispersion slope at low energy is essentially independent of doping and temperature over a significant range. The energy at which the excitations cross the commensurate antiferromagnetic wave vector increases roughly linearly with doping through the underdoped regime.
Title:: Effect of the electric polarization on the modulation wave vector of the antiferromagnetic structure of TbMnO3
Authors:: Chupis, IE; Ushakova, IV Author Full Names: Chupis, I. E.; Ushakova, I. V.
Source:: LOW TEMPERATURE PHYSICS 34 (11): 898-900 NOV 2008
Abstract:: The effect of electric polarization on the temperature and field dependences of the modulation vector k of the antiferromagnetic structure in terbium manganite is analyzed. It is shown that in contrast to anharmonicity the electric polarization increases k, which could be why a nonmonotonic temperature dependence of the modulation vector is observed in TbMnO3.
Title:: Nuclear Magnetism in Two-Dimensional Solid Helium Three on Graphite
Authors:: Fukuyama, H Author Full Names: Fukuyama, Hiroshi
Source:: JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 77 (11): Art. No. 111013 NOV 2008
Abstract:: Recent studies of nuclear magnetism of monolayer helium three (He-3) adsorbed on graphite are reviewed. This system provides us a fascinating testing ground for physics of highly frustrated quantum spins of two dimensions (2D) such as spin liquids. Particular emphasis is devoted to the gapless spin liquid state observed in the low-density commensurate phase (4/7 phase) in the second layer. Existing experiments on heat capacity in zero magnetic field and magnetization in low fields of this phase show unambiguously the gapless excitations down to three orders of magnitude lower temperatures than the relevant exchange interactions (approximate to 1 mK). This is a new class of spin liquid, and recently electronic counterparts are found in quasi-1D and -2D conductors. On the other hand, measured magnetic properties of the incommensurate phase at much higher densities can be described as a nearly ideal 2D S = 1/2 ferromagnet on a triangular lattice. We propose the existence of a new ferromagnetic commensurate phase at a density in between the 4/7 and incommensurate phases based on new heat capacity data. None of these phases show signatures of finite temperature phase transitions being consistent with the Mermin-Wagner theorem. The exchange interactions among He-3 nuclear spins originate from atom-atom tunnel exchanges due to the large zero-point motions. Because of the steric hindrance, higher order exchanges like three-, four-, five-, and six-spin ring exchanges are expected to compete each other in similar strengths (MSE model). The applicability of the MSE model to the experimental magnetic properties of this system including its density variation is discussed. It is satisfactory except the fact that the model does not reproduce the gapless nature of the 4/7 phase, which recently Stimulates different theoretical approaches such Lis the Hubbard model.
Title:: Symmetry determination following structure solution in P1
Authors:: Palatinus, L; van der Lee, A Author Full Names: Palatinus, L.; van der Lee, A.
Source:: JOURNAL OF APPLIED CRYSTALLOGRAPHY 41: 975-984 Part 6 DEC 2008
Abstract:: A new method for space-group determination is described. It is based on a symmetry analysis of the structure-factor phases resulting from a structure solution in space group P1. The output of the symmetry analysis is a list of all symmetry operations compatible with the lattice. Each symmetry operation is assigned a symmetry agreement factor that is used to select the symmetry operations that are the elements of the space group of the structure. On the basis of the list of the selected operations the complete space group of the structure is constructed. The method is independent of the number of dimensions, and can also be used in solution of aperiodic structures. A number of cases are described where this method is particularly advantageous compared with the traditional symmetry analysis. (C) 2008 International Union of Crystallography Printed in Singapore - all rights reserved
Title:: >From space to superspace and back: Superspace Group Finder
Authors:: Orlov, I; Palatinus, L; Chapuis, G Author Full Names: Orlov, Ivan; Palatinus, Lukas; Chapuis, Gervais
Source:: JOURNAL OF APPLIED CRYSTALLOGRAPHY 41: 1182-1186 Part 6 DEC 2008
Abstract:: The symmetry of a commensurately modulated crystal structure can be described in two different ways: in terms of a conventional three-dimensional space group or using the superspace concept in (3 + d) dimensions. The three-dimensional space group is obtained as a real-space section of the (3 + d) superspace group. A complete network was constructed linking (3 + 1) superspace groups and the corresponding three-dimensional space groups derived from rational sections. A database has been established and is available at http:// superspace.epfl.ch/finder/. It is particularly useful for finding common superspace groups for various series of modular ('composition-flexible') structures and phase transitions. The use of the database is illustrated with examples from various fields of crystal chemistry.
Title:: Tetrahedral Chain Order in the Sr2Fe2O5 Brownmillerite
Authors:: D'Hondt, H; Abakumov, AM; Hadermann, J; Kalyuzhnaya, AS; Rozova, MG; Antipov, EV; Van Tendeloo, G Author Full Names: D'Hondt, Hans; Abakumov, Artem M.; Hadermann, Joke; Kalyuzhnaya, Anna S.; Rozova, Marina G.; Antipov, Evgeny V.; Van Tendeloo, Gustaaf
Source:: CHEMISTRY OF MATERIALS 20 (22): 7188-7194 NOV 25 2008
Abstract:: The crystal structure of the Sr2Fe2O5 browninillerite has been investigated using electron diffraction and high resolution electron microscopy. The Sr2Fe2O5 structure demonstrates two-dimensional order: the tetrahedral chains with two mirror-related configurations (L and k) are arranged within the tetrahedral layers according to the -L-R-L-R- sequence, and the layers themselves are displaced with respect to each other over 1/2[111] or 1/2[11 (1) over bar] vectors of the brownmillerite unit cell, resulting in different ordered stacking variants. A unified superspace model is constructed for ordered stacking sequences in brownmillerites based on the averacge brownmillerite structure with a = 5.5298(4)angstrom, b = 15.5875(12)angstrom, c = 5.6687(4)angstrom, and (3 + 1)-dimensional superspace group 12/m(0 beta gamma)0s, q = beta b* + gamma c*, 0 <= beta <= 1/2, 0 <= gamma <= 1.
Title:: Crystal structure of a synthetic tin-selenium representative of the cylindrite structure type
Authors:: Makovicky, E; Petricek, V; Dusek, M; Topa, D Author Full Names: Makovicky, E.; Petricek, V.; Dusek, M.; Topa, D.
Source:: AMERICAN MINERALOGIST 93 (11-12): 1787-1798 NOV-DEC 2008
Abstract:: The synthetic tin-selenium member of the cylindrite structural family, with the empirical formula Sn31.51Sb6.23Fe3.12S59.(12) based on electron-microprobe data, has a triclinic crystal structure composed of two alternating layer types, both with a pronounced one-dimensional modulation, and with a non-commensurate layer match in two dimensions. The pseudotetragonal (Q) layer is a MeSe layer two-atomic planes thick with lattice parameters a = 5.969(2) angstrom, b = 6.004(1) angstrom, and the layer-stacking vector c = 12.238(1) angstrom, alpha = 87.98(4)degrees, beta = 83.14(3)degrees, and gamma = 90.01(4)degrees. The pseudohexagonal (H) layer is a single-octahedral MeSe2 layer with a = 3.831(1) angstrom, b = 6.580(3) angstrom, c = 12.151(5) angstrom, alpha = 87.79(4)degrees, beta = 90.59(3)degrees, and gamma = 89.99(3)degrees; the a and b vectors of the two subsystems are parallel, the c vectors diverge. The transversal wave-like modulation has the wave-normal parallel to b, so that the modulation vector q is 0.0001(3) a* + 0.1921(4) b* - 0.0119(3) c* in terms of the pseudohexagonal subsystem. Superspace structure refinement in the superspace group X (1) over bar where X stands for non-primitive centering vectors (1/2,1/2,0,0,0), (0,0,0,0,1/2), (1/2,1/2,0,0,1/2) in five-dimensional superspace, and based on 2128 observed reflections, resulted in R-1 = 0.038 for all reflections. Composition of the H layer has been modeled as Sn2404+Fe542+Se588, that of the Q layer as Sn3062+Sb1083+Se414. The cation-anion distances in Q layer vary between 2.63 and 3.30 angstrom, indicating that the cations present are primarily Sn2+ (and Sb3+), whereas distances in the H layer lie between 2.665 and 2.721 angstrom and correspond to Sn4+ with admixture of Fe2+. The shortest cation-anion distance across the interlayer space is 3.24 angstrom. Relations between layer match and the modulation vector, divergence of layer stackings of the two components, and reasons for the modulation and for the pronounced disorder of the Q component, as well as the differences and similarities with levyclaudite, franckeite, and synthetic layer-misfit compounds are discussed in detail. In its structural principles, although not in numerical values, the Sn-Se cylindrite corresponds fully to the natural Pb-Sn-S cylindrite previously described.
Title:: Original disorder-order transition related to electronic and magnetic properties in the thermoelectric misfit phase [Ca2CoO3][CoO2](1.62)
Authors:: Muguerra, H; Grebille, D Author Full Names: Muguerra, Herve; Grebille, Dominique
Source:: ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 64: 676-683 Part 6 DEC 2008
Abstract:: A structural phase transition is shown around 400 K for the thermoelectric lamellar misfit cobalt oxide [Ca2CoO3][CoO2](1.62). This transition is related to a rearrangement of the central [CoO] layer of the [Ca2CoO3] slab of this structure, characterized by a commensurate intrinsic modulation q(2) = 2/3a* -1/3c*. The partial residual disorder related to split Co and O atomic sites along the misfit b direction disappears and one can describe this layer with its triple chains as a modulated configuration with a regular and not distorted periodicity along b. This phase transition is associated with small changes observed in the transport and magnetic properties as a function of temperature.
Title:: Modular crystals as modulated structures: the case of the lillianite homologous series
Authors:: Elcoro, L; Perez-Mato, JM; Friese, K; Petricek, V; Balic-Zunic, T; Olsen, LA Author Full Names: Elcoro, Luis; Perez-Mato, J. M.; Friese, Karen; Petricek, Vaclav; Balic-Zunic, Tonci; Olsen, Lars Arnskov
Source:: ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 64: 684-701 Part 6 DEC 2008
Abstract:: The use of the superspace formalism is extended to the description and refinement of the homologous series of modular structures with two symmetry-related modules with different orientations. The lillianite homologous series has been taken as a study case. Starting from a commensurate modulated composite description with two basic subsystems corresponding to the two different modules, it is shown how a more efficient description can be achieved using so-called zigzag modulation functions. These linear zigzag modulations, newly implemented in the program JANA2006, have very large fixed amplitudes and introduce in the starting model the two orientations of the underlying module sublattices. We show that a composite approach with this type of function, which treats the cations and anions as two separate subsystems forming a misfit compound, is the most appropriate and robust method for the refinements.
Update: 5-Dec-2008
Title:: Structural State of Surface Layers of Aluminum after Laser Alloying Using a Mixture of Copper and Iron Powders
Authors:: Girzhon, VV; Smolyakov, AV; Tantsyura, IV Author Full Names: Girzhon, V. V.; Smolyakov, A. V.; Tantsyura, I. V.
Source:: PHYSICS OF METALS AND METALLOGRAPHY 106 (4): 384-388 OCT 2008
Abstract:: X-ray diffraction, metallographic, and electron-microscopic methods were used to study the regularities of the structure formation in the surface layers of aluminum upon pulse laser alloying using copper and iron powders taken in an atomic ratio of two to one. It is shown that, in the zone of laser alloying, a quasicrystalline phase can form, which leads to a considerable increase in microhardness. The effect of the thickness of the alloying layer on the structural and phase state of the laser-affected zone is analyzed.
Title:: Phase and Structural Transformations in the Alloy on the Basis of the Orthorhombic Titanium Aluminide
Authors:: Popov, AA; Illarionov, AG; Grib, SV; Demakov, SL; Karabanalov, MS; Elkina, OA Author Full Names: Popov, A. A.; Illarionov, A. G.; Grib, S. V.; Demakov, S. L.; Karabanalov, M. S.; Elkina, O. A.
Source:: PHYSICS OF METALS AND METALLOGRAPHY 106 (4): 399-410 OCT 2008
Abstract:: Phase and structural transformations in the Ti-24.3 Al-24.8 Nb-1.0 Zr-1.4 V-0.6 Mo-0.3 Si (at %) alloy that take place during heating in the temperature range of 700-1050 degrees C have been investigated. The temperature ranges of existence of the O + beta, O + beta + alpha(2), beta + alpha(2), and beta phase fields have been established. A scheme of the relationships between the volume fractions of the O, beta, and alpha(2) phases depending on the temperature of heating of the alloy have been investigated. The formation of an ordered incommensurate omega (V (omega)) phase has been revealed in the alloy during quenching from 900 degrees C. The existence of a correlation between the hardness properties and changes in the phase composition and morphology of particles precipitating in the alloy has been shown.
Title:: Domain fluctuations near the field-induced incommensurate-commensurate phase transition of TbMnO3
Authors:: Barath, H; Kim, M; Cooper, SL; Abbamonte, P; Fradkin, E; Mahns, I; Rubhausen, M; Aliouane, N; Argyriou, DN Author Full Names: Barath, H.; Kim, M.; Cooper, S. L.; Abbamonte, P.; Fradkin, E.; Mahns, I.; Ruebhausen, M.; Aliouane, N.; Argyriou, D. N.
Source:: PHYSICAL REVIEW B 78 (13): Art. No. 134407 OCT 2008
Abstract:: We present temperature- and field-dependent inelastic light-scattering studies of multiferroic TbMnO3. By carefully examining the evolution of magneto-elastic modes in various phases of TbMnO3, our study reveals several features of the field-induced incommensurate-commensurate (IC-C) transition in TbMnO3. We find that, for fields applied along the b axis, there is a coexistence of distinct structural phases in the intermediate field regime (H=4-7 T) around the IC-C-phase transition. We present evidence for the existence of dynamical fluctuations of the C phase for fields lower than the critical field for H along the b axis, H < H-c(b). Furthermore, we present evidence for strong spin-lattice coupling effects in TbMnO3 in the form of zone-boundary phonon modes that strongly couple to the spins by modulating the exchange interaction in this material.
Title:: Raman scattering from the spin-gap mode in the Ni-doped spin-Peierls compound CuGeO3
Authors:: Sekine, T; Kaneko, T; Kuroe, H; Masuda, T Author Full Names: Sekine, Tomoyuki; Kaneko, Tomomi; Kuroe, Haruhiko; Masuda, Takatsugu
Source:: PHYSICAL REVIEW B 78 (13): Art. No. 134409 OCT 2008
Abstract:: By means of Raman scattering we have studied the spin-Peierls (SP) transition in Ni-doped CuGeO3 crystals. The folded-phonon peak extremely broadens and the two-magnetic-excitation mode disappears when the Ni concentration is above about 2.0%, indicating that the SP phase collapses. The spin-gap mode is activated in lightly Ni-doped samples. This peak neither splits nor shifts under magnetic fields in the SP phase, but its frequency increases in the incommensurate phase. The activation of the spin-gap mode is interpreted in terms of a mixing between the spin-singlet ground state and the S-z=0 triplet excited one by staggered fields around the doped impurities. Meanwhile, the two-magnetic-excitation mode gradually diminishes in intensity with increasing magnetic field in the incommensurate phase.
Title:: Fermi-surface-induced lattice modulation and charge-density wave in optimally doped YBa2Cu3O7-x
Authors:: Liu, X; Islam, Z; Sinha, SK; Moss, SC; McQueeney, RJ; Lang, JC; Welp, U Author Full Names: Liu, X.; Islam, Z.; Sinha, S. K.; Moss, S. C.; McQueeney, R. J.; Lang, J. C.; Welp, U.
Source:: PHYSICAL REVIEW B 78 (13): Art. No. 134526 OCT 2008
Abstract:: We have observed a Fermi-surface (FS) induced lattice modulation in a YBa2Cu3O7-x superconductor with a wave vector along CuO chains; i.e., q(1)=(0,delta,0). The value of delta similar to 0.21 is twice the Fermi wave vector (2k(F)) along b(*) connecting nearly nested FS "ridges." The q(1) modulation exists only within O-vacancy-ordered islands [characterized by q(0)=(1/4,0,0)] and persists well above and below T-c. Our results are consistent with the presence of a FS-induced charge-density wave.
Title:: Competing order, Fermi surface reconstruction, and quantum oscillations in underdoped high-temperature superconductors
Authors:: Dimov, I; Goswami, P; Jia, X; Chakravarty, S Author Full Names: Dimov, Ivailo; Goswami, Pallab; Jia, Xun; Chakravarty, Sudip
Source:: PHYSICAL REVIEW B 78 (13): Art. No. 134529 OCT 2008
Abstract:: We consider incommensurate order parameters for electrons on a square lattice which reduce to d-density wave order when the ordering wave vector Q is close to Q(0)=(pi/a,pi/a), a being the lattice spacing and describe the associated charge and current distributions within a single-harmonic approximation that conserves current to lowest order. Such incommensurate orders can arise at the mean-field level in extended Hubbard models, but the main goal here is to explore thoroughly the consequences within a Hartree-Fock approximation. We find that Fermi surface reconstruction in the underdoped regime can correctly capture the phenomenology of the recent quantum oscillation experiments that suggest incommensurate order, in particular the de Haas-van Alphen oscillations of the magnetization in high fields and very low temperatures in presumably the mixed state of these superconductors. For 10% hole doping in YBa2Cu3O6+delta, we find in addition to the main frequency around 530 T arising from the electron pocket and a hole frequency at around 1650 T, a new low frequency from a smaller hole pocket at 250 T for which there are some indications that require further investigations. The oscillation corresponding to the electron pocket will be further split due to bilayer coupling, but the splitting is sufficiently small to require more refined measurements. The truly incommensurate d-density wave breaks both time reversal and inversion, but the product of these two symmetry operations is preserved. The resulting Fermi surface splits into spin-up and spin-down sectors that are inversion conjugates. Each of the spin sectors results in a band structure that violates reflection symmetry, which can be determined in spin and angle-resolved photoemission spectroscopies. For those experiments such as the current photoemission experiments or the quantum oscillation measurements that cannot resolve the spin components, the bands will appear to be symmetric because of the equal mixture of the two spin sectors. There is some similarity of our results with the spiral spin-density wave order which, as pointed out by Overhauser, also breaks time reversal and inversion. Calculations corresponding to higher order commensuration produce results similar to antiphase spin stripes but appear to us to be an unlikely explanation of the experiments. The analysis of the Gorkov equation in the mixed state shows that the oscillation frequencies are unshifted from the putative normal state and the additional Dingle factor arising from the presence of the mixed state can provide a subtle distinction between the spiral spin-density wave and the d-density wave, although this is very difficult to establish precisely.
Title:: Static magnetic order in the triangular lattice of LixNiO2 (x <= 1): Muon-spin spectroscopy measurements
Authors:: Sugiyama, J; Mukai, K; Ikedo, Y; Russo, PL; Nozaki, H; Andreica, D; Amato, A; Ariyoshi, K; Ohzuku, T Author Full Names: Sugiyama, Jun; Mukai, Kazuhiko; Ikedo, Yutaka; Russo, Peter L.; Nozaki, Hiroshi; Andreica, Daniel; Amato, Alex; Ariyoshi, Kingo; Ohzuku, Tsutomu
Source:: PHYSICAL REVIEW B 78 (14): Art. No. 144412 OCT 2008
Abstract:: In spite of numerous experimental and theoretical reports on LiNiO2, no consistent picture has emerged of the nature of its ground state. We have investigated the LixNiO2 system (0.1 <= x <= 1) by means of muon-spin spectroscopy and susceptibility to gain further insight from the effects of varying the magnetic ion concentration. Static magnetic order, most likely to be incommensurate to the spatial lattice period, was found for x >= 0.6 at low temperatures (T), while disordered magnetism due to localized Ni moments appears for x=1/2-1/4 and, finally, Li0.1NiO2 exhibits almost fully nonmagnetic behavior down to the lowest T measured. The ground state of LiNiO2 is inferred to be a "static but short-range" A-type antiferromagnetic ordered system, in which the Ni3+ moments align ferromagnetically along the c axis in the NiO2 plane with an incommensurate modulation probably due to canting of the Ni3+ moments, but align antiferromagnetically between adjacent NiO2 planes.
Title:: Theory of the ordered phase in A-site antiferromagnetic spinels
Authors:: Lee, SB; Balents, L Author Full Names: Lee, SungBin; Balents, Leon
Source:: PHYSICAL REVIEW B 78 (14): Art. No. 144417 OCT 2008
Abstract:: Insulating spinel materials, with the chemical formula AB(2)X(4), behave as diamond lattice antiferromagnets when only the A-site atom is magnetic. Many exhibit classic signatures of frustration, induced not geometrically but by competing first- and second-neighbor exchange interactions. In this paper, we further develop a theory [D. Bergman , Nat. Phys. 3, 487 (2007)] of the magnetism of these materials, focusing on the physics observable within the ordered state. We derive a phenomenological Landau theory that predicts the orientation of the spins within incommensurate spiral ordered states. It also describes how the spins reorient in a magnetic field and how they may undergo a low-temperature "lock-in" transition to a commensurate state. We discuss microscopic mechanisms for these magnetic-anisotropy effects. The reduction in the ordered moment by quantum fluctuations is shown to be enhanced due to frustration. Our results are compared to experiments on MnSc2S4, the best characterized of such A-site spinels, and more general implications are discussed. One prediction is that magnetically induced ferroelectricity is generic in these materials, and a detailed description of the relation of the electric polarization to the magnetism is given.
Title:: Direct measurement of charge transfer in thermoelectric Ca3Co4O9
Authors:: Yang, G; Ramasse, Q; Klie, RF Author Full Names: Yang, G.; Ramasse, Q.; Klie, R. F.
Source:: PHYSICAL REVIEW B 78 (15): Art. No. 153109 OCT 2008
Abstract:: The misfit-layered cobalt oxide Ca3Co4O9 exhibits outstanding physical properties including high thermoelectric power, low thermal conductivity, low resistivity, and high thermal stability. We utilize atomic-resolution Z-contrast imaging in conjunction with electron energy-loss spectroscopy (EELS) in an aberration-corrected scanning transmission electron microscope (STEM) to characterize the local atomic and electronic structure of Ca3Co4O9. We will show that the position of the O atoms in the CoO2 layers can be directly imaged, and that the CoO columns in the rocksalt layer exhibit a strong modulation in the (010) direction. Further, we measure the local Co valence and find significant hole transfer from the rocksalt CoO to the hexagonal CoO2 layers. Our results are confirmed by self-consistent multiple-scattering calculations and we conclude that this hole transfer increases the mobile hole concentration and breaks the electron-hole symmetry in the CoO2 layers, thereby enabling the high thermoelectric power in the strongly correlated CoO2 subsystem.
Title:: Growth of Bi thin films on quasicrystal surfaces
Authors:: Sharma, HR; Fournee, V; Shimoda, M; Ross, AR; Lograsso, TA; Gille, P; Tsai, AP Author Full Names: Sharma, H. R.; Fournee, V.; Shimoda, M.; Ross, A. R.; Lograsso, T. A.; Gille, P.; Tsai, A. P.
Source:: PHYSICAL REVIEW B 78 (15): Art. No. 155416 OCT 2008
Abstract:: We present a comprehensive study of Bi thin-film growth on quasicrystal surfaces. The substrates used for the growth are the fivefold surface of icosahedral (i)-Al-Cu-Fe and i-Al-Pd-Mn and the tenfold surface of decagonal (d)-Al-Ni-Co quasicrystals. The growth is investigated at 300 and 525 K substrate temperatures and at different coverage (theta) ranging from submonolayer to ten monolayers. The film is characterized by scanning tunneling microscopy, reflection high-energy electron diffraction, and x-ray photoelectron spectroscopy. At 300 K, the deposited Bi yields a quasicrystalline film for theta <= 1. For 1
Title:: Effect of composition on the formability of quasicrystalline phase in mechanically alloyed Al-Cu-Fe powders
Authors:: Yin, SL; Li, CX; Blan, Q; Lu, M Author Full Names: Yin, Shilong; Li, Caixia; Blan, Qing; Lu, Min
Source:: MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 496 (1-2): 362-365 NOV 25 2008
Abstract:: A systematic study has been carried out to investigate the effect of composition on the ability of mechanically alloyed Al-Cu-Fe powders to form quasicrystalline (QC)-phases. Their microstructures were measured by means of X-ray diffraction and transmission electron microscopy (TEM). The results show that the formation of Al-Cu-Fe QC-phases is sensitive to the starting ratio of the elements Al, Cu and Fe and that Al70Cu20Fe10 is the optimum composition among those studied. No single QC-phase was obtained, but a high volume fraction of the QC-phase can be obtained by a suitable choice of the milling time, annealing temperature and annealing time. The volume fraction of the QC-phase in Al70Cu20Fe10 powders milled for 2 h and annealed for 5 h at 750 degrees C is greater than 90%. (C) 2008 Elsevier B.V. All rights reserved.
Title:: Icosahedral quasicrystal phase in Mg-Zn-Nd ternary system
Authors:: Zhang, JS; Yan, J; Liang, W; Xu, CX; Zhou, CL Author Full Names: Zhang, J. S.; Yan, J.; Liang, W.; Xu, C. X.; Zhou, C. L.
Source:: MATERIALS LETTERS 62 (30): 4489-4491 DEC 15 2008
Abstract:: Mg-Zn-Nd master alloy containing icosahedral quasicrystal phase with an interesting macro-shape has been prepared under conventional casting conditions. The microstructures and phases of Mg-Zn-Nd ternary alloy have been investigated by using SEM, EDS and TEM. The results show that the spherical phase in Mg-Zn-Nd master alloy is a simple icosahedral quasicrystal with stoichiometric composition of Mg40Zn55Nd5 and quasilattice a(R) = 0.525 nm. In this research, when the content of Nd is 1.20 at.% and atom ratio value of Mg/Zn at the range of 2.4-2.7, the as-cast solidification microstructure mainly consists of primary I-phase and Mg7Zn3 single-phase matrix. (C) 2008 Elsevier B.V. All rights reserved.
Title:: Deuterium dynamics in the icosahedral and amorphous phases of the Ti40Zr40Ni20 hydrogen-absorbing alloy studied by H-2 NMR
Authors:: Gradisek, A; Kocjan, A; McGuiness, PJ; Apih, T; Kim, HJ; Dolinsek, J Author Full Names: Gradisek, A.; Kocjan, A.; McGuiness, P. J.; Apih, T.; Kim, Hae Jin; Dolinsek, J.
Source:: JOURNAL OF PHYSICS-CONDENSED MATTER 20 (47): Art. No. 475209 NOV 26 2008
Abstract:: The Ti40Zr40Ni20 hydrogen-absorbing alloy was prepared in the icosahedral and amorphous phases by controlling the rotation speed of the melt-spinning method of sample preparation, and the deuterium dynamics was investigated by H-2 NMR dynamic lineshape and spin-lattice relaxation. The results were analysed by the lineshape and relaxation models that assume deuterium thermally activated hopping within a manifold of different chemical environments. The observed 8% larger activation energy for the deuterium hopping over the interstitial sites and the 10% larger static spectrum width of the amorphous phase, as compared to the icosahedral phase, can be accounted for by the larger deuterium content of the investigated amorphous sample. From the deuterium dynamics point of view, the icosahedral phase is not special with respect to the amorphous modification of the same material.
Title:: Noncentrosymmetric commensurate magnetic ordering of multiferroic ErMn2O5
Authors:: Roessli, B; Fischer, P; Brown, PJ; Janoschek, M; Sheptyakov, D; Gvasaliya, SN; Ouladdiaf, B; Zaharko, O; Golovenchits, E; Sanina, V Author Full Names: Roessli, B.; Fischer, P.; Brown, P. J.; Janoschek, M.; Sheptyakov, D.; Gvasaliya, S. N.; Ouladdiaf, B.; Zaharko, O.; Golovenchits, Eu; Sanina, V.
Source:: JOURNAL OF PHYSICS-CONDENSED MATTER 20 (48): Art. No. 485216 DEC 3 2008
Abstract:: The noncentrosymmetric magnetic structure of ErMn2O5 has been shown to be very similar to that of HoMn2O5 (Vecchini et al 2008 Phys. Rev. B 77 134434). The magnetic modulation at 25 K has propagation vector (k) over right arrow = (1/2, 0, 1/4) and the symmetry imposes very few constraints on the magnetic configurations allowed. Only by combining the results of bulk magnetization measurements, powder and single crystal neutron diffraction and spherical neutron polarization analysis was it possible to distinguish clearly between different models. The susceptibility measurements show that the erbium magnetic moments are aligned parallel to the c-axis indicating strong single ion anisotropy. Spherical neutron polarimetry demonstrates the presence of two unequally populated chirality domains in ErMn2O5 single crystals. X-ray diffraction measurements on an ErMn2O5 powder using synchrotron radiation show that the buckling angles of the Mn-O-Mn bond change below the transition to the ferroelectric phase.
Title:: Possible mechanisms of formation of long-periodic magnetic structure in high-symmetry crystals
Authors:: Zavorotnev, YD; Medvedyeva, LI Author Full Names: Zavorotnev, Yu. D.; Medvedyeva, L. I.
Source:: JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 321 (3): 231-233 FEB 2009
Abstract:: On the example of a crystal with point symmetry group and based on the method of integral rational basis of invariants, linear and nonlinear invariants of first spatial derivatives with respect to the order parameters of the exchange origin have been calculated. It is shown the competition of what kind of parameters can initiate modulated magnetic structures in crystals of this symmetry. (C) 2008 Elsevier B.V. All rights reserved.
Title:: Nanoindentation studies on single crystals of Zn-Mg-Er and Zn-Mg-Ho icosahedral phases
Authors:: Mukhopadhyay, NK; Belger, A; Paufler, P; Uhrig, E; Bruhne, S; Assmus, W Author Full Names: Mukhopadhyay, N. K.; Belger, A.; Paufler, P.; Uhrig, E.; Bruehne, S.; Assmus, W.
Source:: JOURNAL OF ALLOYS AND COMPOUNDS 466 (1-2): 160-164 OCT 20 2008
Abstract:: Single crystals of Zn-Mg-Er and Zn-Mg-Ho icosahedral phases were grown from the melt using the liquid encapsulated top seeded solution growth technique. The fivefold planes of these as-grown single crystals were polished and used for the present nanoindentation studies using Hysitron triboscope attached to an atomic force microscope with a maximum load up to 16 mN. The reduced Young's modulus (E-r) and nanohardness (H) were found to be 135 +/- 10 GPa and 8.5 +/- 0.2 GPa for the F-type Zn65Mg25Er10 quasicrystal whereas for the P-type Zn74Mg15Ho11 quasicrystal (QC) these were 135 +/- 10 GPa and 7.8 +/- 0.2 GPa, respectively. Using the appropriate constants, the average E in both the quasicrystalline alloys was estimated as 140 10 GPa. The elastic and plastic deformation characteristics in load-displacement, F-h, curve appears to be identical in both the QC phases. The peculiarity in the load-displacement curves, in terms of pop-ins were observed frequently. AFM images showed the steps in the pile-up material which can be identified as shear bands and correlated with the pop-ins. The first pop-in was observed in the load range of 70 mu N in case Zn-Mg-Ho and 84 mu N in case of Zn-Mg-Er QC. The contact pressure, p, turns out to be 13 GPa for Zn-Mg-Ho and 18 GPa for Zn-Mg-Er QC. The maximum shear stress under the indent, TT,,c, is found to vary from 6 to 8 GPa, which is close to the theoretical shear strength of this material (similar to E/20). The energy required for the indentation was determined from the first pop-ins and it turned out to be 0.88 eV/atom, close to the thermal energy required for deformation of quasicrystals. Thus the 'pop-ins' are attributed to the elastic-plastic transition during indentation. (c) 2007 Elsevier B. V. All rights reserved.
Title:: On the Magnetically Driven Ferroelectric Phase in GdMnO3
Authors:: Ribeiro, JL Author Full Names: Ribeiro, J. L.
Source:: FERROELECTRICS 368: 352-357 2008
Abstract:: At room temperature, GdMnO3 is a paraelectric and paramagnetic with a distorted perovskite structure of orthorhombic symmetry (space group Pnma). On cooling, it undergoes a phase transition sequence to a magnetic incommensurate phase ([image omitted] = (T)[image omitted]*; Tc1 = 42 K) and a A-type antiferromagnetic phase (Tc2 = 27 K). At low temperatures (T 12 K), a magnetic field applied along the a-axis destabilizes the antiferromagnetic phase and induces a first order transition to a magnetic commensurate modulated phase ([image omitted] = 1/4[image omitted]*) that is also ferroelectric ([image omitted]//[image omitted]). This work analyses this field induced phase transition from the point of view of the symmetry and Landau theory.
Title:: Crystal Structures and Phase Transitions in A-Site Deficient Perovskites Ln(1/3)TaO(3)
Authors:: Zhou, QD; Saines, PJ; Sharma, N; Ting, J; Kennedy, BJ; Zhang, ZM; Withers, RL; Wallwork, KS Author Full Names: Zhou, Qingdi; Saines, Paul J.; Sharma, Neeraj; Ting, Jimmy; Kennedy, Brendan J.; Zhang, Zhaoming; Withers, Ray L.; Wallwork, Kia S.
Source:: CHEMISTRY OF MATERIALS 20 (21): 6666-6676 NOV 11 2008
Abstract:: The synthesis and structures of the perovskites Ln(1/3)TaO(3) are described. As the size of the Ln cation is reduced, the compounds display a sequence of structure: P4/mmm/La -> Cmmm/Ce-Gd -> Pmma/Tb, Dy -> Pmc2(1)/Ho. Er. Although apparently tetragonal in P4/mmm, electron diffraction patterns of Tm1/3TaO3 reveal this has a complex incommensurate structure. Likewise Gd1/3TaO3 appears metrically tetragonal. but electron diffraction and synchrotron X-ray powder diffraction demonstrate this is actually orthorhombic. The suppression of the spontaneous orthorhombic strain in Gd1/3TaO3 is thought to be due to the proximity to the first-order Cmmm-Pmma transition. Variable temperature studies show both Tb1/3TaO3 and Dy1/3TaO3 undergo a first-order Cmmm-Pmma transition upon heating.
Title:: Applications of Mossbauer Spectroscopy to Studies of Quasicrystals
Authors:: Stadnik, ZM Author Full Names: Stadnik, Z. M.
Source:: ACTA PHYSICA POLONICA A 114 (6): 1475-1482 DEC 2008
Abstract:: A review is presented of the application of the Mossbauer spectroscopy to the study of quasicrystals. The usefulness of the Mossbauer spectroscopy to solving the atomic structure of a complex icosahedral system is illustrated. The role of the Mossbauer spectroscopy in studies of magnetism of quasicrystals is discussed. The Mossbauer spectroscopy results on phason dynamics in quasicrystals are reviewed.
Update: 27-Nov-2008
Title:: Magnetization of Polycrystalline BiFeO3 in High Magnetic Fields
Authors:: Wardecki, D; Przenioslo, R; Sosnowska, I; Skourski, Y; Loewenhaupt, M Author Full Names: Wardecki, Dariusz; Przenioslo, Radoslaw
Source:: JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 77 (10): Art. No. 103709 OCT 2008
Abstract:: The magnetization of polycrystalline ceramic BiFeO3 has been studied with pulsed magnetic fields up to 58T. We observe a magnetic transition in both, increasing and decreasing magnetic fields. The critical field of the transition decreases with temperature. It is observed at 18.1 T at 80 K and 16.1 T at 235 K for increasing fields, whereas with decreasing fields the transition is observed at about 1.5 T below these values. The observed transition is the same as that reported in BiFeO3 single crystals at 10K [Kadomtseva et al.: JETP Lett. 79 (2004) 571]. It was attributed to the destruction of the modulated magnetic ordering in BiFeO3.
Title:: Evolution of an Unconventional Superconducting State inside the Antiferromagnetic Phase of CeNiGe3 under Pressure: A Ge-73-Nuclear-Quadrupole-Resonance Study
Authors:: Harada, A; Mukuda, H; Kitaoka, Y; Thamizhavel, A; Okuda, Y; Settai, R; Onuki, Y; Itoh, KM; Haller, EE; Harima, H Author Full Names: Harada, Atsushi; Mukuda, Hidekazu
Source:: JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 77 (10): Art. No. 103710 OCT 2008
Abstract:: We report a Ge-73 nuclear-quadrupole-resonance (NQR) Study on novel evolution of unconventional superconductivity in antiferromagnetic (AFM) CeNiGe3. The measurements of the Ge-73-NQR spectrum and the nuclear spin-lattice relaxation rate (1/T-1) have revealed that the unconventional superconductivity evolves inside a commensurate AFM phase around the pressure (P) where Neel temperature T-N exhibits its maximum at 8.5 K. The superconducting transition temperature T-SC has been found to be enhanced with increasing T-N, before reaching the quantum critical point at which the AFM order collapses. Above T-SC, the AFM structure transits from an incommensurate spin-density-wave order to a commensurate AFM order at T similar to 2 K. accompanied by a longitudinal spin-density fluctuation. With regard to heavy-fermion compounds, these novel phenomena have hitherto never been reported in the P-T phase diagram.
Title:: The roles of "ammonium" and "hydrogen-bond" protons in single crystals of the superionic conductor NH4HSeO4 by H-1 NMR relaxation
Authors:: Lim, AR; Jang, SW; Chang, JH Author Full Names: Lim, Ae Ran; Jang, Seo Won
Source:: JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS 69 (10): 2360-2365 OCT 2008
Abstract:: The variations with temperature of the line-shape, spin-lattice relaxation time, T-1, and spin-spin relaxation time, T-2, of the H-1 nuclei in NH4HSeO4 single crystals were investigated, and with these H-1 NMR results we were able to distinguish the crystals' "ammonium" and "hydrogen-bond" protons. The line width of the signal due to the ammonium protons abruptly narrows near the temperature of the superionic phase transition, T-si, which indicates that they play an important role in this phase transition. The H-1 T-1 for NH4+ and HSeO4- in NH4HSeO4 do not change significantly near the ferroelectric phase transition of T-c1 (= 250 K) and the incommensurate phase transition of T-i (= 261 K), whereas they change near the temperature of the superionic phase transition T-s1 (= 400 K). Our results indicate that the main contribution to the low-temperature phase transition below T-s1 is that of the molecular motion of ammonium and hydrogen-bond protons, and the main contribution to the conductivity at high temperatures above T-s1 is the breaking of the O-H...O bonds and the formation of new H- bonds in HSeO4-. In addition, we compare these results with those for the NH4HSO4 and (NH4)(3)H(SO4)(2) single crystals, which have similar hydrogen-bonded structure. (C) 2008 Elsevier Ltd. All rights reserved.
