Update: 29-Dec-2011

Title:
Microscopically derived Ginzburg-Landau theory for magnetic order in the iron pnictides
Authors:
Brydon, PMR; Schmiedt, J; Timm, C Author Full Names: Brydon, P. M. R.; Schmiedt, Jacob; Timm, Carsten
Source:
PHYSICAL REVIEW B, 84 (21):10.1103/PhysRevB.84.214510 DEC 7 2011
Abstract:
We examine the competition of the observed stripe spin density wave (SDW) with other commensurate and incommensurate SDW phases in a two-band model of the pnictides. Starting from this microscopic model, we rigorously derive an expansion of the free energy in terms of the different order parameters at the mean-field level. We show that three distinct commensurate SDW states are possible and study their appearance as a function of the doping and the electronic structure. We show that the stripe phase is generally present, but its extent in the phase diagram depends strongly upon the number of hole Fermi pockets that are nested with the electron Fermi pockets. Electron pockets competing for the same portion of a hole pocket play a crucial role. We discuss the relevance of our results for the antiferromagnetism of the pnictides.
Title:
(57)Fe Mossbauer spectroscopy studies of CaFe(4)As(3)
Authors:
Nowik, I; Felner, I; Karki, AB; Jin, R Author Full Names: Nowik, I.; Felner, I.; Karki, A. B.; Jin, R.
Source:
PHYSICAL REVIEW B, 84 (21):10.1103/PhysRevB.84.212402 DEC 7 2011
Abstract:
We report on the (57)Fe Mossbauer spectroscopy and direct-current magnetization studies of orthorhombic CaFe(4)As(3), which undergoes two magnetic transitions with the formation of spin density wave at T(N1) = 88 K (incommensurate) and T(N2) = 26 K (commensurate). The magnetic Mossbauer spectroscopy spectra below T(N1) are composed of four subspectra attributed to the four in-equivalent Fe crystallographic sites: three Fe ions in the divalent state (Fe(2+)) and one as Fe(1+). However, the magnetic lines are much broader than that below T(N2), indicating an incommensurate magnetic state. In the paramagnetic state, the Mossbauer spectroscopy spectra are composed of three doublets; one of them is related to Fe(1+). Evidence for spin fluctuations above T(N1) is observed.
Title:
Atomic dynamics and interatomic interaction in quasicrystals
Authors:
Parshin, PP; Zemlyanov, MG; Brand, RA Author Full Names: Parshin, P. P.; Zemlyanov, M. G.; Brand, R. A.
Source:
CRYSTALLOGRAPHY REPORTS, 56 (7):1145-1148; 10.1134/S1063774511070285 DEC 2011
Abstract:
The previous experimental data on the partial spectra of thermal atomic vibrations in icosahedral (Al(62)Cu(25.5)Fe(12.5)) and decagonal (Al(71.3)Ni(24)Fe(4.7)) quasicrystals have been used to perform a comparative analysis of the atomic dynamics features and determine the role that Al, Cu, Ni, and Fe atoms play in the formation of interatomic interaction in the alloys studied. A physical model of the decagonal quasicrystal structure is proposed.
Title:
Atomic packing and short-to-medium range order evolution of Zr-Pd metallic glass
Authors:
Qi, L; Liu, M; Zhang, SL; Zhang, XY; Tan, CL Author Full Names: Qi Li; Liu Mei; Zhang ShiLiang; Zhang XinYu; Tan ChunLin
Source:
CHINESE SCIENCE BULLETIN, 56 (36):3908-3911; 10.1007/s11434-011-4841-0 DEC 2011
Abstract:
A larger-scale Zr(70)Pd(30) alloy system has been simulated using molecular dynamics (MD) to investigate structure evolution in Zr(70)Pd(30) metallic glass. The simulated pair distribution function of Zr(70)Pd(30) metallic glass agrees well with the experimental results. Voronoi polyhedron analysis indicates that the icosahedra are not randomly distributed in space, but form characteristic intercrossed icosahedral clusters with medium-range order. Intercrossed icosahedral clusters are the dominant local configurations in Zr(70)Pd(30) metallic glass and probably cause the quasicrystalline phase discovered in Zr(70)Pd(30) metallic glass.
Title:
Highly mobile twinned interface in 10 M modulated Ni-Mn-Ga martensite: Analysis beyond the tetragonal approximation of lattice
Authors:
Straka, L; Heczko, O; Seiner, H; Lanska, N; Drahokoupil, J; Soroka, A; Fahler, S; Hanninen, H; Sozinov, A Author Full Names: Straka, L.; Heczko, O.; Seiner, H.; Lanska, N.; Drahokoupil, J.; Soroka, A.; Faehler, S.; Hanninen, H.; Sozinov, A.
Source:
ACTA MATERIALIA, 59 (20):7450-7463; 10.1016/j.actamat.2011.09.020 DEC 2011
Abstract:
The huge strains that Ni-Mn-Ga magnetic shape memory alloys can achieve are usually described in a tetragonal unit cell approximation of a five-layered modulated (10 M) crystal structure. Here we analyze the impact of a slight orthorhombic and monoclinic distortion of the 10 M structure in Ni(50.2)Mn(28.3)Ga(21.5)at(.%) single crystal. Combining dedicated experiments to probe the microstructure, structure and mechanical properties with calculation using elastic continuum theory, we prove the existence of fine a/b-laminates within modulation macrotwins of the order of 100 micrometers in size. This complex twin microstructure containing a Type II macrotwin interface is associated with an extraordinarily low twinning stress of between 0.05 and 0.3 MPa, while Type I twins exhibit twinning stress of about 1 MPa. The findings provide important guidelines for designing the martensitic microstructure for more efficient actuators. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Phase evolution and magnetic property of Bi(1-x)Ho(x)FeO(3) powders
Authors:
Wu, YJ; Zhang, J; Chen, XK; Chen, XJ Author Full Names: Wu, Yu-Jie; Zhang, Jing; Chen, Xiao-Kun; Chen, Xiao-Jia
Source:
SOLID STATE COMMUNICATIONS, 151 (24):1936-1940; 10.1016/j.ssc.2011.09.020 DEC 2011
Abstract:
The structural, vibrational, and magnetic properties of well prepared Bi(1-x)Ho(x)FeO(3) (x = 0-0.175) powders are investigated by combining X-ray diffraction, Raman scattering, and magnetometry measurements. A structural symmetry breaking from the rhombohedral R3c to orthorhombic Pnma between x = 0.10 and 0.125 is identified from the X-ray and Raman measurements, accompanying a ferroelectric-paraelectric phase transition. The remnant magnetization of Bi(1-x)Ho(x)FeO(3) is enhanced before approaching the ferroelectric-paraelectric phase boundary, and then it slightly decreases until x = 0.175. Such enhancement (0 <= x <= 0.10) is suggested to result from the destruction of the spin cycloid structure. The decrease in the remnant magnetization with higher substitution concentration is due to the further destruction in the space modulated spin structure allowing a more perfect antiferromagnetic ordering. (C) 2011 Elsevier Ltd. All rights reserved.
Title:
Incommensurate Antiferromagnetic Insulating State in (MDT-TS)(AuI(2))(x)
Authors:
Yoshioka, H; Seo, H; Otsuka, Y Author Full Names: Yoshioka, Hideo; Seo, Hitoshi; Otsuka, Yuichi
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 80 (12):10.1143/JPSJ.80.123702 DEC 2011
Abstract:
We theoretically study the metal-insulator transition in a molecular conductor (MDT-TS)(AuI(2))(x) composed with an incommensurate ratio (x = 0.441), where the conduction band originated from the HOMO of donor MDT-TS molecules is incommensurately filled. We consider a two-dimensional Hubbard model taking account of anisotropic transfer integrals in the donor layer, under a periodic potential due to the anions (AuI(2))(-) which mismatches the donor lattice period, and investigate the ground state within mean-field approximation. An antiferromagnetic insulating state with induced charge disproportionation is obtained in the large U and delta region; the symmetry in the charge sector is unchanged from the paramagnetic metallic state realized at small U and delta, therefore this state corresponds to the incommensurate Mott insulating state predicted previously [H. Yoshioka et al.: J. Phys. Soc. Jpn. 74 (2005) 1922] based on a simplified one-dimensional model.
Title:
Complex magnetoelastic properties in the frustrated kagome-staircase compounds (Co(1-x)Ni(x))(3)V(2)O(8)
Authors:
Zhang, Q; Knafo, W; Adelmann, P; Schweiss, P; Grube, K; Qureshi, N; Wolf, T; von Lohneysen, HV; Meingast, C Author Full Names: Zhang, Q.; Knafo, W.; Adelmann, P.; Schweiss, P.; Grube, K.; Qureshi, N.; Wolf, Th.; v. Loehneysen, H.; Meingast, C.
Source:
PHYSICAL REVIEW B, 84 (18):10.1103/PhysRevB.84.184429 NOV 28 2011
Abstract:
High-resolution heat-capacity and thermal-expansion measurements on single crystals of the kagome-staircase compounds (Co(1-x)Ni(x))(3)V(2)O(8) are presented. The parent compounds Co(3)V(2)O(8) and Ni(3)V(2)O(8) undergo a sequence of first-and second-order magnetic phase transitions. The low-temperature (T <= 40 K) magnetic entropy evolves monotonically with the doping content x from the full value expected for Ni(2+) S = 1 magnetic moments in Ni(3)V(2)O(8) to only half the value expected for Co(2+) S = 3/2 moments in Co(3)V(2)O(8). The thermal-expansion coefficients alpha(i) (i = a, b, and c) show a strong anisotropy for all (Co(1-x)Ni(x))(3)V(2)O(8) compounds. The low temperature expansivities indicate that Co doping (Ni doping) yields changes similar to uniaxial pressures along a or b (c). Linear Gruneisen parameters Gamma(i) are extracted for the three main axes i and are found to exhibit a complex temperature and doping dependence. For each axis, Gamma(i) and alpha(i) exhibit a sign change at low temperature at the critical concentration x(c) similar or equal to 0.25 where the incommensurate magnetic propagation vector changes. Our study motivates further investigations to understand how the multiple and complex parameters such as magnetic frustration, magnetic anisotropy, and mixture of S = 1 and 3/2 ions affect the rich magnetoelastic properties of (Co(1-x)Ni(x))(3)V(2)O(8).
Title:
Investigation of the Formation of Quasicrystalline Al(70)-Pd(20)-Re(10) Phase in situ during Annealing
Authors:
Makhotkin, IA; Yakunin, SN; Seregin, AY; Shaitur, DS; Tsetlin, MB; Tereshchenko, EY Author Full Names: Makhotkin, I. A.; Yakunin, S. N.; Seregin, A. Yu.; Shaitur, D. S.; Tsetlin, M. B.; Tereshchenko, E. Yu.
Source:
CRYSTALLOGRAPHY REPORTS, 56 (5):871-874; 10.1134/S106377451105018X SEP 2011
Abstract:
The change in the phase composition of thin-film layered AlPdRe nanostructures during annealing, which led to the formation of a quasicrystalline layer, has been studied in situ. It is shown that the Al(3)Pd phase is formed at a temperature above 260 degrees C, which transforms into the AlPd phase at 580 degrees C, and the icosahedral quasicrystalline Al-Pd-Re phase is formed at 680 degrees C. DOI: 10.1134/S106377451105018X

Update: 22-Dec-2011

Title:
Determination of the orientation relationship between austenite and 5M modulated martensite in Ni-Mn-Ga alloys
Authors:
Li, ZB; Zhang, YD; Esling, C; Zhao, X; Zuo, L Author Full Names: Li, Zongbin; Zhang, Yudong; Esling, Claude; Zhao, Xiang; Zuo, Liang
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY, 44 1222-1226; Part 6 10.1107/S0021889811043366 DEC 2011
Abstract:
The microstructural and crystallographic characteristics of 5M martensite in an Ni(50)Mn(28)Ga(22) alloy were investigated by electron backscatter diffraction (EBSD) analysis. The microstructure of 5M martensite observed at room temperature can be characterized by broad plates with alternately distributed fine lamellae (variants). With the accurate EBSD orientation measurements and by application of monoclinic superstructure information, four twin-related variants in one broad plate were identified. On the basis of the correct orientation data of martensite variants acquired from the EBSD measurements, the more favourable orientation relationship between austenite and 5M martensite was revealed to be the Pitsch relation with (101)(A)//(1 (2) over bar(5) over bar)(5M) and [10 (1) over bar](A)//[(5) over bar(5) over bar1](5M) by detailed crystallographic calculation without residual austenite.
Title:
Mossbauer investigations of crystalline and quasicrystalline Al(3)(Mn, Fe) compounds
Authors:
Ali, K; Reissner, M; Steiner, W; Feuerbacher, M Author Full Names: Ali, K.; Reissner, M.; Steiner, W.; Feuerbacher, M.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 23 (47):10.1088/0953-8984/23/47/475501 NOV 30 2011
Abstract:
(57)Fe Mossbauer and magnetic measurements are reported on Taylor phase compounds T-Al(3)(Mn, Fe), which can be seen as complex metallic alloys. The orthorhombic unit cell contains 156 atoms. These investigations are further extended to Al(71)Mn(19)Fe(10) crystallizing as a decagonal quasicrystal. Common to both structures are layers, which are oriented perpendicular to the b axis in the crystalline or to the periodic axis in the quasicrystalline compound, allowing the formation of characteristic building blocks. At low temperatures for all samples spin glass behavior is observed with freezing temperatures T(f) increasing with Fe content. Above T(f) the (57)Fe Mossbauer spectra were analyzed by a superposition of two subspectra with intensity ratio around 75: 25, which can be allocated to Fe substituted on Mn sites surrounded either by Al and Mn or solely by Al with Mn only at the edge of the nearest neighbor shell. For both subspectra quadrupole splitting and center shift do not change significantly with Fe content and with structure. Below T(f) broad hyperfine field distributions with non-vanishing contributions at zero hyperfine field are present. Magnetic and electrostatic hyperfine interactions are governed by length scales which are determined by the very similar interatomic configurations forming the T-Al(3)Mn phase as well as the decagonal compound. The presence of long range atomic order is of less importance.
Title:
Coexistence of the long-range and short-range magnetic order components in SrEr(2)O(4)
Authors:
Hayes, TJ; Balakrishnan, G; Deen, PP; Manuel, P; Chapon, LC; Petrenko, OA Author Full Names: Hayes, T. J.; Balakrishnan, G.; Deen, P. P.; Manuel, P.; Chapon, L. C.; Petrenko, O. A.
Source:
PHYSICAL REVIEW B, 84 (17):10.1103/PhysRevB.84.174435 NOV 23 2011
Abstract:
Single-crystal neutron diffraction reveals two distinct components to the magnetic ordering in geometrically frustrated SrEr(2)O(4). One component is a long-range ordered k = 0 structure which appears below T(N) = 0.75 K. Another component is a short-range incommensurate structure which manifests itself by the presence of a strong diffuse scattering signal. On cooling from higher temperatures down to 0.06 K, the partially ordered component does not undergo a pronounced phase transition. The magnetic moments in the long-range commensurate and short-range incommensurate structures are predominantly pointing along the [001] and [100] axes, respectively. The unusual coexistence of two magnetic structures is probed using both unpolarized and XYZ-polarized neutron scattering techniques. The observed diffuse scattering pattern can be satisfactorily reproduced with a classical Monte Carlo simulation by using a simple model based on a ladder of triangles.

Update: 7-Dec-2011

Title:
Successive magnetic transitions and static magnetic order in RCoAsO (R = La, Ce, Pr, Nd, Sm, Gd) confirmed by muon-spin rotation and relaxation
Authors:
Sugiyama, J; Mansson, M; Ofer, O; Kamazawa, K; Harada, M; Andreica, D; Amato, A; Brewer, JH; Ansaldo, EJ; Ohta, H; Michioka, C; Yoshimura, K Author Full Names: Sugiyama, Jun; Mansson, Martin; Ofer, Oren; Kamazawa, Kazuya; Harada, Masashi; Andreica, Daniel; Amato, Alex; Brewer, Jess H.; Ansaldo, Eduardo J.; Ohta, Hiroto; Michioka, Chishiro; Yoshimura, Kazuyoshi
Source:
PHYSICAL REVIEW B 84 (18): 10.1103/PhysRevB.84.184421 NOV 16 2011
Abstract:
The presence of antiferromagnetic (AF) order seems to be a common feature for the parent compounds of cuprate as well as some pnictide high-temperature superconductors. In order to search for antiferromagnetic order in the closely related rare-earth cobalt arsenic oxides (RCoAsO), we have measured muon-spin rotation and relaxation (mu(+)SR) spectra on a series of powder samples with R = La, Ce, Pr, Nd, Sm, and Gd. It was found that, besides GdCoAsO, all the other five compounds enter into a static ferromagnetic ordered phase below around 70 K (=T(C)), while additional transitions into a static AF ordered phase were found for NdCoAsO and SmCoAsO. For GdCoAsO, a static ferrimagnetic phase appeared below 60.5 K and then an incommensurate spin-density-wave ordered phase followed below 3.2 K. The AF spin structure was also found to strongly depend on R.
Title:
Degenerate Quasicrystal of Hard Triangular Bipyramids
Authors:
Haji-Akbari, A; Engel, M; Glotzer, SC Author Full Names: Haji-Akbari, Amir; Engel, Michael; Glotzer, Sharon C.
Source:
PHYSICAL REVIEW LETTERS 107 (21): 10.1103/PhysRevLett.107.215702 NOV 15 2011
Abstract:
We report a degenerate quasicrystal in Monte Carlo simulations of hard triangular bipyramids each composed of two regular tetrahedra sharing a single face. The dodecagonal quasicrystal is similar to that recently reported for hard tetrahedra [Haji-Akbari et al., Nature (London) 462, 773 (2009)] but degenerate in the pairing of tetrahedra, and self-assembles at packing fractions above 54%. This notion of degeneracy differs from the degeneracy of a quasiperiodic random tiling arising through phason flips. Free energy calculations show that a triclinic crystal is preferred at high packing fractions.
Title:
Low-temperature structure of xi '-Al-Pd-Mn optimized by ab initio methods
Authors:
Frigan, B; Santana, A; Engel, M; Schopf, D; Trebin, HR; Mihalkovic, M Author Full Names: Frigan, Benjamin; Santana, Alejandro; Engel, Michael; Schopf, Daniel; Trebin, Hans-Rainer; Mihalkovic, Marek
Source:
PHYSICAL REVIEW B 84 (18): 10.1103/PhysRevB.84.184203 NOV 14 2011
Abstract:
We have studied and resolved occupancy correlations in the existing average structure model of the complex metallic alloy xi'-Al-Pd-Mn [Boudard et al., Philos. Mag. A 74, 939 (1996)], which has approximately 320 atoms in the unit cell and many fractionally occupied sites. Model variants were constructed systematically in a tiling-decoration approach and subjected to simulated annealing by use of both density functional theory and molecular dynamics with empirical potentials. To obtain a measure for thermodynamic stability, we reproduce the Al-Pd-Mn phase diagram at T = 0 K, and derive an enthalpy of formation for each structure. Our optimal structure resolves a cloud of fractionally occupied sites in pseudo-Mackay clusters. In particular, we demonstrate the presence of rotational degrees of freedom of an Al(9) inner shell, which is caged within two icosahedrally symmetric outer shells Al(30) and Pd(12). Outside these clusters, the chemical ordering on a chain of three nearby sites surprisingly breaks the inversion symmetry of the surrounding structure, and couples to an Al/vacancy site nearby. Our refined tiling-decoration model applies to any structure within the epsilon-phases family, including the metastable decagonal quasicrystalline phase.
Title:
Order in a spatially anisotropic triangular antiferromagnet
Authors:
Ghamari, S; Kallin, C; Lee, SS; Sorensen, ES Author Full Names: Ghamari, Sedigh; Kallin, Catherine; Lee, Sung-Sik; Sorensen, Erik S.
Source:
PHYSICAL REVIEW B 84 (17): 10.1103/PhysRevB.84.174415 NOV 14 2011
Abstract:
The phase diagram of the spin-1/2 Heisenberg antiferromagnet on an anisotropic triangular lattice of weakly coupled chains, a model relevant to Cs(2)CuCl(4), is investigated using a renormalization group analysis, which includes marginal couplings important for connecting to numerical studies of this model. In particular, the relative stability of incommensurate spiral spin-density order and collinear antiferromagnetic order is studied. While incommensurate spiral order is found to exist over most of the phase diagram in the presence of a Dzyaloshinskii-Moriya (DM) interaction, at small interchain and extremely weak DM couplings, collinear antiferromagnetic order can survive. Our results imply that Cs(2)CuCl(4) is well within the part of the phase diagram where spiral order is stable. The implications of the renormalization group analysis for numerical studies, many of which have found spin-liquidlike behavior, are discussed.
Title:
Mixed Acoustic Phonons and Phase Modes in an Aperiodic Composite Crystal
Authors:
Toudic, B; Lefort, R; Ecolivet, C; Guerin, L; Currat, R; Bourges, P; Breczewski, T Author Full Names: Toudic, B.; Lefort, R.; Ecolivet, C.; Guerin, L.; Currat, R.; Bourges, P.; Breczewski, T.
Source:
PHYSICAL REVIEW LETTERS 107 (20): 10.1103/PhysRevLett.107.205502 NOV 9 2011
Abstract:
Aperiodic crystals which are long range ordered materials present original dynamics features due to the lack of translational symmetry formally implying the nonvalidity of the Brillouin zone concept. This Letter reports the observation by neutron scattering of an overdamped acousticlike mode at a Bragg peak position in a n-alkane-urea inclusion crystal. This result implies the existence of a gap in the dispersion branch. The gap and anomalous damping of these collective modes are discussed in terms of specific dynamics and interaction in aperiodic materials.
Title:
Comment on "Origin of Friction Anisotropy on a Quasicrystal Surface" Reply
Authors:
Filippov, AE; Vanossi, A; Urbakh, M Author Full Names: Filippov, Aleksander E.; Vanossi, Andrea; Urbakh, Michael
Source:
PHYSICAL REVIEW LETTERS 107 (20): 10.1103/PhysRevLett.107.209402 NOV 8 2011
Title:
Comment on "Origin of Friction Anisotropy on a Quasicrystal Surface"
Authors:
McLaughlin, K; Rabson, D; Thiel, P Author Full Names: McLaughlin, K.; Rabson, D.; Thiel, P.
Source:
PHYSICAL REVIEW LETTERS 107 (20): 10.1103/PhysRevLett.107.209401 NOV 8 2011
Title:
Magnetic Structures of Pr(0.8)Lu(0.2)Mn(2)Ge(2) and Pr(0.6)Lu(0.4)Mn(2)Ge(2)
Authors:
Wang, JL; Studer, AJ; Campbell, SJ; Kennedy, SJ; Zeng, R; Dou, SX; Wu, GH Author Full Names: Wang, J. L.; Studer, A. J.; Campbell, S. J.; Kennedy, S. J.; Zeng, R.; Dou, S. X.; Wu, G. H.
Source:
IEEE TRANSACTIONS ON MAGNETICS 47 (10): 2893-2896 10.1109/TMAG.2011.2151180 OCT 2011
Abstract:
The magnetic structures of Pr(0.8)Lu(0.2)Mn(2)Ge(2) and Pr(0.6)Lu(0.4)Mn(2)Ge(2) have been determined by neutron powder diffraction over the temperature range 10-450 K. On cooling from the paramagnetic region the Mn sublattice of Pr(0.8)Lu(0.2)Mn(2)Ge(2) orders in a similar manner to PrMn(2)Ge(2) with first ab-plane intralayer antiferromagnetism (AFI) below T(N)(intra) similar to 397 K followed by canted ferromagnetism (Fmc) at T(C)(inter) similar to 330 K and then a conical (Fmi) spin structure below T(c/c) similar to 192 K. The transition at T(C)(Pr) = 35 K with related enhancement in magnetization, is assigned to the additional ferromagnetic contribution of the Pr sublattice leading to the combined (Fmc+F(Pr)). For Pr(0.6)Lu(0.4)Mn(2)Ge(2) the transition from PM to AFI occurs at T(N)(intra) similar to 375 K while the canted ferromagnetic (Fmc) state forms at T(C)(intra) similar to 321 K. The increased Lu concentration of Pr(0.6)Lu(0.4)Mn(2)Ge(2) destroys the incommensurate Fmi conical spin structure of Pr(0.8)Lu(0.4)Mn(2)Ge(2). Rather, in common with similar mixed RT(2)X(2) systems (e.g., La(1-x)Y(x)Mn(2)Si(2), La(1-x)Pr(x)Mn(2)Si(2)), the Pr(0.6)Lu(0.4)Mn(2)Ge(2) compound exhibits co-existence of the AFmc and Fmc phases on cooling from the pure Fmc state. Transformation to the combined ferromagnetic state (Fmc+F(Pr)) takes place on c-axis ordering of the Pr sublattice at T(C)(Pr) similar to 31 K. In the region of phase co-existence, the Fmc unit cell is larger than the AFmc unit cell indicating strong magneto-structural coupling with a change of the lattice inducing a change of the magnetic state.
Title:
Three-dimensional reconstruction of the atomic arrangement of icosahedral quasicrystals by binary discrete tomography
Authors:
Ishibashi, Y; Sugiura, H; Saitoh, K; Tanaka, N Author Full Names: Ishibashi, Y.; Sugiura, H.; Saitoh, K.; Tanaka, N.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2519-2527 SI 10.1080/14786435.2010.523717 2011
Abstract:
A three-dimensional reconstruction of the structure of icosahedral quasicrystals from high-resolution transmission electron microscope images observed along high-symmetry zone-axis projections is studied. As in discrete tomography, the quasicrystalline structure is treated as a discrete set of atoms arranged on the icosahedral lattice, including atom flip sites, which is a structural disorder originating from the degrees of freedom in the internal space. The occupancy of the atoms on each site of the lattice is determined using only the zone-axis projection images without any knowledge of the image intensity. Simulation studies using icosahedral model lattices composed of several thousands of atoms were carried out to test the present reconstruction method. In the case of the ideal icosahedral lattice, a reconstruction rate of 90% is achieved from 10 projection images and a reconstruction rate of 99% is achieved from 18 projections. The reconstruction rate degrades when the projection images are misaligned. Reconstruction of the three-dimensional distribution of the atom flips is discussed.

Update: 30-Nov-2011

Title:
Double-k phase of the Dzyaloshinskii-Moriya helimagnet Ba(2)CuGe(2)O(7)
Authors:
Muhlbauer, S; Gvasaliya, SN; Pomjakushina, E; Zheludev, A Author Full Names: Muehlbauer, S.; Gvasaliya, S. N.; Pomjakushina, E.; Zheludev, A.
Source:
PHYSICAL REVIEW B 84 (18): 10.1103/PhysRevB.84.180406 NOV 10 2011
Abstract:
Neutron diffraction is used to reinvestigate the magnetic phase diagram of the noncentrosymmetric tetragonal antiferromagnet Ba(2)CuGe(2)O(7). An incommensurate double-k magnetic phase is detected near the commensurate-incommensurate phase transition. This phase is stable only for field closely aligned with the fourfold symmetry axis. The results emphasize the inadequacy of existing theoretical models for this unique material, and points to additional terms in the Hamiltonian or lattice effects.
Title:
Conductivity of icosahedral AlPdRe
Authors:
Rapp, O; Poon, SJ Author Full Names: Rapp, O.; Poon, S. J.
Source:
PHYSICAL REVIEW B 84 (17): 10.1103/PhysRevB.84.174206 NOV 10 2011
Abstract:
The electrical conductivity sigma(T) of icosahedral (i) AlPdRe has been studied in order to address current problems and controversies. Two new approaches are presented. The temperature T(0) below which variable range hopping occurs was estimated directly from d sigma(T)/dT, avoiding the problem of the finite sigma(0) in i-AlPdRe. Secondly, sigma(T) is compared in detail for samples with radically different defects and morphologies. The temperature dependence of sigma(T) is found to be independent of these varying sample conditions. This finding rules out some proposed conduction mechanisms.
Title:
Symmetry and magnetic field driven transitions in the 2D triangular lattice compound RbFe(MoO(4))(2)
Authors:
Ribeiro, JL; Perez-Mato, JM Author Full Names: Ribeiro, J. L.; Perez-Mato, J. M.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 23 (44): 10.1088/0953-8984/23/44/446003 NOV 9 2011
Abstract:
The temperature versus magnetic field phase diagram of the 2D triangular lattice and multiferroic compound RbFe(MoO(4))(2) is analysed from the point of view of symmetry. The paramagnetic space group and its irreducible representations are used in order to obtain the magnetic symmetry of the possible modulated phases and characterize the restrictions imposed by this symmetry on the corresponding magnetic structures. Superspace symmetry is considered in the case of incommensurate phases. It is shown that the experimentally observed phases correspond to different isotropy subgroups originating in the same irreducible representation of the paramagnetic symmetry group. The relevant couplings between the primary transverse spin modulation and the electric polarization, the in-plane magnetization and the secondary longitudinal magnetic modulation are discussed. The mechanisms for the destabilization of the improper ferroelectric chiral phase and the origin of the different orienta! tion of the spins with respect to the external field in the two collinear phases are analysed from a symmetry based perspective.
Title:
Quasicrystals - Interfaces to Hyperspace
Authors:
Steurer, W Author Full Names: Steurer, Walter
Source:
NACHRICHTEN AUS DER CHEMIE 59 (11): 1035-1038 NOV 2011

Update: 23-Nov-2011

Title:
Microstructure development and properties of the AlCuFe quasicrystalline coating on near-alpha titanium alloy
Authors:
Moskalewicz, T; Kot, M; Wendler, B Author Full Names: Moskalewicz, T.; Kot, M.; Wendler, B.
Source:
APPLIED SURFACE SCIENCE 258 (2): 848-859 10.1016/j.apsusc.2011.09.013 NOV 1 2011
Abstract:
A protective quasicrystalline AlFeCu coating was deposited on TIMETAL 834 substrate by nonreactive magnetron sputtering in order to improve resistance of the alloy to oxidation. Microstructure characterisation of the substrate and the coating was performed by analytical scanning-and transmission electron microscopy as well as X-ray diffractometry. Depending on annealing temperature and time, the deposited coating (2.7 mu m thick) has a different microstructure. The coating in Specimen 1 (annealed 600 degrees C/4 h in vacuum) consisted of two zones: outer, composed of Al(5)Fe(2) and Al(2)Cu(3) phases and inner, in which only quasicrystalline psi phase was present. The coating in Specimen 2 (annealed 600 degrees C/4 h + 700 degrees C/2 h in vacuum) was fully quasicrystalline and consisted of icosahedral psi phase. Both coatings exhibit higher microhardness than the substrate material. It was established that the applied surface treatment essentially improves oxidation resistance of the alloy tested at 750 degrees C during 250 h in static air. Sample weight gain was 60% lower than in the case of uncoated sample. Oxide scale spallation occurred for uncoated alloy while the coated one did not show any spallation. It was found that the very brittle scale formed during oxidation on the uncoated alloy was consisting of TiO(2), while that on the coated one consisted mainly of alpha-Al(2)O(3). (C) 2011 Elsevier B. V. All rights reserved.
Title:
Lead adsorption on the Al(13)Co(4)(100) surface: heterogeneous nucleation and pseudomorphic growth
Authors:
Addou, R; Shukla, AK; Villaseca, SA; Gaudry, E; Deniozou, T; Heggen, M; Feuerbacher, M; Widmer, R; Groning, O; Fournee, V; Dubois, JM; Ledieu, J Author Full Names: Addou, R.; Shukla, A. K.; Villaseca, S. Alarcon; Gaudry, E.; Deniozou, Th; Heggen, M.; Feuerbacher, M.; Widmer, R.; Groening, O.; Fournee, V.; Dubois, J-M; Ledieu, J.
Source:
NEW JOURNAL OF PHYSICS 13 10.1088/1367-2630/13/10/103011 OCT 11 2011
Abstract:
We have investigated the adsorption of Pb atoms on the (100) surface of an orthorhombic Al(13)Co(4) crystal at 300 and 573K substrate temperatures. This complex metallic alloy is an approximant to the decagonal Al-Ni-Co quasicrystal. At submonolayer coverage and at 300 K, Pb adatoms remain highly mobile and adsorb preferentially within the hollow site situated in between adjacent Al pentagonal clusters present at the surface. These experimental findings are supported by ab initio calculations based on density functional theory (DFT). For both temperature regimes, Pb adsorption leads to the formation of pseudomorphic monolayers above which the high adsorbate mobility prohibits the growth of additional layers. For the high-temperature deposition, we propose a structural model for the Pb film and discuss its relationship with the underneath substrate.

Update: 16-Nov-2011

Title:
Magnetic and thermal properties of Er(75)Dy(25) single crystals
Authors:
Khan, M; Schlagel, DL; Lograsso, TA; Gschneidner, KA; Pecharsky, VK Author Full Names: Khan, Mahmud; Schlagel, D. L.; Lograsso, T. A.; Gschneidner, K. A., Jr.; Pecharsky, V. K.
Source:
PHYSICAL REVIEW B 84 (13): 10.1103/PhysRevB.84.134424 OCT 18 2011
Abstract:
We report on an experimental study of the thermal and magnetic properties of Er(75)Dy(25) single crystals with magnetic fields applied parallel to the [0001] and [10 (1) over bar0] directions. The [0001] direction is the easy axis of magnetization, while the [10 (1) over bar0] direction is the hard axis of magnetization. Three major transitions are observed in the heat capacity, magnetization, and alternating current magnetic susceptibility data. A first-order transition is observed at similar to 30 K, and two second-order transitions occur at similar to 45 and similar to 110 K. The H-T phase diagrams constructed from the experimental data reveal that several magnetic phases, including ferromagnetic cone, ferromagnetic fan, and c axis-modulated phases, exist in an Er(75)Dy(25) single crystal. Both similarities and dissimilarities are observed in the H-T phase diagrams of Er(75)Dy(25) when compared to the H-T phase diagrams of pure Er single crystals.

Update: 10-Nov-2011

Title:
Electrical transport and anomalous structural behavior of alpha-Eu(2) (MoO(4))(3) at high temperature
Authors:
Guzman-Afonso, C; Torres, ME; Gonzalez-Silgo, C; Sabalisck, N; Gonzalez-Platas, J; Matesanz, E; Mujica, A Author Full Names: Guzman-Afonso, C.; Torres, M. E.; Gonzalez-Silgo, C.; Sabalisck, N.; Gonzalez-Platas, J.; Matesanz, E.; Mujica, A.
Source:
SOLID STATE COMMUNICATIONS 151 (22): 1654-1658 10.1016/j.ssc.2011.08.009 NOV 2011
Abstract:
The study of XRD patterns of alpha-Eu(2)(MoO(4))(3) modulated scheelite reveals an anomalous behavior of its lattice parameter a in the range of temperatures from 473 to 973 K. We have analyzed the real part of the complex conductivity in the frequency range from 0.1 to 10,000 kHz and the temperature range from 550 to 900 K, and found that it follows a universal dielectric response. Detailed analysis of the temperature dependence of the adjusted parameters within this model shows that, in a temperature range, the dominant mechanism of electrical transport is due to the overlapping of large polarons. Rietveld refinements were performed using symmetry adapted modes at 523, 723 and 923 Kin order to study the thermal dependence of the distortion from the scheelite structure and to interpret the structural effects that favor the formation of polarons. (C) 2011 Elsevier Ltd. All rights reserved.
Title:
New type of incommensurate magnetic ordering in Mn(3)TeO(6)
Authors:
Ivanov, SA; Nordblad, P; Mathieu, R; Tellgren, R; Ritter, C; Golubko, NV; Politova, ED; Weil, M Author Full Names: Ivanov, S. A.; Nordblad, P.; Mathieu, R.; Tellgren, R.; Ritter, C.; Golubko, N. V.; Politova, E. D.; Weil, M.
Source:
MATERIALS RESEARCH BULLETIN 46 (11): 1870-1877 10.1016/j.materresbull.2011.07.041 NOV 2011
Abstract:
The complex metal oxide Mn(3)TeO(6) exhibits a corundum related structure and has been prepared both in forms of single crystals by chemical transport reactions and of polycrystalline powders by a solid state reaction route. The crystal structure and magnetic properties have been investigated using a combination of X-ray and neutron powder diffraction, electron microscopy, calorimetric and magnetic measurements. At room temperature this compound adopts a trigonal structure, space group R (3) over bar with a = 8.8679(1) angstrom. c = 10.6727(2) angstrom. A long-range magnetically ordered state is identified below 23 K. An unexpected feature of this magnetic structure is several types of Mn-chains. Under the action of the incommensurate magnetic propagation vector k = [0, 0, 0.4302(1)] the unique Mn site is split into two magnetically different orbits. One orbit forms a perfect helix with the spiral axis along the c-axis while the other orbit has a sine wave character along the c-axis. (C) 2011 Elsevier Ltd. All rights reserved.
Title:
Structural stability and magnetic properties of Bi(1-x)La(Pr)(x)FeO(3) solid solutions
Authors:
Karpinsky, DV; Troyanchuk, IO; Mantytskaya, OS; Khomchenko, VA; Kholkin, AL Author Full Names: Karpinsky, D. V.; Troyanchuk, I. O.; Mantytskaya, O. S.; Khomchenko, V. A.; Kholkin, A. L.
Source:
SOLID STATE COMMUNICATIONS 151 (22): 1686-1689 10.1016/j.ssc.2011.08.002 NOV 2011
Abstract:
In this work, X-ray diffraction data taken on Bi(1-x)La(x)FeO(3) solid solutions are used to verify the following structural phase transitions: "polar rhombohedral-antipolar orthorhombic" at x approximate to 0.16 and "commensurate-incommensurate" within the orthorhombic phase at x approximate to 0.18. In contrast, in the Bi(1-x)Pr(x)FeO(3) series, the polar rhombohedral phase transforms into an antipolar orthorhombic one at x >= 0.13. The polar rhombohedral phase near the morphotropic phase boundary exhibits an isothermal transformation into an antipolar orthorhombic phase, though the transformation occurs much faster in the case of La-doped compounds. The incommensurate structural phase was not detected in Bi(1-x)Pr(x)FeO(3) solid solutions. The ternary structural phase diagram is constructed for (Bi, La, Pr)FeO(3) systems. In addition, the polar rhombohedral phase exhibits a magnetic field-induced transition from the modulated antiferromagnetic state into a homogeneous weak ferromagnetic state whereas the antipolar phase is a weak ferromagnetic state in the absence of an external field. (C) 2011 Elsevier Ltd. All rights reserved.
Title:
Seeing is Believing: Quasicrystals and the Demise of Perfect Order
Authors:
Balaram, P Author Full Names: Balaram, P.
Source:
CURRENT SCIENCE 101 (8): 981-982 OCT 25 2011
Title:
Electrical, magnetic, and thermal properties of the single-grain Ag(42)In(42)Yb(16) icosahedral quasicrystal: Experiment and modeling
Authors:
Bobnar, M; Vrtnik, S; Jaglicic, Z; Wencka, M; Cui, C; Tsai, AP; Dolinsek, J Author Full Names: Bobnar, M.; Vrtnik, S.; Jaglicic, Z.; Wencka, M.; Cui, Can; Tsai, An Pang; Dolinsek, J.
Source:
PHYSICAL REVIEW B 84 (13): 10.1103/PhysRevB.84.134205 OCT 17 2011
Abstract:
We have investigated the anisotropy of physical properties (themagnetic susceptibility, the electrical resistivity, the thermoelectric power, the Hall coefficient, and the thermal conductivity) of single-grain icosahedral i-Ag(42)In(42)Yb(16) quasicrystal along the two-, three-, and fivefold symmetry directions of the crystallographic structure. The specific heat, being a scalar quantity, was determined as well. The symmetry analysis predicts that the tensorial physical properties reduce to scalars for the ideal icosahedral symmetry. The experiments have shown that the anisotropy of the electronic transport coefficients of i-Ag(42)In(42)Yb(16) is either small enough to be considered within the range of the experimental uncertainty (the electrical resistivity and the thermal conductivity) or negligible (the Seebeck and the Hall coefficients). The anisotropy of the magnetization and magnetic susceptibility was also found small, originating from different Yb(3+) magnetic fractions (of the order 10(-3) of all Yb atoms) determined along the three symmetry directions. Our experimental results support the consideration that perfect icosahedral quasicrystals should be isotropic solids regarding their physical properties, unlike decagonal quasicrystals that are strongly anisotropic. Theoretical reproduction of the temperature-dependent electron transport coefficients of i-Ag(42)In(42)Yb(16) by a spectral conductivity model was another aim of this paper.
Title:
Structural evolution of one-dimensional spin-ladder compounds Sr(14-x)Ca(x)Cu(24)O(41) with Ca doping and related evidence of hole redistribution
Authors:
Deng, GC; Pomjakushin, V; Petricek, V; Pomjakushina, E; Kenzelmann, M; Conder, K Author Full Names: Deng, Guochu; Pomjakushin, Vladimir; Petricek, Vaclev; Pomjakushina, Ekaterina; Kenzelmann, Michel; Conder, Kazimierz
Source:
PHYSICAL REVIEW B 84 (14): 10.1103/PhysRevB.84.144111 OCT 17 2011
Abstract:
Incommensurate crystal structures of spin-ladder series Sr(14-x)Ca(x)Cu(24)O(41) (x = 3, 7, 11, and 12.2) were characterized by powder neutron scattering method and refined using the superspace group Xmmm(00 gamma)ss0 [ equivalent to superspace group Fmmm(0, 0, 1 + gamma)ss0; X stands for nonstandard centering (0, 0, 0, 0), (0, 1/2, 1/2, 1/2), (1/2, 1/2, 0, 0), (1/2, 0, 1/2, 1/2)] with a modulated structure model. The Ca doping effects on the lattice parameters, atomic displacement, Cu-O distances, Cu-O bond angles, and Cu bond valence sum were characterized. The refined results show that the CuO(4) planar units in both chain and ladder sublattices become closer to square shape with an increase of Ca doping. The Cu bond valence sum calculation provided new evidence for the charge transfer from the chains to ladders (approximately 0.16 holes per Cu from x = 0 to 12.2). The charge transfer was attributed to two different mechanisms: (a) the Cu-O bond distance shrinkage on the ladder and (b) increase of the interaction between two sublattices, resulting in Cu-O bonding between the chains and ladders. The low-temperature structural refinement resulted in the similar conclusion with a slight charge backflow to the chains.
Title:
Germanium Selenophosphates: The Incommensurately Modulated 1/infinity[Ge(4-x)P(x)Se(12)(4-)] and the Molecular [Ge(2)P(2)Se(14)](6-)
Authors:
Morris, CD; Malliakas, CD; Kanatzidis, MG Author Full Names: Morris, Collin D.; Malliakas, Christos D.; Kanatzidis, Mercouri G.
Source:
INORGANIC CHEMISTRY 50 (20): 10241-10248 10.1021/ic201249w OCT 17 2011
Abstract:
The new germanium selenophosphates K(4)Ge(4-x)P(x)Se(12) (1) and Rb(6)Ge(2)P(2)Se(14) (2) are reported. The former is a one-dimensional metastable compound synthesized using the polychalcogenide flux method that crystallizes in the monoclinic space group P2(1)/c with lattice parameters a = 6.7388(7) angstrom, b = 13.489(1) angstrom, c = 6.3904(6) angstrom, and beta = 91.025(8)degrees. At a glance, a mixed Ge(4+)/P(5+) tetrahedral site and disordered Se position are found among the corner sharing tetrahedra that make up the polymeric anion. After careful examination, the structure was found to be incommensurately modulated and a single q-vector of q = 0.4442(6)a* + 0.3407(6)c* was determined after annealing single crystals below their decomposition point for 30d. The latter compound contains the new discrete molecular anion [Ge(2)P(2)Se(14)](6-) and crystallizes in P (1) over bar with lattice parameters a = 7.2463(8) angstrom, b = 9.707(1)angstrom, c = 11.987(1)angstrom, alpha = 79.516(9)degrees, beta = 89.524(9)degrees, and gamma = 68.281(9)degrees. Both compounds are semiconductors with band gaps of 1 and 2 being 1.9 eV and 2.2 eV, respectively.
Title:
XRD and HREM studies from the decomposition of icosahedral AlCuFe single-phase by high-energy ball milling
Authors:
Patino-Carachure, C; Tellez-Vazquez, O; Rosas, G Author Full Names: Patino-Carachure, C.; Tellez-Vazquez, O.; Rosas, G.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 509 (41): 10036-10039 10.1016/j.jallcom.2011.08.026 OCT 13 2011
Abstract:
In this investigation the Al(64)Cu(24)Fe(12) alloy was melted in an induction furnace and solidified under normal casting conditions. In order to obtain the icosahedral phase (i-phase) in a single-phase region, the as-cast sample was subject to a heat treatment at 700 degrees C under argon atmosphere. Subsequently, the i-phase was milled for different times in order to evaluate phase stability under heavy deformation. X-ray diffraction (XRD) and high-resolution electron microscopy (HREM) analysis were conducted to the structural characterization of ball-milled powders. XRD results indicated a reduction in quasicrystal size during mechanical ball milling to about 30 h. HREM analysis revealed the presence of aperiodic nanodomains, for example, with apparent fivefold symmetry axis. Therefore, the i-phase remains stable over the first 30 h of ball-milling time. However, among 30-50 h of mechanical milling the i-phase transforms progressively into beta-cubic phase. (C) 2011 Elsevier B.V. All rights reserved.
Title:
Vacancies and atomic processes in intermetallics - From crystals to quasicrystals and bulk metallic glasses
Authors:
Schaefer, HE; Baier, F; Muller, MA; Reichle, KJ; Reimann, K; Rempel, AA; Sato, K; Ye, F; Zhang, XY; Sprengel, W Author Full Names: Schaefer, Hans-Eckhardt; Baier, Falko; Mueller, Markus A.; Reichle, Klaus J.; Reimann, Klaus; Rempel, Andrey A.; Sato, Kiminori; Ye, Feng; Zhang, Xiangyi; Sprengel, Wolfgang
Source:
PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS 248 (10): 2290-2299 10.1002/pssb.201147103 OCT 2011
Abstract:
A review is given on atomic vacancies in intermetallic compounds. The intermetallic compounds cover crystalline, quasicrystalline, and bulk metallic glass (BMG) structures. Vacancies can be specifically characterized by their positron lifetimes, by the coincident measurement of the Doppler broadening of the two quanta emitted by positron-electron annihilation, or by time-differential dilatometry. By these techniques, high concentrations and low mobilities of thermal vacancies were found in open-structured B2 intermetallics such as FeAl or NiAl, whereas the concentrations of vacancies are low and their mobilities high in close-packed structure as, e.g., L1(2)-Ni(3)Al. The activation volumes of vacancy formation and migration are determined by high-pressure experiments. The favorable sublattice for vacancy formation is found to be the majority sublattice in Fe(61)Al(39) and in MoSi(2). In the icosahedral quasicrystal Al(70)Pd(21)Mn(9) the thermal vacancy concentration is low, whereas in the BMG Zr(57)Cu(15.4)Ni(12).(6)Nb(3)Al(10) thermal vacancies are found in high concentrations with low mobilities. This may determine the basic mechanisms of the glass transition. Making use of the experimentally determined vacancy data, the main features of atomic diffusion studies in crystalline intermetallics, in quasicrystals, and in BMGs can be understood. Manfred Fahnle and his group have substantially contributed to the theoretical understanding of vacancies and diffusion mechanisms in intermetallics. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Title:
Grain size effect on the phase transformations of higher manganese silicide thermoelectric materials: An in situ energy dispersive x-ray diffraction study
Authors:
Zhou, AJ; Zhu, TJ; Zhao, XB; Mueller, E Author Full Names: Zhou, Aijun; Zhu, Tiejun; Zhao, Xinbing; Mueller, Eckhard
Source:
JOURNAL OF MATERIALS RESEARCH 26 (15): 1900-1906 10.1557/jmr.2011.80 AUG 2011
Abstract:
Phase structures of microscale and nanoscale higher manganese silicides (HMSs) were investigated using in situ energy dispersive x-ray diffraction at high temperatures or/and high pressure. A few phase transformations accompanied with the presence of MnSi phase were observed in different temperature regions, which were associated with the interevolution of several incommensurate HMS phases. It was found that in nanostructured HMS, the interevolution of HMS was remarkable and accelerated compared to that in the micropowders. Meanwhile, high pressure was able to influence these phase transformations due to giant strain in the materials. The phase transformations were discussed from thermodynamic aspects with respect to the different formation enthalpy of Mn-Si system and the large surface energy and structural instability of the nanopowders.
Title:
Surprising luminescent properties of the polyphosphates Ln(PO(3))(3): Eu (Ln = Y, Gd, Lu)
Authors:
Hoppe, HA; Kazmierczak, K; Kacprzak, S; Schellenberg, I; Pottgen, R Author Full Names: Hoeppe, Henning A.; Kazmierczak, Karolina; Kacprzak, Sylwia; Schellenberg, Inga; Poettgen, Rainer
Source:
DALTON TRANSACTIONS 40 (39): 9971-9976 10.1039/c1dt10043b 2011
Abstract:
The optical emission properties of the lanthanoid catena-polyphosphates Ln(PO(3))(3) (Ln = Y, Gd, Lu) doped with europium were investigated. Incommensurately modulated b-Y(PO(3))(3) : Eu (super space group Cc (0 vertical bar 0.364 vertical bar 0)0) and Gd(PO(3))(3) : Eu (space group I2/a) show the usual emission characteristics of Eu(3+), while in Lu(PO(3))(3) : Eu (space group Cc) the europium is unprecedentedly partially reduced to the divalent state, as proven by both a broad emission band at 406 nm excited at 279 nm and an EPR spectroscopic investigation. (151)Eu-Mossbauer spectroscopy showed that only a very small part of the europium is reduced in Lu(PO(3))(3) : Eu. An explanation for this unusual behaviour is given.

Update: 3-Nov-2011

Title:
Coexistence of superconductivity and incommensurate magnetic order
Authors:
Ptok, A; Maska, MM; Mierzejewski, M Author Full Names: Ptok, Andrzej; Maska, Maciej M.; Mierzejewski, Marcin
Source:
PHYSICAL REVIEW B 84 (9): 10.1103/PhysRevB.84.094526 SEP 26 2011
Abstract:
The influence of incommensurate spin-density waves (SDW) on superconductivity in unconventional superconductors is studied by means of the Bogolubov-de Gennes (BdG) equations. Exploiting translational symmetries of a magnetically ordered two-dimensional system, we propose an approach that allows to solve the BdG equations on much larger clusters than it is usually possible for inhomogeneous systems. Applying this approach, we demonstrate that the presence of incommensurate spin-density waves induces real-space inhomogeneity of the superconducting order parameter even in the absence of external magnetic field. In this case, a homogeneous order parameter of the Bardeen-Cooper-Schrieffer-type superconducting state is slightly modulated, or equivalently, a small fraction of the charge carriers form Cooper pairs with nonzero total momentum. However, when a sufficiently strong magnetic field is applied, the homogeneous component of the order parameter is suppressed and the system transits to the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state, where the order parameter oscillates changing sign. We show that for s-wave pairing, the presence of external magnetic field diminishes the destructive influence of the SDW order on superconductivity. A simple explanation of this effect is also proposed.
Title:
Spontaneous phase transitions in magnetic films with a modulated structure
Authors:
Arzamastseva, GV; Evtikhov, MG; Lisovskii, FV; Mansvetova, EG Author Full Names: Arzamastseva, G. V.; Evtikhov, M. G.; Lisovskii, F. V.; Mansvetova, E. G.
Source:
JOURNAL OF EXPERIMENTAL AND THEORETICAL PHYSICS 113 (3): 450-458 10.1134/S1063776111080024 SEP 2011
Abstract:
The influence of monoperiodic and biperiodic bias fields on the nucleation of domain structures in quasi-uniaxial magnetic films near the Curie point has been studied experimentally. The main types of observed nonuniform magnetic moment distributions have been established and chains of a devil's staircase phase transitions are shown to be realized when the films are slowly cooled.
Title:
Electrochemical properties of Ti(45)Zr(38-x)Ni(17+x) (0 <= x <= 8) quasicrystals produced by rapid-quenching
Authors:
Takasaki, A; Kuroda, C; Lee, SH; Kim, JY Author Full Names: Takasaki, Akito; Kuroda, Chihiro; Lee, Sang-Hwa; Kim, Jae-Yong
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 509 S782-S785 2 10.1016/j.jallcom.2010.11.042 SEP 2011
Abstract:
Discharge performances of Ti(45)Zr(38-x)Ni(17+x) (0 <= x <= 8) ribbons produced by rapid-quenching were measured by a three-electrode cell at room temperature, and the effect of substitution of Ni for Zr was investigated. All the ribbons after rapid-quenching were mostly the icosahedral (i) quasicrystal phase with a negligible amount of C14 Laves phase (hcp). The discharge capacity increased with increasing amount of Ni substituted for Zr. The maximum discharge capacity achieved was about 90 mAh/g from (Ti(45)Zr(30)Ni(25)) ribbon after substitution of Ni for Zr. The discharge performance was almost stable against the charge/discharge cycle (until 15 cycles) for all the ribbons, and the i-phase structure was also stable even after the 15th charge/discharge cycle. No metal hydride formation was observed. (C) 2010 Elsevier B.V. All rights reserved.

Update: 27-Oct-2011

Title:
Low-temperature evolution of the modulated magnetic structure in the ferroelectric antiferromagnet BiFeO(3)
Authors:
Sosnowska, I; Przenioslo, R Author Full Names: Sosnowska, I.; Przenioslo, R.
Source:
PHYSICAL REVIEW B 84 (14): 10.1103/PhysRevB.84.144404 OCT 3 2011
Abstract:
High-resolution time-of-flight neutron diffraction studies of the magnetic ordering in the multiferroic BiFeO(3) are presented. Our results show that the cycloidal modulated ordering proposed earlier [I. Sosnowska, T. Peterlin-Neumaier, and E. Steichele, J. Phys. C 15, 4835 (1982)] is stable between 10 and 295 K. The concept of the anharmonic character of the magnetic modulation in BiFeO(3) that was used for the interpretation of NMR, Raman, and THz spectroscopy studies of BiFeO(3) is discussed. The influence of the anharmonic modulation on the magnetic contributions to the BiFeO(3) neutron diffraction patterns is presented. Our experimental data can be described by assuming anharmonic effects with m < 0.25. We propose a method for the anharmonicity strength evaluation based on neutron diffraction data.
Title:
Five-Dimensional Incommensurate Structure of the Melilite Electrolyte [CaNd](2)[Ga](2)[Ga(2)O(7)](2)
Authors:
Wei, FX; Baikie, T; An, T; Schreyer, M; Kloc, C; White, TJ Author Full Names: Wei, Fengxia; Baikie, Tom; An, Tao; Schreyer, Martin; Kloc, Christian; White, Tim J.
Source:
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 133 (38): 15200-15211 10.1021/ja206441x SEP 28 2011
Abstract:
Melilite-type gallium oxides are potential intermediate temperature electrolytes for solid oxide fuel cells. Single crystals of [CaNd](2)[Ga](2)[Ga(2)O(7)](2) grown using an optical floating zone furnace have been investigated using transmission electron microscopy and powder and single-crystal X-ray diffraction. The anion array topologically conforms to a [(3.5.4.5)(2), 3.5.3.5] network that contains distorted pentagonal tunnels. The distortion is necessary to achieve space filling and accommodate structural misfit between the layers. Satisfactory bond lengths and angles are obtained through two-dimensional modulation in the tetragonal based plane, leading to five-dimensional symmetry in the superspace group P (4) over bar2(1)m(alpha,alpha,0)00s((a) over bar ,a,0)000, alpha = 0.2319(2), with modulation vectors q(1) = alpha(a* + b*) and q(2) = alpha(-a* + b*). Both displacive and occupational modulations are found. Through this mechanism, melilites are primed to accommodate mobile oxygen interstitials, suggesting a rational approach to crystallochemical tailoring that will enhance ionic diffusion and optimize electrolyte performance.