Title:: A Theory of General Solutions of Plane Problems in Two-Dimensional Octagonal Quasicrystals
Authors:: Gao, Y; Zhao, BS; Xu, SP Author Full Names: Gao, Yang; Zhao, Bao-Sheng
Source:: JOURNAL OF ELASTICITY 93 (3): 263-277 DEC 2008
Abstract:: A theory of general solutions of plane problems is developed for the coupled equations in plane elasticity of two-dimensional octagonal quasicrystals. In virtue of the operator method, the general solutions of the antiplane and inplane problems are given constructively with two displacement functions. The introduced displacement functions have to satisfy higher order partial differential equations, and therefore it is difficult to obtain rigorous analytic solutions directly and is not applicable in most cases. In this case, a decomposition and superposition procedure is employed to replace the higher order displacement functions with some lower order displacement functions, and accordingly the general solutions are further simplified in terms of these functions. In consideration of different cases of characteristic roots, the general solution of the antiplane problem involves two cases, and the general solution of the inplane problem takes three cases, but all are in simple forms that are convenient to be applied. Furthermore, it is noted that the general solutions obtained here are complete in x(3)-convex domains.
Title:: Thermoelectric properties of polygrained icosahedral Al71-xGaxPd20Mn9 (x=0,2,3,4) quasicrystals
Authors:: Takagiwa, Y; Kamimura, T; Hosoi, S; Okada, JT; Kimura, K Author Full Names: Takagiwa, Y.; Kamimura, T.
Source:: JOURNAL OF APPLIED PHYSICS 104 (7): Art. No. 073721 OCT 1 2008
Abstract:: The electrical and thermal transport properties of quaternary icosahedral Al71-xGaxPd20Mn9 (x=0,2,3,4) quasicrystals, obtained by replacing Al in icosahedral Al-Pd-Mn quasicrystal with Ga, have been measured in accordance with the guiding principle of "weakly bonded rigid heavy clusters" (WBRHCs). While the electrical conductivity and Seebeck coefficient were not dramatically changed, the thermal conductivity effectively decreased with increasing Ga concentration except for the sample with x=4. Although the thermoelectric properties do not obey the WBRHCs, the dimensionless figure of merit increased by a factor of 1.4 from 0.18 for Al71Pd20Mn9 to 0.26 for Al68Ga3Pd20Mn9 quasicrystal. (c) 2008 American Institute of Physics.
Title:: Fe-57 Mossbauer Effect Study of Zn-Sc-Fe Icosahedral Quasicrystal and Its 1/1 Crystal Approximant
Authors:: Edagawa, K; Tamura, R; Yamada, T; Oda, K Author Full Names: Edagawa, Keiichi; Tamura, Ryuji
Source:: JAPANESE JOURNAL OF APPLIED PHYSICS 47 (5): 3581-3583 Part 1 MAY 2008
Abstract:: The Zn-Sc-Fe icosahedral quasicrystal and its 1/1 crystal approximant have been studied with Fe-57 Mossbauer spectroscopy at room temperature. The spectra for the two phases exhibit substantially different features, indicating largely different local atomic environments in the two phases. This is in contrast to the results previously reported for the Al-Cu-Fe(-Si) system, in which the icosahedral phase and its crystal approximants show similar features in Mossbauer spectra, indicating similar local atomic environments. Possible Fe sites in the Zn-Sc-Fe approximant phase are discussed on the basis of the crystal structure determined previously. [DOI: 10.1143/JJAP.47.3581]
Title:: A Layered Iron-Rich 2234-Type with a Mixed Valence of Iron: The Ferrimagnetic Tl-Doped Fe-2(Sr2-epsilon Tl epsilon)Sr(3)Fe(4)O14.65
Authors:: Lepoittevin, C; Malo, S; Nguyen, N; Hebert, S; Van Tendeloo, G; Hervieu, M Author Full Names: Lepoittevin, Christophe; Malo, Sylvie
Source:: CHEMISTRY OF MATERIALS 20 (20): 6468-6476 OCT 28 2008
Abstract:: A new Tl-doped strontium ferrite Fe-2(Sr2-epsilon Tl epsilon)Sr3Fe4O14.65, with an original structure, has been synthesized and structurally characterized by powder X-ray diffraction and transmission electron microscopy. The TGA and Mossbauer studies evidence a mixed valence of iron. The structure exhibits a commensurate modulation, with a F-type subcell a approximate to b approximate to 5.4 angstrom ( approximate to a(p)root/2), c approximate to 42 angstrom with a modulation vector (q) over right arrow = alpha(a) over right arrow* with alpha = 0.4. The supercell parameters have been refined as a= 27.1101(8) angstrom, b= 5.5187(2) angstrom and c= 42.0513(9) angstrom, in the space group Fmmm. The electron diffraction and electron microscopy data of this novel ferrite show that it can be described as a Fe-Tl-2234-type structure corresponding to the intergrowth of a quadruple perovskite slice [(SrFeO2.8)(4)] with a complex rock salt related slice Fe-2(Sr2-epsilon Tl epsilon)O-3.4](infinity), built up of one double iron layer [Fe2O2.4] sandwiched between two [SrO] layers. The HRTEM images show that the oxygen atoms and vacancies are randomly distributed in the perovskite layers while the HAADF STEM images evidence the absence of Tl segregation in the matrix. Fe-2(Sr2-epsilon Tl epsilon)Sr3Fe4O14.65 exhibits a very large value of chi (1 lemu/mol) at 5 K, which remains large at 400 K; the M(H) loop presents a shape characteristic of ferrimagnetism, with a large coercive field of 0.3 T. The value of magnetization saturates at 400 K at 0.68 mu(B)/17e. At 10 K. the value of magnetization reaches a maximum of 2 mu(B)/Fe. The resistivity presents a semiconducting-like behavior, with rho similar to 800 Omega.cm at 300 K.
Update: 14-Nov-2008
Title:: On the Ferroelectric Phase Transition in Polytypes of beta-TlInS2 Crystals
Authors:: Borovoi, NA; Gololobov, YP; Gorb, AN; Isaenko, GL Author Full Names: Borovoi, N. A.; Gololobov, Yu. P.
Source:: PHYSICS OF THE SOLID STATE 50 (10): 1946-1950 OCT 2008
Abstract:: Permittivity measurements and x-ray diffraction study were performed for polytypes c and 2c of beta-TlInS2 crystals in the temperature range T = 160-250 K. Substantial differences are revealed in the temperature, sequence, and character of the structural phase transitions associated with the formation of incommensurate modulated structures and the occurrence of a ferroelectric state in these polytypes.
Title:: Quasicrystals - The Silver Jubilee PREFACE
Authors:: Lifshitz, R Author Full Names: Lifshitz, Ron
Source:: PHILOSOPHICAL MAGAZINE 88 (13-15): 1879-1882 2008
Title:: Structures of quasicrystals: Where are the atoms?
Authors:: Gratias, D; Quiquandon, M Author Full Names: Gratias, D.; Quiquandon, M.
Source:: PHILOSOPHICAL MAGAZINE 88 (13-15): 1887-1903 2008
Abstract:: This paper is an attempt to present a chronological review of the structural concepts that have been developed to characterize quasicrystals, starting from the experimental discovery of D. Shechtman and the concomitant theoretical definition of quasicrystal as proposed by D. Levine and P. Steinhardt, up to the present research in the field. The largest part of the paper is a discussion of the specific points that make the atomic structure determination of quasicrystals an original and difficult scientific challenge. We finally discuss the soundness of our knowledge of the actual atomic structure in quasicrystals: we do have quite a solid idea of where the atoms are but we are not sure about the distribution of the chemical species.
Title:: Geometrical property of the cluster model of the Yb-Cd icosahedral quasicrystal
Authors:: Takakura, H Author Full Names: Takakura, H.
Source:: PHILOSOPHICAL MAGAZINE 88 (13-15): 1905-1912 2008
Abstract:: The geometrical property of an atomic structure model of the Yb-Cd icosahedral quasicrystal is discussed from the higher-dimensional viewpoint. An occupation domain for the framework that specifies the arrangement of the three building units of the structure is presented based on a specific archetype occupation domain for the cluster centres. Different cluster configurations are enumerated and the numerical values of their frequencies are given.
Title:: Coordination and cluster packing in quasicrystals
Authors:: Fujita, N; Niizeki, K Author Full Names: Fujita, N.; Niizeki, K.
Source:: PHILOSOPHICAL MAGAZINE 88 (13-15): 1913-1919 2008
Abstract:: We discuss some local and global characteristics of quasicrystalline structures. Firstly, we present an analysis of the coordination numbers in the Cd5.7Yb binary quasicrystal. A majority of the Cd and Yb atoms occupy 12- and 16-fold coordinated sites, respectively. It is argued that the coordination properties are closely related to the local stability of the quasicrystals. Secondly, a simple inflation algorithm is presented for generating an icosahedral quasilattice which has a dense packing of a given structural motif or cluster. The atomic surface of a P-type icosahedral quasilattice generated in this way has a fractal boundary.
Title:: Structure of quasicrystals described by statistical methods
Authors:: Kozakowski, B; Wolny, J; Kuczera, P Author Full Names: Kozakowski, B.; Wolny, J.
Source:: PHILOSOPHICAL MAGAZINE 88 (13-15): 1921-1927 2008
Abstract:: The structure of quasicrystals can be described by using a statistical approach, which can be either in higher dimensions or in three-dimensional physical space only. In the multidimensional approach, complete statistical information is gathered in a so-called atomic surface. In the case of the physical approach, we use the idea of an average unit cell. These two approaches are linked by an oblique projection. For a full description of a diffraction pattern, two projections are required. Statistical methods have been used for the diffraction analysis of the model structures and the structure of real decagonal quasicrystals.
Title:: Structural vacancies in Al-Pd-Mn quasicrystal and its (1/1,2/1)-AlPdMnSi approximant crystals: Positron lifetime studies
Authors:: Takagiwa, Y; Okada, JT; Kimura, K; Kitahata, H; Matsushita, Y; Kanazawa, I Author Full Names: Takagiwa, Y.; Okada, J. T.
Source:: PHILOSOPHICAL MAGAZINE 88 (13-15): 1929-1934 2008
Abstract:: Positron annihilation lifetimes of the stable icosahedral (i) Al-Pd-Mn quasicrystal and its (1/1, 2/1)-AlPdMnSi and 1/0-Al12Re approximant crystals were measured at ambient temperature. The observed single-lifetime of the i-Al-Pd-Mn quasicrystal is very close to that of the (1/1, 2/1)-AlPdMnSi approximant crystals, indicating that the same type of structural vacancies exists in all these specimens. On the other hand, the lifetime of 1/0-Al12Re approximant crystal, which has no structural vacancies, is significantly shorter than the above results. We discuss the relationship between the positron lifetimes and mean valence-electron density.
Title:: HAADF-STEM study of B-Mg-Ru approximant crystals
Authors:: Miyazaki, Y; Okada, JT; Abe, E; Kimura, K Author Full Names: Miyazaki, Y.; Okada, J. T.
Source:: PHILOSOPHICAL MAGAZINE 88 (13-15): 1935-1940 2008
Abstract:: Two-dimensional structures of decagonal approximant crystals have been studied in a B-Mg-Ru system where decagonal quasicrystals have been predicted. High-angle annular detector dark-field scanning transmission electron microscopy (HAADF-STEM) imaging confirms that four approximant phases, which form at high temperatures, can be described as tessellations of hexagon and boat subunits with the same atomic decorations as B11Mg5Ru13. The images also support the existence of bow-tie flip structures in the all four approximant crystals. Long periodicities in one direction up to 8.5 nm are interpreted to be caused by modulation of rows of boat tiles.
Title:: Simulations of high-resolution electron microscopy images of icosahedral quasicrystals
Authors:: Quiquandon, M; Beauchesne, JT; Gratias, D Author Full Names: Quiquandon, M.; Beauchesne, J. -T.
Source:: PHILOSOPHICAL MAGAZINE 88 (13-15): 1941-1948 2008
Abstract:: We apply the scattering matrix formulation for calculating the images of high-resolution electron microscopy (HREM) images of quasiperiodic crystals and discuss their basic properties. The main feature in the image formation comes from the truncation effects of the q-basis, especially the perpendicular components which must be numerous enough for properly reproducing quasiperiodicity. A comparison between two types of atomic structural model is presented that illustrates the difficulties of differentiating the models from the HREM observations.
Title:: Highly-perfect decagonal quasicrystalline Al64Cu22Co14 with non-centrosymmetry
Authors:: Taniguchi, S; Abe, E Author Full Names: Taniguchi, S.; Abe, E.
Source:: PHILOSOPHICAL MAGAZINE 88 (13-15): 1949-1958 2008
Abstract:: The structure of a decagonal quasicrystal of Al64Cu22Co14, which was a single-grain specimen (a few mm in size) grown by slow-cooling from a melt and subsequently annealed at 1073 K, was investigated using electron diffraction and scanning transmission electron microscopy (STEM). Electron diffraction patterns of the Al64Cu22Co14 revealed a large number of sharp reflections that indicate a good long-range quasiperiodic order, and convergent-beam electron diffraction (CBED) analysis identified the space group of the decagonal Al64Cu22Co14 as being non-centrosymmetric P (10) over bar m2. Atomic-resolution Z-contrast STEM imaging showed that the structure can be described based on a fivefold-symmetric decagonal cluster 2 nm across, most of which is found to be located at ideal positions in the pentagonal Penrose tiling with significantly less phason disorders. Therefore, to our knowledge, the present decagonal Al64Cu22Co14 provides one of the best quasiperiodic ordered structures among those belonging to non-centrosymmetric P (10) over bar m2. Further details of atomic configurations within the fivefold-symmetric cluster were also examined using ultrahigh-resolution Z-contrast STEM with an aberration-corrector for the objective lens. This clearly revealed both the Al and Cu/Co sites at resolution close to 1 . Atomic arrangements within the cluster are found to be fairly well described based on the fivefold-symmetry cluster that exists in the W-(AlCoNi) approximant crystal, except for the atomistic disorders localized around the cluster centres.
Title:: Stability of the decagonal quasicrystal in the Lennard-Jones-Gauss system
Authors:: Engel, M; Trebin, HR Author Full Names: Engel, M.; Trebin, H. -R.
Source:: PHILOSOPHICAL MAGAZINE 88 (13-15): 1959-1965 2008
Abstract:: Although quasicrystals have been studied for 25 years, there are many open questions concerning their stability: What is the role of phason fluctuations? Do quasicrystals transform into periodic crystals at low temperature? If yes, by what mechanisms? We address these questions here for a simple two-dimensional model system, a monatomic decagonal quasicrystal, which is stabilized by the Lennard-Jones-Gauss potential in thermodynamic equilibrium. It is known to transform to the approximant Xi, when cooled below a critical temperature. We show that the decagonal phase is an entropically stabilized random tiling. By determining the average particle energy for a series of approximants, it is found that the approximant Xi is the one with lowest potential energy.
Title:: Ground-state configurations of decagonal and dodecagonal binary dipolar quasicrystals
Authors:: Roth, J Author Full Names: Roth, J.
Source:: PHILOSOPHICAL MAGAZINE 88 (13-15): 1967-1976 2008
Abstract:: We search for ground states of binary decagonal dipolar quasicrystals increasing the parameter space step by step: first testing tiling types and small-scale approximants, then allowing continuous deformation of the tiles, and finally by simulated annealing through tile flips followed by local optimization. It turns out that the quasicrystals are not a true ground state but can be favoured in finite systems by the lack of costly defects. Similar studies for square-triangle binary dipolar quasicrystals show that there the energy reduces with the number of square pairs. Phase-separated crystals turn out to be more stable then quasicrystals.
Title:: Penrose matching rules from realistic potentials in a model system
Authors:: Lim, S; Mihalkovic, M; Henley, CL Author Full Names: Lim, S.; Mihalkovic, M.
Source:: PHILOSOPHICAL MAGAZINE 88 (13-15): 1977-1984 2008
Abstract:: We exhibit a toy model of a binary decagonal quasicrystal of composition Al80.1Co19.9 - closely related to actual structures - in which realistic pair potentials yield a ground state which appears to perfectly implement Penrose's matching rules, for Hexagon-Boat-Star (HBS) tiles of edge 2.45 angstrom. The second minimum of the potentials is crucial for this result.
Title:: Growth of facetted microvoids in Zn-Fe-Sc quasicrystal
Authors:: Ishimasa, T; Matsunagi, J Author Full Names: Ishimasa, T.; Matsunagi, J.
Source:: PHILOSOPHICAL MAGAZINE 88 (13-15): 1985-1993 2008
Abstract:: Microvoids, the size of which ranges from 1 to 50 mu m in diameter, have been observed on the fracture surface of a millimeter-sized single icosahedral quasicrystal of stable Tsai-type Zn-Fe-Sc. The shape of the voids consists of planes related to the icosahedral symmetry, typically a dodecahedron with additional truncations by the planes perpendicular to the 2- and 3-fold axes. During controlled cooling from the melting point, approximately 824 degrees C, and additional annealing at 650 similar to 700 degrees C, the growth of the microvoids was observed. Corresponding to the increase of the size, the number density of voids is decreased so as to conserve the total volume of the voids, i.e. the porosity. This is the first direct evidence indicating that the growth process is essentially Ostwald ripening. The origin of the growth between 600 and 800 degrees C is considered to be not the supersaturated thermal vacancies, but vacancies coming from nearby shrinking voids. The growth is well explained by a thermally activated process with activation energy approximately 3.1 eV.
Title:: Formation and stability of icosahedral phase in Al65Ga5Pd17Mn13 alloy
Authors:: Yadav, TP; Shaz, MA; Tiwari, RS; Srivastava, ON Author Full Names: Yadav, T. P.; Shaz, M. A.
Source:: PHILOSOPHICAL MAGAZINE 88 (13-15): 1995-2002 2008
Abstract:: The formation and characterization are described of a quaternary (pseudo-ternary) icosahedral quasicrystal in Al65Ga5Pd17Mn13 alloy. X-ray diffraction and transmission electron microscopy observations confirmed the formation of icosahedral, B2 type and xi' crystalline (orthorhombic structure with unit cell a = 23.5 angstrom, b = 16.6 angstrom and c = 12.4 angstrom) phases in as-cast alloy. The icosahedral phase is formed after annealing at 800 degrees C for 60 h. This is the first report of the formation of an icosahedral phase in an Al-Ga-Pd-Mn quaternary alloy by present technique. The energy dispersive X-ray analysis investigations suggest the presence of Ga (similar to 5 at.%) in the alloy. Icosahedral Al-Ga-Pd-Mn provides a new opportunity to investigate various characteristics, including surface characteristics. Attempts are made to discuss the micromechanisms for the formation of the quasicrystalline phase in Al-Ga-Pd-Mn alloys.
Title:: Mapping the aperiodic landscape, 1982-2007
Authors:: Senechal, M Author Full Names: Senechal, M.
Source:: PHILOSOPHICAL MAGAZINE 88 (13-15): 2003-2016 2008
Abstract:: The discovery of quasicrystals galvanized mathematics research in long-range aperiodic order, accelerating the dissolution of the the ancient periodic/non-periodic dichotomy begun by Penrose, Ammann, de Bruijn, and Mackay. What does the aperiodic landscape look like now, 25 years later, and what frontiers are still to be mapped?
Title:: Symmetry properties of Penrose type tilings
Authors:: Cotfas, N Author Full Names: Cotfas, N.
Source:: PHILOSOPHICAL MAGAZINE 88 (13-15): 2017-2023 2008
Abstract:: The Penrose tiling is directly related to the atomic structure of certain decagonal quasicrystals and, despite its aperiodicity, is highly symmetric. It is known that the numbers 1, -tau , (-tau )(2), (-tau )(3),..., where tau = (1 + root 5)/2, are scaling factors of the Penrose tiling. We show that the set of scaling factors is much larger, and for most of them the number of the corresponding inflation centres is infinite.
Title:: Coincidences in four dimensions
Authors:: Baake, M; Zeiner, P Author Full Names: Baake, M.; Zeiner, P.
Source:: PHILOSOPHICAL MAGAZINE 88 (13-15): 2025-2032 2008
Abstract:: The coincidence site lattices (CSLs) of prominent four-dimensional lattices are considered. CSLs in three dimensions have been used for decades to describe grain boundaries in crystals. Quasicrystals suggest also looking at CSLs in dimensions d > 3. Here, we discuss the CSLs of the root lattice A(4) and the hypercubic lattices, which are of particular interest both from the mathematical and the crystallographic viewpoints. Quaternion algebras are used to derive their coincidence rotations and the CSLs. We make use of the fact that the CSLs can be linked to certain ideals and compute their indices, their multiplicities and encapsulate all this in generating functions in terms of Dirichlet series. In addition, we sketch how these results can be generalized for four-dimensional Z-modules by discussing the icosian ring.
Title:: Aperiodic order and pure point diffraction
Authors:: Lenz, D Author Full Names: Lenz, D.
Source:: PHILOSOPHICAL MAGAZINE 88 (13-15): 2059-2071 2008
Abstract:: The paper gives a leisurely introduction to mathematical diffraction theory with a focus on pure point diffraction. In particular, various characterizations of pure point diffraction and common models arising from cut and project schemes are discussed. It finishes with a list of open problems.
Title:: Ordering of adsorbed species on quasicrystal surfaces
Authors:: Smerdon, JA; Wearing, LH; Parle, JK; Leung, L; Sharma, HR; Ledieu, J; McGrath, R Author Full Names: Smerdon, J. A.
Source:: PHILOSOPHICAL MAGAZINE 88 (13-15): 2073-2082 2008
Abstract:: We present an overview of experimental studies of the structure of adsorbed atomic and molecular species on quasicrystal surfaces with a particular focus on those systems where quasiperiodic ordering of the adsorbate structure occurs. Atomic adsorption is illustrated with examples from studies of Fe and Gd adsorption on the five-fold surface of i-Al-Pd-Mn. Overlayer structure is correlated with several physical parameters to identify trends. It is concluded that the chemical properties of the adsorbate (metallic radius, electronegativity, melting temperature) are important indicators of quasiperiodic structuring of the adsorbate system. These correlations allow predictions of those elements likely to yield pseudomorphic overlayers. Structural effects upon molecular adsorption on clean quasicrystal surfaces have been less successful. A new approach to ordered molecular adsorption is described and illustrated for C-60 adsorption on a Pb monolayer film on the ten-fold surface of d-Al-Ni-Co.
Title:: Testing bulk models of icosahedral quasicrystals with STM images of clean surfaces
Authors:: Papadopolos, Z; Widmer, R; Groning, O Author Full Names: Papadopolos, Z.; Widmer, R.
Source:: PHILOSOPHICAL MAGAZINE 88 (13-15): 2083-2093 2008
Abstract:: In the case of icosahedral Al-Pd-Mn we compare the STM (scanning tunnelling microscopy) image of the real fivefold surface to the STM simulations on the candidates of the fivefold bulk terminations. We make the choice of which termination fits best to the real image. It leads us to some hints important either for the chemistry of the bulk-model or for the eventual correction of the model of atomic positions itself. We work in the frame of the particular model of atomic positions, based on the diffraction data for Al70Pd21Mn9 and Al62Cu25.5Fe12.5. We also discuss the possibilities beyond this model.
Title:: X-ray photoelectron diffraction on the 6-fold (001) mu-Al4Mn approximant surface
Authors:: Widmer, R; Maeder, R; Heggen, M; Feuerbacher, M; Groning, O Author Full Names: Widmer, R.; Maeder, R.
Source:: PHILOSOPHICAL MAGAZINE 88 (13-15): 2095-2102 2008
Abstract:: In theoretical investigations, the study of the properties of quasicrystals via analysis of periodic approximant structures has proven to be very successful. We performed experimental surface structure studies on the mu-Al4Mn approximant, exhibiting a large unit cell of 563 atoms, to get on to the origin of the unusual physical properties of complex quasicrystalline systems. The 6-fold (001) mu-Al4Mn surface was investigated by surface-sensitive low energy electron diffraction and X-ray photoelectron diffraction. Detailed analysis of the experimental data using single scattering cluster calculations revealed a pure bulk truncated surface, which is cut at the z = c/2 and 3c/4 layers of the unit cell, with a slight preference for the z = 3c/4 termination. The possibility of preparing well ordered, bulk terminated surfaces of such a complex, yet periodic, crystal structure in the Al-Mn system allows the application of a wealth of surface analytical tool to obtain a greater understanding of the physical properties of complex metallic alloys in relation to quasicrystals.
Title:: Low-energy electron diffraction (LEED) study of an aperiodic thin film of Cu on 5-fold i-Al-Pd-Mn
Authors:: Pussi, K; Reid, DE; Ferralis, N; McGrath, R; Lograsso, TA; Ross, AR; Diehl, RD Author Full Names: Pussi, K.; Reid, D. E.
Source:: PHILOSOPHICAL MAGAZINE 88 (13-15): 2103-2110 2008
Abstract:: Thin films of copper grown on five-fold i-AlPdMn at room temperature consist of domains that are rotationally aligned with the five primary symmetry directions of the substrate and which have one-dimensional aperiodic order. This aperiodic order is evident in scanning tunnelling microscopy images as wide and narrow rows that are spaced according to a Fibonacci sequence. A low-energy electron diffraction (LEED) study of this film indicates that the structure within the domains is periodic along the rows, with a repeat distance equal to the nearest-neighbour separation in bulk Cu. To determine the complete structure, a dynamical LEED experiment was performed for a five-layer Cu film at a sample temperature of 85 K. The analysis was performed using two different computational methods, one based on quasicrystalline slabs and the other on periodic approximants. Of the model structures tested, the film is found to be most consistent with a structure based on the Cu{100} surface structure, but having aperiodic displacements, both in-plane and out-of-plane, along a < 110 > direction.
Title:: Co nanocrystallites on an icosahedral Al-Pd-Mn quasicrystal
Authors:: Burkardt, S; Erbudak, M; Longchamp, JN; Weisskopf, Y Author Full Names: Burkardt, S.; Erbudak, M.
Source:: PHILOSOPHICAL MAGAZINE 88 (13-15): 2111-2116 2008
Abstract:: Recently, we reported that submonolayer deposits of Co onto the pentagonal surface of i-Al-Pd-Mn form a stable intermetallic compound of five CsCl-type AlCo domains rotated by 72 degrees with respect to each other. For multilayer deposition, Co was found to grow epitaxially on the AlCo domains in a body-centred cubic structure. Here we discuss this conclusion in more detail and report the formation of atomic rows at the surface for deposits larger than three monolayers. The details of the growth resulting in ordered nanostructures are extracted from low-energy electron diffraction investigations. Surface magneto-optical Kerr effect measurements confirm the decrease in the domain size for thicker films.
Title:: Alkaline-earth metal monolayers on 5-fold i-Al-Pd-Mn surface: Influence of adatom size on quasiperiodic ordering
Authors:: Krajci, M; Hafner, J Author Full Names: Krajci, M.
Source:: PHILOSOPHICAL MAGAZINE 88 (13-15): 2117-2122 2008
Abstract:: The structure and stability of a quasiperiodic alkaline-earth metal monolayer formed on a five-fold surface of an icosahedral Al-Pd-Mn quasicrystal have been investigated using ab initio density-functional methods. We study the influence of the size of the adatom on the regularity of the quasiperiodic ordering. It was found that Ca adatoms at a coverage 0.066 atoms/angstrom(2) (Theta = 0.5)form a highly regular quasiperiodic monolayer on the i-Al-Pd-Mn surface, with an ordering described by a decagonal DHBS tiling of decagons, hexagons, boats and pentagonal stars.
Title:: Discussion on the surface science of quasicrystals
Authors:: Thiel, PA Author Full Names: Thiel, P. A.
Source:: PHILOSOPHICAL MAGAZINE 88 (13-15): 2123-2129 2008
Abstract:: This paper contains a short review of four aspects of the surface science of quasicrystals, together with a list of challenges for the scientific community in the near future. The first issue concerns the ability of surface science to shed light on bulk atomic structure. The second is the use of surfaces as quasiperiodic templates, particularly for films of periodic metals. Here, enforcing quasiperiodicity in the film may lead to unusual magnetic, tribological or adsorption properties. The third aspect concerns the effects of surface phasons and phonons on dynamical interactions with adsorbates, such as sticking coefficient, as well as on diffusion between the surface and near-surface region. The final area is tribology, where studies of quasicrystals have suggested that both adhesion and phononic friction may be important.
Title:: Electronic transport in AlMn(Si) and AlCuFe quasicrystals: Breakdown of the semiclassical model
Authors:: de Laissardiere, GT; Julien, JP; Mayou, D Author Full Names: de Laissardiere, G. Trambly; Julien, J. -P.
Source:: PHILOSOPHICAL MAGAZINE 88 (13-15): 2131-2144 2008
Abstract:: The semiclassical Bloch-Boltzmann theory is at the heart of our understanding of conduction in solids, ranging from metals to semiconductors. Physical systems that are beyond the range of applicability of this theory are thus of fundamental interest. It appears that in quasicrystals and related complex metallic alloys, a new type of breakdown of this theory operates. This phenomenon is related to the specific propagation of electrons. We develop a theory of quantum transport that applies to a normal ballistic law, and also to these specific diffusion laws. As we show, phenomenological models based on this theory describe correctly the anomalous conductivity in quasicrystals. Ab initio calculations performed on approximants also confirm the validity of this anomalous quantum diffusion scheme. This provides us with an ab initio model of transport in approximants such as alpha-AlMnSi and AlCuFe 1/1 cubic approximant.
Title:: Anisotropic electrical, magnetic and thermal transport properties of the Al80Cr15Fe5 decagonal approximant
Authors:: Dolinsek, J; Vrtnik, S; Smontara, A; Jagodic, M; Jaglicic, Z; Bauer, B; Gille, P Author Full Names: Dolinsek, J.; Vrtnik, S.
Source:: PHILOSOPHICAL MAGAZINE 88 (13-15): 2145-2153 2008
Abstract:: The anisotropic magnetic, electrical and thermal transport properties were studied of a single-crystalline Al80Cr15Fe5 approximant to the decagonal quasicrystal. The temperature-dependent electrical resistivity along the b and c crystalline directions shows non-metallic behaviour with a broad maximum, whereas it exhibits a metallic positive temperature coefficient along the a direction perpendicular to the (b, c) atomic planes. The resistivity can be treated with the model of slow charge carriers, where the increased electron-phonon scattering upon raising the temperature induces a transition from dominant Boltzmann (metallic) to dominant non-Boltzmann (insulating-like) regime. The magnetic susceptibility and thermal conductivity also reveal a small anisotropy.
Title:: Coupled quasicrystals
Authors:: Vekilov, YK; Isaev, EI Author Full Names: Vekilov, Yu. Kh.; Isaev, E. I.
Source:: PHILOSOPHICAL MAGAZINE 88 (13-15): 2171-2173 2008
Abstract:: We predict that under certain experimental conditions external radiation with frequency half of that for the alternating Josephson effect can appear when a constant voltage is applied to a quasicrystal-quasicrystal tunnelling junction 1. The background for this possibility is the phase coherence of the wavefunctions across the barrier and the absence of scattering on the dynamical degrees of freedom (phonons).
Title:: Magnetism in quasicrystals
Authors:: Hippert, F; Prejean, JJ Author Full Names: Hippert, F.; Prejean, J. J.
Source:: PHILOSOPHICAL MAGAZINE 88 (13-15): 2175-2190 2008
Abstract:: The present understanding of magnetic properties of quasicrystals (QCs) is reviewed. In AlMn and AlPdMn QCs, only a few Mn atoms, with concentrations from a few per cent down to 10(-4) carry a localized magnetic moment. These moments are coupled via RKKY interactions, leading to a canonical spin-glass ordering at low temperature. They also exhibit a Kondo effect and AlPdMn QCs turned out to be a model system for studying experimentally the competition between Kondo and RKKY interactions in the absence of long-range magnetic ordering. Besides, the presence of localized moments has very unusual consequences for the electronic transport in AlPdMn QCs. In RMgZn and RMgCd QCs ( R is a magnetic rare earth), with R concentration around 9%, a spin-glass like freezing is observed. However the short-range antiferromagnetic correlations detected above the freezing temperature are unusual and are certainly influenced by the quasiperiodicity.
Title:: Local environment and magnetism in icosahedral quasicrystals
Authors:: Godonyuk, AV; Isaev, EI; Vekilov, YK Author Full Names: Godonyuk, A. V.; Isaev, E. I.
Source:: PHILOSOPHICAL MAGAZINE 88 (13-15): 2191-2196 2008
Abstract:: Based on density functional theory and all-electron projector-augmented wave (PAW) potentials, we studied the onset of local magnetic moments in the model icosahedral quasicrystal, Al46-xPd14Mn5Bx, where x is the number of boron (B) atoms with 0 <= x <= 3. We previously studied the dependence of local magnetic moment in Mn atoms on their atomic concentration [J. Magn. Magn. Mater. 300 567 (2006)]. In the current study, however, we have kept the number of Mn atoms constant. We have shown that the magnitude of local magnetic moment in a Mn atom depends significantly on the presence of Pd atoms inside the first coordination sphere. In qualitative agreement with experimental conclusion of Peng et al. [J. Magn. Magn. Mater. 184 319 (1998)], we also found that the average local magnetic moment in Mn depends on B concentration. The influence of B atoms is more pronounced if they are located inside the second coordination sphere.
Title:: In search of multipolar order on the Penrose tiling
Authors:: Vedmedenko, EY; Mandel, SED; Lifshitz, R Author Full Names: Vedmedenko, E. Y.; Mandel, S. Even-Dar
Source:: PHILOSOPHICAL MAGAZINE 88 (13-15): 2197-2207 2008
Abstract:: We use Monte Carlo calculations to analyse multipolar ordering on the Penrose tiling, relevant for two-dimensional molecular adsorbates on quasicrystalline surfaces and for nanomagnetic arrays. Our initial investigations are restricted to multipolar rotors of rank one through four-described by spherical harmonics Ylm with l = 1,....,4 and restricted to m = 0-positioned on the vertices of the rhombic Penrose tiling. At first sight, the ground states of odd-parity multipoles seem to exhibit long-range order, in agreement with previous investigations of dipolar systems. Yet, careful analysis performed here establishes that, despite earlier claims, long-range order is absent for all types of rotors, and only short-range order exists. Nevertheless, we show here that short-range order suffices to yield a superstructure in the form of the decagonal Hexagon-Boat-Star tiling. Our results should be taken as a warning for any future analysis of order in either real or simulated arrangements of multipoles on quasiperiodic templates.
Title:: Discussion of electronic properties of quasicrystals
Authors:: Mayou, D Author Full Names: Mayou, D.
Source:: PHILOSOPHICAL MAGAZINE 88 (13-15): 2209-2215 2008
Abstract:: This article gives a short review of some important achievements in the field of electronic properties of quasicrystals. It focuses essentially on: the nature of quasicrystals as Hume-Rothery alloys, the energetics of quasicrystals and related phases, the magnetic properties, the localization of electronic states, and the transport properties. For each part we emphasize some promising directions of research. We end by listing some problems that are related to that of electrons in a quasiperiodic potential.
Title:: Quasicrystals and complex metallic alloys: Trends for potential applications
Authors:: Barthes-Labrousse, MG; Dubois, JM Author Full Names: Barthes-Labrousse, M. -G.; Dubois, J. -M.
Source:: PHILOSOPHICAL MAGAZINE 88 (13-15): 2217-2225 2008
Abstract:: Although the industrial development of complex metallic alloys (CMAs) and quasicrystals (QCs) has remained quite limited so far, these materials exhibit interesting and sometimes unexpected properties in terms of technological applications. A few selected examples of the most promising properties and trends for potential applications are presented.
Title:: Low-temperature synthesis of nanocrystalline spinel by mechanical milling and annealing of Al-Ni-Fe decagonal quasicrystals
Authors:: Yadav, TP; Mukhopadhyay, NK; Tiwari, RS; Srivastava, ON Author Full Names: Yadav, T. P.; Mukhopadhyay, N. K.
Source:: PHILOSOPHICAL MAGAZINE 88 (13-15): 2227-2236 2008
Abstract:: Attempts were made to synthesize a nanocrystalline spinel phase by mechanical milling and subsequent annealing of Al-Ni-Fe decagonal quasicrystalline alloy. The milling of the decagonal phase was carried out in an attritor ball mill at 400 rpm for 1-40 h with ball to powder ratio of 100:1 in hexane medium. Subsequently annealing was performed in vacuum as well as an air ambience for 10, 20, 40 and 80 h. The quasicrystal powders milled for 40 h showed the formation of B2-type nanocrystalline phase (a=2.91 angstrom). Annealing of 40 h milled powder in air at 500 degrees C resulted in the formation of spinel structure (a=8.15 angstrom). X-ray diffraction and transmission electron microscopy investigations confirmed the formation of spinel phase with an average grain size of similar to 60nm. The formation of nanospinels and the advantages of this synthesis route compared to the existing routes for the formation of spinels are discussed.
Title:: Correlation between charge state and diffusion of hydrogen in Ti-based quasicrystals
Authors:: Morozov, AY; Belov, MP; Barbin, NA; Isaev, EI; Vekilov, YK Author Full Names: Morozov, A. Y.; Belov, M. P.
Source:: PHILOSOPHICAL MAGAZINE 88 (13-15): 2237-2243 2008
Abstract:: The dependence of the charge state of hydrogen as a function of H content in the 1/1 approximant to icosahedral Ti-based quasicrystals (QCs) was studied using a first-principles method based on the density functional theory and norm-conserving pseudopotentials. It was found that the dependence is strong and non-monotonic. Hydrogen diffusion is significantly hindered in QCs with a charged hydrogen atom.
Title:: Dodecagonal quasicrystal in a polymeric alloy II: specific heat
Authors:: Dotera, T Author Full Names: Dotera, T.
Source:: PHILOSOPHICAL MAGAZINE 88 (13-15): 2245-2251 2008
Abstract:: In a previous paper, we reported the formation of a dodecagonal quasicrystal (DDQC) in a quasi-two-dimensional lattice Monte Carlo simulation of a star-shaped polymer. In this paper, we show a series of Archimedean and quasicrystalline phases (4.8(2)) -> (3(2).4.3.4) -> DDQC -> (4.6.12) with increase of one component of ABC star polymers. The phase behaviour can be regarded as a transition between square tiling and triangle tiling via square-triangle tiling. We compare the specific heat for the phases and find that the DDQC sample possesses higher specific heat at high temperatures, which may be attributed to phason dynamics.
Title:: Electronic energy spectra of square and cubic Fibonacci quasicrystals
Authors:: Mandel, SED; Lifshitz, R Author Full Names: Mandel, S. Even-Dar; Lifshitz, R.
Source:: PHILOSOPHICAL MAGAZINE 88 (13-15): 2261-2273 2008
Abstract:: Understanding the electronic properties of quasicrystals, in particular the dependence of these properties on dimension, is among the interesting open problems in the field of quasicrystals. We investigate an off-diagonal tight-binding hamiltonian on the separable square and cubic Fibonacci quasicrystals. We use the well-studied Cantor-like energy spectrum of the one-dimensional Fibonacci quasicrystal to obtain exact results regarding the transitions between different spectral behaviours of the square and cubic quasicrystals. We use analytical results for the addition of one-dimensional spectra to obtain bounds on the range in which the higher-dimensional spectra contain an interval as a component. We also perform a direct numerical study of the spectra, obtaining good results for the square Fibonacci quasicrystal, and rough estimates for the cubic Fibonacci quasicrystal.
Title:: The square Thue-Morse tiling for photonic application
Authors:: Moretti, L; Mocella, V Author Full Names: Moretti, L.; Mocella, V.
Source:: PHILOSOPHICAL MAGAZINE 88 (13-15): 2275-2284 2008
Abstract:: The photonic properties of a two-dimensional (2D) photonic aperiodic crystal based on the Thue-Morse (ThMo) substitutional sequence were investigated theoretically. In contrast to traditional photonic quasicrystals based on the Penrose tiling, these structures were obtained by removing the lattice points from a square arrangement, following the inflation rules emerging from the ThMo sequence. The resulting structure does not exhibit the typical translational symmetry of photonic crystals. In particular, it is well known that the ThMo sequence has a singular continuous Fourier transform. This property was transferred directly on the 2D ThMo photonic aperiodic crystal represented by an array of pillars in air. The electromagnetic field distribution can be described as a quasi-localized state, with characteristics lying between the localized states, corresponding to the defect state in a photonic crystal, and the Bloch states, as in the case of the eigenmode in a photonic crystal. The photonic bandgap formation was explored as a function of pillar radius. Furthermore, a preliminary investigation of the defect behaviour in square ThMo tiling was carried out. The electric field in the defect state was revealed to be strictly localized in the defect pillar. These structures provide interesting properties, which could be used to design novel optical devices.
Title:: Nonlinear photonic quasicrystals for novel optical devices
Authors:: Bahabad, A; Lifshitz, R; Voloch, N; Arie, A Author Full Names: Bahabad, A.; Lifshitz, R.
Source:: PHILOSOPHICAL MAGAZINE 88 (13-15): 2285-2293 2008
Abstract:: Two well-known methods for the design of quasicrystal models are used to create novel nonlinear optical devices. These devices are useful for efficient three-wave mixing of several different processes, and therefore offer greater flexibility with respect to the more common periodic nonlinear photonic crystals. We demonstrate applications for polarization switching as well as multi-wavelength and multi-directional frequency doubling. The generalized dual grid method is proven to be efficient for designing photonic quasicrystals for one-dimensional collinear devices as well as elaborate two-dimensional multi-directional devices. The cut-and-project method is physically realized by sending finite-width optical beams at an irrational angle through a periodic two-dimensional nonlinear photonic crystal. This enables the creation of two simultaneous collinear optical processes that can be varied by changing the angle of the beams.
Title:: Phason modes in quasicrystals
Authors:: De Boissieu, M Author Full Names: De Boissieu, M.
Source:: PHILOSOPHICAL MAGAZINE 88 (13-15): 2295-2309 2008
Abstract:: Studies on phason modes in quasicrystals, but more generally in aperiodic phases, which encompass incommensurately modulated phases, composites and quasicrystals, are reviewed. After an introduction on phason modes in aperiodic phases, the hydrodynamic theory is presented. The case of incommensurately modulated phases is illustrated by results on ThBr4. Atomic models used to simulate phason modes in quasicrystals are then presented, followed by an overview of results obtained for icosahedral and decagonal phases.
Title:: Atomic dynamics of i-ScZnMg and its 1/1 approximant phase: Experiment and simulation
Authors:: Mihalkovic, M; Francoual, S; Shibata, K; De Boissieu, M; Baron, AQR; Sidis, Y; Ishimasa, T; Wu, D; Lograsso, T; Regnault, LP; Gahler, F; Tsutsui, S; Hennion, B; Bastie, P; Sato, TJ; Takakura, H; Currat, R; Tsai, AP Author Full Names: Mihalkovic, M.; Francoual, S.
Source:: PHILOSOPHICAL MAGAZINE 88 (13-15): 2311-2318 2008
Abstract:: Quasicrystals are long-range ordered materials that lack translational invariance so that the study of their physical properties remains a challenging problem. In order to study the respective influence of the local order and of the long-range order (periodic or quasiperiodic) on lattice dynamics, we have carried out inelastic X-ray and neutron scattering experiments on single grain samples of the Zn-Mg-Sc icosahedral quasicrystal and of the Zn-Sc periodic cubic 1/1 approximant. Besides the overall similarities and the existence of a pseudo-gap in the transverse dispersion relation, marked differences are observed, the pseudo-gap being larger and better defined in the approximant than in the quasicrystal. This can be qualitatively explained using the concept of pseudo-Brillouin zone in the quasicrystal. These results are compared to simulations on atomic models and using oscillating pair potentials, which have been fitted against ab-initio data. The simulated response function reproduces both the dispersion relation but also the observed intensity distribution in the measured spectra. The partial vibrational density of states, projected on the cluster shells, is computed from this model.
Title:: High-temperature specific heat of icosahedral Al-Cu-Fe and decagonal Al-Ni-Co
Authors:: Shulyatev, DA; Nigmatulin, AS; Lobanova, AV; Gasparyan, TA Author Full Names: Shulyatev, D. A.; Nigmatulin, A. S.
Source:: PHILOSOPHICAL MAGAZINE 88 (13-15): 2319-2323 2008
Abstract:: The high-temperature specific heat, c(p)(T), of icosahedral Al-Cu-Fe and decagonal Al-Ni-Co was measured at various temperature ranges between 420 and 1350 K. For both materials, the specific heat increases with increasing temperature, reaching the values that are substantially higher than the Dulong and Petit value. Comparisons are made with previously reported data for icosahedral and decagonal phases.
Title:: Quasicrystal plasticity in the framework of a constitutive model: Interaction of the microstructural parameters at high strain rates
Authors:: Heggen, M; Feuerbacher, M Author Full Names: Heggen, M.; Feuerbacher, M.
Source:: PHILOSOPHICAL MAGAZINE 88 (13-15): 2325-2331 2008
Abstract:: A unified description of quasicrystal plasticity in terms of a quantitative model using constitutive equations was presented by Feuerbacher and co-workers in 2001 [1]. In a later work, the model was successfully applied to a wide range of experimental parameters where various stress-strain behaviours were observed [2]. At high strain rates, for example, the occurrence of a low-strain work-hardening stage, the formation of a stress maximum at around 5%, and work softening at higher strains was observed. In the present work, the complex stress-strain behaviour of quasicrystals at high strain rates is analyzed in terms of the constitutive model. The evolution of the two microstructural parameters, the dislocation density and the order parameter, their interaction with other microstructural parameters and the influence on the macroscopic plastic deformation behaviour are analyzed and discussed.
Title:: Discussion of phasons in quasicrystals and their dynamics
Authors:: Widom, M Author Full Names: Widom, M.
Source:: PHILOSOPHICAL MAGAZINE 88 (13-15): 2339-2350 2008
Abstract:: Phasons are a type of excitation peculiar to quasicrystals and other incommensurate phases arising as a consequence of their spatial quasiperiodicity. Phason-related excitations are also observed in complex crystal structures known as approximants. This article briefly reviews the concepts of phasons with focus on current issues in their regard. We examine both continuum (hydrodynamic) and discrete (tiling) descriptions of phasons and review the state of experimental validation of the basic theoretical notions.
Title:: Twenty-five years of quasicrystals: Where are we now and what does the future hold? - A personal outlook
Authors:: Dubois, JM Author Full Names: Dubois, J. -M.
Source:: PHILOSOPHICAL MAGAZINE 88 (13-15): 2351-2356 2008
Abstract:: Twenty-five years after the historic discovery of a real material exhibiting fivefold symmetry, the scientific field opened as a result is still robust and active. On the experimental side, it has been strengthened in recent years by new inputs coming from studies of transport properties, surface physics, coating technology, catalysis, etc. Its future probably relies upon combining these very exotic, but now extremely well documented materials with more conventional materials in composites, or challenging the discovery of new, or more exciting properties in a systematic screening of intermetallics compounds with untried compositions. An effort towards making quasicrystals better understood outside our own community has become mandatory with a view to developing the field.
Title:: Transport properties of Ti-Zr-Ni quasicrystalline and glassy alloys
Authors:: Kuo, YK; Kaurav, N; Syu, WK; Sivakumar, KM; Shan, UT; Lin, ST; Wang, Q; Dong, C Author Full Names: Kuo, Y. K.; Kaurav, N.
Source:: JOURNAL OF APPLIED PHYSICS 104 (6): Art. No. 063705 SEP 15 2008
Abstract:: We report on measurements of the temperature dependence of the electrical resistivity (p), thermopower (S), and thermal conductivity (kappa) of Ti-Zr-Ni alloys between 10 and 300 K. A series of Ti-Zr-Ni quasicrystals (QCs) Ti40Zr40Ni20, Ti45Zr35Ni20, and Ti50Zr30Ni20 and metallic glasses Ti35Zr45Ni20 and Ti40Zr40Ni20 was prepared to systematically study the compositional and structural dependences of their transport properties. The resistivity of all these alloys was found to be very weakly temperature dependent with a negative temperature coefficient of resistance. Further, the observed increase in electrical resistivity with increasing Ti/Zr ratio is most likely due to the increase in disorder. The SIT against temperature curves exhibited a maximum between 20 and 50 K and a noticeable deviation from the expected linear behavior in S(T) at higher temperatures. Such observations in the thermopower of QCs have been attributed to the electron-phonon enhancement and phonon drag effect. The measured thermal conductivities were analyzed by separating the electronic and phonon contributions that provide a reasonable explanation for plateau-type feature in kappa(T) of QCs. Our present results suggest that the transport properties of glassy phase are influenced by the same mechanisms as those of quasicrystalline phase. (C) 2008 American Institute of Physics. [DOI: 10.1063/1.2977721]
Title:: Crystal structure of the 2/1 cubic approximant Ag42In42Yb16
Authors:: Li, MR; Hovmoller, S; Sun, JL; Zou, XD; Kuo, KH Author Full Names: Li, M. R.
Source:: JOURNAL OF ALLOYS AND COMPOUNDS 465 (1-2): 132-138 OCT 6 2008
Abstract:: The crystal structure of the 2/1 cubic approximant Ag42In42Yb16 was determined by single crystal X-ray diffraction. The structure model has the composition of Ag40.42In44.50Yb15.08 with a=24.8687 angstrom, space group Pa (3) over bar (No. 205). Among the 14 independent Ag, 13 In, and 5 Yb sites, 6 Ag sites and 6 In sites are icosahedrally coordinated, whereas two sites (In13, Yb1) are Frank-Kasper polyhedrally coordinated. Four Yb sites (Yb2-5) are double pentagonal antiprisms. The basic structural unit can be described as a 102-atom pseudo-Bergman cluster with three successive shells, of which the second shell consists of a dodecahedron and an only nine-atom polyhedron that breaks icosahedral symmetry. (C) 2007 Elsevier B.V. All rights reserved.
Title:: The effect of cooling rate on the microstructure and mechanical properties of Mg-Zn-Gd-based alloys
Authors:: Liu, Y; Yuan, GY; Yin, J; Lu, C; Ding, WJ; Jiang, JZ Author Full Names: Liu, Yong
Source:: INTERNATIONAL JOURNAL OF MATERIALS RESEARCH 99 (9): 973-978 SEP 2008
Abstract:: The microstructure and mechanical properties of Mg3.5Zn0.6Gd and Mg3.5Zn0.6Gd1.5Cu alloys were investigated under different solidification conditions. The microstructure and phase constitutions of alloys were characterized using optical microscopy, scanning electron microscopy, X-ray diffraction and differential thermal analysis. The results indicate that the cooling rate plays an important role in grain refinement and phase constitutions of Mg-Zn-Gd alloys. In the cooling rate range from 4.8 K s(-1) to 18.5 K s(-1) for the Mg-Zn-Gd system, higher content of the icosahedral phase (I-phase) was obtained under the condition of higher cooling rate which accelerated the nucleation and growth of the I-phase. Under the cooling rate of 18.5 K s(-1), the mechanical properties of the Mg3.5Zn0.6Gd alloy were further improved by the high I-phase content due to its unique icosahedral structure, in addition to the contribution of grain refinement.
Title:: Computing with almost periodic functions
Authors:: Moody, RV; Nesterenko, M; Patera, J Author Full Names: Moody, R. V.; Nesterenko, M.
Source:: ACTA CRYSTALLOGRAPHICA SECTION A 64: 654-669 Part 6 NOV 2008
Abstract:: This paper develops a method for discrete computational Fourier analysis of functions defined on quasicrystals and other almost periodic sets. A key point is to build the analysis around the emerging theory of quasicrystals and diffraction in the setting on local hulls and dynamical systems. Numerically computed approximations arising in this way are built out of the Fourier module of the quasicrystal in question and approximate their target functions uniformly on the entire infinite space. The methods are entirely group theoretical, being based on finite groups and their duals, and they are practical and computable. Examples of functions based on the standard Fibonacci quasicrystal serve to illustrate the method (which is applicable to all quasicrystals modeled on the cut-and-project formalism). (C) 2008 International Union of Crystallography Printed in Singapore - all rights reserved
Update: 6-Nov-2008
Title:: Electron microscopy of an icosahedral phase in a rapidly solidified Al18Mg3Mn2 complex metallic alloy
Authors:: Mukhopadhyay, NK; Chang, HJ; Lee, JY; Kim, DH Author Full Names: Mukhopadhyay, N. K.; Chang, H. J.
Source:: SCRIPTA MATERIALIA 59 (10): 1119-1122 NOV 2008
Abstract:: The icosahedral quasicrystal (QC) has been found to form, along with a minor amount of alpha-Al, in the rapidly solidified Al18Mg3Mn2 complex metallic alloy. From the compositional analysis, the QC was found to be close to (AlMg)(82)Mn-18. The quasilattice constant (a(R) = 0.4604 nm) of the QC phase suggests that it is basically an Al-Mn type of Mackay quasicrystal, which conforms to the composition analysis. The rationale behind the formation of the Al-Mg-Mn ternary quasicrystal from the T-Al18Mg3Mn2 alloy is discussed. (c) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:: Electronic structure of CePdAl experiment and calculations
Authors:: Glogowski, W; Goraus, J; Slebarski, A Author Full Names: Glogowski, W.; Goraus, J.
Source:: MATERIALS SCIENCE-POLAND 26 (3): 729-734 2008
Abstract:: CePdAl exhibits an antiferromagnetic phase below T-N = 2.7 K; its physical properties are typical of heavy fermion compounds (specific heat coefficient gamma = C/T = 270 mJ/(mol.K-2)). The triangular coordination symmetry of the magnetic Ce ions gives rise to geometrical frustration and leads to an incommensurate antiferromagnetic structure below T-N, showing a coexistence of ordered and frustrated Ce moments. The purpose of this work was to discuss electronic structure of CePdAl and its influence on the geometrical frustration in the Kagome-like lattice and the Kondo effect in CePdAl. We present the results of the X-ray diffraction analysis and the XPS Ce 3d core and valence band spectra. We also present the spin-polarized band structure calculations for CePdAl, using the LAPW method.
Title:: Crystallography and morphology of twins in equiatomic TiPt martensite
Authors:: Nishida, M; Matsuda, M; Yasumoto, Y; Yano, S; Yamabe-Mitarai, Y; Hara, T Author Full Names: Nishida, M.; Matsuda, M.
Source:: MATERIALS SCIENCE AND TECHNOLOGY 24 (8): 884-889 AUG 2008
Abstract:: Twins in the B19 (2H) martensite in Ti-Pt shape memory alloy have been investigated by transmission electron microscopy. There are three twinning modes evident, i.e. {111}(2H) Type I, < 121 >(2H) Type II and {101}(2H) compound twins. In addition to the 2H martensite, various long period stacking structures are observed such as 2112 stacking and incommensurate like modulated martensites. It is frequently observed that two martensite structures derived from the identical closed packed plane of the parent phase coexist in the same area, namely, 'two-in-one' morphology. The crystallographic aspects of the 'two-in-one' morphology are also discussed.
Title:: TEM investigation of intermediate phase transformation and micromodulation in Ni-Mn-Ga ferromagnetic shape memory alloys
Authors:: Tsuchiya, K; Todaka, Y; Umemoto, M Author Full Names: Tsuchiya, K.
Source:: MATERIALS SCIENCE AND TECHNOLOGY 24 (8): 920-926 AUG 2008
Abstract:: Intermediate phase transformation, martensitic transformations and modulated structures in Ni-Mn-Ga ferromagnetic shape memory alloys were investigated by TEM. The transformation from high temperature L2(1) phase to intermediate phase was characterised by the appearance of diffuse satellite spots at 0.167q(220) positions in electron diffraction patterns and intense fine striations in bright field images. These results are consistent with the reported results of neutron diffraction measurements related to the phonon anomaly. Also, high resolution TEM observations and fast Fourier transformation analysis on the near intermediate phase state in Ni-Mn-Ga-Gd were conducted. It was revealed that the coarse tweed contrast was associated with a long wavelength strain field while the fine striations are associated with the satellite spots and domains of micromodulation aligned parallel to {110}.
Title:: Some symmetry aspects of ferroics and single phase multiferroics
Authors:: Schmid, H Author Full Names: Schmid, Hans
Source:: JOURNAL OF PHYSICS-CONDENSED MATTER 20 (43): Art. No. 434201 OCT 29 2008
Abstract:: The symmetry conditions for the occurrence in a same phase of one or more of the four primary ferroic properties, i.e., ferroelectricity, ferromagnetism, ferrotoroidicity and ferroelasticity, are discussed. Analogous conditions are outlined for the admission of so-called secondary and tertiary ferroic effects, such as magnetoelectric, piezoelectric, piezomagnetic, piezotoroidic, etc. Formerly postulated `magnetotoroidic' and 'electrotoroidic' effects are found to be describable as tertiary ferroic magnetoelectric effects. For understanding ferroic and multiferroic domains and their possibilities of switching, knowledge of the pairs of prototype point group/ferroic phase point group (so-called 'Aizu species') is decisive. A classification into ensembles of species with common properties, recently extended to ferrotoroidic crystals, allows distinguishing between full, partial or no coupling between order parameters and understanding domain patterns and poling procedures. The switching by reorientation with angles other than 180 degrees of ferromagnetic, antiferromagnetic and ferroelectric domains by magnetic fields, electric fields or by stress requires the ferroic phase to be ferroelastic. For ferromagnetic/ ferrotoroidic and antiferromagnetic/ ferrotoroidic phases, the ferrotoroidic domains are found to be identical with the ferromagnetic and antiferromagnetic ones, respectively. As a consequence and depending on symmetry, ferrotoroidic domains can be switched by crossed electric and magnetic fields, by collinear electric and magnetic fields or by a magnetic field alone. Examples of ferrotoroidic domains are discussed for Fe2-xGaxO3, Co3B7O13Br and LiCoPO4. Recent new results on symmetry and domains of the antiferromagnetic incommensurate phase of BiFeO3 are also discussed.
Title:: Magnetically induced ferroelectricity in the buckled Kagome antiferromagnet Ni3V2O8
Authors:: Lawes, G; Kenzelmann, M; Broholm, C Author Full Names: Lawes, G.; Kenzelmann, M.
Source:: JOURNAL OF PHYSICS-CONDENSED MATTER 20 (43): Art. No. 434205 OCT 29 2008
Abstract:: Ni3V2O8 is one of several recently identified multiferroic materials in which ferroelectricity is produced by long-range magnetic order. This staircase Kagome compound adopts a sequence of distinct low temperature magnetic phases, which exhibit different optical, dielectric, and transport properties, most notably ferroelectric order arising from a polar incommensurate magnetic structure. We give an overview of the experimental results from the existing literature on Ni3V2O8, and briefly discuss models that describe the coupling between magnetic and ferroelectric properties. We show that the temperature dependence of the dielectric constant provides evidence for spin-charge coupling in Ni3V2O8 away from the ferroelectric phase. An anomaly in the thermal conductivity at the incommensurate-commensurate phase transition suggests that spin scattering may limit thermal transport in the incommensurate phase. We associate each of the two incommensurate phase transitions with one magnetic order parameter, and we show that the temperature dependence of the ferroelectric polarization closely follows the product of these two magnetic order parameters-corroborating the validity of the phenomenological trilinear coupling model. Finally, we present inelastic powder neutron scattering measurements that provide evidence of several weakly dispersive magnetic modes that are typical for strongly frustrated antiferromagnets with large spin anisotropies.
Title:: Magnetic and ferroelectric properties of multiferroic RMn2O5
Authors:: Noda, Y; Kimura, H; Fukunaga, M; Kobayashi, S; Kagomiya, I; Kohn, K Author Full Names: Noda, Y.; Kimura, H.
Source:: JOURNAL OF PHYSICS-CONDENSED MATTER 20 (43): Art. No. 434206 OCT 29 2008
Abstract:: The magnetic and ferroelectric properties of multiferroic RMn2O5 (R = Y, Tb, Ho, Er, Tm) are reviewed based on recent neutron diffraction and dielectric measurements. Successive phase transitions of magnetic and dielectric ordering were found to occur simultaneously in this system. The characteristic magnetic ordering of the system exhibits an incommensurate-commensurate phase transition, and again transitions to an incommensurate phase. Special attention is given to the magnetic structure in order to discuss the mechanism for the introduction of ferroelectric polarization. For all the compounds examined, the spin configuration for Mn4+ and Mn3+ ions in the commensurate magnetic phase, where spontaneous electric polarization occurs, was determined to be a transverse spiral spin structure propagating along the c-axis. By contrast, the alignment of the induced 4f moment of R3+ ions showed variation, depending on the character of each of the elements. Corresponding responses to external fields such as a magnetic field, hydrostatic pressure etc at low temperature are strongly dependent on the rare earth element present in the RMn2O5 system. The so-called colossal magnetoelectric effect in this system can be easily interpreted by the phase transition from the magnetic incommensurate and weak ferroelectric phase to the commensurate and ferroelectric phase.
Title:: Phonons and magnetoelectric interactions in Ni3V2O8
Authors:: Yildirim, T; Vergara, LI; Iniguez, J; Musfeldt, JL; Harris, AB; Rogado, N; Cava, RJ; Yen, F; Chaudhury, RP; Lorenz, B Author Full Names: Yildirim, T.
Source:: JOURNAL OF PHYSICS-CONDENSED MATTER 20 (43): Art. No. 434214 OCT 29 2008
Abstract:: We present a detailed study of the zone-center phonons and magnetoelectric interactions in Ni3V2O8. Using combined neutron scattering, polarized infrared (IR) measurements and first-principles LDA + U calculations, we successfully assigned all IR-active modes, including eleven B-2u phonons which can induce the observed spontaneous electric polarization. We also calculated the Born-effective charges and the IR intensities which are in surprisingly good agreement with the experimental data. Among the eleven B2u phonons, we find that only a few of them can actually induce a significant dipole moment. The exchange interactions up to a cutoff of 6.5 A are also calculated within the LDA + U approach with different values of U for Ni, V and O atoms. We find that LSDA (i.e. U = 0) gives excellent results concerning the optimized atomic positions, bandgap and phonon energies. However, the magnitudes of the exchange constants are too large compared to the experimental Curie-Weiss constant, Theta. Including U for Ni corrects the magnitude of the superexchange constants but opens a too large electronic bandgap. We observe that including correlation at the O site is very important to get simultaneously the correct phonon energies, bandgap and exchange constants. In particular, the nearest and next-nearest exchange constants along the Ni-spine sites result in incommensurate spin ordering with a wavevector that is consistent with the experimental data. Our results also explain how the antiferromagnetic coupling between sublattices in the b and c directions is consistent with the relatively small observed value of Theta. We also find that, regardless of the values of U used, we always get the same five exchange constants that are significantly larger than the rest. Finally, we discuss how the B2u phonons and the spin structure combine to yield the observed spontaneous polarization. We present a simple phenomenological model which shows how trilinear (and quartic) couplings of one (or two) phonons to two spin operators perturbatively affects the magnon ( i.e. electromagnon) and phonon energies.
Title:: Laser deposition of a Cu-based metallic glass powder on a Zr-based glass substrate
Authors:: Sun, H; Flores, KM Author Full Names: Sun, H.; Flores, K. M.
Source:: JOURNAL OF MATERIALS RESEARCH 23 (10): 2692-2703 OCT 2008
Abstract:: Laser Engineered Net Shaping (LENS (TM)) is a laser-assisted manufacturing process that offers the possibility of producing metallic coatings and components with highly nonequilibrium microstructures. In this work, the microstructure developed by LENS deposition of Cu47Ti33Zr11Ni8Si1 powder on a bulk metallic glass substrate, with nominal composition Zr58.5Nb2.8Cu15.6Ni12.8Al10.3, is investigated. Single-layer deposition results in the formation of an inhomogeneous but partially amorphous layer above a crystalline heat-affected zone. Elemental analysis of the deposited layer indicates incomplete mixing of the powder with the melt pool. The as-deposited alloy exhibits a single glass transition event and its primary crystallization event is consistent with the first crystallization temperature of the Cu-based powder. Subsequent remelting of this layer results in a still partially amorphous deposit with a uniform composition of (Zr + Nb)(51.8)Cu24.7Ti3.4Ni16.4Al3.7. The remelted layer exhibits a structural rearrangement immediately prior to the primary crystallization event, possibly associated with the formation of a quasicrystalline phase.
Title:: The isostructural phase transition and frustrated magnetic ordering in TbPd0.9Ni0.1Al studied by neutron diffraction
Authors:: Donni, A; Keller, L; Kitazawa, H; Prchal, J; Fischer, P Author Full Names: Doenni, A.; Keller, L.
Source:: JOURNAL OF ALLOYS AND COMPOUNDS 464 (1-2): 67-74 SEP 22 2008
Abstract:: By using powder neutron diffraction we provide a detailed structural and magnetic investigation of the pseudo-ternary compound TbPd0.9Ni0.1Al with hexagonal ZrNiAl-type crystal structure and disorder of palladium and nickel atoms on two crystallographic sites, We provide experimental evidence for the Occurrence of an isostructural phase transition in TbPd0.9Ni0.1Al at 157 K, which is affected by structural disorder compared to that observed in TbPdAl. In TbPd0.9Ni0.1Al the step of the c/a ratio at the first-order phase transition appears about four times smaller than in TbPdAl. TbPd0.9Ni0.1Al undergoes two successive magnetic phase transitions at T-NI = 41 K and T-N2 approximate to 21.5 K. Two third of non-frustrated ordered Tb moments form commenstrate antiferromaganetic chains (k(1) = [1/2, 0, 1/2]) and coexist with one third of frustrated ordered Tb moments, which change from a commensurate structure (k(1) = [1/2. 0, 1/2]) between T-N2 and T-NI to an incommensurate structure (k(2i) = [0.50(1), 0.12(1). 1/21]) below T-N2. Due to the strong magneto-crystal line anisotropy all ordered Tb moments stay perpendicular to the ab-plane and reach at 1.5 K saturation values of 8.6 (2) mu(B) (non-frustrated) and 7.2 (2) mu(B) (frustrated). The symmetry of the magnetic structure of TbPd0.9Ni0.1Al is lower than that of TbNiAl. (C) 2007 Elsevier B.V. All rights reserved.
Title:: Al-rich region of Al-Pd-Ru at 1000 to 1100 degrees C
Authors:: Pavyuchkov, D; Grushko, B; Velikanova, TY Author Full Names: Pavyuchkov, D.
Source:: JOURNAL OF ALLOYS AND COMPOUNDS 464 (1-2): 101-106 SEP 22 2008
Abstract:: Partial isothermal sections of the Al-Pd-Ru phase diagram at 1000, 1050 and 1100 degrees C are presented here. The Al-Pd orthorhombic epsilon-phases dissolve up to similar to 15.5 at.% Ru, Al13Ru4 < 2.5 at.% Pd and Al2Ru up to 1 at.% Pd. Between 66 and 75 at.% Al, ternary quasiperiodic icosahedral phase and three cubic phases: C (Pm (3) over bar, a = 0.7757 nm) C-1 (lm (3) over bar, a = 1.5532 nm) and C-2 (Fm (3) over bar, a = 1.5566 nm) were revealed. An additional complex cubic structure with a approximate to 3.96 nm was found to be formed at compositions close to those of the icosahedral phase. (C) 2007 Elsevier B.V. All rights reserved.
Title:: Constitution of the high-Al region of Al-Cu-Rh
Authors:: Grushko, B; Kowalski, W; Przepiorzynski, B; Pavlyuchkov, D Author Full Names: Grushko, B.; Kowalski, W.
Source:: JOURNAL OF ALLOYS AND COMPOUNDS 464 (1-2): 227-233 SEP 22 2008
Abstract:: Phase equilibria between 540 and 1010 degrees C were studied in Al-Cu-Rh alloys containing more than 50 at.% Al. Congruent equiatomic AlRh dissolves more than 40 at.% Cu and extends up to 58 at.% Al at the high-Cu part of its compositional range. High-temperature cubic C-Al5Rh2 (C-phase) dissolves up to 13 at.% Cu, "Al3Rh" (epsilon(6)-phase) up to 15 at.% Cu and Al9Rh2 up to 1.5 at.% Cu. The solubility of the third element in other binary Al-Rh and Al-Cu phases is below 0.5 at.%. Close to the high-Cu limit of the C-phase region the fee C-2-phase structurally related to the C-phase is formed. Stable decagonal phase (D1-phase) is formed below 1005 degrees C in a compositional range extending from Al65Cu16Rh19 to Al62Cu23Rh15, which shifts to higher Cu concentrations with decreasing temperature. An additional ternary phase forming around the Al70Cu20Rh10 composition below 660 degrees C was revealed. Partial 1010, 990, 900, 800, 700, 600 and 540 degrees C isothermal sections were determined. (c) 2007 Elsevier B.V. All rights reserved.
Title:: Microstructures and mechanical properties of quasicrystal reinforced Mg matrix composites
Authors:: Zhang, YB; Yu, SR; Song, YL; Zhu, XY Author Full Names: Zhang, Yingbo; Yu, Sirong
Source:: JOURNAL OF ALLOYS AND COMPOUNDS 464 (1-2): 575-579 SEP 22 2008
Abstract:: Mg-based composites reinforced with stable in situ icosahedral quasicrystal phase (I-phase) were fabricated in this Study. The effects of Y content on the microstructures and mechanical properties of the composites were investigated. The results Show that the composites comprised dendrites of alpha-Mg matrix separated by interdendritic I-phase and lamellar (I-phase + alpha-Mg) eutectic. With the increase of Y content, the content of I-phase increases; the content and size of (I-phase + alpha-Mg) eutectic cell increase; the lamellar space between I-phase and alpha-Mg in eutectic cell also increases but the grain size of alpha-Mg matrix decreases. The failure mode of M-Zn-Y alloy matrix composites in tensile tests is quasi-cleavage fracture. With the increase of Y content, the tensile strengths of the composites increase, and (he elongation rates increase firstly and then decrease. (C) 2007 Elsevier B.V. All rights reserved.
Title:: Hydrogenation study of suction-cast Ti40Zr40Ni20 quasicrystal
Authors:: Huang, HG; Li, R; Yin, C; Zheng, ST; Zhang, PC Author Full Names: Huang, Huogen; Li, Rong
Source:: INTERNATIONAL JOURNAL OF HYDROGEN ENERGY 33 (17): 4607-4611 SEP 2008
Abstract:: Suction casting was predicted to be an usable method for improving the hydriding kinetics of Ti/Zr-based icosahedral quasicrystals (IQCs) in our previous work. To further determine it, a suction-cast Ti40Zr40Ni20 IQC alloy was used for hydrogenation studies by Pressure Composition Isotherm (PCI) and Temperature Programmed Desorption (TPD) techniques. The results showed that, this alloy absorbed hydrogen rapidly with obvious hydrogen pressure plateau and some reversibility, however, displayed very limited hydrogen capacity (about 0.7 wt.%) and low equilibrium pressure. After several hydrogenation/dehydrogenation cycles, the IQC structure transformed into two hydride phases, ZrH2-x and one unknown, both of which decomposed at above 600 degrees C, suggesting high thermo-stability for them. On the whole, indeed the suction-casting method can increase the hydrogen absorption rate of Ti/Zr-based IQCs, however, the hydrogenation properties of the Ti40Zr40Ni20 IQC alloy still need a mighty advancement. (C) 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.
Title:: Crystal structure of 7M modulated Ni-Mn-Ga martensitic phase
Authors:: Righi, L; Albertini, F; Villa, E; Paoluzi, A; Calestani, G; Chernenko, V; Besseghini, S; Ritter, C; Passaretti, F Author Full Names: Righi, L.; Albertini, F.
Source:: ACTA MATERIALIA 56 (16): 4529-4535 SEP 2008
Abstract:: For the first time, the 7M modulated structure, frequently observed in ferromagnetic shape memory Ni-Mn-Ga martensitic phases, is solved by powder diffraction analysis. Two polycrystalline samples with composition Ni2Mn1.2Ga0.8 and Ni2.15Mn0.85Ga, respectively, showing a 7M martensitic state stable at room temperature, were studied. The determination of the modulated crystal structure of Ni2Mn1.2Ga0.8 martensite was achieved by refining the X-ray powder diffraction pattern by the Rietveld method. The basic structure belongs to monoclinic symmetry. The crystal structure, solved within the superspace approach, is found to show an incommensurate 7M modulation with q = 0.308c*. The Rietveld refinement for Ni2.15Mn0.85Ga martensite on the basis of neutron powder data surprisingly provides a very similar incommensurate 7M structure with the same periodicity and analogous modulation function. The incommensurate structure presents typical displacive modulation with several analogies with the Zhdanov (5,(2) over bar)(2) stacking sequence. (C) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Update: 31-Oct-2008
Title:: Tl-4(PO2NH)(4) center dot H2O - A commensurately modulated tetrametaphosphimate
Authors:: Sedlmaier, SJ; Oeckler, O; Schnick, W Author Full Names: Sedlmaier, Stefan J.; Oeckler, Oliver
Source:: SOLID STATE SCIENCES 10 (9): 1150-1158 SEP 2008
Abstract:: Tetrathallium(I) tetra-mu-imidocyclotetraphosphate monohydrate, Tl-4(PO2NH)(4)center dot H2O, was obtained by evaporation of combined aqueous solutions of K-4(PO2NH)(4)center dot 4H(2)O and TlOOCCH3 corresponding to the molar ratio of 1:4. The structure determination of Tl-4(PO2NH)(4)center dot H2O was performed by single-crystal X-ray diffraction methods. In addition to the basic structure (P (1) over bar, no. 2, a = 928.3(2), b = 974.6(2), c = 1018.0(2) pm, alpha = 74.47(3)degrees, beta = 64.68(3)degrees, gamma = 78.81(3)degrees, Z = 2), satellite reflections indicate a fourfold superstructure (AT, a = 928.0(2), b = 3897.1(8), c = 2035.4(4), a = 74.47(3)degrees, beta = 64.68(3)degrees, gamma = 78.81(3)degrees, Z = 16) that is described by an a x 4b x 2c, A-centered supercell which mainly concerns one thallium site of the basic structure. In order to reduce the number of parameters, this superstructure was handled as a commensurate occupancy modulation using the structural description in (3 + 1)-dimensional superspace (P (1) over bar(alpha beta gamma), q = 0.25b* + 0.50c*). The crystal structure of Tl-4(PO2NH)(4) center dot H2O consists of infinite columns of the cyclic [(PO2NH)(4)](4-) anions (saddle conformation) which are interconnected by four N-H center dot center dot center dot O hydrogen bonds. By coordination to the Tl+ ions the [(PO2NH)(4)](4-) columns form a three-dimensional network with channels along [100] wherein the thallium ions that are mainly affected by the modulation are located. The commensurate occupancy modulation of these Tl+ ions has been described with a single harmonic wave function. The modulation is verified by P-31 NMR spectroscopy. The thermal behavior of Tl-4(PO2NH)(4)center dot H2O and the IR data are discussed as well. (C) 2008 Elsevier Masson SAS. All rights reserved.
Title:: Characterization of atomized and extruded Al92Fe3Cr2Mn3 alloy
Authors:: Rios, CT; Fogagnolo, JB; Bolfarini, C; Botta, WJ; Kiminami, CS Author Full Names: Rios, C. Triveno; Fogagnolo, J. B.
Source:: REVIEWS ON ADVANCED MATERIALS SCIENCE 18 (4): 408-414 SEP 2008
Abstract:: Powders of the Al92Fe3Cr2Mn3 quaternary alloy were produced by spray atomization processing;, then they were processed by warm extrusion to obtain extruded ingots. The results revealed that in both the powder particles and the extruded bulk samples, alpha-Al, quasicrystalline and intermetallic phases coexist. The quasicrystalline phase was observed as aggregates and its decomposition to crystalline phase occurs above 500 degrees C. Microstructural changes after extrusion were not observed, indicating that the quasicrystalline phase and the intermetallic compounds are stable against coarsening during the time and temperature of extrusion. The presence of micro-porosities after the extrusion is attributed to the spherical form of the powders and mainly to the high volume of intermetallic faceted-particles.