Update: 20-Oct-2011

Title:
Damping properties in Mg-Zn-Y alloy with dispersion of quasicrystal phase particle
Authors:
Somekawa, H; Watanabe, H; Mukai, T Author Full Names: Somekawa, Hidetoshi; Watanabe, Hiroyuki; Mukai, Toshiji
Source:
MATERIALS LETTERS 65 (21-22): 3251-3253 10.1016/j.matlet.2011.07.001 NOV 2011
Abstract:
The effect of the interface structure between the matrix and the particle on the damping capacity was investigated using Mg-Zn and Mg-Zn-Y alloys in this study. The damping capacity was not affected by the interface structure at room temperature. However, the onset of temperature, which was higher in the Mg-Zn-Y alloy than in the Mg-Zn alloy despite their similar grain sizes, increased the damping capacity through grain boundary relaxation by grain boundary sliding. Compared to the Mg-Zn alloy, the existence of the quasicrystal phase particles, which had the coherent interface with low interface energy, was likely to have suppressed and delayed the grain boundary sliding in the Mg-Zn alloy. (C) 2011 Elsevier By. All rights reserved.
Title:
Ti-Doping to Reduce Conductivity in Bi(0.85)Nd(0.15)FeO(3) Ceramics
Authors:
Kalantari, K; Sterianou, I; Karimi, S; Ferrarelli, MC; Miao, S; Sinclair, DC; Reaney, IM Author Full Names: Kalantari, Kambiz; Sterianou, Iasmi; Karimi, Sarah; Ferrarelli, Matthew C.; Miao, Shu; Sinclair, Derek C.; Reaney, Ian M.
Source:
ADVANCED FUNCTIONAL MATERIALS 21 (19): 3737-3743 10.1002/adfm.201100191 OCT 7 2011
Abstract:
In 2009, Karimi et al. reported that Bi(1-x)Nd(x)FeO(3) 0.15 <= x <= 0.25 exhibited a PbZrO(3) (PZ)-like structure. These authors presented some preliminary electrical data for the PZ-like composition but noted that the conductivity was too high to obtain radio-frequency measurements representative of the intrinsic properties. In this study, Bi(0.85)Nd(0.15)Fe(1-y)Ti(y)O(3) (0 <= y <= 0.1) were investigated, in which Ti acted as a donor dopant on the B-site. In contrast to the original study of Karimi et al., X-ray diffraction (XRD) of Bi(0.85)Nd(0.15)FeO(3) revealed peaks which were attributed to a mixture of PZ-like and rhombohedral structures. However, as the Ti (0 < y <= 0.05) concentration increased, the rhombohedral peaks disappeared and all intensities were attributed to the PZ-like phase. For y = 0.1, broad XRD peaks indicated a significant decrease in effective diffracting volume. Electron diffraction confirmed that the PZ-like phase was dominant for y <= 0.05, but for y = 0.1, an incommensurate structure was present, consistent with the broadened XRD peaks. The substitution of Fe(3+) by Ti(4+) decreased the dielectric loss at room temperature from >0.3 to <0.04 for all doped compositions, with a minimum (0.015) observed for y = 0.03. The decrease in dielectric loss was accompanied by a decrease in the room temperature bulk conductivity from similar to 1 mS cm(-1) to < 1 mu S cm(-1) and an increase in bulk activation energy from 0.29 to >1 eV. Plots of permittivity (epsilon(r)) versus temperature for 0.01 <= y <= 0.05 revealed a step rather than a peak in epsilon(r) on heating at the same temperature determined for the antiferroelectric-paraelectric phase transition by differential scanning calorimetry. Finally, large electric fields were applied to all doped samples which resulted in a linear dependence of polarisation on the electric field similar to that obtained for PbZrO(3) ceramics under equivalent experimental conditions.
Title:
Detailed structure of the low-energy magnetic dispersion of the diagonal incommensurate phase in La(1.975)Sr(0.025)CuO(4)
Authors:
Matsuda, M; Fernandez-Baca, JA; Fujita, M; Yamada, K; Tranquada, JM Author Full Names: Matsuda, M.; Fernandez-Baca, J. A.; Fujita, M.; Yamada, K.; Tranquada, J. M.
Source:
PHYSICAL REVIEW B 84 (10): 10.1103/PhysRevB.84.104524 SEP 30 2011
Abstract:
Inelastic neutron scattering experiments have been performed on lightly doped La(1.975)Sr(0.025)CuO(4), which contains a hole concentration slightly higher than the critical concentration for three-dimensional long-range antiferromagnetic order. We previously found that the magnetic excitation spectrum in the insulating phase with a diagonal incommensurate spin modulation has similarities to that in the superconducting regime, where the spin modulation is bond parallel. In this study, we investigate the excitations in detail around Ecross, at which the excitations become most nearly commensurate. It is found that both the magnitude and the anisotropy of the momentum width of the excitations change abruptly at Ecross. Our experimental results suggest that the magnetic excitations rising from the pair of (diagonally) incommensurate wave vectors merge at Ecross into isotropic excitations.
Title:
Magnetic excitations in the geometric frustrated multiferroic CuCrO(2)
Authors:
Frontzek, M; Haraldsen, JT; Podlesnyak, A; Matsuda, M; Christianson, AD; Fishman, RS; Sefat, AS; Qiu, Y; Copley, JRD; Barilo, S; Shiryaev, SV; Ehlers, G Author Full Names: Frontzek, M.; Haraldsen, J. T.; Podlesnyak, A.; Matsuda, M.; Christianson, A. D.; Fishman, R. S.; Sefat, A. S.; Qiu, Y.; Copley, J. R. D.; Barilo, S.; Shiryaev, S. V.; Ehlers, G.
Source:
PHYSICAL REVIEW B 84 (9): 10.1103/PhysRevB.84.094448 SEP 28 2011
Abstract:
In this paper detailed neutron scattering measurements of the magnetic excitation spectrum of CuCrO(2) in the ordered state below T(N1) = 24.2 K are presented. The spectra are analyzed using a model Hamiltonian which includes intralayer exchange up to the next-next-nearest neighbor and interlayer exchange. We obtain a definite parameter set and show that exchange interaction terms beyond the next-nearest neighbor are important to describe the inelastic excitation spectrum. The magnetic ground state structure generated with our parameter set is in agreement with the structure proposed for CuCrO(2) from the results of single crystal diffraction experiments previously published. We argue that the role of the interlayer exchange is crucial to understand the incommensurability of the magnetic structure as well as the spin-charge coupling mechanism.
Title:
Effects of chemical doping and pressure on CaFe(4)As(3)
Authors:
Zhao, LL; Kim, SK; McCandless, GT; Torikachvili, MS; Canfield, PC; Chan, JY; Morosan, E Author Full Names: Zhao, Liang L.; Kim, S. K.; McCandless, Gregory T.; Torikachvili, Milton S.; Canfield, P. C.; Chan, Julia Y.; Morosan, E.
Source:
PHYSICAL REVIEW B 84 (10): 10.1103/PhysRevB.84.104444 SEP 28 2011
Abstract:
The effects of chemical doping by P, Yb, Co, and Cu, and hydrostatic pressure on CaFe(4)As(3), were studied on single-crystalline samples. While the former two dopants substitute the nonmagnetic ions, the latter two partially occupy the Fe sites within the magnetic sublattice. The incommensurate spin density wave (IC-SDW) ordering at T(N) similar to 88 K in CaFe(4)As(3) changes only by up to similar to 40% with doping and applied pressure. Thus the IC-SDW state appears more robust than in the layered Fe pnictides. The commensurate SDW (C-SDW) state below T(2) similar to 26 K is suppressed in the Co-doped series, while it moves up in temperature in the P-, Yb-, and Cu-doped compounds. A new magnetic phase transition is observed at an intermediate temperature T(3) in Ca(Fe(1-x)Co(x))(4)As(3). Resistivity and magnetization measurements on CaFe(4)As(3) were performed under hydrostatic pressure up to 5 GPa, showing a systematic decrease of T(N) and a domelike phase boundary at T(2) up to p(c) similar to 2.10 GPa. At higher pressures, a possible structural phase transition occurs, marked by a slowly increasing transition temperature. A phase diagram is shown to compare the effects of chemical doping and pressure.
Title:
Ordering and growth of Xe films on the 10-fold quasicrystalline approximant Al(13)Co(4)(100) surface
Authors:
Shin, H; Karimi, M; Setyawan, W; Curtarolo, S; Diehl, RD Author Full Names: Shin, Heekeun; Karimi, M.; Setyawan, W.; Curtarolo, S.; Diehl, R. D.
Source:
PHYSICAL REVIEW B 84 (11): 10.1103/PhysRevB.84.115454 SEP 27 2011
Abstract:
Xe adsorption on the (100) surface of the complex alloy Al(13)Co(4) has been carried out using low-energy electron diffraction (LEED) and grand canonical Monte Carlo (GCMC) simulations. This surface is an approximant to the 10-fold surface of decagonal Al-Ni-Co, on which Xe adsorption has been studied previously. The adsorption behavior on the periodic surface is largely similar to that on the quasicrystal (layer-by-layer growth, hexagonal ordering near the onset of the second-layer adsorption), but it also has some differences, such as the complete lack of registry of the Xe layer with the substrate structure in the hexagonal phase, and a high sensitivity of the Xe epitaxial direction to trace impurities. In the simulations, an ordering transition was observed between the low-density and high-density monolayer regimes that involves a uniaxial compression of the monolayer film.

Update: 13-Oct-2011

Title:
Quinary icosahedral quasicrystalline Ti-V-Ni-Mn-Cr alloy: A novel anode material for Ni-MH rechargeable batteries
Authors:
Hu, W; Wang, LD; Wang, LM Author Full Names: Hu, Wen; Wang, Lidong; Wang, Limin
Source:
MATERIALS LETTERS 65 (19-20): 2868-2871 10.1016/j.matlet.2011.06.059 OCT 2011
Abstract:
The substitution of manganese and chromium for 6 at.% nickel in Ti(1.6)V(0.4)Ni leads the rapid quenching synthesis of quinary icosahedral phase (i-phase) evidenced by the observations of 2-. 3- and 5-fold symmetries. As negative electrode in Ni-MH battery, the quinary Ti-V-Ni-Mn-Cr i-phase can deliver a maximum discharge capacity of 278 mAh g(-1) at 30 mA g(-1) larger than that of Ti(1.6)V(0.4)Ni master alloy anode owing to Mn and/or Cr doping. After a preliminary test of 30 consecutive cycles the cycling capacity retention rate (CR%) is 80%. The strong chemisorption of hydrogen shown in cyclic voltammetric (CV) response indicates that the electrocatalytic activity improvement for the i-phase negative electrode is highly demanded. (C) 2011 Elsevier B.V. All rights reserved.

Update: 6-Oct-2011

Title:
Modulated superconductivity due to vacancy and magnetic order in A(y)Fe(2-x/2)Se(2) [A = Cs, K, (Tl,Rb), (Tl,K)] iron-selenide superconductors
Authors:
Das, T; Balatsky, AV Author Full Names: Das, Tanmoy; Balatsky, A. V.
Source:
PHYSICAL REVIEW B 84 (11): 10.1103/PhysRevB.84.115117 SEP 19 2011
Abstract:
We present a calculation of a "modulated" superconducting state in iron-selenide superconductors. The zero-momentum d-wave pairing breaks the translational symmetry of the conventional BaFe(2)Se(2)-like crystal of the I4/mmm space group. This pairing state becomes compatible when the Fe vacancies form an ordered state and the crystal symmetry changes to a low-temperature I4/m one. For the specific case of an incommensurate vacancy order at Q(v) = (1/5, 3/5) in K(0.82(2))Fe(1.626(3))Se(2), we find that it induces a block checkerboard antiferromagnetic phase at wave vector Q(m) = 4Q(v). The coexistence of vacancy order and magnetic order leads to a reconstructed ground state which naturally couples to the d-wave superconductivity in a uniform phase in what we propose will be a general coupling for all iron-selenide superconductors. Our results agree with numerous experimental data available to date. We thus suggest that the incommensurability leads to a uniform coexistence of multiple phases as a viable alternative to a nanoscale phase separation in high-T(c) superconductors and play an important role in the enhancement of superconductivity.
Title:
Disordered polyhalide anion effect on the Fermi surface of the incommensurate organic superconductor (MDT-TSF)I(0.77)Br(0.52)
Authors:
Kawamoto, T; Mori, T; Enomoto, K; Konoike, T; Terashima, T; Uji, S; Kitagawa, H; Takimiya, K; Otsubo, T Author Full Names: Kawamoto, Tadashi; Mori, Takehiko; Enomoto, Kengo; Konoike, Takako; Terashima, Taichi; Uji, Shinya; Kitagawa, Hiroshi; Takimiya, Kazuo; Otsubo, Tetsuo
Source:
PHYSICAL REVIEW B 84 (9): 10.1103/PhysRevB.84.094518 SEP 19 2011
Abstract:
The effect of disorder in polyhalide anions is investigated in terms of the degree of charge transfer and the Fermi surface in the incommensurate organic superconductor (MDT-TSF)I(0.77)Br(0.52), where MDT-TSF is methylenedithio-tetraselenafulvalene. The Raman spectra suggest that the infinite polyhalide chains include the asymmetric trihalide anion I(2)Br(-) and that the degree of charge transfer from the donor molecule to the anion is 0.429, estimated from the lattice constants. The Shubnikov-de Haas (SdH) oscillation is in good agreement with this charge transfer degree. The beating behavior of the SdH oscillation gives a large interlayer transfer integral, which is consistent with a corrugated conducting sheet structure. The randomness of the disordered anions reduces the periodicity of the incommensurate anion potential; this destroys the Fermi surface reconstruction by the incommensurate anion potential. The factor dominating the superconducting transition temperature is not the randomness of the polyhalide anions but the effective cyclotron mass enhancement, i.e., the many-body effect.
Title:
Persistent multiferroicity without magnetoelectric effects in CuO
Authors:
Wang, F; Zou, T; Liu, Y; Yan, LQ; Sun, Y Author Full Names: Wang, Fen; Zou, Tao; Liu, Yi; Yan, Li-Qin; Sun, Young
Source:
JOURNAL OF APPLIED PHYSICS 110 (5): 10.1063/1.3636106 SEP 1 2011
Abstract:
Multiferroicity and magnetoelectric effects in CuO have been investigated by measurements of magnetization, dielectric constant, and electric polarization with and without magnetic fields. Dielectric anomalies which indicate ferroelectric transitions were observed at two magnetic transition temperatures. Ferroelectric polarization was well detected in the incommensurate spiral phase. However, both dielectric constant and polarization have little changes in a 7 T magnetic field. Our study suggests that although with a high multiferroic temperature, the spiral spin structure in CuO is very stable and the induced ferroelectricity sustains even in a high magnetic field, which results in little magnetoelectric effects. (C) 2011 American Institute of Physics. [doi:10.1063/1.3636106]

Update: 28-Sep-2011

Title:
Metamagnetism and soliton excitations in the modulated ferromagnetic Ising chain CoV(2)O(6)
Authors:
Kimber, SAJ; Mutka, H; Chatterji, T; Hofmann, T; Henry, PF; Bordallo, HN; Argyriou, DN; Attfield, JP Author Full Names: Kimber, Simon A. J.; Mutka, Hannu; Chatterji, Tapan; Hofmann, Tommy; Henry, Paul F.; Bordallo, Heloisa N.; Argyriou, Dimitri N.; Attfield, J. Paul
Source:
PHYSICAL REVIEW B 84 (10): 10.1103/PhysRevB.84.104425 SEP 15 2011
Abstract:
We report a combination of physical property and neutron scattering measurements for polycrystalline samples of the one-dimensional spin-chain compound CoV(2)O(6). Heat capacity measurements show that an effective S = 1/2 state is found at low temperatures and that magnetic fluctuations persist up to similar to 6T(N). Above T(N) = 6.3 K, measurements of the magnetic susceptibility as a function of T and H show that the nearest-neighbor exchange is ferromagnetic. In the ordered state, we have discovered a crossover from a metamagnet with strong fluctuations between 5 K and T(N) to a state with a 1/3 magnetization plateau at 2 < T < 5 K. We use neutron powder diffraction measurements to show that the antiferromagnetic state has incommensurate long-range order and inelastic time-of-flight neutron scattering to examine the magnetic fluctuations as a function of temperature. Above T(N), we find two broad bands between 3.5 and 5 meV and thermally activated low-energy features which correspond to transitions within these bands. These features show that the excitations are deconfined solitons rather than the static spin reversals predicted for a uniform ferromagnetic Ising spin chain. Below T(N), we find a ladder of states due to the confining effect of the internal field. A region of weak confinement below T(N), but above 5 K, is identified which may correspond to a crossover between two- and three-dimensional magnetic ordering.
Title:
Effect of dimension on charge order domain in Ruddlesden-Popper manganites
Authors:
Nagao, M; Nagai, T; Hara, T; Kimoto, K Author Full Names: Nagao, M.; Nagai, T.; Hara, T.; Kimoto, K.
Source:
PHYSICA B-CONDENSED MATTER 406 (17): 3192-3195 10.1016/j.physb.2011.05.024 SEP 1 2011
Abstract:
The charge order (CO) domains of dimensionally controlled manganites Pr(1-x)Ca(x)MnO(3) and Pr(1-x)Ca(1+x) MnO(4) (x=0.5, 0.6 and 0.67), which have three-dimensional (3D) and two-dimensional (2D) Mn-O networks, respectively, have been studied by transmission electron microscopy (TEM). Although the electron diffraction data show similar dependences of the modulation wave vector on hole doping x, there are distinctive differences between the 3D and 2D systems in terms of the CO domain sizes. In the 2D system, the TEM images show that the domain size is almost constant irrespective of hole doping x. On the other hand, in the 3D system, the domain size of the incommensurate CO for x=0.6 is much smaller than those of the commensurate CO for x=0.5 and 0.67. Namely, in the 3D system, the CO states are strongly influenced by the incommensurability for the parent lattice. This difference indicates that the dimension of the Mn-O network plays a crucial role in the CO domain and suggests that the electron-lattice coupling of the 3D system is stronger than that of the 2D system. (C) 2011 Elsevier B.V. All rights reserved.
Title:
Effect of chemical composition on the microstructure and hardness of Al-Cu-Fe alloy
Authors:
Suarez, MA; Esquivel, R; Alcantara, J; Dorantes, H; Chavez, JF Author Full Names: Suarez, M. A.; Esquivel, R.; Alcantara, J.; Dorantes, H.; Chavez, J. F.
Source:
MATERIALS CHARACTERIZATION 62 (9): 917-923 10.1016/j.matchar.2011.06.009 SEP 2011
Abstract:
Four Al-Cu-Fe alloys with compositions; a) Al(65)Cu(20)Fe(15), b) Al(64)Cu(22.5)Fe(13.5), c) Al(61)Cu(26)Fe(13) and d) Al(62)Cu(25.5)Fe(12.5), where the icosahedral phase is present, have been experimentally studied in both as-cast and annealed conditions in order to investigate the effect of chemical composition on the percentage of icosahedral phase and the changes in hardness of the alloy and each phase. It was found that the a) Al(65)Cu(20)Fe(15) and b) Al(64)cu(22.5)Fe(13.5) alloys, which present the highest Fe content, showed the largest amount of lambda-Al(13)Fe(4) phase as well as the highest hardness in all phases. In contrast, the same alloys developed the lowest amount of icosahedral phase after heat treatment. The c) Al(61)Cu(26)Fe(13) and d) Al(62)Cu(25.5)Fe(12.5) alloys had a better response to heat treatment, reaching amounts of icosahedral phase up to 87% and 99% respectively. The hardness of phases after heat treatment increased with respect to alloys in as-! cast condition, the hardness of icosahedral phase increased between 20% and 25%, while the hardness of lambda-Al(13)Fe(4) phase increased 9%. The icosahedral phase of annealed a) Al(65)Cu(20)Fe(15) alloy was the toughest with a hardness value of 844HV. (c) 2011 Elsevier Inc. All rights reserved.
Title:
Fermi-surface reconstruction by stripe order in cuprate superconductors
Authors:
Laliberte, F; Chang, J; Doiron-Leyraud, N; Hassinger, E; Daou, R; Rondeau, M; Ramshaw, BJ; Liang, R; Bonn, DA; Hardy, WN; Pyon, S; Takayama, T; Takagi, H; Sheikin, I; Malone, L; Proust, C; Behnia, K; Taillefer, L Author Full Names: Laliberte, F.; Chang, J.; Doiron-Leyraud, N.; Hassinger, E.; Daou, R.; Rondeau, M.; Ramshaw, B. J.; Liang, R.; Bonn, D. A.; Hardy, W. N.; Pyon, S.; Takayama, T.; Takagi, H.; Sheikin, I.; Malone, L.; Proust, C.; Behnia, K.; Taillefer, Louis
Source:
NATURE COMMUNICATIONS 2 10.1038/ncomms1440 AUG 2011
Abstract:
The origin of pairing in a superconductor resides in the underlying normal state. In the cuprate high-temperature superconductor YBa(2)Cu(3)Oy (YBCO), application of a magnetic field to suppress superconductivity reveals a ground state that appears to break the translational symmetry of the lattice, pointing to some density-wave order. Here we use a comparative study of thermoelectric transport in the cuprates YBCO and La(1.8-x)Eu(0.2)Sr(x)CuO(4) (Eu-LSCO) to show that the two materials exhibit the same process of Fermi-surface reconstruction as a function of temperature and doping. The fact that in Eu-LSCO this reconstruction coexists with spin and charge modulations that break translational symmetry shows that stripe order is the generic non-superconducting ground state of hole-doped cuprates.
Title:
RELATIONSHIP BETWEEN CHEMICAL AND ICOSAHEDRAL LOCAL ORDERINGS IN Al-Ni-Fe MELTS
Authors:
Roik, AS; Samsonnikov, AV; Kazimirov, VP; Sokol'skii, VE Author Full Names: Roik, A. S.; Samsonnikov, A. V.; Kazimirov, V. P.; Sokol'skii, V. E.
Source:
JOURNAL OF STRUCTURAL CHEMISTRY 52 (2): 310-318 APR 2011
Abstract:
An X-ray diffraction study and simulation of the structure of ternary Al(81.6)Ni(14.9)Fe(3.5), Al(71.6)Ni(23)Fe(5.4), and Al(61.1)Ni(31.1)Fe(7.3) melts by the reverse Monte Carlo method are conducted. An analysis of the structural models of melts is performed by the Voronoi-Delaunay partition. It is shown that the prepeak on the structure factor curves in the diffraction vector range of 13 nm(-1) to 22 nm(-1) is due to two factors: chemical ordering of atoms and non-crystalline close packing. The origin of the icosahedral short-range order in the melts as one of the variants of ordering of atoms in non-crystalline close packed clusters is discussed.

Update: 22-Sep-2011

Title:
Spatial inhomogeneity and planar symmetry breaking of the lattice incommensurate supermodulation in the high-temperature superconductor Bi(2)Sr(2)CaCu(2)O(8+y)
Authors:
Poccia, N; Campi, G; Fratini, M; Ricci, A; Saini, NL; Bianconi, A Author Full Names: Poccia, Nicola; Campi, Gaetano; Fratini, Michela; Ricci, Alessandro; Saini, Naurang L.; Bianconi, Antonio
Source:
PHYSICAL REVIEW B 84 (10): 10.1103/PhysRevB.84.100504 SEP 12 2011
Abstract:
Using scanning micro-x-ray diffraction we report a mixed real and reciprocal space visualization of the spatial heterogeneity of the lattice incommensurate supermodulation in a single crystal of Bi(2)Sr(2)CaCu(2)O(8+y) with T(c) = 84 K. The mapping shows an amplitude distribution of the supermodulation with large lattice fluctuations at a microscale with similar to 50% amplitude variation. The angular distribution of the supermodulation amplitude in the a-b plane shows a lattice chiral symmetry, forming a left-handed oriented striped pattern. The spatial correlation of the supermodulation is well described by a compressed exponential with an exponent of 1.5 +/- 0.3 and a correlation length of similar to 50 mu m, showing intrinsic lattice disorder in high-temperature superconductors.
Title:
Magnetic structure and electric field effects in multiferroic YMn(2)O(5)
Authors:
de Souza, RA; Staub, U; Scagnoli, V; Garganourakis, M; Bodenthin, Y; Huang, SW; Garcia-Fernandez, M; Ji, S; Lee, SH; Park, S; Cheong, SW Author Full Names: de Souza, R. A.; Staub, U.; Scagnoli, V.; Garganourakis, M.; Bodenthin, Y.; Huang, S. -W.; Garcia-Fernandez, M.; Ji, S.; Lee, S. -H.; Park, S.; Cheong, S. -W.
Source:
PHYSICAL REVIEW B 84 (10): 10.1103/PhysRevB.84.104416 SEP 9 2011
Abstract:
The magnetic structure of multiferroic RMn(2)O(5) (R = Y, Er) has been investigated by means of resonant soft x-ray diffraction. Energy, temperature, and azimuthal angle scans were performed in addition to reciprocal space maps on the magnetic reflection in the different magnetic phases of YMn(2)O(5). We also investigated the orbital magnetic moment at the oxygen K-edge for RMn(2)O(5) with both, R = Y and R = Er compositions. These moments reflect the strong hybridization between Mn 3d and oxygen 2p states. Experiments with applied electric fields are additionally presented, showing that the helical component of the magnetic structure in the CM phase of YMn(2)O(5) can be reversed by the application of an electric field. However, the incommensurate magnetic reflection in the high-temperature phase is unaffected. Interestingly, this is observed only in the presence of a small electrical current, indicative of a current-induced/-enhanced switching of magnetic domains.

Update: 16-Sep-2011

Title:
Magnetoelectric Ordering of BiFeO(3) from the Perspective of Crystal Chemistry
Authors:
Volkova, LM; Marinin, DV Author Full Names: Volkova, L. M.; Marinin, D. V.
Source:
JOURNAL OF SUPERCONDUCTIVITY AND NOVEL MAGNETISM 24 (7): 2161-2177 10.1007/s10948-011-1178-5 OCT 2011
Abstract:
In this paper we examine the role of crystal chemistry factors in creating conditions for formation of magnetoelectric ordering in BiFeO(3). It is generally accepted that the main reason of the ferroelectric distortion in BiFeO(3) is concerned with a stereochemical activity of the Bi lone pair. However, the lone pair is stereochemically active in the paraelectric orthorhombic -phase as well. We demonstrate that a crucial role in emerging of phase transitions of the metal-insulator, paraelectric-ferroelectric and magnetic disorder-order types belongs to the change of the degree of the lone pair stereochemical activity-its consecutive increase with the temperature decrease. Using the structural data, we calculated the sign and strength of magnetic couplings in BiFeO(3) in the range from 945 A degrees C down to 25 A degrees C and found the couplings, which undergo the antiferromagnetic -> aEuro parts per thousand ferromagnetic transition with the temperature decrease and give rise to the antiferromagnetic ordering and its delay in regard to temperature, as compared to the ferroelectric ordering. We discuss the reasons of emerging of the spatially modulated spin structure and its suppression by doping with La(3+).
Title:
Antiferromagnetic Order in Pauli-Limited Unconventional Superconductors
Authors:
Kato, Y; Batista, CD; Vekhter, I Author Full Names: Kato, Yasuyuki; Batista, C. D.; Vekhter, I.
Source:
PHYSICAL REVIEW LETTERS 107 (9): 10.1103/PhysRevLett.107.096401 AUG 26 2011
Abstract:
We develop a theory of the coexistence of superconductivity (SC) and antiferromagnetism (AFM) in CeCoIn(5). We show that in Pauli-limited nodal superconductors the nesting of the quasiparticle pockets induced by Zeeman pair breaking leads to incommensurate AFM with the magnetic moment normal to the field. We compute the phase diagram and find a first order transition to the normal state at low temperatures, the absence of normal state AFM, and the coexistence of SC and AFM at high fields, in agreement with experiments. We also predict the existence of a new double-Q magnetic phase.
Title:
PHOTOINDUCED CHANGES IN THE SPACE-MODULATED MAGNETIC ORDER OF A FeBO(3):Mg SINGLE CRYSTAL
Authors:
Dzhuraev, DR; Sokolov, BY; Faiziev, SS Author Full Names: Dzhuraev, D. R.; Sokolov, B. Yu.; Faiziev, Sh. Sh.
Source:
RUSSIAN PHYSICS JOURNAL 54 (3): 382-385 AUG 2011
Abstract:
An effect of nonpolarized white light on the modulated magnetic structure of a FeBO(3):Mg single crystal, which arises in this light-plane weak ferromagnet in the low temperature range during technical magnetization, has been revealed. It has been found that the degree of the light action on the magnetic state of FeBO(3):Mg depends both on its duration and on the orientation of the spontaneous magnetization vector M of the crystal during illumination. Interpretation of the results obtained has been performed in the context of the "magnetic ripple" theory on the assumption that the absorbed light induces additional uniaxial magnetic anisotropy in the easy plane of the crystal and that the anisotropy axis is collinear to the vector M during illumination.
Title:
Ordered and disordered states in NiAs/Ni(2)In-type Ni(1+delta)Sn: Crystallography and order formation
Authors:
Leineweber, A Author Full Names: Leineweber, Andreas
Source:
INTERNATIONAL JOURNAL OF MATERIALS RESEARCH 102 (7): 861-873 10.3139/146.110540 JUL 2011
Abstract:
An overview on the occupational order disorder behaviour of NiAs/Ni(2)In-type Ni(1+delta)Sn alloys is given. This order disorder behaviour leads to the occurrence of one disordered high-temperature phase HT and three different low-temperature phases LT, LT' and LT". The low-temperature phases, forming in different compositional regimes, are characterised by long-range order of Ni atoms against vacancies on trigonal-bipyramidal sites formed by Sn, leading to a commensurate superstructure in LT whereas LT' and LT" are incommensurate. Different order disorder related phase transformation were monitored by X-ray powder diffraction. In particular during the formation of long-range order starting from disordered HT-Ni(1+delta)Sn, non-equilibrium crystal structures and microstructures evolve prior to formation of the ideally established equilibrium low-temperature phases. Quantitative analysis of the transformation kinetics including determination of activation energies was done by X-ray powder diffraction. The activation energies of the different processes can be related with the mobility of the Ni atoms in the crystal structure.

Update: 8-Sep-2011

Title:
First-principles investigations of the five-layer modulated martensitic structure in Ni(2)Mn(Al(x)Ga(1-x)) alloys
Authors:
Luo, HB; Li, CM; Hu, QM; Kulkova, SE; Johansson, B; Vitos, L; Yang, R Author Full Names: Luo, H. B.; Li, C. M.; Hu, Q. M.; Kulkova, S. E.; Johansson, B.; Vitos, L.; Yang, R.
Source:
ACTA MATERIALIA 59 (15): 5938-5945 10.1016/j.actamat.2011.06.002 SEP 2011
Abstract:
In this paper, the five-layer modulated (5M) martensitic structures of Ni(2)Mn(Al(x)Ga(1-x)), with x = 0, 0.1 and 0.2, are investigated by the use of the exact muffin-tin orbital method in combination with the coherent potential approximation. The 5M martensite is modeled by varying c/a (shear) and wave-like displacements of the atoms on (1 1 0) plane (shuffle) scaled by eta according to Martynov and Kokorin (J. Phys. III 2, 739 (1992)). For Ni(2)MnGa, we obtain 5M martensite with equilibrium c/a of 0.92 and eta of 0.08, in reasonable agreement with the experiment results (0.94 and 0.06, respectively). c/a and eta are linearly coupled to each other. Al-doping increases c/a and decreases eta, but the linear c/a similar to eta coupling remains. Comparing the total energies of the 5M martensite and L2(1) austenite, we find that the martensite is more stable than the austenite. Al-doping increases the relative stability of the austenite and finally becomes energetically degenerated with the 5M martensite at an Al atomic fraction (x) of about 0.26. The relative phase stability is analyzed based on the calculated density of states. The calculated total magnetic moments mu(0) as a function of c/a exhibit a maximum around the equilibrium c/a. Al-doping reduces mu(0) (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Unraveling the Perplexing Structure of the Zeolite SSZ-57
Authors:
Baerlocher, C; Weber, T; McCusker, LB; Palatinus, L; Zones, SI Author Full Names: Baerlocher, Christian; Weber, Thomas; McCusker, Lynne B.; Palatinus, Lukas; Zones, Stacey I.
Source:
SCIENCE 333 (6046): 1134-1137 10.1126/science.1207466 AUG 26 2011
Abstract:
Previous high-resolution x-ray powder diffraction and transmission electron microscopy studies of the zeolite SSZ-57 could not fully elucidate the structural basis for its puzzling adsorption behavior, which appears to be intermediate between that of a medium-(10-ring) and a large-pore (12-ring) zeolite. Now by applying advanced crystallographic techniques (structure solution in four-dimensional space and interpretation of three-dimensional diffuse scattering by Monte Carlo simulation) and crystal chemistry considerations to high-quality single-crystal x-ray diffraction data collected on a microcrystal (about 2 micrometers by 2 micrometers by 8 micrometers), we have been able to derive a comprehensive description of its silicate framework structure. The framework is related to that of ZSM-11 but is commensurately modulated along the c axis (P (4) over bar m2, a = b = 20.091 angstrom, c = 110.056 angstrom) to yield a structure with a 12-ring:10-ring ratio of 1:15. Disorder of the 12-rings results in a three-dimensional 10-ring channel system with large isolated pockets. The structure helps to clarify the material's catalytic activity.
Title:
GOVERNING EQUATIONS AND GENERAL SOLUTIONS OF PLANE ELASTICITY OF TWO-DIMENSIONAL DECAGONAL QUASICRYSTALS
Authors:
Gao, Y; Shang, LG Author Full Names: Gao, Yang; Shang, Lan-Ge
Source:
INTERNATIONAL JOURNAL OF MODERN PHYSICS B 25 (20): 2769-2778 10.1142/S0217979211101065 AUG 10 2011
Abstract:
Two-dimensional problem is systematically investigated for the coupled equations in two-dimensional decagonal quasicrystals, and three general solutions are presented by an operator method. To simplify governing equations, each general solution shall take three different forms expressed in terms of three displacement functions, which satisfy partial three differential equations of second order. To illustrate its utility, the closed-form solutions are obtained for problems of point phonon forces and phason force acting at the apex of a quasicrystal wedge, all in terms of the general solutions. Furthermore, these solutions can be degenerated to those of problems of point forces applied on the boundary of a quasicrystal half-plane.
Title:
Martensitic transformation in rapidly solidified Heusler Ni(49)Mn(39)Sn(12) ribbons
Authors:
Zheng, HX; Wu, DZ; Xue, SC; Frenzel, J; Eggeler, G; Zhai, QJ Author Full Names: Zheng, Hongxing; Wu, Dianzhen; Xue, Sichuang; Frenzel, Jan; Eggeler, Gunther; Zhai, Qijie
Source:
ACTA MATERIALIA 59 (14): 5692-5699 10.1016/j.actamat.2011.05.044 AUG 2011
Abstract:
In the present work, the microstructure evolution and kinetics of the martensitic transformation are investigated in as-spun and annealed ribbons of Heusler Ni(49)Mn(39)Sn(12) using electron microscopy, X-ray diffraction and differential scanning calorimetry. Both ribbons undergo a reversible martensitic transformation during thermal cycling and the low-temperature martensite is confirmed to be a modulated four-layered orthorhombic (4O) structure through in situ cooling transmission electronic microscopy investigation. The annealing effect on the martensitic transformation behavior is discussed from the viewpoints of electron concentration, Mn-Mn inter-atomic distance, atomic order degree and grain size. A strong cooling-rate dependence of phase transition kinetics is found and the mechanism is analyzed. The satisfactory reproducibility obtained during thermal cycling test of this alloy ribbons offers great potential for practical applications. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Antiferromagnet-Long-Period Structure Phase Transition in RMn(2)O(5) Oxides
Authors:
Men'shenin, VV; Nikolaev, VV; Dmitriev, AV Author Full Names: Men'shenin, V. V.; Nikolaev, V. V.; Dmitriev, A. V.
Source:
PHYSICS OF METALS AND METALLOGRAPHY 112 (1): 25-35 10.1134/S0031918X11010315 JUL 2011
Abstract:
An analysis of the magnetic phase transition from an antiferromagnetic into an incommensurate phase in oxides RMn(2)O(5) has been performed. It has been shown that this is a second-order phase transition and that it can occur through one of complete irreducible representations of the space group Pbam, i.e., without a decrease in the symmetry of the crystal lattice. It has been established that the decrease in the electric polarization of the oxides in this transition is due to the development of long-period magnetic ordering.

Update: 31-Aug-2011

Title:
Magnetic correlation in the square-lattice spin system (CuBr)Sr(2)Nb(3)O(10): A neutron diffraction study
Authors:
Yusuf, SM; Bera, AK; Ritter, C; Tsujimoto, Y; Ajiro, Y; Kageyama, H Author Full Names: Yusuf, S. M.; Bera, A. K.; Ritter, C.; Tsujimoto, Yoshihiro; Ajiro, Yoshitami; Kageyama, Hiroshi
Source:
PHYSICAL REVIEW B 84 (6): 10.1103/PhysRevB.84.064407 AUG 18 2011
Abstract:
Magnetic correlation in the quantum S = 1/2 square-lattice system (CuBr) Sr(2)Nb(3)O(10) has been studied by neutron diffraction. A novel commensurate in-plane, helical antiferromagnetic (AFM) ordering, characterized by the propagation vector k = (0 3/8 1/2), has been confirmed from the appearance of magnetic Bragg peaks below T(N) similar to 7.5 K. The ordered moment at 2 K is found to be 0.79(7) mu B/Cu(2+)-ion. The observed helical AFM structure differs from the ground state predicted theoretically from the J(1)-J(2) model as well as from experimentally reported states for other quantum S = 1/2 square-lattice systems. However, the observed helical magnetic structure can be described in a J(1)-J(2)-J(3) model. Under a 4.5 T magnetic field, the spin-order changes drastically and is characterized by the propagation vector k(1) = (0 1/3 0.446) and a probable k(2) = (0 0 0) vector.
Title:
Mechanical properties of clusters in quasicrystal approximants: The example of the 1/1 Al-Cu-Fe approximant
Authors:
Jung, DY; Steurer, W Author Full Names: Jung, Daniel Y.; Steurer, Walter
Source:
PHYSICAL REVIEW B 84 (5): 10.1103/PhysRevB.84.054116 AUG 15 2011
Abstract:
Quantum-mechanical molecular dynamics have been used to investigate structural and physical properties of the 1/1 approximant of the icosahedral Al-Cu-Fe quasicrystal. Particular local structural arrangements of atoms, referred to here as clusters, have been analyzed with respect to their properties within the crystal structure. Artificial strain and cracks have been introduced to probe their mechanical properties, and artificial surfaces have been created to investigate their role for surface termination. From the energetics of the ab initio calculations results that flat surfaces cutting clusters are favored over puckered surfaces keeping clusters intact. The Vienna Ab-initio Simulation Package (VASP) was used for all calculations.
Title:
Pressure-induced formation of intermediate-valence quasicrystalline system in a Cd-Mg-Yb alloy
Authors:
Watanuki, T; Kawana, D; Machida, A; Tsai, A Author Full Names: Watanuki, Tetsu; Kawana, Daichi; Machida, Akihiko; Tsai, AnPang
Source:
PHYSICAL REVIEW B 84 (5): 10.1103/PhysRevB.84.054207 AUG 15 2011
Abstract:
A quasiperiodic intermediate-valence system was prepared by applying pressure to an icosahedral Cd-Mg-Yb quasicrystal. X-ray absorption spectroscopy near the Yb L(3) edge demonstrates that the Yb valence increases continuously upon compression from the divalent state (4f(14)) at ambient pressure and reaches a value of 2.71 at 57.6 GPa, which is close to the trivalent state (4f(13)). By following the trend of Yb-based intermediate-valence crystalline compounds, this large valence increase suggests the change of 4f character in the Cd-Mg-Yb quasicrystal from an itinerant state with weak electron correlations to an intermediate region between an itinerant and a localized state with strong correlations. The valence increases sensitively with pressure below similar to 30 GPa; however, the increase is significantly suppressed above similar to 30 GPa. The rate of valence increase with respect to pressure in the lower-pressure region is twice larger than that of a Cd-Yb quasicrystal in our previous study [Phys. Rev. B 81, 220202(R) (2010)]. This is mainly explained by the smaller bulk modulus of the Cd-Mg-Yb quasicrystal compared to the Cd-Yb system. The suppression of valence increase with respect to pressure in the higher-pressure region is most likely due to an increase of conduction-4f electron hybridization that counteracts 4f localization and reduces the Yb valence increase.
Title:
Effect of relaxation state on nucleation and grain growth of nanoscale quasicrystal in Zr-based bulk metallic glasses prepared under various cooling rates
Authors:
Saida, J; Setyawan, AD; Matsubara, E Author Full Names: Saida, Junji; Setyawan, Albertus Deny; Matsubara, Eiichiro
Source:
APPLIED PHYSICS LETTERS 99 (6): 10.1063/1.3622117 AUG 8 2011
Abstract:
Zr(65)Al(7.5)Ni(10)Cu(12.5)Pd(5) bulk metallic glasses (BMGs) in various relaxation states were prepared under different cooling rates. The grain growth rate of the primary quasicrystal was examined near the crystallization temperature. It was approximately 1 x 10(-9) m/s in less relaxed BMGs and approximately twice as large in relaxed BMGs. In contrast, the calculated homogeneous nucleation rate of the less relaxed samples was five to ten times higher (5 x 10(19)-1 x 10(20)/m(3)s) than those in the relaxed BMGs. The results indicate that the relaxation state of glassy alloys has a marked effect on nucleation and grain growth behaviors. (C) 2011 American Institute of Physics. [doi:10.1063/1.3622117]
Title:
Structural behavior and thermoelectric properties of the brownmillerite system Ca(2)(Zn(x)Fe(2-x))O(5)
Authors:
Asenath-Smith, E; Misture, ST; Edwards, DD Author Full Names: Asenath-Smith, Emily; Misture, Scott T.; Edwards, Doreen D.
Source:
JOURNAL OF SOLID STATE CHEMISTRY 184 (8): 2167-2177 10.1016/j.jssc.2011.06.009 AUG 2011
Abstract:
The Ca(2)(Zn(x)Fe(2-x))O(5) series was synthesized and characterized to determine the influence of zinc dopant on the brownmillerite structure for thermoelectric applications. All single-phase compounds exhibited Pnma symmetry at room temperature up to the solubility limit at x=0.10. High-temperature X-ray powder diffraction was used to show that the nature of the Pnma-Imma(0 0 gamma)s00 transition in Ca(2)Fe(2)O(5) is modified by the presence of zinc. While the Zn-free composition transitions to an incommensurate phase, the Zn-containing phases transition instead to a commensurate phase, Imma(0 0 gamma)s00 with gamma=1/2. Both the Neel temperature and the onset temperature of the Pnma-Imma(0 0 gamma)s00 phase transition decreased with increasing zinc concentration. Rietveld analysis of the in situ diffraction pattern for the x=0 sample at 1300 degrees C demonstrates that the structure contains statistically disordered chain orientations as described by space group Imma. Thermoelectric properties were analyzed in air from 100 to 800 degrees C. The positive Seebeck coefficient revealed hole-type conduction for all compositions. Doped samples exhibited electrical conductivities up to 3.4 S/cm and thermal conductivity of 1.5 W/mK Transport analysis revealed thermally activated mobility consistent with polaron conduction behavior for all compositions. (C) 2011 Elsevier Inc. All rights reserved.
Title:
OPTICAL TRANSMISSION COEFFICIENT OF CRYSTALLINE [N(CH(3))(4)](2)MeCl(4) IN THE INCOMMENSURATE PHASE
Authors:
Sveleba, SA; Karpa, IV; Katerynchuk, IM; Semotyuk, OV; Shymkiv, RM; Kunyo, IM; Fitsych, OI Author Full Names: Sveleba, S. A.; Karpa, I. V.; Katerynchuk, I. M.; Semotyuk, O. V.; Shymkiv, R. M.; Kunyo, I. M.; Fitsych, O. I.
Source:
JOURNAL OF APPLIED SPECTROSCOPY 78 (2): 228-233 MAY 2011
Abstract:
This a study of the optical transmission of [N(CH(3))(4)](2)ZnCl(4) and [N(CH(3))(4)](2)CuCl(4) crystals in the incommensurate phase when a defect density wave is present. It is found that an anomalous reduction in the transmission coefficient is caused by scattering of light owing to a realignment of the superstructure during transitions between metastable states. When a defect density wave is present, the anomalous optical transmission of the crystal is related to the scattering of light on superstructure inhomogeneities produced by a superposition of existing modulation waves.

Update: 25-Aug-2011

Title: Magnetic phase diagrams of the CrB- and FeB-type HoSi compounds

Author(s): Schobinger-Papamantellos, P (Schobinger-Papamantellos, P.); Buschow, KHJ (Buschow, K. H. J.); Rodriguez-Carvajal, J (Rodriguez-Carvajal, J.)

Source: JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS Volume: 323 Issue: 21 Pages: 2592-2607 DOI: 10.1016/j.jmmm.2011.05.044 Published: NOV 2011

Abstract: The temperature magnetic phase diagrams of the dimorphic HoSi compound were studied by neutron diffraction. The sample comprises 35.5% CrB- (Cmcm) and 64.5% FeB-type (Pnma) of structure. Both phases order antiferromagnetically below T(N)=25 K and undergo first-order magnetic transitions at T(ic) = 16.5 K. Their T-phase diagrams comprise a low temperature (LT) 2.7 K - T(ic) and a high temperature (HT) range T(ic) - T(N) with distinct wave vectors. The LT magnetic ordering of the CrB-type HoSi with the wave vector q(1)=(1/2, 0, 1/2) corresponds to a uniaxial magnetic structure, with the Ho moments along the shortest axis c. At 2.7 K the ordered moment value is 8.6(2) mu(B)/Ho atom. The HT ordering, described by the wave vector q(2)=(q(2x), 0, q(2z)) with a T-variable length, corresponds to an amplitude modulated structure. The magnetic ordering of the FeB-type HoSi requires two symmetry independent vectors q(3)=(0, q(3y), q(3z)) for the LT- and q(4)=(q(4x), q(4y), 0) for the HT range. Both vectors correspond to sine wave modulated structures with the Ho magnetic moments confined along the shortest axis b. The q(3) vector has an almost invariable length vs. T close to approximate to (0, 9/17, 1/11). At 2.7 K the amplitude of the wave is 10.9(1) mu(B)/Ho atom. At T(ic) q(3) jumps to the wave vector q(4)=(q(4x), q(4y), 0) with a T-variable length. At 17 K q(4)=(0.092(1), 0.538(3), 0). Around T(ic) there is a narrow coexistence range of the q(3) and q(4) competing phases. Various models are discussed and compared with the isomorphic RSi (R=rare earth) compounds counterparts of HoSi, a comparison that has led us to briefly review the magnetic structures available in the literature for this interesting class of compounds. (C) 2011 Elsevier B.V. All rights reserved.

Title: Antiferromagnetic resonance in ferroborate NdFe(3)(BO(3))(4)

Author(s): Kobets, MI (Kobets, M. I.); Dergachev, KG (Dergachev, K. G.); Khatsko, EN (Khatsko, E. N.); Gnatchenko, SL (Gnatchenko, S. L.); Bezmaternykh, LN (Bezmaternykh, L. N.); Temerov, VL (Temerov, V. L.)

Source: PHYSICA B-CONDENSED MATTER Volume: 406 Issue: 18 Pages: 3430-3435 DOI: 10.1016/j.physb.2011.06.014 Published: SEP 15 2011

Abstract: The AFMR spectra of the NdFe(3)(BO(3))(4) crystal are measured in a wide range of frequencies and temperatures. It is found that by the type of its magnetic anisotropy the compound is an "easy-plane" antiferromagnet with a weak anisotropy in the basal plane. The effective magnetic parameters are determined: anisotropy fields H(a1) = 1.14 kOe and H(a2) = 60 kOe and magnetic excitation gaps Delta v(1) = 101.9 GHz and Delta v(2) = 23.8 GHz. It is shown that commensurate-incommensurate phase transition causes a shift in resonance field and a considerable change in absorption line width. At temperatures below 4.2 K nonlinear regimes of AFMR excitation at low microwave power levels are observed. (C) 2009 Elsevier B.V. All rights reserved.

Title: Incommensurate spin-density wave and a multiband superconducting phase in Na(x)FeAs revealed by nuclear magnetic resonance

Author(s): Klanjsek, M (Klanjsek, M.); Jeglic, P (Jeglic, P.); Lv, B (Lv, B.); Guloy, AM (Guloy, A. M.); Chu, CW (Chu, C. W.); Arcon, D (Arcon, D.)

Source: PHYSICAL REVIEW B Volume: 84 Issue: 5 Article Number: 054528 DOI: 10.1103/PhysRevB.84.054528 Published: AUG 11 2011

Abstract: We report a (23)Na and (75)As nuclear magnetic resonance (NMR) investigation of Na(x)FeAs series (x = 1, 0.9, 0.8) exhibiting a spin-density-wave (SDW) order below T(SDW) = 45, 50, and 43 K for x = 1, 0.9, 0.8, respectively, and a bulk superconductivity below T(c) approximate to 12 K for x = 0.9. Below T(SDW), a spin-lattice relaxation reveals the presence of gapless particle-hole excitations in the whole x range, meaning that a portion of the Fermi surface remains gapless. The superconducting fraction as deduced from the bulk susceptibility scales with this portion, while the SDW order parameter as deduced from the NMR linewidth scales inversely with it. The NMR line shape can only be reproduced assuming an incommensurate (IC) SDW. These findings qualitatively correspond to the mean-field models of competing interband magnetism and intraband superconductivity, which lead to an IC SDW order coexisting with superconductivity in part of the phase diagram.

Title: Effect of selective substitution of Co for Ni or Mn on the superstructure and microstructural properties of Ni(50)Mn(29)Ga(21)

Author(s): Kumar, AS (Kumar, A. Satish); Ramudu, M (Ramudu, M.); Seshubai, V (Seshubai, V.)

Source: JOURNAL OF ALLOYS AND COMPOUNDS Volume: 509 Issue: 32 Pages: 8215-8222 DOI: 10.1016/j.jallcom.2011.05.064 Published: AUG 11 2011

Abstract: Results from a systematic study of the effect of cobalt, selectively substituted for Ni and Mn, in the modulated orthorhombic (7 M) Ni(50)Mn(29)Ga(21) alloy are contrasted. Substitution of Co for Mn resulted in the stabilization of a non-modulated tetragonal (NM) phase at higher Co content. At lower Co contents, a mixture of 7 M and NM phases were found to co-exist. Increasing in Co content caused suppression of long-range twin deformation leading to sporadic islands within which twin variants were confined. These effects are attributed to the considerable stresses generated by an atomic volume change of 9.5% caused locally when Co is substituted for Mn. On the other hand, substitution of Co for Ni, which causes only 1.7% atomic volume change locally, was observed not to alter either the superstructural ordering or the long-range twin deformation. Our results show that the microstructures resultant on Co doping have a strong correlation to the structural ordering, which in turn depends on whether Co is substituted for Mn or for Ni, and also on the concentration of Co. (C) 2011 Elsevier B. V. All rights reserved.

Title: Thermal and electrical transport in the spin density wave antiferromagnet CaFe(4)As(3)

Author(s): Kim, MS (Kim, M. S.); Yin, ZP (Yin, Z. P.); Zhao, LL (Zhao, L. L.); Morosan, E (Morosan, E.); Kotliar, G (Kotliar, G.); Aronson, MC (Aronson, M. C.)

Source: PHYSICAL REVIEW B Volume: 84 Issue: 7 Article Number: 075112 DOI: 10.1103/PhysRevB.84.075112 Published: AUG 5 2011

Abstract: We present here measurements of the thermopower, thermal conductivity, and electrical resistivity of the newly reported compound CaFe(4)As(3). Evidence is presented from specific heat and electrical resistivity measurements that a substantial fraction of the Fermi surface survives the onset of spin density wave (SDW) order at the Neel temperature T(N) = 88 K and its subsequent commensurate lock-in transition at T(2) = 26.4 K. The specific heat below T(2) consists of a normal metallic component from the ungapped parts of the Fermi surface and a Bardeen-Cooper-Schrieffer (BCS) component that represents the SDW gapping of the Fermi surface. A large Kadowaki-Woods ratio is found at low temperatures, showing that the ground state of CaFe(4)As(3) is a strongly interacting Fermi liquid. The thermal conductivity kappa of CaFe(4)As(3) is an order of magnitude smaller than those of conventional metals at all temperatures, due to a strong phonon scattering. The thermoelectric power S displays a sign change from positive to negative indicating that a partial gap forms at the Fermi level with the onset of commensurate spin density wave order at T(2) = 26.4 K. The small value of the thermopower S and the enhancements of the resistivity due to gap formation and strong quasiparticle interactions offset the low value of the thermal conductivity kappa, yielding only a modest value for the thermoelectric figure of merit Z <= 5 x 10(-6) K(-1) in CaFe(4)As(3). The results of ab initio electronic structure calculations are reported, confirming that the sign change in the thermopower at T(2) is reflected by a sign change in the slope of the density of states at the Fermi level. Values for the quasiparticle renormalization Z are derived from measurements of the specific heat and thermopower, indicating that as T -> 0, CaFe(4)As(3) is among the most strongly correlated of the known Fe-based pnictide and chalcogenide systems.

Title: Switching behaviour of modulated ferroelectrics: the kinetics of the field induced lock-in transition in K(2)SeO(4)

Author(s): Leist, J (Leist, J.); Gibhardt, H (Gibhardt, H.); Hradil, K (Hradil, K.); Eckold, G (Eckold, G.)

Source: JOURNAL OF PHYSICS-CONDENSED MATTER Volume: 23 Issue: 30 Article Number: 305901 DOI: 10.1088/0953-8984/23/30/305901 Published: AUG 3 2011

Abstract: The field induced switching process across the ferroelectric lock-in transition in K(2)SeO(4) has been studied on a millisecond timescale using stroboscopic neutron diffraction. The time evolution of both the first and the third order satellites was examined. The time constants are found to vary with temperature between 0.2 and 1.2 ms. This is an order of magnitude faster than in the isostructural Rb(2)ZnCl(4). Moreover, the time dependence of the satellite's linewidth provides information about the evolution of the coherence of the modulated structure.

Title: Pressure-induced change in the magnetic ordering of TbMnO(3)

Author(s): Makarova, OL (Makarova, O. L.); Mirebeau, I (Mirebeau, I.); Kichanov, SE (Kichanov, S. E.); Rodriguez-Carvajal, J (Rodriguez-Carvajal, J.); Forget, A (Forget, A.)

Source: PHYSICAL REVIEW B Volume: 84 Issue: 2 Article Number: 020408 DOI: 10.1103/PhysRevB.84.020408 Published: JUL 20 2011

Abstract: We have studied TbMnO(3) by high-pressure neutron diffraction up to 3.6 GPa and down to 1.5 K. The incommensurate spin structures of the Mn and Tb moments are strongly suppressed under pressure, and an E-type commensurate spin structure with (0,1/2,0) propagation vector is stabilized for the Mn moments. The Mn and Tb incommensurate orders which persist at low pressures or low temperatures are also affected, with a change of phase of the modulation between neighboring Mn chains and a reorientation of the Mn moments along the a axis. The results suggest both a change of the balance of the different Mn-Mn interactions and a strengthening of the Tb-Tb (or Tb-Mn) interactions under pressure.

Title: Transverse and longitudinal lattice modulations in the charge-orbital-ordered manganite Sr(2-x)La(x)MnO(4) around x=0.5

Author(s): Arao, M (Arao, Masazumi); Inoue, Y (Inoue, Yasuhide); Toyoda, K (Toyoda, Kensei); Koyama, Y (Koyama, Yasumasa)

Source: PHYSICAL REVIEW B Volume: 84 Issue: 1 Article Number: 014102 DOI: 10.1103/PhysRevB.84.014102 Published: JUL 15 2011

Abstract: For Sr(2-x)La(x)MnO(4), having a nearly two-dimensional electronic system of e(g) electrons, we have examined the crystallographic features of the charge-orbital-ordered (COO) and charge-exchange (CE)-type magnetic states for 0.40 <= x <= 0.55 by transmission electron microscopy. Incommensurate and commensurate longitudinal lattice modulations were found below similar to 150 K for 0.47 <= x <= 0.51, while the cooling from the disordered tetragonal state resulted in the appearance of transverse modulations below T(COO) for 0.40 <= x <= 0.52. For 0.47 <= x <= 0.51, thus, the longitudinal and transverse modulations were present in both the lower-temperature region of the COO state and the CE-type magnetic state. In addition to these two states, the COO state for 0.40 <= x < 0.47 and 0.51 < x <= 0.52 accompanies only the transverse modulation and should be referred to as the orbital modulated state without a charge modulation.