Title:: Anisotropic magnetic, electrical, and thermal transport properties of the Y-Al-Ni-Co decagonal approximant
Authors:: Smontara, A; Smiljanic, I; Ivkov, J; Stanic, D; Barisic, OS; Jaglicic, Z; Gille, P; Komelj, M; Jeglic, P; Bobnar, M; Dolinsek, J Author Full Names: Smontara, Ana; Smiljanic, I.
Source:: PHYSICAL REVIEW B 78 (10): Art. No. 104204 SEP 2008
Abstract:: We have investigated anisotropic physical properties (magnetic susceptibility, electrical resistivity, thermoelectric power, Hall coefficient, and thermal conductivity) of Y-Al-Ni-Co decagonal approximant with composition Al76Co22Ni2. The crystalline-direction-dependent measurements were performed along three orthogonal directions a*,b, and c of the Y-Al-Ni-Co unit cell, where (a,c) monoclinic atomic planes are stacked along the perpendicular b direction. Anisotropic magnetic susceptibility of conduction electrons is paramagnetic for the field lying within the (a,c) atomic planes and diamagnetic for the field along the b direction. Anisotropic electrical resistivity is low in all crystalline directions, appearing in the order rho(a*)>rho(c)>>rho(b). Thermopower shows electron-phonon enhancement effect. Anisotropic bare thermopower (in the absence of electron-phonon interactions) was extracted, appearing in the same order as the resistivity, vertical bar S-a*(bare)/T vertical bar>S-c(bare)/T vertical bar>vertical bar S-b(bare)/T vertical bar. Anisotropic thermal conductivity appears in the order kappa(b)>kappa(c)>kappa(a*), so that b is the most conducting direction for both electricity and heat. Hall coefficient R-H exhibits pronounced anisotropy, where the magnetic field in a given crystalline direction yields the same R-H for the current along the other two crystalline directions in the perpendicular plane. These anisotropies are analyzed in terms of the anisotropic structure of the Y-Al-Ni-Co phase and the ab initio calculated anisotropic Fermi surface. The results are compared with the literature-reported anisotropy of the physical properties of the d-Al-Ni-Co decagonal quasicrystal.
Title:: Determination of magnetic order of the rare-earth ions in multiferroic TbMn2O5
Authors:: Johnson, RD; Bland, SR; Mazzoli, C; Beale, TAW; Du, CH; Detlefs, C; Wilkins, SB; Hatton, PD Author Full Names: Johnson, R. D.; Bland, S. R.
Source:: PHYSICAL REVIEW B 78 (10): Art. No. 104407 SEP 2008
Abstract:: We have employed resonant x-ray magnetic scattering to specifically probe the magnetic order of the rare-earth ions in multiferroic TbMn2O5. Two energy resonances were observed, one originated from the E1-E1 dipolar transition and the other from the E2-E2 quadrupolar transition. These resonances directly probe the valence 5d band and the partially occupied 4f band, respectively. First, full polarization analysis, which is a measurement of the scattered polarization as a function of incident polarization, confirmed a spin polarization of the terbium valence states (probed by the E1-E1 transition) by the Mn4+ spin density in the commensurate phase. Second, full polarization analysis data were collected in the low-temperature incommensurate and commensurate phases when tuned to the E2-E2 resonance. By employing a least-squares fitting procedure, the spin orientations of the terbium ion sublattice were refined.
Title:: Diagonal and collinear incommensurate spin structures in underdoped La2-xBaxCuO4
Authors:: Dunsiger, SR; Zhao, Y; Gaulin, BD; Qiu, Y; Bourges, P; Sidis, Y; Copley, JRD; Kallin, A; Mazurek, EM; Dabkowska, HA Author Full Names: Dunsiger, S. R.; Zhao, Y.
Source:: PHYSICAL REVIEW B 78 (9): Art. No. 092507 SEP 2008
Abstract:: We have studied incommensurate spin ordering in single-crystal underdoped La2-xBaxCuO4 with x similar to 0.08, 0.05, and 0.025 using neutron-scattering techniques. Static incommensurate magnetic order is observed in the La2-xBaxCuO4 (x = 0.05 and 0.025) compounds with ordering wave vectors which are rotated by 45 about the commensurate (0.5,0.5,0) position, with respect to that in the superconducting x = 0.08 material. These spin modulations are one dimensional in the x = 0.05 and 0.025 samples, with ordering wave vectors lying along the orthorhombic b* direction. Such a rotation in the orientation of the static spin ordering as a function of increasing Ba doping, from diagonal to collinear, is roughly coincident with the transition from an insulating to a superconducting ground state and is similar to that observed in the related La2-xSrxCuO4 system. This phenomenon is therefore a more generic property of underdoped La-214 cuprates.
Title:: Nonlocal Landau theory of the magnetic phase diagram of highly frustrated magnetoelectric CuFeO2
Authors:: Plumer, ML Author Full Names: Plumer, M. L.
Source:: PHYSICAL REVIEW B 78 (9): Art. No. 094402 SEP 2008
Abstract:: A nonlocal Landau-type free-energy functional of the spin density is developed to model the large variety of magnetic states, which occur in the magnetic-field-temperature phase diagram of magnetoelectric CuFeO2. Competition among long-range quadratic exchange, biquadratic antisymmetric exchange, and trigonal anisotropy terms, consistent with the high-temperature rhombohedral R (3) over barm crystal symmetry, are shown to all play important roles in stabilizing the unusual combination of commensurate and incommensurate spin structures in this highly frustrated triangular antiferromagnet. It is argued that strong magnetoelastic coupling is largely responsible for the nonlocal nature of the free energy. A key feature of the analysis is that an electric polarization is induced by a canting of the noncollinear incommensurate spin structure. Application of the model to ordered spin states in the triangular antiferromagnets MnBr2 and NaFeO2 is also discussed.
Title:: Differences between the R-phase and the commensurate phase in iron-doped Ti-Ni shape memory alloys
Authors:: Choi, MS; Yamamoto, T; Fukuda, T; Kakeshita, T; Taguchi, E; Mori, H Author Full Names: Choi, Mi-Seon; Yamamoto, Takuya
Source:: PHILOSOPHICAL MAGAZINE 88 (16): 2449-2460 2008
Abstract:: A Ti-44Ni-6Fe (at. %) alloy was recently reported to exhibit a second order-like incommensurate-commensurate transformation. Whether or not the commensurate (C) phase and the R-phase in Ti-Ni alloys are the same phase has now been investigated. Transformation behaviour was examined in a series of Ti-(50-x)Ni-Fe-x (at. %) alloys with x = 2.0, 4.0, 5.0, 5.5, 5.7, 6.0. Transformation temperature, entropy change and the transformation strain decrease continuously as x increases up to x = 5.7, where the product phase is apparently the R-phase. However, there is an obvious discontinuity in these values between x = 5.7 and x = 6.0. In addition, electron diffraction experiments have revealed that the intensity of satellite reflections of the C-phase is obviously weaker than that of the R-phase. These results strongly suggest that the C-phase is different from the R-phase.
Title:: Electric field induced anomalies in ferroelectric K2SeO4
Authors:: Leist, J; Gibhardt, H; Hradil, K; Eckold, G Author Full Names: Leist, J.; Gibhardt, H.
Source:: JOURNAL OF PHYSICS-CONDENSED MATTER 20 (41): Art. No. 415209 OCT 15 2008
Abstract:: The lock-in transition of K2SeO4 at 93.2 K was studied using high-resolution. gamma-ray diffraction, in situ dielectric measurements and neutron scattering. The phase transition shows a coexistence regime of 1.0 K with clearly resolved incommensurate and commensurate satellite reflections. Within a temperature interval of several K above the lock-in transition, strong third order satellites are observed, indicating a pronounced squaring of the modulation wave. Under the influence of high electric fields an intermediate phase is observed, which is characterized by a diffuse intensity distribution. In addition, the dielectric permittivity exhibits two maxima, indicating the existence of two separate phase transitions. This behaviour is attributed to distortions of the discommensuration lattice and pinning of the discommensurations by accumulated charged defects. It seems to be characteristic for modulated ferroelectrics of the A(2)BX(4) group, since a similar behaviour is also found in isostructural Rb2ZnCl4 and K2ZnCl4. The soft-mode dynamics close to T-c is found to be essentially independent of the electric field and not affected by the discommensuration lattice.
Title:: Increasing the structural complexity of chromium(IV) oxides by high-pressure and high-temperature reactions of CrO2
Authors:: Castillo-Martinez, E; Arevalo-Lopez, AM; Ruiz-Bustos, R; Alario-Franco, MA Author Full Names: Castillo-Martinez, E.; Arevalo-Lopez, A. M.
Source:: INORGANIC CHEMISTRY 47 (19): 8526-8542 OCT 6 2008
Abstract:: This work presents an overview of a series of increasingly complex oxides synthesized from CrO2, under high-pressure and high-temperature conditions, having C l in octahedral coordination. Although the emphasis is on the structure and microstructure of the compounds as obtained from X-ray diffraction and transmission electron microscopy and diffraction, attention is also given to their interesting electronic and magnetic properties. The study is complemented with an electron energy loss spectroscopic analysis of the different phases. These are the cubic perovskite SrCrO3, the orthorhombic perovskite CaCrO3, the solid solution Sr1-xCaxCrO3, the Ruddlesden-Popper-type Sr3Cr2O7, the family CrSr2RECu2O8 (RE = rare earth), a compositionally modulated perovskite "PbCrO3", and the misfit layer oxide SrO2[CrO2](1.85).
Title:: Transition-metal oxides with triangular lattices: Generation of new magnetic and electronic properties
Authors:: Maignan, A; Kobayashi, W; Hebert, S; Martinet, G; Pelloquin, D; Bellido, N; Simon, C Author Full Names: Maignan, A.; Kobayashi, W.
Source:: INORGANIC CHEMISTRY 47 (19): 8553-8561 OCT 6 2008
Abstract:: The search for multifunctional materials as multiferroics to be applied in microelectronic or for new, chemically stable and nontoxic, thermoelectric materials to recover waste heat is showing a common interest in the oxides whose structures contain a triangular network of transition-metal cations. To illustrate this point, two ternary systems, Ba-Co-O and Ca-Co-O, have been chosen. It is shown that new phases with a complex triangular structure can be discovered, for instance, by introduction of Ga3+ into the Ba-Co-O system to stabilize Ba6Ga2Co11O26 and Ba2GaCo8O14, which both belong to a large family of compounds with formula [Ba(Co,Ga)O3-delta](n)[BaCo8O11]. In the latter, both sublattices contain triangular networks derived from the hexagonal perovskite and the spinel structure. Among the hexagonal perovskite, the Ca3Co2O6 Crystals give clear evidence where the coupling of charges and spins is at the origin of a magnetocapacitance effect. In particular, the ferrimagnetic to ferromagnetic transition, with a one-third plateau on the M(M curve characteristic of triangular magnetism, is accompanied by a peak in the dielectric constant. A second class of cobaltites is the focus of much interest. Their 2D structure, containing CoO2 planes isostructural to a Cdl(2) slice that are stacked in an incommensurate way with rock salt type layers, is referred to misfit cobaltite. The 2D triangular network of edge-shared CoO6 octahedra is believed to be responsible for large values of the Seebeck coefficient and low electrical resistivity. A clear relationship between the structures-incommensurability ratios-and the electronic properties is evidenced, showing that the charge carrier concentration can be tuned via the control of the ionic radius of the cations in the separating layers.
Title:: Phase transitions in [N(CH3)(4)](2)ZnCl4 and [N(CH3)(4)](2)CuCl4 crystals related with the incommensurate modulation existence
Authors:: Sveleba, S; Semotyuk, O; Katerynchuk, I; Kunyo, I; Karpa, I; Pankivskyi, Y Author Full Names: Sveleba, S.; Semotyuk, O.
Source:: ACTA PHYSICA POLONICA A 114 (4): 791-806 OCT 2008
Abstract:: The continuous phase transitions are observed in the crystals with incommensurate phase. They are transitions of parent-incommensurate phases (T-i); transitions between metastable states; phases (T-i). It was set that phase transition between parent and incommensurate phase is a continuous second-order phase transition with a critical index beta = 0.5. The transition between metastable states is, a continuous phase transition through the intermediate temperature region - incommensurate phase. The wave vector changes with the temperature here and wave vector q* = q(1) - q(2) appears, where q(1), q(2) denote commensurate values of incommensurabilty wave vector of neighboring metastable states. It, was shown that the phase transition between incommensurate and commensurate phases is a continuous phase transition.
Update: 24-Oct-2008
Title:: Synthesis and crystal structure of commensurate polymorph of Ln(4)AlCu(2)B(9)O(23) (Ln=Lu,Ho) and refinement of Cu2Al6B4O17
Authors:: Plachinda, PA; Belokoneva, EL Author Full Names: Plachinda, P. A.; Belokoneva, E. L.
Source:: ZEITSCHRIFT FUR ANORGANISCHE UND ALLGEMEINE CHEMIE 634 (11): 1965-1970 2008
Abstract:: Single crystals of new Cu,Lu(Ho) - alumoborate and known Cu,Al-borate were synthesized through reaction between CuB2O4 and LnBO(3) on the Al2O3 surface by annealing at 1100 degrees C. Structure of commensurate modification of Ln(4)AlCu(2)B(9)O(23), (Ln = Lu,Ho), sp. gr. P (4) over bar2(1)m, was solved at room temperature. It was found that a low-temperature (110 K) modification possesses incommensurate modulations with modulation vector q =(0, 0, 0.132). The nonaborate block - [B9O23](19-)- 9[6T+3 Delta] forms an isolated unique dense closed anionic unit. This block is terminated by Al-tetrahedrons in the chessboard pattern, resulting in formation of complex alumoborate layer [AlB9O23](16-). Apical oxygen of central BO3 triangle of the nonaborate block seems to be the source of modulations observed in low temperature polymorph. Cationic layers with the Ln and Cu atoms are alternating along c axis with anionic layers. The structure Cu2Al6B4O17, previously studied by the Rietveld method, was corroborated by single crystal data and was compared with LiAl7B4O17.
Title:: Field-induced discommensuration in charge density waves in o-TaS3
Authors:: Inagaki, K; Tsubota, M; Higashiyama, K; Ichimura, K; Tanda, S; Yamamoto, K; Hanasaki, N; Ikeda, N; Nogami, Y; Ito, T; Toyokawa, H Author Full Names: Inagaki, Katsuhiko; Tsubota, Masakatsu
Source:: JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 77 (9): Art. No. 093708 SEP 2008
Abstract:: We report a synchrotron X-ray Study of charge density waves (CDWs) in an o-TaS3 crystal. We found that two independent CDWs coexist ill the temperature range of 130-50K. These waves are incommensurate and commensurate CDWs with longitudinal wave vectors q(c) = 0.252c* and 0.250c*, respectively. The temperature and electric current dependences of the intensity of the two CDW satellites were measured. We found that the commensurate CDW was converted to the incommensurate CDW at 80 K by inducing current flow. Our observation was interpreted in terms of the dynamics of topological defects. We determined the edge dislocation configuration from the electric Current dependence of the intensity of the two CDWs. The result implies Cor the first time that discommensurations are induced ill the commensurate CDW by applying an electric field.
Title:: Effect of quenched disorder on charge ordering structure in RE(1.67)AE(0.33)NiO(4) (RE = La, Pr, Nd, Sm; AE = Ca, Sr)
Authors:: Yu, XZ; Arima, TH; Seki, S; Asaka, T; Kimoto, K; Tokura, Y; Matsui, Y Author Full Names: Yu, Xiuzhen; Arima, Taka-hisa
Source:: JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 77 (9): Art. No. 093709 SEP 2008
Abstract:: The structure feature of charge ordering (CO) has been investigated for the layered nickelates RE(1.67)AE(0.33)NiO(4) by transmission electron microscopy (TEM). A long-range commensurate CO is observed along the b-axis in Pr1.67Ca0.33NiO4 with minimal quenched disorder, while only a short-range incommensurate CO is observed in Sm1.67Sr0.33NiO4 with larger disorder. Increasing the quenched disorder, hence the number of stacking faults, leads, to an abrupt decrease in CO correlation length, indicating that the quenched disorder plays an important role in the CO collapse process.
Title:: Discovery of polarization flop transition and simultaneous measurements of magnetic ordering and dielectric properties of TmMn2O5
Authors:: Fukunaga, M; Nishihata, K; Kimura, H; Noda, Y; Kohn, K Author Full Names: Fukunaga, Mamoru; Nishihata, Keisuke
Source:: JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 77 (9): Art. No. 094711 SEP 2008
Abstract:: We have performed simultaneous measurements of magnetic neutron diffraction, ferroelectric D-E hysteresis loops and permittivity along the b- and a-axes of multiferroic TmMn(2)O(5)down to 2.5 K. It was confirmed that the permittivity peak coincides with an increase in both the polarization along the b-axis and a magnetic commensurate phase, which agrees with a previous similar experiment on ErMn2O5. We also discovered it polarization flop from the b-axis to the a-axis below 5 K coincident with a magnetic phase transition from one incommensurate phase to another incommensurate phase, which was confirmed by the simultaneous measurements. Although both phases are almost equivalent in the magnetic propagation wave vector, different magnetic structures induce it completely different ferroelectricity. Ferroelectric hysteresis loops along both the b- and a-axes were clearly observed by the double-wave method.
Title:: Full-field strain evolution during intermartensitic transformations in single-crystal NiFeGa
Authors:: Efstathiou, C; Sehitoglu, H; Carroll, J; Lambros, J; Maier, HJ Author Full Names: Efstathiou, C.; Sehitoglu, H.
Source:: ACTA MATERIALIA 56 (15): 3791-3799 SEP 2008
Abstract:: Using in situ digital image correlation to obtain full-field measurements, we study the intermartensitic transformations in single-crystal NiFeGa. Full-field strain measurements identify the coexistence of modulated martensite phases during the first plateau of the multistage stress-strain Curve at room temperature. At a higher temperature, the measurements indicate the bypassing of one of the modulated phases. Strain as high as 13% is measured as a result of the transformation to the intermediate monoclinic modulated and final tetragonal phase. Based on the full-field strain measurements, the phase fractions during the nucleation and the progression of the transformation are obtained. The evolution of the local strain and the phase fractions prove critical in explaining strain softening, hysteresis and other phenomena observed in the stress-strain curves. (c) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:: Orientational ordering in the low-temperature stable phases of deuterated thiophene
Authors:: Damay, F; Rodriguez-Carvajal, J; Andre, D; Dunstetter, F; Szwarc, H Author Full Names: Damay, F.; Rodriguez-Carvajal, J.
Source:: ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 64: 589-595 Part 5 OCT 2008
Abstract:: The stable structures of deuterated thiophene C4D4S were investigated at 155 (phase III), 115 (phase IV), 100 and 1.5 K (phase V) by neutron powder diffraction. At 155 K, thiophene is orthorhombic with space group Pbnm. Although there is some degree of in-plane orientational disorder, molecules begin to order along two symmetrically equivalent main orientations. At 115 K the structure is incommensurate, with a wavevector q similar or equal to 0.55a*. At 100 K and below, there is a doubling of the a cell parameter and the structure space group is P2(1). For the first time, it is shown that, unlike C4H4S, phase V of C4D4S is not an orientational glass: thiophene molecules are perfectly ordered and are oriented within the molecular plane along two alternating directions, corresponding to the two main orientations observed at 155 K. This ordering probably originates in the slowing down of the in-plane reorientational dynamics upon deuteration.
Update: 17-Oct-2008
Title:: Structural and magnetic properties of the ferroelectric magnet BaMn1-xZnxF4, a site diluted square-lattice two-dimensional Heisenberg antiferromagnet with S=5/2
Authors:: Veira, JR; Argyriou, DN; Kiefer, K; Wolter, AUB; Alber, D; Meissner, M; Almairac, R; Reehuis, M; Bordallo, HN Author Full Names: Veira, J. R.; Argyriou, D. N.; Kiefer, K.; Wolter, A. U. B.; Alber, D.; Meissner, M.; Almairac, R.; Reehuis, M.; Bordallo, H. N.
Source:: PHYSICAL REVIEW B 78 (5): Art. No. 054104 AUG 2008
Abstract:: The influence of Zn doping on the structural and magnetic properties of multiferroic BaMnF4 has been investigated using temperature dependent x-ray diffraction and magnetization measurements. With increasing Zn content the transition temperatures of the structural incommensurate phase transition as well as the AF ordering decrease. For x=0.75 no incommensurate phase is found anymore. The suppression of the structural transition can be explained due to the smaller size of Zn compared with Mn. The suppression of the antiferromagnetic ordering can be explained by a site dilution of the magnetic structure with nonmagnetic Zn. The percolation threshold is found to be x(p)=0.393(4). This is in agreement with predictions for a site-diluted square-lattice weak-anisotropy two-dimensional Heisenberg antiferromagnet with S = 5/2.
Title:: Origin of incommensurate modulations in the high-pressure phosphorus IV phase
Authors:: Marques, M; Ackland, GJ; Lundegaard, LF; Falconi, S; Hejny, C; McMahon, MI; Contreras-Garcia, J; Hanfland, M Author Full Names: Marques, M.; Ackland, G. J.; Lundegaard, L. F.; Falconi, S.; Hejny, C.; McMahon, M. I.; Contreras-Garcia, J.; Hanfland, M.
Source:: PHYSICAL REVIEW B 78 (5): Art. No. 054120 AUG 2008
Abstract:: We present results from x-ray diffraction experiments and density functional theory calculations which provide a fully consistent picture of the high-pressure phosphorus-IV phase (P-IV). P-IV has an incommensurately-modulated crystal structure described by the four-dimensional superspace group Cmmm(00 gamma)s00. Electronic structure calculations using a three-dimensional commensurate approximant to this structure give excellent agreement with experiment for the structural parameters and their variation with pressure. Density functional perturbation theory shows a phonon instability at the incommensurate wave vector, related to the opening of a pseudogap at the Fermi surface, showing that the atomic motions comprising the incommensuration occur to eliminate Fermi-surface nesting. Unusually, the pseudogap opens not at the incommensurate wave vector (00 gamma) itself, but at two larger wave vectors corresponding to strong reflections in the diffraction pattern.
Title:: Nucleation and growth of a quasicrystalline monolayer: Bi adsorption on the fivefold surface of i-Al70Pd21Mn9
Authors:: Smerdon, JA; Parle, JK; Wearing, LH; Lograsso, TA; Ross, AR; McGrath, R Author Full Names: Smerdon, J. A.; Parle, J. K.; Wearing, L. H.; Lograsso, T. A.; Ross, A. R.; McGrath, R.
Source:: PHYSICAL REVIEW B 78 (7): Art. No. 075407 AUG 2008
Abstract:: Scanning tunneling microscopy has been used to study the formation of a Bi monolayer deposited on the fivefold surface of i-Al70Pd21Mn9. Upon deposition of low submonolayer coverages, the nucleation of pentagonal clusters of Bi adatoms of edge length 4.9 angstrom is observed. The clusters have a, common orientation leading to a film with fivefold symmetry. By inspection of images where both the underlying surface and the Bi atoms are resolved, the pentagonal clusters are proposed to nucleate on pseudo-Mackay clusters truncated such that a Mn atom lies centrally in the surface plane. The density of these sites is sufficient to form a quasiperiodic framework, and subsequent adsorption of Bi atoms ultimately leads to the formation of a quasicrystalline monolayer. The suggested nucleation site is different from that proposed on the basis of recent density-functional theory calculations.
Title:: Neutron powder diffraction study of the magnetic and crystal structures of SrFe2(PO4)(2)
Authors:: Belik, AA; Huang, QZ; Takayama-Muromacchi, E; Lynn, JW Author Full Names: Belik, Alexei A.; Huang, Qingzhen; Takayama-Muromacchi, Eiji; Lynn, Jeffrey W.
Source:: JOURNAL OF SOLID STATE CHEMISTRY 181 (9): 2292-2297 SEP 2008
Abstract:: The crystal and magnetic structures of SrFe22+(PO4)(2) have been determined by neutron powder diffraction data at low temperatures (space group P2(1)/c (no. 14); Z=4: a=9.35417(13)angstrom, b = 6.83808(10) angstrom, c = 10.51899(15) angstrom, and beta = 109.5147(7)degrees at 15 K). Two magnetic phase transitions were found at T-1 = 7.4 K (first-order phase transition) and T-2 = 11.4 K (second-order phase transition). The transition at T2 was hardly detectable by dc and ac magnetization measurements, and a small anomaly was observed by specific heat measurements. At T1, strong anomalies were found by dc and ac magnetization and specific heat. The structure of SrFe2(PO4)(2) consists of linear four-spin cluster units, Fe2-Fe1-Fe1-Fe2. Below T-1, the propagation vector of the magnetic structure is k [0,0,0]. The magnetic moments of the inner Fe1-Fe1 atoms of the four-spin cluster unit are ferromagnetically coupled. The magnetic moment of the outer Fe2 atom is also ferromagnetically Coupled with that of the Fe1 atom but with spin canting. The four-spin cluster units form ferromagnetic layers parallel to the [-101] plane, while these layers are stacked antiferromagnetically in the [-101] direction. Spill canting of the Outer Fe2 atoms provides a weak ferromagnetic moment of about 1 (mu B) along the b-axis. The refined magnetic moments at 3.5 K are 4.09 (mu B) for Fe1 and 4.07 (mu B) for Fe2. Between T-1 and T-2, a few weak magnetic reflections were observed probably due to incommensurate magnetic order. (C)2008 Elsevier Inc. All rights reserved.
Update: 10-Oct-2008
Title:: Devitrification of mechanically alloyed Zr-Ti-Nb-Cu-Ni-Al glassy powders studied by time-resolved X-ray diffraction
Authors:: Scudino, S; Sordelet, DJ; Eckert, J Author Full Names: Scudino, S.; Sordelet, D. J.; Eckert, J.
Source:: REVIEWS ON ADVANCED MATERIALS SCIENCE 18 (3): 221-224 AUG 2008
Abstract:: The crystallization of mechanically alloyed Zr67Ti6.14Nb1.92Cu10.67Ni8.52Al5.75 glassy powder is investigated by time-resolved X-ray diffraction. The powder displays a multi-step crystallization behavior characterized by the formation of a metastable nanoscale quasicrystalline phase during the first stage of the crystallization process. At higher temperatures, coinciding with the second crystallization event, the amorphous-to-quasicrystalline transformation is followed by the precipitation of the tetragonal Zr2Cu phase (space group 14/mmm) and the tetragonal Zr2Ni phase (space group 14/mcm). The transformations are gradual and the quasicrystals and the subsequent phases coexist over a temperature interval of about 25K.
Title:: Manipulating the magnetic structure of Co Core/CoO shell nanoparticles: Implications for controlling the exchange bias
Authors:: Inderhees, SE; Borchers, JA; Green, KS; Kim, MS; Sun, K; Strycker, GL; Aronson, MC Author Full Names: Inderhees, S. E.; Borchers, J. A.; Green, K. S.; Kim, M. S.; Sun, K.; Strycker, G. L.; Aronson, M. C.
Source:: PHYSICAL REVIEW LETTERS 101 (11): Art. No. 117202 SEP 12 2008
Abstract:: We present an experimental study of the effects of oxidation on the magnetic and crystal structures of exchange biased epsilon-Co/CoO core-shell nanoparticles. Transmission electron microscopy measurements reveal that oxidation creates a Co-CoO interface which is highly directional and epitaxial in quality. Neutron diffraction measurements find that below a Neel temperature T-N of similar to 235 K the magnetization of the CoO shell is modulated by two wave vectors, q(1)= (1/2 1/2 1/2)2 pi/alpha and q(2) = (100)2 pi/alpha. Oxidation affects the q(1) component of the magnetization very little, but hugely enhances the q(2) component, resulting in the magnetic decompensation of the core-shell interface. We propose that the large exchange bias effect results from the highly ordered interface between the Co core and CoO shell, and from enhanced core-shell coupling by the uncompensated interface moment.
Title:: Nature of the magnetic order in Ca3Co2O6
Authors:: Agrestini, S; Chapon, LC; Daoud-Aladine, A; Schefer, J; Gukasov, A; Mazzoli, C; Lees, MR; Petrenko, OA Author Full Names: Agrestini, S.; Chapon, L. C.; Daoud-Aladine, A.; Schefer, J.; Gukasov, A.; Mazzoli, C.; Lees, M. R.; Petrenko, O. A.
Source:: PHYSICAL REVIEW LETTERS 101 (9): Art. No. 097207 AUG 29 2008
Abstract:: We present a detailed powder and single-crystal neutron diffraction study of the spin chain compound Ca3Co2O6. Below 25 K, the system orders magnetically with a modulated partially disordered antiferromagnetic structure. We give a description of the magnetic interactions in the system which is consistent with this magnetic structure. Our study also reveals that the long-range magnetic order coexists with a shorter-range order with a correlation length scale of similar to 180 angstrom in the ab plane. Remarkably, on cooling, the volume of material exhibiting short-range order increases at the expense of the long-range order.
Title:: Frustration-induced quantum phases in mixed spin chain with frustrated side chains
Authors:: Hida, K; Takano, K Author Full Names: Hida, Kazuo; Takano, Ken'ichi
Source:: PHYSICAL REVIEW B 78 (6): Art. No. 064407 AUG 2008
Abstract:: A mixed Heisenberg spin chain with frustrated side chains is investigated by numerical and perturbational calculations. A frustration-induced quantum partially polarized ferrimagnetic phase and a nonmagnetic spin quadrupolar phase are found adjacent to the conventional Lieb-Mattis-type ferrimagnetic phase or the nonmagnetic singlet cluster solid phases. The partially polarized ferrimagnetic phase has an incommensurate spin structure. Similar structures are commonly found in other frustration-induced partially polarized ferrimagnetic phases. Numerical results also suggest a series of almost critical nonmagnetic ground states in a highly frustrated regime if the side chain spins weakly couple to the main chain.
Title:: Noncollinear magnetism in the high-pressure hcp phase of iron
Authors:: Lizarraga, R; Nordstrom, L; Eriksson, O; Wills, J Author Full Names: Lizarraga, Raquel; Nordstroem, Lars; Eriksson, Olle; Wills, John
Source:: PHYSICAL REVIEW B 78 (6): Art. No. 064410 AUG 2008
Abstract:: The magnetic structure of iron in its high-pressure hcp phase has been investigated with the full-potential augmented plane wave with local orbitals method that allows for noncollinear magnetism. In our study we consider different spin spiral structures and, three antiferromagnetic configurations that have been previously discussed in the literature. We found that some of the magnetic structures are only metastable, and that a nonsymmetric incommensurate spin spiral state with wave vector q = (0.56, 0.22, 0)2 pi/a and two different antiferromagnetic structures are the most stable ones being almost degenerate around the equilibrium volume. These magnetic structures ought to exist in the pressure range where hcp iron becomes stable.
Title:: Soft x-ray induced Ag diffusion in amorphous pulse laser deposited As50Se50 thin films: An x-ray photoelectron and secondary ion mass spectroscopy study
Authors:: Kalyva, M; Siokou, A; Yannopoulos, SN; Wagner, T; Krbal; Orava, J; Frumar, M Author Full Names: Kalyva, M.; Siokou, A.; Yannopoulos, S. N.; Wagner, T.; Krbal; Orava, J.; Frumar, M.
Source:: JOURNAL OF APPLIED PHYSICS 104 (4): Art. No. 043704 AUG 15 2008
Abstract:: In the present paper, x-ray photoelectron spectroscopy (XPS) is used to induce and study the Ag diffusion and dissolution in pulsed laser deposited As50Se50 amorphous chalcogenide films. Dynamic secondary ion mass spectroscopy (SIMS) is also employed to investigate the Ag atomic concentration in depth. Dynamic SIMS measurements reveal that even before x-ray irradiation a considerable percentage of the total silver amount diffuses into the matrix forming an similar to 70 nm mixed Ag-Se-As layer. XPS analysis shows that x-ray irradiation induces further diffusion of silver into the chalcogenide matrix. At the end of the procedure silver is found to be homogeneously dissolved into the matrix leaving only a 5-7 nm thick surface layer with excess silver concentration. In this surface layer stable Ag2Se clusters existing probably in quasicrystalline form prohibit further diffusion. The origin of the mechanism of the x-ray induced Ag diffusion and dissolution in amorphous chalcogenides is discussed in light of the present results. (c) 2008 American Institute of Physics.
Title:: Disordered structures of the TM-Mg-Zn 1/1 quasicrystal approximants (TM = Hf, Zr, or Ti) and chemical intergrowth
Authors:: Gomez, CP; Ohhashi, S; Yamamoto, A; Tsai, AP Author Full Names: Gomez, Cesar Pay; Ohhashi, Satoshi; Yamamoto, Akiji; Tsai, An Pang
Source:: INORGANIC CHEMISTRY 47 (18): 8258-8266 SEP 15 2008
Abstract:: The structures of three quasicrystal approximant phases in the TM-Mg-Zn (TM = Hf, Zr, Ti) systems with the analyzed compositions Hf5Mg18Zn77, Zr5Mg18Zn77, and Ti5.5Mg17.5Zn77 have been synthesized, and their structures have been analyzed by single-crystal X-ray diffraction. The structure analyses revealed that these cubic phases with the space group Pm contain two different rhombic-triacontahedral clusters. These clusters are so-called Bergman-type atomic clusters and previously known approximants of face-centered icosahedral (F-type) quasicrystals are composed only of Mackay-type clusters, thus these compounds are seen as new prototype structures. Electron density maps calculated by the maximum entropy method (MEM) show that one of the atomic clusters displays characteristic structural disorder. The disorder in these phases is related to the chemical intergrowth of different Friauf polyhedra, and the prospects of new guide lines for finding quasicrystals composed of such polyhedra are discussed.
Update: 3-Oct-2008
Title:: Structure and microstructure of the high pressure synthesised misfit layer compound [Sr2O2][CrO2](1.85)
Authors:: Castillo-Martinez, E; Schonleber, A; van Smaalen, S; Arevalo-Lopez, AM; Alario-Franco, MA Author Full Names: Castillo-Martinez, E.; Schoenleber, A.; van Smaalen, S.; Arevalo-Lopez, A. M.; Alario-Franco, M. A.
Source:: JOURNAL OF SOLID STATE CHEMISTRY 181 (8): 1840-1847 AUG 2008
Abstract:: The strontium chromium oxide [Sr2O2][CrO2](1.85) misfit layer compound has been synthesised at high-pressure and high-temperature conditions. Electron diffraction patterns and high-resolution transmission electron microscopy images along [001] show the misfit character of the different layers composing the structure with a supercell along the incommensurate parameter b approximate to 7b(1)approximate to 13b(2). The modulated crystal structure has been refined within the superspace formalism against single-crystal X-ray diffraction data, employing the (3+1)-dimensional superspace group C'nrnb(0 sigma(2)0)0 0s. The compound has a composite structure with lattice parameters a(1) =5.182(1)angstrom, b(1) = 5.471(1)angstrom, c(1) = 18.194(3)angstrom for the first, SrO, subsystem and the same a and c, but with 152 = 2.925(1) angstrom for the second, CrO2, subsystem. The layer stacking is similar to that of orthorhombic PbS(TiS2)(1.18), but with a much stronger intersubsytem bonding in the case of the oxide. The intersubsystem lattice mismatch is mainly handled by displacement modulations of the Sr atoms, correlated with modulations of the valence, the coordination and the anisotropic displacement parameters. (C) 2008 Elsevier Inc. All rights reserved.
Title:: Single-crystal NMR for the layered semiconductor TlGaSe2
Authors:: Panich, AM; Kashida, S Author Full Names: Panich, A. M.; Kashida, S.
Source:: JOURNAL OF PHYSICS-CONDENSED MATTER 20 (39): Art. No. 395211 OCT 1 2008
Abstract:: We report on a Ga-69 and Tl-205 NMR study of single-crystal thallium gallium selenide. Our findings show that transformation from the high temperature paraelectric phase to the low temperature ferroelectric phase occurs via an incommensurate phase that exists in the temperature range from T-c = 107.5 to T-i = 118 K. On approaching phase transition at Ti from above, the crystal exhibits soft mode behavior, which is somewhat different for thallium and gallium substructures. Redistribution of Ga-69 line intensities with temperature in the ferroelectric phase indicates a variation of the domain structure of this phase.
Update: 26-Sep-2008
Title:: Microstructure of Al-Mn-Be melt-spun ribbons
Authors:: Zupanic, F; Boncina, T; Sustarsic, B; Anzel, I; Markoli, B Author Full Names: Zupanic, Franc; Boncina, Tonica; Sustarsic, Borivoj; Anzel, Ivan; Markoli, Bostjan
Source:: MATERIALS CHARACTERIZATION 59 (9): 1245-1251 SEP 2008
Abstract:: Microstructures of two alloys with the nominal compositions of Al92Mn3Be5 and Al89Mn6Be5 were characterized in the initial as-cast condition (after vacuum induction melting and casting) and after melt spinning. In the initial conditions, both alloys consisted of an aluminum-rich solid solution and two metastable intermetallic phases: Be4AlMn and Al10Mn3(Be). Both alloys melted over a rather large temperature range (between 230 degrees C and 310 degrees C). This was the main reason for the presence of unmelted particles in the melt-spun ribbons. Nonetheless, with the use of optimized melt-spinning parameters a microstructure composed of the Al-rich solid solution and finely dispersed quasicrystalline particles in ribbons with thicknesses ranging from 30-200 mu m was achieved. The dispersion of quasicrystalline particles was finest on the wheel side of the thinnest ribbons, attaining microhardness values between 250 HV and 300 HV. (C) 2007 Elsevier Inc. All rights reserved.