Title: Neutron diffraction studies of RSn(1+x)Ge(1-x) (R=Tb-Er) compounds

Author(s): Gil, A (Gil, A.); Penc, B (Penc, B.); Baran, S (Baran, S.); Hoser, A (Hoser, A.); Szytula, A (Szytula, A.)

Source: JOURNAL OF SOLID STATE CHEMISTRY Volume: 184 Issue: 7 Pages: 1631-1637 DOI: 10.1016/j.jssc.2011.04.040 Published: JUL 2011

Abstract: The magnetic structures of RSn(1+x)Ge(1-x) (R=Tb, Dy, Ho and Er, x approximate to 0.1) compounds have been determined by neutron diffraction studies on polycrystalline samples. The data recorded in a paramagnetic state confirmed the orthorhombic crystal structure described by the space group Cmcm. These compounds are antiferromagnets at low temperatures. The magnetic ordering in TbSn(1.12)Ge(0.88) is sine-modulated described by the propagation vector k=(0.4257(2), 0, 0.5880(3)). Tb magnetic moment equals 9.0(1)mu(B) at 1.62 K. It lies in the b-c plane and form an angle theta=17.4(2)degrees with the c-axis. This structure is stable up to the Neel temperature equal to 31 K. The magnetic structures of RSn(1+x)Ge(1-x), where R are Dy, Ho and Er at low temperatures are described by the propagation vector k=(1/2, 1/2,0) with the sequence (++- +) of magnetic moments in the crystal unit cell. In DySn(1.09)Ge(0.91) and HoSn(1.1)Ge(0.9) magnetic moments equal 7.25(15) and 8.60(6)mu(B) at 1.55 K, respectively. The moments are parallel to the c-axis. For Ho-compound this ordering is stable up to T(N)=10.7 K. For ErSn(1.08)Ge(0.92), the Er magnetic moment equals 7.76(7)mu(B) at T=1.5 K and it is parallel to the b-axis. At T(t)=3.5 K it tunes into the modulated structure described by the k=(0.496(1), 0.446(4), 0). With the increase of temperature there is a slow decrease of k(x) component and a quick decrease of k(y) component. The Er magnetic moment is parallel to the b-axis up to 3.9 K while at 4 K and above it lies in the b-c plane and form an angle 48(3)degrees with the c-axis. In compounds with R=Tb, Ho and Er the magnetostriction effect at the Neel temperature is observed. (C) 2011 Elsevier Inc. All rights reserved.

Title: Microstructural features and domain formation in (Ba,Sr)(2)TiSi(2)O(8) fresnoites

Author(s): Wong, CL (Wong, Chui Ling); Ferraris, C (Ferraris, Cristiano); White, TJ (White, T. J.)

Source: JOURNAL OF SOLID STATE CHEMISTRY Volume: 184 Issue: 7 Pages: 1768-1776 DOI: 10.1016/j.jssc.2011.05.009 Published: JUL 2011

Abstract: The formation and co-existence of crystallographically modulated and non-modulated regions in (Ba,Sr)(2)TiSi(2)O(8) fresnoites is reviewed, particularly the dependence on local composition. It is shown that perturbations of the average fresnoite structure, determined from appreciable single crystals, are in some cases better described as nanometric domain intergrowths where departures from ideal stoichiometry are characteristics of incommensuration, while modulation is absent from volumes that are less perturbed chemically. Evidence for this differentiation is obtained from selected area electron diffraction (SAED) patterns and high-resolution transmission electron microscopy (HRTEM) images. The domains are readily distinguished by their unique contrast in bright field electron micrographs. Fourier reconstructions of HRTEM images collected from areas with darker contrast show that modulation can change within relatively small volumes. Nearby areas with lighter contrast were found by SAED to be free of structural disorder and incommensurate reflections. (C) 2011 Elsevier Inc. All rights reserved.

Title: Phase diagram studies of Ti-Zr-Ni alloys containing less than 40 at.% Ni and estimated critical cooling rate for icosahedral quasicrystal formation from the liquid

Author(s): Lee, GW (Lee, G. W.); Gangopadhyay, AK (Gangopadhyay, A. K.); Kelton, KF (Kelton, K. F.)

Source: ACTA MATERIALIA Volume: 59 Issue: 12 Pages: 4964-4973 DOI: 10.1016/j.actamat.2011.04.045 Published: JUL 2011

Abstract: A detailed phase diagram study of Ti-Zr-Ni alloys has been conducted using conventional X-ray scattering, microstructural and thermal annealing, and levitation techniques, to improve on the existing phase diagram. Various phases, such as simple crystalline, approximant, icosahedral quasicrystalline, and complex polytetrahedral phases, have been identified. A eutectic composition has been found near 21 at.% Ni for nearly equal Ti and Zr concentrations. From containerless processing studies, using electrostatic levitation, the phase boundary of the icosahedral quasicrystal (i-phase) is placed between 29 and 45 at.% Ti with 21 at.% Ni. A first-time estimate of the critical cooling rate for the formation of the i-phase directly from the liquid in alloys with 21 at.% Ni is less than 100 degrees C s(-1), which is much smaller than for most of the known metastable quasicrystals. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Title: Mechanism of exchange striction of ferroelectricity in multiferroic orthorhombic oMnO(3) single crystals

Author(s): Lee, N (Lee, N.); Choi, YJ (Choi, Y. J.); Ramazanoglu, M (Ramazanoglu, M.); atcliff, W (Ratcliff, W., II); Kiryukhin, V (Kiryukhin, V.); Cheong, SW (Cheong, S. -W.)

Source: PHYSICAL REVIEW B Volume: 84 Issue: 2 Article Number: 020101 DOI: .1103/PhysRevB.84.020101 Published: JUL 1 2011

Abstract: E-type perovskite magnet HoMnO(3) is considered to be a prototype Mn-Mn change-striction driven multiferroic. We have grown orthorhombic HoMnO(3) single cryd studied the directional dependence of their electric polarization P. The direction of P is not ong the crystallographic a axis, as predicted, but along the c axis. The magnetic state is commensurate. The direction P along the c axis is primarily induced by Ho-Mn exchange riction, and Mn-Mn striction in the incommensurate spin state leads to an antiferroelecder along the a axis. We predict the rotation of P with temperature in commensurate E-tyMnO(3) (R denotes magnetic rare earth).

Title: Incommensurate Spin-Density Wave Order in Electron-Doped BaFe(2)As(2) uperconductors

Author(s): Pratt, DK (Pratt, D. K.); Kim, MG (Kim, M. G.); Kreyssig, A (Kreyssig, A.); Lee, B (Lee, Y. B.); Tucker, GS (Tucker, G. S.); Thaler, A (Thaler, A.); Tian, W (Tian, W.); arestky, JL (Zarestky, J. L.); Bud'ko, SL (Bud'ko, S. L.); Canfield, PC (Canfield, P. C.); armon, BN (Harmon, B. N.); Goldman, AI (Goldman, A. I.); McQueeney, RJ (McQueeney, R.)

Source: PHYSICAL REVIEW LETTERS Volume: 106 Issue: 25 Article Number: 57001 DOI: 10.1103/PhysRevLett.106.257001 Published: JUN 20 2011

Abstract: Neutron diffraction studies of Ba(Fe(1-x)Co(x-2))As(2) reveal that commensurate ntiferromagnetic order gives way to incommensurate magnetic order for Co compositions etween 0.056 < x < 0.06. The incommensurability has the form of a small transverse splitting , +/-epsilon, 0) from the commensurate antiferromagnetic propagation vector Q(AFM) = (1, 0, ) (in orthorhombic notation) where epsilon approximate to 0.02 - 0.03 and is composition ependent. The results are consistent with the formation of a spin-density wave driven by Ferface nesting of electron and hole pockets and confirm the itinerant nature of magnetise iron arsenide superconductors.

SN: 0031-9007

Title: Stability of the Sr(2)B(3)O(6.5-delta) Phases (B = Fe, Co, Ga): Existence Range, tructural and Physical Properties

Author(s): Desmoulins, H (Desmoulins, H.); Malo, S (Malo, S.); Perez, O (Perez, O.); elloquin, D (Pelloquin, D.); Maignan, A (Maignan, A.); Hervieu, M (Hervieu, M.)

Source: CHEMISTRY OF MATERIALS Volume: 23 Issue: 11 Pages: 2786-2794 DOI: 0.1021/cm103635g Published: JUN 14 2011

Abstract: A large solid solution Sr(2)(Fe(3-x)Co(x-y)Ga(y))O(6.5-delta)), isostructural with thodulated Fe-2201 and Co-2201-type structures, has been characterized using X-ray powdiffraction (XRPD), transmission electron microscopy (TEM), and energy dispersive pectroscopy (EDS) analyses. The disorder phenomena have been studied using High Rransmission Electron Microscopy (HREM). The evolution of the cell parameters, wavelength f the modulated structures, and transport properties are analyzed versus the three B (Fe, Co, o) cation contents, showing a violation of the Vegard law for a ratio Fe/(Fe + Co + Go) close o x approximate to 0.6. By decreasing the Fe content from that x value, an abrupt variation of esistivity of about 2 orders of magnitude is observed. This spectacular behavior is associated ith the creation of percolative - (Co-O-Co)- pathways. A double effect of the (Co/Ga) ubstitution for Fe is observed on the magnetic properties. First, the B-O-B magnetic nteractions (B = Fe, Co, Ga) are diluted because Ga(3+) is a d(10)s(0) cation and, second, the o(3+)-O-Co(3+) magnetic exchange in that structure is smaller than the Fe(3+)-O-Fe(3) ones. his explained why both the magnitude of the ferromagneto-like component and the T(N) vare reduced as compared to the Fe-2201's.

Title: Effect of Quasicrystal Phase Particle Dispersion on Mechanical Properties in Mg-Zn-Al lloys

Author(s): Somekawa, H (Somekawa, Hidetoshi); Osawa, Y (Osawa, Yoshiaki); Singh, A Singh, Alok); Mukai, T (Mukai, Toshiji)

Source: MATERIALS TRANSACTIONS Volume: 52 Issue: 6 Pages: 1111-1115 DOI: 0.2320/matertrans.MC201014 Published: JUN 11 2011

Abstract: Four kinds of Mg-x mass%Zn-y mass%Al (x = 6, 8, 10, 12 and y = 3, 4, 5, 6) alloys, ach with a grain size of 2 similar to 3 gm and containing quasicrystal phase particles, were uccessfully produced by casting and extrusion. These rare-earth free wrought processed agnesium alloys showed a reduction in mechanical asymmetry and a weak basal texture. lthough the yield strength improved, the elongation decreased with increasing volume fraction f quasicrystal phase particle. The decrease in ductility was related to the existence of coarse uasicrystal phase particles. The strength was affected by the interface strength mechanism; owever, the coherency strain in the quasicrystal phase was smaller than that in the cohase, due to the strong matching between the matrix and the quasicrystal phase. [doi: 0.2320/matertrans.MC201014]

Title: Medium-range icosahedral order in quasicrystal-forming Zr(2)Pd binary metallic glass

Author(s): Huang, L (Huang, Li); Fang, XW (Fang, X. W.); Wang, CZ (Wang, C. Z.); Kramer, MJ (Kramer, M. J.); Ding, ZJ (Ding, Z. J.); Ho, KM (Ho, K. M.)

Source: APPLIED PHYSICS LETTERS Volume: 98 Issue: 23 Article Number: 231906 DOI: 10.1063/1.3597302 Published: JUN 6 2011

Abstract: Medium-range order in Zr(2)Pd metallic glass was studied using a combination of x-ray diffraction experiment and atomistic simulations. We show that, in contrast to earlier experimental interpretations, the icosahedral-like polyhedron is centered around Pd, rather than Zr. Furthermore, we find that the ordered icosahedral packing around Pd extends to the third shell in the way similar to that in the Bergman-type clusters. The existence of Bergman-type clusters sheds interesting light into the formation of nanoquasicrystal phase during cprocess of Zr(2)Pd metallic glass. (C) 2011 American Institute of Physics. [doi:10.1063/1.3597302]

Title: Atomic structure of nanoscale quasicrystal-forming Zr-noble metal binary metallic glasses

Author(s): Saida, J (Saida, J.); Itoh, K (Itoh, K.); Sanada, T (Sanada, T.); Sato, S (Sato, S.); Imafuku, M (Imafuku, M.); Ohnuma, M (Ohnuma, M.); Inoue, A (Inoue, A.)

Source: JOURNAL OF ALLOYS AND COMPOUNDS Volume: 509 Pages: S27-S33 DOI: 10.1016/j.jallcom.2010.12.076 Supplement: 1 Published: JUN 2011

Abstract: We report the results of the local structural evaluation and mechanism of QC formation in the Zr(70)Pd(30) and Zr(80)Pt(20) glassy alloys. Voronoi analysis indicates the difference of local environment between two alloys. The perfect icosahedron frequently exists around Zr atom and major polyhedra have prism-like structure around Pd in Zr(70)Pd(30). In contrast, icosahedral-like distorted polyhedra formation is favorable around Pt as well as Zr in Zr(80)Pt(20). It is therefore, concluded that the quasicrystallization originates from the medium-range order based on the Zr-centered perfect icosahedron and the Pd-centered prism-like ones remain during the QC phase formation in Zr(70)Pd(30). Icosahedral-like local structure around Zr and Pt might contribute together to the nucleation of QC phase in Zr(80)Pt(20). This feature with a different mechanism of QC formation in the two alloys may correlate to the difference of solute concentration and the structure of stable crystalline phase after the decomposition of QC phase. (C) 2010 Elsevier B.V. All rights reserved.

Update: 15-Jul-2011

Title:
THE Al-Cr-Fe PHASE DIAGRAM. I. PHASE EQUILIBRIA AT SUBSOLIDUS TEMPERATURES OVER COMPOSITION RANGE 58-100 AT.% Al
Authors:
Khoruzha, VG; Kornienko, KE; Pavlyuchkov, DV; Grushko, B; Velikanova, TY Author Full Names: Khoruzha, V. G.; Kornienko, K. E.; Pavlyuchkov, D. V.; Grushko, B.; Velikanova, T. Ya
Source:
POWDER METALLURGY AND METAL CERAMICS 50 (1-2): 83-97 MAY 2011
Abstract:
Based on transmission and scanning electron microscopy, x-ray diffraction, electron microprobe and differential thermal analyses, the solidus surface of the ternary Al-Cr-Fe system is constructed for the first time on the concentration triangle over composition range 58-100 at.% Al. Four ternary compounds, D-3, O-1, H, and epsilon, with decagonal, orthorhombic base-centered, hexagonal, and orthorhombic primitive lattices participate in phase equilibria on the solidus surface. Solid solutions based on aluminum and binary compounds as well as ternary phases form 12 single-phase surfaces, 25 ruled surfaces of two-phase equilibria bounding two-phase regions, and 14 three-phase isothermal planes corresponding to invariant four-phase equilibria on the solidus surface.
Title:
Magnetic structure of azurite above the magnetization plateau at 1/3 of saturation
Authors:
Aimo, F; Kramer, S; Klanjsek, M; Horvatic, M; Berthier, C Author Full Names: Aimo, F.; Kraemer, S.; Klanjsek, M.; Horvatic, M.; Berthier, C.
Source:
PHYSICAL REVIEW B 84 (1): Art. No. 012401 JUL 1 2011
Abstract:
The transition from the 1/3 magnetization plateau toward saturation magnetization in azurite has been studied by low-temperature, high-magnetic-field, high-frequency proton nuclear magnetic resonance (NMR). The observed symmetrical splitting of the NMR spectra is incompatible with the longitudinal incommensurate order appearing when the longitudinal correlation function becomes dominant over the transverse one, which is the expected framework for the existence of the 2/3 magnetization plateau. The spectra are instead interpreted in terms of a more standard transverse antiferromagnetic (canted) order.
Title:
Mechanism of exchange striction of ferroelectricity in multiferroic orthorhombic HoMnO3 single crystals
Authors:
Lee, N; Choi, YJ; Ramazanoglu, M; Ratcliff, W; Kiryukhin, V; Cheong, SW Author Full Names: Lee, N.; Choi, Y. J.; Ramazanoglu, M.; Ratcliff, W., II; Kiryukhin, V.; Cheong, S. -W.
Source:
PHYSICAL REVIEW B 84 (2): Art. No. 020101 JUL 1 2011
Abstract:
E-type perovskite magnet HoMnO3 is considered to be a prototype Mn-Mn exchange-striction driven multiferroic. We have grown orthorhombic HoMnO3 single crystals and studied the directional dependence of their electric polarization P. The direction of P is not along the crystallographic a axis, as predicted, but along the c axis. The magnetic state is incommensurate. The direction P along the c axis is primarily induced by Ho-Mn exchange striction, and Mn-Mn striction in the incommensurate spin state leads to an antiferroelectric order along the a axis. We predict the rotation of P with temperature in commensurate E-type RMnO3 (R denotes magnetic rare earth).
Title:
First-order nature of the ferromagnetism in CeIn2 investigated using muon spin rotation and by systematic substitution of La for Ce
Authors:
Rojas, DP; Espeso, JI; Fernandez, JR; Sal, JCG; Rusu, C; Andreica, D; Dudric, R; Amato, A Author Full Names: Rojas, D. P.; Espeso, J. I.; Rodriguez Fernandez, J.; Gomez Sal, J. C.; Rusu, C.; Andreica, D.; Dudric, R.; Amato, A.
Source:
PHYSICAL REVIEW B 84 (2): Art. No. 024403 JUL 5 2011
Abstract:
The nature of the first-order ferromagnetic transition in binary CeIn2 alloy is investigated by muon spin rotation (mu SR) measurements and chemical substitution of Ce by La in the La1-xCexIn2 (0.9 <= x <= 1.0) series of alloys. Below 22 K, the analysis of mu SR spectra shows two spin precession frequencies associated with the local field at the muon site created by the surrounding ferromagnetic ordered magnetic moments. These frequencies abruptly disappear above T-C, indicating the first-order character of this transition, as previously reported. For temperatures between 22 and 24 K, the shape of the mu SR spectra indicates the existence of an additional magnetic phase with features of an incommensurate magnetic structure. The presence of this magnetic phase is supported by dc(ac)- magnetic susceptibility and specific-heat results obtained on chemical diluted samples, which also show a magnetic contribution above the ferromagnetic transition. The combined analysis of these results clarifies the first-order character of the ferromagnetic transition in CeIn2, based on the existence of an intermediate magnetic phase between the paramagnetic and ferromagnetic states.
Title:
Commensurate-incommensurate phase transition in bilayer graphene
Authors:
Popov, AM; Lebedeva, IV; Knizhnik, AA; Lozovik, YE; Potapkin, BV Author Full Names: Popov, Andrey M.; Lebedeva, Irina V.; Knizhnik, Andrey A.; Lozovik, Yurii E.; Potapkin, Boris V.
Source:
PHYSICAL REVIEW B 84 (4): Art. No. 045404 JUL 5 2011
Abstract:
A commensurate-incommensurate phase transition in bilayer graphene is investigated in the framework of the Frenkel-Kontorova model extended to the case of two interacting chains of particles. Analytic expressions are derived to estimate the critical unit elongation of one of the graphene layers at which the transition to the incommensurate phase takes place, the length and formation energy of incommensurability defects (IDs), and the threshold force required to start relative motion of the layers on the basis of dispersion-corrected density functional theory (DFT-D) calculations of the interlayer interaction energy as a function of the relative position of the layers. These estimates are confirmed by atomistic calculations using the DFT-D based classical potential. The possibility to measure the barrier for relative motion of graphene layers by the study of formation of IDs in bilayer graphene is discussed.
Title:
Enhanced piezoelectric and magnetic properties of Bi1-xCaxFe1-x/2Nbx/2O3 solid solutions
Authors:
Troyanchuk, IO; Tereshko, NV; Karpinsky, DV; Kholkin, AL; Kopcewicz, M; Barner, K Author Full Names: Troyanchuk, I. O.; Tereshko, N. V.; Karpinsky, D. V.; Kholkin, A. L.; Kopcewicz, M.; Baerner, K.
Source:
JOURNAL OF APPLIED PHYSICS 109 (11): Art. No. 114102 JUN 1 2011
Abstract:
An investigation of the crystal structure, the magnetic and the piezoelectric properties of polycrystalline Bi1-xCaxFe1-x/2Nbx/2O3 (I) and Bi1-xPbxFe1-x/2Nbx/2O3 (II) systems was performed by x-ray diffraction, Mossbauer spectroscopy, vibrating sample magnetometry, and piezoresponse force microscopy. It is shown that an increasing niobium content induces a polar-to-nonpolar morphotropic boundary near x = 0.19 (I) and x = 0.3 (II). Within the polar region of the system (I), (0.15 <= x <= 0.18), the solid solutions are homogeneous weak ferromagnets whereas compounds of the system (II) do not exhibit an appreciable spontaneous magnetization. It is assumed that chemical substitutions leading to a decrease of the initial volume of the unit cell favor the stabilization of the weak ferromagnetic state within the rhombohedral ferroelectric phase. The piezoresponse is significantly enhanced near the morphotropic boundary. The piezoelectric properties of the parent antiferromagnet BiFeO3, harboring a cycloidal spatially modulated spin structure, are compared with those of the polar weak ferromagnet Bi0.82Ca0.18Fe0.91Nb0.09O3. (C) 2011 American Institute of Physics. [doi:10.1063/1.3594251]

Update: 8-Jul-2011

Title:
Phase Transition and Mechanical Properties of Al-Based Composites Reinforced by Al72Ni12Co16 Decagonal Quasicrystalline Particles
Authors:
Zhu, M; Yang, GC; Cheng, SL; Yao, LJ; Zhou, YH Author Full Names: Zhu Man; Yang Gencang; Cheng Suling; Yao Lijuan; Zhou Yaohe
Source:
RARE METAL MATERIALS AND ENGINEERING 39 (9): 1604-1608 SEP 2010
Abstract:
Aluminum-based composites, using Al72Ni12Co16 decagonal quasicrystalline as reinforcing particles and pure Al and Al-5.5%Zn alloys (mass fraction) as base alloy, were fabricated. The microstructure and the particle distribution of the composite were analyzed by scanning electron microscopy (SEM) and energy dispersive spectrum (EDS). Results show that the phase transition occurs because the decagonal quaicrystalline particles are unstable in the melt. Regular polygon-like theta-phase distributes in the Al matrix, with particle sizes mainly ranging from 3.45-40 mu m. At the same time, fine strip-like gamma-phase with the size of 1.15-8.57 mu m are formed along the grain boundaries. Mechanical property testing results reveal that, due to the existence of the final crystallized phases, yield strength, ultimate tensile strength and Young's modulus of the composites are improved, but the elongation is decreased rapidly.
Title:
Lattice modulation induced by magnetic order in the magnetoelectric helimagnet Ba0.5Sr1.5Zn2Fe12O22
Authors:
Asaka, T; Yu, XZ; Hiraoka, Y; Kimoto, K; Hirayama, T; Kimura, T; Matsui, Y Author Full Names: Asaka, T.; Yu, X. Z.; Hiraoka, Y.; Kimoto, K.; Hirayama, T.; Kimura, T.; Matsui, Y.
Source:
PHYSICAL REVIEW B 83 (13): Art. No. 130401 APR 26 2011
Abstract:
By means of an electron diffraction technique, crystal-lattice modulations were investigated for a hexaferrite, Ba0.5Sr1.5Zn2Fe12O22, showing a helimagnetic order below T-N = 320 K. We observed a lattice modulation with a wave vector Q = (0,0,3 delta) below T-N. The value of delta varies between similar to 0.23 and 0.5 as a function of temperature and corresponds well to that of the magnetic modulation vector. By applying magnetic fields, Ba0.5Sr1.5Zn2Fe12O22 was found to exhibit successive changes in the lattice modulation, accompanied by the modifications of the helical magnetic order. We concluded that the observed lattice modulation is induced by the helical magnetic order via exchange magnetostriction.
Title:
Effects of pressure and temperature on the thermal conductivity of Sn2P2S6
Authors:
Andersson, O; Chobal, O; Rizak, I; Rizak, V; Sabadosh, V Author Full Names: Andersson, O.; Chobal, O.; Rizak, I.; Rizak, V.; Sabadosh, V.
Source:
PHYSICAL REVIEW B 83 (13): Art. No. 134121 APR 26 2011
Abstract:
The thermal conductivity kappa of the ferroelectric, paraelectric, and incommensurate phases of polycrystalline Sn2P2S6 has been measured in the 0.1-0.7 GPa range. The thermal conductivity kappa of the ferroelectric phase decreases with increasing pressure p. This unusual behavior, which is found in only a few other phases, is attributed to a negative Gruneisen parameter. The temperature T dependence of kappa for the ferroelectric phase (kappa similar to T-1) is well described by the Debye model for kappa, with three-phonon Umklapp scattering serving as the dominant scattering mechanism near and above the Debye temperature (similar to 100 K) up to a few tenths of degrees below the ferro- to paraelectric phase transition, where kappa(T) gradually changes and becomes temperature independent upon further heating. The thermal conductivity of the paraelectric and incommensurate phases was temperature independent and indistinguishable. Possible causes for the unu! sually weak T dependence at high temperatures and implications of the p dependence of kappa are discussed.
Title:
Noncollinear spin-density-wave antiferromagnetism in FeAs
Authors:
Rodriguez, EE; Stock, C; Krycka, KL; Majkrzak, CF; Zajdel, P; Kirshenbaum, K; Butch, NP; Saha, SR; Paglione, J; Green, MA Author Full Names: Rodriguez, E. E.; Stock, C.; Krycka, K. L.; Majkrzak, C. F.; Zajdel, P.; Kirshenbaum, K.; Butch, N. P.; Saha, S. R.; Paglione, J.; Green, M. A.
Source:
PHYSICAL REVIEW B 83 (13): Art. No. 134438 APR 28 2011
Abstract:
The nature of the magnetism in the simplest iron arsenide is of fundamental importance in understanding the interplay between localized and itinerant magnetism and superconductivity. We present the magnetic structure of the itinerant monoarsenide FeAs with the B31 structure. Powder neutron diffraction confirms incommensurate modulated magnetism with wave vector q = (0.395 +/- 0.001)c* at 4 K, but can not distinguish between a simple spiral and a collinear spin-density-wave structure. Polarized single-crystal diffraction confirms that the structure is best described as a noncollinear spin-density wave arising from a combination of itinerant and localized behavior with spin amplitude along the b-axis direction being (15 +/- 5)% larger than in the a direction. Furthermore, the propagation vector is temperature dependent, and the magnetization near the critical point indicates a two-dimensional Heisenberg system. The magnetic structures of closely related systems are discussed and compared to that of FeAs.
Title:
Stabilization of commensurate antiferromagnetism in CePt2In7 by pressure up to 2.4 GPa: In-115 NMR and NQR under zero field
Authors:
Sakai, H; Tokunaga, Y; Kambe, S; Lee, HO; Sidorov, VA; Tobash, PH; Ronning, F; Bauer, ED; Thompson, JD Author Full Names: Sakai, H.; Tokunaga, Y.; Kambe, S.; Lee, H. -O.; Sidorov, V. A.; Tobash, P. H.; Ronning, F.; Bauer, E. D.; Thompson, J. D.
Source:
PHYSICAL REVIEW B 83 (14): Art. No. 140408 APR 19 2011
Abstract:
Zero-field In-115-nuclear magnetic resonance (NMR) has been used to study single crystals of CePt2In7, a heavy-fermion antiferromagnet with a Neel temperature (T-N) of 5.2 K at ambient pressure. Narrow linewidths of In-115-nuclear quadrupolar resonance spectra are observed from each of three crystallographically inequivalent In(1), In(2), and In(3) sites. The NMR spectra under zero field near the 3 nu(Q) line of the orthorhombic In(3) sites are tracked by temperatures down to 1.6 K and by hydrostatic pressures up to 2.4 GPa. These data reveal the coexistence of commensurate and incommensurate antiferromagneic orders at ambient pressure and that the commensurate ordering is stabilized by increasing pressures where bulk superconductivity emerges.
Title:
Field-induced incommensurate-to-commensurate phase transition in the magnetoelectric hexaferrite Ba0.5Sr1.5Zn2(Fe1-xAlx)(12)O-22
Authors:
Lee, HB; Song, YS; Chung, JH; Chun, SH; Chai, YS; Kim, KH; Reehuis, M; Prokes, K; Mat'as, S Author Full Names: Lee, Hak Bong; Song, Young-Sang; Chung, Jae-Ho; Chun, Sae Hwan; Chai, Yi Sheng; Kim, Kee Hoon; Reehuis, M.; Prokes, K.; Mat'as, S.
Source:
PHYSICAL REVIEW B 83 (14): Art. No. 144425 APR 26 2011
Abstract:
Using neutron diffraction, we investigated the spin structures of magnetoelectric hexaferrite, Ba0.5Sr1.5Zn2(Fe1-xAlx)(12)O-22 (x = 0.08) under a magnetic field (H perpendicular to c). When the crystal was cooled in a zero field, longitudinal spin cones were observed at low temperatures. These incommensurate phases, however, were replaced by the commensurate phase [ k(1) = (0,0,3/2)] when the ferroelectricity was induced by an external field perpendicular to the c axis. Magnetic structure refinement confirms that this commensurate order is compatible with the spin-current polarization. We argue that planar magnetic anisotropy plays an important role in determining the magnetic structure that is responsible for its magnetoelectricity.
Title:
Electronically phase-separated charge-density waves in Lu2Ir3Si5
Authors:
Lee, MH; Chen, CH; Chu, MW; Lue, CS; Kuo, YK Author Full Names: Lee, M. H.; Chen, C. H.; Chu, M. -W.; Lue, C. S.; Kuo, Y. K.
Source:
PHYSICAL REVIEW B 83 (15): Art. No. 155121 APR 26 2011
Abstract:
We report the investigation of charge density waves (CDW's) in Lu2Ir3Si5 by electron diffraction and dark-field imaging in transmission electron microscopy using superlattice diffraction spots. The CDW state is confirmed by the presence of superlattice reflections. Most interestingly, the CDW state at low temperatures is found to be electronically phase separated, with the coexistence of CDW domains and low-temperature normal phase domains. With a change in temperature, unlike other typical incommensurate CDW systems in which commensurability varies with temperature, we find that commensurability remains unchanged in the present case and that the predominant change is in the redistribution of the area ratio of the two coexisting phases, which is clearly revealed in the dark-field images obtained from the CDW superlattice reflections. The electronic phase separation in the CDW state of Lu2Ir3Si5 is unprecedented in CDW systems, and its temperature dependence is also anomalous.
Title:
Emergent antiferromagnetism in a d-wave superconductor with strong paramagnetic pair-breaking
Authors:
Hatakeyama, Y; Ikeda, R Author Full Names: Hatakeyama, Yuhki; Ikeda, Ryusuke
Source:
PHYSICAL REVIEW B 83 (22): Art. No. 224518 JUN 28 2011
Abstract:
It is theoretically shown that, in the fourfold symmetric d-wave superconducting phase, a paramagnetic pair-breaking (PPB) enhanced sufficiently by increasing the applied magnetic field induces not only the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) superconducting state but also an incommensurate antiferromagnetic (AFM) order with the Q vector parallel to a gap node. This AFM ordering tends to occur only below H-c2 at low temperatures, i.e., in the presence of a nonvanishing superconducting energy gap Delta rather than in the normal phase. Through a detailed study on the resulting AFM order and its interplay with the FFLO spatial modulation of Delta, it is argued that the strange high-field, low-temperature (HFLT) superconducting phase of CeCoIn5 is a coexisting phase of the FFLO and incommensurate AFM orders, and that this PPB mechanism of an AFM ordering is also the origin of the AFM quantum critical fluctuation which has occurred close to H-c2(0) in several unconventional superconductors including CeCoIn5.
Title:
Magnetic fluctuations and self-energy effects in two-dimensional itinerant systems with a van Hove singularity in the electronic spectrum
Authors:
Igoshev, PA; Irkhin, VY; Katanin, AA Author Full Names: Igoshev, P. A.; Irkhin, V. Yu.; Katanin, A. A.
Source:
PHYSICAL REVIEW B 83 (24): Art. No. 245118 JUN 22 2011
Abstract:
We investigate a competition of tendencies toward ferromagnetic and incommensurate order in two-dimensional fermionic systems within functional renormalization-group technique, accounting for the self-energy corrections and using temperature as a scale parameter. We assume that the Fermi surface (FS) is substantially curved and lies in the vicinity of van Hove singularity points. It is shown that the character of magnetic fluctuations is strongly asymmetric with respect to the Fermi level position relative to van Hove singularity (VHS). For the Fermi level above VHS, we find at low temperatures dominant incommensurate magnetic fluctuations, while below the VHS level, we find indications for the ferromagnetic ground state. In agreement with the Mermin-Wagner theorem, at finite temperatures and in small magnetic fields, we obtain small magnetization, which appears to be a power-law function of magnetic field. It is found that the FS curvature is slightly increased by correlation effects, and the renormalized bandwidth decreases at sufficiently low temperatures.
Title:
Modulated martensite: why it forms and why it deforms easily
Authors:
Kaufmann, S; Niemann, R; Thersleff, T; Rossler, UK; Heczko, O; Buschbeck, J; Holzapfel, B; Schultz, L; Fahler, S Author Full Names: Kaufmann, S.; Niemann, R.; Thersleff, T.; Roessler, U. K.; Heczko, O.; Buschbeck, J.; Holzapfel, B.; Schultz, L.; Faehler, S.
Source:
NEW JOURNAL OF PHYSICS 13: Art. No. 053029 MAY 16 2011
Abstract:
Diffusionless phase transitions are at the core of the multifunctionality of (magnetic) shape memory alloys, ferroelectrics and multiferroics. Giant strain effects under external fields are obtained in low symmetric modulated martensitic phases. We outline the origin of modulated phases, their connection with tetragonal martensite and consequences owing to their functional properties by analysing the martensitic microstructure of epitaxial Ni-Mn-Ga films from the atomic to the macroscale. Geometrical constraints at an austenite-martensite phase boundary act down to the atomic scale. Hence, a martensitic microstructure of nanotwinned tetragonal martensite can form. Coarsening of twin variants can reduce twin boundary energy, a process we could observe from the atomic to the millimetre scale. Coarsening is a fractal process, proceeding in discrete steps by doubling twin periodicity. The collective defect energy results in a substantial hysteresis, which allows the retention of modulated martensite as a metastable phase at room temperature. In this metastable state, elastic energy is released by the formation of a 'twins within twins' microstructure that can be observed from the nanometre to the millimetre scale. This hierarchical twinning results in mesoscopic twin boundaries. Our analysis indicates that mesoscopic boundaries are broad and diffuse, in contrast to the common atomically sharp twin boundaries of tetragonal martensite. We suggest that the observed extraordinarily high mobility of such mesoscopic twin boundaries originates from their diffuse nature that renders pinning by atomistic point defects ineffective.
Title:
Textures and mechanical properties in rare-earth free quasicrystal reinforced Mg-Zn-Zr alloys prepared by extrusion
Authors:
Ohhashi, S; Kato, A; Demura, M; Tsai, AP Author Full Names: Ohhashi, S.; Kato, A.; Demura, M.; Tsai, A. P.
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 528 (18): 5871-5874 JUL 15 2011
Abstract:
Microstructure and mechanical properties of quasicrystals dispersed Mg alloys prepared by warm extrusion of the mixtures of Mg and Zn-Mg-Zr quasicrystalline (Qc) powders have been studied. Strong texture oriented along a [10 (1) over bar 0] direction observed in pure Mg was reduced in Qc-dispersed samples, as verified by pole figure method and electron back scattering diffraction. The ultimate tensile strengths at 150 degrees C for Qc-dispersed extrusions were much higher than 110 MPa for pure Mg, which drastically reached 156 MPa for 15 wt.% Qc by preventing the motion of dislocations. Elongation was improved by the randomization of grain orientation: from 5.7% for pure Mg to 12.9% for 10 wt.% Qc at room temperature; from 15% for pure Mg to 37.1% for 5 wt.% Qc at 150 degrees C. (C) 2011 Elsevier B.V. All rights reserved.
Title:
Does the modulated magnetic structure of BiFeO3 change at low temperatures?, (vol 18, pg 2069, 2006)
Authors:
Przenioslo, R; Palewicz, A; Regulski, M; Sosnowska, I; Ibberson, RM; Knight, KS Author Full Names: Przenioslo, R.; Palewicz, A.; Regulski, M.; Sosnowska, I.; Ibberson, R. M.; Knight, K. S.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 23 (27): Art. No. 279501 JUL 11 2011
Title:
Kaleidoscopic morphologies from ABC star-shaped terpolymers
Authors:
Matsushita, Y; Hayashida, K; Dotera, T; Takano, A Author Full Names: Matsushita, Yushu; Hayashida, Kenichi; Dotera, Tomonari; Takano, Atsushi
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 23 (28): Art. No. 284111 JUL 20 2011
Abstract:
Star-shaped terpolymers of the ABC type composed of incompatible polymer components give a variety of ordered structures with mesoscopic length scales depending on their composition ratio. Their peculiar features are summarized in this report. Polymer components adopted are polyisoprene (I), polystyrene (S) and poly(2-vinylpyridine) (P), and many monodisperse samples of the IXSY P-Z type were anionically prepared. Firstly our focus is on molecules of the I1.0S1.0Px1 type, where x(1) is only a variable. The complex but systematic morphology change was displayed within the range 0.2 <= x(1) <= 10, that is, their structures change from spherical plus lamellae structure for I1.0S1.0P0.2 to periodic tilings (0.4 <= x(1) <= 1.9), then to lamellae-in-lamella (3.0 <= x(1) <= 4.9) and lamellae-in-cylinder (7.9 <= x(1) <= 10) structures with increasing x(1). Here if we pay attention to the structural variation of the P domain inclusively, it transforms from sphere to cylinder, lamel! la and then to matrix, which is the same as that for linear polymers. Among them, several periodic Archimedean tiling patterns can be naturally formed when the relative lengths of the three chains are close to one another. Moreover, it has been found that the tiling zone is spread out widely. For example, the series I1.0S1.8Px2 (with 0.8 <= x(2) <= 2.9) and the other series I1.0SyP2.0 (with 1.1 <= y <= 2.7) show mostly Archimedean tilings. Additionally, block copolymer/homopolymer blends with a composition of I1.0S2.7P2.5 reveal a quasicrystalline tiling with dodecagonal symmetry. Furthermore, a zinc-blende-type four-branched network structure was created just a little outside of the tiling region for a block copolymer/homopolymer blend of I1.0S2.3P0.8. When some more asymmetry in chain length is introduced, hyperbolic tiling on a gyroid membrane has successfully been constructed for the sample I1.0S1.8P3.2 and it transforms into a hierarchical cylinders-in-lamella structure with further increase in P content to I1.0S1.8P6.4. Thus, kaleidoscopic morphologies have been generated from ABC star-shaped terpolymers and their structural change has turned out to be very sensitive to relative compositions.
Title:
Ductile quasicrystalline alloys (vol 76, pg 967, 2000)
Authors:
Inoue, A; Chen, MW; Sakurai, T; Zhang, T; Saida, J; Matsushita, M Author Full Names: Inoue, A.; Chen, M. W.; Sakurai, T.; Zhang, T.; Saida, J.; Matsushita, M.
Source:
APPLIED PHYSICS LETTERS 98 (25): Art. No. 259902 JUN 20 2011

Update: 1-Jul-2011

Title:
Organic molecular compounds with modulated crystal structures
Authors:
Schonleber, A Author Full Names: Schoenleber, Andreas
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE 226 (6): 499-517 2011
Abstract:
Even though the higher-dimensional superspace approach is an established method to describe aperiodic crystal structures, it is not yet fully considered and applied by a larger community of scientists. In this contribution the structural description of incommensurately and commensurately modulated molecular compounds is discussed and it is shown, that the higher-dimensional superspace approach is an elegant way for an exact structural description and an exact crystal-chemical analysis of such structures. While discussing several modulated molecular compounds, the idea behind the higher-dimensional superspace approach is shown. On the examples treated in the discussion it is explained, how to understand and how to interprete modulated molecular compounds. Also a short introduction is given to the higher-dimensional superspace approach itself, to the basic principles and to the applied nomenclature.
Title:
Medium-range icosahedral order in quasicrystal-forming Zr2Pd binary metallic glass
Authors:
Huang, L; Fang, XW; Wang, CZ; Kramer, MJ; Ding, ZJ; Ho, KM Author Full Names: Huang, Li; Fang, X. W.; Wang, C. Z.; Kramer, M. J.; Ding, Z. J.; Ho, K. M.
Source:
APPLIED PHYSICS LETTERS 98 (23): Art. No. 231906 JUN 6 2011
Abstract:
Medium-range order in Zr2Pd metallic glass was studied using a combination of x-ray diffraction experiment and atomistic simulations. We show that, in contrast to earlier experimental interpretations, the icosahedral-like polyhedron is centered around Pd, rather than Zr. Furthermore, we find that the ordered icosahedral packing around Pd extends to the third shell in the way similar to that in the Bergman-type clusters. The existence of Bergman-type clusters sheds interesting light into the formation of nanoquasicrystal phase during crystallization process of Zr2Pd metallic glass. (C) 2011 American Institute of Physics. [doi:10.1063/1.3597302]

Update: 24-Jun-2011

Title:
THE FIBONACCI-PENROSE SEMIGROUP FORMALISM AND MORPHOGENETIC SYNTHESIS OF QUASICRYSTAL MOSAICS
Authors:
Yudin, VV; Startzev, ES; Permyakova, IG Author Full Names: Yudin, V. V.; Startzev, E. S.; Permyakova, I. G.
Source:
THEORETICAL AND MATHEMATICAL PHYSICS 167 (1): 517-537 APR 2011
Abstract:
We construct the group bundle for the inverse Fibonacci semigroups in the axiomatic approach framework. The proper Fibonacci semigroup is the corresponding group bundle for the Penrose semigroups, which can be interpreted as the generating grammar of the morphogenetic synthesis of the pentasymmetric Penrose parquet in the numbers of tiling by golden rhombuses. This morphogenetic synthesis of the Penrose parquet satisfies the scaling principle. Parquet plates are not absolutely rigid, and the relations between their metric characteristics are governed by the golden section and other magic numbers. The characteristic form factors of three-level dual alphabets are the corresponding invariants. We realize the morphogenetic synthesis in the examples of square-octagonal and bihexagonal lattices. We consider cumulative properties of magic series and the evolutionary aspects of semigroup orbits in the entropy representation.
Title:
Improvement of microstructure and mechanical properties of Mg-8Gd-3Y by adding Mg3Zn6Y icosahedral phase alloy
Authors:
Kang, HJ; Wu, SP; Li, XZ; Guo, JJ; Wang, Y Author Full Names: Kang, Huijun; Wu, Shiping; Li, Xinzhong; Guo, Jingjie; Wang, Ye
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 528 (16-17): 5585-5591 JUN 25 2011
Abstract:
Mg-Zn-Y quasicrystal alloy (QA) particles reinforced composite was prepared using an adscititious method, and characterized using scanning electron microscope (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and tensile testing technique at room temperature. Experimental results indicate that alpha-Mg columnar dendrite gradually becomes fine equiaxed dendrite and ellipsoidal cellular dendrite as more Mg-Zn-Y QA particles are added into the matrix alloy. Thread-like Mg-24(Gd,Y)(5) phases and rod-like Mg-5(Gd,Y) phases are replaced by lamellar Mg-24(Zn,Gd,Y)(5) compounds and granule Mg3Zn6(Y,Gd) quasicrystal l-phases. The ultimate tensile strength and yield strength of the composite increase by about 45 MPa and 20 MPa respectively when the amount of QA particles added increases from 3% to 15%. It can therefore be concluded that the microstructure and mechanical properties of Mg-8Gd-3Y alloy can be improved by adding QA particles. (C) 2011 Elsevier B.V. All rights reserved.
Title:
Inelastic neutron and x-ray scattering from incommensurate magnetic systems
Authors:
Boni, P; Roessli, B; Hradil, K Author Full Names: Boeni, Peter; Roessli, Bertrand; Hradil, Klaudia
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 23 (25): Art. No. 254209 JUN 29 2011
Abstract:
Neutrons and x-rays are powerful probes for studying magnetic and lattice excitations in strongly correlated materials over very wide ranges of momentum and energy transfers. In the focus of the present work are the incommensurate magnetic systems MnSi and Cr. Under application of a magnetic field, helically ordered MnSi transforms into a weak itinerant ferromagnet. Using polarized neutrons we demonstrate that the Stoner excitations are spin-flip excitations. The amplitude (longitudinal) fluctuations associated with the magnon modes are already strong far away from T-c. Interestingly, even the non-spin-flip excitations associated with the Stoner modes are observable. In Cr, we have observed Kohn anomalies in the phonon spectrum at those incommensurate positions in reciprocal space, where the spin density wave is observed. The corresponding phonon and magnon modes are not coupled. In addition, an anomalous softening of a transverse phonon branch along the N-H zone boundary line is observed that is caused by strong electron-phonon coupling. High resolution neutron scattering indicates that the low energy Fincher-Burke excitations may rather correspond to localized modes in momentum and energy and not to propagating collective modes. Finally, we demonstrate that in the near future it may become feasible to investigate excitations in very small samples, thus allowing us to measure the dynamics of strongly correlated materials under extreme conditions and in the vicinity of quantum phase transitions.
Title:
Fano line shape and anti-crossing of Raman active E-2g peaks in the charge density wave state of NbSe2
Authors:
Mialitsin, A Author Full Names: Mialitsin, Aleksej
Source:
JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS 72 (5): 568-571 Sp. Iss. SI MAY 2011
Abstract:
Low energy Raman scattering from the ab-plane of the 2H polytype single crystal NbSe2 has been investigated in the normal (N), incommensurate charge density wave (ICDW) and superconducting (SC) phases. The temperature dependence of the polarization resolved Raman response has been obtained for the excitation wavelength of 647 nm and fitted to phenomenological models for the E-2g and A(1g) symmetry channels. The A(1g) response can be fitted by a simple damped oscillator peak superimposed on continuous background. The E-2g response displays an anti-resonance interference pattern between the inter-layer phonon and the CDW-induced mode such that a hybridized configuration (Fano line shape [1]) is required for modelling. The polarization specific peak maxima positions and line widths as a function of temperature, deduced in this manner, are presented. Partial suppression of the electronic continuum scattering in the Raman shift range up to 110 cm(-1) in the A(1g) symmetry channel and beyond 300 cm(-1) in the E-2g symmetry channel is indicative of high energy electronic states far away from the Fermi surface participating in the ICDW formation. Published by Elsevier Ltd.
Title:
Atomic structure of nanoscale quasicrystal-forming Zr-noble metal binary metallic glasses
Authors:
Saida, J; Itoh, K; Sanada, T; Sato, S; Imafuku, M; Ohnuma, M; Inoue, A Author Full Names: Saida, J.; Itoh, K.; Sanada, T.; Sato, S.; Imafuku, M.; Ohnuma, M.; Inoue, A.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 509: S27-S33 Suppl. 1 JUN 2011
Abstract:
We report the results of the local structural evaluation and mechanism of QC formation in the Zr70Pd30 and Zr80Pt20 glassy alloys. Voronoi analysis indicates the difference of local environment between two alloys. The perfect icosahedron frequently exists around Zr atom and major polyhedra have prism-like structure around Pd in Zr70Pd30. In contrast, icosahedral-like distorted polyhedra formation is favorable around Pt as well as Zr in Zr80Pt20. It is therefore, concluded that the quasicrystallization originates from the medium-range order based on the Zr-centered perfect icosahedron and the Pd-centered prism-like ones remain during the QC phase formation in Zr70Pd30. Icosahedral-like local structure around Zr and Pt might contribute together to the nucleation of QC phase in Zr80Pt20. This feature with a different mechanism of QC formation in the two alloys may correlate to the difference of solute concentration and the structure of stable crystalline phase after the decomposition of QC phase. (C) 2010 Elsevier B.V. All rights reserved.
Title:
The quasicrystalline phase formation in Al-Cu-Cr alloys produced by mechanical alloying
Authors:
Sviridova, TA; Shevchukov, AP; Shelekhov, EV; Diakonov, DL; Tcherdyntsev, VV; Kaloshkin, SD Author Full Names: Sviridova, T. A.; Shevchukov, A. P.; Shelekhov, E. V.; Diakonov, D. L.; Tcherdyntsev, V. V.; Kaloshkin, S. D.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 509: S299-S303 Suppl. 1 JUN 2011
Abstract:
Almost single-phase decagonal quasicrystal with periodicity of 1.26 nm along 10-fold axis was produced in Al69Cu21Cr10 and Al72.5Cu16.5Cr11 alloys using combination of mechanical alloying (MA) and subsequent annealing. Phase transformations of as-milled powders depending on annealing temperature in the range of 200-800 degrees C are examined. Since the transformations can be explained based on kinetic and thermodynamic reasons it seems that applied technique (short preliminary MA followed by the annealing) permits to produce the equilibrium phases rather than metastable ones. (C) 2010 Elsevier B.V. All rights reserved.
Title:
Microstructures and mechanical properties of conventionally solidified Al63Cu25Fe12 alloy
Authors:
Gogebakan, M; Avar, B; Tarakci, M Author Full Names: Gogebakan, M.; Avar, B.; Tarakci, M.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 509: S316-S319 Suppl. 1 JUN 2011
Abstract:
In this study, the microstructures and mechanical properties of conventionally solidified Al63Cu25Fe12 alloy after different heat-treatments were investigated. The microstructures of the as-cast and subsequently heat-treated samples were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and differential thermal analysis (DTA). The XRD results showed the presence of quasicrystalline icosahedral phase (i-phase) together with crystalline phases corresponding to beta-AlFe(Cu) solid solution phase (beta-phase) and tau-AlCu(Fe) solid solution phase (tau-phase). The SEM investigations clearly showed the formation of i-phase with pentagonal dodecahedra structure. However, the i-phase together with beta-phase was also observed in the heat-treated samples and the peak intensity of the beta-phase decreased with increasing heat-treatment temperature. From the DTA curves, the melting point of i-phase was determined as 890 degrees C for this alloy composition. Mechanical properties of the as-cast and subsequently heat-treated samples were measured by a Vickers indenter. Results showed that the microhardness (HV) and the elastic modulus (E) of the as-cast sample were around 598 kg fmm(-2) (5.86 GPa) and 104 GPa, respectively. In addition, the characteristic of material plasticity (delta(H)) value was calculated to be 0.54. (C) 2010 Elsevier B.V. All rights reserved.
Title:
Stability of the Sr2B3O6.5-delta Phases (B = Fe, Co, Ga): Existence Range, Structural and Physical Properties
Authors:
Desmoulins, H; Malo, S; Perez, O; Pelloquin, D; Maignan, A; Hervieu, M Author Full Names: Desmoulins, H.; Malo, S.; Perez, O.; Pelloquin, D.; Maignan, A.; Hervieu, M.
Source:
CHEMISTRY OF MATERIALS 23 (11): 2786-2794 JUN 14 2011
Abstract:
A large solid solution Sr-2(Fe3-xCox-yGay)O6.5-delta), isostructural with the modulated Fe-2201 and Co-2201-type structures, has been characterized using X-ray powder diffraction (XRPD), transmission electron microscopy (TEM), and energy dispersive spectroscopy (EDS) analyses. The disorder phenomena have been studied using High Resolution Transmission Electron Microscopy (HREM). The evolution of the cell parameters, wavelength of the modulated structures, and transport properties are analyzed versus the three B (Fe, Co, Go) cation contents, showing a violation of the Vegard law for a ratio Fe/(Fe + Co + Go) close to x approximate to 0.6. By decreasing the Fe content from that x value, an abrupt variation of resistivity of about 2 orders of magnitude is observed. This spectacular behavior is associated with the creation of percolative - (Co-O-Co)- pathways. A double effect of the (Co/Ga) substitution for Fe is observed on the magnetic properties. First, the B-O-B magnetic interactions (B = Fe, Co, Ga) are diluted because Ga3+ is a d(10)s(0) cation and, second, the Co3+-O-Co3+ magnetic exchange in that structure is smaller than the Fe3+-O-Fe-3 ones. This explained why both the magnitude of the ferromagneto-like component and the T-N values are reduced as compared to the Fe-2201's.