Update: 19-Sep-2008
Title:: Synthesis and characterization of GaP nanochains with a twin-modulated quasi-periodic structure
Authors:: Liu, YK; Shan, YY; Wang, HB; Lee, CS; Lee, ST Author Full Names: Liu, Y. K.; Shan, Y. Y.; Wang, H. B.; Lee, Chun-Shen; Lee, Shu-Tong
Source:: SUPERLATTICES AND MICROSTRUCTURES 44 (2): 208-215 AUG 2008
Abstract:: GaP nanochains have been synthesized by hydrogen-assisted thermal evaporation, and characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), photoluminescence (PL), and Raman spectroscopy. GaP nanochains possess a (111) twin crystal plane-modulated quasi-periodic structure, that gives a strong green photoluminescence at 618 nm. While the Raman spectrum of the nanochains is similar to that of the GaP crystal, the intensity of the longitudinal optical (LO) peak is stronger than that of the transverse optical (TO) peak, which is supposedly related to the nanochain microstructures. (C) 2008 Published by Elsevier Ltd.
Title:: Interaction between the chain and ladder subsystems in (Ca, Sr, La)(14)Cu24O41 compounds
Authors:: Schwingenschlogl, U; Schuster, C Author Full Names: Schwingenschloegl, U.; Schuster, C.
Source:: JOURNAL OF PHYSICS-CONDENSED MATTER 20 (38): Art. No. 382201 SEP 24 2008
Abstract:: We investigate the influence of structural modulations on the electronic properties of incommensurate (Ca, Sr, La)(14)Cu24O41 compounds by band structure calculations based on density functional theory and the local density approximation (LDA). Using a supercell approach with ten CuO2 chain and seven Cu2O3 ladder segments, we take into account the major effects of the structural incommensurability. We find that the LDA electronic states show very little response to these modulations. The coupling between the electronic and structural degrees of freedom, hence, can be well described in terms of two independent subsystems. The incommensurate charge density waves (CDWs) in the chains and the ladders are formed independently of each other.
Title:: Directional growth and characterizations of orthorhombic HoMnO3 films
Authors:: Lin, JG; Han, TC; Wu, CT; Chu, MW; Chen, CH Author Full Names: Lin, J. G.; Han, T. C.; Wu, C. T.; Chu, M. -W.; Chen, C. H.
Source:: JOURNAL OF CRYSTAL GROWTH 310 (16): 3878-3880 AUG 1 2008
Abstract:: In this work, we synthesize the orthorhombic HoMnO3 films on the SrTiO3(1 0 0) and LaAlO3(1 1 0) substrates by pulsed laser deposition and study their crystalline and magnetic properties. The orthorhombic HoMnO3 film with its b-axis perpendicular to the film surface is grown on the LaAlO3(1 1 0) substrate, and shows clearly three magnetic transitions at 45, 10 and 7K, which are attributed to the magnetization process of incommensurate spin structure of Mn3+ for 10K
Title:: Evolution of a nanocrystalline (Co,Ni)Al2O4 spinel phase from quasicrystalline precursor
Authors:: Yadav, TP; Tiwari, RS; Srivastava, ON; Mukhopadhyay, NK Author Full Names: Yadav, Thakur Prasad; Tiwari, Radhey Shyam; Srivastava, Onkar Nath; Mukhopadhyay, Nilay Krishna
Source:: INTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY 5 (5): 449-457 2008
Abstract:: This work reports on the synthesis of a spinel phase from a thermodynamically stable decagonal quasicrystalline Al70Co15Ni15 alloy. The Al70Co15Ni15 alloy, synthesized through slow cooling of the molten alloy, was subjected to milling in an attritor ball mill at 400 rpm for 5, 10, 20, 30, and 40 h with a ball to powder ratio of 20:1 in the hexane medium. The differential thermal analysis, X-ray diffraction, scanning, and transmission electron microscopy techniques have been used for characterization of milled as well as annealed powders. The Voigt function analysis has been used for calculation of the effective crystallite size and relative strain of ball-milled samples. The crystallite size has been found to be similar to 14 nm after 40 h of milling along with a lattice strain of 8.1%. The annealing experiments have been carried out under two different conditions: (i) in vacuum and (ii) in air. The results of the present investigation clearly revealed that the nano-decagonal phase was stable in vacuum while annealing at 600 degrees C for 40 h. However, during annealing under a similar condition in air, the formation of a nanospinel of (Ni,Co)Al2O4 of size similar to 60 nm was identified. The possible structural evolution of the spinel from the quasicrystalline phase has been discussed.
Update: 12-Sep-2008
Title:: Temperature behavior of magnetic susceptibility and paramagnetism of the conduction electrons of an icosahedral quasicrystal Al63Cu25Fe12
Authors:: Prekul, AF; Shchegolikhina, NI; Shalaeva, EV Author Full Names: Prekul, A. F.; Shchegolikhina, N. I.; Shalaeva, E. V.
Source:: PHYSICS OF METALS AND METALLOGRAPHY 106 (2): 157-163 AUG 2008
Abstract:: Problem of the origin of the enhanced paramagnetism of icosahedral phases below room temperature is studied experimentally. Temperature dependences of the magnetic susceptibility (chi(T)), Hall constant (R-H(T)), and conductivity (chi(T)) of the i phase of a nominal composition of Al63Cu25Fe12 are studied at temperatures of 4.2-400 K in magnetic fields of to 5 T. Temperature-dependent components of these quantities, namely, sigma (t) , chi(t) , and R-t were separated. The temperature-dependent component of the magnetic susceptibility chi(t) is approximately proportional to T-2. The number of thermally-induced charge carries n (t) and the ratio chi(t)/n (t) are approximately proportional to T-3 and T-1, respectively. Thus, we found two distinctive criteria indicating that temperature-induced changes in the conduction-electron paramagnetism play a substantial role in the magnetic properties of icosahedral phases at low temperatures. Earlier, these changes were considered to be substantial only at temperatures above the Debye temperature.
Title:: Local density of states of one-dimensional Mott insulators and charge-density wave states with a boundary
Authors:: Schuricht, D; Essler, FHL; Jaefari, A; Fradkin, E Author Full Names: Schuricht, Dirk; Essler, Fabian H. L.; Jaefari, Akbar; Fradkin, Eduardo
Source:: PHYSICAL REVIEW LETTERS 101 (8): Art. No. 086403 AUG 22 2008
Abstract:: We determine the local density of states of one-dimensional incommensurate charge-density wave states in the presence of a strong impurity potential, which is modeled by a boundary. We find that the charge-density wave gets pinned at the impurity, which results in a singularity in the Fourier transform of the local density of states at momentum 2k(F). At energies above the spin gap we observe dispersing features associated with the spin and charge degrees of freedom, respectively. In the presence of an impurity magnetic field we observe the formation of a bound state localized at the impurity. All of our results carry over to the case of 1D Mott insulators by exchanging the roles of spin and charge degrees of freedom. We discuss the implications of our result for scanning tunneling microscopy experiments on spin-gap systems such as two-leg ladder cuprates.
Title:: On the nature and stability of phases present in a rapidly solidified aluminium alloy 7010 containing scandium
Authors:: Prasad, KS; Mukhopadhyay, AK; Majumdar, B; Akhtar, D Author Full Names: Prasad, K. S.; Mukhopadhyay, A. K.; Majumdar, B.; Akhtar, D.
Source:: MATERIALS AND MANUFACTURING PROCESSES 23 (7): 658-664 2008
Abstract:: The influence of Sc on the nature and stability of phases present in rapidly solidified (RS) Al alloy 7010 (hereafter termed base alloy) produced by melt spinning were examined and compared with the phases present in the same alloys when produced by the conventional ingot metallurgical (IM) route. Transmission electron microscopy (TEM) revealed that the second phases present in the IM alloys have an HCP structure but with varying lattice parameters. On the other hand, the second phase particles present in the base alloy when produced by rapid solidification (RS) route always have a quasi-crystalline, icosahedral structure. In the rapidly solidified 7010+Sc alloy, however, the icosahedral phase is located only at the grain boundary triple point junctions, and the grain interfaces are populated by the second phase particles having an HCP structure. An analysis of the chemistry of the second phase particles revealed that the icosahedral phase is stabilized by certain minimum concentrations of Zn+Mg/Zn+Mg+Cu. The reason for the absence of the icosahedral phase at the grain interfaces of the rapidly solidified 7010+Sc alloy is the partitioning of relatively lower concentrations of the major alloying elements into the second phases formed at those sites. Micro-hardness measurements revealed higher hardness values for the RS 7010+Sc alloy in both as-melt spun as well as artificially aged conditions. These results are correlated with the microstructures developed in these materials.
Title:: Approximant phases and an icosahedral quasicrystal in the Ca-Au-Ga system: The influence of size of gallium versus indium
Authors:: Lin, QS; Corbett, JD Author Full Names: Lin, Qisheng; Corbett, John D.
Source:: INORGANIC CHEMISTRY 47 (17): 7651-7659 SEP 1 2008
Abstract:: Two crystalline approximants (ACs) and their corresponding icosahedral quasicrystal (i-QC) are obtained in the Ca-Au-Ga system through conventional solid-state exploratory syntheses. Single crystal structural analyses reveal that the 1/1 AC, Ca3AuxGa19-x (x = similar to 9.3-12.1) [Im3, a = 14.6941(6)-14.7594(6) angstrom], has the empty cubes in the prototypic YCd6 (= Y3Cd18) now fully occupied by Ga, resulting in a 3:19 stoichiometry. In parallel, the distorted cubes in the 2/1 AC, Ca13Au57.1Ga23.4 [Pa3, a = 23.9377(8) angstrom] are fully or fractionally occupied by Ga. The valence electron count per atom (e/a) for the 2/1 AC (1.64) is smaller than that over the 1/1 AC composition range (1.76-2.02), and the e/a of the Ca15.2Au50.3Ga34.5 i-QC, 1.84, is somewhat distant from typical values for Tsai-type i-QCs (similar to 2.0). Comparisons of the gallium results with the corresponding In phases suggest that the structural differences result mainly from size rather than electronic factors. The 1/1 and 2/1 appear to be thermodynamically stable on slow cooling, as usual, whereas the i-QC isolated by quenching decomposes on heating at similar to 660 degrees C, mainly into 2/1 AC and Ca-3(Au,Ga)(11). Calculations of the electronic structure of 1/1 AC suggest that the Fermi sphere-Brillouin zone interactions remain important for the Ca-Au-Ga i-QC.
Update: 5-Sep-2008
Title:: Incommensurate spin-density modulation in a copper oxide chain compound with commensurate charge order
Authors:: Raichle, M; Reehuis, M; Andre, G; Capogna, L; Sofin, M; Jansen, M; Keimer, B Author Full Names: Raichle, M.; Reehuis, M.; Andre, G.; Capogna, L.; Sofin, M.; Jansen, M.; Keimer, B.
Source:: PHYSICAL REVIEW LETTERS 101 (4): Art. No. 047202 JUL 25 2008
Abstract:: Neutron diffraction has been used to determine the magnetic structure of Na8Cu5O10, a stoichiometric compound containing chains based on edge-sharing CuO4 plaquettes. The chains are doped with 2/5 hole per Cu site and exhibit long-range commensurate charge order with an onset well above room temperature. Below T-N = 23 K, the neutron data indicate long-range collinear magnetic order with a spin-density modulation whose propagation vector is commensurate along, and incommensurate perpendicular to, the chains. Competing interchain exchange interactions are discussed as a possible origin of the incommensurate magnetic order.
Title:: Magnetic ground state and transition of a quantum multiferroic LiCu2O2
Authors:: Huang, SW; Huang, DJ; Okamoto, J; Mou, CY; Wu, WB; Yeh, KW; Chen, CL; Wu, MK; Hsu, HC; Chou, FC; Chen, CT Author Full Names: Huang, S. W.; Huang, D. J.; Okamoto, J.; Mou, C. Y.; Wu, W. B.; Yeh, K. W.; Chen, C. L.; Wu, M. K.; Hsu, H. C.; Chou, F. C.; Chen, C. T.
Source:: PHYSICAL REVIEW LETTERS 101 (7): Art. No. 077205 AUG 15 2008
Abstract:: Based on resonant soft x-ray magnetic scattering, we report that LiCu2O2 exhibits a large interchain coupling which suppresses quantum fluctuations along spin chains, and a quasi-2D short-range magnetic order prevails at temperatures above the magnetic transition. These observations unravel the fact that the ground state of LiCu2O2 possesses long-range 2D-like incommensurate magnetic order rather than being a gapped spin liquid as expected from the nature of quantum spin-1/2 chains. In addition, the spin coupling along the c axis is found to be essential for inducing electric polarization.
Title:: The synthesis and characterization of new [(BiSe)(1.10)](m)[NbSe2](n), [(PbSe)(1.10)](m)[NbSe2](n), [(CeSe)(1.14)](m)[NbSe2](n) and [(PbSe)(1.12)](m)[TaSe2](n) misfit layered compounds
Authors:: Heideman, C; Nyugen, N; Hanni, J; Lin, Q; Duncombe, S; Johnson, DC; Zschack, P Author Full Names: Heideman, Colby; Nyugen, Ngoc; Hanni, Jonathan; Lin, Qiyin; Duncombe, Scott; Johnson, David C.; Zschack, Paul
Source:: JOURNAL OF SOLID STATE CHEMISTRY 181 (7): 1701-1706 JUL 2008
Abstract:: Fifty-three new misfit layered compounds within the [(BiSe)(1.10)](m)[NbSe2](n), [(PbSe)(1.10)](m)[NbSe2](n), [(CeSe)(1.14)](m)[NbSe2](n) and [(PbSe)(1.12)](m)[TaSe2](n) families of compounds were successfully synthesized. This is the first report of compounds with n and m larger than 3, as self-assembly from designed precursors allows Compounds with particular n and m values to be selectively prepared. The compounds form as crystallographically aligned films, with the c-axis perpendicular to the Substrate, The Compounds are well ordered along the c-axis and in the ab plane, with shorter coherence lengths between the constituent layers. All 18 compounds that were measured were found to be metallic. (C) 2008 Elsevier Inc. All rights reserved.
Title:: The role of nanoquasicrystals on the ductility enhancement of as-extruded Mg-Zn-Gd alloy at elevated temperature
Authors:: Liu, Y; Yuan, GY; Lu, C; Ding, WJ; Jiang, JZ Author Full Names: Liu, Yong; Yuan, Guangyin; Lu, Chen; Ding, Wenjiang; Jiang, Jiangzhong
Source:: JOURNAL OF MATERIALS SCIENCE 43 (16): 5527-5533 AUG 2008
Abstract:: The microstructure and mechanical properties of Mg3.5Zn0.6Gd alloy containing quasicrystals was investigated after extrusion, the role of nanoquasicrystals on the ductility of alloy was analyzed. The results indicate that nanoquasicrystal was formed and distributed along grain boundary and in the matrix for Mg3.5Zn0.6Gd alloy after extrusion. As-extruded Mg3.5Zn0.6Gd alloy containing I-phase showed one relatively random and homogeneous texture due to the local lattice rotation during deformation. The Mg3.5Zn0.6Gd alloy extruded at 673 K exhibits larger elongation about 94% at 473 K, which could been ascribed to the combination of random texture and higher content of I-phase precipitated during extrusion at higher temperature. The a + c type dislocations can be effectively active due to the existence of nanoquasicrystals. The strengthening mechanism of Mg3.5Zn0.6Gd alloy can be explained as the dislocations annihilation effect. This annihilation of dislocations can play a role in the increase of flow strain during deformation.
Title:: Low thermal conductivity in nanoscale layered materials synthesized by the method of modulated elemental reactants
Authors:: Chiritescu, C; Cahill, DG; Heideman, C; Lin, QY; Mortensen, C; Nguyen, NT; Johnson, D; Rostek, R; Bottner, H Author Full Names: Chiritescu, Catalin; Cahill, David G.; Heideman, Colby; Lin, Qiyin; Mortensen, Clay; Nguyen, Ngoc T.; Johnson, David; Rostek, Raimar; Boettner, Harald
Source:: JOURNAL OF APPLIED PHYSICS 104 (3): Art. No. 033533 AUG 1 2008
Abstract:: We report the room-temperature, cross-plane thermal conductivities, and longitudinal speeds of sound of multilayer films [(TiTe2)(3)(Bi2Te3)(x)(TiTe2)(3)(Sb2Te3)(y)](i) (x=1-5, y=1-5) and misfit-layer dichalcogenide films [(PbSe)(m)(TSe2)(n)](i) (T=W or Mo, m=1-5, and n=1-5) synthesized by the modulated elemental reactants method. The thermal conductivities of these nanoscale layered materials fall below the predicted minimum thermal conductivity of the component compounds: two times lower than the minimum thermal conductivity of Bi2Te3 for multilayer [(TiTe2)(3)(Bi2Te3)(x)(TiTe2)(3)(Sb2Te3)(y)](i) films and five to six times lower than the minimum thermal conductivity of PbSe for misfit-layer dichalcogenides [(PbSe)(m)(TSe2)(n)](i). We attribute the low thermal conductivities to the anisotropic bonding of the layered crystals and orientational disorder in the stacking of layered crystals along the direction perpendicular to the surface. (C) 2008 American Institute of Physics.
Update: 29-Aug-2008
Title:: Reducing the positional modulation of NbO6-octahedra in SrxBa1-xNb2O6 by increasing the barium content: A single crystal neutron diffraction study at ambient temperature for x=0.61 and x=0.34
Authors:: Schefer, J; Schaniel, D; Petricek, V; Woike, T; Cousson, A; Wohlecke, M Author Full Names: Schefer, Juerg; Schaniel, Dominik; Petricek, Vaclav; Woike, Theo; Cousson, Alain; Woehlecke, Manfred
Source:: ZEITSCHRIFT FUR KRISTALLOGRAPHIE 223 (6): 399-407 2008
Abstract:: We report on the influence of the barium content on the modulation amplitude in SrxBa1-xNb2O6 compounds by comparing Sr0.61Ba0.39Nb2O6 (SBN61) and Sr0.34Ba0.66Nb2O6 (SBN34). Our single crystal neutron diffraction results demonstrate that the amplitude of the positional modulation of the NbO6 octahedra is reduced with increasing barium content, indicating that the origin of the modulation is the partial occupation of the pentagonal channels by Sr and Ba atoms. By increasing the Sr content the bigger Ba atoms are replaced by the smaller Sr atoms, which leads to a larger deformation of the surrounding lattice and hence to a larger modulation amplitude. The more homogeneous the filling of these channels with one atomic type (Ba) the lower the modulation amplitude. Our results also show that the structure can be described with a two-dimensional incommensurate harmonic modulation. No second order modulation has been observed, both by single crystal diffraction measurements and q-scans. The positional modulation of the Nb atoms is much smaller than that of the oxygen atoms, such that the modulation can be seen as a rotational modulation of almost rigid NbO6-octahedra.
Title:: Icosahedral quasicrystal phase in Al15Mg50Zn35 ternary alloy by rapid quenching
Authors:: Zhu, M; Yang, GC; Liu, F; Wan, DQ; Cheng, SL; Zhou, YH Author Full Names: Zhu Man; Yang Gencang; Liu Feng; Wan Diqing; Cheng Suling; Zhou Yaohe
Source:: RARE METAL MATERIALS AND ENGINEERING 37 (7): 1179-1182 JUL 2008
Abstract:: Almost an icosahedral quasicrstyal phase is obtained in the Mg-riched region off the Bergman line by means of rapid quenching in a cool copper mould. The microstructures, chemical composition and atom cluster of the icosahedral phase are charactered by X-ray diffraction (XRD), scanning electron microscopy (SEM), field-emission scanning electron microscopy and transmission electron microscopy (TEM). It is found that the icosahedral quasicrystal phase is obtained with the composition of 39.76 at% Mg, 18.34 at% Al, and 41.90 at% Zn, which nucleates and grows directly from the melt with icosahedral symmetries. It exhibits a characteristic faceted dendritic growth with the fastest growth direction along a three-fold axes. At the same time, the regular hexagonal-polygon icosahedral quasicrystal grains with a size of 0.2 mu m can also be observed. The atomic cluster of icosahedral phase is pentagonal dodecahedron with icosahedral symmetries and micro-lobes on the each faceted pentagonal face.
Title:: Analytic study on specific heat of icosahedral Al-Mn-Pd quasicrystals
Authors:: Wang, J; Fan, TY Author Full Names: Wang, Jian; Fan, Tianyou
Source:: MODERN PHYSICS LETTERS B 22 (17): 1653-1659 JUL 10 2008
Abstract:: A simple and explicit formula for specific heat of icoschedral Al-Mn-Pd quasicrystals is obtained, theoretical predictions of which are in good agreement with that given by experiment.
Title:: Effect of icosahedral phase particles on the texture evolution in Mg-Zn-Y alloys
Authors:: Lee, JY; Lim, HK; Kim, DH; Kim, WT; Kim, DH Author Full Names: Lee, Ju Youn; Lim, Hyun Kyu; Kim, Do Hyung; Kim, Won Tae; Kim, Do Hyang
Source:: MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 491 (1-2): 349-355 SEP 15 2008
Abstract:: In order to understand the role of the icosahedral phase (I-phase) particles on the improved mechanical properties of Mg-3Zn-0.6Y and Mg-6Zn-1.2Y alloys, the texture evolution has been investigated by the X-ray diffraction and electron back-scattered diffraction (EBSD) analyses. Mg-6Zn-1.2Y alloy exhibits higher strength than Mg-3Zn-0.6Y alloy due to the presence of larger amount of I-phase particles. However, Mg-6Zn-1.2Y alloy exhibits a larger elongation than Mg-3Zn-0.6Y alloy. With increasing the volume fraction of I-phase particles and rolling speeds, the relatively random texture is developed, which is attributed to local lattice rotations around I-phase particles during shear deformation. The relatively random texture plays an important role in enhancing the ductility when larger amount of I-phase particles are present in Mg-6Zn-1.2Y alloy. (C) 2008 Elsevier B.V. All rights reserved.
Title:: Distortion and charge density wave in the Ga square net coupled to the site occupancy wave in YCo0.88Ga3Ge
Authors:: Gray, DL; Francisco, MC; Kanatzidis, MG Author Full Names: Gray, Danielle L.; Francisco, Melanie C.; Kanatzidis, Mercouri G.
Source:: INORGANIC CHEMISTRY 47 (16): 7243-7248 AUG 18 2008
Abstract:: YCo0.88Ga3Ge has an incommensurately modulated structure that was solved with (3 + 1)D superspace techniques. YCo0.88Ga3Ge crystallizes in the orthorhombic superspace group Immm(alpha 00)00s with unit cell constants of a = 4.1639(4), b = 4.1639(4), c = 23.541(2) angstrom and a modulation vector of q = 0.3200(4)a* at 293 K. The incommensurate modulation, which creates a very large supercell (similar to 25 fold), arises from a charge density wave (CDW) in the square net of Ga atoms that is coupled with a site occupancy wave (SOW) of Co atoms. The distorted Ga net features polygallide ribbons, chains, as well as single atoms. Temperature dependent crystallographic studies of the structure from 100-500 K indicate that the CDW is "locked in". Electrical conductivity and thermopower measurements in the temperature range of 300-500 K show that YCo0.88Ga3Ge is a poor metal.
Title:: Formation and properties of quasicrystals
Authors:: Louzguine-Luzgin, DV; Inoue, A Author Full Names: Louzguine-Luzgin, D. V.; Inoue, A.
Source:: ANNUAL REVIEW OF MATERIALS RESEARCH 38: 403-423 2008
Abstract:: This article summarizes the general structural features and important properties of quasicrystals, a relatively new class of materials belonging to solid-state substances. Quasicrystals, which have a long-range quasiperiodic order but no three-dimensional translational periodicity, are structurally different from both conventional crystals and glassy solids. Although applications are still highly limited, quasicrystals are attracting significant attention as a structural constituent of mixed-phase materials exhibiting high strength together with certain ductility and can be applied as structural materials.
Update: 22-Aug-2008
Title:: Magnetic order of LiCu2O2 studied by resonant soft x-ray magnetic scattering
Authors:: Huang, SW; Huang, DJ; Okamoto, J; Wu, WB; Chen, CT; Yeh, KW; Chen, CL; Wu, MK; Hsu, HC; Chou, FC Author Full Names: Huang, S. W.; Huang, D. J.; Okamoto, J.; Wu, W. B.; Chen, C. T.; Yeh, K. W.; Chen, C. L.; Wu, M. K.; Hsu, H. C.; Chou, F. C.
Source:: SOLID STATE COMMUNICATIONS 147 (5-6): 234-237 AUG 2008
Abstract:: We present results of resonant soft x-ray magnetic scattering measurements on single crystals of LiCu2O2 to address the magnetic order. LiCu2O2 exhibits a long-range magnetic order incommensurate with the lattice, and the modulation vector is (0.5, zeta, 0) in reciprocal lattice units with zeta similar to 0.174, depending upon the temperature. The spin-spin correlation length along the spin chain deduced from the width of momentum scan is larger than 2100 angstrom. The inter-chain correlation length that lies within the ab plane was discovered to be substantial, similar to 690 angstrom. (c) 2008 Elsevier Ltd. All rights reserved.
Title:: Phase transformations induced by nitridation of quasicrystalline AlCuFeB powders
Authors:: Kenzari, S; Bonina, D; Dubois, JM; Fournee, V Author Full Names: Kenzari, S.; Bonina, D.; Dubois, J. M.; Fournee, V.
Source:: SCRIPTA MATERIALIA 59 (6): 583-586 SEP 2008
Abstract:: Nitridation is an important reaction which has never been investigated for Al-based quasicrystals. Here we show that AlCuFeB quasicrystalline particles undergo phase transformations upon annealing at high temperature in pure nitrogen. A thick nitride layer grows on the surface of the particles, and Al depletion in the bulk results in transformation of the quasicrystalline phase first into the cubic P-phase and then into the monoclinic X-phase. The kinetics of this transformation is much faster than that of oxidation. (C) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:: Large-scale synthesis of Al-Cu-Fe submicron quasicrystals
Authors:: Li, LJ; Bi, QL; Yang, J; Fu, LC; Wang, LP; Wang, SC; Liu, WM Author Full Names: Li, Laijun; Bi, Qinling; Yang, Jun; Fu, Licai; Wang, Liping; Wang, Shuncai; Liu, Weimin
Source:: SCRIPTA MATERIALIA 59 (6): 587-590 SEP 2008
Abstract:: Al-Cu-Fe alloy with a nominal composition of Al62Cu25.5Fe12.5 (at.%) has been fabricated by a combination of pressure-assisted self-propagating high-temperature synthesis and rapid solidification. The as-synthesized Al-Cu-Fe alloy mainly consists of icosahedral quasicrystalline (IQC) Psi-Al65Cu20Fe15 and cubic beta-Al (Cu, Fe) solid solution phases, and exhibits finely equiaxed grains with a size ranging from 50 to 200 nm. The mechanism for the formation of the ultrafine-grained IQC phase has been explained. (C) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:: Pressure-induced phase transitions in PrB6: Electrical resistivity measurements
Authors:: Iwakubo, H; Ikeda, S; Kishino, Y; Tanida, H; Sera, M; Iga, F Author Full Names: Iwakubo, H.; Ikeda, S.; Kishino, Y.; Tanida, H.; Sera, M.; Iga, F.
Source:: PHYSICAL REVIEW B 78 (1): Art. No. 012409 JUL 2008
Abstract:: We have studied the electrical resistivity of PrB6 under pressure up to P=0.8 GPa, with magnetic fields applied along the [001] and [111] directions. The commensurate (C) magnetic ordered phase is significantly stabilized by pressure, and another extra phase (denoted phase A) is observed under a low pressure of similar to 0.3 GPa. This phase appears above the transition temperature T-IC1=7 K at which the incommensurate magnetic order sets in at the ambient pressure. The magnetic phase diagram for H parallel to[111] changes drastically under pressure. Short-range interactions, which are strongly dependent on the Pr-Pr distances, are likely to play a dominant role in the relative stability of the different phases.
Title:: Signature of hidden order in heavy fermion superconductor URu2Si2: Resonance at the wave vector Q(0)=(1,0,0)
Authors:: Villaume, A; Bourdarot, F; Hassinger, E; Raymond, S; Taufour, V; Aoki, D; Flouquet, J Author Full Names: Villaume, A.; Bourdarot, F.; Hassinger, E.; Raymond, S.; Taufour, V.; Aoki, D.; Flouquet, J.
Source:: PHYSICAL REVIEW B 78 (1): Art. No. 012504 JUL 2008
Abstract:: Simultaneous neutron scattering and thermal expansion measurements on the heavy-fermion superconductor URu2Si2 under hydrostatic pressure of 0.67 GPa have been performed in order to detect the successive paramagnetic, hidden order, and large moment antiferromagnetic phases on cooling. The temperature dependence of the sharp low energy excitation at the wave vector Q(0)=(1,0,0) shows clearly that this resonance is a signature of the hidden order state. In the antiferromagnetic phase, this resonance disappears. The higher energy excitation at the incommensurate wave vector Q(1)=(1.4,0,0) persists in the antiferromagnetic phase but increases in energy.
Title:: Ga-substitution-induced single ferroelectric phase in multiferroic CuFeO2
Authors:: Terada, N; Nakajima, T; Mitsuda, S; Kitazawa, H; Kaneko, K; Metoki, N Author Full Names: Terada, N.; Nakajima, T.; Mitsuda, S.; Kitazawa, H.; Kaneko, K.; Metoki, N.
Source:: PHYSICAL REVIEW B 78 (1): Art. No. 014101 JUL 2008
Abstract:: We have succeeded in realizing a single ferroelectric phase in CuFe0.963Ga0.037O2 by substituting nonmagnetic Ga3+ for Fe3+ sites in CuFeO2. Ferroelectric polarization P in CuFe0.963Ga0.037O2 is observed below 7.5 K, and has the relatively large value of similar to 250 mu C/m(2), which is comparable to P=300 similar to 400 mu C/m(2) in the magnetic-field-induced ferroelectric phase of CuFeO2. In neutron-diffraction measurements, a single magnetic diffraction peak with an incommensurate wave number was observed below 7.5 K in CuFe0.963Ga0.037O2, indicating that the ferroelectric-incommensurate (FEIC) phase is realized as a single phase. Therefore, CuFe0.963Ga0.037O2 with a single FEIC phase is strongly expected to provide the best opportunity to investigate unresolved problems regarding the ferroelectric mechanism in CuFeO2. In this paper, we report measurements of magnetic susceptibility, specific heat, pyroelectric, dielectric constant, and neutron diffraction of a single crystal of CuFe0.963Ga0.037O2.
Title:: Effect of inversion symmetry on the incommensurate order in multiferroic RMn2O5 (R=rare earth)
Authors:: Harris, AB; Kenzelmann, M; Aharony, A; Entin-Wohlman, O Author Full Names: Harris, A. B.; Kenzelmann, M.; Aharony, Amnon; Entin-Wohlman, O.
Source:: PHYSICAL REVIEW B 78 (1): Art. No. 014407 JUL 2008
Abstract:: Starting from the irreducible representations of the group of the wave vector, we construct the spin-wave functions consistent with inversion symmetry, neglected in the usual representation analysis. We obtain the relation between the basis functions of different members of the star of the wave vector. We introduce order parameters and determine their transformation properties under the operations of the space group of the paramagnetic crystal. The results are applied to construct terms in the magnetoelectric interaction, which are quadratic and quartic in the magnetic order parameters. The higher-order magnetoelectric interactions can in principle induce components of the spontaneous polarization, which are not allowed by the lowest-order magnetoelectric interaction. We also obtain the relation between the spin-wave functions of the incommensurate phase and those of the commensurate phase, which lead to analogous relations between the order parameters of these two phases.
Title:: Magnetic order and multipole interactions in CexPr1-xB6 solid solutions
Authors:: Mignot, JM; Andre, G; Robert, J; Sera, M; Iga, F Author Full Names: Mignot, J. -M.; Andre, G.; Robert, J.; Sera, M.; Iga, F.
Source:: PHYSICAL REVIEW B 78 (1): Art. No. 014415 JUL 2008
Abstract:: Magnetic ordering phenomena in CexPr1-xB6 solid solutions have been studied using both powder and single-crystal neutron diffraction. A variety of magnetic structures are observed depending on temperature and Ce concentration. Over a broad composition range (x <= 0.7), Pr-Pr interactions play a dominant role, giving rise to incommensurate structures with wave vectors of the form k(IC1)=(1/4-delta,1/4,1/2) or k(IC2)=(1/4-delta,1/4-delta,1/2). The crossover to a CeB6-like regime takes place near x=0.7-0.8. For the latter composition, the antiferroquadrupolar phase transition observed in transport measurements precedes the onset, at lower temperature, of a commensurate magnetic order similar to that existing in CeB6. However, unlike in the pure compound, an incommensurate magnetic order is formed at even higher temperature and persists in the antiferroquadrupolar phase down to the lock-in transition. These results are shown to reflect the interplay between various type of dipole exchange and higher multipole interactions in this series of compounds.
Title:: Competing magnetic structures and magnetic transitions in Er2Ni2Pb: Powder neutron diffraction measurements
Authors:: Prokes, K; Munoz-Sandoval, E; Chinchure, AD; Mydosh, JA Author Full Names: Prokes, K.; Munoz-Sandoval, E.; Chinchure, Aravind D.; Mydosh, J. A.
Source:: PHYSICAL REVIEW B 78 (1): Art. No. 014425 JUL 2008
Abstract:: We have studied the magnetic structures of Er2Ni2Pb using a powder neutron diffraction technique in zero field. Previous bulk measurements suggested three distinct magnetic phase transitions. Our neutron diffraction experiments, which were made in the range 1.5-5 K, showed that magnetic Bragg reflections in Er2Ni2Pb can be indexed by several propagation vectors that coexist over an extensive temperature range. Rather than a homogeneous magnetic structure that is simultaneously described by all the existing propagation vectors, several spatially separated structures appear to exist in Er2Ni2Pb. The appearance/disappearance of representative reflections at T-N=3.5 K, T-m1=3.0 K, T-m2=2.3 K, and T-m3=1.8 K denote magnetic phase transitions. The only magnetic state that is determined by a single propagation vector exists just below T-N. In all other magnetic states, more than one propagation vectors are stable. Except for the lowest temperature state, which is commensurate, all other propagation vectors are incommensurate with respect to the crystal structure. Although the coexistence of several spatially separated magnetic structures can be explained by the competition of magnetic interactions along particular crystallographic directions, some of the details, e.g., the exact ground-state magnetic structure, are still unclear and need further study.
Title:: Magnetic ordering of weakly coupled frustrated quantum spin chains
Authors:: Zvyagin, AA; Drechsler, SL Author Full Names: Zvyagin, A. A.; Drechsler, S. -L.
Source:: PHYSICAL REVIEW B 78 (1): Art. No. 014429 JUL 2008
Abstract:: The ordering temperature of a quasi-one-dimensional system, consisting of weakly interacting quantum spin-1/2 chains with antiferromagnetic spin-frustrating couplings (or zigzag ladder), is calculated. The results show that a quantum critical point between two phases of the one-dimensional subsystem plays a crucial role. If the one-dimensional subsystem is in the antiferromagneticlike phase in the ground state, similar to the phase of a spin chain without frustration, weak couplings yield magnetic ordering of the Neel type. For intrachain spin-frustrating interactions larger than the critical one (at which the quantum phase transition takes place), the quasi-one-dimensional spin system manifests a spiral magnetic incommensurate ordering. The obtained results of our quantum theory are compared with the quasiclassical approximations. The calculated features of magnetic ordering are expected to be generic for weakly-coupled quantum spin chains with gapless excitations and spin-frustrating nearest- and next-nearest-neighbor interactions.
Title:: Identification of microscopic spin-polarization coupling in the ferroelectric phase of magnetoelectric multiferroic CuFe1-xAlxO2
Authors:: Nakajima, T; Mitsuda, S; Inami, T; Terada, N; Ohsumi, H; Prokes, K; Podlesnyak, A Author Full Names: Nakajima, Taro; Mitsuda, Setsuo; Inami, Toshiya; Terada, Noriki; Ohsumi, Hiroyuki; Prokes, Karel; Podlesnyak, Andrei
Source:: PHYSICAL REVIEW B 78 (2): Art. No. 024106 JUL 2008
Abstract:: We have performed synchrotron radiation x-ray and neutron diffraction measurements on magnetoelectric multiferroic CuFe1-xAlxO2 (x=0.0155), which has a proper helical magnetic structure with incommensurate propagation wave vector in the ferroelectric phase. The present measurements revealed that the ferroelectric phase is accompanied by lattice modulation with a wave number 2q, where q is the magnetic modulation wave number. We have calculated the Fourier spectrum of the spatial modulations in the local electric polarization using a microscopic model proposed by T. Arima [J. Phys. Soc. Jpn. 76, 073702 (2007)]. Comparing the experimental results with the calculation results, we found that the origin of the 2q-lattice modulation is not the conventional magnetostriction but the variation in the metal-ligand hybridization between the magnetic Fe3+ ions and ligand O2- ions. Combining the present results with the results of a previous polarized neutron diffraction study [Nakajima , Phys. Rev. B 77, 052401 (2008)], we conclude that the microscopic origin of the ferroelectricity in CuFe1-xAlxO2 is the variation in the metal-ligand hybridization with spin-orbit coupling.
Title:: Relaxor ferroelectric behavior in Ca-doped TbMnO3
Authors:: Mufti, N; Nugroho, AA; Blake, GR; Palstra, TTM Author Full Names: Mufti, N.; Nugroho, A. A.; Blake, G. R.; Palstra, T. T. M.
Source:: PHYSICAL REVIEW B 78 (2): Art. No. 024109 JUL 2008
Abstract:: We have studied the effect of Ca-doping in single-crystal Tb1-xCaxMnO3(x <= 0.1) on the crystal and magnetic structure, magnetocapacitance, and electric polarization. For low doping (x=0.05), the presence of Mn4+ ions gives rise to a state with behavior resembling that of a relaxor ferroelectric. The coherence length of the Mn magnetic spin spiral is reduced, while the Mn-modulation wave vector is unchanged. For doping larger than 5%, the ferroelectric state is suppressed, which we ascribe to breakdown of the spiral magnetic structure.