Update: 17-Jun-2011

Title:
Symmetry mode analysis of the phase transitions in Rb2ZnBr4
Authors:
Zuniga, FJ; Perez-Mato, JM; Orobengoa, D; Petricek, V; Breczewski, T Author Full Names: Javier Zuniga, Fco; Manuel Perez-Mato, J.; Orobengoa, Danel; Petricek, Vaclav; Breczewski, Tomasz
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE 226 (5): 454-466 2011
Abstract:
Crystal structures of low temperature phases HI, IV and V of rubidium zinc bromide have been determined by single crystal X-ray diffraction at 90 K, 85 K, and 30 K, respectively. The analysis of the structures in terms of symmetry-adapted modes of the high temperature prototype phase permits the identification of the modes responsible for each phase and to assess its thermal evolution. The primary mode responsible for the incommensurate and lock-in phases remains dominant throughout the whole transition sequence, maintaining its structure and slightly increasing its amplitude as temperature decreases. The two monoclinic phases IV and V are presumably due to the instability of a second mode associated with a single active irreducible representation. However, the presence with similar weights of several symmetry-adapted distortions of different symmetry indicates a strong hybridization in phase permits the identification of the softer normal modes. A symmetry-mode description of the structures of phase IV and V fully consistent with a simple Landau model, can then only be obtained if phase III is taken as effective parent phase. Besides the insight on the microscopic origin of the different phases, the symmetry modes were used as crystallographic coordinates in the refinement of the structure of phase V. The result shows the advantages of using these non-conventional collective structural parameters instead of individual atomic coordinates. The refinable parameters can be reduced to the amplitudes of those symmetry modes with significant weight in the distortions.
Title:
Spiral ground state against ferroelectricity in the frustrated magnet BiMnFe2O6
Authors:
Abakumov, AM; Tsirlin, AA; Perez-Mato, JM; Petricek, V; Rosner, H; Yang, T; Greenblatt, M Author Full Names: Abakumov, Artem M.; Tsirlin, Alexander A.; Perez-Mato, Juan Manuel; Petricek, Vaclav; Rosner, Helge; Yang, Tao; Greenblatt, Martha
Source:
PHYSICAL REVIEW B 83 (21): Art. No. 214402 JUN 2 2011
Abstract:
The spiral magnetic structure and underlying spin lattice of BiMnFe2O6 are investigated by low-temperature neutron powder diffraction and density functional theory band structure calculations. In spite of the random distribution of the Mn3+ and Fe3+ cations, this centrosymmetric compound undergoes a transition into an incommensurate antiferromagnetically ordered state below T-N similar or equal to 220 K. The magnetic structure is characterized by the propagation vector k = [0, beta, 0] with beta similar or equal to 0.14 and the P22(1)2(1)1'(0 beta 0)0s0s magnetic superspace symmetry. It comprises antiferromagnetic helixes propagating along the b axis. The magnetic moments lie in the ac plane and rotate about pi(1 + beta) similar or equal to 204.8-deg angle between the adjacent magnetic atoms along b. The spiral magnetic structure arises from the peculiar frustrated arrangement of exchange couplings in the ab plane. The antiferromagnetic coupling along the c axis cancels the possible electric polarization and prevents ferroelectricity in BiMnFe2O6.
Title:
Vacancy and substitutional impurities in the spin-density wave state of Cr from first principles
Authors:
Soulairol, R; Fu, CC; Barreteau, C Author Full Names: Soulairol, R.; Fu, Chu-Chun; Barreteau, C.
Source:
PHYSICAL REVIEW B 83 (21): Art. No. 214103 JUN 3 2011
Abstract:
Density functional theory (DFT) calculations are carried out to study magnetic and energetic properties of vacancy, and magnetic and nonmagnetic substitutional impurities (respectively Fe and Cu) in the ground state of bcc Cr, i.e., spin-density wave (SDW). We find the lowest energy site for all the defects to be around a magnetic node, as compared with the high-spin SDW sites and (100)- layered antiferromagnetic (AF) and nonmagnetic (NM) phases. The corresponding differences for vacancy formation energy are 0.29, 0.32, and 0.23 eV, respectively. The migration of a vacancy is revealed to be highly anisotropic in the SDW state, mainly confined in the nodal and adjacent planes. The energy barrier for such a quasi-bidimensional motion is indeed 0.52 eV lower than that for migration in perpendicular directions. Regarding magnetic modifications of the SDW introduced by point defects, they are confirmed to be weak and rather local at low defect concentrations (0.27% and 0.55%). Cu behaves similarly to a vacancy-inducing magnetic moment enhancement on neighboring Cr atoms. On the other side, the presence of Fe atoms leads to multiple energy minima with different local magnetic arrangements, particularly around a node, due to competition between neighboring Fe-Cr, Cr-Cr, and Fe-Fe magnetic coupling tendencies. The present results strongly suggest that simple AF and NM phases may not allow an accurate description of defect properties in the ground state of Cr. Instead, an explicit SDW representation is required. In addition, we point out that the presence of vacancy and both Cu and Fe may promote a migration of SDW nodes, which may activate the SDW-to-AF phase transition through a node-annihilation mechanism as proposed in previous works.
Title:
Competing charge density waves and temperature-dependent nesting in 2H-TaSe2
Authors:
Leininger, P; Chernyshov, D; Bosak, A; Berger, H; Inosov, DS Author Full Names: Leininger, Ph; Chernyshov, D.; Bosak, A.; Berger, H.; Inosov, D. S.
Source:
PHYSICAL REVIEW B 83 (23): Art. No. 233101 JUN 2 2011
Abstract:
Multiple charge density wave (CDW) phases in 2H-TaSe2 are investigated by high-resolution synchrotron x-ray diffraction. In a narrow temperature range immediately above the commensurate CDW transition, we observe a multi-q superstructure with coexisting commensurate and incommensurate order parameters, clearly distinct from the fully incommensurate state at higher temperatures. This multi-q ordered phase, characterized by a temperature hysteresis, is found both during warming and cooling, in contrast to previous reports. In the normal state, the incommensurate superstructure reflection gives way to a broad diffuse peak that persists nearly up to room temperature. Its position provides a direct and accurate estimate of the Fermi surface nesting vector, which evolves nonmonotonically and starts approaching the commensurate position as the temperature is increased. This behavior agrees with our recent observations of the temperature-dependent Fermi surface in the same compound [D. S. Inosov, D. V. Evtushinsky, V. B. Zabolotnyy, A. A. Kordyuk, B. Buchner, R. Follath, H. Berger, and S. V. Borisenko, Phys. Rev. B 79, 125112 (2009).].
Title:
Elastic and antiferromagnetic anomalies in Pr0.48Ca0.52MnO3 as determined by resonant ultrasonic spectroscopy
Authors:
Salje, EKH; Carpenter, MA Author Full Names: Salje, E. K. H.; Carpenter, M. A.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 23 (24): Art. No. 245401 JUN 22 2011
Abstract:
The Pnma incommensurate phase transition in the perovskite Pr0.48Ca0.52MnO3 at similar to 235 K is accompanied by shear strains of up to similar to 2.5% (from neutron diffraction) and changes in the shear modulus of up to similar to 40% (from resonant ultrasound spectroscopy, RUS), indicating strong coupling between the structural order parameter and strain. In contrast, the antiferromagnetic (AFM) ordering transition at similar to 180 K displays no detectable static strain, implying that there is either no coupling or only very weak coupling between the magnetic order parameter and strain. Conventional analysis of RUS data, based on measurements of resonance peak frequencies and peak widths, also failed to detect any anomaly in elastic or anelastic properties due to the AFM ordering. A new approach to the analysis the RUS data, based on autocorrelation and convolution of the entire spectra, however, has revealed that the AFM order does indeed affect the elastic behaviour in an unexpected manner. The new analysis shows, firstly, that dynamical fluctuations of the charge density ordering at T > T-c = 237 K lead to an increase of the RUS amplitude and of the spectral convolution function. Secondly, fluctuations and convolution effects peak at the transition point and decrease with decreasing temperatures. Below 180 K the stripe structure is essentially static. Finally, AFM ordering leads to an increase in the damping of the elastic resonances.
Title:
Helical magnetism and structural anomalies in triangular lattice alpha-SrCr2O4
Authors:
Dutton, SE; Climent-Pascual, E; Stephens, PW; Hodges, JP; Huq, A; Broholm, CL; Cava, RJ Author Full Names: Dutton, S. E.; Climent-Pascual, E.; Stephens, P. W.; Hodges, J. P.; Huq, A.; Broholm, C. L.; Cava, R. J.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 23 (24): Art. No. 246005 JUN 22 2011
Abstract:
alpha-SrCr2O4 has a triangular planar lattice of d(3) Cr3+ made from edge sharing CrO6 octahedra; the plane shows a very small orthorhombic distortion from hexagonal symmetry. With a Weiss temperature of -596 K and a three-dimensional magnetic ordering temperature of 43 K, the magnetic system is quasi-two-dimensional and frustrated. Neutron powder diffraction shows that the ordered state is an incommensurate helical magnet, with an in-plane propagation vector of k = (0, 0.3217(8), 0). Temperature dependent synchrotron powder diffraction characterization of the structure shows an increase in the inter-plane spacing on cooling below 100 K and an inflection in the cell parameters at the magnetic ordering temperature. These anomalies indicate the presence of a moderate degree of magnetostructural coupling.
Title:
Magnetic structure of the Mn5Si3-type Er5Si3 compound
Authors:
Morozkin, AV; Isnard, O; Granovsky, SA Author Full Names: Morozkin, A. V.; Isnard, O.; Granovsky, S. A.
Source:
INTERMETALLICS 19 (7): 871-875 JUL 2011
Abstract:
Neutron diffraction study has been performed on the Er5Si3 compound (hexagonal Mn5Si3-type, hP16, P6(3)/mcm) to understand its magnetic structure. The temperature dependent neutron diffraction results prove that this compound shows a complex antiferromagnetic ordering with sine modulated magnetic moments collinear to the c axis, presenting three subsequent changes in magnetization at similar to 29 K, 13 K and 10 K on cooling. The high-temperature magnetic component of Er5Si3 (C-3v, magnetic point group, P31m magnetic space group, K-1 = [0, 0, +/- 0.277(2)]) exists from 29 K to 10 K, whereas low-temperature magnetic component (symmetry C-1v, magnetic point group, Pm magnetic space group, K-2 = [0, +/- 1/4, 0]) exists from 13 K down to 1.5 K. The low-temperature and high-temperature magnetic components coexist between 13 K and 10 K. (C) 2011 Elsevier Ltd. All rights reserved.
Title:
Magnetocaloric properties of as-quenched Ni50.4Mn34.9In14.7 ferromagnetic shape memory alloy ribbons
Authors:
Llamazares, JL; Garcia, C; Hernando, B; Prida, VM; Baldomir, D; Serantes, D; Gonzalez, J Author Full Names: Sanchez Llamazares, J. L.; Garcia, C.; Hernando, B.; Prida, V. M.; Baldomir, D.; Serantes, D.; Gonzalez, J.
Source:
APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING 103 (4): 1125-1130 JUN 2011
Abstract:
The temperature dependences of magnetic entropy change and refrigerant capacity have been calculated for a maximum field change of Delta H = 30 kOe in as-quenched ribbons of the ferromagnetic shape memory alloy Ni50.4Mn34.9In14.7 around the structural reverse martensitic transformation and magnetic transition of austenite. The ribbons crystallize into a single-phase austenite with the L2(1)-type crystal structure and Curie point of 284 K. At 262 K austenite starts its transformation into a 10-layered structurally modulated monoclinic martensite. The first- and second-order character of the structural and magnetic transitions was confirmed by the Arrott plot method. Despite the superior absolute value of the maximum magnetic entropy change obtained in the temperature interval where the reverse martensitic transformation occurs (vertical bar Delta S-M(max)vertical bar = 7.2 J kg(-1) K-1) with respect to that obtained around the ferromagnetic transition of austenite (vertical bar Delta S-M(max)vertical bar = 2.6 J kg(-1) K-1), the large average hysteretic losses due to the effect of the magnetic field on the phase transformation as well as the narrow thermal dependence of the magnetic entropy change make the temperature interval around the ferromagnetic transition of austenite of a higher effective refrigerant capacity (RCeffmagn = 95 J kg(-1) versus RCeffstruct = 60 J kg(-1)).
Title:
Regenerating deuterium absorption of Ti36Zr40Ni20Pd4 icosahedral quasicrystal
Authors:
Huang, HG; Li, R; Liu, TW; Chen, L; Luo, DL Author Full Names: Huang, Huogen; Li, Rong; Liu, Tianwei; Chen, Liang; Luo, Deli
Source:
ACTA METALLURGICA SINICA-ENGLISH LETTERS 23 (6): 446-450 DEC 2010
Abstract:
Ti/Zr-based icosahedral quasicrystals are a kind of promising hydrogen storage materials, however their absorption regeneration after oxidation-poisoning has been scarcely studied. This work is intended to investigate the deuterium-storage regeneration of a suction-cast Ti36Zr40Ni20Pd4 quasicrystal. It was found that only through hot vacuuming the quasicrystal could be refreshed from air-flow poisoning to absorb deuterium in two cycles. During the first absorption course, a pregnancy period was observed before the real deuterium uptake while deuterium was loaded rapidly during the second one. The deuterium concentration in the alloy can reach 0.011 mol.D-2/(g.M) (corresponding to a hydrogen mass percent of 2.2%. D-2 and M denote molecular deuterium and the metallic alloy). But the loaded deuterium was very difficult to release completely even by eight-stage desorption at different temperatures. After the second desorption, the quasicrystal phase remained in a small! volume, as though the desorption temperature was beyond the crystallization temperature of the quasicrystal. This probably is attributed to the solution function of residual deuterium in the alloy.

Update: 10-Jun-2011

Title:
CHANGES OF STRUCTURE CHARACTERISTICS IN Ti41,5Zr41,5Ni17 AND Ti41,5Hf41,5Ni17 RAPIDLY QUENCHED RIBBONS UNDER RADIATION INFLUENCE
Authors:
Azhazha, VM; Lavrinenko, SD; Lonin, YF; Pylypenko, MM; Sereda, BV; Kryachko, SV; Malykhin, SV; Pugachov, AT; Reshetnyak, MV Author Full Names: Azhazha, V. M.; Lavrinenko, S. D.; Lonin, Yu. F.; Pylypenko, M. M.; Sereda, B. V.; Kryachko, S. V.; Malykhin, S. V.; Pugachov, A. T.; Reshetnyak, M. V.
Source:
PROBLEMS OF ATOMIC SCIENCE AND TECHNOLOGY (2): 33-38 2011
Abstract:
Influence of irradiation by X-ray fluxes with energies <= 1 MeV and doses up to 10(4) rad on phase and structural stability of the icosahedral quasicrystal phase (i-phase) and related crystals-approximant phases in Ti41,5Zr41,5Ni17 and Ti(41,5)Hf(41,5)Ni(17)ribbons prepared by rapid quenching was studied by the X-ray diffraction method.
Title:
Short-range and long-range incommensurate magnetic ordering in the frustrated antiferromagnets Ca3Co2-xFexO6: A neutron diffraction study
Authors:
Jain, A; Yusuf, SM Author Full Names: Jain, Anil; Yusuf, S. M.
Source:
PHYSICAL REVIEW B 83 (18): Art. No. 184425 MAY 25 2011
Abstract:
We present the results of a detailed neutron powder diffraction study on the spin-chain compounds Ca3Co2-xFexO6 (x = 0.2 and 0.4), crystallizing in the rhombohedral structure (space group R (3) over barc), in the temperature range of 1.5-20 K. At low temperature, these compounds show a long-range magnetic ordering (LRO) with an incommensurate structure having an amplitude modulation of the moments along the crystallographic c axis. Our analysis also shows that a short-ranged spin-spin correlation along the c axis (incommensurate type such as that of the LRO), however, with a long-range spin-spin correlation in the ab plane, coexists with the LRO below the LRO temperature of 20 and 17 K for x = 0.2 and 0.4 samples, respectively. The observed long-range as well as the short-range magnetic ordering can be described by a model of platelet-like-shaped magnetic crystallites, disorderly stacked along the crystallographic c direction. At 1.5 K, the LRO and short-range ordering (SRO) contribute in the magnetic phase in volume ratios of 13: 7 and 3: 2 for x = 0.2 and x = 0.4, respectively. The magnetic correlation lengths at 1.5 K for the LRO (xi(c)(I)) and SRO (xi(c)(II)) along the c axis are similar to 1027 and 60 angstrom for x = 0.2, and 1021 and 47 angstrom for x = 0.4, respectively. The relative contribution of the LRO and SRO in the magnetic phase remains constant down to 1.5 K (below transition temperature).
Title:
Homogeneous coexistence of superconducting and spin-density-wave states in CaFe1-xCoxAsF as seen via nuclear magnetic resonance
Authors:
Nakano, T; Tsutsumi, S; Fujiwara, N; Matsuishi, S; Hosono, H Author Full Names: Nakano, T.; Tsutsumi, S.; Fujiwara, N.; Matsuishi, S.; Hosono, H.
Source:
PHYSICAL REVIEW B 83 (18): Art. No. 180508 MAY 26 2011
Abstract:
We investigated the homogeneous coexistence of spin-density-wave (SDW) and superconducting (SC) states via As-75-nuclear magnetic resonance (NMR) in CaFe1-xCoxAsF and found that the electronic and magnetic properties of this compound are intermediate between those of LaFeAsO1-xFx and Ba(Fe1-xCox)(2)As-2. For 6% Co-doped samples, the paramagnetic spectral weight completely disappears in the crossover regime between the SDW and SC phases followed by anomalous behavior of relaxation rate (1/T-1), implying that the two phases are not segregated. Co-59-NMR spectra show that spin moments are not commensurate but spatially modulated. These experimental results suggest that incommensurate SDW (IC-SDW) and SC states are compatible in this compound.
Title:
Layered Perovskite-Like Pb2Fe2O5 Structure as a Parent Matrix for the Nucleation and Growth of Crystallographic Shear Planes
Authors:
Batuk, D; Hadermann, J; Abakumov, A; Vranken, T; Hardy, A; Van Bael, M; Van Tendeloo, G Author Full Names: Batuk, Dmitry; Hadermann, Joke; Abakumov, Artem; Vranken, Thomas; Hardy, An; Van Bael, Marlies; Van Tendeloo, Gustaaf
Source:
INORGANIC CHEMISTRY 50 (11): 4978-4986 JUN 6 2011
Abstract:
The Pb2Fe2O5 compound with a layered intergrowth structure has been prepared by a solid-state reaction at 700 degrees C. The incommensurate compound crystallizes in a tetragonal system with alpha = 3.9037(2) angstrom, c = 3.9996(4) angstrom, and q = 0.1186(4)c star, or when treated as a commensurate approximant, alpha = 3.9047(2) angstrom, c = 36.000(3) angstrom, space group I4/mmm. The crystal structure of Pb2Fe2O5 was resolved from transmission electron microscopy data. Atomic coordinates and occupancies of the cation positions were estimated from high-angle annular dark-field scanning transmission electron microscopy data. Direct visualization of the positions of the oxygen atoms was possible using annular bright-field scanning transmission electron microscopy. The structure can be represented as an intergrowth of perovskite blocks and partially disordered blocks with a structure similar to that of the Bi2O2 blocks in Aurivillius-type phases. The A-cation positions at the border of the perovskite block and the cation positions in the Aurivillius-type blocks are jointly occupied by Pb2+ and Fe3+ cations, resulting in a layer sequence along the c axis: -PbO-FeO2-PbO-FeO2-Phys(7/8)Fe(1/8)-O1-x-Fe-5/8/Pb-3/8-O-2-Fe5/8Pb3/8-. Upon heating, the layered Pb2Fe2O5 structure transforms into an anion-deficient perovskite modulated by periodically spaced crystallographic shear (CS) planes. Considering the layered Pb2Fe2O5 structure as a parent matrix for the nucleation and growth of CS planes allows an explanation of the specific microstructure observed for the CS structures in the Pb-Fe-O system.
Title:
Investigation of the thermal diffusion during the formation of a quasicrystalline phase in thin Al-Pd-Re films
Authors:
Seregin, AY; Makhotkin, IA; Yakunin, SN; Erko, AI; Tereshchenko, EY; Shaitura, DS; Chikina, EA; Tsetlin, MB; Mikheeva, MN; Ol'shanskii, ED Author Full Names: Seregin, A. Yu.; Makhotkin, I. A.; Yakunin, S. N.; Erko, A. I.; Tereshchenko, E. Yu.; Shaitura, D. S.; Chikina, E. A.; Tsetlin, M. B.; Mikheeva, M. N.; Ol'shanskii, E. D.
Source:
CRYSTALLOGRAPHY REPORTS 56 (3): 497-501 MAY 2011
Abstract:
The layer mixing during the formation of the Al70Pd20Re10 icosahedral quasicrystalline phase in thin (55 nm) Al-Pd-Re layered film systems subjected to vacuum annealing has been studied. It is shown that a combined layer of Pd and Al atoms (with the Al3Pd2 phase dominating) is formed in the first stage (at 350A degrees C), while the rhenium layer remains invariable. In the second annealing stage (at 450A degrees C), the beta'-AlPd phase is formed and the Re layer is diffused. In the third stage (700A degrees C), Pd and Re atoms are uniformly distributed throughout the film with the formation of a quasicrystalline phase.

Update: 3-Jun-2011

Title:
Stability of quasicrystals composed of soft isotropic particles
Authors:
Barkan, K; Diamant, H; Lifshitz, R Author Full Names: Barkan, Kobi; Diamant, Haim; Lifshitz, Ron
Source:
PHYSICAL REVIEW B 83 (17): Art. No. 172201 MAY 19 2011
Abstract:
Quasicrystals whose building blocks are of mesoscopic rather than atomic scale have recently been discovered in several soft-matter systems. Contrary to metallurgic quasicrystals whose source of stability remains a question of great debate to this day, we argue that the stability of certain soft-matter quasicrystals can be directly explained by examining a coarse-grained free energy for a system of soft isotropic particles. We show, both theoretically and numerically, that the stability can be attributed to the existence of two natural length scales in the pair potential, combined with effective three-body interactions arising from entropy. Our newly gained understanding of the stability of soft quasicrystals allows us to point at their region of stability in the phase diagram, and thereby may help control the self-assembly of quasicrystals and a variety of other desired structures in future experimental realizations.
Title:
Spin-Peierls transition in the S=1/2 compound TiPO4 featuring large intrachain coupling
Authors:
Law, JM; Hoch, C; Glaum, R; Heinmaa, I; Stern, R; Kang, J; Lee, C; Whangbo, MH; Kremer, RK Author Full Names: Law, J. M.; Hoch, C.; Glaum, R.; Heinmaa, I.; Stern, R.; Kang, J.; Lee, C.; Whangbo, M. -H.; Kremer, R. K.
Source:
PHYSICAL REVIEW B 83 (18): Art. No. 180414 MAY 23 2011
Abstract:
We investigated the magnetic and structural properties of the quasi-one-dimensional 3d(1) quantum chain system TiPO4 (J similar to 965 K) by magnetic susceptibility, heat capacity, electron spin resonance, x-ray diffraction, and nuclear magnetic resonance (NMR) measurements, and by density functional theory (DFT) calculations. TiPO4 undergoes two magnetostructural phase transitions, one at 111 K and the other at 74 K. Below 74 K, NMR detects two different P-31 signals and the magnetic susceptibility vanishes, while DFT calculations evidence a bond alternation of the Ti-Ti distances within each chain. Thus, the 74 K phase transition is a spin-Peierls transition which evolves from an incommensurate phase existing between 111 and 74 K.
Title:
Characteristic chemical shift of quasicrystalline alloy Al53Si27Mn20 studied by EELS and SXES
Authors:
Koshiya, S; Terauchi, M; Tsai, AP Author Full Names: Koshiya, S.; Terauchi, M.; Tsai, A. P.
Source:
PHILOSOPHICAL MAGAZINE 91 (18): 2309-2316 2011
Abstract:
Chemical shifts of all constituent atoms for amorphous (Am), quasicrystalline (QC) and crystalline (Cryst) alloys of Al53Si27Mn20 were investigated for the first time by high energy-resolution electron energy-loss spectroscopy (EELS) and soft-X-ray emission spectroscopy (SXES). Among Al L-shell excitation EELS spectra of Am, QC and Cryst alloys, only QC alloy showed an apparent chemical shift to the larger binding energy side by 0.4 eV. In Al-K-alpha and Si-K-alpha emission SXES spectra of these alloys, only QC alloy showed a chemical shift to the larger binding energy side by 4 eV for Al-K-alpha and 6 eV for Si-K-alpha. These chemical shift values are comparable to those of corresponding metal oxides. This indicates a smaller amount of valence charge at Al and Si atomic sites in QC alloy. On the other hand, Mn-L SXES spectra did not show any chemical shift. Therefore, the decreased charge from Al and Si sites should be distributed between atomic sites, indicating the pres! ence of covalent bonding nature for QC ordered alloy.
Title:
The Eleventh International Conference on Quasicrystals
Authors:
Ishimasa, T; Ishii, Y Author Full Names: Ishimasa, Tsutomu; Ishii, Yasushi
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2419-2420 Sp. Iss. SI 2011
Title:
Once upon a time in Kamchatka: the search for natural quasicrystals
Authors:
Steinhardt, PJ; Bindi, L Author Full Names: Steinhardt, Paul J.; Bindi, Luca
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2421-2426 Sp. Iss. SI 2011
Abstract:
We present evidence for a naturally occurring quasicrystal consisting of micron-sized grains of Al63Cu24Fe13 with icosahedral symmetry embedded in a sample of khatyrkite (nominally, (Cu,Zn)Al2) obtained from the Khatyrka ultramafic zone of the Koryak Mountains in the northern half of the Kamchatka Peninsula.
Title:
High-energy X-ray diffraction studies of i-Sc12Zn88
Authors:
Goldman, AI; Kreyssig, A; Nandi, S; Kim, MG; Caudle, ML; Canfield, PC Author Full Names: Goldman, A. I.; Kreyssig, A.; Nandi, S.; Kim, M. G.; Caudle, M. L.; Canfield, P. C.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2427-2433 Sp. Iss. SI 2011
Abstract:
Although quasicrystals form in a wide variety of ternary and quaternary metallic alloys, examples of stable binary icosahedral quasicrystals are quite rare. Indeed, it has been a decade since the discovery of icosahedral phases in Yb-Cd and Ca-Cd. We have discovered millimeter-sized facetted grains of i-Sc12Zn88 with icosahedral (pentagonal dodecahedral and rhombic triacontahedral) morphologies in solution-grown samples. Structural characterization of the bulk icosahedral phase was accomplished through single-grain high-energy X-ray diffraction. For both growth morphologies, all diffraction peaks could be indexed by a primitive (P-type) icosahedral phase. The two types of morphology do, however, present interesting differences in their respective degrees of quasicrystalline order.
Title:
Solution growth of a decagonal quasicrystal and its related periodic crystals in the Al-Ni-Ru system
Authors:
Dasai, S; Takakura, H Author Full Names: Dasai, Shogo; Takakura, Hiroyuki
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2434-2442 Sp. Iss. SI 2011
Abstract:
Single crystals, with a typical size of several millimetres, of a decagonal phase with 1.6 nm periodicity in the Al-Ni-Ru system were grown successfully by the solution-growth method. The conditions for crystal growth were that the initial composition was Al80Ni16Ru4, the taking-out temperature 900-930 degrees C and the cooling rate 2 degrees C h-1. The lattice parameters were a = 0.2764(2) and c = 1.6523(5) nm, and the composition was in a small range around Al75.2Ni14.6Ru10.2. Single crystals of the orthorhombic Al13(Ni, Ru)4 phase and the monoclinic Al13(Ni, Ru)4 phase located at the high-Ni end also formed under slightly different conditions.
Title:
Synthesis of large single-grain 1/1 approximant crystals in the Ag-In-Eu system by the self-flux method
Authors:
Cui, C; Tsai, AP Author Full Names: Cui, Can; Tsai, An Pang
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2443-2449 Sp. Iss. SI 2011
Abstract:
In this work, we investigate single-grain 1/1 quasicrystal approximant crystals, grown via the self-flux method, in the Ag-In-Eu system, the structure of which is similar to the 1/1 approximant in the Cd-Eu system. Due to the similarities between the Cd-RE (RE = rare earth) and Ag-In-RE systems, Ag-In-RE can be regarded as a pseudo-binary phase, in which Ag and In replace Cd. Thus, based on the binary phase diagram of Cd-Eu, the growth conditions, including the nominal composition and decanting temperatures, for single-grain Ag-In-Eu 1/1 approximant crystal growth from indium-rich melt-solution were studied. A faceted, centimeter-sized single-grain 1/1 approximant crystal was obtained and characterized using powder X-ray diffraction, scanning electron microscopy and back-reflection Laue X-ray diffraction methods. The results are promising for the synthesis of single-grain approximant crystals in other Ag-In-RE systems.
Title:
Rapid synthesis and densification of single-phase Al-Cu-Fe quasicrystals by spark plasma sintering or microwave heating
Authors:
Nicula, R; Ishizaki, K; Stir, M; Shen, Z; Vaucher, S Author Full Names: Nicula, R.; Ishizaki, K.; Stir, M.; Shen, Z.; Vaucher, S.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2450-2457 Sp. Iss. SI 2011
Abstract:
Quasicrystalline (QC) phases are often stable only within narrow composition domains. For this reason, the synthesis of larger amounts of single-phase quasicrystalline powders is difficult. Powder metallurgical approaches, based on mechanical milling followed by conventional heating, have been explored in the recent past. The manufacturing process for single-phase quasicrystals - either in the form of powders or as bulk parts - can be accelerated by orders of magnitude using rapid heating methods that involve pulsed electric currents and/or high-frequency electromagnetic fields. Prior knowledge of the phase transformation sequence and transformation kinetics, as revealed by in situ time-resolved synchrotron radiation experiments, is crucial in obtaining single-phase quasicrystals. We report on the simultaneous synthesis and densification of bulk single-phase Al-Cu-Fe QCs by spark plasma sintering (SPS) within minutes and on the ultrafast synthesis of single-phase Al-Cu-Fe quasicrystalline powders by microwave heating within seconds. The effect of electric current application in the rapid processing of pre-alloyed powders is discussed in relation to the faster diffusion and enhanced phase transformation kinetics.
Title:
Growth morphology of single-crystal grains obtained by directional crystallisation of an Al-Cu-Fe alloy
Authors:
Surowiec, M; Bogdanowicz, W; Krawczyk, J; Formanek, B; Sozanska, M Author Full Names: Surowiec, Marian; Bogdanowicz, Wlodzimierz; Krawczyk, Jacek; Formanek, Boleslaw; Sozanska, Maria
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2458-2465 Sp. Iss. SI 2011
Abstract:
Quasicrystalline as well as crystalline faceted single grains of four phases were obtained during directional crystallisation of an Al-Cu-Fe alloy by the Bridgman technique. The monoclinic phase, Al13(Cu, Fe)4, dominating at high temperatures formed single-crystal lamellae 0.5 mm to 1 mm thick. A second type of attractive morphological form exhibiting flux dissolution terraces was observed on spherical single crystals of phase Al(Fe, Cu). Rectangular, hexagonal and octagonal shaped dissolution terraces were revealed at the positions of two-, three- and four-fold symmetry axes, respectively. A single quasicrystalline phase, Al6Cu2Fe, exhibited icosahedral symmetry with growth forms of a dodecahedron with pentagonal facets. The flux dissolution of the phase apparently plays an essential role in a peritectic reaction leading to quasicrystalline phase formation. Polygonal single grains of phase Al7Cu2Fe exhibiting tetragonal symmetry formed the fourth type of thermodynam ically stable growth forms. Single grains of the phase crystallised in the form of pellets with an octagonal cross-section. The growth morphology of the stable phases was investigated by scanning electron microscopy. The chemical composition of the growth forms described was confirmed by X-ray microanalysis using a scanning electron microscope, whereas the phase composition was determined using electron selected area diffraction and X-ray powder diffraction.
Title:
Synthesis of decagonal Zn-Mg-RE compounds
Authors:
Ors, T; Steurer, W Author Full Names: Oers, Taylan; Steurer, Walter
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2466-2473 Sp. Iss. SI 2011
Abstract:
In this study, the formation of decagonal (d-) quasicrystals in some Zn-Mg-RE systems (with RE = Dy, Er, Ho and Tm) was investigated. For samples with composition Zn58Mg40RE2 reported in literature, decagonal quasicrystals can be obtained as single phase after annealing the prealloys for 100 h at 350 degrees C. However, prolonged annealing at this temperature causes transformation of the d-phase into a hexagonal phase. The d-phase could also be obtained in systems with Er and Ho under different annealing conditions. For Dy- and Er-containing samples, slow cooling (instead of quenching) from higher temperatures also yields predominantly the d-phase.
Title:
Formation of quasicrystalline phase in Al70-xGaxPd17Mn13 alloys
Authors:
Yadav, TP; Singh, D; Shahi, RR; Shaz, MA; Tiwari, RS; Srivastava, ON Author Full Names: Yadav, T. P.; Singh, Devinder; Shahi, Rohit R.; Shaz, M. A.; Tiwari, R. S.; Srivastava, O. N.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2474-2481 Sp. Iss. SI 2011
Abstract:
In the present investigation, the formation and stability of icosahedral phase in Al70-xGaxPd17Mn13 alloys has been explored using X-ray diffraction, scanning, transmission electron microscopy and energy dispersive X-ray analysis. Cast alloys and melt-spun ribbons with x = 2.5, 5, 7.5, 10, 12.5, 15 and 20 have been investigated. In both cases, the alloys up to 5 at% Ga exhibit the formation of pure icosahedral phase. However, for x epsilon 5 at% Ga content, the cast alloy exhibits the formation of multiphase material, consisting of an icosahedral phase along with AlPd-type B2 and ' crystalline (orthorhombic structure with unit cell a = 23.5 angstrom, b = 16.6 angstrom and c = 12.4 angstrom) phases. In the case of the melt spun ribbon for x = 5 at% Ga, only an icosahedral phase has been found, but for 15 x 5 at% Ga, an icosahedral phase is the majority phase with AlPd-type B2 phase being the minority component. For x = 15 at% Ga, a Al3Pd2-type hexagonal phase together with a small amount of quasicrystalline phase is formed. However, for x = 20, only a hexagonal Al3Pd2 phase results.
Title:
Strain-induced structural transformation of single-phase Al-Cu-Fe icosahedral quasicrystal during mechanical milling
Authors:
Mukhopadhyay, NK; Ali, F; Srivastava, VC; Yadav, TP; Sakaliyska, M; Surreddi, KB; Scudino, S; Uhlenwinkel, V; Eckert, J Author Full Names: Mukhopadhyay, N. K.; Ali, F.; Srivastava, V. C.; Yadav, T. P.; Sakaliyska, M.; Surreddi, K. B.; Scudino, S.; Uhlenwinkel, V.; Eckert, J.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2482-2490 Sp. Iss. SI 2011
Abstract:
A single-phase stable icosahedral quasicrystalline sample of high quality with the composition Al62.5Cu25Fe12.5 was produced by the spray forming technique. The material was further investigated by mechanical milling under an argon atmosphere to avoid oxidation during milling. At the initial stages of milling (within 5 h) a significant broadening of the diffraction peaks was observed, indicating a reduction of crystallite size and the introduction of lattice strain, which can be linked to phason strain of the quasilattice. Line broadening was noticed to increase with increasing milling time and in the material milled for longer time only a few broad diffraction peaks, which can be identified as a nanoscale bcc phase (i.e. disordered B2 phase, a 2.9 angstrom), were visible. At this stage the diffraction signals belonging to the quasicrystals were no longer observable, indicating a complete transformation of the quasicrystals into the bcc phase. Finally, the bcc phase formed during milling transformed back to the quasicrystalline phase during subsequent annealing treatment. The microhardness measured on the milled powders was found to decrease with increasing milling time, most likely as a consequence of the increased volume fraction of the ductile bcc phase. Attempts are made to rationalize the structural transformation.
Title:
Anisotropic local structure of decagonal quasicrystals by DAFS
Authors:
Abe, H; Saitoh, H; Nakao, H; Yamamoto, K Author Full Names: Abe, H.; Saitoh, H.; Nakao, H.; Yamamoto, K.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2491-2499 Sp. Iss. SI 2011
Abstract:
Diffraction anomalous fine structure (DAFS) analyses were performed on Al-Ni-Co (ANC) and Al-Ni-Fe (ANF) decagonal quasicrystals at the K-edges of Ni, Co and Fe. In ANC, an order-disorder phase transition with anisotropic atomic short-range order (SRO) is clearly recognizable at high temperature. During in situ observation, a zigzag correlation along the periodic direction developed during the early stage of ordering. Far above the phase transition temperature, this weak correlation along the periodic direction is independent of other correlations along the quasiperiodic one. In ANF, SRO of Fe developed along the quasiperiodic direction, although the local environment of Ni was almost random.
Title:
Structure refinement of decagonal Al-Ni-Co, superstructure type I
Authors:
Kuczera, P; Wolny, J; Fleischer, F; Steurer, W Author Full Names: Kuczera, P.; Wolny, J.; Fleischer, F.; Steurer, W.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2500-2509 Sp. Iss. SI 2011
Abstract:
The structure of decagonal Al-Ni-Co, superstructure type I (the so-called Edagawa phase), was refined in physical space. A statistical approach was used to calculate the structure factors based on a rhombic Penrose tiling, with tile edge length 12.1 angstrom, as reference frame. A total number of 691 parameters was refined against 6843 structure amplitudes, merged in Laue group 10/m.
Title:
Spectroscopic study of Ni-rich Al-Co-Ni quasicrystal
Authors:
Soda, K; Inukai, M; Kato, M; Yagi, S; So, YG; Edagawa, K Author Full Names: Soda, K.; Inukai, M.; Kato, M.; Yagi, S.; So, Y. -G.; Edagawa, K.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2510-2518 Sp. Iss. SI 2011
Abstract:
The valence-band electronic structure of a decagonal Ni-rich Al-Co-Ni quasicrystal, Al72Co8Ni20, was investigated using soft X-ray photoelectron spectroscopy. In particular, the energy distributions of the transition metal 3d bands were determined from the Co and Ni 2p-3d resonance photoemission and compared with those calculated by the discrete variational X method for a model cluster based on a proposed Ni-rich Al-Co-Ni approximant, as well as the 3d band observed in the Co-rich Al-Co-Ni quasicrystal, Al72Co16Ni12. In the Ni-rich Al-Co-Ni, the transition metal 3d band exhibits a peak at a binding energy, EB, of 2.3 eV, which is higher than that of the Co-rich Al-Co-Ni. The observed Ni 3d band has a single-peaked distribution around EB 2.4 eV, in contrast to the calculated bimodal and wide-spread distribution for the proposed Ni-rich Al-Co-Ni model cluster, whereas the Co 3d band is located at EB 1.7 eV, consistent with the model calculation.
Title:
Three-dimensional reconstruction of the atomic arrangement of icosahedral quasicrystals by binary discrete tomography
Authors:
Ishibashi, Y; Sugiura, H; Saitoh, K; Tanaka, N Author Full Names: Ishibashi, Y.; Sugiura, H.; Saitoh, K.; Tanaka, N.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2519-2527 Sp. Iss. SI 2011
Abstract:
A three-dimensional reconstruction of the structure of icosahedral quasicrystals from high-resolution transmission electron microscope images observed along high-symmetry zone-axis projections is studied. As in discrete tomography, the quasicrystalline structure is treated as a discrete set of atoms arranged on the icosahedral lattice, including atom flip sites, which is a structural disorder originating from the degrees of freedom in the internal space. The occupancy of the atoms on each site of the lattice is determined using only the zone-axis projection images without any knowledge of the image intensity. Simulation studies using icosahedral model lattices composed of several thousands of atoms were carried out to test the present reconstruction method. In the case of the ideal icosahedral lattice, a reconstruction rate of 90% is achieved from 10 projection images and a reconstruction rate of 99% is achieved from 18 projections. The reconstruction rate degrad es when the projection images are misaligned. Reconstruction of the three-dimensional distribution of the atom flips is discussed.
Title:
Multiple diffraction in an icosahedral Al-Cu-Fe quasicrystal
Authors:
Fan, CZ; Weber, T; Deloudi, S; Steurer, W Author Full Names: Fan, C. Z.; Weber, Th.; Deloudi, S.; Steurer, W.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2528-2535 Sp. Iss. SI 2011
Abstract:
In order to reveal its influence on quasicrystal structure analysis, multiple diffraction (MD) effects in an icosahedral Al-Cu-Fe quasicrystal have been investigated in-house on an Oxford Diffraction four-circle diffractometer equipped with an Onyx CCD area detector and MoK radiation. For that purpose, an automated approach for Renninger scans (-scans) has been developed. Two weak reflections were chosen as the main reflections (called P) in the present measurements. As is well known for periodic crystals, it is also observed for this quasicrystal that the intensity of the main reflection may significantly increase if the simultaneous (H) and the coupling (P-H) reflections are both strong, while there is no obvious MD effect if one of them is weak. The occurrence of MD events during -scans has been studied based on an ideal structure model and the kinematical MD theory. The reliability of the approach is revealed by the good agreement between simulation and experimen! t. It shows that the multiple diffraction effect is quite significant.
Title:
Hume-Rothery stabilisation mechanism and d-states-mediated Fermi surface-Brillouin zone interactions in structurally complex metallic alloys
Authors:
Mizutani, U; Inukai, M; Sato, H Author Full Names: Mizutani, U.; Inukai, M.; Sato, H.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2536-2542 Sp. Iss. SI 2011
Abstract:
The stability of Co2Zn11 and Al8V5 gamma-brasses, both of which are composed of a transition metal element and polyvalent elements Zn or Al, can be discussed in terms of d-states-mediated Fermi surface-Brillouin zone (FsBz) interactions in the context of first-principles full-potential linearised augmented plane wave (FLAPW) band calculations. A FsBz-induced pseudogap is revealed in the FLAPW-Fourier spectrum, though it is hidden behind a much larger d-band in the total density of states. The stability range of three families of complex metallic alloys (CMAs) that include gamma-brasses, RT-, MI- and Tsai-type 1/1-1/1-1/1 approximants and 2/1-2/1-2/1 approximant, each of which is characterised by [image omitted] = 18, 50 and 125, respectively, can be well scaled in terms of the number of electrons per unit cell (e/uc) given by the product of the number of atoms per unit cell and the e/a value determined by the Hume-Rothery plot on the basis of the FLAPW-Fourier method. This! is taken as the evidence for the justification of the Hume-Rothery stabilisation mechanism for all these CMAs having a pseudogap at the Fermi level.
Title:
Energetics and dynamics of caged Zn4 in i-ScZn
Authors:
Mihalkovic, M; Henley, CL Author Full Names: Mihalkovic, M.; Henley, C. L.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2548-2556 Sp. Iss. SI 2011
Abstract:
In i-ScZn, like other quasicrystals of the i-CaCd class, the innermost shell of the icosahedral cluster is a Zn4 tetrahedron, which thus breaks the symmetry of the outer cluster shells. We investigate theoretically the dynamics of individual tetrahedra, using interatomic pair potentials, fitted from an ab initio database, and molecular dynamics (MD). This includes the formulation of an effective Hamiltonian written in terms of a rigid-body rotation representing the state of each tetrahedron. We characterize the minimum-energy orientations of a tetrahedron, as well as the paths of the transitions between minima (reorientations). The velocity autocorrelations were evaluated for the tetrahedral atoms in the MD dynamics; the corresponding spectral density S() is fairly well fitted by a simplified model in which each atom hops in a double well.
Title:
Cell-constrained melt-quench simulation of d-AlCoNi: Ni-rich versus Co-rich structures
Authors:
Mihalkovic, M; Widom, M; Henley, CL Author Full Names: Mihalkovic, M.; Widom, M.; Henley, C. L.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2557-2566 Sp. Iss. SI 2011
Abstract:
Complex crystalline ground state structures may be obtained by direct (simulated) quenches from the melt for systems of up to a few hundred atoms, given the constraint of a fixed unit cell, coupled with use of (i) replica-exchange Monte Carlo, and (ii) realistic empirical interaction pair potentials. We applied this procedure to decagonal approximants of Al72Co8Ni20 and Al73Co27, obtaining the best energies seen to date for d-AlCoNi models (respectively +20 meV/atom and +9 meV/atom above the tie-plane of competing phases). We elucidated the reasons why different decagonal structures are associated with the Ni-rich and Co-rich compositions. We found a cell doubling to c = 8 angstrom due to layer puckering not only in the Co-rich structure, but (locally) in the nominally c = 4 angstrom Ni-rich structure.
Title:
Ab initio investigations on the stability of seven-fold approximants
Authors:
Orsini-Rosenberg, H; Steurer, W Author Full Names: Orsini-Rosenberg, Heinrich; Steurer, Walter
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2567-2578 Sp. Iss. SI 2011
Abstract:
The stability of theoretical heptagonal approximants was investigated. No approximant phase has yet been confirmed consisting of all three heptagonal rhomb prototiles. To solve this problem, two new approximant structures were constructed from supertiles taken from the ThB4 and YCrB4 structure types. In order to compare structural stability, the total energy convex hulls were calculated for the ternary systems B-Cr-RE (RE = Dy, Er, Ho, Y), as well as B-Mn-Dy and B-Mn-Y, by means of ab initio calculations, using density functional theory. This included all known stable monary, binary and ternary phases. Additionally, several layered boride structure types, which are not stable in the respective ternary systems but show four-, five-, six- or seven-fold local environments, were included by chemical substitution. In all ternary systems, the theoretical approximants were found to be mechanically stable, but chemically unstable by an amount of energy larger than the margin of error. A tendency towards the stabilization of structures showing five- or 10-fold local environments was observed. This is consistent with the findings of decagonal approximants in the systems B-Ti-Ru and B-Mg-Ru.
Title:
Eight different decagonal tilings derived from rhombic Penrose tiling
Authors:
Kato, K; Yamamoto, A Author Full Names: Kato, Kazuyuki; Yamamoto, Akiji
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2579-2586 Sp. Iss. SI 2011
Abstract:
We found 32 variations of dot tiling (DT) reported previously [J. Alloy. Comp. 342 (2002) p.206], which is similar to a tiling consisting of pentagon, hexagons, nonagon and decagons (PHND) [Phil. Mag. A l76 (1997) p.85] employed in the structure analysis of decagonal quasicrystals. They are its superstructures, with a five times larger unit cell in four-dimensional space. These tilings are built up by adding one dot in each fat rhombus in the rhombic Penrose tiling. Eight tilings among 32 DTs do not break the local symmetries of the eight types of vertices in the rhombic Penrose tiling. The eight tilings and their occupation domains are shown.
Title:
Low-temperature structural stability of Cd6M (M = Ho, Er, Tm and Lu) cubic crystalline approximants
Authors:
Nishimoto, K; Sato, T; Muraki, M; Tamura, R Author Full Names: Nishimoto, Kazue; Sato, Takeru; Muraki, Miki; Tamura, Ryuji
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2587-2593 Sp. Iss. SI 2011
Abstract:
TEM observations and electrical resistivity measurements have been performed to investigate the low temperature stability, e.g. the occurrence of a phase transition, in Cd6M (M = Ho, Er, Tm and Lu) approximants, which have the smallest M atomic radii among a series of Cd6M compounds. Unlike other Cd6M compounds, no changes or anomalies were observed in selected-area electron diffraction patterns or in electrical resistivity down to 20 and 15 K, respectively. Therefore, we conclude that a phase transition does not occur in Cd6M (M = Ho, Er, Tm and Lu) and orientational ordering of the Cd4 tetrahedron is kinetically suppressed when the space inside the icosahedral cluster is reduced to a certain level.
Title:
Crystal structure of 1/0-2/1-1/0 Cu-Al-Sc approximant
Authors:
Ishimasa, T; Hirao, A; Honma, T; Mihalkovic, M Author Full Names: Ishimasa, Tsutomu; Hirao, Arina; Honma, Takahiro; Mihalkovic, Marek
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2594-2602 Sp. Iss. SI 2011
Abstract:
The new crystal structure of an orthorhombic phase formed at the alloy composition Cu48.1Al36.4Sc15.5 was analyzed by means of the Rietveld method using synchrotron radiation diffraction data. The starting model for this analysis was constructed theoretically using the so-called 'cell constrained melt-quenching technique'. The space group of the final model is Cmmm, and the unit cell includes 49.0 Cu, 39.0 Al and 16.0 Sc atoms. The lattice parameters are a = 8.337(4) angstrom, b = 22.02(1) angstrom and c = 8.305(4) angstrom, which are related to the six-dimensional lattice parameter, a6D = 6.959 angstrom, of the corresponding Cu-Al-Sc icosahedral quasicrystal as 1/0, 2/1 and 1/0 approximations, respectively. The characteristics of the structure can be understood as a framework consisting of Sc atoms, which is regarded as a tiling of five local structural units; the largest is an icosahedron similar to that included in the Tsai-type quasicrystal. The second exhibits structural similarity to a Mg2Zn11-type crystal and the third is an octahedron.
Title:
Crystal structure of a new orthorhombic Al72Pd18Mn5Si5 approximant phase
Authors:
Simura, R; Kaji, N; Sugiyama, K; Hiraga, K Author Full Names: Simura, Rayko; Kaji, Nobutaka; Sugiyama, Kazumasa; Hiraga, Kenji
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2603-2609 Sp. Iss. SI 2011
Abstract:
The structure of an orthorhmbic Al72Pd18Mn5Si5 phase was determined by single crystal X-ray diffraction: space group Pnma (No.148), a = 1.4396(3) nm, b = 2.4003(2) nm, c = 0.7603(2) nm, V = 2.6272(9) nm3, atoms/cell = 168, F(000) = 3341, = 7.355 mm-1, Dcalc = 4.613 Mgm-3, R(F) = 0.0312 for observed 3919 reflections measured by Mo-K radiation ( = 0.071073 nm). The orthorhombic AlPdMnSi structure is well described by the stacking of a decagonal (0.72 nm) and pentagonal column (0.48 nm) along the b-axis. A new type of decagonal column structures with a periodicity of 1.2 nm (=0.48 + 0.72 nm) is proposed for the decagonal quasicrystals.
Title:
Structure of an approximant crystal in Ni-rich Al71Ni22Co7
Authors:
Abe, E; Yamamoto, A Author Full Names: Abe, E.; Yamamoto, A.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2617-2623 Sp. Iss. SI 2011
Abstract:
A novel approximant crystalline structure formed in an Al71Ni22Co7 alloy annealed at 973 K is reported, for which the S1-type superlattice decagonal quasicrystal forms as a major phase. Electron diffraction and atomic-resolution Z-contrast scanning transmission electron microscope investigations successfully identified the approximant as having a monoclinic unit cell with a = c = 3.2 nm (b = 0.4 nm), = 108 degrees; the structure is constructed by the five-fold symmetric decagonal clusters 2 nm across, which are arrayed by inverting their pentagonal directions between the neighbours (antiferro order of the cluster sense). A plausible atomic model of the approximant is proposed by referring to a model structure of the S1-type decagonal quasicrystal, which is composed of the similar local linkages of the five-fold symmetry clusters. The present approximant is shown to share some structural characteristics with the PD3c-approximant reported for a Co-rich Al71.5Ni12.5Co16 alloy.
Title:
Approximant of dodecagonal quasicrystal formed in Mn-Si-V alloy
Authors:
Iga, H; Mihalkovic, M; Ishimasa, T Author Full Names: Iga, Hayato; Mihalkovic, Marek; Ishimasa, Tsutomu
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2624-2633 Sp. Iss. SI 2011
Abstract:
The crystal structure of a hexagonal phase formed in Mn70Si20V10 has been analyzed by the Rietveld method using synchrotron radiation diffraction data. Analysis was carried out by assuming an average metallic element Mn0.875V0.125 via high resolution electron microscopy. The space group of the refined model is P6/mmm (No. 191) and the unit cell includes 18.9 Si and 78.1 metallic atoms. The lattice parameters are a = 17.058(6) angstrom, c = 4.640(1) angstrom. This hexagonal phase is regarded as an approximant of a dodecagonal quasicrystal. The electron diffraction pattern along the c-axis exhibits pseudo 12-fold diffraction symmetry. In the c-projection, the structure is interpreted as the tiling of two types of local structural units, namely an equilateral triangle and square with the same edge length of 4.57 angstrom, which correspond to A15-type and Zr4Al3-type structures in the three dimensions, respectively. Both bond orientational order and scaling property, cha racteristic of a dodecagonal quasicrystal, are imitated in this periodic tiling.
Title:
Diffraction of limit periodic point sets
Authors:
Baake, M; Grimm, U Author Full Names: Baake, Michael; Grimm, Uwe
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2661-2670 Sp. Iss. SI 2011
Abstract:
Limit periodic point sets are aperiodic structures with pure point diffraction supported on a countably, but not finitely generated Fourier module that is based on a lattice and certain integer multiples of it. Examples are cut and project sets with p-adic internal spaces. We illustrate this by explicit results for the diffraction measures of two examples with 2-adic internal spaces. The first and well-known example is the period doubling sequence in one dimension, which is based on the period doubling substitution rule. The second example is a weighted planar point set that is derived from the classic chair tiling in the plane. It can be described as a fixed point of a block substitution rule.
Title:
Colourings of lattices and coincidence site lattices
Authors:
Loquias, MJC; Zeiner, P Author Full Names: Loquias, Manuel Joseph C.; Zeiner, Peter
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2680-2689 Sp. Iss. SI 2011
Abstract:
The relationship between the coincidence indices of a lattice 1 and a sublattice 2 of 1 is examined via the colouring of 1 that is obtained by assigning a unique colour to each coset of 2. In addition, the idea of colour symmetry, originally defined for symmetries of lattices, is extended to coincidence isometries of lattices. An example involving the Ammann-Beenker tiling is provided to illustrate the results in the quasicrystal setting.
Title:
Semi-perfect colourings of hyperbolic tilings
Authors:
de Las Penas, MLAN; Felix, RP; Gozo, BR; Laigo, GR Author Full Names: de Las Penas, Ma Louise Antonette N.; Felix, Rene P.; Gozo, Beaunonie R., Jr.; Laigo, Glenn R.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2700-2708 Sp. Iss. SI 2011
Abstract:
If G is the symmetry group of an uncoloured tiling, then a colouring of the tiling is semi-perfect if the associated colour group is a subgroup of G of index 2. Results are presented that show how to identify and construct semi-perfect colourings of symmetrical tilings. Semi-perfectly coloured tilings that emerge from the hyperbolic semi-regular tiling 8 center dot 10 center dot 16 are reported.
Title:
Determining quasicrystal structures on substitution tilings
Authors:
Akiyama, S; Lee, JY Author Full Names: Akiyama, Shigeki; Lee, Jeong-Yup
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2709-2717 Sp. Iss. SI 2011
Abstract:
Quasicrystals are characterized by the diffraction patterns which consist of pure bright peaks. Substitution tilings are commonly used to obtain geometrical models for quasicrystals. We consider certain substitution tilings and show how to determine a quasicrystalline structure for the substitution tilings computationally. In order to do this, it is important to have the Meyer property on the substitution tilings. We use the recent result of Lee and Solomyak, which determines the Meyer property on the substitution tilings from the expansion maps.
Title:
Aperiodic structures and notions of order and disorder
Authors:
Ben-Abraham, SI; Quandt, A Author Full Names: Ben-Abraham, S. I.; Quandt, A.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2718-2727 Sp. Iss. SI 2011
Abstract:
The fabrication of artificial heterostructures is mainly based on substitution systems. We present simple ways to construct double-sided versions of the Fibonacci, Prouhet-Thue-Morse, paperfolding, period doubling and Golay-Rudin-Shapiro sequences. We also construct a generic instance of the two-dimensional Prouhet-Thue-Morse structure and explore its symbolic complexity. The complexity turns out to be polynomial and hence, the entropy goes to zero.
Title:
A long-range hierarchical clustering model for constructing perfect quasicrystalline formations
Authors:
Al Ajlouni, RA Author Full Names: Al Ajlouni, Rima A.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2728-2738 Sp. Iss. SI 2011
Abstract:
Since their discovery, the unique structural signature of quasicrystals has posed a perplexing puzzle. Whereas significant progress has been made in determining their physical properties, a deeper understanding of the structure of quasicrystals remains an open question. Although available structural models provide important insights into understanding the quasiperiodic structural order, there is still significant information lacking concerning the determination of the long-range order of quasicrystals. A global multi-level hierarchical framework is presented that is able to describe the long-range translational and orientational order of the global empire pertaining to perfect Penrose tiling (PPT) models. In this order, the global empire is constructed of infinite levels of hierarchical clusters. Any cluster level, in this hierarchy, is composed of four smaller building clusters; two highly symmetrical clusters and their two fragments. Cluster configurations and the geometric arrangements of the multi-level clusters are determined entirely by a geometric progression of framework of nested decagrams. The proposed model suggests that the position of building units, locally and globally, is defined by one global framework, and not tiled based on local rules (matching or overlapping, etc). In this way, quasicrystal formations can grow rapidly ad infinitum without the need for any defects or mismatches.
Title:
Anisotropic Hall effect in Al13TM4 approximants
Authors:
Ivkov, J; Popcevic, P; Stanic, D; Bauer, B; Gille, P; Dolinsek, J; Smontara, A Author Full Names: Ivkov, J.; Popcevic, P.; Stanic, D.; Bauer, B.; Gille, P.; Dolinsek, J.; Smontara, A.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2739-2745 Sp. Iss. SI 2011
Abstract:
The Hall coefficient, RH, in monoclinic Y-Al-Ni-Co, orthorhombic Al13Co4 and monoclinic Al13Fe4 and Al13(Fe,Ni)4 single crystals was investigated for all combinations of the electrical current and magnetic field directions and in the temperature interval from 90 to 370 K. In all three intermetallics, which belong to the Al13TM4 (TM = transition metal) class of approximants to the decagonal quasicrystals, the Hall coefficient exhibits well-defined anisotropy. RH is positive hole-like or zero for the magnetic field parallel to the plane that corresponds to the quasiperiodic plane in decagonal (d-) quasicrystals, and is negative electron-like or zero for the magnetic field perpendicular to this plane. The only exception is RH in Al13Fe4 for the field parallel to the stacking direction, which changes its sign from positive to negative value with an increase of temperature. The results for the anisotropy of RH are correlated to the anisotropy of RH in d-Al-Ni-Co and d-Al-Cu-Co quasicrystals and a brief overview of the theoretical results is presented.
Title:
Anisotropic transport properties of the Al13TM4 and T-Al-Mn-Fe complex metallic alloys
Authors:
Smontara, A; Popcevic, P; Stanic, D; Velebit, K; Dolinsek, J Author Full Names: Smontara, A.; Popcevic, P.; Stanic, D.; Velebit, K.; Dolinsek, J.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2746-2755 Sp. Iss. SI 2011
Abstract:
Anisotropy of the transport properties (electrical resistivity, (T), thermoelectric power, S(T), and thermal conductivity, (T)) of the Al76Co22Ni2 (Y-Al-Ni-Co), o-Al13Co4 and T-Al72.5Mn21.5Fe6.0 complex metallic alloys was investigated experimentally. These compounds belong to the class of approximants in decagonal quasicrystals phases with stacked-layer crystallographic structure and enabled us to study the evolution of transport properties with increasing structural complexity and the unit cell size. For Y-Al-Ni-Co and o-Al13Co4, the anisotropic electronic transport coefficients were analyzed theoretically by Boltzmann transport theory and ab initio calculated anisotropic Fermi surface. The non-metallic anisotropic electrical resistivity of the T-Al72.5Mn21.5Fe6.0 may be analyzed in a semi-quantitative way by the theory of quantum transport of slow charge carriers.
Title:
Novel properties of frustrated low-dimensional magnets with pentagonal symmetry
Authors:
Jagannathan, A; Motz, B; Vedmedenko, E Author Full Names: Jagannathan, A.; Motz, Benjamin; Vedmedenko, E.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2765-2772 Sp. Iss. SI 2011
Abstract:
We consider a new type of frustrated spin network with pentagonal loops and long-range quasiperiodic structural order. Five-fold loops can be expected to occur naturally in quasicrystals, and experimental studies of icosahedral alloys show manifestations of local five-fold symmetry in a variety of different physical contexts. Our model considers classical spins placed on the vertices of a subtiling of the two-dimensional Penrose tiling, and interacting with nearest neighbours via antiferromagnetic bonds. The ground state of this fractal system has a complex magnetic structure, and is studied analytically as well by Monte Carlo simulation on finite clusters.
Title:
Fermi surface effects in icosahedral quasicrystals
Authors:
Chernikov, MA; Vekilov, YK Author Full Names: Chernikov, M. A.; Vekilov, Yu. Kh.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2773-2777 Sp. Iss. SI 2011
Abstract:
In icosahedral quasicrystals, due to an interaction of the Fermi sphere with the boundaries of the pseudo-Brillouin zone associated with the strongest Fourier components of the pseudopotential, the Fermi surface consists of many small electron and hole pockets. Such a scenario can be described by the fractional multicomponent model of the Fermi surface. A discussion is provided of the electronic and thermal properties that follow from this model, in particular at high temperatures.
Title:
Breakdown of semi-classical conduction theory in approximants of the octagonal tiling
Authors:
de Laissardiere, GT; Oguey, C; Mayou, D Author Full Names: de Laissardiere, G. Trambly; Oguey, C.; Mayou, D.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2778-2786 Sp. Iss. SI 2011
Abstract:
We present numerical calculations of quantum transport in perfect octagonal approximants. These calculations include a Boltzmann (intra-band) contribution and a non-Boltzmann (inter-band) contribution. When the unit cell size of the approximant increases, the magnitude of the Boltzmann terms decreases, whereas the magnitude of the non-Boltzmann terms increases. This shows that, in large approximants, the non-Boltzmann contributions should dominate the transport properties of electrons. This confirms the breakdown of the Bloch-Boltzmann theory for understanding the transport properties in approximants with very large unit cells, and then in quasicrystals, as found in actual Al-based approximants.
Title:
Variable-range-hopping conductivity in polygrain samples of icosahedral Al-Re-Pd
Authors:
Vekilov, YK; Chernikov, MA Author Full Names: Vekilov, Yu. Kh.; Chernikov, M. A.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2787-2791 Sp. Iss. SI 2011
Abstract:
We further develop a model, based on an analogy with granular electronic conductors, which explains the nature of the variable-range-hopping conductivity in polygrain samples of icosahedral Al-Re-Pd with resistivity ratios of [image omitted] in an excess of 13. The electrical conductivity of the model is determined by intergranular tunnelling and electrostatic energy. In polygrain icosahedral Al-Re-Pd, pores and precipitates of secondary phases create the barriers. Depending on the barrier height and electrostatic disorder, either an insulating variable-range-hopping regime of an Efros-Shklovskii or Mott type with elastic co-tunnelling or a metallic regime typical of homogeneously disordered conductors is possible.
Title:
Observation of log-periodic oscillations in the quantum dynamics of electrons on the one-dimensional Fibonacci quasicrystal
Authors:
Lifshitz, R; Mandel, SED Author Full Names: Lifshitz, Ron; Mandel, Shahar Even-Dar
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2792-2800 Sp. Iss. SI 2011
Abstract:
We revisit the question of quantum dynamics of electrons on the off-diagonal Fibonacci tight-binding model. We find that typical dynamical quantities, such as the probability of an electron to remain in its original position as a function of time, display log-periodic oscillations on top of the leading-order power-law decay. These periodic oscillations with the logarithm of time are similar to the oscillations that are known to exist with the logarithm of temperature in the specific heat of Fibonacci electrons, yet they offer new possibilities for the experimental observation of this unique phenomenon.
Title:
Negative refraction and localized states of a classical wave in high-symmetry quasicrystals
Authors:
Zhang, XD; Zhong, W; Feng, ZF; Wang, YQ; Li, ZY; Zhang, DZ Author Full Names: Zhang, Xiangdong; Zhong, Wei; Feng, Zhifang; Wang, Yiquan; Li, Zhi-Yuan; Zhang, Dao-Zhong
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2811-2819 Sp. Iss. SI 2011
Abstract:
Recently, negative refraction of electromagnetic waves in periodic photonic crystals has been demonstrated experimentally and sub-wavelength images observed. A theoretical and experimental investigation is reported of the electromagnetic wave transport in high-symmetry photonic quasicrystals (QCs). It is shown that negative refraction can appear in these transparent quasicrystalline photonic structures. It is interesting that highly symmetric two-dimensional photonic QCs possess a universal feature for non-near-field focus of two kinds of polarized waves (S wave and P wave). That is, the non-near-field focus for two kinds of polarized waves can be realized by using flat lenses, which consist of some high-symmetric two-dimensional photonic QCs with the same structures and parameters. In addition, some two-dimensional and three-dimensional localized states in defect-free photonic QCs have been found. It is evident that these unusual localized states can be explored by means of electron energy loss spectroscopy.
Title:
Internal friction of an Al-Cu-Fe icosahedral quasicrystal and its crystal approximant
Authors:
So, YG; Sato, S; Edagawa, K; Tamura, R Author Full Names: So, Yeong-Gi; Sato, Shun; Edagawa, Keiichi; Tamura, Ryuji
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2820-2827 Sp. Iss. SI 2011
Abstract:
The internal friction was measured for an Al-Cu-Fe icosahedral phase (i-phase) and an Al-Cu-Fe-Si 1/1 approximant phase (1/1-phase) by using a dynamical mechanical analyzer (DMA) in the frequency range 0.05-10 Hz and the temperature range 300-873 K. For the i-phase, four absorption peaks were observed at around 420, 580, 620 and 800 K, respectively. These were of the thermally activated relaxation type, and their activation parameters were evaluated. The parameters evaluated for the peak at 800 K indicate a relaxation process involving a collective atomic motion, which can be attributed to correlated phason jumps. This peak was absent for the 1/1-phase. These results are similar to the results of the internal friction measurements previously reported for an Al-Pd-Mn i-phase and its 1/1 approximant phase. Based on the phonon-phason dynamics model, the magnitudes of phason elastic constants were estimated for the Al-Cu-Fe i-phase.
Title:
On nature of the excess heat capacity in icosahedral quasicrystals
Authors:
Prekul, AF; Shchegolikhina, NI; Edagawa, K Author Full Names: Prekul, A. F.; Shchegolikhina, N. I.; Edagawa, K.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2828-2836 Sp. Iss. SI 2011
Abstract:
Experimental evidence is presented which indicates that the total heat capacity in the Al63Cu25Fe12 icosahedral phase contains a contribution associated with inconstancy of the charge carrier concentration. The contribution has an oscillating temperature dependence and is supposedly traceable to two Schottky-like heat anomalies.
Title:
Effect of Ti addition on the quasicrystalline phase formation and indentation characteristics of Zr69.5Al7.5Cu12Ni11 alloy
Authors:
Singh, D; Yadav, TP; Mandal, RK; Tiwari, RS; Srivastava, ON Author Full Names: Singh, Devinder; Yadav, T. P.; Mandal, R. K.; Tiwari, R. S.; Srivastava, O. N.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2837-2845 Sp. Iss. SI 2011
Abstract:
The crystallisation behaviour and indentation characteristics of melt-spun (Zr69.5Al7.5Cu12Ni11)100-xTix (x = 0-16 at. %) metallic glasses was investigated. Differential scanning calorimetry traces revealed changes in crystallisation behaviour with addition of Ti. Formation of a nanoquasicrystalline phase by annealing the glass was found up to x = 12. Further increase of Ti content gives rise to formation of a Zr2Ni-type crystalline phase. In addition to this, the size of nanoquasicrystals decreases with increasing addition of Ti. The load-dependent hardness behaviour of the metallic glasses and nanoquasicrystal-glass composites is reported in detail. The value of the yield strength of the materials was estimated with the help of hardness values based on the empirical correlations available in literature. The formation of shear bands around the indentation periphery was observed. It was found that microstructural and morphological changes alter the indentation characteristic! s of glasses as well as composites formed after controlled crystallisation.
Title:
Multi-cluster model of Al-Co-Ni Co-rich quasicrystal
Authors:
Yuhara, J; Sato, M; Matsui, T; Tsai, AP Author Full Names: Yuhara, J.; Sato, M.; Matsui, T.; Tsai, A. P.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2846-2853 Sp. Iss. SI 2011
Abstract:
We studied the surface modification of Al-Co-Ni Co-rich quasicrystals by Co or Ni deposition, using low-energy electron diffraction (LEED) and scanning tunneling microscopy (STM). After depositing 0.2 monolayers (ML) of Co or Ni with post-annealing, no clear changes were observed in the spot intensity or pattern of LEED. Only the uppermost surface was successfully modified. Based on the STM images of the modified surface, we found that excess Co atoms modified the 2-nm Co clusters to form 0.47-nm clusters and that excess Ni atoms only formed 0.29-nm Ni clusters on the Al-Co-Ni Co-rich quasicrystal surface. Finally, based on the STM images of a clean Co-rich surface, the Al positions proposed by transmission electron microscopy has been modified to match the STM image. To account for the data, we propose a multi-cluster model - based in part on the Hiraga model - composed of three main clusters for both A and B stacking layers.
Title:
Asymmetric pentagonal cluster on an Al-Cu-Co quasicrystal surface
Authors:
Zenkyu, R; Matsui, T; Tsai, AP; Yuhara, J Author Full Names: Zenkyu, R.; Matsui, T.; Tsai, A. P.; Yuhara, J.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2854-2861 Sp. Iss. SI 2011
Abstract:
The 10-fold surface of a decagonal Al66Cu17Co17 quasicrystal has been studied by scanning tunneling microscopy (STM). Three kinds of characteristic pentagonal clusters are observed in the STM images. Clusters within a given terrace have the same orientation, while those in adjacent terraces have opposite orientations. We show that two of the pentagonal cluster types are part of the 2-nm cluster, which is considered to be the basic structural unit of the Al-Cu-Co quasicrystal. The local atomic arrangement in the 2-nm clusters is found to be asymmetric.
Title:
Step-terrace morphology and reactivity to C60 of the five-fold icosahedral Ag-In-Yb quasicrystal
Authors:
Nugent, PJ; Smerdon, JA; McGrath, R; Shimoda, M; Cui, C; Tsai, AP; Sharma, HR Author Full Names: Nugent, P. J.; Smerdon, J. A.; McGrath, R.; Shimoda, M.; Cui, C.; Tsai, A. P.; Sharma, H. R.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2862-2869 Sp. Iss. SI 2011
Abstract:
The surface of the icosahedral i-Ag-In-Yb quasicrystal provides one of the first non-Al-based aperiodic surfaces that is suitable for study under ultra-high vacuum conditions. We present a scanning tunnelling microscopy (STM) study of the five-fold surface of this new quasicrystal demonstrating detailed structure of the terraces and steps. The analysis of the autocorrelation functions of STM images at opposite bias polarities and of the in-plane structure of the bulk model of i-Cd-Yb, which is isostructural to i-Ag-In-Yb, reveals that the surface terminations occur at the centres of the rhombic triacontrahedral (RTH) clusters, which are the basic building blocks of this material. The study further confirms that the unoccupied electronic states are located on Yb sites. Step edges display a Fibonacci sequence of truncated clusters, which can also be explained in terms of the model structure. Occasionally, a single terrace is found to display different structures at negative bias, whereas the same terrace shows a uniform structure at positive bias. Depositing C60 creates a disordered overlayer on the surface with no resulting FFT or LEED patterns.
Title:
Influence of the substrate temperature and deposition flux in the growth of a Bi thin film on the ten-fold decagonal Al-Ni-Co surface
Authors:
Sharma, HR; Ledieu, J; Fournee, V; Gille, P Author Full Names: Sharma, H. R.; Ledieu, J.; Fournee, V.; Gille, P.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2870-2878 Sp. Iss. SI 2011
Abstract:
We compare the growth of a Bi thin film on the ten-fold surface of the decagonal Al-Ni-Co quasicrystal at different substrate temperatures and fluxes using scanning tunneling microscopy (STM) and low energy electron diffraction (LEED). The growth at 29 K leads to the formation of a quasicrystalline monolayer, consistent with the results obtained at 300 K. Further deposition at low temperature produces pseudocubic islands with {100} surface orientation. The islands have two or four atomic layer heights. Both STM and LEED measurements reveal that there is a transition from the pseudocubic {100} film to the hexagonal {0001} surface orientation at coverage () 4 6 ML. The hexagonal domains are oriented along the high symmetry directions of the substrate. Growth at room temperature with different fluxes results in different island-height distributions. High flux predominantly produces islands of uniform four-layer high islands, whereas low flux yields islands of varying heig! hts, yielding a rough film morphology. The two-layer high islands are found to be more stable at low temperature than at room temperature.
Title:
Weak bonding of Zn in an Al-based approximant based on surface measurements
Authors:
Yuen, CD; Unal, B; Jing, DP; Thiel, PA Author Full Names: Yuen, Chad D.; Unal, Baris; Jing, Dapeng; Thiel, Patricia A.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2879-2888 Sp. Iss. SI 2011
Abstract:
We have studied two surfaces of a new Al-Pd-Zn approximant using mass spectrometry, X-ray photoemission spectroscopy (XPS) and scanning tunneling microscopy (STM). Zn is bonded weakly in this approximant, perhaps as weakly as in elemental Zn. This is based upon three observations: (1) the low vapor pressure of Zn above the approximant (detectable in the gas phase at 600 K), (2) preferential sputtering of Zn (contrary to the usual preferential sputtering of Al in Al-rich quasicrystals), and (3) preferential surface segregation of Zn. We further show that preferential segregation - and perhaps incipient evaporation - causes the surface to roughen, preventing it from forming a terrace-step morphology. Finally, our data show that at low O2 pressures, Al oxidizes. In air, Zn oxidizes as well. All results and conclusions are similar for the two-fold and pseudo-10-fold surfaces.
Title:
XPS study of adsorption and desorption of a Bi thin film on the five-fold icosahedral Al-Pd-Mn surface
Authors:
Young, KM; Cross, N; Smerdon, JA; Dhanak, VR; Sharma, HR; Lograsso, TA; Ross, AR; McGrath, R Author Full Names: Young, K. M.; Cross, N.; Smerdon, J. A.; Dhanak, V. R.; Sharma, H. R.; Lograsso, T. A.; Ross, A. R.; McGrath, R.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2889-2893 Sp. Iss. SI 2011
Abstract:
We have employed X-ray photoelectron spectroscopy to characterise the growth and thermal stability of a Bi thin film on the five-fold icosahedral Al-Pd-Mn surface. The growth can be characterised as Stranski-Krastanov, in agreement with previous STM studies. As a function of annealing temperature, the multilayer desorbs first and thereafter coverages of 1 ML and 0.5 ML are stable for significant temperature ranges.
Title:
Catalytic properties of Al13Co4 studied by ab initio methods
Authors:
Krajci, M; Hafner, J Author Full Names: Krajci, M.; Hafner, J.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2904-2912 Sp. Iss. SI 2011
Abstract:
While the surfaces of ordinary crystals provide only a few inequivalent adsorption sites, the complex landscape of the surfaces of quasicrystals and their approximants provides a rich variety of different adsorption sites. Recently, Armbruster et al. reported that Al13Co4, whose structure is closely related to decagonal Al-Ni-Co quasicrystals, is an efficient and selective hydrogenation catalyst for alkynes. In the present work, the hydrogenation of acetylene to ethylene on the (100) surface of Al13Co4 has been studied using ab initio density-functional simulations. Surprisingly, the stable cleavage surface of Al13Co4 is strongly corrugated. The surface is covered by zig-zag chains of edge-sharing Al pentagons, each centered on a Co atom and separated from neighboring chains by wide troughs. The binding energies for adsorption and co-adsorption of H2 and C2H2 molecules at various surface sites have been calculated. Surprisingly, in the energetically most favorable conf! iguration, acetylene is bound in a di-sigma configuration to two Al atoms, not to the Co atom. We have searched for the optimal reaction pathway for the dissociatible adsorption of hydrogen and for the hydrogenation of acetylene to vinyl, ethylene by a Langmuir-Hinshelwood mechanism. The energetic barriers for all reaction steps were calculated by the nudged-elastic-band method. It was found that the energetic barrier of any reaction step does not exceed 0.65 eV (63 kJ/mol). This value is lower than the activation energies for acetylene to ethylene hydrogenation over a Pd catalyst where barriers of 78 kJ/mol and 85 kJ/mol were reported for the rate-determining steps.
Title:
Theoretical studies on clean and adsorbed surfaces of Ag-In-Yb
Authors:
Nozawa, K; Ishii, Y Author Full Names: Nozawa, Kazuki; Ishii, Yasushi
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2913-2919 Sp. Iss. SI 2011
Abstract:
The adsorption structure of Pb atoms on the five-fold surface of a AgInYb quasicrystal is studied using a first-principles calculation. The aperiodic five-fold surface is replaced by a cluster model, following the quasicrystal model by Takakura et al. The potential energy surface (PES) for a single Pb adsorption reflects the five-fold symmetry of the substrate. The most preferred adsorbed site is a five-fold hollow site surrounded by three In and two Yb atoms, and the most preferred sites form a pentagon with edge length 9.9 angstrom. The PES for the second adsorbed atom is calculated to examine the effects of interadsorbate interaction. It turns out that the interadsorbate interaction is limited, and it does not change the PES essentially. Thus, at low coverage, the Pb atoms presumably adsorb onto the five-fold hollow sites, forming a Pb pentagon with edge length 9.9 angstrom around the cluster center. Possible adsorption structures at higher coverage are also discussed.
Title:
Synthesis of porous Cu from Al-Cu-Co decagonal quasicrystalline alloys
Authors:
Vani, VK; Kwon, OJ; Hong, SM; Fleury, E Author Full Names: Vani, V. Kalai; Kwon, O. J.; Hong, S. M.; Fleury, E.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2920-2928 Sp. Iss. SI 2011
Abstract:
The formation of a porous Cu structure from cast Al-Cu-Co decagonal quasicrystalline alloys has been studied using a selective corrosion technique. Two alkaline solutions were selected based on the electrochemical properties of the constituent elements. Selective corrosion of Al and Co was achieved by chemical immersion of the cast Al-Cu-Co alloy in both 5 M NaOH and 0.5 M Na2CO3 solutions; values for BET surface-to-weight ratio of up to 30 m2/g could be reached. Microstructural analyses indicated that the architecture of the resulting porous structures was composed of a needle-type phase, remaining from the decagonal phase, in addition to Cu and Cu-Co phases.
Title:
Preparation and wear resistance of Ti-Zr-Ni quasicrystal and polyamide composite materials
Authors:
Wang, XL; Li, XS; Zhang, ZJ; Zhang, SS; Liu, WQ; Wang, LM Author Full Names: Wang, Xinlu; Li, Xuesong; Zhang, Zhenjiang; Zhang, Shanshan; Liu, Wanqiang; Wang, Limin
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2929-2936 Sp. Iss. SI 2011
Abstract:
Ti-Zr-Ni icosahedral quasicrystal powders (Ti-QC), prepared by mechanical alloying and then annealing in a vacuum furnace, were used as a novel filler material in polyamide 12 (PA12). The melt processability of the composite was studied using a Haake torque rheometer. This indicates that PA12/Ti-QC composites can be melt-processed into a wear-resistant material. Further, these composites, fabricated by compression molding, were tested in sliding wear against a polished bearing steel counterface. The results from wear testing show that the addition of Ti-QC filler to PA12 enhances wear resistance and reduces volume loss by half compared with neat PA12. Furthermore, it is found that the hardness of the composite increases with increasing content of Ti-QC filler. In addition, PA12/Ti-QC composites exhibit a slightly higher crystallization temperature and better thermal stability than PA12. These combined results demonstrate that Ti-QC filler may be a desirable alternative when attempting to increase the wear resistance of PA12.
Title:
Pressure-composition-temperature curves and structure stability induced by hydrogen in TiZrNi quasicrystals
Authors:
Choi, SB; Lee, SH; Kim, JY Author Full Names: Choi, Soo-bin; Lee, Sang-hwa; Kim, Jae Yong
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2937-2943 Sp. Iss. SI 2011
Abstract:
To evaluate the potential applications of Ti-based quasicrystals as hydrogen storage materials, metastable Ti53-xZr27Ni20Pdx (x = 0, 2, 4, 6) quasicrystals were prepared by a rapid quenching method and equilibrium vapor pressures for hydrogen were measured. Pressure-composition-temperature curves measured in Pd-added TiZrNi quasicrystals revealed a significantly increased equilibrium vapor pressure for hydrogen with increasing Pd concentration, while hydrogen loading capacity decreased. After hydrogen absorption, no hydride phase was found for samples made with less than x = 4. The main peaks shifted to the lower angle of 2 in X-ray diffraction patterns, demonstrating that the quasi-lattice constants increased from 5.13 to 5.38 angstrom after hydrogenation. The quasi-lattice constants linearly expanded with increasing absorption amount of hydrogen. Interestingly, analyzing the full width at half maximum values of the main peaks in the X-ray diffraction patterns showed that the coherence lengths of the quasicrystals significantly increased from 120 to 240 angstrom after hydrogenation, presumably due to kinetic rather than thermal factors.
Title:
Novel HDPE-quasicrystal composite fabricated for wear resistance
Authors:
Kothalkar, A; Sharma, AS; Biswas, K; Basu, B Author Full Names: Kothalkar, Ankush; Sharma, Amit S.; Biswas, Krishanu; Basu, Bikramjit
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2944-2953 Sp. Iss. SI 2011
Abstract:
The present paper reports, for the first time, the processing, characterization and wear property of a novel HDPE-decagonal quasicrystal (QC) composite prepared by compression molding. The composites were prepared at 130 degrees C and an applied pressure of 0.735 MPa with different holding time to obtain a fully dense product. It was found that a holding time of 60 min is the optimum at the specified melting temperature and pressure. The second phase (QC) content was varied from 5 to 20 wt% to obtain optimum mechanical properties. SEM observations indicate well-dispersed QC particles within the HDPE matrix, with fine scale distribution for 20 wt% QC. Ball-on-disc wear tests revealed that the composites showed better wear resistance than pure HDPE samples. The results are discussed using the currently available literature.
Title:
Atomic pair distribution function (PDF) analysis of Raney Pd and Rh fine particles
Authors:
Murao, R; Sugiyama, K; Kashiwagi, Y; Kameoka, S; Tsai, AP Author Full Names: Murao, R.; Sugiyama, K.; Kashiwagi, Y.; Kameoka, S.; Tsai, A. P.
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2954-2961 Sp. Iss. SI 2011
Abstract:
Raney Pd and Rh fine particles were prepared from decagonal Al75Pd25 and Al9Rh2 with an Al9Co2-type structure, respectively, by leaching with NaOH aqueous solution. The atomic pair distribution functions (PDFs) for the Raney Pd and Rh fine particles indicate structural features similar to an fcc structure, suggesting atomic rearrangement toward the closest packing of constituents during the leaching process. Transmission electron micrographs indicate that Raney Pd and Rh are aggregates of fcc-structured nano-crystallites with a diameter of 5-6 nm.
Title:
Quasicrystals: diversity and complexity
Authors:
Dubois, JM; Lifshitz, R Author Full Names: Dubois, Jean-Marie; Lifshitz, Ron
Source:
PHILOSOPHICAL MAGAZINE 91 (19-21): 2971-2982 Sp. Iss. SI 2011
Abstract:
Scientific presentations at ICQ11 the 11th International Conference on Quasicrystals, which took place in Sapporo, Japan, in June 2010 offered a variety of stimulating new experimental data and novel theoretical results. New aperiodic crystals were presented; new theoretical ideas were described; exciting experimental results were revealed; and potential applications of quasicrystals were reviewed, showing an unprecedented level of development. ICQ11 was a great success thanks to the high standard of its scientific content and to the efficiency of its organization. ICQ11 proved that quasicrystal research is sure to continue offering diverse challenges and profound insights into the complexity of matter.
Title:
Hydrothermal synthesis of compounds in the fresnoite mineral family (Ba2TiSi2O8)
Authors:
Abbott, EE; Mann, M; Kolis, JW Author Full Names: Abbott, Edward E.; Mann, Matthew; Kolis, Joseph W.
Source:
JOURNAL OF SOLID STATE CHEMISTRY 184 (5): 1257-1262 MAY 2011
Abstract:
Crystals of Ba2TiSi2O8, Sr2TiSi2O8, and Ba2VSi2O8, all belonging to the fresnoite family were prepared by the hydrothermal method. Attempts to synthesize other members by substitution at the alkaline earth site, transition metal site, and tetrahedral site were not successful, but did lead to the formation of a variety of other mineral phases as well as the incommensurate structure, Ba2TiGe2O8. Structural studies on this compound and analysis of the other known fresnoite phases were performed to elucidate the nature of the incommensurate structure. (C) 2011 Elsevier Inc. All rights reserved.
Title:
Critical behaviour of optical birefringence near the normal-incommensurate phase transition in [N(CH3)(4)](2)ZnCl4 crystals under the influence of hydrostatic pressure
Authors:
Kushnir, OS; Kityk, AV; Dzyubanski, VS; Shopa, RY Author Full Names: Kushnir, O. S.; Kityk, A. V.; Dzyubanski, V. S.; Shopa, R. Y.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 23 (22): Art. No. 225403 JUN 8 2011
Abstract:
We have estimated the Ginzburg number G governing crossover from the asymptotic to the classical critical behaviour near the normal-incommensurate phase transition in [N(CH3)(4)](2)ZnCl4 (TMAZC) crystals and the dependence of G on the hydrostatic pressure (0.1-330 MPa), following from the experimental data for the optical birefringence and the quantitative analysis of temperature derivatives of the birefringence in the framework of the approximation of weak Gaussian fluctuations. The Ginzburg number found experimentally for TMAZC is G similar to 8 x 10(-3) at the atmospheric pressure and a considerable part of it is assumed to refer to structural defects. It is shown that the G value for TMAZC decreases with increasing hydrostatic pressure and, based on analysis of the literature birefringence data for Cs2CdBr4 and Cs2HgBr4 crystals, this behaviour might be expected to be generally typical for all the A(2)BX(4) family. The results obtained are discussed using a phenomenological theory of second-order structural phase transitions. In particular, they provide a basis for estimating the limits of the asymptotic critical region in TMAZC and demonstrate that the major part of the incommensurate phase should belong to the crossover region.
Title:
The first find of dodecagonal quasiperiodic tiling in historical Islamic architecture
Authors:
Makovicky, E; Makovicky, NM Author Full Names: Makovicky, Emil; Makovicky, Nicolette M.
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY 44: 569-573 Part 3 JUN 2011
Abstract:
The tympanum of the entrance of the Zaouia Moulay Idriss II in Fez contains the only known example of a dodecagonal cartwheel quasiperiodic pattern in Islamic art, dating possibly from the Merinid epoch. This pattern, carved in a marble plate, is based on a type of Ammann quasilattice known also from modern mathematical literature. The central portions of this pattern were used as elements in a periodic pattern on the walls of the Saadian mausoleum in Marrakech.
Title:
Three-Dimensional Atomic Images of TlInSe2 Thermoelectric Material Obtained by X-ray Fluorescence Holography
Authors:
Hosokawa, S; Happo, N; Hayashi, K; Mimura, K; Wakita, K; Hu, W; Ishii, H; Yoshimura, M; Jeyakanthany, J; Mamedov, N Author Full Names: Hosokawa, Shinya; Happo, Naohisa; Hayashi, Kouichi; Mimura, Kojiro; Wakita, Kazuki; Hu, Wen; Ishii, Hirofumi; Yoshimura, Masato; Jeyakanthany, Jeyaraman; Mamedov, Nazim
Source:
JAPANESE JOURNAL OF APPLIED PHYSICS 50 (5): Art. No. 05FC06 Part 3 Sp. Iss. SI MAY 2011
Abstract:
Three-dimensional (3D) atomic images around the Tl atoms in single-crystal TlInSe2 thermoelectric material in the incommensurate phase were reconstructed by Tl L-III X-ray fluorescence holography measured at room temperature. In the obtained 3D image, the In atoms are clearly visible at the proper positions in the normal phase. The Tl atomic images are also observed but very weakly. By comparing the experimental image with a theoretically calculated one, it is concluded that only the Tl atoms have large spatial fluctuations, which are related to the incommensurate phase of this material. (C) 2011 The Japan Society of Applied Physics
Title:
Charged Defects as an Origin of the Memory Effect in Incommensurate Phase of TlInS2 Ferroelectric-Semiconductors
Authors:
Seyidov, MY; Suleymanov, RA; Mammadov, TG; Fedotov, AK; Babayev, SS; Sharifov, GM Author Full Names: Seyidov, MirHasan Yu.; Suleymanov, Rauf A.; Mammadov, Tofig G.; Fedotov, Aleksandr K.; Babayev, Sardar S.; Sharifov, Galib M.
Source:
JAPANESE JOURNAL OF APPLIED PHYSICS 50 (5): Art. No. 05FD07 Part 3 Sp. Iss. SI MAY 2011
Abstract:
The effects of annealing within the incommensurate phase and doping with the lanthanum impurity on the dielectric function epsilon of the TlInS2 single crystals have been investigated. It is shown that illumination and application of external electric field transform the epsilon(T) dependences for both the annealed and doped samples in the same manner. The inference is made that the correlation between observed effects is conditioned by the internal electric fields induced either by activation (polarization) of native defects during the annealing procedure or after the doping the crystals with active La centers. (C) 2011 The Japan Society of Applied Physics
Title:
An Incommensurately Modulated Structure of eta '-Phase of Cu3+xSi Determined by Quantitative Electron Diffraction Tomography
Authors:
Palatinus, L; Kementova, M; Drinek, V; Jarosova, M; Petricek, V Author Full Names: Palatinus, Lukas; Kementova, Mariana; Drinek, Vladislav; Jarosova, Marketa; Petricek, Vaclav
Source:
INORGANIC CHEMISTRY 50 (8): 3743-3751 APR 18 2011
Abstract:
The diffraction data of eta'-Cu3+x(Si,Ge) were collected by 3D quantitative electron diffraction tomography on a submicrometer-sized sample, and the structure was solved by the charge-flipping algorithm in superspace. It is shown that the structure is trigonal, and it is incommensurately modulated with two modulation vectors q(1) = (alpha, alpha, 1/3) and q(2) = (-2 alpha, alpha, 1/3), superspace group P (3) over bar 1m (alpha, alpha, 1/3)000(-2 alpha, alpha, 1/3)000. The modulation functions of some atoms are very complicated and reach amplitudes comparable with the unit cell dimensions. The modulated structure can be described as sheets of Cu clusters separated by honeycomb layers of mixed Si/Ge positions. The shape of the Cu clusters in the sheets strongly varies with the modulation phase, and the predominant form is an icosahedron. The striving of the Cu layers to form icosahedral clusters is deemed to be the main driving force of the modulation. The combination of methods used in this work can be applied to other structures that are difficult to crystallize in large crystals and opens new perspectives, especially for investigations of aperiodic or otherwise complex metallic alloys.
Title:
Icosahedrite, Al63Cu24Fe13, the first natural quasicrystal
Authors:
Bindi, L; Steinhardt, PJ; Yao, N; Lu, PJ Author Full Names: Bindi, Luca; Steinhardt, Paul J.; Yao, Nan; Lu, Peter J.
Source:
AMERICAN MINERALOGIST 96 (5-6): 928-931 MAY-JUN 2011
Abstract:
Icosahedrite, ideally Al63Cu24Fe13, is a new mineral from the Khatyrka River, southeastern Chukhotka, Russia. It occurs as dark gray-black anhedral to subhedral grains up to 100 mu m across, closely associated with spine!, diopside, forsterite, nepheline, sodalite, corundum, stishovite, khatyrkite, cupalite, and an unnamed phase of composition AlCuFe. Icosahedrite is opaque with a metallic luster, possesses a gray streak, and is brittle with an uneven fracture. The density could not be determined. For quasicrystals, by definition, the structure is not reducible to a single three-dimensional unit cell, so neither cell parameters nor Z can be given. In plane-polarized incident light, icosahedrite exhibits neither bireflectance nor pleochroism. Between crossed polars, it is isotropic. Reflectance percentages (R-min = R-max) for the four standard COM wavelengths are 62.3 (471.1 nm), 60.6 (548.3 nm), 58.1 (586.6 nm), and 56.0 (652.3 nm), respectively. The X-ray powder pattern was indexed on the basis of six integer indices, as conventionally used with quasicrystals, where the lattice parameter (in six-dimensional notation) is measured to be a(6D) = 12.64 angstrom, with probable space group Fm (3) over bar (5) over bar. The four strongest X-ray powder-diffraction lines [d in angstrom (I/I-0)(n(1),n(2),n(3),n(4),n(5),n(6))] are: 2.006 (100) (4 (2) over bar0 042), 2.108 (90) (42 (2) over bar (2) over bar 22), 1.238 (30) (60 (4) over bar 064), and 3.41 (25) (31 (1) over bar (1) over bar 11). Average results of 34 electron-microprobe analyses gave, on the basis of total atoms = 100, the formula Al63.11Cu24.02Fe12.78Si0.03Co0.01Ca0.01Zn0.01Cr0.02Cl0.01. The simplified formula is Al63Cu24Fe13, which requires the mass fractions Al 43.02, Cu 38.60, Fe 18.38, total 100.00 wt%. The new mineral is named for the icosahedral symmetry of its internal atomic structure, as observed in its diffraction pattern. Both the new mineral and mineral name have been approved by the Commission on New Minerals, Nomenclature and Classification, IMA (2010-042).
Title:
Twin relationships of 5M modulated martensite in Ni-Mn-Ga alloy
Authors:
Li, ZB; Zhang, YD; Esling, C; Zhao, X; Zuo, L Author Full Names: Li, Zongbin; Zhang, Yudong; Esling, Claude; Zhao, Xiang; Zuo, Liang
Source:
ACTA MATERIALIA 59 (9): 3390-3397 MAY 2011
Abstract:
For Ni-Mn-Ga ferromagnetic shape memory alloys, the characteristic features of modulated martensite (including the number/shape of constituent variants, the inter-variant orientation relationship and the geometrical distribution of variant interfaces) determine the attainability of the shape memory effect. In the present work, a comprehensive microstructural and crystallographic investigation has been conducted on a bulk polycrystalline Ni50Mn28Ga22 alloy. As a first attempt, the orientation measurements by electron backscatter diffraction (EBSD) - using the precise information on the commensurate 5M modulated monoclinic superstructure (instead of the conventionally simplified non-modulated tetragonal structure) - were successfully performed to identify the crystallographic orientations on an individual basis. Consequently, the morphology of modulated martensite, the orientation relationships between adjacent variants and the characters of twin interfaces were unambiguously determined. With the thus-obtained full-featured image on the configuration of martensitic variants, the possibility of microstructural modification by proper mechanical "training" was further discussed. This new effort makes it feasible to explore the crystallographic/microstructural correlations in modulated martensite with high statistical reliability, which in turn provides useful guidance for optimizing the microstructure and shape memory performance. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Modulated anharmonic ADPs are intrinsic to aperiodic crystals: a case study on incommensurate Rb2ZnCl4
Authors:
Li, L; Wolfel, A; Schonleber, A; Mondal, S; Schreurs, AMM; Kroon-Batenburg, LMJ; van Smaalen, S Author Full Names: Li, Liang; Woelfel, Alexander; Schoenleber, Andreas; Mondal, Swastik; Schreurs, Antoine M. M.; Kroon-Batenburg, Loes M. J.; van Smaalen, Sander
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 67: 205-217 Part 3 JUN 2011
Abstract:
A combination of structure refinements, analysis of the superspace MEM density and interpretation of difference-Fourier maps has been used to characterize the incommensurate modulation of rubidium tetrachlorozincate, Rb2ZnCl4, at a temperature of T = 196 K, close to the lock-in transition at T (lock-in) = 192 K. The modulation is found to consist of a combination of displacement modulation functions, modulated atomic displacement parameters (ADPs) and modulated third-order anharmonic ADPs. Up to fifth-order Fourier coefficients could be refined against diffraction data containing up to fifth-order satellite reflections. The center-of-charge of the atomic basins of the MEM density and the displacive modulation functions of the structure model provide equivalent descriptions of the displacive modulation. Modulations of the ADPs and anharmonic ADPs are visible in the MEM density, but extracting quantitative information about these modulations appears to be difficult. In the structure refinements the modulation parameters of the ADPs form a dependent set, and ad hoc restrictions had to be introduced in the refinements. It is suggested that modulated harmonic ADPs and modulated third-order anharmonic ADPs form an intrinsic part, however small, of incommensurately modulated structures in general. Refinements of alternate models with and without parameters for modulated ADPs lead to significant differences between the parameters of the displacement modulation in these two types of models, thus showing the modulation of ADPs to be important for a correct description of the displacive modulation. The resulting functions do not provide evidence for an interpretation of the modulation by a soliton model.