Title:: Magnetic-field-induced transitions in multiferroic TbMnO3 probed by resonant and nonresonant x-ray diffraction
Authors:: Strempfer, J; Bohnenbuck, B; Zegkinoglou, I; Aliouane, N; Landsgesell, S; Zimmermann, MV; Argyriou, DN Author Full Names: Strempfer, J.; Bohnenbuck, B.; Zegkinoglou, I.; Aliouane, N.; Landsgesell, S.; Zimmermann, M. V.; Argyriou, D. N.
Source:: PHYSICAL REVIEW B 78 (2): Art. No. 024429 JUL 2008
Abstract:: Multiferroic TbMnO3 is investigated using x-ray diffraction in high magnetic fields. Measurements on first- and second-harmonic structural reflections due to modulations induced by the Mn and Tb magnetic order are presented as function of temperature and field oriented along the a and b directions of the crystal. The relation to changes in ordering of the rare earth moments in applied field is discussed. Observations below T-N(Tb) without and with applied magnetic field point to a strong interaction of the rare earth order, the Mn moments, and the lattice. Also, the incommensurate to commensurate transition of the wave vector at the critical fields is discussed with respect to the Tb and Mn magnetic order, and a phase diagram on basis of these observations for magnetic fields H parallel to a and H parallel to b is presented. The observations point to a complicated and delicate magnetoelastic interaction as function of temperature and field.
Title:: Very weak electron-phonon coupling and strong strain coupling in manganites
Authors:: Cox, S; Loudon, JC; Williams, AJ; Attfield, JP; Singleton, J; Midgley, PA; Mathur, ND Author Full Names: Cox, S.; Loudon, J. C.; Williams, A. J.; Attfield, J. P.; Singleton, J.; Midgley, P. A.; Mathur, N. D.
Source:: PHYSICAL REVIEW B 78 (3): Art. No. 035129 JUL 2008
Abstract:: We describe transmission electron microscopy experiments that demonstrate the validity of the charge density wave (CDW) Landau theory in describing the so-called stripe phase of the manganites and that permit quantitative estimates of some of the theoretical parameters that describe this state. In polycrystalline Pr0.48Ca0.52MnO3 a lock-in to q/a(*)=0.5 in a sample with x>0.5 has been observed. Such a lock-in has been predicted as a key part of the Landau CDW theory of the stripe phase. Thus it is possible to constrain the size of the electron-phonon coupling in the CDW Landau theory to between 0.08% and 0.50% of the electron-electron coupling term. In the thin film samples, films of the same thickness grown on two different substrates exhibited different wave vectors. The different strains present in the films on the two substrates can be related to the wave vector observed via Landau theory. It is demonstrated that the elastic term, which favors an incommensurate modulation, has a similar size to the coupling between the strain and the wave vector, meaning that the coupling of strain to the superstructure is unexpectedly strong.
Title:: Incommensurability and atomic structure of c(2x2)N/Cu(100): A scanning tunneling microscopy study
Authors:: Choi, T; Ruggiero, CD; Gupta, JA Author Full Names: Choi, T.; Ruggiero, C. D.; Gupta, J. A.
Source:: PHYSICAL REVIEW B 78 (3): Art. No. 035430 JUL 2008
Abstract:: We use a scanning tunneling microscope operating in a low-temperature ultrahigh vacuum environment to study the atomic structure of single layer films of Cu2N grown on Cu(100). The c(2x2) lattice of Cu2N is incommensurate, with a lattice constant of 0.372 +/- 0.001 nm that is 3% larger than the bare Cu(100) surface. This finding suggests that the strain due to lattice mismatch contributes to self-assembly in this system. We find that the image contrast on Cu2N islands depends on bias voltage, which reconciles several interpretations in the literature. We assign features in these STM images to the Cu, N, and hollow sites in the Cu2N lattice with the aid of coadsorbed CO molecules. This atomic registry allows us to characterize four different defects on Cu2N, which influence the sticking coefficient and electronic coupling of adsorbates.
Title:: Structure of Al-Co-Ni pentagonal quasicrystal studied by HAADF-STEM and ab initio calculations
Authors:: Song, S; Wang, J; Wang, R; Xiong, D; Zhao, D; Gui, J; Liu, H; Yan, Y Author Full Names: Song, S.; Wang, J.; Wang, R.; Xiong, D.; Zhao, D.; Gui, J.; Liu, H.; Yan, Y.
Source:: PHILOSOPHICAL MAGAZINE LETTERS 88 (7): 519-531 2008
Abstract:: Using a combination of atomic-resolution high-angle annular dark-field (HAADF) Z-contrast imaging and ab initio calculations, atomic models of clusters 2 nm in diameter and 0.8 nm in height are proposed for the Al-Co-Ni pentagonal quasicrystal. This quasicrystal has 5-fold symmetry (the so-called 5f state) without superstructures, and is one of numerous modifications of the Al-Co-Ni decagonal quasicrystal. HAADF results reveal that the two-dimensional quasi-periodic lattice contains mainly Penrose pentagonal tiling. The centres within the decorated pentagonal tiles, i.e. the so-called pentagonal super-clusters, show structural characteristics having both a satellite-orbit shape and a pentagon-symmetry shape. The proposed atomic models, based directly on the HAADF images, are subjected to ab initio total energy calculations. After relaxation, the calculations demonstrate that the models with 5-fold symmetry are energetically more favourable than those with 10-fold symmetry.
Title:: Commensurate-incommensurate phase transition in muthmannite, AuAgTe2: first evidence of a modulated structure at low temperature
Authors:: Bindi, L Author Full Names: Bindi, Luca
Source:: PHILOSOPHICAL MAGAZINE LETTERS 88 (7): 533-541 2008
Abstract:: To study the temperature-dependent structural changes and to analyze the crystal chemical behavior of silver as a function of temperature, a crystal of muthmannite, AuAgTe2, has been investigated by X-ray single-crystal diffraction methods at 300 K and 110 K. At room temperature, muthmannite was confirmed as belonging to the space group P2/m, while at low temperature (110 K) it undergoes a reversible commensurate-incommensurate phase transition with a modulation wave vector q = 0.215(1)a* + 0.379(2)c*. Muthmannite reconverts to the commensurate type upon returning to room temperature, thus indicating that the phase transition is completely reversible in character. The average structure of the low-temperature muthmannite remains monoclinic, space group P2/m, and shows only normal thermal compression over the entire temperature range investigated. Crystal-chemical characteristics are compared with published data on the other members of the system Au-Ag-Te. Speculations on the possible origin of the modulated structure at low temperature are also given.
Title:: Dielectric, ferroelectric properties, and grain growth of CaxBa1-xNb2O6 ceramics with tungsten-bronzes structure
Authors:: Ke, SM; Fan, HQ; Huang, HT; Chan, HLW; Yu, SH Author Full Names: Ke, Shanming; Fan, Huiqing; Huang, Haitao; Chan, H. L. W.; Yu, Shuhui
Source:: JOURNAL OF APPLIED PHYSICS 104 (2): Art. No. 024101 JUL 15 2008
Abstract:: Dielectric properties, microstructures, and phase transition behaviors of alpha and beta phases of CaxBa1-xNb2O6 (x= 0.22, 0.30, and 0.38) ceramics were investigated. All the three compositions had partially filled tungsten-bronze structure (TTB) and relatively high Curie temperatures (up to 345 degrees C) compared with Sr1-xBaxNb2O6. The alpha phase exhibits unambiguously a diffused phase transition, while the beta phase is associated with an incommensurate phase and needs to be further studied. The dielectric and ferroelectric properties of CaxBa1-xNb2O6 ceramics were strongly processing-dependent. A mechanism was proposed to explain the grain growth behavior of TTB ceramic niobates. (c) 2008 American Institute of Physics.
Title:: Laves phases, gamma-brass, and 2x2x2 superstructures: A new class of quasicrystal approximants and the suggestion of a new quasicrystal
Authors:: Berger, RF; Lee, S; Johnson, J; Nebgen, B; So, ACY Author Full Names: Berger, Robert F.; Lee, Stephen; Johnson, Jeffreys; Nebgen, Ben; So, Adrian Chi-Yau
Source:: CHEMISTRY-A EUROPEAN JOURNAL 14 (22): 6627-6639 2008
Abstract:: Of the most common cubic intermetallic structure types, several (MgCU2, CU5Zn8, Ti2Ni, and alpha-Mn) have superstructures with unusual symmetry properties. These superstructures (Be5Au, Li21Si5, Sm11Cd45, and Mg44Ir7) have the unusual property of pairs of perpendicular pseudo fivefold axes, most apparent in their X-ray diffraction patterns. The current work shows that an 8D to 3D projection method cleanly describes most (and in one case, all) of the atomic positions in the four superstructures mentioned above. This type of projection, which maps the E-8 lattice (a mathematically simple 8D crystal) into 3D space, combines the desired higher dimensional point group's perpendicular fivefold rotations with 3D translational symmetry-exactly what we see in the experimental crystal structures. The projection method successfully accounts for all heavy atom positions in the four superstructures, and at least 60-70% of the light atom positions. The results suggest that all of these structures, previously known to be connected only by qualitative similarities in their atomic "clusters", are approximants of a single, as-yet unknown, class of quasicrystal.
Update: 15-Aug-2008
Title:: Mossbauer study of antiferromagnetic CuFeO2
Authors:: Choi, DH; Shim, IB; Kim, CS Author Full Names: Choi, Dong Hyeok; Shim, In-Bo; Kim, Chul Sung
Source:: JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 320 (20): E575-E577 OCT 2008
Abstract:: We have studied the magnetic spin structure of antiferromagnetic CuFeO2 by X-ray diffraction (XRD) and Mossbauer spectroscopy. Its crystal structure determined by XRD analysis was a rhombohedral structure ( space group R-3m) and lattice constants a(0) and c(0) were 3.0333 and 17.1595 angstrom, respectively. In spite of 4-Fe sublattices in a delafossite CuFeO2, its Mossbauer spectra were analyzed with 1-set (6-Lorentzian lines) below 10K due to the collinear-commensurate spin structure, but the spectra were fitted with 4-sextet above 10K due to the incommensurate spin structure. This phenomenon was attributed to the spin-lattice relaxation effect. Magnetic Neel temperature was also determined at 18 K, which corresponded to the high-spin Fe3+ valance state. On the other hand, CuFe0.98Al0.02O2 powder with a noncollinear spin structure was fitted with 4-sextet at 4.2 K. (c) 2008 Elsevier B.V. All rights reserved.
Title:: Mechanical alloying and self-propagating high-temperature synthesis of stable icosahedral quasicrystals
Authors:: Bokhonov, BB Author Full Names: Bokhonov, B. B.
Source:: JOURNAL OF ALLOYS AND COMPOUNDS 461 (1-2): 150-153 AUG 11 2008
Abstract:: The phase evolution of the mechanically alloyed ternary 63%Al + 25%Cu + 12%Fe and 65%Al + 20%Cu + 15%Fe powder mixtures with milling time has been studied by X-ray diffraction method. It was found that an icosahedral quasicrystalline phase was formed directly during high-energy ball milling of the Al-Cu-Fe mixtures. The X-ray and scanning electron microscopic investigations demonstrated the possibility to use self-propagating high-temperature synthesis (SHS) in combination with preliminary mechanical activation for the synthesis of stable icosahedral quasicrystals. The typical morphology of the Al63Cu25Fe12 icosahedral quasicrystals formed in the SHS process is a pentagonal dodecahedron with a size of 3-5 mm. The phase composition of the SHS products depends on the time of preliminary mechanical activation. The content of cubic intermetallic phase in SHS products increases with the time of preliminary mechanical activation of the 63%Al + 25%Cu + 12%Fe powder mixtures. (c) 2007 Elsevier B. V. All rights reserved.
Update: 8-Aug-2008
Title:: Quasicrystals at interfaces
Authors:: Fournee, V; Ledieu, J; Thiel, P Author Full Names: Fournee, Vincent; Ledieu, Julian; Thiel, Patricia
Source:: JOURNAL OF PHYSICS-CONDENSED MATTER 20 (31): Art. No. 310301 AUG 6 2008
Title:: Microstructural evolution and the role of interfaces in Mg-Zn-Y alloys with high strength and formability
Authors:: Chang, HJ; Lee, JY; Kim, DH Author Full Names: Chang, H. J.; Lee, J. Y.; Kim, D. H.
Source:: JOURNAL OF PHYSICS-CONDENSED MATTER 20 (31): Art. No. 314001 AUG 6 2008
Abstract:: Composites consisting of a quasicrystalline, icosahedral phase (I-phase) and ductile alpha-Mg can be fabricated by controlling the alloy composition in the Mg-Zn-Y alloy system. The I-phase in Mg-Zn-Y alloys shows a variation in structural order from a well-ordered icosahedral phase to a 1/1 rhombohedral approximant phase. The structural change in the icosahedral phase can be explained by microdomain formation due to compositional change during solidification. The characteristic of strong bonding between icosahedral particles and the alpha-Mg matrix indicates that the structural change from I-phase to crystalline phase is not discontinuous, but gradual. The interface layer of alpha-Mg with several nm thickness preserves an orientational relationship with the I-phase, although the remaining alpha-Mg shows a different orientation due to plastic deformation during deformation (rolling process). Such a strong interface can provide an excellent combination of high str ength and formability in Mg-based alloys, enabling application as lightweight structural parts.
Title:: Quasicrystal-crystal interfaces in bulk materials
Authors:: Singh, A; Tsai, AP Author Full Names: Singh, Alok; Tsai, A. P.
Source:: JOURNAL OF PHYSICS-CONDENSED MATTER 20 (31): Art. No. 314002 AUG 6 2008
Abstract:: The formation of interfaces of simple crystals with icosahedral quasicrystals has been described. Crystals take on various orientation relationships (ORs) with the quasicrystals in order to make low energy interfaces by matching close packed planes across the interfaces. In the icosahedral phase the closest packed planes are fivefold and twofold. Among various possibilities, an OR will get selected by the surface on which nucleation of a phase occurs. Since one of the phases is quasicrystalline and the other is crystalline, even within the same OR there are variations of several degrees. The high symmetry of the icosahedral phase ensures many possible orientations for planar matching with another phase. The quasiperiodicity ensures an epitaxy with periodic planes of many possible spacings at the interface. Epitaxy can be observed as coincidence of spots in the reciprocal space and verified by imaging in high resolution electron microscopy. In this article examples of interfaces of Al-Cu-Fe icosahedral phases with lead, bismuth and tin, and Mg-Zn-Y icosahedral phases with magnesium are shown. The high symmetry of the icosahedral phase ensures that epitaxy is produced on nearly all interfaces in bulk. Slight misorientations across interfaces are accommodated by dislocations.
Title:: Models for quasicrystal-crystal epitaxy
Authors:: Widjaja, EJ; Marks, LD Author Full Names: Widjaja, E. J.; Marks, L. D.
Source:: JOURNAL OF PHYSICS-CONDENSED MATTER 20 (31): Art. No. 314003 AUG 6 2008
Abstract:: Not long after the discovery of quasicrystals, a specific orientation relationship between crystalline and quasicrystalline structures was observed. The specific orientational relationships were discovered in many systems, for instance surface alterations of bulk quasicrystals, the growth of atomic overlayers on quasicrystalline substrates and quasicrystalline thin films on crystalline substrates. In this paper, we review various models described in the literature in explaining such quasicrystal-crystal epitaxy.
Title:: Epitaxial interfaces between half-crystals of quasicrystalline and periodic material
Authors:: Theis, W; Franke, KJ Author Full Names: Theis, W.; Franke, K. J.
Source:: JOURNAL OF PHYSICS-CONDENSED MATTER 20 (31): Art. No. 314004 AUG 6 2008
Abstract:: We recently demonstrated that epitaxial interfaces can be formed between periodic and quasiperiodic materials (Franke et al 2007 Phys. Rev. Lett. 99 036103). Such interfaces exhibit the same defining characteristic as epitaxial interfaces between commensurate periodic materials, namely the locking into registry of the two half-crystals' atomic structures. This real space characteristic is equivalent to the requirement of a coincidence of reciprocal lattice points. Here, we explore the characteristics of the potential interfaces within the class of quasicrystals exhibiting a periodic direction, including decagonal quasicrystals. We derive our results geometrically from a higher dimensional description, thus providing visual insight into the underlying concepts. Since the reciprocal lattice of quasicrystalline structures is generated by more basis vectors than their periodic counterparts', suitable quasicrystalline interlayers can be designed to epitaxially link incommensurate half-crystals. We give examples of selected model structures as illustrations.
Title:: Nucleation and growth of pseudomorphic monolayers on quasicrystal surfaces
Authors:: Smerdon, JA; Sharma, HR; Ledieu, J; McGrath, R Author Full Names: Smerdon, J. A.; Sharma, H. R.; Ledieu, J.; McGrath, R.
Source:: JOURNAL OF PHYSICS-CONDENSED MATTER 20 (31): Art. No. 314005 AUG 6 2008
Abstract:: We present a review of experimental studies of adsorption systems where pseudomorphic growth on quasicrystal surfaces has been observed. From these studies, we correlate information on the known or suggested adsorption and nucleation sites. For fivefold surfaces of icosahedral quasicrystals, two favoured locations emerge: the centres of equatorially truncated pseudo-Mackay clusters, and the centres of pentagonal hollows. The information on adsorption sites on decagonal quasicrystals is less definitive. Nevertheless the correlation of known information leads to a simple picture of pseudomorphic growth, at least for the first monolayer. We also remark on the possibilities for studies using quantitative surface structural techniques.
Title:: Bulk and surface structure of the clean and adsorbate-covered decagonal Al-Co-Ni quasicrystal
Authors:: Burkardt, S; Deloudi, S; Erbudak, M; Kortan, AR; Mungan, M; Steurer, A Author Full Names: Burkardt, S.; Deloudi, S.; Erbudak, M.; Kortan, A. R.; Mungan, M.; Steurer, Andw
Source:: JOURNAL OF PHYSICS-CONDENSED MATTER 20 (31): Art. No. 314006 AUG 6 2008
Abstract:: We review our Al adsorption experiments on the tenfold-symmetry surface of the decagonal Al-Co-Ni quasicrystal and present computational simulations of adsorption on a structural model based on a fundamental Al-Co cluster with 20 angstrom diameter, symmetry (102) over barm, and 8 angstrom periodicity. This cluster is the building unit of tau(2)-Al13Co4, from which, by a sequence of minor changes, the structures of the phases in the stability region of decagonal Al-Co-Ni can be derived. The model used for the decagonal Al70Co15Ni15 is an idealized model with a two-layer periodicity (4 angstrom) and no chemical or structural disorder. We find that the bulk and surface properties of this model are in good agreement with experiments. Our molecular-dynamics simulations of Al adsorption reproduce the experimental results and show that by varying the thermal relaxation rates of the adsorbed layer, a variety of different surface morphologies can be achieved. We also present our recent experiments on dissociative adsorption of oxygen on the decagonal surface.
Title:: Gas adsorption on quasicrystalline surfaces
Authors:: Diehl, RD; Setyawan, W; Curtarolo, S Author Full Names: Diehl, R. D.; Setyawan, W.; Curtarolo, S.
Source:: JOURNAL OF PHYSICS-CONDENSED MATTER 20 (31): Art. No. 314007 AUG 6 2008
Abstract:: The low-friction properties of quasicrystal surfaces suggest their use as coatings on moving machine parts, including those in internal combustion engines. In such applications, additional lubricants are typically used. Since the low-friction properties of quasicrystals are thought to depend on their aperiodic structures, the interactions of lubricants on quasicrystalline surfaces may have an impact on their frictional properties. In this paper, we address the fundamental issues that affect the growth and structural properties of gases on a quasicrystal surface. Studies of the adsorption and growth of rare gases on quasicrystal surfaces are reviewed, and new results are presented for the modeling and simulation of hydrocarbons on quasicrystal surfaces. The calculated interaction parameters are presented for methane adsorption on ten-fold Al-Ni-Co. Methane is found to form aperiodically ordered structures, consistent with the rules established earlier for rare gases on Al-Ni-Co.
Title:: Sputter-induced crystalline layers and epitaxial overlayers on quasicrystal surfaces
Authors:: Shimoda, M; Sharma, HR Author Full Names: Shimoda, M.; Sharma, H. R.
Source:: JOURNAL OF PHYSICS-CONDENSED MATTER 20 (31): Art. No. 314008 AUG 6 2008
Abstract:: We present here an overview of surface and interface studies on various quasicrystals, focusing on areas where reflection high-energy electron diffraction plays an important role. Subjects included here are sputter-induced crystalline layers, surface alloying and epitaxial films. These phenomena are observed on the high symmetry surface of Al-based quasicrystals, such as decagonal Al-Ni-Co, icosahedral (i) Al-Cu-Fe and i-Al-Cu-Ru. For comparison, studies on i-Ag-In-Yb quasicrystal, an isostructure of the binary i-Cd-Yb quasicrystal, and. xi'-Al-Pd-Mn approximant are also included.
Title:: Surface alloys as interfacial layers between quasicrystalline and periodic materials
Authors:: Duguet, T; Ledieu, J; Dubois, JM; Fournee, V Author Full Names: Duguet, T.; Ledieu, J.; Dubois, J. M.; Fournee, V.
Source:: JOURNAL OF PHYSICS-CONDENSED MATTER 20 (31): Art. No. 314009 AUG 6 2008
Abstract:: Low adhesion with normal metals is an intrinsic property of many quasicrystalline surfaces. Although this property could be useful to develop low friction or non-stick coatings, it is also responsible for the poor adhesion of quasicrystalline coatings on metal substrates. Here we investigate the possibility of using complex metallic surface alloys as interface layers to enhance the adhesion between quasicrystals and simple metal substrates. We first review some examples where such complex phases are formed as an overlayer. Then we study the formation of such surface alloys in a controlled way by annealing a thin film deposited on a quasicrystalline substrate. We demonstrate that a coherent buffer layer consisting of the gamma-Al4Cu9 approximant can be grown between pure Al and the i-Al-Cu-Fe quasicrystal. The interfacial relationships between the different layers are defined by [111](A1) parallel to [110](Al4Cu9) parallel to [5f](i-Al-Cu-Fe).
Title:: Contact angles of liquid metals on quasicrystals
Authors:: Bergman, C; Girardeaux, C; Perrin-Pellegrino, C; Gas, P; Dubois, JM; Rivier, N Author Full Names: Bergman, Claire; Girardeaux, Christophe; Perrin-Pellegrino, Carine; Gas, Patrick; Dubois, Jean-Marie; Rivier, Nicolas
Source:: JOURNAL OF PHYSICS-CONDENSED MATTER 20 (31): Art. No. 314010 AUG 6 2008
Abstract:: Wetting with mu m-sized Pb droplets on thin polycrystalline films of decagonal Al13Co4 is reported. The films were prepared under high vacuum conditions in order to have Pb droplets lying on a clean surface. The method used is sequential deposition and annealing of specific stackings of Al and Co layers of nanometric thicknesses. A 300 nm thick Pb slab was then deposited on top of the films and dewetting experiments were followed in situ in a scanning Auger microprobe. The contact angle between the Pb droplet and the surface of the film is measured to be 49 degrees +/- 7 degrees. Further investigation performed by cross section transmission electron microscopy allows us to better characterize the interface. Taking into account the rugosity of the film, it is concluded that there is partial wetting of the film, which corresponds to a smaller contact angle. The comparison with other results obtained either with pure metals or with a cubic AlCo compound leads to the conclusion that the wetting behaviour of Pb on the surface of a decagonal compound is close to that of a metal with a high melting point and not significantly different from that of a crystalline compound with a small unit cell.
Title:: Measurements of contact angles of water on Al-based intermetallic surfaces
Authors:: Dubois, JM; Fournee, V; Thiel, PA; Belin-Ferre, E Author Full Names: Dubois, J. M.; Fournee, V.; Thiel, P. A.; Belin-Ferre, E.
Source:: JOURNAL OF PHYSICS-CONDENSED MATTER 20 (31): Art. No. 314011 AUG 6 2008
Abstract:: A systematic study was performed of the contact angle of minute droplets of water deposited on various aluminium-based intermetallics in ambient conditions. The dataset was complemented by measurements of electronic partial densities of states and oxide layer thicknesses. We studied a broad variety of specimens, ranging from simple cubic, CsCl-type phases to quasicrystals and high-order approximants. The thickness of the oxide layer, that is always present in air, was varied between 2 and more than 10 nm. Within these limits, the contact angle varies considerably and, surprisingly, decreases with increasing thickness of the oxide dielectric. Furthermore, it is clearly the highest on samples that show the largest crystal complexity, i.e. quasicrystals. It follows that the reversible adhesion energy directly deduced from contact angle is essentially controlled by the (squared) density of states at Fermi energy in the bulk of the sample and the inverse of the (squared) thickness of the native oxide film at the surface of the material. We interpret these results in terms of electrostatic image forces developed in the conduction cloud by the dipoles of the water molecules.
Title:: Atomic scale friction and adhesion properties of quasicrystal surfaces
Authors:: Park, JY; Thiel, PA Author Full Names: Park, Jeong Young; Thiel, P. A.
Source:: JOURNAL OF PHYSICS-CONDENSED MATTER 20 (31): Art. No. 314012 AUG 6 2008
Abstract:: In this paper, we highlight recent studies of the atomic scale friction and adhesion properties of quasicrystals. We review tribological studies carried out in different mechanical regimes (elastic and inelastic) and at different length scales (macroscale and nanoscale). We address the role of the surface oxide and the nature of mechanical contact in determining friction and adhesion properties. We discuss the relationship between the aperiodic atomic structure of quasicrystals and their low friction, for both elastic and inelastic regimes.
Title:: First-principles studies for structural transitions in ordered phase of cubic approximant Cd6Ca
Authors:: Nozawa, K; Ishii, Y Author Full Names: Nozawa, K.; Ishii, Y.
Source:: JOURNAL OF PHYSICS-CONDENSED MATTER 20 (31): Art. No. 315206 AUG 6 2008
Abstract:: Recently a low-temperature structural transition has been reported for complex cubic compounds Cd6M (M = Ca, Yb, Y, rare earth) and it is believed that the transition is due to orientational ordering of an atomic shell in the icosahedral cluster in Cd6M. The first-principles electronic structure calculations and structural relaxations are carried out to investigate structures and orientational ordering of the innermost tetrahedral shell of the icosahedral cluster in Cd6Ca. The very short interatomic distances in the experimental average structures are relaxed and the innermost tetrahedral shell of an almost regular shape is obtained. Three types of orientation for the tetrahedral shell and eight different combinations of them for the clusters at a vertex and body-centre of a cubic cell are obtained. A possible model describing the orientational ordering at low temperatures or high pressures is discussed.
Title:: Reciprocal-space imaging of a real quasicrystal. A feasibility study with PILATUS 6M
Authors:: Weber, T; Deloudi, S; Kobas, M; Yokoyama, Y; Inoue, A; Steurer, W Author Full Names: Weber, Thomas; Deloudi, Sofia; Kobas, Miroslav; Yokoyama, Yoshihiko; Inoue, Akihisa; Steurer, Walter
Source:: JOURNAL OF APPLIED CRYSTALLOGRAPHY 41: 669-674 Part 4 AUG 2008
Abstract:: How many of the theoretically densely distributed Bragg reflections of a quasicrystal can be observed employing an area detector and synchrotron radiation? How does the reflection density of a real quasicrystal change as a function of exposure time, and what is the minimum distance between reflections? What does the distribution of diffuse scattering look like? To answer these questions, the Bragg reflection density of a perfect icosahedral quasicrystal with composition Al64Cu23Fe13 was measured employing a novel type of single-photon-counting X-ray pixel detector, PILATUS 6M, which allows noise-free data collection with the extraordinarily large dynamic range of 20 bit. The reflection density was found to be two orders of magnitude lower than expected for a strictly quasiperiodic structure. Moreover, diffuse scattering reflects significant structural disorder, breaking six-dimensional F-lattice symmetry. These findings have some implications for the interpretation! of physical properties.
Title:: Anomalous small-angle scattering from nanoquasicrystalline precipitates in Zr80Pt20 ribbons
Authors:: Okuda, H; Fukumoto, T; Saida, J; Ochiai, S; Sasaki, S; Masunaga, H Author Full Names: Okuda, Hiroshi; Fukumoto, Takefumi; Saida, Junji; Ochiai, Shojiro; Sasaki, Sono; Masunaga, Hiroyasu
Source:: JOURNAL OF APPLIED CRYSTALLOGRAPHY 41: 675-679 Part 4 AUG 2008
Abstract:: Anomalous small-angle X-ray scattering (ASAXS) profiles of Zr80Pt20 ribbons have been measured at the Zr K absorption edge. By annealing the melt-spun ribbons at 800 K, well defined SAXS patterns from nanoquasicrystals were observed, although the compositions of the quasicrystals (QC) and the amorphous matrix have previously been reported to be the same. The SAXS intensities were found to show a small anomalous effect at the Zr K edge. Contrast analysis suggested that the origin of the small-angle scattering is a small compositional fluctuation coupled with a small density difference, which enhances SAXS intensity but reduces the anomalous effect. A constant ASAXS intensity ratio for QC microstructure suggests that the ratio of the composition difference to the density difference between QC and the amorphous matrix is almost constant for the ZrPt ribbons examined here.
Title:: Incommensurate structure of InAl1-xTixO3+x/2 [x=0.701 (1)]: comparison between modulated and composite models
Authors:: Bereciartua, PJ; Zuniga, FJ; Breczewski, T Author Full Names: Bereciartua, P. J.; Zuniga, F. J.; Breczewski, T.
Source:: ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 64: 405-416 Part 4 AUG 2008
Abstract:: The structure of the monoclinic phase of the compound InAl1-xTixO3+x/2 with x = 0.701 (1) has been analyzed within the (3 + 1)-dimensional superspace formalism. Two different models were refined describing the structure as an incommensurate modulated layer and modulated composite, respectively. Both models include the same composition structure relation. In the composite approach it is derived from the mismatching between the two subsystems. In the incommensurate modulated system, it is derived from a closeness condition between O atomic domains. The distribution and coordination of the cations is discussed and compared with previously proposed models for similar compounds.
Title:: Incommensurate structure of Ca2Al2O5 at high temperatures - structure investigation and Raman spectroscopy
Authors:: Lazic, B; Kruger, H; Kahlenberg, V; Konzett, J; Kaindl, R Author Full Names: Lazic, Biljana; Krueger, Hannes; Kahlenberg, Volker; Konzett, Juergen; Kaindl, Reinhard
Source:: ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 64: 417-425 Part 4 AUG 2008
Abstract:: A high-temperature X-ray diffraction study revealed that brownmillerite-type Ca2Al2O5 transforms to an incommensurately modulated structure at elevated temperatures. Single crystals of Ca2Al2O5 were synthesized in an end-loaded piston cylinder press at 2.5 GPa and 1273 K. The diffraction pattern observed at 1090 (10) K by in situ single-crystal diffraction experiments can be indexed by an I-centred orthorhombic cell and a modulation wavevector of q = 0.595 (1) c*. A (3 + 1)-dimensional model in superspace group Imma(00 gamma)s00 was used to refine the modulated structure. The structure is assembled from two building units: (i) layers of corner-sharing [AlO6] octahedra, stacked along b alternate with (ii) layers of zweier single chains of [AlO4] tetrahedra running along a. The modulated structure arises from an aperiodic sequence of two different configurations of the chains within the tetrahedral layers. The modulated high-temperature phase of Ca2Al2O5 is isotypic to the modulated high-temperature modification of Ca2Fe2O5. A large hysteresis was found in the phase-transition temperature. On heating, the transition occurs at ca 1075 (10) K; on cooling, satellite reflections can be observed down to 975 (10) K. The characterization of Ca2Al2O5 is completed by Raman spectroscopy, including a partial interpretation of the spectra.
Title:: Order, disorder and structural modulations in Bi-Fe-W-O-Br Sillen-Aurivillius intergrowths
Authors:: Avila-Brande, D; Landa-Canovas, AR; Otero-Diaz, LC Author Full Names: Avila-Brande, David; Landa-Canovas, Angel R.; Otero-Diaz, L. Carlos
Source:: ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 64: 438-447 Part 4 AUG 2008
Abstract:: Transmission electron microscopy observations on a new complex oxybromide with nominal composition Bi4Fe1/3W2/3O8Br, heated at high temperature, reveal the transformation of its basic structure yielding two types of crystals. The first crystal type shows ordered and disordered extended defects leading to a new family of intergrowths between one Sillen block and n Aurivillius blocks and occasionally between one Aurivillius block and n Sillen blocks. The second type presents a compositionally modulated structure, determined by electron diffraction, with an average composition Bi4Fe1/2W1/2O8-delta Br and unit-cell parameters a = (1/gamma) 3.8, b = 3.8, c = 14.5 angstrom (gamma = 0.10-0.15) in the superspace group Immm[(1-gamma)00] no. 71.1.
Update: 1-Aug-2008
Title:: Ab initio calculations of the vibrational spectra of 1/1 approximant of i-AlCuFe quasicrystal
Authors:: Rudenko, AN; Mazurenko, VG Author Full Names: Rudenko, A. N.; Mazurenko, V. G.
Source:: PHYSICS OF THE SOLID STATE 50 (7): 1326-1332 JUL 2008
Abstract:: The partial and total densities of vibrational states of the 1/1 crystal approximant of the icosahedral i-AlCuFe quasicrystal are calculated using the method of pseudopotentials in the generalized gradient approximation (to describe the electronic states) and the frozen-phonon method (to determine the dynamic matrix). The results obtained agree well with experimental inelastic neutron scattering data, which indicates that the method of calculations is appropriate and could be used to calculate other crystal approximants.
Title:: Materials science - A tale of two tilings
Authors:: Glotzer, SC; Keys, AS Author Full Names: Glotzer, Sharon C.; Keys, Aaron S.
Source:: NATURE 454 (7203): 420-421 JUL 24 2008
Title:: Archimedean-like tiling on decagonal quasicrystalline surfaces
Authors:: Mikhael, J; Roth, J; Helden, L; Bechinger, C Author Full Names: Mikhael, Jules; Roth, Johannes; Helden, Laurent; Bechinger, Clemens
Source:: NATURE 454 (7203): 501-504 JUL 24 2008
Abstract:: Monolayers on crystalline surfaces often form complex structures with physical and chemical properties that differ strongly from those of their bulk phases (1). Such hetero-epitactic overlayers are currently used in nanotechnology and understanding their growth mechanism is important for the development of new materials and devices. In comparison with crystals, quasicrystalline surfaces exhibit much larger structural and chemical complexity leading, for example, to unusual frictional(2), catalytical(3) or optical properties(4,5). Deposition of thin films on such substrates can lead to structures that may have typical quasicrystalline properties. Recent experiments have indeed showed 5-fold symmetries in the diffraction pattern of metallic layers adsorbed on quasicrystals (6,7). Here we report a real-space investigation of the phase behaviour of a colloidal monolayer interacting with a quasicrystalline decagonal substrate created by interfering five laser beams. We find a pseudomorphic phase that shows both crystalline and quasicrystalline structural properties. It can be described by an archimedean-like tiling (8,9) consisting of alternating rows of square and triangular tiles. The calculated diffraction pattern of this phase is in agreement with recent observations of copper adsorbed on icosahedral Al70Pd21Mn9 surfaces(10). In addition to establishing a link between archimedean tilings and quasicrystals, our experiments allow us to investigate in real space how single-element monolayers can form commensurate structures on quasicrystalline surfaces.
Title:: Electronic properties and phase transitions in low-dimensional semiconductors
Authors:: Panich, AM Author Full Names: Panich, A. M.
Source:: JOURNAL OF PHYSICS-CONDENSED MATTER 20 (29): Art. No. 293202 JUL 23 2008
Abstract:: We present the first review of the current state of the literature on electronic properties and phase transitions in T1X and T1MX2 (M = Ga, In; X = Se, S, Te) compounds. These chalcogenides belong to a family of the low-dimensional semiconductors possessing chain or layered structure. They are of significant interest because of their highly anisotropic properties, semi-and photoconductivity, nonlinear effects in their I-V characteristics (including a region of negative differential resistance), switching and memory effects, second harmonic optical generation, relaxor behavior and potential applications for optoelectronic devices. We review the crystal structure of T1X and T1MX2 compounds, their transport properties under ambient conditions, experimental and theoretical studies of the electronic structure, transport properties and semiconductor -metal phase transitions under high pressure, and sequences of temperature-induced structural phase transitions with intermediate incommensurate states. The electronic nature of the ferroelectric phase transitions in the above-mentioned compounds, as well as relaxor behavior, nanodomains and possible occurrence of quantum dots in doped and irradiated crystals is discussed.
Title:: Dynamic crack propagation in decagonal Al-Ni-Co quasicrystal
Authors:: Zhu, AY; Fan, TY Author Full Names: Zhu, Ai-Yu; Fan, Tian You
Source:: JOURNAL OF PHYSICS-CONDENSED MATTER 20 (29): Art. No. 295217 JUL 23 2008
Abstract:: The appearance of unusual internal variables - phason degrees - in quasicrystals challenges the traditional theory of condensed matter in macro- as well as in microscopy, especially for a dynamic process. The elasto-/hydrodynamic model for quasicrystals is suggested and investigated. With this model and the finite difference method the wave propagation and diffusion and their interaction through a cracked sample are revealed in this study. Even though the phason degrees of freedom present the diffusion nature according to the present model, this influences the dynamic process greatly. The influences are different for dynamic initiation of crack growth and fast crack propagation; for the latter the nonlinear effect - moving boundary effect - is evident as well as the wave propagation effect, diffusion effect and phonon-phason coupling effect.
Title:: Effect of hot forging on the microstructure and mechanical properties of Mg-Zn-Y alloy
Authors:: Garces, G; Muller, A; Onorbe, E; Perez, P; Adeva, P Author Full Names: Garces, G.; Mueller, A.; Onorbe, E.; Perez, P.; Adeva, P.