Update: 27-May-2011

Title:
Spatially modulated antiferromagnetic structures in an easy-plane multiferroic
Authors:
Kulagin, NE; Popkov, AF; Zvezdin, AK Author Full Names: Kulagin, N. E.; Popkov, A. F.; Zvezdin, A. K.
Source:
PHYSICS OF THE SOLID STATE 53 (5): 970-977 MAY 2011
Abstract:
Possible types of spatially modulated periodic antiferromagnetic structures in a uniaxial rhombohedral multiferroic with BiFeO3 crystal symmetry have been studied depending on the ratio of the uniaxial anisotropy and magnetoelectric interaction parameters. It has been shown that, along with symmetric cycloid antiferromagnetic structures with zero transverse component of the antiferromagnetism vector, there are changes in the antiferromagnetism vector direction with both right and left nonzero components of the antiferromagnetic moment, which are branched from the high-symmetry spatially modulated distribution. These solutions degenerate into a homogeneous state at a critical value of the normalized easy-plane anisotropy parameter. The existence of the found spatially inhomogeneous antiferromagnetic states with an incommensurate period can lead to additional features in magnetoelectric properties in multiferroics of the type under consideration near magnetic phase transitions in electric and magnetic fields.
Title:
Short-range-order diffuse scattering in decagonal Ni-rich Al-Ni-Co quasicrystals
Authors:
Yamamoto, A Author Full Names: Yamamoto, Akiji
Source:
PHYSICAL REVIEW B 83 (18): Art. No. 184203 MAY 12 2011
Abstract:
An analytical expression of the diffuse scattering (DS) intensity due to short-range order derived in a recent paper [A. Yamamoto, Acta Crystallogr. Sect. A 66, 372 (2010)] is applied to analyze DS intensities of the S1 phase at 1120 K and the quenched basic Ni rich (b-Ni) phase in decagonal Al70Ni22Co8 (d-Al70Ni22Co8) quasicrystals. The analysis is based on a microdomain model consisting of 20 angstrom clusters. The S1 and b-Ni phases are low-and high-temperature phases of d-Al70Ni22Co8 so that microdomains with the S1 phase structure are assumed to be formed in the b-Ni phase and vice versa. The intercluster correlation of the 20 angstrom clusters within the microdomains is assumed to be the same as that in a corresponding completely ordered structure up to the third intercluster distance similar or equal to 32 angstrom. It is demonstrated that simulated DS intensity distributions reproduce characteristic features in the observed DS intensity in these phases. This sugg! ests that the analysis of DS intensity is efficient for understanding phase transition mechanisms of quasicrystals. It also shows the effectiveness of the theory and applicability of cluster-based DS intensity calculations to real quasicrystals, which reduce the number of short-range-order parameters drastically.
Title:
Microstructure of Rapidly Solidified Al-12Zn-3Mg-1.5Cu Alloy with Zr and Sc Additions
Authors:
Litynska-Dobrzynska, L; Dutkiewicz, J; Maziarz, W; Goral, A Author Full Names: Litynska-Dobrzynska, Lidia; Dutkiewicz, Jan; Maziarz, Wojciech; Goral, Anna
Source:
MATERIALS TRANSACTIONS 52 (3): 309-314 Sp. Iss. SI MAR 2011
Abstract:
The rapid solidification of Al-12 Mg-1.5 Cu (in mass%) alloy was investigated in order to determine structure changes and the effect of Zr or Sc+Zr additions. Rapidly solidified ribbons with the thickness of 30-50 pm were obtained by a melt spinning technique. The alloys cast into a copper mould were used as a reference material. The mould cast alloys as well as the melt spun ribbons revealed the dendritic microstructure of alpha(Al) solid solution and eta(MgZn2) phase in the interdendritic areas. Additionally the T-Mg-32(Zn. Al)(49) phase with icosahedral quasicrystalline symmetry was found in the form of small particles located mainly at the wheel side in the Zr or Zr+Sc containing ribbons. The refinement of the microstructure and the reduction of volume fraction of the eta phase was observed in the ribbons. Large Al3Zr primary precipitates were observed in the mould cast alloy containing zirconium, while almost whole Zr in the ribbons dissolved in the aluminium solid ! solution. Annealing of ribbons at 400 degrees C led to the precipitation of spherical L1(2)-Al3Zr or Al-3(Sc, Zr) particles, coherent with the matrix. They could be responsible for the improvement of properties of the aluminium alloys by the retardation of recrystallization and grain growth. Plate like precipitates of metastable eta' phase appeared after ageing at 120 degrees C and led to the increase of microhardness up to about 230 HV. [doi:10.2320/matertrans.MB201009]
Title:
Neutron Diffraction Investigations of Magnetism in BiFeO3 Epitaxial Films
Authors:
Ratcliff, W; Kan, D; Chen, WC; Watson, S; Chi, SX; Erwin, R; McIntyre, GJ; Capelli, SC; Takeuchi, I Author Full Names: Ratcliff, William, II; Kan, Daisuke; Chen, Wangchun; Watson, Shannon; Chi, Songxue; Erwin, Ross; McIntyre, Garry J.; Capelli, Sylvia C.; Takeuchi, Ichiro
Source:
ADVANCED FUNCTIONAL MATERIALS 21 (9): 1567-1574 MAY 10 2011
Abstract:
The recovery of a modulated magnetic structure in epitaxial BiFeO3 thin films as revealed by neutron diffraction is reported. The magnetic structure in thin films is found to strongly depend on substrate orientation. The substrate orientation causes different strain-relaxation processes resulting in different thin-film crystal structures. The (110) oriented film with a monoclinic structural phase has a single-domain modulated magnetic structure where the magnetic moment lies in the HHL plane. For the (111) oriented film that has a rhombohedral structure, a modulated structure superimposed on the G-type antiferromagnetic order is found. These results indicate that slight structural modifications in the BiFeO3 thin film cause drastic changes in the magnetic structure.

Update: 20-May-2011

Title:
Ground State of the Quasi-1D Compound BaVS3 Resolved by Resonant Magnetic X-Ray Scattering
Authors:
Leininger, P; Ilakovac, V; Joly, Y; Schierle, E; Weschke, E; Bunau, O; Berger, H; Pouget, JP; Foury-Leylekian, P Author Full Names: Leininger, Ph.; Ilakovac, V.; Joly, Y.; Schierle, E.; Weschke, E.; Bunau, O.; Berger, H.; Pouget, J. -P.; Foury-Leylekian, P.
Source:
PHYSICAL REVIEW LETTERS 106 (16): Art. No. 167203 APR 21 2011
Abstract:
Resonant magnetic x-ray scattering near the vanadium L-2,L-3-absorption edges has been used to investigate the low temperature magnetic structure of high quality BaVS3 single crystals. Below T-N = 31 K, the strong resonance revealed a triple-incommensurate magnetic ordering at the wave vector (0.226 0.226 xi) in hexagonal notation, with xi = 0.033. The azimuthal-angle dependence of the scattering signal and time-dependent density functional theory simulations indicate an antiferromagnetic order within the ab plane with the spins polarized along a in the monoclinic structure.
Title:
Non-nesting spin-density-wave antiferromagnetism in FeAs from first principles
Authors:
Parker, D; Mazin, II Author Full Names: Parker, David; Mazin, I. I.
Source:
PHYSICAL REVIEW B 83 (18): Art. No. 180403 MAY 2 2011
Abstract:
The antiferromagnetic (AFM) state of FeAs is very different from that of the FeAs-based superconductor parent compounds, and it is rather complicated, with the Fe spins forming an incommensurate magnetic spiral pattern with a wavelength of about 15 A. To model this, we perform first-principles calculations and find the nearest-neighbor AFM ordering to be energetically favorable, with the lowest-energy pattern reproducing the experimentally found nearest-neighbor correlations. Other AFM orderings are also very stable, although higher in energy. Unlike in the superconductor parent compounds, the Fermi-surface geometry thus plays a small role. We calculate the bare Lindhard susceptibility in the AFM state and find that the observed spin-density-wave ordering vector Q similar or equal to (0,0,0.4) is not that given by this calculation. This is again unlike the superconductor parent compounds, which generally show a magnetic pattern matching the Lindhard susceptibility maximum. Thus in FeAs, the observed pattern must be due to a subtler mechanism.
Title:
Fermionic Representation of Two-Dimensional Dimer Models
Authors:
Grande, HLC; Salinas, SR; da Costa, FA Author Full Names: Casa Grande, Helder L.; Salinas, S. R.; da Costa, F. A.
Source:
BRAZILIAN JOURNAL OF PHYSICS 41 (1): 86-93 MAY 2011
Abstract:
Dimer models in two dimensions give rise to well-known statistical lattice problems, which can be exactly solved by the same combinatorial techniques associated with the Ising model and which have been used to account for the phase transitions in a number of physically interesting systems. More recently, dimer models have been regarded as classical limits of the quantum ground state of some antiferromagnetic systems. We then revisit an early transfer-matrix calculation for the dimer model on the simple square lattice. We write a spin representation for the transfer matrix associated with the canonical partition function of two paradigmatic dimers models, on the 4-8 lattice, with an Ising-type transition, and on the brick lattice, with a peculiar commensurate-incommensurate transition. Using standard techniques, the problem is reduced to the calculation of the eigenvalues of a system of free fermions.

Update: 13-May-2011

Title:
Effects of Reciprocating Extrusion on Microstructures and Mechanical Properties of as-Cast Mg-0.85Zn-0.15Y-0.6Zr Alloys
Authors:
Li, AT; Wang, JC; Si, L; Lai, YT; Yang, GC Author Full Names: Li Antao; Wang Jincheng; Si Lin; Lai Yunting; Yang Gencang
Source:
RARE METAL MATERIALS AND ENGINEERING 40 (3): 515-518 MAR 2011
Abstract:
Effects of reciprocating extrusion on the microstructures and mechanical properties of as-cast Mg-0.85Zn-0.15Y-0.6Zr alloys enforced by quasicrystal particles were investigated by OM, SEM and XRD. The results show that the reciprocating extrusion can greatly refine the microstructure of as-cast Mg-0.85Zn-0.15Y-0.6Zr alloy, and make I phase relatively uniformly distribute in the alpha-Mg matrix. Compared with that of the as-cast alloy, the yield strength, tensile strength and elongation of the Mg-0.85Zn-0.15Y-0.6Zr magnesium alloys after reciprocating extrusion are increased by 75.8%, 43.2% and 35%, respectively.
Title:
Precipitation hardening through sacrificial phase in aluminum-quasicrystal metal matrix composites
Authors:
Kim, SD; Ko, DS; Jang, WK; Shin, KS; Kim, YW Author Full Names: Kim, Sung-Dae; Ko, Dong-Su; Jang, Woo Kil; Shin, Kwang Seon; Kim, Young-Woon
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 528 (13-14): 4845-4848 MAY 24 2011
Abstract:
Al65Cu20Fe15 quasi-crystalline phase worked as a donor of copper by phase dissociation to form Al-Cu-Mg precipitates in mechanically alloyed, Al-Mg-based composite. Fine precipitates played a major role in the improvement of the strength up to 1 GPa of compressive yield strength. (C) 2011 Elsevier B.V. All rights reserved.
Title:
Temperature effects in ion-electron emission of graphite quasicrystal
Authors:
Avilkina, VS; Andrianova, NN; Borisov, AM; Virgiliev, YS; Kulikauskas, VS; Mashkova, ES; Pitirimova, EA Author Full Names: Avilkina, V. S.; Andrianova, N. N.; Borisov, A. M.; Virgiliev, Yu. S.; Kulikauskas, V. S.; Mashkova, E. S.; Pitirimova, E. A.
Source:
JOURNAL OF SURFACE INVESTIGATION-X-RAY SYNCHROTRON AND NEUTRON TECHNIQUES 5 (2): 221-224 APR 2011
Abstract:
Analysis of the comparative influence of complete amorphization of a polycrystalline graphite surface layer and radiation-induced disordering of highly oriented pyrolytic graphite UPV-1T on the character of temperature dependences of the ion-electron emission yield under high-dose (10(18)-10(19) ion/cm(2)) 30 keV Ar+ ion irradiation has been carried out.
Title:
Plastic analysis of the crack problem in two-dimensional decagonal Al-Ni-Co quasicrystalline materials of point group 10, (10)over-bar
Authors:
Li, W; Fan, TY Author Full Names: Li Wu; Fan Tian You
Source:
CHINESE PHYSICS B 20 (3): Art. No. 036101 MAR 2011
Abstract:
The fundamental plastic nature of the quasicrystalline materials remains an open problem due to its essential complicacy. By developing the proposed generalized cohesive force model, the plastic deformation of crack in point group 10, (10) over bar decagonal quasicrystals is analysed strictly and systematically. The crack tip opening displacement (CTOD) and the size of the plastic zone around the crack tip are determined exactly. The quantity of the crack tip opening displacement can be used as a parameter of nonlinear fracture mechanics of quasicrystalline material. In addition, the present work may provide a way for the plastic analysis of quasicrystals.
Title:
The relation between the generalised Eshelby integral and the generalised BCS and DB models
Authors:
Fan, TY; Fan, L Author Full Names: Fan Tian-You; Fan Lei
Source:
CHINESE PHYSICS B 20 (3): Art. No. 036102 MAR 2011
Abstract:
The generalised BCS dislocation group model and the generalised DB atomic cohesive force zone model have obtained the same results on nonlinear fracture study of some one-, two- and three-dimensional quasicrystals. This work reveals some inherent connection between the two models, and finds that their common basis is the generalised Eshelby integral based on the generalised Eshelby energy momentum tensor for quasicrystals. Further applications of the theory in solving nonlinear fracture problems of the materials are also discussed.

Update: 6-May-2011

Title:
Single crystal growth of Al-based intermetallic phases being approximants to quasicrystals
Authors:
Gille, P; Bauer, B; Hahne, M; Smontara, A; Dolinsek, J Author Full Names: Gille, Peter; Bauer, Birgitta; Hahne, Michael; Smontara, Ana; Dolinsek, Janez
Source:
JOURNAL OF CRYSTAL GROWTH 318 (1): 1016-1020 MAR 1 2011
Abstract:
Decagonal (d) quasicrystals are formed in a number of Al-based ternary systems with d-AlCoNi being the best studied decagonal phase. They are highly anisotropic showing unusual properties of e.g. electric and thermal transport when measured along the periodic or quasiperiodic directions. For a long time, this has been attributed to the lack of periodicity in certain crystallographic orientations. Some neighbouring phases in the Al-Co-Ni system as well as in related ternaries consist of the same type of large icosahedral clusters, but are periodic in all three directions, sometimes with very large unit cells. Therefore, they are called approximants to the decagonal quasicrystals. They allow comparative studies of these phases as to judge whether some unusual properties of quasicrystals arise from the lack of periodicity or from the common atomic arrangements. Additional to decagonal AlCoNi quasicrystals, various approximants (monoclinic Al-13(Co,Ni)(4), orthorhombic Al13CO4, orthorhombic Al-4(Cr,Fe), monoclinic Al13Fe4 and its ternary extensions Al-13(Fe,Cr)(4) and Al-13(Fe,Ni)(4)) were grown by the Czochralski method as large single crystals as to carry out transport orientation-dependent measurements. It could be found that transport properties show remarkably similar anisotropic features when comparing corresponding crystallographic directions in these phases that can be related to the periodic stacking of layers. (C) 2010 Elsevier B.V. All rights reserved.

Update: 29-Apr-2011

Title:
Evidence for Charge Orbital and Spin Stripe Order in an Overdoped Manganite
Authors:
Ulbrich, H; Senff, D; Steffens, P; Schumann, OJ; Sidis, Y; Reutler, P; Revcolevschi, A; Braden, M Author Full Names: Ulbrich, H.; Senff, D.; Steffens, P.; Schumann, O. J.; Sidis, Y.; Reutler, P.; Revcolevschi, A.; Braden, M.
Source:
PHYSICAL REVIEW LETTERS 106 (15): Art. No. 157201 APR 12 2011
Abstract:
Overdoped La0.42Sr1.58MnO4 exhibits a complex ordering of charges, orbitals, and spins. Neutron diffraction experiments reveal three incommensurate and one commensurate order parameters to be tightly coupled. The position and the shape of the distinct superstructure scattering as well as higher-order signals are inconsistent with a harmonic charge and spin-density-wave picture but point to a stripe arrangement in which ferromagnetic zigzag chains are disrupted by excess Mn4+.
Title:
Shape of spin density wave versus temperature in AFe(2)As(2) (A = Ca, Ba, Eu): A Mossbauer study
Authors:
Blachowski, A; Ruebenbauer, K; Zukrowski, J; Rogacki, K; Bukowski, Z; Karpinski, J Author Full Names: Blachowski, A.; Ruebenbauer, K.; Zukrowski, J.; Rogacki, K.; Bukowski, Z.; Karpinski, J.
Source:
PHYSICAL REVIEW B 83 (13): Art. No. 134410 APR 11 2011
Abstract:
Parent compounds AFe(2)As(2) (A = Ca, Ba, Eu) of the 122 family of the iron-based superconductors have been studied by 57Fe Mossbauer spectroscopy in the temperature range 4.2-similar to 300 K. Spin density waves (SDW) have been found with some confidence. They are either incommensurate with the lattice period or the ratio of the respective periods is far away from the ratio of small integers. SDW shape is very unconventional (i.e., differs from the sinusoidal shape). Magnetic order starts with lowered temperature as narrow sheets of the significant electron spin density separated by areas with very small spin density. Magnetic sheets are likely to be ordered in the alternate antiferromagnetic fashion as the material as a whole behaves similarly to the collinear antiferromagnet. A further lowering of temperature simply expands sheet thickness leading to the near triangular SDW. Finally, sheets fill the whole available space and the almost rectangular shape of the SDW is reached. The substantial maximum amplitude of SDW appears at the temperature just below the magnetic onset temperature, and this maximum amplitude increases slightly with lowering temperature. The square root from the mean squared hyperfine field behaves versus temperature according to the universality class (1,2) (i.e., with the electronic spin space having dimensionality equal to unity and the real space having dimensionality equal to 2). The more or less pronounced tail above transition temperature due to the development of incoherent SDW is seen.
Title:
Magnetic phase diagram of alpha-NdIr2Si2
Authors:
Mihalik, M; Pospisil, J; Hoser, A; Sechovsky, V Author Full Names: Mihalik, M.; Pospisil, J.; Hoser, A.; Sechovsky, V.
Source:
PHYSICAL REVIEW B 83 (13): Art. No. 134414 APR 12 2011
Abstract:
Magnetism in alpha-NdIr2Si2 single crystals has been probed through specific-heat, magnetization, magnetic susceptibility, and electrical resistivity measurements as a function of temperature, under an applied magnetic field, and for the magnetization curves under high hydrostatic pressures. Neutron diffraction experiments performed with powder and single-crystal samples were focused on microscopic aspects. Two collinear (Nd moments along the c axis) antiferromagnetic phases are found at low temperatures: a longitudinal sine-modulated structure with the magnetic propagation vector k = (0 0 5/6) at temperatures 18.2(2) K < T < 32.3(3) K (+T-N) and a simple AF1-type structure; k = (0 0 1/2) for T < 18.2(2) K (+T-t). Both of the magnetically ordered phases can be destabilized by applying a strong magnetic field along the c axis. The character of the unusual magnetic-field-induced phases is discussed, and the complex magnetic phase diagram is constructed. Applied hydrostatic pressure yields an increase of both TN and Tt. The determined physical properties of a-NdIr2Si2 are discussed in the context of behavior of alpha-PrIr2Si2.
Title:
Long-range magnetic interactions in the multiferroic antiferromagnet MnWO4
Authors:
Ye, F; Fishman, RS; Fernandez-Baca, JA; Podlesnyak, AA; Ehlers, G; Mook, HA; Wang, YQ; Lorenz, B; Chu, CW Author Full Names: Ye, Feng; Fishman, Randy S.; Fernandez-Baca, Jaime A.; Podlesnyak, Andrey A.; Ehlers, Georg; Mook, Herbert A.; Wang, Yaqi; Lorenz, Bernd; Chu, C. W.
Source:
PHYSICAL REVIEW B 83 (14): Art. No. 140401 APR 12 2011
Abstract:
The spin-wave excitations of the multiferroic MnWO4 have been measured in its low-temperature collinear commensurate phase using high-resolution inelastic neutron scattering. These excitations can be well described by a Heisenberg model with competing long-range exchange interactions and a single-ion anisotropy term. The magnetic interactions are strongly frustrated within the zigzag spin chain along the c axis and between chains along the a axis, while the coupling between spin along the b axis is much weaker. The balance of these interactions results in the noncollinear incommensurate spin structure associated with the magnetoelectric effect, and the perturbation of the magnetic interactions leads to the observed rich phase diagrams of the chemically doped materials. This delicate balance can also be tuned by the application of external electric or magnetic fields to achieve magnetoelectric control of this type of materials.
Title:
Dynamic microstructural changes during hot extrusion and mechanical properties of a Mg-5.0 Zn-0.9 Y-0.16 Zr (wt.%) alloy
Authors:
Xu, SW; Zheng, MY; Kamado, S; Wu, K; Wang, GJ; Lv, XY Author Full Names: Xu, S. W.; Zheng, M. Y.; Kamado, S.; Wu, K.; Wang, G. J.; Lv, X. Y.
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 528 (12): 4055-4067 MAY 15 2011
Abstract:
In this study, firstly, dynamic microstructural changes of an as-cast Mg-5.0 Zn-0.9 Y-0.16 Zr (wt.%) alloy (designated ZWK510) during hot extrusion at 350 degrees C and a ram speed of 3.33 mm s(-1) was systematically investigated by electron backscattering diffraction (EBSD) analysis. The dynamic recrystallization (DRX) mechanism during hot extrusion was discussed. Then, the effect of microstructure and texture on the mechanical properties of the as-extruded alloy specimens at room temperature was discussed. The as-cast ZWK510 alloy consists of a-Mg and quasicrystalline I-phase. During hot extrusion at 350 degrees C, the main DRX mechanism is the continuous DRX near the original grain boundaries. The I-phase can accelerate the DRX behavior near these areas by obstructing the slip of dislocations. The deformation twins and massive blocky substructures formed in original grains can coordinate the DRX process near the original grain boundaries, however the DRX seldom occurs inside of these area. After further deformation, these deformation twins and massive blocky substructures are elongate I along the material flow and become so-called unDRXed area, then a bimodal "necklace structure" composed of fine DRXed grains of about 2.1 mu m and unrecrystallized coarse area is formed. The extruded ZWK510 alloy shows a DRX ratio of about 58% and a typical basal fiber texture of (0 0 0 1) < 1 0 (1) over bar 0 >(matrix)// extrusion direction (ED). In the DRXed area around the crushed eutectic I-phase a large number or fine I-phase precipitates are observed pinning at the newly formed DRXed grain boundaries. The 0.2% proof strength and the ultimate tensile strength of the extruded ZWK510 alloy specimen are 317 and 363 MPa, respectively, with an elongation to failure of 12%, which have been attributed to strong basal fiber texture, refined grain size as well as the existence of fine precipitates formed during the hot extrusion. (C) 2011 Elsevier B.V. All rights reserved.
Title:
Change in local environment upon quasicrystallization of Zr-Cu glassy alloys by addition of Pd and Pt
Authors:
Saida, J; Sanada, T; Sato, S; Imafuku, M; Ohnuma, M; Ohkubo, T; Hono, K; Matsubara, E Author Full Names: Saida, Junji; Sanada, Takashi; Sato, Shigeo; Imafuku, Muneyuki; Ohnuma, Masato; Ohkubo, Tadakatsu; Hono, Kazuhiro; Matsubara, Eiichiro
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 23 (17): Art. No. 175303 MAY 4 2011
Abstract:
The effects of Pd and Pt, which are known quasicrystal (QC)-forming elements, on the local atomic structure in Zr70Cu30 glassy alloys are investigated. A QC phase precipitates from a glassy phase above a certain temperature by a cooperative-like motion of icosahedral clusters. Quasicrystallization is accompanied by a significant change in the local environment around the Zr atoms and a slight change around the noble metal. However, the local environment around the Cu atoms remains almost the same during QC formation. It is suggested that two types of icosahedral polyhedra exist in the glassy state: one has a relatively perfect icosahedral structure formed around the Zr atoms. The other is in a distorted state around the Cu atoms. We speculate that the medium-range order (i.e. QC nucleus) has a Zr-centered icosahedral cluster as its core, and the QC grows via aggregation of possible clusters in the initial stage. Pd or Pt atoms stabilize and/or connect individual Zr-centered icosahedral clusters, facilitating the formation of the nucleus and growth of the QC phase.
Title:
Microstructure and properties of Ni-Mn-Ga alloys produced by rapid solidification and pulsed electric current sintering
Authors:
Soderberg, O; Brown, D; Aaltio, I; Oksanen, J; Syren, J; Pulkkinen, H; Hannula, SP Author Full Names: Soderberg, Outi; Brown, David; Aaltio, Ilkka; Oksanen, Jussi; Syren, Jesse; Pulkkinen, Heikki; Hannula, Simo-Pekka
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 509 (20): 5981-5987 MAY 19 2011
Abstract:
Ni-Mn-Ga alloys were compacted using pulsed electric current sintering (PECS) at 850-875 degrees C (50 MPa, 8 min) of flake-like powders made from the rapidly quenched melt-spun ribbons. Two kinds of ribbons were used: one made with a relatively slow wheel speed (6 m/s; average grain size similar to 14 mu m), and another with a faster wheel speed (23 m/s; average grain size similar to 5 mu m). Both sets of flake-like powders consisted of a mixture of non-modulated martensite (NM) and seven-layered modulated martensite (7M) structure. The amount of NM was greater in the slower speed material, while the other one exhibited mostly the 7M structure. These crystal structures were inherited by the sintered samples. In the compacts having the NM structure the multi-step martensitic reaction overlapped with the magnetic transition, and the Curie temperatures during heating and cooling differed from each other. In the compacts having mainly 7M structure the Curie point was about 100 degrees C and the martensitic transition took place in the paramagnetic state, while the intermartensitic one occurred in the region of 60-85 degrees C. This material demonstrated good magnetic properties and saturation magnetization, at best similar to 50 emu/g. Mechanical properties of the compacts were good, and comparable to those of the polycrystalline Ni-Mn-Ga samples in compression. (C) 2011 Elsevier B.V. All rights reserved.
Title:
Phase Transitions in Incommensurate Composites
Authors:
Janssen, T Author Full Names: Janssen, T.
Source:
FERROELECTRICS 412: 4-7 2011
Abstract:
Incommensurate phases show a rich variety of phase transitions. We discuss here two types of phase transitions in a class of aperiodic crystals, the incommensurate composites. A model is presented to understand a recently observed phase transition in nona-decane-urea.
Title:
Incommensurate Phases Induced by a Weak Electric Field
Authors:
Sannikov, DG Author Full Names: Sannikov, D. G.
Source:
FERROELECTRICS 412: 8-11 2011
Abstract:
It is shown that an external electric field E-3 (even if it is arbitrary weak) can induce an incommensurate phase in the crystal. The components M-1 and M-2 of the magnetic moment M-i are chosen as the order parameter components.
Title:
Growth temperature dependent graphene alignment on Ir(111)
Authors:
Hattab, H; N'Diaye, AT; Wall, D; Jnawali, G; Coraux, J; Busse, C; van Gastel, R; Poelsema, B; Michely, T; Heringdorf, FJMZ; Horn-von Hoegen, M Author Full Names: Hattab, H.; N'Diaye, A. T.; Wall, D.; Jnawali, G.; Coraux, J.; Busse, C.; van Gastel, R.; Poelsema, B.; Michely, T.; Heringdorf, F. -J. Meyer Zu; Horn-von Hoegen, M.
Source:
APPLIED PHYSICS LETTERS 98 (14): Art. No. 141903 APR 4 2011
Abstract:
The morphology of graphene monolayers on Ir(111) prepared by thermal decomposition of ethylene between 1000 and 1530 K was studied with high resolution low energy electron diffraction. In addition to a well-oriented epitaxial phase, randomly oriented domains are observed for growth temperatures between 1255 and 1460 K. For rotational angles of +/- 3 degrees around 30 degrees these domains lock-in in a 30 degrees oriented epitaxial phase. Below 1200 K the graphene layer exhibits high disorder and structural disintegrity. Above 1500 K the clear moire spots reflect graphene in a single orientation epitaxial incommensurate phase. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3548546]

Update: 22-Apr-2011

Title:
Lattice study of the incommensurate omega phase transition in Zr-Nb alloys
Authors:
Kubo, H; Farjami, S Author Full Names: Kubo, H.; Farjami, S.
Source:
PHYSICAL REVIEW B 83 (13): Art. No. 134302 APR 7 2011
Abstract:
The stability of the incommensurate omega phase has been studied in the scheme of the Landau-Lifshitz (L-L) free-energy model reformed for the weak first-order phase transition. It is revealed that the negative third-order term of the L-L expansion drives the transition and works, in competition with the second-harmonic term, to form the modulated omega phase; moreover, it functions to maintain soliton walls with constant width against temperature changes. The modulated omega phase is elucidated to have a microstructure with the sequence of subvariants-omega 1-omega 3-omega 2-separated by soliton walls of anti-omega structure. A series of primitive activation units of the modulated omega phase, which can be depicted in a phase diagram, is obtained in the Zr-20 wt% Nb-alloy system by analyzing the L-L free-energy function with the appropriate numerical calculations.
Title:
Anomalous vibrational dynamics in the Mg2Zn11 phase
Authors:
Euchner, H; Mihalkovic, M; Gahler, F; Johnson, MR; Schober, H; Rols, S; Suard, E; Bosak, A; Ohhashi, S; Tsai, AP; Lidin, S; Gomez, CP; Custers, J; Paschen, S; de Boissieu, M Author Full Names: Euchner, H.; Mihalkovic, M.; Gaehler, F.; Johnson, M. R.; Schober, H.; Rols, S.; Suard, E.; Bosak, A.; Ohhashi, S.; Tsai, A. -P.; Lidin, S.; Gomez, C. Pay; Custers, J.; Paschen, S.; de Boissieu, M.
Source:
PHYSICAL REVIEW B 83 (14): Art. No. 144202 APR 7 2011
Abstract:
We present a combined experimental and theoretical study of the structure and the lattice dynamics in the complex metallic alloy Mg2Zn11, by means of neutron and x-ray scattering, as well as ab initio and empirical potential calculations. Mg2Zn11 can be seen as an intermediate step in structural complexity between the simple Laves-phase MgZn2 on one side, and the complex 1/1 approximants and quasicrystals ZnMgAl and Zn(Mg)Sc on the other. The structure can be described as a cubic packing of a triacontahedron whose center is partially occupied by a Zn atom. This partially occupied site turned out to play a major role in understanding the lattice dynamics. Data from inelastic neutron scattering evidence a Van Hove singularity in the vibrational spectrum of Mg2Zn11 for an energy as low as 4.5 meV, which is a unique feature for a nearly-close-packed metallic alloy. This corresponds to a gap opening at the Brillouin zone boundary and an interaction between a low-lying optical branch and an acoustic one, as could be deduced from the dispersion relation measured by inelastic x-ray scattering. Second, the measured phonon density of states exhibits many maxima, indicating strong mode interactions across the whole energy range. The origin of the low-energy modes in Mg2Zn11 and other features of the vibrational spectra are studied, using both ab initio and empirical potential calculations. A detailed analysis of vibrational eigenmodes is presented, linking features in the vibrational spectrum to atomic motions within structural building blocks.
Title:
Effect of particle size and annealing on spin and phonon behavior in TbMnO3
Authors:
Das, R; Jaiswal, A; Adyanthaya, S; Poddar, P Author Full Names: Das, Raja; Jaiswal, Adhish; Adyanthaya, Suguna; Poddar, Pankaj
Source:
JOURNAL OF APPLIED PHYSICS 109 (6): Art. No. 064309 MAR 15 2011
Abstract:
Interest has grown to study TbMnO3 as it was recently reported to show a gigantic magnetoelectric effect. Here, we report the synthesis and detailed magnetic and Raman spectroscopy study on TbMnO3 particles of size similar to 25 nm and 2-3 mu m, respectively. The incommensurate-commensurate (lock-in) transition, usually observed at 27 K for bulk phase of TbMnO3 was not observed in susceptibility versus T curve but was seen at 30 K in the coercivity versus T curve in similar to 25 nm particles. This transition, which is due to the spin modulation length scale, gets weakened in nanosize due to the increased intrinsic lattice strain observed in 2-3 mu m particles, due to the effect of increased particle size. The increased value of magnetization in the 2-3 mu m sample was attributed to double exchange interactions between Mn+3 and Mn+4 spins. The role of annealing related effects on the fate of the Neel temperature for TbMnO3 was investigated. Raman spectroscopy indicated a decrease in the lattice distortion for similar to 25 nm particles. (c) 2011 American Institute of Physics. [doi:10.1063/1.3563571]
Title:
Crystallographic relationship of orthorhombic phi-Al5Mg11Zn4 phase to icosahedral quasicrystalline phase
Authors:
Singh, A; Rosalie, JM; Somekawa, H; Mukai, T Author Full Names: Singh, Alok; Rosalie, J. M.; Somekawa, H.; Mukai, T.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 509 (14): 4676-4681 APR 7 2011
Abstract:
The orthorhombic phi-Al5Mg11Zn4 phase is known to be related to quasicrystalline phases, but the exact relationship has not been shown yet. In this study, the relationship of this phase to the icosahedral quasicrystalline phase is explored through analysis of the electron diffraction patterns. It is shown that icosahedral coordinations in three orientations occur in the unit cell - one with three mutually perpendicular twofold axes along (100) of the unit cell, and two with a twofold axis along [100] and a fivefold along [001]. In this, this phase is similar to aluminum and zinc based hexagonal phases which are related to quasicrystals. (C) 2011 Elsevier B.V. All rights reserved.

Update: 15-Apr-2011

Title:
Evolution of Paramagnetic Quasiparticle Excitations Emerged in the High-Field Superconducting Phase of CeCoIn5
Authors:
Kumagai, K; Shishido, H; Shibauchi, T; Matsuda, Y Author Full Names: Kumagai, K.; Shishido, H.; Shibauchi, T.; Matsuda, Y.
Source:
PHYSICAL REVIEW LETTERS 106 (13): Art. No. 137004 MAR 30 2011
Abstract:
We present In-115 NMR measurements in a novel thermodynamic phase of CeCoIn5 in a high magnetic field, where exotic superconductivity exists with the incommensurate spin-density wave order. We show that the NMR spectra in this phase provide direct evidence for the emergence of the spatially distributed normal quasiparticle regions. The quantitative analysis for the field evolution of the paramagnetic magnetization and newly emerged low-energy quasiparticle density of states is consistent with the nodal plane formation, which is characterized by an order parameter in the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state. The NMR spectra also suggest that the spatially uniform spin-density wave is induced in the FFLO phase.
Title:
Magnetic structure of epitaxial multiferroic BiFeO3 films with engineered ferroelectric domains
Authors:
Ke, X; Zhang, PP; Baek, SH; Zarestky, J; Tian, W; Eom, CB Author Full Names: Ke, X.; Zhang, P. P.; Baek, S. H.; Zarestky, J.; Tian, W.; Eom, C. B.
Source:
PHYSICAL REVIEW B 82 (13): Art. No. 134448 OCT 29 2010
Abstract:
We report on neutron scattering and piezoresponse force microscopy studies of multiferroic BiFeO3 films epitaxially grown on vicinal SrTiO3 substrates. We find that these BiFeO3 films exhibit a G-type antiferromagnetic structure modulated with cycloidal spiral magnetic ordering with the features of magnetic domains depending upon the ferroelectric domain states: a single antiferromagnetic domain for the films with a ferroelectric monodomain while two- or multiantiferromagnetic domains existing in the films displaying two- or four-ferroelectric variants, respectively. These results imply the correlation between ferroelectric and magnetic order parameters in the BiFeO3 films and the expected strong magnetoelectric coupling makes these multiferroic films promising candidates for device applications with the capability to tune the magnetism using an electric field.
Title:
Magnetic structure of epitaxial multiferroic BiFeO3 films with engineered ferroelectric domains
Authors:
Ke, X; Zhang, PP; Baek, SH; Zarestky, J; Tian, W; Eom, CB Author Full Names: Ke, X.; Zhang, P. P.; Baek, S. H.; Zarestky, J.; Tian, W.; Eom, C. B.
Source:
PHYSICAL REVIEW B 82 (13): Art. No. 134448 OCT 29 2010
Abstract:
We report on neutron scattering and piezoresponse force microscopy studies of multiferroic BiFeO3 films epitaxially grown on vicinal SrTiO3 substrates. We find that these BiFeO3 films exhibit a G-type antiferromagnetic structure modulated with cycloidal spiral magnetic ordering with the features of magnetic domains depending upon the ferroelectric domain states: a single antiferromagnetic domain for the films with a ferroelectric monodomain while two- or multiantiferromagnetic domains existing in the films displaying two- or four-ferroelectric variants, respectively. These results imply the correlation between ferroelectric and magnetic order parameters in the BiFeO3 films and the expected strong magnetoelectric coupling makes these multiferroic films promising candidates for device applications with the capability to tune the magnetism using an electric field.
Title:
Analysis and modelling of structural disorder by the use of the three-dimensional pair distribution function method exemplified by the disordered twofold superstructure of decagonal Al-Cu-Co
Authors:
Schaub, P; Weber, T; Steurer, W Author Full Names: Schaub, Philippe; Weber, Thomas; Steurer, Walter
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY 44: 134-149 Part 1 FEB 2011
Abstract:
Theoretical concepts and the practical application of the three-dimensional pair distribution function (3D-PDF) method and its variant, the three-dimensional delta-pair distribution function (3D-delta PDF) method, are presented. In analogy to traditional Patterson function analysis, advantage is taken of the Fourier transformation either of the full three-dimensional diffraction pattern of a disordered crystal or just of the isolated diffuse scattering, respectively. By the use of three-dimensional information, analysis of disorder becomes straightforward, and it becomes possible to investigate far more complicated structures than is feasible with well established powder diffraction-based PDF analysis. Compared to more traditional modelling techniques, such as Monte Carlo simulation, the 3D-delta PDF provides direct access to disorder models and allows selective modelling of distinct structural features, which are, in contrast to reciprocal space, well localized in PDF space. The principles of the 3D-delta PDF approach are exemplified using an analysis of the twofold (similar to 8 A) periodic superstructure of a decagonal Al65Cu20Co15 quasicrystal. Although analysis of disorder in quasicrystals is far more demanding than in the case of periodic structures, details of the disordered structure could be elucidated. The superstructure is found to be built from columnar units, having a maximum diameter of similar to 14.5 A. The lateral correlation between these columns is weak. Internally, the columns consist of a long-range-ordered alternation of flat and puckered layers. The development of the model and the atomic structure of the columns are described in detail.
Title:
Zn2LiGaO4, Wurtzite- Derived Wide Band Gap Oxide
Authors:
Omata, T; Kita, M; Nose, K; Tachibana, K; Otsuka-Yao-Matsuo, S Author Full Names: Omata, Takahisa; Kita, Masao; Nose, Katsuhiro; Tachibana, Kosuke; Otsuka-Yao-Matsuo, Shinya
Source:
JAPANESE JOURNAL OF APPLIED PHYSICS 50 (3): Art. No. 031102 MAR 2011
Abstract:
The phase that appeared in the pseudo-binary LiGaO2-ZnO system was investigated by powder X-ray diffraction (XRD), selected area electron diffraction by transmission electron microscopy (TEM-SAD) and Raman spectroscopy, especially focusing on the 0.5(LiGaO2)(1/2) - 0.5ZnO composition. A new quaternary wurtzite-derived Zn2LiGaO4 phase was found in this system. The TEM-SAD indicated that the phase possesses an incommensurately modulated ordering. The optical energy band gap of Zn2LiGaO4 was determined to be similar to 4: 0 eV from its diffuse reflectance and photoluminescence spectra; and it was suggested that the Zn2LiGaO4 was a direct semiconductor. (C) 2011 The Japan Society of Applied Physics
Title:
Three dimensional elastodynamics of 2D quasicrystals: The derivation of the time-dependent fundamental solution
Authors:
Yakhno, VG; Yaslan, HC Author Full Names: Yakhno, V. G.; Yaslan, H. Cerdik
Source:
APPLIED MATHEMATICAL MODELLING 35 (6): 3092-3110 JUN 2011
Abstract:
The time-dependent differential equations of elasticity for 20 quasicrystals with general structure of anisotropy (dodecagonal, octagonal, decagonal, pentagonal, hexagonal, triclinic) are considered in the paper. These equations are written in the form of a vector partial differential equation of the second order with symmetric matrix coefficients. The fundamental solution (matrix) is defined for this vector partial differential equation. A new method of the numerical computation of values of the fundamental solution is suggested. This method consists of the following: the Fourier transform with respect to space variables is applied to vector equation for the fundamental solution. The obtained vector ordinary differential equation has matrix coefficients depending on Fourier parameters. Using the matrix computations a solution of the vector ordinary differential equation is numerically computed. Finally, applying the inverse Fourier transform numerically we find the values of the fundamental solution. Computational examples confirm the robustness of the suggested method for 2D quasicrystals with arbitrary type of anisotropy. (C) 2010 Elsevier Inc. All rights reserved.
Title:
Determination of the orientation relationship between austenite and incommensurate 7M modulated martensite in Ni-Mn-Ga alloys
Authors:
Li, ZB; Zhang, YD; Esling, C; Zhao, X; Zuo, L Author Full Names: Li, Z. B.; Zhang, Y. D.; Esling, C.; Zhao, X.; Zuo, L.
Source:
ACTA MATERIALIA 59 (7): 2762-2772 APR 2011
Abstract:
For Ni-Mn-Ga ferromagnetic shape memory alloys, a large magnetic-field-induced strain could be reached through the reorientation of martensitic variants in the martensite state. Owing to the collective and displacive nature of the austenite to martensite transformation, a certain orientation relationship (OR) between the parent and the product phase is required to minimize the transformation strain and the strain energy generated, which brings about self-accommodating groups of martensitic variants with specific orientation correlations. In this work, the microstructural and crystallographic characteristics of martensitic variants in a polycrystalline Ni50Mn30Ga20 alloy were investigated by electron backscatter diffraction analysis. With accurate orientation measurement on inherited martensitic variants, the local orientations of parent austenite grains were predicted using four classical OR for the martensitic transformation. Furthermore, a specific OR, namely the Pitsch relation with (1 0 1)(A)//(1 (2) over bar (10) over bar)(7M) and [1 0 (1) over bar](A)//[(10) over bar (10) over bar 1](7M), was unambiguously determined by considering the magnitude of discontinuity between the lattices of the product and parent phases and the structural modulation of the incommensurate 7M modulated martensite. The present procedure to determine the OR, without recourse to the presence of retained austenite, is in general applicable to a variety of materials with modulated superstructure for insight into their martensitic transformation processes. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Elastic and viscoelastic properties of glassy, quasicrystalline and crystalline phases in Zr65Cu5Ni10Al7.5Pd12.5 alloys
Authors:
Pelletier, JM; Louzguine-Luzgin, DV; Li, S; Inoue, A Author Full Names: Pelletier, Jean-Marc; Louzguine-Luzgin, Dmitri V.; Li, Song; Inoue, Akihisa
Source:
ACTA MATERIALIA 59 (7): 2797-2806 APR 2011
Abstract:
The elastic and viscoelastic properties of Zr65Ni10Cu5Al7.5Pd12.5 bulk metallic glass have been studied over a wide temperature and frequency range. In the amorphous state the mechanical response of the alloy is simple, similar to that observed in other bulk metallic glasses. In contrast, the phase-transformation process which occurs during annealing at elevated temperature induces a complex evolution. This alloy transforms to a supercooled liquid and then primarily forms an icosahedral phase followed by the formation of a mixture of crystalline phases. The mechanical properties in the amorphous state are well described using a physical model based on the concept of defects in amorphous materials. Atomic mobility is then governed by two parameters: activation energy U-el (0.92 eV) and correlation factor chi (0.39). The influence of the phase composition on the properties is discussed. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Relation between icosahedral short-range ordering and plastic deformation in Zr-Nb-Cu-Ni-Al bulk metallic glasses
Authors:
Zhu, ZW; Gu, L; Xie, GQ; Zhang, W; Inoue, A; Zhang, HF; Hu, ZQ Author Full Names: Zhu, Z. W.; Gu, L.; Xie, G. Q.; Zhang, W.; Inoue, A.; Zhang, H. F.; Hu, Z. Q.
Source:
ACTA MATERIALIA 59 (7): 2814-2822 APR 2011
Abstract:
The relation between icosahedral short-range ordering (ISRO) and plastic deformation was investigated in Zr70-xNbxCu13.5Ni8.5Al8 (at.%, x = 0, 2, 4, 6, 7, 8, 10) bulk metallic glasses (BMG). The formation of icosahedral quasicrystal (I-phase) during the annealing process implies that ISRO widely exists in these materials. The degree of ISRO is thermodynamically evaluated to show that ISRO increases with increasing Nb content. Compression tests indicate that BMG with 0-7 at.% Nb possess similar unusual plastic deformability, which is attributed to ISRO-mediated local distribution of free volume (FV) and ISRO prompted deformation-induced crystallization. A proposed core shell model coupled with transmission electron microscopy analysis demonstrates that the FV is distributed more heterogeneously with increasing ISRO, which is beneficial for multiplying the shear bands. Deformation-induced crystallization is facilitated, owing to the low interfacial energy of the nucleation and growth of the crystals attributed to ISRO in the amorphous matrix, which improves plasticity by consuming energy and the product altering the stress field in the amorphous matrix. Design of new ductile BMG is discussed in these strategies. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Update: 8-Apr-2011

Title:
Quantitative atom column position analysis at the incommensurate interfaces of a (PbS)(1.14)NbS2 misfit layered compound with aberration-corrected HRTEM
Authors:
Garbrecht, M; Spiecker, E; Tillmann, K; Jager, W Author Full Names: Garbrecht, M.; Spiecker, E.; Tillmann, K.; Jaeger, W.
Source:
ULTRAMICROSCOPY 111 (3): 245-250 FEB 2011
Abstract:
Aberration-corrected HRTEM is applied to explore the potential of NCSI contrast imaging to quantitatively analyse the complex atomic structure of misfit layered compounds and their incommensurate interfaces. Using the (PbS)(1.14)NbS2 misfit layered compound as a model system it is shown that atom column position analyses at the incommensurate interfaces can be performed with precisions reaching a statistical accuracy of +/- 6 pm. The procedure adopted for these studies compares experimental images taken from compound regions free of defects and interface modulations with a structure model derived from XRD experiments and with multi-slice image simulations for the corresponding NCSI contrast conditions used. The high precision achievable in such experiments is confirmed by a detailed quantitative analysis of the atom column positions at the incommensurate interfaces, proving a tetragonal distortion of the monochalcogenide sublattice. (C) 2010 Elsevier B.V. All rights reserved.
Title:
Magnetic transitions in Mn3O4 and an anomaly at 38 K in magnetization and specific heat
Authors:
Guillou, F; Thota, S; Prellier, W; Kumar, J; Hardy, V Author Full Names: Guillou, F.; Thota, S.; Prellier, W.; Kumar, J.; Hardy, V.
Source:
PHYSICAL REVIEW B 83 (9): Art. No. 094423 MAR 23 2011
Abstract:
Mn3O4 is one of the archetypal examples of tetragonally distorted spinels. In this paper we reinvestigate its complex magnetic ordering process by using high-resolution magnetic and calorimetric measurements. The first-order transition to the ground state is found to exhibit a latent heat of similar or equal to 4 J mol(-1) and a thermal hysteresis of similar or equal to 0.6 K. Moreover, the peculiar field-induced broadening observed at this transition is shown to be consistent with general predictions about incommensurate-to-commensurate transition. In addition to the known sequence of transitions at T-N similar or equal to 43 K, T-1 similar or equal to 40 K, and T-2 similar or equal to 34 K, a new anomaly close to T* similar or equal to 38 K is observed in both *magnetization* and heat capacity data. A possible origin of this feature is discussed in terms of magnetic instability within the incommensurate spiral spin configuration.
Title:
Structural and magnetic properties of Sc1.1Fe3.9Al8 alloy
Authors:
Recko, K; Dobrzynski, L; Senyshyn, A; Fuess, H; Szymanski, K; Kotur, BY; Suski, W Author Full Names: Recko, K.; Dobrzynski, L.; Senyshyn, A.; Fuess, H.; Szymanski, K.; Kotur, B. Yu; Suski, W.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 323 (14): 1860-1867 JUL 2011
Abstract:
The crystallochemical and magnetic nature of ternary Sc1+delta Fe4-delta Al8 intermetallic with a small Sc excess delta = 0.1 was investigated by scanning electron microscope, X-ray powder diffraction, neutron diffraction, Mossbauer effect and superconducting quantum interference device techniques. The sample crystallizes in a tetragonal ThMn12 type structure. The excess of Sc atoms substitute Fe at the (8f) positions and have a pronounced effect on the magnetic properties. The experiments carried out in temperature range 4-320 K show that below 120 K the magnetic structure of the alloy forms a double cycloid with magnetic moments rotating according to the incommensurate in-plane wave vector, which is temperature independent upto 160 K. The value of Fe magnetic moment is close to 0.9 mu(B) atom(-1) at 4K. Temperature dependence of unit cell dimensions can be explained within the Debye-Gruneisen approximation. (c) 2011 Elsevier B.V. All rights reserved.
Title:
New high magnetic field phase of the frustrated S=1/2 chain compound LiCuVO4
Authors:
Svistov, LE; Fujita, T; Yamaguchi, H; Kimura, S; Omura, K; Prokofiev, A; Smirnov, AI; Honda, Z; Hagiwara, M Author Full Names: Svistov, L. E.; Fujita, T.; Yamaguchi, H.; Kimura, S.; Omura, K.; Prokofiev, A.; Smirnov, A. I.; Honda, Z.; Hagiwara, M.
Source:
JETP LETTERS 93 (1): 21-25 MAR 2011
Abstract:
Magnetization of the frustrated S = 1/2 chain compound LiCuVO4, focusing on high magnetic field phases, is reported. Besides a spin-flop transition and the transition from a planar spiral to a spin modulated structure observed recently, an additional transition was observed just below the saturation field. This newly observed magnetic phase is considered as a spin nematic phase, which was predicted theoretically but was not observed experimentally. The critical fields of this phase and its dM/dH curve are in good agreement with calculations performed in a microscopic model (M.E. Zhitomirsky and H. Tsunetsugu, Europhys. Lett. 92, 37001 (2010)).
Title:
TEMPERATURE AND SPECTRAL CHANGES IN THE REFRACTIVE INDICES OF LiKSO4 CRYSTALS UNDER UNIAXIAL PRESSURES
Authors:
Stadnyk, VI; Romanyuk, MO; Kushnir, OS; Brezvin, RS; Franiv, AV; Gaba, VM Author Full Names: Stadnyk, V. I.; Romanyuk, M. O.; Kushnir, O. S.; Brezvin, R. S.; Franiv, A. V.; Gaba, V. M.
Source:
INTERNATIONAL JOURNAL OF MODERN PHYSICS B 24 (32): 6219-6233 DEC 30 2010
Abstract:
We have studied spectral and temperature variations of the principal refractive indices of lithium potassium sulfate crystals, LiKSO4, subjected to uniaxial mechanical pressures. Notable baric increases in the refractive indices are found, which have been interpreted using classical single-oscillator dispersion Sellmeier equation and Lorentz-Lorenz formula. Significant pressure-induced shifts of low-temperature phase transitions in LiKSO4 are revealed and qualitatively explained in terms of modifications of crystalline structure imposed by the pressures. It is established that high enough pressures applied along the crystallographic axis c can generate a "triple point" on the phase diagram "temperature-uniaxial pressure". It is inferred that the temperature behavior of the refractive indices below the room temperature cannot be interpreted as a pure result of spontaneous strains and should possibly involve some other mechanisms, e.g., a hypothesis of incommensurately modulated phase existing about below 255 K.
Title:
Selective hydrogenation of Ti-Zr-Ni alloys
Authors:
Kocjan, A; Kovacic, S; Gradisek, A; Kovac, J; McGuiness, PJ; Apih, T; Dolinsek, J; Kobe, S Author Full Names: Kocjan, A.; Kovacic, S.; Gradisek, A.; Kovac, J.; McGuiness, P. J.; Apih, T.; Dolinsek, J.; Kobe, S.
Source:
INTERNATIONAL JOURNAL OF HYDROGEN ENERGY 36 (4): 3056-3061 FEB 2011
Abstract:
We prepared series of Ti-Zr-Ni samples by melt-spinning and subsequent thermal treatment at 700 degrees C for 2 h in dynamic 10(-5) mbar vacuum in order to obtain mixture of crystalline C14 Laves and alpha,beta-(Tr,Zr) phases. These samples were exposed to hydrogen gas at 300 degrees C and 50 bar for 1000 min. The mass% of H was obtained gravimetrically and volumetrically. When approximately 1% of air was present in the Sievert device we found relatively narrow area in Ti-Zr-Ni phase diagram, so-called zero-zone, where hydrogen amounts in crystalline samples varied between 0 and 0.8 mass%. Surprisingly, icosahedral quasicrystalline (i-QC) samples showed no selective hydrogenation and absorbed more than 1.5 mass% H in the interval of compositions, where the i-phase is formed. XPS analysis revealed that the oxide layer thickness is similar after melt-spinning and thermal treatment for both type of samples, i.e. from inside and outside of the zero-zone. However, after hydrogenation the zero-zone samples had 5-times thicker surface oxide layer. In order to find, whether this is correlated to different electronic structure, DOS near E-F was examined by H-1 NMR. In parallel, thermal desorption of hydrogen was performed in order to reveal, if H-bonding sites are correlated to different hydrogenation behaviour of various samples. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.
Title:
Polarization reversal by intramolecular disordering in organic ferroelectrics: trichloroacetamide
Authors:
Saito, K; Yamamura, Y; Kikuchi, N; Nakao, A; Yasuzuka, S; Akishige, Y; Murakami, Y Author Full Names: Saito, Kazuya; Yamamura, Yasuhisa; Kikuchi, Naoya; Nakao, Akiko; Yasuzuka, Syuma; Akishige, Yukikuni; Murakami, Youichi
Source:
CRYSTENGCOMM 13 (7): 2693-2698 2011
Abstract:
Mechanism of successive ferroelectric-paraelectric phase transitions exhibited by an organic ferroelectric, trichloroacetamide, is clarified through structural and calorimetric experiments. The transition mechanism, intramolecular disordering, reasonably explains the polarization reversal. This mechanism is only possible in molecular solids and is applicable to other compounds as a possible strategy to design new molecular ferroelectrics. Also revealed is the incommensurate nature of the intermediate phase, the origin of which is briefly discussed at phenomenological and molecular levels.

Update: 1-Apr-2011

Title:
Electronic structure of Mg-Zn-based compounds
Authors:
Ishii, Y; Dankhazi, Z; Belin-Ferre, E Author Full Names: Ishii, Yasushi; Dankhazi, Zoltan; Belin-Ferre, Esther
Source:
PHILOSOPHICAL MAGAZINE 91 (11): 1643-1652 2011
Abstract:
We present a comparison between calculated densities of states of the Laves phase MgZn2 and hexagonal Mg28Zn65Y7 and experimental results obtained using both X-ray emission and photoabsorption spectroscopy techniques. We show that there is general agreement between both sets of data for both alloys. We also point out that the two samples retain a metallic character, yet the hexagonal approximant of the Mg-Zn-Y quasicrystal family is less metallic than the Laves phase.
Title:
Structure of liquid Al-Cu-Co alloys near the quasicrystal-forming range
Authors:
Roik, OS; Galushko, SM; Samsonnikov, OV; Kazimirov, VP; Sokolskii, VE Author Full Names: Roik, O. S.; Galushko, S. M.; Samsonnikov, O. V.; Kazimirov, V. P.; Sokolskii, V. E.
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS 357 (3): 1147-1152 FEB 1 2011
Abstract:
A local short-to-intermediate range order in liquid Al63.9Cu19.4Co16.7. Al71Cu5Co23, and Al60Cu29Co11 alloys was investigated by X-ray diffraction technique and the reverse Monte Carlo modeling. A prepeak at Q similar to 17 nm(-1) originating from the unique bonding between the TM-TM pair (TM = Co, Cu) is observed in the structure factors of all investigated melts. The Voronoi-Delaunay analysis of RMC models indicates that a medium-range ordering of TM atoms in dense non-crystalline polytetrahedral clusters is associated with a chemical short-range order. The icosahedral short-range order is also closely related to the dense packing polytetrahedral clusters. A decrease of temperature leads to an enhancement of both chemical short-range order and icosahedral short-range order. (C) 2010 Elsevier B.V. All rights reserved.
Title:
Raman study of lattice dynamics in quasicrystals
Authors:
Ponosov, YS; Shchegolikhina, NI; Prekul, AF Author Full Names: Ponosov, Yu. S.; Shchegolikhina, N. I.; Prekul, A. F.
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS 357 (3): 1235-1238 FEB 1 2011
Abstract:
We present the first Raman investigation of icosahedral quasicrystals. Broad structured bands in the energy range up to similar to 500 cm(-1) have been observed in a series of AlCuFe, AlPdMn and AlPdRe systems. Original information on the vibrational density of states g(omega) was obtained for AlPdRe; for AlCuFe and AlPdMn estimated g(omega) shows a good agreement with the previous neutron results, but demonstrates finer structure. Strong increase in the parameter of electron-vibrational coupling for the low-energy vibrations and its correlation with changes in electronic conductivity has been observed in the series from AlCuFe to AlPdRe. This suggests the increase of the degree of localization for these vibrational excitations and involved electronic states. (C) 2010 Elsevier B.V. All rights reserved.
Title:
Magnetic properties of the 1/1 approximant Ag42In42Gd16 to the icosahedral quasicrystal Ag-In-Gd
Authors:
Wang, P; Stadnik, ZM; Przewoznik, J Author Full Names: Wang, P.; Stadnik, Z. M.; Przewoznik, J.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 509 (8): 3435-3440 FEB 24 2011
Abstract:
The structural, magnetic, and Gd-155 Mossbauer spectral properties of the 1/1 approximant Ag42In42Gd16 to an icosahedral quasicrystal Ag-In-Gd are reported. Based on dc magnetic susceptibility measurements, it is shown that the studied compound develops no long-range magnetic order in the temperature range 1.8-300K. The dc zero-field-cooled and field-cooled susceptibility data indicate that the 1/1 approximant Ag42In42Gd16 is a spin glasss with freezing temperature T-f = 3.6(1)K. This is further confirmed by the analysis of the frequency dependence of T-f using the Vogel-Fulcher law and the dynamic scaling behavior near T-f. It is argued that the spin freezing process is a true equilibrium phase transition rather than a nonequilibrium phenomenon. The large frustration parameter of the studied compound indicates that it belongs to a category of strongly geometrically frustrated magnets. The Gd-155 Mossbauer spectra of the 1/1 approximant Ag42In42Gd16 confirm that the Gd spins are frozen at 1.5K and are fluctuating at 4.6 K. The Debye temperature of the 1/1 approximant Ag42In42Gd16 is 200(1) K. (c) 2010 Elsevier B.V. All rights reserved.
Title:
Planar Symmetry Incompatibility in Ru-Sn-Zn Pseudo-Decagonal Approximants Composed of Novel Pentagonal Antiprisms
Authors:
Xiong, DB; Okamoto, NL; Inui, H Author Full Names: Xiong, Ding-Bang; Okamoto, Norihiko L.; Inui, Haruyuki
Source:
INORGANIC CHEMISTRY 50 (3): 827-835 FEB 7 2011
Abstract:
Two new ternary compounds in the Ru-Sn-Zn system were synthesized by conventional high-temperature reactions, and their crystal structures were analyzed by means of the single crystal X-ray diffraction: Ru2Sn2Zn3 (orthorhombic, Pnma, Pearson symbol oP28, a = 8.2219(16), b = 4.1925(8), c = 13.625(3) angstrom, V=469.66(16) angstrom(3), Z = 4) and Ru4.15Sn4.96Zn5.85 (orthorhombic, Pnma, Pearson symbol oP60-delta, a = 8.3394(17), b = 4.2914(9), c = 28.864(6) angstrom, V = 1032.98(40) angstrom(3), Z = 4). With the increase in the Sn content, the half-decagon structure unit with a triangle center in Ru2Sn2Zn3 grows up to a symmetry incompatible decagonal unit with a central triangle in the common plane in Ru4.15Sn4.96Zn5.85. Both structures can be described by hexagonal arrays of Sn-centered novel pentagonal antiprisms. In light of their pseudodecagonal diffraction in the h0l section and point group mmm, both phases are considered as new quasicrystal approximants in the Ru-Zn Sn ternary system. The temperature dependences of the electrical resistivity for both compounds exhibit metallic behavior, but their Seebeck coefficients are of opposite sign.

Update: 25-Mar-2011

Title:
NdRhSn: A ferromagnet with an antiferromagnetic precursor
Authors:
Mihalik, M; Prokleska, J; Kamarad, J; Prokes, K; Isnard, O; McIntyre, GJ; Donni, A; Yoshii, S; Kitazawa, H; Sechovsky, V; de Boer, FR Author Full Names: Mihalik, M.; Prokleska, J.; Kamarad, J.; Prokes, K.; Isnard, O.; McIntyre, G. J.; Doenni, A.; Yoshii, S.; Kitazawa, H.; Sechovsky, V.; de Boer, F. R.
Source:
PHYSICAL REVIEW B 83 (10): Art. No. 104403 MAR 9 2011
Abstract:
NdRhSn has a ferromagnetic ground state [T-t = 7.6(1) K] with a magnetic moment equal to 2/3 of the free Nd3+-ion moment. Upon cooling from the paramagnetic state, the ferromagnetism is preceded by an incommensurate antiferromagnetic state between T-N = 9.8(1) K and T-t. In both magnetic phases the magnetic moments are locked along the c axis, which is the easy-magnetization axis of the system. We have investigated this unusual situation by measuring anomalies of several bulk physical properties characteristic for the magnetic phase transitions at T-N and T-t and the response of these properties to an applied magnetic field. Neutron-diffraction experiments have been also performed at low temperatures. Furthermore, in order to understand better the physical properties of NdRhSn, single crystals have been studied under external hydrostatic and uniaxial pressure and in high magnetic fields. An antiferromagnetic phase with a propagation vector (0 0 1/11) has been found between T-N and T-t. The magnetic-ordering temperatures T-N and T-t are sensitive to both hydrostatic and uniaxial pressures, but in a different manner. Application of hydrostatic pressure leads to a reduction of the ordering temperatures at rates Delta T-N/Delta p = -0.76(5) K/GPa and Delta T-t/Delta p = -0.9(2) K/GPa while uniaxial pressure applied along the c axis leads to an increase of the ordering temperatures at rates Delta T-N/Delta p = +1.2(5) K/GPa and Delta T-t/Delta p = +2.7(4) K/GPa. No considerable influence of pressure on the antiferromagnetic propagation vector has been found. The peculiar evolution of magnetism in NdRhSn with temperature indicates a complex hierarchy of exchange interactions.
Title:
Electronic structure of EuPtSi3 studied from the first principles calculation
Authors:
Pan, D; Wan, XG Author Full Names: Pan, D.; Wan, X. G.
Source:
PHYSICA B-CONDENSED MATTER 406 (5): 1129-1131 MAR 1 2011
Abstract:
We investigate the electronic structure of EuPtSi3 using full potential linearized augmented plane wave method within the generalized gradient approximation. We reproduce the observed easy axis of magnetization as well as magnetic moment and propose that the magnetic configuration for this compound is incommensurate or noncollinear. We find that the spin configuration has only negligible effect on the band around Fermi energy. EuPtSi3 and its isostructural superconductor BaPtSi3 have similar band structures. Despite the shorter Pt-Si bond, EuPtSi3 possesses larger density of state near the Fermi energy compared with BaPtSi3, thus the structural difference and the associated difference in band structure cannot explain the non-superconductivity of EuPtSi3. (C) 2010 Elsevier B.V. All rights reserved.
Title:
A general solution of elasto-hydrodynamics of two-dimensional quasicrystals
Authors:
Li, XF Author Full Names: Li, X-F
Source:
PHILOSOPHICAL MAGAZINE LETTERS 91 (4): 313-320 2011
Abstract:
Dynamic problems of quasicrystals are analysed within the framework of continuum mechanics. Phonon excitations yield wave propagation while phason excitations yield atomic diffusion. Phonon fields obey the equations of motion and phason fields obey the diffusion equations. Governing equations of elasto-hydrodynamics of decagonal quasicrystals combine characteristics of the equations of motion and diffusion. A general solution is derived in terms of two introduced auxiliary functions. It provides an easy-to-use approach to solve initial-boundary value problems encountered in elasticity problems for quasicrystals. Explicit expressions for displacements and stresses in the phonon and phason fields can be directly obtained. A derived general solution is also applicable to some planar quasicrystals such as pentagonal quasicrystals with fivefold symmetry.
Title:
Mechanical Property and Corrosion Resistance of Mg-Zn-Y Alloys Containing Icosahedral Phase
Authors:
Kim, DH; Kim, YK; Kim, WT; Kim, DH Author Full Names: Kim, Do Hyung; Kim, Young Kyun; Kim, Won Tae; Kim, Do Hyang
Source:
KOREAN JOURNAL OF METALS AND MATERIALS 49 (2): 145-152 FEB 2011
Abstract:
Mechanical and property corrosion resistance of Mg-Zn-Y alloys with an atomic ratio of Zn/Y of 6.8 are investigated using optical microscopy, scanning electron microscopy, transmission electron microscopy, uniaxial tensile test and corrosion test with immersion and dynamic potentiometric tests. The alloys showed an in-situ composite microstructure consisting of alpha-Mg and icosahedral phase (I-phase) as a strengthening phase. As the volume fraction of the I-phase increases, the yield and tensile strengths of the alloys increase while maintaining large elongation (26 similar to 30%), indicating that I-phase is effective for strengthening and forms a stable interface with surrounding alpha-Mg matrix. The presence of I-phase having higher corrosion potential than alpha-Mg, decreased the corrosion rate of the cast alloy up to I-phase volume fraction of 3.7%. However further increase in the volume fraction of the I-phase deteriorates the corrosion resistance due to enhanced internal galvanic corrosion cell between alpha-Mg and I-phase.
Title:
Hydrogen and Zr-based metallic glasses: Gas/solid absorption process and structure evolution
Authors:
Paillier, J; Rongeat, C; Gutfleisch, O; Gebert, A Author Full Names: Paillier, Jerome; Rongeat, Carine; Gutfleisch, Oliver; Gebert, Annett
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 509 (5): 1636-1643 FEB 3 2011
Abstract:
The absorption of hydrogen by means of gas-solid reaction and its consequence on the structure have been studied for fully amorphous alloys as well as quasicrystals/glassy composite alloys based on the composition Zr59Ti3Cu20Al10Ni8. The process of hydrogen absorption has been performed and monitored under 20 bar of H-2 using high pressure-differential scanning calorimetry (HP-DSC). The structure evolution of the samples has been followed by X-ray diffractometry (XRD). Results show that the nature of the surface oxide layer strongly affects the process of hydrogen absorption, especially its starting temperature. The structure evolves nevertheless along the same basic sequence, regardless of the sample: (i) the alloys keep a global amorphous structure up to roughly H/M =0.8 and T= 350 degrees C; (ii) then ZrH2 and at higher temperature Cu2AlZr are formed. The stability of the glass is weakened and the formation of quasicrystals is inhibited under 20 bar of H-2. An heterogeneous distribution of hydrogen atoms inside the amorphous matrix has been inferred from the results. (C) 2010 Elsevier B.V. All rights reserved.
Title:
Formation of nano quasicrystalline and crystalline phases by mechanical alloying
Authors:
Shamah, AM; Ibrahim, S; Hanna, FF Author Full Names: Shamah, A. M.; Ibrahim, S.; Hanna, F. F.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 509 (5): 2198-2202 FEB 3 2011
Abstract:
In the present work, the formation of nano quasicrystalline icosahedral phase in Al86Cr14, Al84Fe16 and Al62.5Cu25Fe12.5 alloys has been investigated by mechanical alloying. Mixtures of quasicrystalline and related crystalline phases have been observed under various milling conditions. The X-ray diffraction, differential thermal analysis and electrical resistivity techniques have been used for characterization and physical property measurements. The particle size was calculated by X-ray profile using Williamson-Hall plot method and it was found to be 25-50 nm size. (C) 2010 Elsevier B.V. All rights reserved.
Title:
Effect of processing parameter on hydrogen storage characteristics of as quenched Ti45Zr38Ni17 quasicrystalline alloys
Authors:
Shahi, RR; Yadav, TP; Shaz, MA; Srivastava, ON; van Smaalen, S Author Full Names: Shahi, Rohit R.; Yadav, T. P.; Shaz, M. A.; Srivastava, O. N.; van Smaalen, S.
Source:
INTERNATIONAL JOURNAL OF HYDROGEN ENERGY 36 (1): 592-599 JAN 2011
Abstract:
The present study deals with the microstructural changes with respect to the processing parameter (quenching rate) and their correlation with hydrogen storage characteristics of Ti45Zr38Ni17 quasicrystalline alloys. The ribbons of the alloy have been synthesized at different quenching rates obtained through different wheel speeds (35, 40, 45 and 50 m/s) and investigated for their hydrogen storage characteristics. The lower cooling rate obtained through low wheel speed (35 m/s) produces, i-phase grains whose size ranges from 300-350 nm, whereas higher cooling rates obtained through high wheel speed (45 and 50 m/s) promote the formation of grains with size ranges from 100-150 nm in Ti45Zr38Ni17 ribbons. It has been found that the ribbons synthesized at 35 m/s absorbed similar to 2.0 wt%, whereas ribbons synthesized at 50 m/s absorbed similar to 2.84 wt. % of hydrogen. Thus the hydrogen storage capacity of ribbon increases for the ribbons produced at higher quenching rate. One of the salient features of the present study is that the improvement of hydrogen storage capacity obtained through higher quenching rates (similar to 45 to 50 m/s wheel speed) leading to the formation of lower grain size. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.
Title:
Electrochemical performance of TiVNi-Quasicrystal and AB(3)-Type hydrogen storage alloy composite materials
Authors:
Liu, WQ; Wang, XL; Hu, W; Kawabe, Y; Watada, M; Wang, LM Author Full Names: Liu, Wanqiang; Wang, Xinlu; Hu, Wen; Kawabe, Yoshiteru; Watada, Masaharu; Wang, Limin
Source:
INTERNATIONAL JOURNAL OF HYDROGEN ENERGY 36 (1): 616-620 JAN 2011
Abstract:
The Ti1.4V0.6Ni ribbon alloy and AB(3)-type (La0.65Nd0.12Mg0.23Ni2.9Al0.1) alloy ingot are prepared by melt-spinning technique and induction levitation melting technique, respectively. The Ti1.4V0.6Ni + 20 wt.% AB(3) mixture powders are synthesized by ball-milling the above prepared alloy ingots, and their structures and the electrochemical hydrogen storage properties are investigated. It is found that the icosahedral quasicrystal, Ti2Ni, BCC structural solid solution and AB3-type phases are all presented in the composite material. The maximum electrochemical discharge capacity of the composite electrode is 294.7 mAh/g at the discharge current density of 30 mA/g and 303 K. In addition, the electrode made of Ti1.4V0.6Ni and AB(3) composite holds better high-rate discharge ability than that of Ti1.4V0.6Ni. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.
Title:
The formation of quasicrystals and their hydrides in Ti-Zr-Ni system
Authors:
Shekhtman, VS; Hakobyan, HG; Aleksanyan, AG; Dolukhanyan, SK; Ter-Galstyan, OP; Sakharov, MK Author Full Names: Shekhtman, V. Sh.; Hakobyan, H. G.; Aleksanyan, A. G.; Dolukhanyan, S. K.; Ter-Galstyan, O. P.; Sakharov, M. K.
Source:
INTERNATIONAL JOURNAL OF HYDROGEN ENERGY 36 (1): 1206-1208 JAN 2011
Abstract:
In the present work, an essentially new approach to production of quasicrystals in Ti-Zr-Ni system is described. It consists in co-compaction and dehydrogenation-sintering of mixture of powders of Ni with two and more hydrides of transition metals of IV group (Ti, Zr). The interaction of some of received quasicrystals with hydrogen in combustion mode is studied, the hydrides of these quasicrystals are synthesized and investigated. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.