Source:: JOURNAL OF MATERIALS PROCESSING TECHNOLOGY 206 (1-3): 99-105 SEP 12 2008
Abstract:: The use of hot forging as an alternative thermo-mechanical treatment to refine a quasicrystalline reinforced Mg-Zn-Y cast alloy has been explored. Hot forging refines the grain size of the cast Mg-Zn-Y alloy and induces a strong texture with the basal planes perpendicular. to the forging direction. However, forging is not effective to distribute the I-phase homogeneously through the magnesium matrix. At low temperature, grain refinement is the main strengthening mechanism and contributes to increasing the mechanical strength of the forged-Mg-Zn-Y alloy. Furthermore, the basal texture affords an additional strengthening contribution whose magnitude depends only on the texture intensity. (c) 2008 Published by Elsevier B.V.
Title:: Reaction efficiency of diffusion-controlled processes on finite, aperiodic planar arrays
Authors:: Garza-Lopez, RA; Kaufman, A; Patel, R; Chang, J; Brzezinski, J; Kozak, JJ Author Full Names: Garza-Lopez, Roberto A.; Kaufman, Aaron; Patel, Reena; Chang, Joseph; Brzezinski, Jack; Kozak, John J.
Source:: CHEMICAL PHYSICS LETTERS 459 (1-6): 137-140 JUN 27 2008
Abstract:: Using the theory of finite Markov processes, we show quantitatively that diffusion-limited, reactive events on two finite planar arrays having an aperiodic lattice structure are kinetically advantaged relative to processes on platelets having a regular, hexagonal [6(3)] structure. The possible relevance of the results obtained to catalytic processes on quasicrystals and zeolite 'rafts' is noted. (c) 2008 Elsevier B. V. All rights reserved.
Update: 25-Jul-2008
Title:: Main features and the driving force for the formation of the quasicrystalline phase in Al-Cu-Fe powders after mechanoactivation
Authors:: Cherdyntsev, VV; Kaloshkin, SD; Tomilin, IA; Principi, G Author Full Names: Cherdyntsev, V. V.; Kaloshkin, S. D.; Tomilin, I. A.; Principi, G.
Source:: PHYSICS OF METALS AND METALLOGRAPHY 105 (6): 610-621 JUN 2008
Abstract:: The evolution of the phase and structural states during heating of a powder mixture of composition Al65Cu23Fe12 subjected to mechanoactivation has been investigated. The solid-state transformations have been studied using Mossbauer spectroscopy, X-ray diffraction, and differential scanning calorimetry. The sequence of phase formation during heating was compared with the data on the heat of formation of binary solutions and compounds in the system. The analysis performed showed that the nature of transformations in the process of the formation of the quasicrystalline phase was caused by the thermodynamic parameters of the system.
Title:: Metal-insulator transition and its relation to magnetic structure in (LaMnO3)(2n)/(SrMnO3)(n) superlattices
Authors:: Bhattacharya, A; May, SJ; Velthuis, SGET; Warusawithana, M; Zhai, X; Jiang, B; Zuo, JM; Fitzsimmons, MR; Bader, SD; Eckstein, JN Author Full Names: Bhattacharya, A.; May, S. J.; Velthuis, S. G. E. te; Warusawithana, M.; Zhai, X.; Jiang, Bin; Zuo, J. -M.; Fitzsimmons, M. R.; Bader, S. D.; Eckstein, J. N.
Source:: PHYSICAL REVIEW LETTERS 100 (25): Art. No. 257203 JUN 27 2008
Abstract:: Superlattices of (LaMnO3)(2n)/(SrMnO3)(n) (1 <= n <= 5), composed of the gapped insulators LaMnO3 and SrMnO3, undergo a metal-insulator transition as a function of n, being metallic for n <= 2 and insulating for n >= 3. Measurements of transport, magnetization, and polarized neutron reflectivity reveal that the ferromagnetism is relatively uniform in the metallic state, and is strongly modulated in the insulating state, being high in LaMnO3 and suppressed in SrMnO3. The modulation is consistent with a Mott transition driven by the proximity between the (LaMnO3)/(SrMnO3) interfaces. The insulating state for n >= 3 obeys variable range hopping at low temperatures. We suggest that this is due to states at the Fermi level that emerge at the (LaMnO3)/(SrMnO3) interfaces and are localized by disorder.
Title:: Martensitic transformation of Ni2FeGa ferromagnetic shape-memory alloy studied via transmission electron microscopy and electron energy-loss spectroscopy
Authors:: Zhang, HR; Ma, C; Tian, HF; Wu, GH; Li, JQ Author Full Names: Zhang, H. R.; Ma, C.; Tian, H. F.; Wu, G. H.; Li, J. Q.
Source:: PHYSICAL REVIEW B 77 (21): Art. No. 214106 JUN 2008
Abstract:: The structural properties of Ni2FeGa Heusler alloy synthesized by melt-spinning technique have been systematically studied by means of in situ heating and cooling transmission electron microscopy. It was found that the Ni2FeGa alloy was annealed into a well-defined L2(1) structure at around 980 K, and complex microstructural domains appeared along with lowering temperature. At room temperature (293 K), a rich variety of micromodulated domains were observed. The domain structures were aligned along the < 110 > or < 100 > directions resulting to complex tweed structures. Below martensitic transformation (MT) temperature (M-s,similar to 142 K), the cubic parent phase transformed into unmodulated martensitic variants and modulated martensitic variants. The variants were alternated along the < 100 > direction with various arrangements and steplike incommensurate boundaries. The modulated martensitic variants were composed of lamellar structures that have predominately a 5M modulation structure along the < 110 > directions. The electron energy-loss spectroscopy analysis of the low-loss region and the electron energy-loss near-edge fine structure revealed a visible change of the electronic structure along with MT, which can be well interpreted by means of intra-atomic or intraband charge redistribution due to spd orbital hybridization among the Ni-Fe-Ga atoms.
Title:: Ordered magnetic phases of the frustrated spin-dimer compound Ba3Mn2O8
Authors:: Samulon, EC; Jo, YJ; Sengupta, P; Batista, CD; Jaime, M; Balicas, L; Fisher, IR Author Full Names: Samulon, E. C.; Jo, Y. -J.; Sengupta, P.; Batista, C. D.; Jaime, M.; Balicas, L.; Fisher, I. R.
Source:: PHYSICAL REVIEW B 77 (21): Art. No. 214441 JUN 2008
Abstract:: Ba3Mn2O8 is a spin-dimer compound based on pairs of S=1, 3d(2), Mn5+ ions arranged on a triangular lattice. Antiferromagnetic intradimer exchange leads to a singlet ground state in zero field. Here we present the first results of thermodynamic measurements for single crystals probing the high-field ordered states of this material associated with closing the spin gap to the excited triplet states. Specific heat, magnetocaloric effect, and torque magnetometry measurements were performed in magnetic fields up to 32 T and temperatures down to 20 mK. For fields above H-c1 similar to 8.7 T, these measurements reveal a single magnetic phase for H parallel to c but two distinct phases (approximately symmetric about the center of the phase diagram) for H perpendicular to c. Analysis of the simplest possible spin Hamiltonian describing this system yields candidates for these ordered states corresponding to a simple spiral structure for H parallel to c and to two distinct modulated phases for H perpendicular to c. Both single-ion anisotropy and geometric frustration play crucial roles in defining the phase diagram.
Title:: Pressure-induced polarization reversal in multiferroic YMn2O5
Authors:: Chaudhury, RP; dela Cruz, CR; Lorenz, B; Sun, YY; Chu, CW; Park, S; Cheong, SW Author Full Names: Chaudhury, Rajit P.; dela Cruz, Clarina R.; Lorenz, Bernd; Sun, Yanyi; Chu, Ching-Wu; Park, S.; Cheong, Sang-W.
Source:: PHYSICAL REVIEW B 77 (22): Art. No. 220104 JUN 2008
Abstract:: The low-temperature ferroelectric polarization of multiferroic YMn2O5 is completely reversed at a critical pressure of 10 kbar and the phase transition from the incommensurate to the commensurate magnetic phase is induced by pressures above 14 kbar. The high-pressure data correlate with thermal-expansion measurements, indicating a significant lattice strain at the low-temperature transition into the incommensurate phase. The results support the exchange striction model for the ferroelectricity in multiferroic RMn2O5 compounds and they show the importance of magnetic frustration as well as the spin-lattice coupling.
Title:: Incommensurate spin ordering and fluctuations in underdoped La2-xBaxCuO4
Authors:: Dunsiger, SR; Zhao, Y; Yamani, Z; Buyers, WJL; Dabkowska, HA; Gaulin, BD Author Full Names: Dunsiger, S. R.; Zhao, Y.; Yamani, Z.; Buyers, W. J. L.; Dabkowska, H. A.; Gaulin, B. D.
Source:: PHYSICAL REVIEW B 77 (22): Art. No. 224410 JUN 2008
Abstract:: By using neutron scattering techniques, we have studied the incommensurate spin ordering as well as the low energy spin dynamics in single crystal underdoped La2-xBaxCuO4 with x similar to 0.095 and 0.08, which are high temperature superconductors with T-C similar to 27 and 29 K, respectively. Static two dimensional incommensurate magnetic order appears below T-N=39.5 +/- 0.3 K in La2-xBaxCuO4 (x=0.095) and a similar temperature for x=0.08 within the low temperature tetragonal phase. The spin order is unaffected by either the onset of superconductivity or the application of magnetic fields of up to 7 T applied along the c axis in the x=0.095 sample. Such a magnetic field independent behavior is in marked contrast to the field induced enhancement of the staggered magnetization observed in the related La2-xSrxCuO4 system, which indicates that this phenomenon is not a universal property of cuprate superconductors. Surprisingly, we find that the incommensurability delta is only weakly dependent on doping relative to La2-xSrxCuO4. Dispersive excitations in La2-xBaxCuO4 (x=0.095) at the same incommensurate wave vector persist up to at least 60 K. The dynamical spin susceptibility of the low energy spin excitations saturates below T-C in a similar manner to that seen in the superconducting state of La2CuO4+y.
Title:: Change of antiferromagnetic structure near a quantum critical point in CeRh1-xCoxIn5
Authors:: Yokoyama, M; Oyama, N; Amitsuka, H; Oinuma, S; Kawasaki, I; Tenya, K; Matsuura, M; Hirota, K; Sato, TJ Author Full Names: Yokoyama, M.; Oyama, N.; Amitsuka, H.; Oinuma, S.; Kawasaki, I.; Tenya, K.; Matsuura, M.; Hirota, K.; Sato, T. J.
Source:: PHYSICAL REVIEW B 77 (22): Art. No. 224501 JUN 2008
Abstract:: The elastic neutron-scattering experiments were carried out on the solid solutions CeRh1-xCoxIn5 to clarify the nature of the antiferromagnetic (AF) state in the vicinity of the quantum critical point: x(c)similar to 0.8. The incommensurate AF order with the wave vector of q(h)=(1/2,1/2,similar to 0.3) observed in pure CeRhIn5 is weakly suppressed upon doping with Co, and a commensurate q(c)=(1/2,1/2,1/2) and an incommensurate q(1)=(1/2,1/2,similar to 0.42) AF structures evolve at intermediate Co concentrations. The AF orders with q(c) and q(1) are enhanced at x=0.7, and furthermore, the q(h) AF order vanishes. These results suggest that the AF correlations with the q(c) and q(1) modulations are significantly enhanced in the intermediate x range, and may be connected with the evolution of the superconductivity observed above x similar to 0.3.
Title:: Effect of Al addition on the elevated temperature deformation behavior of Mg-Zn-Y alloy
Authors:: Kim, DH; Lee, JY; Lim, HK; Kim, WT; Kim, DH Author Full Names: Kim, Do Hyung; Lee, Ju Yeon; Lim, Hyun Kyu; Kim, Won Tae; Kim, Do Hyang
Source:: MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 487 (1-2): 481-487 JUL 25 2008
Abstract:: The effect of the addition of Al on the high temperature deformation behavior of wrought Mg-4Zn-0.8Y alloy has been investigated. The addition of Al significantly improves the high temperature formability, i.e. increases elongation from 260% to 370% under a strain rate of 1 x 10(-4) s(-1) at 300 degrees C. Strain rate sensitivity measured at different strain rates shows that the addition of Al induces the transition of high temperature deformation mechanism from dislocation creep mode to grain boundary sliding mode. Effect of alloying elements and microstructural evolution including the role of icosahedral-phase during deformation are discussed. (c) 2007 Elsevier B.V. All rights reserved.
Title:: Characterization of Ni-Mn-Ga alloy with Gd addition
Authors:: Zhang, ZY; Du, ZW; Shao, BL; Liu, AS; Sun, ZM Author Full Names: Zhang, Z. Y.; Du, Z. W.; Shao, B. L.; Liu, A. S.; Sun, Z. M.
Source:: MATERIALS CHARACTERIZATION 59 (8): 1041-1045 AUG 2008
Abstract:: The effect of rare earth element Gd additions in an Ni-Mn-Ga alloy on magnetocaloric effect has previously been investigated. In this paper, the microstructure of Ni53.4Mn20Ga25.6Gd1 was studied by TEM. The results show that Gd partly dissolves in the matrix and partly occurs as precipitates such as Gd and Ni-rich Ni-Mn-Ga-Gd quaternary phases. At room temperature, the alloy is mainly composed of non-modulated martensite with a small amount of seven-layered and ten-layered modulated martensite. The high-resolution electron microscopy (HREM) images also reveal that some layered structures in certain zones are microtwins in nature with a thickness of a few atomic planes as the stacking sequence is not periodic. (C) 2007 Elsevier Inc. All rights reserved.
Title:: Superspace description, crystal structures, and electric conductivity of the Ba4In6-xMgxO13-x/2 solid solutions
Authors:: Abakumov, AM; Rossell, MD; Gutnikova, OY; Drozhzhin, OA; Leonova, LS; Dobrovolsky, YA; Istomin, SY; Van Tendeloo, G; Antipovt, EV Author Full Names: Abakumov, Artem M.; Rossell, Marta D.; Gutnikova, Olga Yu.; Drozhzhin, Oleg A.; Leonova, Ludmila S.; Dobrovolsky, Yuri A.; Istomin, Sergey Ya.; Van Tendeloo, Gustaaf; Antipovt, Evgeny V.
Source:: CHEMISTRY OF MATERIALS 20 (13): 4457-4467 JUL 8 2008
Abstract:: Ba3In6-xMgxO13-x/2 solid solutions have been prepar for 0 <= x <= 0.4 and their crystal structures have been studied by transmission electron microscopy and X-ray powder diffraction. The compounds adopt a modulated structure with a face-centered orthorhombic average unit cell with a(0)approximate to a(p) root 2, b(0)approximate to 20.5 angstrom, c(0)approximate to a(p) root 2 (a(p) - parameter of the perovskite subcell) and modulation vector.q=alpha a(0)* , which is compositionally dependent according to the Ba4In4+4 alpha Mg2-4 alpha O12+2 alpha formula.The -superspace group Xmms(alpha 00)0s0 Xrnrn2(a00)0s0 with centering vectors (0,1/2,1/2,1/2), (1/2,0,1/2,0.(1/2,1/2,0 1/2) was propose ed from electron diffraction and structural considerations. A unified suoersoace model is" construtted'to describe the atomic arrangements and the variable oxygen content in the modulated (In, Mg)2Q2+a layers with rock-salt type structure. This model was used to refine the crystai structures of two x= 0 (R-I 0.040, R-p = 0.042) and x = 0.4 (R-I = 0.062, R-p = 0.040) limiting points of the solid solu tions. The cations in these layers adopt a five-fold coordination that can be virtually classified as strongly distorted trigonal bipyramids and tetragonal pyramids. The close similarity of the structural organization of the Ba4In6-xMgxO13-x/2 solid solutions, Sr4Fe6O13 and its anion-deficient derivatives is discussed. Electric conductivity of the Ba4In6-xMgxO13-x/2 was studied by impedance spectroscopy indicating mixed ionicelectronic type of conductivity. Electronic conductivity at different P(O-2) was compared for Ba4In6-xMgxO13-x/2 and Ba2In2O5 and discussed taking into account the peculiarities of their crystal structures.
Update: 18-Jul-2008
Title:: Software package for structure analysis of quasicrystals
Authors:: Yamamoto, A Author Full Names: Yamamoto, Akiji
Source:: SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS 9 (1): Art. No. 013001 JAN-MAR 2008
Abstract:: Recently a software package for the structure analysis of quasicrystals has been released, giving a better environment for determining quasicrystal structures. Therefore we can analyze their structures if we know data collection and indexing methods and a theory of structure analysis. For the use of the package, the structure analysis method and several techniques used in the package are shortly reviewed. How to treat key information in the input files of the programs is described in detail.
Title:: Icosahedral clusters, icosaheral order and stability of quasicrystals - a view of metallurgy
Authors:: Tsai, AP Author Full Names: Tsai, An Pang
Source:: SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS 9 (1): Art. No. 013008 JAN-MAR 2008
Abstract:: We review the stability of various icosahedral quasicrystals ( iQc) from a metallurgical viewpoint. The stability of stable iQcs is well interpreted in terms of Hume-Rothery rules, i.e. atomic size factor and valence electron concentration, e/a. For metastable iQcs, we discuss the role of phason disorder introduced by rapid solidification, in structural stability and its interplay with chemical order and composition.
Title:: Finite doping of a one-dimensional charge density wave: Solitons vs Luttinger liquid charge density
Authors:: Weiss, Y; Goldstein, M; Berkovits, R Author Full Names: Weiss, Yuval; Goldstein, Moshe; Berkovits, Richard
Source:: PHYSICAL REVIEW B 77 (20): Art. No. 205128 MAY 2008
Abstract:: The effects of doping on a one-dimensional wire in a charge density wave state are studied using the density-matrix renormalization group method. We show that for a finite number of extra electrons, the ground state becomes conducting but the particle density along the wire corresponds to a charge density wave with an incommensurate+ wave number determined by the filling. We find that the absence of the translational invariance can be discerned even in the thermodynamic limit is long as the number of doping electrons is finite. The Luttinger liquid behavior is reached only for a finite change in the electron filling factor, which for an infinite wire corresponds to the addition of an infinite number of electrons. In addition to the half filled insulating Mott state and the conducting states, we find evidence for subgap states at fillings different from half filling by a single electron or hole. Finally, we show that by coupling our system to a quantum dot, one ca! n have a discontinuous dependence of its population on the applied gate voltage in the thermodynamic limit, similar to the one predicted for a Luttinger liquid without umklapp processes.
Title:: Phase transformation behaviour in continuously cooled Zr65Al7.5Ni10Cu17.5-xPdx (x=0-17.5) glass-forming alloys and consequences for structure and property control
Authors:: Setyawan, AD; Kato, H; Saida, J; Inoue, A Author Full Names: Setyawan, A. D.; Kato, H.; Saida, J.; Inoue, A.
Source:: PHILOSOPHICAL MAGAZINE 88 (8): 1125-1136 2008
Abstract:: Continuous cooling transformation (CCT) diagrams were successfully constructed for Zr65Al7.5Ni10Cu17.5-xPdx (x=0-17.5) glass-forming alloys, comparing phase-transformation features in the alloy system to composition. While a low-Pd alloy (x=5) showed a single transformation curve, corresponding to the formation of a crystalline phase on the high-temperature side of the undercooled-liquid region, for a given time-scale, a high-Pd alloy (x=17.5) revealed an additional curve, corresponding to quasicrystalline phase formation on the lower temperature side. The result provides a clue to the structural and property control on the alloy system. Glassy specimens of the same size but with different intrinsic structure, evaluated by structural relaxation during continuous heating, could be fabricated for the low-Pd alloy (x=5). Plasticity was found to increase proportionally with the relaxation enthalpy. On the other hand, the critical size for glass formation could be improved considerably from 5 to 7 mm in diameter for the high-Pd alloy (x=17.5).
Title:: A multi-component Fermi surface in the vortex state of an underdoped high-T-c superconductor
Authors:: Sebastian, SE; Harrison, N; Palm, E; Murphy, TP; Mielke, CH; Liang, RX; Bonn, DA; Hardy, WN; Lonzarich, GG Author Full Names: Sebastian, Suchitra E.; Harrison, N.; Palm, E.; Murphy, T. P.; Mielke, C. H.; Liang, Ruixing; Bonn, D. A.; Hardy, W. N.; Lonzarich, G. G.
Source:: NATURE 454 (7201): 200-203 JUL 10 2008
Abstract:: To understand the origin of superconductivity, it is crucial to ascertain the nature and origin of the primary carriers available to participate in pairing(1-6). Recent quantum oscillation experiments on high- transition- temperature ( high- T-c) copper oxide superconductors(7-10) have revealed the existence of a Fermi surface akin to that in normal metals, comprising fermionic carriers that undergo orbital quantization(11). The unexpectedly small size of the observed carrier pocket, however, leaves open a variety of possibilities for the existence or form of any underlying magnetic order, and its relation to d- wave superconductivity(12-15). Here we report experiments on quantum oscillations in the magnetization ( the de Haas- van Alphen effect) in superconducting YBa2Cu3O6.51 that reveal more than one carrier pocket. In particular, we find evidence for the existence of a much larger pocket of heavier mass carriers playing a thermodynamically dominant role in this hole- doped superconductor. Importantly, characteristics of the multiple pockets within this more complete Fermi surface impose constraints on the wavevector of any underlying order and the location of the carriers in momentum space. These constraints enable us to construct a possible density- wave model with spiral or related modulated magnetic order, consistent with experimental observations.
Title:: Origins of superstructure ordering and incommensurability in stuffed CoSn-Type phases
Authors:: Fredrickson, DC; Lidin, S; Venturini, G; Malaman, B; Christensen, J Author Full Names: Fredrickson, Daniel C.; Lidin, Sven; Venturini, Gerard; Malaman, Bernard; Christensen, Jeppe
Source:: JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 130 (26): 8195-8214 JUL 2 2008
Abstract:: The CoSn structure type contains large interstitial void spaces that frequently host electropositive guest atoms, such as rare earth elements. In this stuffing process, an intriguing ordering occurs between the neighboring void spaces leading to a family of long-period superstructures comprising intergrowths of the ScFe6Ge6 and ScFe6Ga6 structure types. This superstucture ordering culminates in incommensurability in the REFe6Ge6_delta Ga6 systems with RE = Sc, Tb, and Lu. In this work, we derive a 3 + 1 D superspace model encompassing this series of structures and investigate the origins of the structural trends in this family with electronic structure calculations, at both the LDA-DFT and extended Huckel levels. Using our 3 + 1 D model, we refine the structures of four new ErFe6Ge6-delta Ga delta (0 <= 6 <= 6) phases, two commensurate and two incommensurate, from powder X-ray diffraction data. The refinement results confirm trends observed in the Sc-, Tb -, and Lu-based series: a gradual lengthening and, eventually, turning of the q-vector as Ge is progressively exchanged for Ga. These trends, and the incommensurate ordering as a whole, are traced to a tension between two modes by which the host lattice responds to stuffing atom insertion: (1) an atomic charge modulation enhancing the anionic character of the cavity walls around the guest atoms, and (2) a positional modulation expanding the cavities occupied by guest atoms. These two modes direct the stuffing atom ordering pattern toward opposite ends of the ScFe6Ge6-ScFe6Ga6 intergrowth series. The full series of structures, complex and incommensurate, reflects various degrees of balance between these two factors.
Title:: Incommensurate strain-induced ordering of interstitial oxygen in Nb
Authors:: Kurta, RP; Bugaev, VN; Stierle, A; Dosch, H Author Full Names: Kurta, R. P.; Bugaev, V. N.; Stierle, A.; Dosch, H.
Source:: JOURNAL OF PHYSICS-CONDENSED MATTER 20 (27): Art. No. 275206 JUL 9 2008
Abstract:: We present a semi-phenomenological theory of the strain-induced interaction between interstitial oxygen dissolved in Nb and predict an incommensurate oxygen ordering wave which is mediated by the intrinsic bcc instability at kappa = 2/3(111). We discuss the stability range of this ordering phenomenon, which may play a role in the performance of Nb radio frequency (RF) cavities for high energy particle accelerators.
Title:: Effects of Nb on the formation of icosahedral quasicrystalline phase in Ti-rich Ti-Zr-Ni-Cu-Be glassy forming alloys
Authors:: Mei, JN; Li, JS; Kou, HC; Fu, HZ; Zhou, L Author Full Names: Mei, J. N.; Li, J. S.; Kou, H. C.; Fu, H. Z.; Zhou, L.
Source:: JOURNAL OF NON-CRYSTALLINE SOLIDS 354 (28): 3332-3335 JUN 15 2008
Abstract:: As-cast (Ti40Zr25Ni8Cu9Be18)(100-x)Nb-x (0 <= x <= 5) (Phi 3) glassy forming alloys were investigated in order to clarify the role of Nb on the formation of icosahedral quasicrystalline phase (I-phase) in Ti-rich Ti-Zr-Ni-Cu-Be glassy system. It is found that an I-phase is formed in Ti-Zr-Ni-Cu-Be glassy alloy by addition of Nb element; however, the nucleation rate of I-phase increases, whereas the grain growth rate decreases with increasing Nb content. Moreover, with increasing Nb content, the thermal stability against crystallization increases, while the temperature range of stability of the I-phase decreases. (C) 2008 Elsevier B.V. All rights reserved.
Title:: Thermal stability, microstructure and crystallization kinetics of melt-spun Zr-Ti-Cu-Ni metallic glass
Authors:: Scudino, S; Venkataraman, S; Eckert, J Author Full Names: Scudino, S.; Venkataraman, S.; Eckert, J.
Source:: JOURNAL OF ALLOYS AND COMPOUNDS 460 (1-2): 263-267 JUL 28 2008
Abstract:: Melt-spun Zr63.33Ti8.89Cu15.45Ni2.33 glassy ribbons display a double-step devitrification behavior characterized by the precipitation of a metastable quasicrystalline phase in the first stage of the crystallization process, followed by the formation of crystalline phases in the following crystallization event. Investigation of the crystallization kinetics reveal that the initial part of the glass-to-quasicrystalline transformation (x <= 55 vol.%) occurs by diffusion controlled growth with an increasing nucleation rate (Avrami exponent n >= 2.5), whereas the later stage of the transformation (x > 55 vol.%) is dominated by the growth of the formed nuclei rather than by the generation of new nuclei (2.0 <= n <= 2.5). The activation energy for quasicrystallization is 360 kJ/mol, which is comparable to the values reported for other quasicrystal-forming Zr-based metallic glasses. (C) 2007 Elsevier B.V. All rights reserved.
Title:: Unusual devitrification behaviour in rapidly solidified Ti45Zr38Ni17 alloy
Authors:: Lefaix, H; Vermaut, P; Janickovic, D; Svec, P; Gloriant, T; Portier, R; Prima, F Author Full Names: Lefaix, H.; Vermaut, P.; Janickovic, D.; Svec, P.; Gloriant, T.; Portier, R.; Prima, F.
Source:: JOURNAL OF ALLOYS AND COMPOUNDS 460 (1-2): 392-399 JUL 28 2008
Abstract:: In this study, Ti45Zr38Ni17 ribbons have been elaborated using planar flow casting method (v(quenching) 106 K s(-1)). The rapidly quenched samples, displaying a dispersion of nanoscaled beta phase particles in an amorphous matrix, have been extensively characterised using transmission electron microscopy (TEM) and X-ray diffraction (XRD). Devitrification behaviour, investigated by four-probe resistivity measurements and differential scanning calorimetry as well as high resolution TEM analysis, revealed the formation of nanometric quasicrystals (QC) during the first exothermic phase transformation as well as the precipitation of omega domains inside beta particles. On the basis of these data, it has been noticed that nanoscaled beta metastable particles had adopted the same temperature dependence as beta metastable bulk. Furthermore, particular orientation relationships have been observed for QCs in the vicinity of beta particles which have suggested probable influence of crystalline structure on the QCs growth, although the presence of such peculiar materials after annealing treatment could be mainly explained by an icosahedral short-range order prevailing in Ti-Zr-Ni melt and favouring their nucleation. (C) 2007 Elsevier B.V. All rights reserved.
Update: 11-Jul-2008
Title:: SEM study of quasi-crystallized Zr65Cu12.5Ni10Al7.5Ag5 amorphous alloy at initial stage
Authors:: Wu, HM; Sun, W; Zhang, Z; Liu, L; Zhang, T Author Full Names: Wu Huimin; Sun Wei; Zhang Ze; Liu Li; Zhang Tao
Source:: RARE METAL MATERIALS AND ENGINEERING 37 (5): 823-826 MAY 2008
Abstract:: Microstructure evolvement during crystallization process for the melt-spun Zr65Cu12.5Ni10Al7.5Ag5 amorphous alloy has been studied by DSC analysis and TEM. We monitor the crystallization process by DSC, and stop at given temperatures, following by cooling down from these temperatures in the DSC furnace to examine the corresponding microstructure evolvement by TEM. The results show that the crystallization of Zr65Cu12.5Ni10Al7.5Ag5 alloy can be divided into three stages. At the initial stage, an icosahedral quasi-crystal (I-phase) is formed as primary phase from the amorphous matrix without apparent compositional variation. In comparison with the amorphous matrix, the I-phase is Zr-rich and Cu-poor slightly with high nucleation and growth rates by consuming the amorphous matrix, leading to a microstructure with closed packed grains at the first stage of crystallization. However, the residual amorphous phase still exists at this stage.
Title:: Pressure dependence of the magnetic ordering in CeRhIn5
Authors:: Raymond, S; Knebel, G; Aoki, D; Flouquet, J Author Full Names: Raymond, S.; Knebel, G.; Aoki, D.; Flouquet, J.
Source:: PHYSICAL REVIEW B 77 (17): Art. No. 172502 MAY 2008
Abstract:: We determine by neutron diffraction the propagation vector of the magnetic structure of CeRhIn5 under pressures of 1.5 and 1.7 GPa down to 375 mK. For both pressures, an incommensurate propagation vector k(IC2)=(1/2,1/2,0.4) is found in contrast to the low pressure one k(ICI)=(1/2,1/2,0.298). At 1.7 GPa, no change is found in the propagation vector and the intensity of the magnetic peaks in the superconducting phase below 1 K.
Title:: Magnetically asymmetiric interfaces in a LaMnO3/SrMnG(3) superlattice due to structural asymmetries
Authors:: May, SJ; Shah, AB; Velthuis, SGET; Fitzsimmons, MR; Zuo, JM; Zhai, X; Eckstein, JN; Bader, SD; Bhattacharya, A Author Full Names: May, S. J.; Shah, A. B.; Velthuis, S. G. E. te; Fitzsimmons, M. R.; Zuo, J. M.; Zhai, X.; Eckstein, J. N.; Bader, S. D.; Bhattacharya, A.
Source:: PHYSICAL REVIEW B 77 (17): Art. No. 174409 MAY 2008
Abstract:: Polarized neutron reflectivity measurements of a ferromagnetic [(LaMnO3)(11.8)/(SrMnO3)(4.4)](6) superlattice reveal a modulated magnetic structure with an enhanced magnetization at the interfaces where LaMnO3 was deposited on SrMnO3 (LMO/SMO). However, the opposite interfaces (SMO/LMO) are found to have a reduced ferromagnetic moment. The magnetic asymmetry is accompanied by a corresponding asymmetry in the lateral structural roughness of the two interfaces observed via electron microscopy, with enhanced ferromagnetism present at the interfaces that are atomically smooth over tens of nanometers. This result demonstrates that atomic-scale roughness can destabilize interfacial phases in complex oxide heterostructures.
Title:: Spin polarization of the magnetic spiral in NaCu2O2 as seen by nuclear magnetic resonance spectroscopy
Authors:: Gippius, AA; Moskvin, AS; Drechsler, SL Author Full Names: Gippius, A. A.; Moskvin, A. S.; Drechsler, S. -L.
Source:: PHYSICAL REVIEW B 77 (18): Art. No. 180403 MAY 2008
Abstract:: The incommensurate (IC) spin ordering in quasi-one-dimensional edge-shared cuprate NaCu2O2 has been studied by Na-23 nuclear magnetic resonance spectroscopy in an external magnetic field near 6 T applied along the main crystallographic axes. The NMR line shape evolution above and below TN approximate to 12 K yields a clear signature of an IC static modulation of the local magnetic field consistent with a Cu2+ spin spiral polarized in the bc plane rather than in the ab plane, as reported from earlier neutron diffraction data.
Title:: Comparison between experimental surface data and bulk structure models for quasicrystalline A1PdMn: Average atomic densities and chemical compositions
Authors:: Unal, B; Jenks, CJ; Thiel, RA Author Full Names: Unal, Baris; Jenks, C. J.; Thiel, R. A.
Source:: PHYSICAL REVIEW B 77 (19): Art. No. 195419 MAY 2008
Abstract:: We have examined bulk structure models for icosahedral A1PdMn in terms of the densities, compositions, and interplanar spacings for the fivefold planes that might represent physical surface terminations. We focus on four models that contain no partial or mixed occupancies, but some comparison is made to a fifth model containing such sites. Each of the four models contains paired planes (layers) that can be separated into two main families on the basis of three features: the relative densities of the two planes, the gap separating the layer from the nearest atomic plane, and the Pd content in the topmost plane. The experimental data and other arguments lead to the conclusion that the family with no Pd in the top plane is favored. Finally, all models show that correlations should be expected between the heights of steps that delineate terraces and average compositional and/or structural features of the terraces.
Title:: Mechanical properties and microstructure of twin-roll cast Mg-Zn-Y alloy
Authors:: Kim, KH; Lee, JG; Bae, GT; Bae, JH; Kim, NJ Author Full Names: Kim, Kyung-Hun; Lee, Jung Gu; Bae, Geun Tae; Bae, Jun Ho; Kim, Nack J.
Source:: MATERIALS TRANSACTIONS 49 (5): 980-985 MAY 2008
Abstract:: Mg97.3Zn2.3Y0.4 alloy has been subjected to twin-roll casting (TRC) process. As-cast microstructure consists of alpha-Mg dendrite and icosahedral interdendritic phase. The icosahedral phase present in TRC alloy is found to be thermally unstable and transforms to H-phase and W-phase during subsequent thermo-mechanical treatment (TMT) at 400 degrees C. It shows that the pre-heating condition has a significant effect on the microstructural evolution during TMT. The specimen pre-heated at 400 degrees C for 30 min shows elongated microstructure after TMT, while the specimen pre-heated at 400 degrees C for 12 h shows equiaxed recrystallized structure after TMT. Such homogeneous microstructure of the specimen pre-heated at 400 degrees C for 12 h results in better combinations of strength and ductility than the specimen pre-heated at 400 degrees C for 30 min.
Title:: Pressure-induced commensurate magnetic order in multiferroic HoMn2O5
Authors:: Kimura, H; Nishihata, K; Noda, Y; Aso, N; Matsubayashi, K; Uwatoko, Y; Fujiwara, T Author Full Names: Kimura, Hiroyuki; Nishihata, Keisuke; Noda, Yukio; Aso, Naofumi; Matsubayashi, Kazuyuki; Uwatoko, Yoshiya; Fujiwara, Tetsuya
Source:: JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 77 (6): Art. No. 063704 JUN 2008
Abstract:: The pressure-temperature (p-T) phase diagram for microscopic magnetism in the multiferroic compound HoMn2O5 was established using neutron diffraction measurements under a hydrostatic pressure up to 1.25 GPa. At ambient pressure, incommensurate-commensurate-incommensurate magnetic phase transitions occur successively with decreasing temperature. Upon applying pressure, the incommensurate phase at the lowest temperature almost decreases and the commensurate phase appears. The p-T phase diagram established shows excellent agreement with the recently reported p-T dielectric phase diagram, where ferroelectricity is induced by applying pressure. We also found that the p-T magnetic phase diagram is quite similar to the previously obtained magnetic field-temperature phase diagram.
Title:: Discommensurate structure in [(Ca0.90Sr0.10)(2)CoO3](0.61)CoO2
Authors:: Yubuta, K; Huang, XY; Miyazaki, Y; Kajitani, T Author Full Names: Yubuta, Kunio; Huang, Xiangyang; Miyazaki, Yuzuru; Kajitani, Tsuyoshi
Source:: JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 77 (6): Art. No. 064604 JUN 2008
Abstract:: The crystal structure of partly Sr-substituted Co-121, i.e., "Ca3Co4Co9", single crystal is studied by means of the electron diffraction measurements and high-resolution transmission electron microscopy (HREM). The crystal structure consists of two interpenetrating subsystems of a CoO2 sheet and a distorted three-layered (Ca,Sr)(2)CoO3 rock-salt (RS)-type block layers, which belong to a triclinic system. Both subsystems have common a-, c-axes and alpha-, beta-, gamma-angle with a = 4.8267(1) angstrom, c = 10.9214(3) angstrom, alpha = 90.916(2)degrees, beta = 98.291(5)degrees, and gamma = 89.957(3)degrees. On the other hand, the crystal structure is modulated parallel to the b-axis, along which the CoO2 sheet has b(1) = 2.8346(1) angstrom and the (Ca,Sr)(2)CoO3 RS-type block layer has b(2) = 4.6391(2) angstrom, respectively. On the basis of the b(1)/b(2) ratio and analyzed chemical compositions, the structure analogue is formulated as [(Ca0.90Sr0.10)(2)CoO3](0.61)CoO2. In electron diffraction patterns, there are many new satellite reflections, namely 0101, 0202, 0204, and 0103, which are not present in the end member Co-121, i.e., (Ca2CoO3)(0.620)CoO2. Because of the new superlattice reflections, the crystal structure of the Sr-doped Compound is different from the end member. HREM images were taken with the incident electron beam parallel to the [0010] and [1000] directions. The basic crystal structure of the present system consists of 5-CoO2 and 3-RS subcells with b = 14 angstrom being connected discommensuratedly parallel to the a- and b-axes. Systematic introduction of stacking faults parallel to the a-b plane is also noticed.
Title:: Twin boundary structure of the modulated variants in a Ni-Mn-Ga alloy
Authors:: Han, M; Kong, FF Author Full Names: Han, M.; Kong, F. F.
Source:: JOURNAL OF ALLOYS AND COMPOUNDS 458 (1-2): 218-222 JUN 30 2008
Abstract:: The micro structure of a Ni-Mn-Ga ferromagnetic shape memory alloy has been characterized by transmission electron microscopy. Electron diffraction reveals that the microstructure of the alloy predominately consists of seven-layer modulated martensite. There exists reflection-twinned relation between the martensitic variants. It is found that there are parallel and equidistant fringes at the boundary. The nature of these fringes is discussed and the results show that the boundary fringes are caused by the elastic strains associated with the coherent interface. (c) 2007 Elsevier B.V All rights reserved.