Update: 18-Mar-2011

Title:
Birefringence Properties of Mechanically Clamped K2ZnCl4 Crystals
Authors:
Stadnyk, VI; Gaba, VM; Andrievskii, BV; Kogut, ZO Author Full Names: Stadnyk, V. I.; Gaba, V. M.; Andrievskii, B. V.; Kogut, Z. O.
Source:
PHYSICS OF THE SOLID STATE 53 (1): 131-137 JAN 2011
Abstract:
The effect of uniaxial pressure applied along the principal crystallographic directions on the dispersion and temperature dependences of the birefringence Delta n(i) of K2ZnCl4 crystals has been studied. It has been established that the birefringence Delta n(i) is sensitive to uniaxial pressures and that the uniaxial stresses do not change the character of the dispersion and temperature dependences of Delta n(i). A new "pseudoisotropic" state of this crystal has been revealed. It has been found that the points of the paraphase-incommensurate phase-commensurate phase transitions can be significantly shifted under pressure toward different temperature ranges depending on the direction of the applied pressure due to the effect of uniaxial stresses on the structure of the K2ZnCl4 crystal.
Title:
Universal Hysteresis Scaling for Incommensurate Magnetic Order in Dysprosium
Authors:
Kobayashi, S Author Full Names: Kobayashi, Satoru
Source:
PHYSICAL REVIEW LETTERS 106 (5): Art. No. 057207 FEB 3 2011
Abstract:
We study the scaling properties of magnetic minor hysteresis loops in a polycrystalline dysprosium metal, varying temperature and magnetic-field amplitudes. We observe irreversibility-related hysteresis loss in the helical antiferromagnetic phase, which is related with remanent flux density as a power law with the same scaling exponent of 1.25 +/- 0.05 as that in ferromagnetic materials. In contrast to hysteresis scalings in ferromagnets associated with 180 degrees Bloch walls, the observed law is governed by spiral walls which separate helical domains with oppositely rotating spins.
Title:
Magnetic excitations in the metallic single-layer ruthenates Ca2-xSrxRuO4 studied by inelastic neutron scattering
Authors:
Steffens, P; Friedt, O; Sidis, Y; Link, P; Kulda, J; Schmalzl, K; Nakatsuji, S; Braden, M Author Full Names: Steffens, P.; Friedt, O.; Sidis, Y.; Link, P.; Kulda, J.; Schmalzl, K.; Nakatsuji, S.; Braden, M.
Source:
PHYSICAL REVIEW B 83 (5): Art. No. 054429 FEB 24 2011
Abstract:
By inelastic neutron scattering, we have analyzed the magnetic correlations in the paramagnetic metallic region of the series Ca2-xSrxRuO4, 0.2 <= x <= 0.62. We find different contributions that correspond to two-dimensional ferromagnetic fluctuations and to fluctuations at incommensurate wave vectors Q(1)(IC) = (0.11,0,0), Q(2)(IC) = (0.26,0,0), and Q(alpha beta)(IC) = (0.3,0.3,0). These components constitute the measured response as a function of the Sr concentration x, of the magnetic field, and of the temperature. A generic model is applicable to metallic Ca2-xSrxRuO4 close to the Mott transition, in spite of their strongly varying physical properties. The amplitude, characteristic energy, and width of the incommensurate components vary only slightly as functions of x, but the ferromagnetic component depends sensitively on concentration, temperature, and magnetic field. While ferromagnetic fluctuations are very strong in Ca1.38Sr0.62RuO4 with a low characteristic energy of 0.2 meV at T = 1.5 K, they are strongly suppressed in Ca1.8Sr0.2RuO4, but reappear upon the application of a magnetic field, and form a magnon mode above the metamagnetic transition. The inelastic neutron scattering results document how the competition between ferromagnetic and incommensurate antiferromagnetic instabilities governs the physics of this system.
Title:
Crossover from Commensurate to Incommensurate Antiferromagnetism in Stoichiometric NaFeAs Revealed by Single-Crystal Na-23,As-75-NMR Experiments
Authors:
Kitagawa, K; Mezaki, Y; Matsubayashi, K; Uwatoko, Y; Takigawa, M Author Full Names: Kitagawa, Kentaro; Mezaki, Yuji; Matsubayashi, Kazuyuki; Uwatoko, Yoshiya; Takigawa, Masashi
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 80 (3): Art. No. 033705 MAR 2011
Abstract:
We report the results of Na-23 and As-75 nuclear magnetic resonance (NMR) experiments on a self-flux grown high-quality single crystal of stoichiometric NaFeAs. The NMR spectra reveal a tetragonal to twinned-orthorhombic structural phase transition at T-O = 57K and an antiferromagnetic (AF) transition at T-AF = 45 K. The divergent behavior of nuclear relaxation rate near T-AF shows significant anisotropy, indicating that the critical slowing down of stripe-type AF fluctuations are strongly anisotropic in spin space. The NMR spectra at sufficiently low temperatures consist of sharp peaks showing a commensurate stripe AF order with a small moment of similar to 0.3 mu(B). However, the spectra just below T-AF exhibit a highly asymmetric broadening pointing to an incommensurate modulation. The commensurate-incommensurate crossover in NaFeAs shows a certain similarity to the behavior of SrFe2As2 under high pressure.
Title:
Incommensurate-to-Commensurate Magnetic Phase Transition in SmIn3 Observed by Muon Spin Relaxation
Authors:
Ito, TU; Higemoto, W; Ninomiya, K; Luetkens, H; Sugai, T; Haga, Y; Suzuki, HS Author Full Names: Ito, Takashi U.; Higemoto, Wataru; Ninomiya, Kazuhiko; Luetkens, Hubertus; Sugai, Takashi; Haga, Yoshinori; Suzuki, Hiroyuki S.
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 80 (3): Art. No. 033710 MAR 2011
Abstract:
Magnetic susceptibility and muon spin relaxation (mu SR) measurements in the intermetallic cubic compound SmIn3 with a Gamma(8) crystalline-electric-field ground state are reported. Anomalies corresponding to successive phase transitions were observed in the magnetic susceptibility at T-I similar to 16.5 K, T-II similar to 15.1 K, and T-III similar to 14.7 K. A spontaneous local magnetic field was detected below T-I using the mu SR technique in zero applied field in contrast to the pure quadrupolar ordering scenario proposed in the phase between T-I and T-II. This result clearly indicates that the primary order parameters in all the ordered phases are magnetic. The local field distribution changes at around TII from a continuous broad one to a sharp one with decreasing temperature, suggesting that an incommensurate-to-commensurate magnetic phase transition takes place at this temperature. A possible magnetic structure in the ground state and the importance of multipolar interactions in the Gamma(8) subspace are discussed.
Title:
Incommensurate Magnetic Structure and Its Long-Time Variation in a Geometrically Frustrated Magnet Ca3Co2O6
Authors:
Moyoshi, T; Motoya, K Author Full Names: Moyoshi, Taketo; Motoya, Kiyoichiro
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 80 (3): Art. No. 034701 MAR 2011
Abstract:
Magnetization and neutron scattering measurements have been performed on a single crystal of the magnetically frustrated compound Ca3Co2O6. This compound has no random magnetic interactions, but has frustrating magnetic interactions arising from its crystal structure. In this material, a long-time variation in magnetic structure has been observed. After cooling the sample below the transition temperature T-c2 = 13 K, the magnetic Bragg peaks at (1, 0, +/-delta) corresponding to an incommensurate antiferromagnetic structure move toward (1,0,0) with time. The characteristic time for this variation follows the Arrhenius law with an activation energy E-a/k(B) similar to 53 K. A new magnetic structure model of this material is also presented.
Title:
The Al-rich region of the Al-Mn-Ni alloy system. Part II. Phase equilibria at 620-1000 degrees C
Authors:
Balanetskyy, S; Meisterernst, G; Grushko, B; Feuerbacher, M Author Full Names: Balanetskyy, S.; Meisterernst, G.; Grushko, B.; Feuerbacher, M.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 509 (9): 3795-3805 MAR 3 2011
Abstract:
Phase equilibria in the Al-rich region of the Al-Mn-Ni alloy system were studied at 1000, 950, 850, 750, 700, 645 and 620 degrees C. Three ternary thermodynamically stable intermetallics, the phi-phase (Al5Co2-type, hP26, P6(3)/mmc; a = 0.76632(16), c = 0.78296(15) nm), the kappa-phase (kappa-Al14.4Cr3.4Ni1.1-type, hP227, P6(3)/m; a = 1.7625(10), c = 1.2516(10) nm), and the O-phase (O-Al77Cr14Pd9-type, Pmmn, oP650,: a = 2.3316(16), b = 1.2424(15), c = 3.2648(14) nm), as well as three ternary metastable phases, the decagonal D-3-phase with periodicity about 1.25 nm, the Al-9(Mn,Ni)(2)-phase (Al9Co2-type, P112(1)/a, mP22; a = 0.8585(16), b = 0.6269(9), c = 0.6205(11) nm, beta = 95.34(10)degrees) and the O-1-phase (base-centered orthorhombic, a approximate to 23.8, b approximate to 12.4, c approximate to 32.2 nm) were revealed. Their physicochemical behaviour in the Al-Mn-Ni alloy system was studied. (C) 2010 Elsevier B.V. All rights reserved.
Title:
Structural and hyperfine properties of Ti48Zr7Fe18 nano-compounds and its hydrides
Authors:
Zywczak, A; Gondek, L; Figiel, H; Zukrowski, J; Czub, J; Takasaki, A Author Full Names: Zywczak, A.; Gondek, L.; Figiel, H.; Zukrowski, J.; Czub, J.; Takasaki, A.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 509 (9): 3952-3957 MAR 3 2011
Abstract:
It is well established that Ti-based nano-alloys are able to absorb hydrogen with relatively high hydrogen to metal ratio of 4/3. In this study the Ti48Zr7Fe18 nano-compound, prepared by mechanical alloying (MA), has been investigated. In its initial state the compound is amorphous, however upon thermal treatment it transforms to the quasicrystalline icosahedral structure (i-phase), which is based on the Mackay cluster type. Structural characterization of the sample was made by means of XRD measurements. Thermodynamic properties were studied by differential scanning calorimetry (DSC) and thermal desorption spectroscopy (TDS). To find the influence of hydrogen and structure type on hyperfine interactions the Mossbauer spectroscopy (MS) experiment was performed, as well. The amorphous sample after MA was hydrogenated in order to unveil hydrogen influence on crystal properties of the sample. Upon hydrogenation of the amorphous sample a decomposition into simple hydrides took place. (C) 2011 Elsevier B. V. All rights reserved.
Title:
Piezo-optic properties of incommensurately modulated K2ZnCl4 crystals
Authors:
Stadnyk, VI; Kogut, ZO; Brezvin, RS Author Full Names: Stadnyk, V. I.; Kogut, Z. O.; Brezvin, R. S.
Source:
CRYSTALLOGRAPHY REPORTS 56 (1): 84-88 JAN 2011
Abstract:
The effect that uniaxial pressures along the principal crystallophysical directions have on the dispersion and temperature dependences of the birefringence in incommensurate K2ZnCl4 crystals has been investigated in a wide temperature range. This parameter has been established to be fairly sensitive to uniaxial pressures. The spectral and temperature dependences of combined piezo-optic coefficients are analyzed. Significant anomalies of these coefficients are found at the incommensurate-commensurate phase transition. They are due to the change in the induced birefringence that results from spontaneous polarization and to the significant effect of uniaxial stress on the soliton structure of the crystal. The contributions that the electrooptic effect, the elasto-optic effect, and the order parameter make to the spontaneous changes in the piezooptic coefficients are separated.
Title:
Vibrational and thermodynamic properties and molecular motions in the incommensurate crystal of morpholinium tetrafluoroborate studied by H-1 NMR
Authors:
Owczarek, M; Jakubas, R; Bator, G; Pawlukojc, A; Baran, J; Przeslawski, J; Medycki, W Author Full Names: Owczarek, M.; Jakubas, R.; Bator, G.; Pawlukojc, A.; Baran, J.; Przeslawski, J.; Medycki, W.
Source:
CHEMICAL PHYSICS 381 (1-3): 11-20 MAR 18 2011
Abstract:
Dynamics of molecules in morpholinium tetrafluoroborate, [NH2(C2H4)(2)O][BF4], has been studied in a wide temperature range by means of AC calorimetry, H-1 NMR and infrared spectroscopy. Simultaneously, DFT (density functional theory) calculations of the molecular structure and normal vibration frequencies have been performed by using various functionals for initial structural data of the low temperature phase. Infrared spectra of polycrystalline [NH2(C2H4)(2)O][BF4] have been analyzed in a frequency range 4000-400 cm (1). Substantial changes in a temperature evolution of internal modes of both morpholinium cations and [BF4] anions are due to the freezing of these moieties motions below 117 K. A dynamic non-equivalence of protons involved in N-H center dot center dot center dot F and N-H center dot center dot center dot O hydrogen bonds has been detected. Heat capacity anomalies around structural phase transitions detected by AC calorimetry (117 and 153 K) have been evaluated and described. A molecular mechanism of the phase transitions is discussed on the basis of presented results. (C) 2011 Elsevier B. V. All rights reserved.
Title:
Unifying cluster-based structure models of decagonal Al-Co-Ni, Al-Co-Cu and Al-Fe-Ni
Authors:
Deloudi, S; Fleischer, F; Steurer, W Author Full Names: Deloudi, Sofia; Fleischer, Frank; Steurer, Walter
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 67: 1-17 Part 1 FEB 2011
Abstract:
The geometrical building principles of Al-based decagonal quasicrystals and their approximants are discussed from a cluster-based approach. Our investigations cover 11 modifications with two-or four-layer periodicity in the systems Al-Co-Ni, Al-Co-Cu and Al-Fe-Ni. We identified a cluster that leads to a unifying view of all these phases. This unit cluster has similar to 20 angstrom diameter, four-layer periodicity along its tenfold axis and rod symmetry group p (10) over bar 2m. The models obtained are in agreement with all the electron-density maps and electron-microscopy images available.
Title:
Modulated structure of nepheline
Authors:
Friese, K; Grzechnik, A; Petricek, V; Schonleber, A; van Smaalen, S; Morgenroth, W Author Full Names: Friese, Karen; Grzechnik, Andrzej; Petricek, Vaclav; Schoenleber, Andreas; van Smaalen, Sander; Morgenroth, Wolfgang
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 67: 18-29 Part 1 FEB 2011
Abstract:
The incommensurately modulated structure of a natural nepheline of composition K0.54Na3.24Ca0.03Al3.84Si4.16O16 has been determined in superspace. The compound crystallizes in the trigonal centered superspace group X3(00 gamma)0 with gamma = 0.2048 (10), X = (0, 0, 0, 0), (1/3, 2/3, 0, 2/3), (2/3, 1/3, 0, 1/3), a = 17.2889 (8) and c = 8.3622 (10) angstrom. The structure is characterized by a framework of corner-connected (Al,Si)O-4 tetrahedra. The additional cations are incorporated in two different types of channels of the framework. All atoms in the structure are displacively modulated with amplitudes below 0.1 angstrom. The modulation can be well described taking into account harmonics of first order only. Atomic positions in the smaller channels of the framework are fully occupied by Na+. Cationic positions in the larger channel are occupationally modulated, yet the variation of electron density as a function of the internal coordinate t is very small and indicates that the incorporation of different types of cations (K+, Na+, Ca2+) and vacancies is realised in a highly disordered way. Average T-O distances indicate a nearly complete Al/Si ordering in the tetrahedral framework. A large part of the O atoms are approximated by split-atom positions, which are additionally affected by occupational modulation resulting in a high degree of disorder in the modulated structure. Occupational probabilities for the split-atom positions are complementary. Occupational modulations of the cations in the larger channels and the O atoms of the tetrahedral framework are coupled and correlations between occupational and displacive modulations exist.

Update: 11-Mar-2011

Title:
Defect structure and electrical conductivity in the Bi3+xNb0.8W0.2O7.1+3x/2 system
Authors:
Borowska-Centkowska, A; Kario, A; Krok, F; Abrahams, I; Chan, SCM; Liu, X; Wrobel, W; Malys, M; Hull, S; Dygas, JR; Suard, E Author Full Names: Borowska-Centkowska, A.; Kario, A.; Krok, F.; Abrahams, I.; Chan, S. C. M.; Liu, X.; Wrobel, W.; Malys, M.; Hull, S.; Dygas, J. R.; Suard, E.
Source:
SOLID STATE IONICS 181 (39-40): 1750-1756 DEC 20 2010
Abstract:
An investigation of electrical conductivity and defect structure in the fluorite related system Bi3+xNb0.8W0.2O7.1+3x2 (0.0 <= x <= 2.0) using a.c. impedance spectroscopy and powder neutron diffraction is presented. All compositions exhibit incommensurate ordering of the cubic fluorite sublattice, with only the x = 2.0 composition showing evidence for an order-disorder transition above 650 degrees C. Non-linear behaviour in the thermal expansion of the cubic lattice parameter and the Arrhenius plot of total conductivity are discussed in terms of the defect structure. (C) 2010 Elsevier B.V. All rights reserved.
Title:
Colloidal hard dumbbells under gravity: structure and crystallization
Authors:
Marechal, M; Dijkstra, M Author Full Names: Marechal, Matthieu; Dijkstra, Marjolein
Source:
SOFT MATTER 7 (4): 1397-1408 2011
Abstract:
We study the structure and phase behavior of hard dumbbells under gravity. The fluid shows layering near the wall, where subsequent layers of dumbbells align alternatingly parallel or perpendicular to the wall. We observe coexistence of a fluid with a plastic crystal (PC) and an aligned crystal (CP1) in a single sediment for short dumbbells. For longer dumbbells, we observe a direct fluid-CP1 coexistence, while for dumbbells of almost tangent spheres, the aperiodic crystal phase appears in between the fluid and CP1 phase. The locations of the coexistences between these phases are well described by a simple expression based on an approximation similar to the local density approximation, which has been successfully applied to hard spheres under gravity [M. Marechal and M. Dijkstra, Phys. Rev. E, 2007, 75, 061404]. The fluid-PC-CP1 coexistence could not be explained using this expression. We attribute this discrepancy to a lattice constant mismatch between the PC and CP1 phases. Finally, we show using direct simulations that the plastic crystal stacks preferably as the hexagonal close packed crystal for short dumbbells, as is the case for a bulk plastic crystal [M. Marechal and M. Dijkstra, Phys. Rev. E, 2008, 77, 061405].
Title:
Ultra-fine grain size and isotropic very high strength by direct extrusion of chill-cast Mg-Zn-Y alloys containing quasicrystal phase
Authors:
Singh, A; Osawa, Y; Somekawa, H; Mukai, T Author Full Names: Singh, Alok; Osawa, Yoshiaki; Somekawa, H.; Mukai, T.
Source:
SCRIPTA MATERIALIA 64 (7): 661-664 APR 2011
Abstract:
Very fine grain sizes up to similar to 1 mu m with yield strengths up to about 400 MPa in tension and compression, with elongations ranging from 12% to 18%, have been achieved by chill casting and direct extrusion of Mg93Zn6Y alloy containing a quasicrystalline phase. These alloys respond to ageing at 150 degrees C, showing two peaks. The hardness stabilizes at the level of the second peak. The effect of precipitation on the yield strength, ductility and yield asymmetry has been studied. (C) 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Title:
Structural studies of a mixed-valence state in the incommensurate composite crystal Sr1.261CoO3
Authors:
Isobe, M; Yoshida, H; Muromachi, ET; Ohoyama, K Author Full Names: Isobe, Masaaki; Yoshida, Hiroyuki; Muromachi, Eiji Takayama; Ohoyama, Kenji
Source:
SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS 11 (6): Art. No. 065004 DEC 2010
Abstract:
The incommensurate modulated crystal structure of the hexagonal cobalt oxide Sr1.261CoO3 has been studied using a four-dimensional (4D) superspace profile analysis of neutron powder diffraction data. Sr1.261CoO3 is a composite crystal that consists of the [CoO3] and [2Sr] subsystems. The [CoO3] subsystem forms 1D chains that run parallel to the c-axis and consist of face-sharing CoO6 polyhedra with octahedral (Oh) and trigonal prismatic (TP) coordinations. The structure analysis reveals that the [CoO3] chains contain 73.9% Oh and 26.1% TP sites, and that the TP sites have longer Co-O bonds than the Oh sites: d(av). = 2.039(4) angstrom (TP) and 1.895(3) angstrom (Oh). The averaged Co bond valences are Co3.56(3)+ in the Oh sites and Co2.45(3)+ in the TP sites, suggesting that a considerable amount of Co3+ ions are mixed with Co4+ ions in the Oh sites and with Co2+ ions in the TP sites. The observed magnetic susceptibility can be well explained assuming that the compound has the Co mixed-valence state with the spin configurations of S = 0 low-spin state for Co3+(d epsilon(6)), S = 1/2 low-spin state for Co4+(d epsilon(5)) and S = 3/2 high-spin state for Co2+(d epsilon(5)d gamma(2)). The Weiss temperature, approximately 0.8 K, implies that Sr1.261CoO3 naturally assumes a Curie paramagnetic state, probably owing to the obstruction of the intrachain magnetic interaction by the nonmagnetic Co3+ ions. These results suggest that the nonmagnetic Co3+ ions play an essential role in the magnetism of Sr2 gamma CoO3 systems.
Title:
MECHANICAL PROPERTIES OF Al-Cu-Fe ALLOYS SINTERED AT HIGH PRESSURE
Authors:
Mil'man, YV; Efimov, NA; Ul'shin, SV; Bykov, AI; Neikov, OD; Samelyuk, AV Author Full Names: Mil'man, Yu. V.; Efimov, N. A.; Ul'shin, S. V.; Bykov, A. I.; Neikov, O. D.; Samelyuk, A. V.
Source:
POWDER METALLURGY AND METAL CERAMICS 49 (5-6): 280-288 NOV 2010
Abstract:
The structure and mechanical behavior of bulk Al-Cu-Fe materials sintered at high hydrostatic pressure are studied at room temperature. Quasicrystalline Al63Cu25Fe12 and Al62.7Cu25Fe12Sc0.3 powders and Al66Cu18Fe8Cr8, powder, which is the quasicrystal approximant, are sintered at high pressure. The powders are obtained by high-pressure water atomization. At an optimal hot compaction pressure of 4.5 GPa, the porosity of the compact materials is lower than 2%. Sintering is conducted at 700 degrees C. The stress-strain curves of quasicrystals and their approximants that are brittle in standard test conditions are obtained using indentation method. It is shown that the crystalline approximants of quasicrystals are much closer in their mechanical behavior to quasicrystals than to crystalline solids.
Title:
Nuclear and incommensurate magnetic structure of NaFeGe2O6 between 5 K and 298 K and new data on multiferroic NaFeSi2O6
Authors:
Redhammer, GJ; Senyshyn, A; Meven, M; Roth, G; Prinz, S; Pachler, A; Tippelt, G; Pietzonka, C; Treutmann, W; Hoelzel, M; Pedersen, B; Amthauer, G Author Full Names: Redhammer, Guenther J.; Senyshyn, Anatoliy; Meven, Martin; Roth, Georg; Prinz, Sebastian; Pachler, Astrid; Tippelt, Gerold; Pietzonka, Clemens; Treutmann, Werner; Hoelzel, Markus; Pedersen, Bjoern; Amthauer, Georg
Source:
PHYSICS AND CHEMISTRY OF MINERALS 38 (2): 139-157 FEB 2011
Abstract:
The compound NaFeGe2O6 was grown synthetically as polycrystalline powder and as large single crystals suitable for X-ray and neutron-diffraction experiments to clarify the low temperature evolution of secondary structural parameters and to determine the low temperature magnetic spins structure. NaFeGe2O6 is isotypic to the clinopyroxene-type compound aegirine and adopts the typical HT-C2/c clinopyroxene structure down to 2.5 K. The Na-bearing M2 polyhedra were identified to show the largest volume expansion between 2.5 K and room temperature, while the GeO4 tetrahedra behave as stiff units. Magnetic susceptibility measurements show a broad maximum around 33 K, which marks the onset of low-dimensional magnetic ordering. Below 12 K NaFeGe2O6 transforms to an incommensurately modulated magnetic spin state, with k = [0.323, 1.0, 0.080] and a helical order of spins within the M1-chains of FeO6 octahedra. This is determined by neutron-diffraction experiments on a single crystal. Comparison of NaFeGe2O6 with NaFeSi2O6 is given and it is shown that the magnetic ordering in the latter compound, aegirine, also is complex and is best described by two different spin states, a commensurate one with C2'/c' symmetry and an incommensurate one, best being described by a spin density wave, oriented within the (1 0 1) plane.
Title:
Incommensurate Magnetism in FeAs Strips: Neutron Scattering from CaFe4As3
Authors:
Nambu, Y; Zhao, LL; Morosan, E; Kim, K; Kotliar, G; Zajdel, P; Green, MA; Ratcliff, W; Rodriguez-Rivera, JA; Broholm, C Author Full Names: Nambu, Yusuke; Zhao, Liang L.; Morosan, Emilia; Kim, Kyoo; Kotliar, Gabriel; Zajdel, Pawel; Green, Mark A.; Ratcliff, William; Rodriguez-Rivera, Jose A.; Broholm, Collin
Source:
PHYSICAL REVIEW LETTERS 106 (3): Art. No. 037201 JAN 18 2011
Abstract:
Magnetism in the orthorhombic metal CaFe4As3 was examined through neutron diffraction for powder and single crystalline samples. Incommensurate [q(m) approximate to (0.37-0.39) x b*] and predominantly longitudinally (parallel to b) modulated order develops through a 2nd order phase transition at T-N = 89.63(6) K with a 3D Heisenberg-like critical exponent beta = 0.365(6). A 1st order transition at T-2 = 25.6(9) K is associated with the development of a transverse component, locking q(m) to 0.375(2)b*, and increasing the moments from 2.1(1) to 2.2(3) mu(B) for Fe2+ and from 1.3(3) to 2.4(4) mu(B) for Fe+. The ab initio Fermi surface is consistent with a nesting instability in cross-linked FeAs strips.
Title:
Incommensurate Spin Fluctuations in Hole-Overdoped Superconductor KFe2As2
Authors:
Lee, CH; Kihou, K; Kawano-Furukawa, H; Saito, T; Iyo, A; Eisaki, H; Fukazawa, H; Kohori, Y; Suzuki, K; Usui, H; Kuroki, K; Yamada, K Author Full Names: Lee, C. H.; Kihou, K.; Kawano-Furukawa, H.; Saito, T.; Iyo, A.; Eisaki, H.; Fukazawa, H.; Kohori, Y.; Suzuki, K.; Usui, H.; Kuroki, K.; Yamada, K.
Source:
PHYSICAL REVIEW LETTERS 106 (6): Art. No. 067003 FEB 11 2011
Abstract:
A neutron scattering study of heavily hole-overdoped superconducting KFe2As2 revealed a well-defined low-energy incommensurate spin fluctuation at [pi(1 +/- 2 delta), 0] with delta = 0.16. The incommensurate structure differs from the previously observed commensurate peaks in electron-doped AFe(2)As(2) (A = Ba, Ca, or Sr) at low energies. The direction of the peak splitting is perpendicular to that observed in Fe(Te, Se) or in Ba(Fe, Co)(2)As-2 at high energies. A band structure calculation suggests interband scattering between bands around the Gamma and X points as an origin of this incommensurate peak. The perpendicular direction of the peak splitting can be understood within the framework of multiorbital band structure. The results suggest that spin fluctuation is more robust in hole-doped than in electron-doped samples, which can be responsible for the appearance of superconductivity in the heavily hole-doped samples.
Title:
Nanodomains due to Phason Defects at a Quasicrystal Surface
Authors:
Duguet, T; Unal, B; Ledieu, J; Dubois, JM; Fournee, V; Thiel, PA Author Full Names: Duguet, T.; Uenal, B.; Ledieu, J.; Dubois, J. -M.; Fournee, V.; Thiel, P. A.
Source:
PHYSICAL REVIEW LETTERS 106 (7): Art. No. 076101 FEB 16 2011
Abstract:
Among the three coexisting types of terraces found on the twofold surface of the d-Al-Cu-Co quasicrystal, nanodomains are essentially observed on the transition-metal rich ones, with a coherent interface boundary. Both clean surface and Ag growth analyses, demonstrate that nanodomain surfaces are structurally identical to one of the two other terraces, which contains 85 at.% Al. We provide evidence that the nanodomains are a manifestation of phason defects that extend downward toward the bulk, and state that nanodomains develop because the energetic cost of creating the phason is outweighed by the change in surface energy. Consequently, the formation of nanodomains involves more than just the surface layer, but is driven by surface energetics.
Title:
Variation of growth morphology with chemical composition of terraces: Ag on a twofold surface of a decagonal Al-Cu-Co quasicrystal
Authors:
Duguet, T; Unal, B; Han, Y; Evans, JW; Ledieu, J; Jenks, CJ; Dubois, JM; Fournee, V; Thiel, PA Author Full Names: Duguet, T.; Uenal, B.; Han, Y.; Evans, J. W.; Ledieu, J.; Jenks, C. J.; Dubois, J. M.; Fournee, V.; Thiel, P. A.
Source:
PHYSICAL REVIEW B 82 (22): Art. No. 224204 DEC 9 2010
Abstract:
Growth of Ag thin films on the twofold surface of a decagonal Al-Cu-Co quasicrystal is characterized by scanning tunneling microscopy, at different temperatures, and for coverages ranging from submonolayer to 11 monolayers. From prior work, three types of clean surface terraces are known to exist. By correlation with a bulk structural model, the major difference between them lies in their transition-metal (TM) content, two being aluminum-rich (0 and 15 at. % TM) and one being TM-rich (40-50 at. % TM). The present article focuses on understanding the difference between Ag film morphologies on these terminations, in terms of their chemical content. Growth is found to be smoother on the TM-rich terraces and rougher on the Al-rich ones. The first Ag atomic layer is even pseudomorphic on the TM-rich terraces. Roughness variation with temperature shows that the equilibrium morphology is two dimensional for TM-rich terraces and three dimensional for Al-rich terraces. The explanation of different growth modes in terms of different terrace compositions is supported by calculations of the adhesion energy of a Ag slab with Ag, Al, Cu, and Co slabs, using density-functional theory. For the Al-rich terraces, the roughness variation with temperature also indicates reentrant growth, i.e., anomalously smooth growth at low temperature due to kinetic effects.
Title:
High-pressure suppression of long-range magnetic order in the triangular-lattice antiferromagnet CuFeO2
Authors:
Terada, N; Osakabe, T; Kitazawa, H Author Full Names: Terada, N.; Osakabe, T.; Kitazawa, H.
Source:
PHYSICAL REVIEW B 83 (2): Art. No. 020403 JAN 10 2011
Abstract:
We succeeded in observing pressure-suppressed magnetic long-range ordering (LRO) in the triangular-lattice antiferromagnet CuFeO2, using neutron-diffraction experiments under an isotropic pressure. The magnetic LRO of the four-sublattice ground state under ambient pressure in CuFeO2 almost disappears at the high pressure of 7.9 GPa, and is replaced by an incommensurate order with temperature-independent wave number of (0.192 0.192 1.5). The incommensurate wave number observed at 7.9 GPa corresponds to that observed just above the temperature at which lattice distortion and magnetic LRO simultaneously occur under ambient pressure. Therefore, the long-range magnetic ordering disappears because the high pressure suppressed the lattice distortion that otherwise relieves spin frustration and leads the spin system to LRO.
Title:
Monte Carlo and Molecular Dynamics Simulation of Disorder in the Ag+ Fast Ion Conductors Pearceite and Polybasite
Authors:
Welberry, TR; Pasciak, M Author Full Names: Welberry, T. R.; Pasciak, M.
Source:
METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE 42A (1): 6-13 JAN 2011
Abstract:
The pearceite-polybasite group of minerals (i.e., pearceite, antimonpearceite, arsenpolybasite, and polybasite) of general stoichiometry [(M6T2S7)-T-I-S-III][(Ag9CuS4)-Cu-I-S-I], with M = Ag+, Cu+ and T = As3+, Sb3+, occur relatively commonly in nature. All have recently been shown to exhibit Ag+ fast ion conduction at rather low temperatures (only slightly above or below room temperature([1])). The average crystal structure determination of these materials shows the positions of the Ag+ ions to be smeared out or delocalized within sheets in an ordered framework structure comprised of the other ions. At the same time, strong and highly structured diffuse scattering has been observed, which contains diffuse peaks that are incommensurate with the diffraction peaks of the framework structure. In order to try to understand the origins of the fast ion conduction properties of these materials, we have used computer simulation of a model system (Monte Carlo and molecular dynamics (MD)) to analyze this observed diffuse scattering.
Title:
Short range magnetic correlations induced by La substitution in Ho1-xLaxMn2O5
Authors:
Wang, CW; Wu, CM; Li, CY; Karna, SK; Hsu, CK; Li, CHC; Li, WH; Yu, CC; Wu, CP; Chou, H; Lynn, JW Author Full Names: Wang, Chin-Wei; Wu, Chun-Ming; Li, Chi-Yen; Karna, Sunil K.; Hsu, Chien-Kang; Li, Carissa H. C.; Li, Wen-Hsien; Yu, Chun-Chen; Wu, Chun-Pin; Chou, Hsiung; Lynn, Jeffrey W.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 22 (24): Art. No. 246002 JUN 23 2010
Abstract:
Magnetic susceptibility, x-ray diffraction, neutron diffraction and Raman scattering measurements are employed to study the effects of La substitution on the magnetic properties of multiferroic HoMn2O5. 9% and 18% La-substituted compounds crystallize into the same orthorhombic Pbam symmetry as the parent compound. The magnetic responses to an ac driving magnetic field between 40 and 140 K are greatly enhanced by 18% La substitution. The neutron magnetic diffraction patterns reveal the development of short range magnetic correlations below 140 K. In addition, two Raman peaks and a series of new x-ray diffraction peaks suddenly develop below this temperature. Incommensurate long range antiferromagnetic order appears below 38 K. Magnetic frustration could be the main mechanism governing the present observations.
Title:
Evolution of microstructure induced by calcination in leached Al-Cu-Fe quasicrystal and its effects on catalytic activity
Authors:
Tanabe, T; Kameoka, S; Tsai, AP Author Full Names: Tanabe, Toyokazu; Kameoka, Satoshi; Tsai, An Pang
Source:
JOURNAL OF MATERIALS SCIENCE 46 (7): 2242-2250 APR 2011
Abstract:
Effects of calcination on catalytic activity for steam reforming of methanol (SRM) over an Al-Cu-Fe quasicrystal (QC) leached with NaOH aq. have been investigated in terms of microstructure with X-ray diffraction and transmission electron microscope (TEM). Calcination at 600 A degrees C in air drastically improved the catalytic activity of the leached QC. TEM observations on cross-section of the samples revealed that cubic Cu (x) Fe3-x-y Al (y) O-4 spinel was formed at the outermost layer of the leached QC after calcinations. Prior to the catalytic reaction, the Cu (x) Fe3-x-y Al (y) O-4 spinel decomposed to a composite where fine Cu nanoparticles dispersed in (Fe,Al)(3)O-4 matrix under H-2 treatment at 300 A degrees C. Drastic increase in catalytic activity is responsible for the fine Cu nanoparticles in the composite. The Cu nanoparticles sit along the same orientation with (Fe,Al)(3)O-4, e.g., Cu [013]//(Fe,Al)(3)O-4 [013] and Cu [200]//(Fe,Al)(3)O-4 [400]. This orientation relationship may stabilize the Cu nanoparticles through a bonding of Cu-O-Fe.
Title:
Modulated magnetic structure in quasi-one-dimensional clinopyroxene NaFeGe2O6
Authors:
Drokina, TV; Petrakovskii, GA; Keller, L; Schefer, J; Balaev, AD; Kartashev, AV; Ivanov, DA Author Full Names: Drokina, T. V.; Petrakovskii, G. A.; Keller, L.; Schefer, J.; Balaev, A. D.; Kartashev, A. V.; Ivanov, D. A.
Source:
JOURNAL OF EXPERIMENTAL AND THEORETICAL PHYSICS 112 (1): 121-126 JAN 2011
Abstract:
The magnetic structure of the NaFeGe2O6 monoclinic compound has been experimentally investigated using the elastic scattering of neutrons. At a temperature of 1.6 K, an incommensurate magnetic structure has been observed in the form of an antiferromagnetic helix formed by a pairs of the spins of the Fe3+ ions with helical modulation in the ac plane of the crystal lattice. The wave vector of the magnetic structure has been determined and its temperature behavior has been studied. The analysis of the temperature dependences of the specific heat and susceptibility, as well as the isotherms of the field dependence of the magnetization, has revealed the existence of not only the order-disorder magnetic phase transition at the point T (N) = 13 K, but also an additional magnetic phase transition at the point T (c) = 11.5 K, which is assumingly an orientation phase transition.
Title:
Highly repulsive interaction in novel inclusion D-2-N-2 compound at high pressure: Raman and x-ray evidence
Authors:
Kim, M; Yoo, CS Author Full Names: Kim, Minseob; Yoo, Choong-Shik
Source:
JOURNAL OF CHEMICAL PHYSICS 134 (4): Art. No. 044519 JAN 28 2011
Abstract:
We present spectral and structural evidences for the formation of a homogeneous cubic delta-N-2-like, noncrystalline solid and an incommensuratelike hexagonal (P6(3)22) inclusion compound (N-2)(12)D-2, formed by compressing a nitrogen-rich mixture to 5.5 and 10 GPa, respectively. A strong repulsive coupling in (N-2)(12)D-2 is evident from a blue shift, discontinuous changes, and the absence of turnover of the D-2 vibron to 70 GPa-all in sharp contrast to both pure D-2 and other inclusion compounds. This repulsive interaction is responsible to the observed incommensuratelike structure and large internal pressure. (C) 2011 American Institute of Physics. [doi:10.1063/1.3533957]
Title:
Ca14Au46Sn5: a "Colored" Gd14Ag51-Type Structure Containing Columns of Well-Differentiated Hexagonal Gold Stars
Authors:
Lin, QS; Corbett, JD Author Full Names: Lin, Qisheng; Corbett, John D.
Source:
INORGANIC CHEMISTRY 50 (5): 1808-1815 MAR 7 2011
Abstract:
A novel hexagonal phase discovered near the Ca15Au60Sn25 quasicrystal and its cubic approximants (ACs) was synthesized by means of high-temperature solid-state reactions. Single-crystal structural analyses show that this is a Gd14Ag51 isotype with composition within the range Ca14Au45.56(4)-46.67(4)Sn5.14(3)-4.14(3), space group P6/m (No. 175), and lattice parameters a =12.763(3)-12.879(3) angstrom and c = 9.326(3)-9.3815(4) angstrom. In this phase, Sn mixes with Au in two of seven anionic sites to give a strong coloring that generates a narrow honeycomb-like Au/Sn template, in which sizable columns of hexagonal Au stars are confined. This phase transforms into the cubic 211 AC phase through a peritectic reaction at similar to 678 degrees C. The valence electron count per atom (eta) of the present phase is in the range 1.41-1.45. However, it does not appear to follow a Hume-Rothery mechanism.

Update: 4-Mar-2011

Title:
Polar Nanodomains and Giant Converse Magnetoelectric Effect in Charge-Ordered Fe2OBO3
Authors:
Yang, HX; Tian, HF; Song, YJ; Qin, YB; Zhao, YG; Ma, C; Li, JQ Author Full Names: Yang, H. X.; Tian, H. F.; Song, Y. J.; Qin, Y. B.; Zhao, Y. G.; Ma, C.; Li, J. Q.
Source:
PHYSICAL REVIEW LETTERS 106 (1): Art. No. 016406 JAN 7 2011
Abstract:
The magnetoelectric coupling and polar nanodomains in the charge-ordered Fe2OBO3 have been extensively studied from room temperature down to 100 K. In situ TEM investigations demonstrate that the charge-ordering transition characterized by an incommensurate modulation could evidently result in remarkable polar nanodomains at low temperatures. This kind of nanodomain could play a critical role in triggering a high dielectric constant and notable dielectric dispersion as observed in Fe2OBO3. Moreover, measurements of the magnetoelectric coupling under electrical field demonstrate the existence of giant electrically induced changes in magnetization around the magnetic transition.
Title:
Fast diffusion of a graphene flake on a graphene layer
Authors:
Lebedeva, IV; Knizhnik, AA; Popov, AM; Ershova, OV; Lozovik, YE; Potapkin, BV Author Full Names: Lebedeva, Irina V.; Knizhnik, Andrey A.; Popov, Andrey M.; Ershova, Olga V.; Lozovik, Yurii E.; Potapkin, Boris V.
Source:
PHYSICAL REVIEW B 82 (15): Art. No. 155460 OCT 29 2010
Abstract:
Diffusion of a graphene flake on a graphene layer is analyzed and a diffusion mechanism is proposed for the system under consideration. According to this mechanism, rotational transition of the flake from commensurate to incommensurate states takes place with subsequent simultaneous rotation and translational motion until the commensurate state is reached again, and so on. The molecular dynamics simulations and analytic estimates based on ab initio and semiempirical calculations demonstrate that the proposed diffusion mechanism is dominant at temperatures T similar to(1-3)T-com, where T-com corresponds to the barrier for transitions of the flake between adjacent energy minima in the commensurate states. For example, for the flake consisting of similar to 40, 200, and 700 atoms the contribution of the proposed diffusion mechanism through rotation of the flake to the incommensurate states exceeds that for diffusion of the flake in the commensurate states by one to two orders of magnitude at temperatures 50-150 K, 200-600 K, and 800-2400 K, respectively. The possibility to experimentally measure the barriers to relative motion of graphene layers based on the study of diffusion of a graphene flake is considered. The results obtained are also relevant for understanding of dynamic behavior of polycyclic aromatic molecules on graphene and should be qualitatively valid for a set of commensurate adsorbate-adsorbent systems.
Title:
Chemical doping-induced flop of ferroelectric polarization in multiferroic Mn0.9Co0.1WO4
Authors:
Song, YS; Yan, LQ; Lee, B; Chun, SH; Kim, KH; Kim, SB; Nogami, A; Katsufuji, T; Schefer, J; Chung, JH Author Full Names: Song, Y. -S.; Yan, Li Qin; Lee, Bumsung; Chun, Sae Hwan; Kim, Kee Hoon; Kim, Sung Baek; Nogami, A.; Katsufuji, T.; Schefer, J.; Chung, J. -H.
Source:
PHYSICAL REVIEW B 82 (21): Art. No. 214418 DEC 15 2010
Abstract:
We studied the multiferroic properties of the incommensurate spiral phase of Mn1-xCoxWO4 using single-crystal neutron-diffraction and ferroelectric measurements. Whereas the rotational plane of the spin spiral is parallel to the b axis for x <= 0.05, it flops by 90 degrees for x=0.10. As a result, the direction of the ferroelectric polarization also flops from the b to the a axis. These results show that the orientation of the ferroelectric polarization in MnWO4 can be controlled via chemical doping.
Title:
Tuning the superconducting and magnetic properties of FeySe0.25Te0.75 by varying the iron content
Authors:
Bendele, M; Babkevich, P; Katrych, S; Gvasaliya, SN; Pomjakushina, E; Conder, K; Roessli, B; Boothroyd, AT; Khasanov, R; Keller, H Author Full Names: Bendele, M.; Babkevich, P.; Katrych, S.; Gvasaliya, S. N.; Pomjakushina, E.; Conder, K.; Roessli, B.; Boothroyd, A. T.; Khasanov, R.; Keller, H.
Source:
PHYSICAL REVIEW B 82 (21): Art. No. 212504 DEC 7 2010
Abstract:
The superconducting and magnetic properties of FeySe0.25Te0.75 single crystals (0.9 <= y <= 1.1) were studied by means of x-ray diffraction, superconducting quantum interference device magnetometry, muon-spin rotation, and elastic neutron diffraction. The samples with y < 1 exhibit coexistence of bulk superconductivity and incommensurate magnetism. The magnetic order remains incommensurate for y >= 1 but with increasing Fe content superconductivity is suppressed and the magnetic correlation length increases. The results show that the superconducting and the magnetic properties of the FeySe1-xTex can be tuned not only by varying the Se/Te ratio but also by changing the Fe content.
Title:
Selective adsorption and electronic interaction of F16CuPc on epitaxial graphene
Authors:
Wang, YL; Ren, J; Song, CL; Jiang, YP; Wang, LL; He, K; Chen, X; Jia, JF; Meng, S; Kaxiras, E; Xue, QK; Ma, XC Author Full Names: Wang, Yi-Lin; Ren, Jun; Song, Can-Li; Jiang, Ye-Ping; Wang, Li-Li; He, Ke; Chen, Xi; Jia, Jin-Feng; Meng, Sheng; Kaxiras, Efthimios; Xue, Qi-Kun; Ma, Xu-Cun
Source:
PHYSICAL REVIEW B 82 (24): Art. No. 245420 DEC 14 2010
Abstract:
We investigate the electronic coupling between copper hexadecafluoro-phthalocyanine (F16CuPc) and epitaxial graphene (EG) on 6H-SiC (0001) using a combined approach of low-temperature scanning tunneling spectroscopy and electronic structure calculations. The molecules are preferentially adsorbed on monolayer EG than bilayer EG. Competing molecule-surface and intermolecular van der Waals interactions result in two well-ordered incommensurate phases. We show that the amount of charge transfer from EG to F16CuPc can be tuned by applied voltage or the thickness of graphene layers. A characteristic feature at similar to 0.4 eV above the Dirac point is identified in bilayer EG, which indicates its electronic structure is modified via introducing extra unoccupied states upon adsorption.
Title:
Helical magnetic state in the distorted triangular lattice of alpha-CaCr2O4
Authors:
Chapon, LC; Manuel, P; Damay, F; Toledano, P; Hardy, V; Martin, C Author Full Names: Chapon, L. C.; Manuel, P.; Damay, F.; Toledano, P.; Hardy, V.; Martin, C.
Source:
PHYSICAL REVIEW B 83 (2): Art. No. 024409 JAN 24 2011
Abstract:
The magnetic properties of the high temperature a form of the CaCr2O4 compound have been investigated for the first time by magnetic susceptibility, specific heat, and powder neutron diffraction. The system undergoes a unique magnetic phase transition at 43 K to a long-range ordered incommensurate helical phase with magnetic propagation vector k = (0,0.3317(2),0). The magnetic model proposed from neutron diffraction data shows that the plane of rotation of the spins is perpendicular to the wave vector and that the magnetic modulation is consistent with two modes belonging to distinct irreducible representations of the group. The magnetic point group 2221 ' is not compatible with ferroelectricity unlike the CuCrO2 delafossite [Kimura et al., Phys. Rev. B, 78 140401 (2008)], but predicts the existence of quadratic magnetoelectric effects, discussed based on a Landau analysis.
Title:
Hysteretic behavior and magnetic ordering in CeRuSn
Authors:
Mydosh, JA; Strydom, AM; Baenitz, M; Chevalier, B; Hermes, W; Pottgen, R Author Full Names: Mydosh, J. A.; Strydom, A. M.; Baenitz, M.; Chevalier, B.; Hermes, W.; Poettgen, R.
Source:
PHYSICAL REVIEW B 83 (5): Art. No. 054411 FEB 9 2011
Abstract:
We report the thermodynamic and transport properties of the newly synthesized Ce-intermetallic compound CeRuSn. This ternary stannide possesses an unconventional structure with two Ce sites at room temperature which exhibit different valencies. Just below room temperature there are large thermal hysteretic effects in the magnetic susceptibility, in the specific heat, as well as in electronic and heat transport properties suggesting the formation of an incommensurate charge density wave modulation whose q vector changes as a function of temperature. Our measurements indicate that one site displays magnetic Ce3+ behavior while the other is a valence fluctuator. At 2.7 K antiferromagnetic long-range order occurs within one-half of the Ce sites, e.g., the magnetic entropy of the transition is 1/2R ln 2. Below T-N a series of metamagnetic transitions takes place in rather small fields (similar to 1-2 T), leaving a magnetically fluctuating background. Such behavior is unique among the many Ce-transition-metal compounds.
Title:
Misfit strain accommodation in epitaxial ABO(3) perovskites: Lattice rotations and lattice modulations
Authors:
Vailionis, A; Boschker, H; Siemons, W; Houwman, EP; Blank, DHA; Rijnders, G; Koster, G Author Full Names: Vailionis, A.; Boschker, H.; Siemons, W.; Houwman, E. P.; Blank, D. H. A.; Rijnders, G.; Koster, G.
Source:
PHYSICAL REVIEW B 83 (6): Art. No. 064101 FEB 11 2011
Abstract:
We present a study of the lattice response to the compressive and tensile biaxial stress in La0.67Sr0.33MnO3 (LSMO) and SrRuO3 (SRO) thin films grown on a variety of single-crystal substrates: SrTiO3, DyScO3, NdGaO3, and (La,Sr)(Al,Ta)O-3. The results show that, in thin films under misfit strain, both SRO and LSMO lattices, which in bulk form have orthorhombic (SRO) and rhombohedral (LSMO) structures, assume unit cells that are monoclinic under compressive stress and tetragonal under tensile stress. The applied stress effectively modifies the BO6 octahedra rotations, whose degree and direction can be controlled by the magnitude and sign of the misfit strain. Such lattice distortions change the B-O-B bond angles and therefore are expected to affect magnetic and electronic properties of the ABO(3) perovskites.
Title:
Strong magnetoelastic effect on the magnetoelectric phenomena of TbMn2O5
Authors:
Oh, YS; Jeon, BG; Haam, SY; Park, S; Correa, VF; Lacerda, AH; Cheong, SW; Jeon, GS; Kim, KH Author Full Names: Oh, Yoon Seok; Jeon, Byung-Gu; Haam, S. Y.; Park, S.; Correa, V. F.; Lacerda, A. H.; Cheong, S. -W.; Jeon, Gun Sang; Kim, Kee Hoon
Source:
PHYSICAL REVIEW B 83 (6): Art. No. 060405 FEB 17 2011
Abstract:
Comparative studies of magnetoelectric susceptibility (alpha), magnetization (M), and magnetostriction (u) in TbMn2O5 reveal that the increment of M owing to the field-induced Tb3+ spin alignment produces a field-asymmetric line shape in the alpha(H) curve, which is conspicuous in a low-temperature incommensurate phase but persistently subsists in the entire ferroelectric phase. Correlations among electric polarization, u, and M-2 variation represent linear relationships, unambiguously showing the significant role of Tb magnetoelastic effects on the low-field magnetoelectric phenomena of TbMn2O5. An effective free energy capturing the observed experimental features is also suggested.
Title:
Wood anomalies in resonant photonic quasicrystals
Authors:
Poddubny, AN Author Full Names: Poddubny, A. N.
Source:
PHYSICAL REVIEW B 83 (7): Art. No. 075106 FEB 8 2011
Abstract:
A theory of light diffraction from a planar quasicrystalline lattice with resonant scatterers is presented. Rich structure, absent in the periodic case, is found in specular reflection spectra, and interpreted as a specific kind of Wood anomaly, characteristic of quasicrystals. The theory is applied to semiconductor quantum dots arranged in Penrose tiling.
Title:
Resonant x-ray scattering investigation of magnetic ordering in NpAs1-xSex (x=0.05, 0.10)
Authors:
Rodrigues, VH; Paixao, JA; Costa, MMR; Mannix, D; Bombardi, A; Rebizant, J; Lander, GH Author Full Names: Rodrigues, V. H.; Paixao, J. A.; Costa, M. M. R.; Mannix, D.; Bombardi, A.; Rebizant, J.; Lander, G. H.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 23 (2): Art. No. 026002 JAN 19 2011
Abstract:
A resonant x-ray scattering investigation of the NpAs1-xSex system with single crystals of 5 and 10% Se content is reported. The main features of the magnetic phase diagram previously studied by neutron scattering were confirmed. The coexistence within a single domain of ferro- and antiferro-components in the low-T ferrimagnetic phase was established, as well as the single-k character of the incommensurate phase and of the antiferromagnetic component of the ferrimagnetic phase. A tetragonal lattice distortion was found in the ferro-and ferrimagnetic phases which is not compatible with the proposed model for the ferromagnetic phase. The study of ferromagnetism was carried out using polarization analysis of the diffracted beam to separate the scattering intensities originating from magnetism and charge, which are superimposed in reciprocal space. The magnetic character of the ferromagnetic signal calculated from the measured intensities in the polarization analysis sigma pi and sigma sigma channels was confirmed by analysis of the corresponding temperature dependence.
Title:
A charge density wave in the hidden order state of URu2Si2
Authors:
Su, JJ; Dubi, Y; Wolfle, P; Balatsky, AV Author Full Names: Su, Jung-Jung; Dubi, Yonatan; Woelfle, Peter; Balatsky, Alexander V.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 23 (9): Art. No. 094214 Sp. Iss. SI MAR 9 2011
Abstract:
We argue that the hidden order (HO) state in URu2Si2 will induce a charge density wave. The modulation vector of the charge density wave will be twice that of the hidden order state, Q(CDW) = 2Q(HO). To illustrate how the charge density wave arises we use a Ginzburg-Landau theory that contains a coupling of the charge density wave amplitude to the square of the HO order parameter Delta(HO). This simple analysis allows us to predict the intensity and temperature dependence of the charge density wave order parameter in terms of the susceptibilities and coupling constants used in the Ginzburg-Landau analysis.
Title:
Temperature-pressure phase diagram of an aperiodic host guest compound
Authors:
Toudic, B; Rabiller, P; Bourgeois, L; Huard, M; Ecolivet, C; McIntyre, GJ; Bourges, P; Breczewski, T; Janssen, T Author Full Names: Toudic, B.; Rabiller, P.; Bourgeois, L.; Huard, M.; Ecolivet, C.; McIntyre, G. J.; Bourges, P.; Breczewski, T.; Janssen, T.
Source:
EPL 93 (1): Art. No. 16003 JAN 2011
Abstract:
This letter reports on the structural instabilities of an aperiodic composite crystal under pressure. The (P, T) phase diagram up to 0.55GPa of nonadecane-urea is reported showing various symmetry breakings in crystallographic superspaces, towards three different orthorhombic phases. These structural phase transitions are characterized by a change in the intermodulation and are described by increasing the rank of the crystallographic superspaces. Copyright (C) EPLA, 2011
Title:
Fabrication of quaternary Mg-Zn-Y-Ce quasicrystal alloys and their strengthening effects on AZ91 magnesium alloys
Authors:
Wang, ZF; Zhao, WM; Li, HP; Liang, CY Author Full Names: Wang Zhifeng; Zhao Weimin; Li Haipeng; Liang Chunyong
Source:
CHINA FOUNDRY 7 (4): 342-348 NOV 2010
Abstract:
Quaternary Mg-Zn-Y-Ce quasi-crystal-containing alloys were fabricated using a metal mold casting route. The microstructures of Mg-Zn-Y-Ce alloys and the distribution of the major elements were analyzed. The differences in morphology and micro-hardness between quaternary Mg-Zn-Y-Ce quasi-crystals and ternary M Zn-Y quasi-crystals were discussed. The result showed that the micro-hardness of Mg-Zn-Y-Ce quasi-crystals reached peak value when the content of Ce was 0.8at.%. Subsequently, various contents of Mg-Zn-Y-0.8Ce alloys were used to strengthen AZ91 magnesium alloys. The microstructural modification and mechanical properties of reinforced AZ91 alloys with and without solution as well as their aging treatments were also studied Further research showed that aging-treated AZ91-10wt.%(Mg-Zn-Y-0.8at.%Ce) alloys exhibited excellent mechanical properties: their Brinell hardness, tensile strength, and elongation were HV91, 252 MPa, and 4.1%, respectively. Through this study, the range of application of AZ91 alloys can further be extended.
Title:
Transmission electron microscopy investigation of Ag-free lillianite and heyrovskyite from Vulcano, Aeolian Islands, Italy
Authors:
Mitolo, D; Capitani, GC; Garavelli, A; Pinto, D Author Full Names: Mitolo, Donatella; Capitani, Gian Carlo; Garavelli, Anna; Pinto, Daniela
Source:
AMERICAN MINERALOGIST 96 (2-3): 288-300 FEB-MAR 2011
Abstract:
We present a transmission electron microscopy (TEM) investigation of lillianite (Pb3Bi2S6) and heyrovskyite (Pb6Bi2S9), from Vulcano, Aeolian Islands, Italy. The minerals investigated represent the only naturally occurring Ag- and Cu-free sulfosalts in the lillianite homologous series (LHS). Three methods (crushing, ion-milling, and ultramicrotomy) were used to prepare TEM specimens. Selected area electron diffraction (SAED) patterns and high-resolution TEM (HRTEM) images indicate well-ordered crystals with only minor stacking faults and, more rarely, nanoscale intergrowths of lillianite and heyrovskyite. The latter were sometimes found to form an incommensurate structural modulation with an angle of similar to 29 degrees relative to b* in the (hk0) plane and a wavelength of similar to 75 angstrom. This represents the first observation of such incommensurate modulations in heyrovskyite. Although considerable evidence points toward an artifact induced by the sample preparation technique (i.e., ion-milling), the possibility that the incommensurate modulation could be a primary feature of heyrovskyite itself cannot be completely ruled out. The modulation could derive from an ordering process of Pb and Bi cations over Me4 and Me5 sites within the PbS-like layer or from ordering of vacancies, naturally present or induced by Bi2S3 sublimation during ion-milling.
Title:
Infrared Reflectance Kramers--Kronig Analysis by Anchor-Window Technique
Authors:
Tumenas, S; Kasalynas, I; Karpus, V; Arwin, H Author Full Names: Tumenas, S.; Kasalynas, I.; Karpus, V.; Arwin, H.
Source:
ACTA PHYSICA POLONICA A 119 (2): 140-142 FEB 2011
Abstract:
An algorithm for the Kramers-Kronig analysis of the reflectivity spectra, based on an anchor-window technique is presented. The high-frequency asymptote, required for the Kramers-Kronig analysis, is determined by minimizing differences between the Kramers Kronig-deduced optical constants of a system under investigation and known optical constants measured in a small anchor-window. The algorithm is illustrated by applying it for a reconstruction of the optical conductivity sigma(omega) of the fci-ZnMgRE quasicrystals in the spectral range of 0.01-6.5 eV from the experimental IR Fourier-transform reflectivity data and the experimental spectral ellipsometry VIS-UV data. The reliability of the suggested Kramers-Kronig analysis technique is confirmed by independent infrared spectral ellipsometry sigma(omega) measurements for fci-ZnMgRE.
Title:
ON THE MECHANICAL MILLING OF AlCuCo QUASICRYSTALLINE PHASE.
Authors:
Tellez-Vazquez, JO; Patino-Carachure, C; Garcia-De Leon, E; Rosas, G Author Full Names: Tellez-Vazquez, J. O.; Patino-Carachure, C.; Garcia-De Leon, E.; Rosas, G.
Source:
ACTA MICROSCOPICA 19 (3): 322-327 2010
Abstract:
In the present work, the Al65Cu15Co20 alloy composition was processed by high-energy ball milled to systematically evaluate the phase transitions of the quasicrystalline prealloyed ingot. The quasicrystalline alloy was previously fabricated by conventional casting techniques. Subsequently, this alloy was milled for different times using an SPEX mixer mill. The microstructures were examined by high-resolution electron microscopy and the structural changes were also analyzed by X-ray diffraction patterns. The results indicate that the quasicrystalline alloy is stable after 5 h of milling, containing nano-quasicrystalline domains. However, the sample milled by 10 h shows a quasicrystal-to-amorphous phase transition. Subsequently, after 20 h of milling, the amorphous phase re-crystallizes to the B2 structure type.

Update: 26-Feb-2011

Title:
Structure of BiFeO3 ceramics treated with hot-pressing
Authors:
Su, WN; Wu, XL; Wu, XS; Wang, DH; Du, YW; Chu, PK Author Full Names: Su, W. N.; Wu, X. L.; Wu, X. S.; Wang, D. H.; Du, Y. W.; Chu, Paul K.
Source:
SOLID STATE COMMUNICATIONS 151 (1): 5-8 JAN 2011
Abstract:
BiFeO3 ceramics synthesized at high temperature and pressure is observed to possess large spontaneous polarization and magnetism The selected-area electron diffraction patterns indicate the coexistence of polycrystalline and nanocrystalline grains in the hot-pressed samples Raman spectroscopic studies reveal that the Bi-O bond strain and cations (Fe3+) away from the oxygen octahedral center Induce the polarization The Fe-O bond strain oxygen octahedral rotation around the [111] axis and electromagnons build a long-range interaction between electrical polarization and magnetic moment reorientation to form an Incommensurate spiral magnetic structure This work clearly shows that the hot-pressed treatment can modify the structure and properties of BiFeO3 ceramics (C) 2010 Elsevier Ltd All rights reserved
Title:
Effects of Calcium Addition on High Temperature Creep Resistance of Magnesium Alloys with High Zinc
Authors:
Wan, XF; Sun, YS; Xue, F; Bai, J; Tao, WJ Author Full Names: Wan Xiaofeng; Sun Yangshan; Xue Feng; Bai Jing; Tao Weijian
Source:
RARE METAL MATERIALS AND ENGINEERING 39 (12): 2112-2116 DEC 2010
Abstract:
The effects of trace Ca addition on microstructure and high-temperature creep resistance of as-cast Mg-12Zn-4Al-0.3Mn alloy were investigated. Results show that the as-cast microstructure of the base alloy consists of alpha-Mg matrix and block quasicrystalline phase at gain boundaries. The composition of this quasicrystalline phase is closed to that of the equilibrium tau phase (Mg-32(Al,Zn)(49)) in the Mg-Zn-Al ternary system. A small amount of Ca addition to the base alloy results in the formation of a lamellar eutectic phi(Al2Mg5Zn2) and the transformation of the quasicrystalline phase to the equilibrium tau phase in the as-cast microstructure of the alloy. The volume fraction of the phi phase increases with the increase of Ca addition. The creep resistance of the alloys is significantly improved by Ca addition. The optimum creep resistance of the alloy is obtained by 0.6% Ca addition under the creep condition of 175 degrees C, 70 MPa, whose steady state creep rate is approximately one order of magnitude lower than that of its base alloy.
Title:
Long-range magnetic order in the quasicrystalline approximant Cd6Tb
Authors:
Tamura, R; Muro, Y; Hiroto, T; Nishimoto, K; Takabatake, T Author Full Names: Tamura, R.; Muro, Y.; Hiroto, T.; Nishimoto, K.; Takabatake, T.
Source:
PHYSICAL REVIEW B 82 (22): Art. No. 220201 DEC 8 2010
Abstract:
We report the observation of a long-range magnetic order in a quasicrystalline approximant, i.e., Cd6Tb, demonstrating that a spin glass is not the ground state for the binary approximant but localized spins on the vertices of an icosahedron become antiferromagnetically ordered below 24 K. The result is in contrast to the spin-glasslike behaviors reported for Cd-Mg-R quasicrystals composed of same icosahedral clusters.
Title:
Single composite crystal structure analysis of incommensurate spin-ladder compound Sr2.5Ca11.5Cu24O41
Authors:
Gotoh, Y; Fujihisa, H; Takeya, S; Yamawaki, H; Akimitsu, J Author Full Names: Gotoh, Y.; Fujihisa, H.; Takeya, S.; Yamawaki, H.; Akimitsu, J.
Source:
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS 470: S219-S220 Sp. Iss. SI Suppl. 1 DEC 2010
Abstract:
Single-crystal X-ray structure analysis of mutually incommensurate (Sr0.36Ca1.64Cu2O3)(0.706)CuO2, "Sr2.5Ca11.5Cu24O41" has been performed on the basis of superspace group approach. The lattice constants of (Sr0.36Ca1.64Cu2O3)(0.706)CuO2 are a = 1.1298(1), b = 1.2582(1), c(1) = 0.2750(1) nm for the CuO2 part and a = 1.1298(1), b = 1.2582(1), c(2) = 0.3897(1) nm for the (Sr0.36Ca1.64Cu2O3) one. From the average structure analysis, it has been expected that the formation of CuO5 with pyramidal coordination by O atoms occurs in the Cu2O3 ladder. The minimum distance between Cu atom in the Cu2O3 ladder and O atom in the CuO2 chain has clearly shown that O in the CuO2 acts as apical oxygen to form the CuO5 coordination. It has been concluded that (Sr0.36Ca1.54Cu2O3)(0.706)CuO2 bears a marked structural resemblance to the cuprate High T-c superconductors. (C) 2009 Elsevier B.V. All rights reserved.
Title:
Phase diagram of the two-dimensional 16-band d-p model for iron-based superconductors
Authors:
Yanagi, Y; Yamakawa, Y; Ono, Y Author Full Names: Yanagi, Y.; Yamakawa, Y.; Ono, Y.
Source:
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS 470: S349-S350 Sp. Iss. SI Suppl. 1 DEC 2010
Abstract:
The electronic state of the Fe2As2 plane in iron-based superconductors is investigated on the basis of the two-dimensional 16-band d-p model. Using the random phase approximation for the on-site Coulomb interaction between Fe d electrons, we obtain the phase diagram including the magnetic ordered states and the superconductivity. It is found that the s(+/-)-wave superconductivity, where the gap functions have different signs between the electron pockets and the hole pockets, is realized near the incommensurate magnetic ordered phase with q similar to (pi, pi). The absolute values of the gap functions on the Fermi surfaces are almost isotropic but largely depend on the energy bands. (C) 2009 Elsevier B.V. All rights reserved.
Title:
NMR studies of field induced magnetism in CeCoIn5
Authors:
Curro, NJ; Young, BL; Urbano, RR; Graf, MJ Author Full Names: Curro, Nicholas J.; Young, Ben-Li; Urbano, Ricardo R.; Graf, Matthias J.
Source:
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS 470: S521-S524 Sp. Iss. SI Suppl. 1 DEC 2010
Abstract:
Recent Nuclear Magnetic Resonance and elastic neutron scattering experiments have revealed conclusively the presence of static incommensurate magnetism in the field-induced B phase of CeCoIn5. We analyze the NMR data assuming the hyperfine coupling to the In(2) nuclei is anisotropic and simulate the spectra for several different magnetic structures. The NMR data are consistent with ordered Ce moments along the [001] direction, but are relatively insensitive to the direction of the incommensurate wavevector. (C) 2009 Published by Elsevier B.V.
Title:
NMR study of magnetically-ordered state in a novel superconducting phase in CeCoIn5
Authors:
Kumagai, K; Kondoh, N; Shishido, H; Matsuda, Y Author Full Names: Kumagai, K.; Kondoh, N.; Shishido, H.; Matsuda, Y.
Source:
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS 470: S533-S535 Sp. Iss. SI Suppl. 1 DEC 2010
Abstract:
The present NMR study indicates an appearance of finite hyperfine fields coupled to incommensurate antiferromagnetic order of the Ce moments in CeCoIn5. The magnetic order is never observed in the normal state and also in the BCS state, but appears only inside the novel superconducting phase. Strong field dependence of the ordered magnetic moments indicates the coexistence of the incommensurate SDW order and an modulated SC (FFLO) state. (C) 2010 Elsevier B.V. All rights reserved.
Title:
Pairing symmetry reflected in vortex lattice structure of noncentrosymmetric superconductors
Authors:
Saiki, T; Hiasa, N; Ikeda, R Author Full Names: Saiki, Taro; Hiasa, Norihito; Ikeda, Ryusuke
Source:
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS 470: S581-S583 Sp. Iss. SI Suppl. 1 DEC 2010
Abstract:
A novel type of modulated vortex states to be realized in Rashba noncentrosymmetric superconductors (NCSs) in parallel fields are studied by examining spatial distributions of the gauge-invariant phase of the order parameter Delta. It is found that a modulated structure reflecting a relative shift of the Fermi surfaces is not due to a single type of nodal lines but rather to rows of vortex-antivortex pairs, and that coalescence of these vortex pairs results in a square vortex lattice separated from the familiar triangular lattice via a first order structural transition. Such a structure supported by rows of vortex pairs is also the origin of striped structures in higher odd LL vortex lattices realizable in centrosymmetric systems with a strong paramagnetic depairing. (C) 2009 Elsevier B.V. All rights reserved.
Title:
Se-77 NMR study of nonmagnetic-magnetic transition in (TMTSF)(2)X
Authors:
Mito, T; Nishiyama, K; Koyama, T; Ueda, K; Kohara, T; Takeuchi, K; Akutsu, H; Yamada, J; Kornilov, A; Pudalov, VM; Qualls, JS Author Full Names: Mito, T.; Nishiyama, K.; Koyama, T.; Ueda, K.; Kohara, T.; Takeuchi, K.; Akutsu, H.; Yamada, J.; Kornilov, A.; Pudalov, V. M.; Qualls, J. S.
Source:
PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS 470: S592-S593 Sp. Iss. SI Suppl. 1 DEC 2010
Abstract:
Se-77 NMR measurements have been carried out on (TMTSF)(2)X (X = PF6 and AsF6) single crystals. For both compounds, NMR lines split into double-peaked spectra in the SDW state, which is explained with sinusoidal internal field at Se nucleus positions having the same incommensurate wave number with that of the SDW order. No change in the lineshape was observed at T-x at which the spin-relaxation rate shows a kink, suggesting that this anomaly does not cause significant static changes in internal field at the Se-site. (C) 2009 Elsevier B.V. All rights reserved.
Title:
Ca-for-Sr substitution in the thermoelectric [(Sr,Ca)(2)(O,OH)(2)](q)[CoO2] misfit-layered cobalt-oxide system
Authors:
Yamauchi, H; Karvonen, L; Egashira, T; Tanaka, Y; Karppinen, M Author Full Names: Yamauchi, Hisao; Karvonen, Lassi; Egashira, Takayuki; Tanaka, Yoshiaki; Karppinen, Maarit
Source:
JOURNAL OF SOLID STATE CHEMISTRY 184 (1): 64-69 JAN 2011
Abstract:
Calcium-for-strontium substituted samples of the misfit-layered cobalt-oxide system, [(Sr1-xCax)(2) (O,OH)(2)](q)[CoO2], were successfully synthesized up to x=0.2 with a sample-encapsulation technique originally developed for the x=0 end phase. While the x=0 sample has a commensurate match between the two layer blocks (i.e. q=0.5), isovalent Ca-for-Sr substitution induces lattice misfit (i.e. q > 0.5). At the same time the Seebeck coefficient gets increased, but the increase in resistivity results in suppressing the thermoelectric power factor. The magnetic anomaly in the x=0 sample gets released upon the Ca substitution for the x=0.2 sample to exhibit an almost Curie-Weiss behavior. It is concluded that with increasing x in [(Sr1-xCax)(2)(O,OH)(2)](q)[CoO2] the properties smoothly evolve towards those previously reported for the x=1.0 end member, [Ca1.7O2.1H2.4](0.58)[CoO2]. (C) 2010 Elsevier Inc. All rights reserved.
Title:
Crystal nucleation of colloidal hard dumbbells
Authors:
Ni, R; Dijkstra, M Author Full Names: Ni, Ran; Dijkstra, Marjolein
Source:
JOURNAL OF CHEMICAL PHYSICS 134 (3): Art. No. 034501 JAN 21 2011
Abstract:
Using computer simulations, we investigate the homogeneous crystal nucleation in suspensions of colloidal hard dumbbells. The free energy barriers are determined by Monte Carlo simulations using the umbrella sampling technique. We calculate the nucleation rates for the plastic crystal and the aperiodic crystal phase using the kinetic prefactor as determined from event driven molecular dynamics simulations. We find good agreement with the nucleation rates determined from spontaneous nucleation events observed in event driven molecular dynamics simulations within error bars of one order of magnitude. We study the effect of aspect ratio of the dumbbells on the nucleation of plastic and aperiodic crystal phases, and we also determine the structure of the critical nuclei. Moreover, we find that the nucleation of the aligned close-packed crystal structure is strongly suppressed by a high free energy barrier at low supersaturations and slow dynamics at high supersaturations. (C) 2011 American Institute of Physics. [doi:10.1063/1.3528222]
Title:
Correlation between primary phases and atomic clusters in a Zr-based metallic glass
Authors:
Liu, XJ; Chen, GL; Liu, CT Author Full Names: Liu, X. J.; Chen, G. L.; Liu, C. T.
Source:
JOURNAL OF APPLIED PHYSICS 108 (12): Art. No. 123516 DEC 15 2010
Abstract:
Atomic clusters exiting in the Zr65Ti10Ni25 metallic glass and primary phases generated during crystallization were studied by x-ray scattering and high-resolution transmission microscopy. An intrinsic correlation between the atomic clusters and the primary phases has been revealed. It is found that there are topological icosahedral short-range orders (ISROs) in the as-cast sample in addition to fcc-Zr2Ni-type chemical SROs. These topological ISRO and fcc-Zr2Ni-type chemical SRO can simultaneously quasicrystallize/crystallize into the corresponding nanoscaled icosahedral quasicrystalline phase (I-phase) and fcc-Zr2Ni crystal as primary products during crystallization. The synchronic precipitation of these two metastable phases can be understood in terms of their structural similarity between the fcc-Zr2Ni and I-phase in local atomic configuration. In comparison with fcc-Zr2Ni crystal, the I-phase has a smaller size and lower volume fraction due to its lower growth rate attributed to its more complex composition and higher structural symmetry. The competitive growth between these two phases results in the development of nanostructured materials in this alloy after annealing. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3525985]
Title:
Cold-sprayed Coatings based on High Strength Aluminium alloys Reinforced by Quasicrystalline Particles: Microstructure and Key Properties
Authors:
Byakova, AV; Kiz, MM; Sirko, AI; Yakovleva, MS; Milman, YV Author Full Names: Byakova, A. V.; Kiz, M. M.; Sirko, A. I.; Yakovleva, M. S.; Milman, Yu. V.
Source:
HIGH TEMPERATURE MATERIALS AND PROCESSES 29 (5-6): 325-337 Sp. Iss. SI 2010
Abstract:
This study presents significant advantages of cold-spraying in performance of coatings based on Al matrix reinforced by metastable nano- and submicrosized quasicrystalline particles as compared to those processed by thermal spraying and, in particular, by high velocity oxy-fuel (HVOF) spraying technique. Two kinds of feedstock powders with nominal compositions. Al94Fe3Cr3 and Al94Fe2.5Cr2.5Ti1 were employed in spraying the coatings on cold rolled steel substrate. Microstructure and key mechanical characteristics of feedstock powders and coatings performed by cold-spraying and HVOF process were studied and discussed. The main benefit of cold-spraying as opposed to HVOF spraying was that the composite quasicrystalline structure of initial feedstock powders is retained in the interior of flattened particles heavily deformed under impact in solid state. Strain hardening of coating and substrate is resulted from impact during cold-spraying. The results showed that unlike to HVOF sprayed coatings important advantage of cold-sprayed quasicrystalline coatings is referred to combination of increased hardness with ductility indicated by plasticity characteristic just about critical value delta(H) approximate to 0.9, which is quite enough for preventing brittle failure of material during particle impact onto substrate or previously deposited particles.
Title:
Interfaces between Lead and Amorphous Matrices in Immiscible Alloy Systems
Authors:
Singh, A; Tsai, AP Author Full Names: Singh, Alok; Tsai, A. P.
Source:
HIGH TEMPERATURE MATERIALS AND PROCESSES 29 (5-6): 523-530 Sp. Iss. SI 2010
Abstract:
Interfaces between solid lead and amorphous matrix are described, with experimental data from system of lead particles embedded into Al-Cu-V amorphous matrix. Since the structure of the amorphous matrix cannot be described with surety, it has been approached by taking known factors in account, such as the relative stability of various facets of lead and its interfaces with quasicrystals. Lead particles take a round shape in accordance with the amorphous matrix, and are often twinned to form more uniform facets (with uniform energy) on the surface/interface. Interface stability of the lead particle; is indicated by their melting and solidification behavior. Therefore melting and solidification behavior of the embedded particles in amorphous matrix has been compared with those in crystalline and quasicrystalline matrices.
Title:
Crystal structure of simple metals at high pressures
Authors:
Degtyareva, O Author Full Names: Degtyareva, Olga
Source:
HIGH PRESSURE RESEARCH 30 (3): 343-371 2010
Abstract:
The effects of pressure on the crystal structure of simple (or sp-) elements are analysed in terms of changes in coordination number, packing density, and interatomic distances, and general rules are established. In the polyvalent elements from groups 14-17, the covalently bonded structures tend to transform to metallic phases with a gradual increase in coordination number and packing density, a behaviour normally expected under pressure. Group 1 and 2 metallic elements, however, show a reverse trend towards structures with low packing density due to intricate changes in their electronic structure. Complex crystal structures such as host-guest and incommensurately modulated structures found in these elements are given special attention in this review in an attempt to determine their role in the observed phase-transition sequences.
Title:
Antiferroelectric (Pb,Bi)(1-x)Fe1+xO3-y Perovskites Modulated by Crystallographic Shear Planes
Authors:
Abakumov, AM; Batuk, D; Hadermann, J; Rozova, MG; Sheptyakov, DV; Tsirlin, AA; Niermann, D; Waschkowski, F; Hemberger, J; Van Tendeloo, G; Antipov, EV Author Full Names: Abakumov, Artem M.; Batuk, Dmitry; Hadermann, Joke; Rozova, Marina G.; Sheptyakov, Denis V.; Tsirlin, Alexander A.; Niermann, Daniel; Waschkowski, Florian; Hemberger, Joachim; Van Tendeloo, Gustaaf; Antipov, Evgeny V.
Source:
CHEMISTRY OF MATERIALS 23 (2): 255-265 JAN 25 2011
Abstract:
We demonstrate for the first time a possibility to vary the anion content in perovskites over a wide range through a long-range-ordered arrangement of crystallographic shear (CS) planes. Anion-deficient perovskites (Pb,Bi)(1-x)Fe1+xO3-y with incommensurately modulated structures were prepared as single phases in the compositional range from Pb0.857Bi0.094Fe1.049O2.572 to Pb0.409Bi0.567Fe1.025O2.796. Using a combination of electron diffraction and high-resolution scanning transmission electron microscopy, we constructed a superspace model describing a periodic arrangement of the CS planes. The model was verified by refinement of the Pb0.64Bi0.32Fe1.04O2.675 crystal structure from neutron powder diffraction data ((3 + 1)D S.G. X2/m(alpha 0 gamma), X = [1/2,1/2,1/2,1/2], a = 3.9082(1) angstrom, b = 3.90333(8) angstrom, c = 4.0900(1) angstrom, beta = 91.936(2)degrees, q = 0.05013(4)a* + 0.09170(3)c* at T = 700 K, R-P = 0.036, R-wP = 0.048). The (Pb,Bi)(1-x)Fe1+xO3-y structures consist of perovskite blocks separated by CS planes confined to nearly the (509)(p) perovskite plane. Along the CS planes, the perovskite blocks are shifted with respect to each other over the 1/2[110](p) vector that transforms the corner-sharing connectivity of the FeO6 octahedra in the perovskite framework to an edge-sharing connectivity of the FeO5 pyramids at the CS plane, thus reducing the oxygen content. Variation of the chemical composition in the (Pb,Bi)(1-x)Fe1+xO3-y series occurs mainly because of a changing thickness of the perovskite block between the interfaces, that can be expressed through the components of the q vector as Pb6 gamma+2 alpha Bi1-7 gamma-alpha Fe1+gamma-alpha O3-3 gamma-alpha. The Pb, Bi, and Fe atoms are subjected to strong displacements occurring in antiparallel directions on both sides of the perovskite blocks, resulting in an antiferroelectric-type structure. This is corroborated by the temperature-, frequency-, and field-dependent complex permittivity measurements . Pb0.64Bi0.32Fe1.04O2.675 demonstrates a remarkably high resistivity > 0.1 T Omega cm at room temperature and orders antiferromagnetically below T-N = 608(10) K.
Title:
Structural Evolution of the BiFeO3-LaFeO3 System
Authors:
Rusakov, DA; Abakumov, AM; Yamaura, K; Belik, AA; Van Tendeloo, G; Takayama-Muromachi, E Author Full Names: Rusakov, Dmitriy A.; Abakumov, Artem M.; Yamaura, Kazunari; Belik, Alexei A.; Van Tendeloo, Gustaaf; Takayama-Muromachi, Eiji
Source:
CHEMISTRY OF MATERIALS 23 (2): 285-292 JAN 25 2011
Abstract:
The (1 - x)BiFeO3-xLaFeO(3) system has been investigated and characterized by room-temperature and high-temperature laboratory and synchrotron powder X-ray diffraction, electron diffraction, high-resolution transmission electron microscopy, differential scanning calorimetry, and magnetization measurements. At room temperature, the ferroelectric R3c phase is observed for 0.0 <= x <= 0.10. The PbZrO3-related root 2a(p) x 2 root 2a(p) x 4a(p) superstructure (where a(p) is the parameter of the cubic perovskite subcell) is observed for Bi0.82La0.18FeO3, while an incommensurately modulated phase is formed for 0.19 <= x <= 0.30 with the root 2a(p) x 2a(p) x root 2a(p) basic unit cell. The GdFeO3-type phase with space group Pnma (root 2a(p) x 2a(p) x root 2a(p)) is stable at 0.50 <= x <= 1. Bi0.82La0.18FeO3 has no detectable homogeneity range (space group Pnma, a = 5.6004(1) angstrom, b = 11.2493(3) angstrom, c = 15.6179(3) angstrom). The incommensurately modulated Bi0.75La0.25FeO3 structure was solved from synchrotron X-ray powder diffraction data (Imma(00 gamma)s00 superspace group, a = 5.5956(1) angstrom, h = 7.8171(1) angstrom, c = 5.62055(8) angstrom; q = 0.4855(4)c*, R-P = 0.023, R-wP = 0.033). In this structure, cooperative displacements of the Bi and O atoms occur, which order within the (AO) (where A = Bi, La) layers, resulting in an antipolar structure. Local fluctuations of the intralayer antipolar ordering are compensated by an interaction with the neighboring (AO) layers. A coupling of the an tipolar displacements with the cooperative tilting distortion of the perovskite octahedral framework is proposed as the origin of the incommensurability. All the phases transform to the GdFeO3-type structure at high temperatures. Bi0.82La0.18FeO3 shows an intermediate PbZrO3-type phase with root 2a(p) x 2 root 2a(p) x 2a(p) (space group Pbam; a = 5.6154(2) angstrom, b = 11.2710(4) angstrom, and c = 7.8248(2) angstrom at 570 K). The compounds in the compositional range of 0.18 <= x <= 0.95 are canted antiferromagnets.
Title:
Observation of anomalous phonons in orthorhombic rare-earth manganites
Authors:
Gao, P; Chen, HY; Tyson, TA; Liu, ZX; Bai, JM; Wang, LP; Choi, YJ; Cheong, SW Author Full Names: Gao, P.; Chen, H. Y.; Tyson, T. A.; Liu, Z. X.; Bai, J. M.; Wang, L. P.; Choi, Y. J.; Cheong, S. -W.
Source:
APPLIED PHYSICS LETTERS 97 (26): Art. No. 262905 DEC 27 2010
Abstract:
We observe the appearance of a phonon near the lock-in temperature in orthorhombic REMnO3 (RE denotes rare earth) (RE: Lu and Ho) and anomalous phonon hardening in orthorhombic LuMnO3. The anomalous phonon occurs at the onset of spontaneous polarization. No such changes were found in incommensurate orthorhombic DyMnO3. These observations directly reveal different electric polarization mechanisms in the E-type and incommensurate-type orthorhombic REMnO3. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3533022]

Update: 18-Feb-2011

Title:
Direct methods beyond small-molecule crystallography
Authors:
Fan, HF Author Full Names: Fan, Hai-fu
Source:
PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE 207 (12): 2621-2638 DEC 2010
Abstract:
The development of direct methods outside their traditional field began since the middle 1960s. New applications were explored gradually in four directions. They are the transition of: (i) from single crystals to powder samples, (ii) from X-ray crystallography to electronmicroscopy (EM), (iii) from periodic structures to incommensurate structures and (iv) from small molecules to macromolecular structures. The research on methods of solving crystal structures at the Institute of Physics in Beijing has been focused on the last three directions. The transition of direct methods from X-ray crystallography to EM led to a two-step image processing technique in high-resolution electron microscopy (HREM). This technique combines information of EM and that of electron diffraction (ED) revealing the structure of minute crystals that are unsuitable for X-ray diffraction analysis. The transition of direct methods from periodic crystal structures to incommensurate structures led to the multi-dimensional direct methods enabling ab initio solution of incommensurate modulated structures and composite structures without relying on an assumed modulation model or even the known basic structure. Finally the combination of direct methods with traditional protein crystallographic methods has greatly enhanced the ability of solving protein structures. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Title:
Electronic properties of stable decagonal quasicrystals
Authors:
Zhang, DL Author Full Names: Zhang, Dianlin
Source:
PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE 207 (12): 2666-2673 DEC 2010
Abstract:
Selected topics of electronic properties of stable decagonal quasicrystals are reviewed. Phonon localization and enhanced electron-phonon interaction may play important roles in the transport properties of these materials. The electronic specific heat measurements support the picture that the Hume-Rothery instability is responsible for the formation of the phase. On the other hand, careful examination of the magnetoresistance on highly oriented quasicrystalline films does not support the applicability of the quantum interference effect to the phenomenon. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Title:
Magnetic Phase Transitions and Magnetic-Field-Induced Polarization Flops in Multiferroic YbMn2O5
Authors:
Fukunaga, M; Sakamoto, Y; Kimura, H; Noda, Y Author Full Names: Fukunaga, Mamoru; Sakamoto, Yuma; Kimura, Hiroyuki; Noda, Yukio
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 80 (1): Art. No. 014705 JAN 2011
Abstract:
We have measured the electric polarization along the b- and a-axes of multiferroic YbMn2O5 under a magnetic field along the c-axis up to 14.5 T. We found that the polarization along the b-axis disappears, while that along the a-axis appears below 5.5 K in 0 T, though the direction of the polarization switches again above 1.5 T at 4.3 K. Ferroelectric hysteresis loops along the both axes of YbMn2O5 were clearly observed by the double-wave method. This polarization-flop phenomenon is very similar to that previously found in TmMn2O5. We have also studied the magnetic phase transitions of YbMn2O5 by neutron diffraction, and compared the data with those of TmMn2O5. The low-temperature incommensurate magnetic phases relating to the polarization flop of YbMn2O5 and TmMn2O5 are similar, though YbMn2O5 lacks a commensurate magnetic and ferroelectric phase which exists in TmMn2O5 and typical similar compounds.
Title:
Magnetic properties of the Ag-In-rare-earth 1/1 approximants
Authors:
Ibuka, S; Iida, K; Sato, TJ Author Full Names: Ibuka, Soshi; Iida, Kazuki; Sato, Taku J.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 23 (5): Art. No. 056001 FEB 9 2011
Abstract:
We have performed magnetic susceptibility and neutron scattering measurements on polycrystalline Ag-In-RE (RE, rare-earth) 1/1 approximants. In the magnetic susceptibility measurements, for most of the RE elements, inverse susceptibility shows linear behaviour in a wide temperature range, confirming well localized isotropic moments for the RE3+ ions. Exceptionally for the light RE elements, such as Ce and Pr, nonlinear behaviour was observed, possibly due to significant crystalline field splitting or valence fluctuation. For RE = Tb, the susceptibility measurement clearly shows a bifurcation of the field-cooled and zero-field-cooled susceptibility at T-f = 3.7 K, suggesting a spin-glass-like freezing. On the other hand, neutron scattering measurements detect significant development of short-range antiferromagnetic spin correlations in the elastic channel, which is accompanied by a broad peak at (sic)omega = 4 meV in the inelastic scattering spectrum. These features have striking similarity to those in the Zn-Mg-Tb quasicrystals, suggesting that the short-range spin freezing behaviour is due to local high-symmetry clusters commonly seen in both systems.
Title:
Temperature and magnetic field induced multiple magnetic transitions in DyAg2
Authors:
Arora, P; Chattopadhyay, MK; Chandra, LSS; Sharma, VK; Roy, SB Author Full Names: Arora, Parul; Chattopadhyay, M. K.; Chandra, L. S. Sharath; Sharma, V. K.; Roy, S. B.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER 23 (5): Art. No. 056002 FEB 9 2011
Abstract:
The magnetic properties of the rare-earth intermetallic compound DyAg2 are studied in detail with the help of magnetization and heat capacity measurements. It is shown that the multiple magnetic phase transitions can be induced in DyAg2 both by temperature and magnetic field. The detailed magnetic phase diagram of DyAg2 is determined experimentally. It was already known that DyAg2 undergoes an incommensurate to commensurate antiferromagnetic phase transition close to 10 K. The present experimental results highlight the first order nature of this phase transition, and show that this transition can be induced by magnetic field as well. It is further shown that another isothermal magnetic field induced transition or metamagnetic transition exhibited by DyAg2 at still lower temperatures is also of first order nature. The multiple magnetic phase transitions in DyAg2 give rise to large peaks in the temperature dependence of the heat capacity below 17 K, which indicates its potential as a magnetic regenerator material for cryocooler related applications. In addition it is found that because of the presence of the temperature and field induced magnetic phase transitions, and because of short range magnetic correlations deep inside the paramagnetic regime, DyAg2 exhibits a fairly large magnetocaloric effect over a wide temperature window, e.g., between 10 and 60 K.
Title:
Effect of composition on the i-phase cell parameter of Ti-(Zr,Cu)-Ni alloys
Authors:
Kocjan, A; McGuiness, PJ; Recnik, A; Kovac, J; Kobe, S Author Full Names: Kocjan, A.; McGuiness, P. J.; Recnik, A.; Kovac, J.; Kobe, S.
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS 356 (50-51): 2769-2773 NOV 2010
Abstract:
Quasicrystalline (i-phase) Ti-Zr-Ni samples were obtained using the melt-spinning technique where the Ti/Zr ratio ranged from 1 to 3 while the Ni content remained nearly constant varying between 17 and 20 at % We replaced the Zr with 3 and 5 at % of Cu in order to test the i-phase-forming ability of the samples which were all subsequently hydrided from the gas phase at 45 bar and 300 C for 1000 min We then made XRD analyses of the as spun and loaded samples in order to determine the influence of the composition and the absorbed hydrogen content on the cell parameter of the i phase An almost linear decrease of this parameter with the ([Ti] + [Cu])/[Zr] ratio was found for the as-prepared and hydrided samples where the slope of the lineal fit is preserved after hydrogenation but with about 6% higher values due to the expansion of the quasi lattice XPS analyses of the melt-spun i-Ti45Zr35Ni17Cu3 revealed an oxide-layer thickness of 4 nm A TEM investigation revealed that the size of the i-phase grains on the wheel side of the ribbon was approximately five times smaller than on the bright side as a result of the higher cooling rate and the resulting faster nucleation rate (C) 2010 Elsevier BV All rights reserved
Title:
Magneto structural transition in the DySi CrB- and micro-structural changes in the FeB-type compounds by XRPD and neutron diffraction
Authors:
Schobinger-Papamantellos, P; Brunelli, M; Rodriguez-Carvajal, J; Buschow, KHJ; Ritter, C; Gramm, F Author Full Names: Schobinger-Papamantellos, P.; Brunelli, M.; Rodriguez-Carvajal, J.; Buschow, K. H. J.; Ritter, C.; Gramm, F.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 323 (7): 903-914 APR 2011
Abstract:
We present the magnetic temperature phase diagrams of the CrB- and FeB-type orthorhombic phases of the DySi compound, determined from high-quality powder XRPD and neutron diffraction, as well as the sample microstructure as determined by HRTEM. Both phase diagrams comprise a HT (T-c1, T-c2 - T-N) and a LT range (5K-T-c1, T-c2) separated by a monoclinic phase transition at T-c1 = T-c2 = 23.5 K well below the second-order Neel transition (T-N = 40 K). The transition paths are for CrB-type Cmcm (HT) T-c1 -> C-2/m11 (LT), and for FeB Pnma (HT) T-c2 -> P2(1)/n11 (LT). The transitions are related to non-monotonous changes of the lattice and structural parameters displaying anomalies at T-c1, T-c2 and slight volume changes. For the CrB-type the monoclinic angle decreases smoothly from T-c1 down to 5 K and the maximum strain experienced by the crystal lattice in the (0 2 1) direction was found at T-c1. In the FeB-type, in addition to the magneto-elastic transition at T-c2 = 23.5 K, minor anomalies are found at 13.5 K in the temperature dependence of the monoclinic angle and the maximum strain along (0 1 1). Both temperatures mark the sequence of changes in the magnetic domain microstructure observed in FeB: below T-2 = 23.5 K the incommensurate HT magnetic phase with q(3) approximate to (01/2 1/7) disproportionates into two LT phases q(3) approximate to (01/2 1/11) T-2 and q(2) approximate to (01/2 1/6) coexisting in the form of domains with portions varying with T going from T-2 down to 13.5 K(q(2) increasing at the cost of q(3)). This behaviour could be related to structural inhomogeneities below the first-order magneto-elastic transition T-c2, if one assumes a broad two phase range, where the HT (Pnma) phase coexists with(P2(1)/n) as a metastable phase at LT in the form of domains with different magnetic behaviour. (C) 2010 Elsevier B.V. All rights reserved.
Title:
Helical Magnetic Structure in a Quasi-One-Dimensional LiCu2O2 Multiferroic Crystal According to Cu-63,Cu-65 NMR Studies
Authors:
Sadykov, AF; Gerashchenko, AP; Piskunov, YV; Ogloblichev, VV; Buzlukov, AL; Verkhovskii, SV; Yakubovskii, AY; Kumagai, K Author Full Names: Sadykov, A. F.; Gerashchenko, A. P.; Piskunov, Yu. V.; Ogloblichev, V. V.; Buzlukov, A. L.; Verkhovskii, S. V.; Yakubovskii, A. Yu.; Kumagai, K.
Source:
JETP LETTERS 92 (8): 527-531 OCT 2010
Abstract:
The NMR spectra of Cu-63 and Cu-65 natural copper isotopes in a LiCu2O2 multiferroic single crystal compound have been measured above and below the temperature of magnetic phase transition (T-c = 23 K) in zero magnetic field and in applied magnetic field H-0 = 94 kOe parallel to the c axis of the crystal. In LiCu(2O)2 below T-c, a complicated helical magnetic structure with the magnetic moment of copper ions Cu2+ varying along the chain according to the harmonic law with the wave vector being incommensurate to the crystal lattice constants has been revealed. The experimental results have been successfully interpreted using the model based on the planar helical magnetic structure. It has been found that the plane of rotation for Cu2+ magnetic moments in LiCu2O2 does not coincide at H-0 = 0 with the ab plane. The high magnetic field (H-0 = 94 kOe) applied along the c axis of the single crystal does not affect the spatial orientation of the plane of rotation.
Title:
Ab initio reconstruction of difference densities by charge flipping
Authors:
Palatinus, L; Fleischer, F; Pattison, P; Weber, T; Steurer, W Author Full Names: Palatinus, Lukas; Fleischer, Frank; Pattison, Phillip; Weber, Thomas; Steurer, Walter
Source:
ACTA CRYSTALLOGRAPHICA SECTION A 67: 9-20 Part 1 JAN 2011
Abstract:
The charge-flipping algorithm in its band-flipping variant is capable of ab initio reconstructions of scattering densities with positive and negative values. It is shown that the method can be applied to reconstructions of difference electron densities of superstructures, i.e. densities obtained as a difference between the true scattering density and the average density over two or more subcells of the true structure. The amplitudes of reflections lying on the reciprocal lattice of the subcell are not required for the procedure. A series of examples shows applications of the method to the solution of superstructures in periodic crystals or quasicrystals as well as the application to ab initio solution of modulation of an incommensurately modulated structure from satellite reflections only and solution of a structure from a crystal twinned by reticular pseudomerohedry. The method is especially suited for solving pseudosymmetry problems occurring frequently in superstructures.
Title:
Generation of (3+d)-dimensional superspace groups for describing the symmetry of modulated crystalline structures
Authors:
Stokes, HT; Campbell, BJ; van Smaalen, S Author Full Names: Stokes, Harold T.; Campbell, Branton J.; van Smaalen, Sander
Source:
ACTA CRYSTALLOGRAPHICA SECTION A 67: 45-55 Part 1 JAN 2011
Abstract:
A complete table of (3 + 1)D, (3 + 2)D and (3 + 3)D superspace groups (SSGs) has been enumerated that corrects omissions and duplicate entries in previous tables of superspace groups and Bravais classes. The theoretical methods employed are not new, though the implementation is both novel and robust. The paper also describes conventions for assigning a unique one-line symbol for each group in the table. Finally, a new online data repository is introduced that delivers more complete information about each SSG than has been presented previously.

Update: 4-Feb-2011

Title:
Investigation of thermodynamic properties and magnetic ordering in TmNiIn
Authors:
Baran, S; Kaczorowski, D; Arulraj, A; Penc, B; Szytula, A Author Full Names: Baran, S.; Kaczorowski, D.; Arulraj, A.; Penc, B.; Szytula, A.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 323 (6): 833-837 MAR 2011
Abstract:
The magnetic, electrical resistivity, specific heat and powder neutron diffraction measurements were performed on a polycrystalline sample of TmNiIn. The compound crystallizes in a hexagonal structure of the ZrNiAl-type. It orders antiferromagnetically below T-N = 2.5 K. The magnetic structure is an incommensurate one and may be described by the propagation vector (k) over right arrow = [k(x),k(x),1/2], where k(x)=0.281(2). The magnetic moments are confined within the basal hexagonal plane. The results are compared with those reported for isostructural thulium compounds like TmAgSi, TmAgGe and TmPtIn. (C) 2010 Elsevier B.V. All rights reserved.

Update: 28-Jan-2011

Title:
Bond orientational ordering in a metastable supercooled liquid: a shadow of crystallization and liquid-liquid transition
Authors:
Tanaka, H Author Full Names: Tanaka, Hajime
Source:
JOURNAL OF STATISTICAL MECHANICS-THEORY AND EXPERIMENT : Art. No. P12001 DEC 2010
Abstract:
It is widely believed that a liquid state can be characterized by a single order parameter, density, and that a transition from a liquid to solid can be described by density ordering (translational ordering). For example, this type of theory has had great success in describing the phase behaviour of hard spheres. However, there are some features that cannot be captured by such theories. For example, hard spheres crystallize into either hcp or fcc structures, without a tendency of bcc ordering which is expected by the Alexander-McTague theory based on the Landau-type free energy of the density order parameter. We also found hcp-like bond orientational ordering in a metastable supercooled liquid, which promotes nucleation of hcp crystals. Furthermore, theories based on the single order parameter cannot explain water-like thermodynamic and kinetic anomalies of a liquid and liquid-liquid transition in a single-component liquid. Based on these facts, we argue that we need an additional order parameter to describe a liquid state. It is bond orientational order, which is induced by dense packing in hard spheres or by directional bonding in molecular and atomic liquids. Bond orientational order is intrinsically of local nature, unlike translational order which is of global nature. This feature plays a unique role in crystallization and quasicrystal formation. We also reveal that bond orientational ordering is a cause of dynamic heterogeneity near a glass transition and is linked to slow dynamics. In relation to this, we note that, for describing the structuring of a highly disordered liquid, we need a structural signature of low configurational entropy, which is more general than bond orientational order. Finally, the water-like anomaly and liquid-liquid transition can be explained by bond orientational ordering due to hydrogen or covalent bonding and its cooperativity, respectively. So we argue that bond orientational ordering is a key to the physical understanding of crystallization, quasicrystallization, glass transition, water-like anomaly and liquid-liquid transition. A unified description of these phenomena may be possible along this line.

Update: 21-Jan-2011

Title:
Effect of infrared illumination on the modulated magnetic structure of the weak ferromagnet FeBO3: Mg
Authors:
Sokolov, BY Author Full Names: Sokolov, B. Yu.
Source:
PHYSICS OF THE SOLID STATE 52 (12): 2527-2534 DEC 2010
Abstract:
The effect of unpolarized white light on the period and conditions of the existence of the modulated magnetic structure of the FeBO3: Mg single crystal, which is formed in this easy-plane weak ferromagnet in the low-temperature range during technical magnetization, has been investigated experimentally. It has been revealed that the degree of light action on the magnetic state of the crystal depends on both the irradiation duration and the orientation of the ferromagnetic vector during illumination. It has been established that light with wavelengths in the range 0.8 mu m < lambda < 0.9 mu m has a maximum effect on the parameters of the modulated magnetic structure formed in the FeBO3: Mg single crystal. The results obtained have been interpreted in the framework of the "magnetic ripple" theory using the model of photosensitivity of anisotropic magnetic centers associated with the presence of Mg impurity ions in the composition of the crystal.
Title:
Quasicrystal-like structure and its crystalline approximant in an Fe48Cr15Mo14C15B6Tm2 bulk metallic glass
Authors:
Hirata, A; Hirotsu, Y; Amiya, K; Inoue, A Author Full Names: Hirata, Akihiko; Hirotsu, Yoshihiko; Amiya, Kenji; Inoue, Akihisa
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 504: S186-S189 Suppl. 1 AUG 2010
Abstract:
Nanoscale quasicrystal-like structural states have been found in the course of crystallization in an Fe-based Fe48Cr15Mo14C15B6Tm2 bulk metallic glass. The quasicrystal-like structure is similar with the chi-FeCrMo structure exhibiting a deformed tenfold diffraction pattern due to projected pentagonal arrangements regarded as a Mo framework. We show the preliminary structural model for the quasicrystal-like structure and discuss the three-dimensional features based on the chi-FeCrMo crystalline approximant. (C) 2010 Elsevier B.V. All rights reserved.
Title:
TEM study of the cooling rate dependent crystallization behavior of (Zr65Al10Ni10Cu15)(98)Nb-2 metallic glass
Authors:
Wang, YM; Shek, CH; Wang, Q; Qiang, JB; Dong, CA Author Full Names: Wang, Yingmin; Shek, Chan Hung; Wang, Qing; Qiang, Jianbing; Dong, Chuang
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 504: S234-S238 Suppl. 1 AUG 2010
Abstract:
The crystallization of (Zr65Al10Ni10Cu15)(98)Nb-2 metallic glasses has been studied using transmission electron microscopy (TEM), X-ray diffraction (XRD) and differential scanning calorimetry (DSC). The ribbon glass and bulk metallic glass (BMG) of this alloy exhibit different crystallization behaviors. For ribbon glass in the first stage crystallization, icosahedral quasicrystal (I-phase) precipitated together with the eta-Zr2Ni (a = 1.226 nm) phase. The BMG alloy transforms into the I-phase and two coherently coexisted phases, namely, the Al2Zr3 phase and an unknown primitive cubic phase (a = 0.76 nm) in this stage. The experimental evidence indicates that the liquid cooling rate for sample preparation has a significant effect on its crystallization behavior of this alloy glass. (C) 2010 Elsevier B.V. All rights reserved.
Title:
Decomposition of icosahedral phase in Ti52Zr28Ni20 powder during electro-discharge sintering
Authors:
Song, GA; Shin, JS; Kang, TJ; Choi, HS; Lee, JK; Lee, MH; Kim, TS; Fleury, E; Prima, F; Lee, WH; Kim, KB Author Full Names: Song, G. A.; Shin, J. S.; Kang, T. J.; Choi, H. S.; Lee, J. K.; Lee, M. H.; Kim, T. S.; Fleury, E.; Prima, F.; Lee, W. H.; Kim, K. B.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 504: S302-S305 Suppl. 1 AUG 2010
Abstract:
A single pulse of 0.57-1.1 kJ/0.45 g-atomized spherical Ti52Zr28Ni20 powders in size range of 10-30 and 30-50 mu m consisting of a mixture of beta-(Ti, Zr) and icosahedral phases was applied to understand the structural evolution of icosahedral phase during electro-discharge sintering (EDS). The structural analysis revealed that high electrical input energies leaded to complete decomposition of icosahedral phase into C14 Laves and beta-(Ti, Zr) phases. Furthermore, the critical input energy inducing decomposition of icosahedral phase during EDS is dependent on the size of the powder. (C) 2010 Elsevier B.V. All rights reserved.
Title:
Characterisation of an Al93Fe3Cr2Ti2 alloy obtained by spray forming
Authors:
Garcia-Escorial, A; Echevarria, M; Lieblich, M; Stone, I Author Full Names: Garcia-Escorial, A.; Echevarria, M.; Lieblich, M.; Stone, I.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS 504: S519-S521 Suppl. 1 AUG 2010
Abstract:
Al93Fe3Cr2Ti2 is a highly promising alloy due to its capacity to form quasicrystals. In the present work bulk Al93Fe3Cr2Ti2 obtained by spray forming is microstructurally characterised. A microstructure gradient is observed, in which the external layer consists of an alpha-Al matrix with Al3Ti precipitates and fine quasicrystals while the internal core presents intermetallics of the equilibrium phases Al13Cr2 + Al13Fe4, with intermediate stages between both areas. The hardness ranges from the 140Hv of the external layer to the 90Hv of the core. Spray forming can therefore produce nanoquasicrystalline Al93Fe3Cr2Ti2 which evolves towards equilibrium as the process proceeds, due to the heating produced by the deposition of successive layers. (C) 2010 Elsevier B.V. All rights reserved.
Title:
Composites reinforced by Al-Cu-Fe quasicrystalline particles with a copper matrix and their tribological properties
Authors:
Shaitura, DS; Teplov, AA; Chikina, EA; Klevachev, AM; Efimochkin, IY; Fedotov, SV; Petrzhik, MI; Levashov, EA; Abuzin, YA Author Full Names: Shaitura, D. S.; Teplov, A. A.; Chikina, E. A.; Klevachev, A. M.; Efimochkin, I. Yu.; Fedotov, S. V.; Petrzhik, M. I.; Levashov, E. A.; Abuzin, Yu. A.
Source:
JOURNAL OF SURFACE INVESTIGATION-X-RAY SYNCHROTRON AND NEUTRON TECHNIQUES 4 (6): 951-955 NOV 2010
Abstract:
Copper-based composite coatings with addition of 34 wt % of Al-Cu-Fe quasicrystalline powder of dispersity less than 20 fum, as well as 70 wt % of quasicrystalline powder of dispersity less than 40fum and less than 3 fum, were produced by the cold spray process. The phase composition during annealing of samples at various temperatures was studied by X-ray phase analysis. Tribological properties of each composite coating and pure copper were investigated. The experimental results showed a considerable improvement of the tribological properties of the material at the addition of quasicrystals. The least wear was observed in the composite sample containing quasicrystalline inclusions of less than 3 fum subjected to thermal treatment. In this case the counterbody wear was practically absent.

Update: 14-Jan-2011

Title:
DELONE MEASURES OF FINITE LOCAL COMPLEXITY AND APPLICATIONS TO SPECTRAL THEORY OF ONE-DIMENSIONAL CONTINUUM MODELS OF QUASICRYSTALS
Authors:
Klassert, S; Lenz, D; Stollmann, P Author Full Names: Klassert, Steffen; Lenz, Daniel; Stollmann, Peter
Source:
DISCRETE AND CONTINUOUS DYNAMICAL SYSTEMS 29 (4): 1553-1571 Sp. Iss. SI APR 2011
Abstract:
We study measures on the real line and present various versions of what it means for such a measure to take only finitely many values. We then study perturbations of the Laplacian by such measures. Using Kotani-Remling theory, we show that the resulting operators have empty absolutely continuous spectrum if the measures are not periodic. When combined with Gordon type arguments this allows us to prove purely singular continuous spectrum for some continuum models of quasicrystals.
Title:
X-ray topography study of deformed composites obtained by directional solidification of Al-Cu-Co alloy
Authors:
Krawczyk, J; Bogdanowicz, W; Goryczka, T Author Full Names: Krawczyk, J.; Bogdanowicz, W.; Goryczka, T.
Source:
CRYSTAL RESEARCH AND TECHNOLOGY 45 (12): 1321-1325 Sp. Iss. SI DEC 2010
Abstract:
Fibre-reinforced composites were produced by the modification of the static horizontal Bridgman method. The single-crystalline composite matrix consisted of the tetragonal T phase (Al72Cu27Co1). Decagonal quasi-crystal D phase (Al64Cu20Co16) was the reinforcement in the form of fibres parallel to the solidification direction. These fibres were surrounded by the tetragonal Theta phase (Al66Cu31Co3). The composite specimens in the shape of plates were studied by tensile tests and X-ray topography. The specimens deformed up to rupture and, from the X-ray topographs, the dependence of the composite structure defects on deformation was examined. It was found that the rupture of specimens is related to low-angle boundaries created during deformation. The influence of defects on the strength of the composites is discussed. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Update: 6-Jan-2011

Title:
QUINARY AXIS: AN ELEMENT OF SYMMETRY THAT OCCURS IN MOLECULES AND QUASICRYSTALS - A DIDACTIC EXPERIMENT OF CRYSTALLOGRAPHY.
Authors:
das Neves, PCP; de Freitas, DV; Baptista, LA Author Full Names: Pereira das Neves, Paulo Cesar; de Freitas, Dareson Vieira; Baptista, Luis Andre
Source:
QUIMICA NOVA 33 (9): 1977-1979 2010
Abstract:
QUINARY AXIS: AN ELEMENT OF SYMMETRY THAT OCCURS IN MOLECULES AND QUASICRYSTALS - A DIDACTIC EXPERIMENT OF CRYSTALLOGRAPHY. Axis of quinary symmetry occur in molecular symmetry, as in the case of fullerenes, and in crystalline symmetry, in the quasicrystals. Minerals with pentagonal faces do not have this element of symmetry, as the pyrite (FeS2) which shows a ridge that is different from the other ones, in any face of the crystal. The purpose of this paper is to demonstrate conceptual differences between pyritohedron and regular pentagonal dodecahedron symmetries, discussing students' difficulties to identify them. Also is proposed a didactic experiment with spatial models of the above-mentioned forms and the demonstration of its symmetries in clinographic projections.
Title:
Structural modulation and magnetic properties of hexagonal Ba(Ti1-xFex)O3-delta ceramics
Authors:
Wei, XK; Yao, LD; Shen, X; Yang, Y; You, SJ; Li, FY; Jin, CQ; Yu, RC Author Full Names: Wei, X. K.; Yao, L. D.; Shen, X.; Yang, Y.; You, S. J.; Li, F. Y.; Jin, C. Q.; Yu, R. C.
Source:
PHYSICA B-CONDENSED MATTER 405 (23): 4851-4854 DEC 1 2010
Abstract:
This paper investigates the structural and magnetic properties of hexagonal Ba(Ti1-xFex)O3-delta (x=0.3 and 0.7) ceramics, synthesized with solid-state reaction method. Transmission electron microscope investigations reveal that structural phase separation featured by non-modulated and modulated phases is identified by the electron diffraction patterns taken along [0 0 1] zone axis in x=0.3 sample (BTF30). While for x=0.7 sample (BTF70), a pure phase with commensurate and incommensurate modulations at different directions is identified. The superstructure peaks observed in their X-ray diffraction patterns are verified by their individual commensurate modulation, q(s)=1/2 (31-2) in the modulated phase of BTF30 and q(4,-1)=4/9(3 0 4)-(0 0 1) in BTF70. In addition to the room-temperature weak ferromagnetism of BTF30 and paramagnetism of BTF70, spin glass transitions with T-f=3.4 K for the former and T-f=33.6 K for the latter are observed. On the basis of the structural characteristics, the influence of O1 and O2 vacancies on magnetic and dielectric properties of the doped system is discussed. (C) 2010 Elsevier B.V. All rights reserved.
Title:
The Role of Strain Tensor in Formation of Incommensurate Phases in Quartz
Authors:
Sannikov, DG Author Full Names: Sannikov, D. G.
Source:
FERROELECTRICS 400: 8-11 2010
Abstract:
It is shown that the strain tensor components play a decisive role in the theory of formation of incommensurate phases in quartz.
Title:
Improper Ferroelectric Antiferromagnetics
Authors:
Sakhnenko, VP; Ter-Oganessian, NV Author Full Names: Sakhnenko, V. P.; Ter-Oganessian, N. V.
Source:
FERROELECTRICS 400: 12-18 2010
Abstract:
Experiments reveal that magnetoelectric crystals usually experience incommensurate magnetic ordering. In this work we present symmetry arguments for the intimate coupling between ferroelectric magnetically ordered phases and modulated magnetic order. The obtained results are applied to crystals belonging to the D-2h (mmm) crystallographic class and illustrated by two examples of rare-earth manganites RMn2O5 and MnWO4.
Title:
The modulated structure of the calcium aluminate Ca6AlO212 center dot Bi2O3
Authors:
Perez, O; Malo, S; Hervieu, M Author Full Names: Perez, O.; Malo, S.; Hervieu, M.
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 66: 585-593 Part 6 DEC 2010
Abstract:
Bismuth calcium aluminate, Bi2Ca6Al12O27, has been prepared as a ceramic and a single crystal. Analysis of reciprocal space using both electron and X-ray diffraction show an R-centred hexagonal unit cell: a = b = 17.3892 (4), c = 6.986 (1) A. Additional weak reflections are observed; they require the introduction of a modulation wavevector q = 0.0453 (2)c* for indexing. The modulated structure has been solved using the superspace formalism [superspace group X (3) over bar (00 gamma)0]. A frame-work of corner-sharing AlO4 tetrahedra forms corrugated sixfold rings and uncommon triple rings. The Ca2+ cations exhibit an eightfold coordination sphere; edge-sharing CaO8 polyhedra form intertwinned zigzagging rows along c creating a three-dimensional net. Bi atoms are located in large hexagonal tunnels parallel to c and form Bi2O3 pairs, which adopt a trigonal bipyramidal configuration. The 6s(2) loneelectron pairs (Lp) point along c, in the opposite direction to the three Bi-O strong bonds to form two BiO(3)Lp tetrahedra with a common base. Different orientations of the Bi(2)O(3)Lp(2) pairs, rotated by 60 degrees around c, are observed. Their stacking modes in each of the hexagonal tunnels are described. The sequence of the stacking varies along c in each of the tunnels.
Title:
Crystal chemistry of transition metal diarsenates M2As2O7 (M = Mn, Co, Ni, Zn): variants of the thortveitite structure
Authors:
Weil, M; Stoger, B Author Full Names: Weil, Matthias; Stoeger, Berthold
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE 66: 603-614 Part 6 DEC 2010
Abstract:
The structures of the 3d divalent transition-metal diarsenates M2As2O7 (M = Mn, Co, Ni, Zn) can be considered as variants of the monoclinic (C2/m) thortveitite [Sc2Si2O7] structure type with a similar or equal to 6.7, b similar or equal to 8.5, c similar or equal to 4.7 angstrom, alpha similar or equal to 90, beta similar or equal to 102, gamma similar or equal to 90 degrees and Z = 2. Co2As2O7 and Ni2As2O7 are dimorphic. Their high-temperature (beta) polymorphs adopt the thortveitite aristotype structure in C2/m, whereas their low-temperature (alpha) polymorphs are hettotypes and crystallize with larger unit cells in the triclinic crystal system in space groups P (1) over bar and P1, respectively. Mn2As2O7 undergoes no phase transition and likewise adopts the thortveitite structure type in C2/m. Zn2As2O7 has an incommensurately modulated crystal structure [C2/m(alpha,0,gamma) 0s] with q = [0.3190 (1), 0, 0.3717 (1)] at ambient conditions and transforms reversibly to a commensurately modulated structure with Z = 12 (I2/c) below 273 K. The Zn phase resembles the structures and phase transitions of Cr2P2O7. Besides descriptions of the low-temperature Co2As2O7, Ni2As2O7 and Zn2As2O7 structures as five-, three-and sixfold superstructures of the thortveitite-type basic structure, the superspace approach can also be applied to descriptions of all the commensurate structures. In addition to the ternary M2As2O7 phases, the quaternary phase (Ni,Co) 2As2O7 was prepared and structurally characterized. In contrast to the previously published crystal structure of the mineral petewilliamsite, which has the same idealized formula and has been described as a 15-fold superstructure of the thortveitite-type basic structure in space group C2, synthetic (Ni,Co)(2)As2O7 can be considered as a solid solution adopting the alpha-Ni2As2O7 structure type. Differences of the two structure models for (Ni,Co)(2)As2O7 are discussed.

M.D.

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