Title:: Bond stretching phonon anomalies due to incommensurate charge density wave instabilities in high-T-c cuprates
Authors:: Citro, R; Cojocaru, S; Marinaro, M Author Full Names: Citro, R.; Cojocaru, S.; Marinaro, M.
Source:: EUROPEAN PHYSICAL JOURNAL B 63 (2): 179-185 MAY 2008
Abstract:: Phonon anomalies observed in various high T-c cuprates are analyzed theoretically within the Hubbard-Holstein model in the limit of strong local electron correlations and in presence of long-range Coulomb interaction. The phonon self-energy is evaluated by taking into account the charge collective modes that become critical upon doping approaching an instability towards an incommensurate charge density wave (ICDW) driven by electron correlations. The doping dependence of phonon softening features and the highly distinctive phonon self-energy dependence on the wave vector agree with experiments. We discuss relevance of dynamical corrections to the density correlation function to achieve a sizeable bond-stretching phonon softening with a kink-like profile away from the zone boundary.
Title:: Reaction efficiency of diffusion-controlled processes on finite, aperiodic planar arrays
Authors:: Garza-Lopez, RA; Kaufman, A; Patel, R; Chang, J; Brzezinski, J; Kozak, JJ Author Full Names: Garza-Lopez, Roberto A.; Kaufman, Aaron; Patel, Reena; Chang, Joseph; Brzezinski, Jack; Kozak, John J.
Source:: CHEMICAL PHYSICS LETTERS 458 (1-6): 137-140 JUN 27 2008
Abstract:: Using the theory of finite Markov processes, we show quantitatively that diffusion-limited, reactive events on two finite planar arrays having an aperiodic lattice structure are kinetically advantaged relative to processes on platelets having a regular, hexagonal [ 63] structure. The possible relevance of the results obtained to catalytic processes on quasicrystals and zeolite 'rafts' is noted. (c) 2008 Elsevier B. V. All rights reserved.
Title:: Inter-martensite strain evolution in NiMnGa single crystals
Authors:: Hamilton, RF; Sehitoglu, H; Aslantas, K; Efstathiou, C; Maier, HJ Author Full Names: Hamilton, R. F.; Sehitoglu, H.; Aslantas, K.; Efstathiou, C.; Maier, H. J.
Source:: ACTA MATERIALIA 56 (10): 2231-2236 JUN 2008
Abstract:: Stress-induced martensitic transformations are clarified in classes of NiMnGa alloys which undergo the stress-free, thermal-induced inter-martensite transformation austenite (A) reversible arrow pre-martensite (PM) reversible arrow martensite. This study implements a comprehensive experimental approach, including analysis of the strain-temperature and stress-strain response, which discloses stress-induced inter-martensite transitions. The evolution of the transitions is elucidated using in situ digital image correlation (DIC) measurements of meso-scale strain fields. Under stress, this body of work unequivocally demonstrates that the transformation path becomes A reversible arrow PM reversible arrow I reversible arrow 10M. The I-phase is an intermediate stress-induced martensite with a modulation period between three and five-layers. Owing to the intermediate transition, the thermal hysteresis in the strain-temperature response is tiny (<10 degrees C) compared with the hysteresis (32 degrees C) for A reversible arrow 10M. The differential hysteresis levels are rationalized based on a thereto-mechanical formulation. Meso-scale DIC measurements quantify inter-martensite strain levels, which are indistinguishable from macro-scale stress-strain and strain-temperature responses. (C) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:: Dislocation-climb plasticity: Modelling and comparison with the mechanical properties of icosahedral AlPdMn
Authors:: Mompiou, F; Caillard, D Author Full Names: Mompiou, F.; Caillard, D.
Source:: ACTA MATERIALIA 56 (10): 2262-2271 JUN 2008
Abstract:: A model of plasticity controlled by the pure climb motion of dislocations is proposed and compared with the mechanical properties of icosahedral AlPdMn. This model takes into account the chemical stress due to an out-of-equilibrium average concentration of vacancies, and the difficult nucleation of jog-pairs on climbing dislocations. It accounts for several unexplained properties of AlPdMn, namely a high strain-hardening at yield, a steady-state flow stress twice higher than the elastic limit, and two-stage relaxation curves. It also explains values of the stress-strain rate sensitivity larger than expected a priori, and activation energies larger than the self-diffusion one. The model may also be applicable to high-temperature deformation of crystals. (C) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:: Elastic properties of two-dimensional quasicrystals
Authors:: Grimmer, H Author Full Names: Grimmer, Hans
Source:: ACTA CRYSTALLOGRAPHICA SECTION A 64: 459-464 Part 4 JUL 2008
Abstract:: Quasicrystals (QC) with two-dimensional quasiperiodic and one-dimensional periodic structure are considered. Their symmetry can be described by embedding the three-dimensional physical space V-E in a five-dimensional superspace V, which is the direct sum of V-E and a two-dimensional internal space V-I. A displacement v in V can be written as v = u + w, where u is an element of V-E and w is an element of V-I. If the QC has a point group P in V-E that is crystallographic, it is assumed that w and a vector u' is an element of V-E lying in the plane in which the crystal is quasiperiodic transform under equivalent representations of P, inequivalent ones if the point group is 5-, 8-, 10-or 12-gonal. From the Neumann principle follow restrictions on the form of the phonon, phason and phonon-phason coupling contributions to the elastic stiffness matrix that can be determined by combining the restrictions obtained for a set of elements generating the point group of interest. For the phonon part, the restrictions obtained for the generating elements do not depend on the system to which the point group belongs. This remains true for the phason and coupling parts in the case of crystallographic point groups but, in general, breaks down for the non-crystallographic ones. The form of the symmetric 12 x 12 matrix giving the phonon, phason and phonon-phason coupling contributions to the elastic stiffness is presented in graphic notation.
Update: 4-Jul-2008
Title:: Single-crystalline B12As2 on m-plane (1(1)over-bar00) 15R-SiC
Authors:: Chen, H; Wang, G; Dudley, M; Xu, Z; Edgar, JH; Batten, T; Kuball, M; Zhang, LH; Zhu, YM Author Full Names: Chen, Hui; Wang, Guan; Dudley, Michael; Xu, Zhou; Edgar, J. H.; Batten, Tim; Kuball, Martin; Zhang, Lihua; Zhu, Yimei
Source:: APPLIED PHYSICS LETTERS 92 (23): Art. No. 231917 JUN 9 2008
Abstract:: Single crystal, heteroepitaxial growth of icosahedral B12As2 (IBA, a boride semiconductor) on m-plane 15R-SiC is demonstrated. Previous studies of IBA on other substrates, i.e., (111)Si and (0001)6H-SiC, produced polycrystalline and twinned epilayers. In contrast, single-crystalline and untwinned IBA was achieved on m-plane 15R-SiC. Synchrotron white beam x-ray topography, Raman spectroscopy, and high resolution transmission electron microscopy confirm the high quality of the films. High quality growth is shown to be mediated by ordered nucleation of IBA on (474) substrate facets. This work demonstrates that m-plane 15R-SiC is a good substrate choice to grow high-quality untwinned IBA epilayers for future device applications. (C) 2008 American Institute of Physics.
Update: 27-Jun-2008
Title:: Analytical solutions for some defect problems in 1D hexagonal and 2D octagonal quasicrystals
Authors:: Wang, X; Pan, E Author Full Names: Wang, X.; Pan, E.
Source:: PRAMANA-JOURNAL OF PHYSICS 70 (5): 911-933 MAY 2008
Abstract:: We study some typical defect problems in one-dimensional (ID) hexagonal and two-dimensional (2D) octagonal quasicrystals. The first part of this investigation addresses in detail a uniformly moving screw dislocation in a ID hexagonal piezoelectric quasicrystal with point group 6mm. A general solution is derived in terms of two functions phi(1), phi(2), which satisfy wave equations, and another harmonic function phi(3). Elementary expressions for the phonon and phason displacements, strains, stresses, electric potential, electric fields and electric displacements induced by the moving screw dislocation are then arrived at by employing the obtained general solution. The derived solution is verified by comparison with existing solutions. Also obtained in this part of the investigation is the total energy of the moving screw dislocation. The second part of this investigation is devoted to the study of the interaction of a straight dislocation with a semi-infinite crack in an octagonal quasicrystal. Here the crack penetrates through the solid along the period direction and the dislocation line is parallel to the period direction. We first derive a general solution in terms of four analytic functions for plane strain problem in octagonal quasicrystals by means of differential operator theory and the complex variable method. All the phonon and phason displacements and stresses can be expressed in terms of the four analytic functions. Then we derive the exact solution for a straight dislocation near a semi-infinite crack in an octagonal quasicrystal, and also present the phonon and phason stress intensity factors induced by the straight dislocation and remote loads.
Title:: Synthesis and stability of Ti-Zr-Ni quasicrystals
Authors:: Azhazha, VM; Bovda, AM; Lavrinenko, SD; Onischenko, LV; Malykhin, SV; Pugachov, AT; Reshetnyak, MV; Stetsenko, OM; Savitskiy, BA Author Full Names: Azhazha, V. M.; Bovda, A. M.; Lavrinenko, S. D.; Onischenko, L. V.; Malykhin, S. V.; Pugachov, A. T.; Reshetnyak, M. V.; Stetsenko, O. M.; Savitskiy, B. A.
Source:: PROBLEMS OF ATOMIC SCIENCE AND TECHNOLOGY (4): 82-87 2007
Abstract:: For the Ti-Zr-Ni ribbons prepared by melt spinning, phase composition, structure, substructure, state of stress and several physical properties were studied as functions of their element compositions; and optimum parameters for single-phase icosahedral quasicrystal synthesis have been found. The icosahedral structure perfection characteristics, namely quasicrystallinity parameter X-ray coherence length, and average micro-strain values were determined for different synthesis regimes. Transversal gradient-like distributions of grain size, micro-and nano-hardness, Young modulus, residual stress, and substructure parameters have been revealed in the ribbons.
Title:: Modulated magnetic structures of the antiferromagnetic hydride CeRuSiH
Authors:: Tence, S; Andre, G; Gaudin, E; Chevalier, B Author Full Names: Tence, S.; Andre, G.; Gaudin, E.; Chevalier, B.
Source:: JOURNAL OF PHYSICS-CONDENSED MATTER 20 (25): Art. No. 255239 JUN 25 2008
Abstract:: The hydride CeRuSiH is derived from the non-magnetic heavy-fermion ternary silicide CeRuSi that crystallizes in the tetragonal CeFeSi-type structure (P4/nmm space group). This hydride exhibits two antiferromagnetic transitions at T-N1 = 7.5( 2) K and T-N2 = 3.1(2) K, evidenced by magnetization and specific heat measurements. Crystal and magnetic structures of CeRuSiH have thus been investigated by means of neutron powder diffraction, which has shown firstly that H-atoms are fully inserted in the [Ce-4]- tetrahedra. Moreover, between T-N1 and T-N2, the Ce magnetic moments are ordered in a collinear antiferromagnetic sinusoidal structure associated with the propagation vector k = (k(x), k(x), 1/2) (k(x) < 1/3 and tends to 1/3 with decreasing temperature). At T-N2, the magnetic structure becomes square wave modulated and commensurate with k = (1/3, 1/3, 1/2) as propagation vector. At 1.5 K, the structure is antiphase with a Ce magnetic moment of 1.68(2) mu(B). These magnetic structures are compared with those previously reported on the substituted ternary silicides (Ce1-xLax)Ru2Si2 and CeRu2(Si1-xGex)(2), which also present an antiferromagnetic behaviour.
Title:: Designed synthesis of families of misfit-layered compounds
Authors:: Lin, Q; Heideman, CL; Nguyen, N; Zschack, P; Chiritescu, C; Cahill, DG; Johnson, DC Author Full Names: Lin, Qiyin; Heideman, Colby L.; Nguyen, Ngoc; Zschack, Paul; Chiritescu, Catalin; Cahill, David G.; Johnson, David C.
Source:: EUROPEAN JOURNAL OF INORGANIC CHEMISTRY (15): 2382-2385 MAY 2008
Abstract:: The synthesis of several new families of misfit-layered compounds is demonstrated. These compounds are crystalline along the c-axis and in the ab-plane, but show very short coherence lengths between ab-planes. This disorder leads to ultra-low and tunable thermal conductivity. Annealing iso-structural samples under a chalcogen vapour until equilibrium is reached results in reproducible Seebeck and resistivity values. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008).
Title:: Quasicrystal mystery unraveled with computer simulation
Authors:: [Anon]
Source:: ADVANCED MATERIALS & PROCESSES 166 (6): 12-12 JUN 2008
Update: 20-Jun-2008
Title:: DFT studies on structure, mechanics and phase behavior of magnetic shape memory alloys: Ni2MnGa
Authors:: Kart, SO; Uludogan, M; Karaman, I; Cagin, T Author Full Names: Kart, S. Oezdemir; Uludogan, M.; Karaman, I.; Cagin, T.
Source:: PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE 205 (5): 1026-1035 MAY 2008
Abstract:: Magnetic shape memory alloys (MSMAs) are the smart materials which can undergo a reversible structural phase transition when a magnetic field is applied. The experimentally most studied MSMA, Ni2MnGa, undergoes a martensitic phase transition from a high temperature cubic phase to a low temperature tetragonal phase. In this work, a detailed study of structure, magnetic and mechanical properties of Ni2MnGa in these phases were performed using density functional theory (DFT). The predicted lattice constant, bulk modulus, magnetic moments and elastic constants of the initial L2(1) structure are in good agreement with experimental results and previous calculations. We report the martensitic phase at cla = 1.26 for non-modulated and cla = 0.93 for 5M modulated structures which are consistent with the experiments. Analysis of electronic density of states showed that the double minority spin peak appeared at the Fermi level is due to the hybridization of Ga 4p and Ni 3d states. The peaks in the minority spin in the cubic structure reverse their order during martensitic transformation. The elastic constants of martensitic phases were also calculated to encourage measurements of these quantities.
Title:: An effective model of magnetoelectricity in multiferroics RMn2O5
Authors:: Fang, C; Hu, JP Author Full Names: Fang, Chen; Hu, Jangping
Source:: EPL 82 (5): Art. No. 57005 JUN 2008
Abstract:: An effective model is developed to explain the phase diagram and the mechanism of magnetoelectric coupling in multiferroics, RMn2O5. We show that the nature of magnetoelectric coupling in RMn2O5 is a coupling between two Ising-type orders, namely, the ferroelectric order in the b-axis, and the. coupled magnetic order between two frustrated antiferromagnetic chains. The frustrated magnetic structure drives the system to a commensurate-incommensurate phase transition, which can be understood as a competition between a collinear order stemming from the "order by disorder" mechanism and a chiral symmetry order. The low-energy excitation is calculated and it quantitatively matches experimental results. Distinct features and the effects of external magnetic field in the electromagnon spectra in the incommensurate phase are predicted. Copyright (c) EPLA, 2008.
Update: 13-Jun-2008
Title:: Local structure of perovskite-based "Pb2Fe2O5"
Authors:: Hadermann, J; Abakumov, AM; Nikolaev, IV; Antipov, EV; Van Tendeloo, G Author Full Names: Hadermann, Joke; Abakumov, Artem M.; Nikolaev, Ivan V.; Antipov, Evgeny V.; Van Tendeloo, Gustaaf
Source:: SOLID STATE SCIENCES 10 (4): 382-389 APR 2008
Abstract:: The reciprocal lattice and defect structure of the crystallographic shear (CS) structures in perovskite-based "Pb2Fe2O5" are investigated using transmission electron microscopy. The reciprocal space for all observed 1/2[110](h0l)p CS structures can be described with the same average pseudocubic unit cell with a approximate to a(p) (a(p) - the parameter of the perovskite subcell), and modulation vector q approximate to alpha a* + gamma c* with alpha/y = h/l and superspace group X2/m(alpha 0 gamma) with a centering vector [1/2,1/2,1/2,1/2]. The defect structure is characterized by numerous mirror twins and coherent intergrowths of 1/2[110](h0l)p CS structures with different (h0l)p. There are no single CS planes in the perovskite matrix and there is no variation of the perovskite block thickness between the successive CS planes. The crystallographic similarity and the structural and chemical differences between the CS structures in "Pb2Fe2O5" and those in ReO3 and/or TiO2-type oxides are discussed. (C) 2007 Elsevier Masson SAS. All rights reserved.
Title:: Indentation creep study on a Zr-based bulk metallic glass containing nano-quasicrystals
Authors:: Lendvai, J; Fatay, D; Gubicza, J Author Full Names: Lendvai, J.; Fatay, D.; Gubicza, J.
Source:: MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 483: 607-610 Sp. Iss. SI JUN 15 2008
Abstract:: The effect of crystallization on the creep behavior of a Zr-based bulk metallic glass (BMG) with the composition of Zr44Ti11Cu10Ni10B25 (at.%) was studied by indentation technique. The crystallization process was studied by isothermal annealing in a differential scanning calorimeter at three different temperatures above the glass transition temperature (677, 682 and 687 K). Two exothermic peaks are detected, the first one corresponds to the formation of a quasicrystalline phase. Indentation creep tests were carried out isothermally at the same three temperatures for studying the correlation between the amount of quasicrystalline phase and the creep behavior. A simple relationship between the viscosity and the crystalline phase fraction was found and the activation energy was found to decrease with the progress of crystallization. (C) 2007 Elsevier B.V. All rights reserved.
Title:: Model for the transformation of an icosahedral phase into a B2 crystalline phase
Authors:: Kraposhin, VS; Talis, AL; Lam, HT; Dubois, JM Author Full Names: Kraposhin, V. S.; Talis, A. L.; Lam, Ha Thanh; Dubois, J-M
Source:: JOURNAL OF PHYSICS-CONDENSED MATTER 20 (23): Art. No. 235215 JUN 11 2008
Abstract:: A model for the transformation of an Al-Cu-Fe icosahedral quasicrystal into a crystal with a B2-type phase is proposed. The model is based on two assumptions: ( 1) the main building block for the quasicrystal structure is a hierarchical dodecahedron composed of two icosahedral clusters, coinciding with two different sections of the {3, 3, 5} polytope; ( 2) the transformation of the quasicrystal into a B2-type crystal phase can be described as the transition between 3D sections of two polytopes, namely {3, 3, 5} and {3, 4, 3}. In the framework of the proposed model, two experimental facts gain plausible explanations: the transformation of the Al-Cu-Fe quasicrystal into the BCC phase specifically and the orientational relationships observed between this BCC phase and the initial icosahedral quasicrystal.
Title:: Amorphous-to-quasicrystalline transformations in the Ti-Zr-Ni and Ti-Hf-Ni systems
Authors:: Kocjan, A; McGuiness, PJ; Linaric, MR; Kobe, S Author Full Names: Kocjan, A.; McGuiness, P. J.; Linaric, M. Rajic; Kobe, S.
Source:: JOURNAL OF ALLOYS AND COMPOUNDS 457 (1-2): 144-149 JUN 12 2008
Abstract:: We have synthesized Ti-Zr-Ni- and Ti-Hf-Ni-based quasicrystals by the mechanical alloying of elementary powders with an average particle size of 35 mu m in a high-energy planetary ball mill followed by a vacuum heat treatment. The X-ray diffraction (XRD) spectra indicate that the mixture was to a large extent amorphous after mechanically alloying for more than 40 h. These largely amorphous precursors, after various times of mechanical alloying, were subsequently analysed by means of differential scanning calorimetry (DSC) in order to obtain the kinetic parameters of crystallization, such as the temperature and the activation energy. DSC was used in combination with XRD to identify the structural changes related to the peaks in the DSC scans. The morphologies and compositions were analysed using scanning electron microscopy with an energy-dispersive spectrometer. We observed agglomerates ranging in size from 5 to 50 mu m; these agglomerates consisted of smaller particles with sub-micrometer diameters. The composition of the agglomerates was not homogenous, since small areas (similar to 1 mu m) of Zr-rich secondary phase were observed inside them. Using a vibrating-sample magnetometer (VSM) we found that the saturation magnetization decreases with mechanical treatment, and is additionally decreased with the time and temperature of a subsequent vacuum heat treatment. The saturation magnetization (M-s) decreases fairly linearly, from the initial mixture of crystalline elements, which is ferromagnetic due to nickel, through to a largely amorphous phase, and then to the quasicrystalline phase, where the M-s value is the lowest. As a result, measuring the magnetic properties allows us to probe the structural transformations in the material. (C) 2007 Elsevier B.V. All rights reserved.
Title:: Collinear second harmonic generations in a nonlinear photonic quasicrystal
Authors:: Sheng, Y; Koynov, K; Dou, JH; Ma, BQ; Li, JJ; Zhang, DZ Author Full Names: Sheng, Yan; Koynov, Kaloian; Dou, Junhong; Ma, Boqin; Li, Jingjuan; Zhang, Daozhong
Source:: APPLIED PHYSICS LETTERS 92 (20): Art. No. 201113 MAY 19 2008
Abstract:: LiNbO3 nonlinear photonic quasicrystal with octagonal symmetry was fabricated. The collinear quasiphase matched second harmonic generations at 22 wavelengths were observed. It is shown that not only the standard type quasiphase matching but also the recently proposed projection-based quasiphase matching plays an important role in these harmonic generations. (c) 2008 American Institute of Physics.
Update: 6-Jun-2008
Title:: Pseudogap and charge density waves in two dimensions
Authors:: Borisenko, SV; Kordyuk, AA; Yaresko, AN; Zabolotnyy, VB; Inosov, DS; Schuster, R; Buchner, B; Weber, R; Follath, R; Patthey, L; Berger, H Author Full Names: Borisenko, S. V.; Kordyuk, A. A.; Yaresko, A. N.; Zabolotnyy, V. B.; Inosov, D. S.; Schuster, R.; Buechner, B.; Weber, R.; Follath, R.; Patthey, L.; Berger, H.
Source:: PHYSICAL REVIEW LETTERS 100 (19): Art. No. 196402 MAY 16 2008
Abstract:: Using angle-resolved photoemission spectroscopy we demonstrate that a normal-state pseudogap exists above TN-IC in one of the most studied two-dimensional charge-density wave (CDW) dichalcogenides 2H-TaSe2. The initial formation of the incommensurate CDW is confirmed as being driven by a conventional nesting instability, which is marked by a pseudogap. The magnitude, character, and anisotropy of the 2D-CDW pseudogap bear considerable resemblance to those seen in superconducting cuprates.
Title:: Commensurate to incommensurate transition in the chiral helimagnet CuB2O4
Authors:: Fujta, T; Fujimoto, Y; Mitsudo, S; Idehara, T; Saito, T; Kousaka, Y; Yano, SI; Akimitsu, J; Kishine, JI; Inoue, K; Motokawa, M Author Full Names: Fujta, Toshiyuki; Fujimoto, Yoshikuni; Mitsudo, Seitaro; Idehara, Toshitaka; Saito, Teruo; Kousaka, Yusuke; Yano, Shin-ichiro; Akimitsu, Jun; Kishine, Jun-ichiro; Inoue, Katsuya; Motokawa, Mitsuhiro
Source:: JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 77 (5): Art. No. 053702 MAY 2008
Abstract:: We have studied a commensurate to incommensurate transition in the novel helimagnet CuB2O4 by means of high-frequency ESR. In the commensurate weak ferromagnetic (CWF) state, two ESR modes have been found at low temperatures, which are explained in terms of an electron paramagnetic resonance of the Cu2+ spins at 8d-sites and an antiferromagnetic resonance of the magnetically ordered Cu2+ spins at 4b-sites with the Dzyaloshinskii-Moriya (DM) interaction. The DM interaction among the Cu2+ spins at 4b-sites that carries the CWF state is evaluated quantitatively. The incommensurate helimagnetic state is discussed in terms of the magnetic frustration.
Title:: Field-induced incommensurate lattice modulations in the delafossite CuFeO2
Authors:: Terada, N; Mitsuda, S; Tanaka, Y; Tabata, Y; Katsumata, K; Kikkawa, A Author Full Names: Terada, Noriki; Mitsuda, Setsuo; Tanaka, Yoshikazu; Tabata, Yoshikazu; Katsumata, Koichi; Kikkawa, Akiko
Source:: JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 77 (5): Art. No. 054701 MAY 2008
Abstract:: The results of synchrotron X-ray diffraction measurements on a single crystal of the triangular lattice antiferromagnet CuFeO2 under zero and non-zero applied magnetic fields are reported. We find four satellite reflections at (0, 3+q, 1/2), (0,4 -q, 1/2), (0,4 -2q, 0), and (0, 3+2q, 0) with the incommensurate wave number q similar to 0.415 in the ferroelectric incommensurate (FEIC) phase which appears in the magnetic field, H, between 7 and 13 T at low temperatures. In the partially disordered (PD) phase which exists in the temperature, T, range between 11 and 14 K, we find two satellite reflections at (0, 4-q, 1/2) and (0, 4-2q, 0) with the incommensurate wave number q similar to 0.4. The T and H dependence of these satellite reflections are studied. We interpret that the reflections observed in the FEIC phase arise from incommensurate lattice modulations caused by a magnetoelastic coupling with the underlying magnetic structure. The observation of the reflection (0, 4-q, 1/2) in finite fields and the (0, 4-2q, 0) reflection at 0 <= H in the PD phase is also explained by the same model. A calculation of the X-ray diffraction intensity assuming the displacement of oxygen ions only successfully explains the observation. We discuss the relevance of these satellite reflections to the ferroelectricity.
Title:: Optical phonon characteristics of incommensurate and commensurate modulated phases of Bi3NbO7 ceramics
Authors:: Moreira, RL; Matinaga, FM; Pirnat, U; Suvorov, D; Dias, A Author Full Names: Moreira, Roberto L.; Matinaga, Franklin M.; Pirnat, Ursa; Suvorov, Danilo; Dias, Anderson
Source:: JOURNAL OF APPLIED PHYSICS 103 (9): Art. No. 094108 MAY 1 2008
Abstract:: Raman and infrared-reflectivity spectroscopies were used to investigate the optical phonon modes of the cubic-incommensurate and tetragonal-commensurate phases of Bi3NbO7 ceramic samples. For both structures, the observed features could be well described by applying the factor-group method to average oxygen-deficient fluorite subcells; i.e., it was possible to predict the correct number and the activities of the observed phonon modes. The spectra showed rather broad bands, which are mainly for the cubic-incommensurate phase, probably because of the disorder of the oxygen vacancies and the folding of the Brillouin zone due to the modulation of the atomic positions. This can partially explain the higher quality factor and the potential interest in the tetragonal phase of this material for applications in microwave devices. (C) 2008 American Institute of Physics.
Title:: Vacancy-ordering effects in AlB2-type ErGe2-x (0.4 < x <= 0.5)
Authors:: Christensen, J; Lidin, S; Malaman, B; Venturini, G Author Full Names: Christensen, Jeppe; Lidin, Sven; Malaman, Bernard; Venturini, Gerard
Source:: ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 64: 272-280 Part 3 JUN 2008
Abstract:: In the Er-Ge system, the compostion range ErGe2 to Er2Ge3 has been investigated. Eight samples were produced by arc melting of the elements, and analyzed using X-ray powder diffraction. Nine crystal structures were found to be present in the samples. The structures are described as a homologous series and presented within the superspace formalism using the superspace group X2/m(alpha 0 gamma)0s, X representing the centring vector (1/2, 1/2, 0, 1/2). In this description the modulation vector q = (alpha a+gamma c) is shown to be a direct measure of the Ge content as ErGe2-alpha (alpha falls in the range 1/3 to 1/2). The large composition range is achieved by extended vacancy ordering in the planar 6(3) net of Ge with subsequent relaxation.
Update: 30-May-2008
Title:: On the magnetic phase diagram of copper metaborate
Authors:: Popov, MA; Petrakovskii, GA; Bolsunovskaya, OA Author Full Names: Popov, M. A.; Petrakovskii, G. A.; Bolsunovskaya, O. A.
Source:: PHYSICS OF THE SOLID STATE 50 (5): 909-912 MAY 2008
Abstract:: A stepwise transition from one incommensurate state of the spin system of a copper metaborate crystal to another incommensurate state was previously revealed using neutron scattering in an applied magnetic field. In this paper, the new state is interpreted as a combination of a commensurate state of one spin subsystem and an incommensurate state of another spin subsystem of the crystal.
Title:: Plastic fracture of quasicrystals
Authors:: Fan, TY; Fan, L Author Full Names: Fan, T. Y.; Fan, L.
Source:: PHILOSOPHICAL MAGAZINE 88 (4): 523-535 FEB 1 2008
Abstract:: Elasto-plastic crack solutions for some one- and two-dimensional quasicrystals have been found based on the generalized Dugdale-Barenblatt model. The size of the plastic zone and crack tip opening displacement are determined, from which a plastic fracture criterion for the materials is suggested.
Title:: Crystallographic studies on the iron-containing intermetallic phases in the 319-type aluminium casting alloys
Authors:: Hwang, JY; Doty, HW; Kaufman, MJ Author Full Names: Hwang, J. Y.; Doty, H. W.; Kaufman, M. J.
Source:: PHILOSOPHICAL MAGAZINE 88 (4): 607-619 FEB 1 2008
Abstract:: The iron-containing intermetallic compounds in type 319 aluminium casting alloys were investigated using convergent beam electron diffraction (CBED) and electron backscatter diffraction (EBSD). The Chinese script U-phase was identified as having the cubic Im 3 space group consistent with the Al19Fe4MnSi2 phase reported in the literature. However, the atomic ordering of this phase results in complex Kikuchi lines in the CBED and EBSD patterns, which makes phase and orientation identification difficult. In fact, it is shown that the EBSD patterns in the scanning electron microscope and Kikuchi patterns in the transmission electron microscope from this phase are closely related to the structurally similar m (3) over bar (5) over bar icosahedral quasicrystals that form in numerous aluminium-transition metal alloys by both conventional and rapid solidification. The other iron-containing phase in these alloys was determined to be plate shaped and to have the orthorhombic Cmcm space group consistent with the beta-Al5FeSi phase, which has sometimes been confused with having a tetragonal or monoclinic structure. The nature of this structure is such that it frequently grows with a high density of faults that separate equivalent variants; these will be described and related to the previously incorrect interpretations of this being a tetragonal phase.
Title:: Inelastic neutron scattering of a Ti-44 at.%Ni-6 at.%Fe alloy exhibiting an incommensurate-commensurate transition
Authors:: Fukuda, T; Choi, MS; Kakeshita, T; Ohba, T Author Full Names: Fukuda, Takashi; Choi, Mi-Seon; Kakeshita, Tomoyuki; Ohba, Takuya
Source:: MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 481: 235-238 Sp. Iss. SI MAY 25 2008
Abstract:: Inelastic neutron scattering has been made for a Ti-44 at.%Ni-6 at.%Fe alloy which exhibits a second-order like incommensurate-commensurate (IC-C) transformation [M.-S. Choi, T. Fukuda, T. Kakeshita, Philos. Mag. 86 (2006) 67] in order to understand the nature of the transformation. The phonon frequencies of the [zeta zeta 0]-TA(2) phonon branch near zeta = 1/3 decrease as temperature decreases, exhibit the lowest value at about 200 K and then increase on further cooling. This temperature (200 K) is near the temperature below which diffuse incommensurate scattering can be noticed, and it is by 20 K higher than the IC-C transition temperature. Presumably, the phonon softening is responsible for the formation of the incommensurate state, but not directly connected to the formation of the commensurate state. (C) 2007 Elsevier B.V. All rights reserved.
Title:: Observation of phonon softening in a Ti-Ni-Fe alloy by inelastic X-ray scattering
Authors:: Ohba, T; Kitanosono, D; Morito, S; Fukuda, T; Kakeshita, T; Baron, AQR; Tsutsui, S Author Full Names: Ohba, T.; Kitanosono, D.; Morito, Shigekazu; Fukuda, T.; Kakeshita, T.; Baron, A. Q. R.; Tsutsui, Santoshi
Source:: MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 481: 254-257 Sp. Iss. SI MAY 25 2008
Abstract:: Phonon softening of the martensitic transformation, which is a typical first-order transformation, is an interesting concept in connection with the transformation mechanism. Recently, Kakeshita and his group studied a wide range of Fe-substituted Ti-Ni alloys [Ti-(50 - x)Ni-xFe, at.%] and reported anomalies in electrical resistivity, magnetic susceptibility and specific heat. Furthermore, they observed electron diffraction patterns and reported second-order-like features in a Ti-44Ni-6Fe alloy with an incommensurate-commensurate phase transformation prior to the transformation to the R phase. Inelastic X-ray scattering experiments were performed in order to observe the phonon behavior in Ti-44Ni-6Fe. Since the energy of phonons is about six orders of magnitude lower than that of X-rays, precise experiments are necessary to observe phonons by X-ray inelastic scattering experiments. The beam-line BL35XU at the synchrotron radiation facility, SPring-8 was utilized f! or the experiments. [zeta zeta 0]TA(2) phonon modes were measured at various temperatures. The temperature at which the softest phonon is observed is at approximately 180 K, corresponding to the incommensurate-commensurate transformation temperature. Possible differences between results of neutron inelastic scattering and X-ray inelastic scattering experiments will be discussed in the text. (C) 2007 Elsevier B.V. All rights reserved.
Title:: Temperature dependence of the damping properties of Ni-Mn-Ga alloys
Authors:: Aaltio, I; Lahelin, M; Soderberg, O; Heczko, O; Lofgren, B; Ge, Y; Seppala, J; Hannula, SP Author Full Names: Aaltio, I.; Lahelin, M.; Soderberg, O.; Heczko, O.; Lofgren, B.; Ge, Y.; Seppala, J.; Hannula, S. -P.
Source:: MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 481: 314-317 Sp. Iss. SI MAY 25 2008
Abstract:: Single-crystalline 5M (exhibiting magnetic shape memory effect) and non-modulated martensitic Ni-Mn-Ga alloys were studied by dynamic mechanical analysis (DMA) at different temperatures. The chemical compositions of the alloys were determined using energy-dispersive X-ray spectrometry in a scanning electron microscope. The crystal structures were confirmed with X-ray diffraction and the transformation temperatures were measured. DMA measurements showed that the mechanical modulus (stiffness) and damping capacity increased during heating and a clear peak of the loss angle, was detected which is related to the reverse phase transformation of martensite to austenite. During cooling, there is a corresponding peak related to the martensite reaction. Significant decrease of the damping capacity occurs during transformation to austenite. Enhanced damping in the martensitic phase can be attributed to the mobility of twin boundaries. (C) 2007 Elsevier B.V. All rights reserved.
Title:: Competing multiple-q magnetic structures in HoGe3: II. Magnetic structures observed in HoGe3
Authors:: Schobinger-Papamantellos, P; Rodriguez-Carvajal, J; Tung, LD; Ritter, C; Buschow, KHJ Author Full Names: Schobinger-Papamantellos, P.; Rodriguez-Carvajal, J.; Tung, L. D.; Ritter, C.; Buschow, K. H. J.
Source:: JOURNAL OF PHYSICS-CONDENSED MATTER 20 (19): Art. No. 195202 MAY 14 2008
Abstract:: The high temperature (HT) and the low temperature (LT) multiple-q vector magnetic structures of the antiferromagnetic HoGe3 compound (T-N = 11 K) are derived from refinements of high resolution neutron data in terms of Fourier analysis. Various models are discussed. Over the HT range T-2 -> T-N, T-2 = 8.1 K (on heating), the magnetic phase is described with the wavevectors (q(1), q(2)) where q(1) = (q(1x), 0, 0) and q(2) = (q(2x), 0, q(2z)), q(1x) = q(2x) approximate to 1 2 and q(2z) approximate to 1 3, with T dependent length. It corresponds to an amplitude modulated magnetic phase with the moments at an angle of 24 degrees (2) with the c axis within the plane (b, c). Surprisingly this structure does not square up to a constant moment structure with q1 = (1 2, 0, 0) and q2 = (1/2, 0, 1/3) or alternatively (2a, b, 3c). Instead of locking, the q(2) vector jumps at T-2 via a first-order transition to a long period structure with an almost 24-times larger cell approximate to (2a, 4b, 3c), or in terms of wavevectors to q(3) = (1/2, q(3y), 0) and q(4) = (1/2, q(4y), 1/3), which dominates the (LT) range 1.6 K -> T-2. The (LT) range subdivides into the lock-in LT1 range 1.6 K -> T-3 (T-3 = 4.8 K on heating) where the q(3y) = q(4y) = 1/4 components have a constant length and the LT2 range T-3 -> T-2 where q(3y) and q(4y) have a length variable with T. In the intermediate temperature range, around the first-order T-2 transition (on heating or cooling), the two structures described with the wavevectors (q(1), q(2)) and (q(3), q(4)) coexist in varying proportions. The most probable LT magnetic structure corresponds to a complex monoclinic multiaxial canted structure with four independent Ho sites as a result of geometric frustration related to the underlying trigonal prism arrangement of the magnetic atoms with antiferromagnetic interactions.
Title:: Protein crystals can be incommensurately modulated
Authors:: Lovelace, JJ; Murphy, CR; Daniels, L; Narayan, K; Schutt, CE; Lindberg, U; Svensson, C; Borgstahl, GEO Author Full Names: Lovelace, Jeffrey J.; Murphy, Cameron R.; Daniels, Lee; Narayan, Kartik; Schutt, Clarence E.; Lindberg, Uno; Svensson, Christer; Borgstahl, Gloria E. O.
Source:: JOURNAL OF APPLIED CRYSTALLOGRAPHY 41: 600-605 Part 3 JUN 2008
Abstract:: For a normal periodic crystal, the X-ray diffraction pattern can be described by an orientation matrix and a set of three integers that indicate the reciprocal lattice points. Those integers determine the spacing along the reciprocal lattice directions. In aperiodic crystals, the diffraction pattern is modulated and the standard periodic main reflections are surrounded by satellite reflections. The successful indexing and refinement of the main unit cell and q vector using TWINSOLVE, developed by Svensson [(2003). Lund University, Sweden], are reported here for an incommensurately modulated, aperiodic crysta

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