Update: 1-Feb-2012

Title:
Neutron powder diffraction study of the ternary RMgSn (R=Ce-Nd, Tb-Tm, Yb) compounds
Authors:
Lemoine, P; Verniere, A; Venturini, G; Capelli, S; Malaman, B Author Full Names: Lemoine, P.; Verniere, A.; Venturini, G.; Capelli, S.; Malaman, B.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 324 (6):961-976; 10.1016/j.jmmm.2011.09.035 MAR 2012
Abstract:
The ternary intermetallic RMgSn compounds are studied by neutron powder diffraction. The CeScSi-type PrMgSn and NdMgSn compounds present a commensurate antiferromagnetic structure, while the (Tb-Tm)MgSn are characterized by an incommensurate sine-wave modulated magnetic structure, which can tend to a square-modulated arrangement at low temperature due to appearance of higher odd integer harmonics. The TiNiSi-type CeMgSn compound is also characterized by an incommensurate sine-wave modulated magnetic structure, while PrMgSn exhibits a ferromagnetic arrangement with a canting at low temperature. Finally, the ZrNiAl-type YbMgSn compound evidences no magnetic ordering. These results are discussed and compared with those published for the other CeScSi-type compounds. (C) 2011 Elsevier B.V. All rights reserved.
Title:
Modeling of decagonal quasicrystal lattice
Authors:
Girzhon, VV; Kovalyova, VM; Smolyakov, OV; Zakharenko, MI Author Full Names: Girzhon, V. V.; Kovalyova, V. M.; Smolyakov, O. V.; Zakharenko, M. I.
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 358 (2):137-144; 10.1016/j.jnoncrysol.2011.09.017 JAN 15 2012
Abstract:
The model of the reciprocal lattice of decagonal quasicrystal has been proposed. It is based on the multiplication of the basis sites' groups according to the proposed rules. This model was shown to provide the information not only on the reciprocal sites location, but also on the intensity of the appropriated diffraction reflections. The physical justification of the proposed model correctness has been provided on the base of projection of six-dimensional hyperlattice onto the three-dimensional space. The possibility of three-indices labeling of the diffraction reflections of decagonal quasicrystals has been exhibited. (C) 2011 Elsevier B.V. All rights reserved.
Title:
The luminescence of Na(x)Eu((2-x)/3)(3+)MoO(4) scheelites depends on the number of Eu-clusters occurring in their incommensurately modulated structure
Authors:
Arakcheeva, A; Logvinovich, D; Chapuis, G; Morozov, V; Eliseeva, SV; Bunzli, JCG; Pattison, P Author Full Names: Arakcheeva, Alla; Logvinovich, Dmitry; Chapuis, Gervais; Morozov, Vladimir; Eliseeva, Svetlana V.; Buenzli, Jean-Claude G.; Pattison, Philip
Source:
CHEMICAL SCIENCE, 3 (2):384-390; 10.1039/c1sc00289a 2012
Abstract:
Scheelite related compounds with general formula M(n)(XO(4))(m) are the subject of hefty interest owing to their optical properties, stability and relatively simple preparation. Eu(3+)-containing scheelites are considered as red-emitting phosphors and the main factors affecting their luminescence are thought to be chemical composition and particle size while the influence of their structure is generally ignored. Here we report eight compounds from the Na(x)Eu((2-x)/3)MoO(4) series prepared by conventional solid-state reaction and present a detailed analysis of their crystal structures. Six of them have modulated structures, a common feature of SRCs, in which dopant Eu(3+) ions are orderly distributed. Moreover, different amounts of Eu(3+) dimers are detected in the modulated structures, characterized by weak satellite reflections appearing in the lower angle part of the XRD patterns. These reflections are indexed and incorporated into Rietveld's refinement using superspace (3 + 1)-dimension symmetry. The remarkable feature of the compounds is that the characteristic luminescence parameters, overall (Q(L)(Eu)) and intrinsic (Q(Eu)(Eu)) quantum yields, Eu((5)D(0)) lifetimes, and sensitization efficiencies (eta(sens)), correlate with the number of Eu(3+) aggregates, but not directly with the composition x of the materials. This provides an efficient tool for understanding and controlling the luminescence properties of scheelite related compounds.
Title:
The success story of crystallography
Authors:
Schwarzenbach, D Author Full Names: Schwarzenbach, Dieter
Source:
ACTA CRYSTALLOGRAPHICA SECTION A, 68 57-67; Part 1 10.1107/S0108767311030303 JAN 2012
Abstract:
Diffractionists usually place the birth of crystallography in 1912 with the first X-ray diffraction experiment of Friedrich, Knipping and Laue. This discovery propelled the mathematical branch of mineralogy to global importance and enabled crystal structure determination. Knowledge of the geometrical structure of matter at atomic resolution had revolutionary consequences for all branches of the natural sciences: physics, chemistry, biology, earth sciences and material science. It is scarcely possible for a single person in a single article to trace and appropriately value all of these developments. This article presents the limited, subjective view of its author and a limited selection of references. The bulk of the article covers the history of X-ray structure determination from the NaCl structure to aperiodic structures and macromolecular structures. The theoretical foundations were available by 1920. The subsequent success of crystallography was then due to the development of diffraction equipment, the theory of the solution of the phase problem, symmetry theory and computers. The many structures becoming known called for the development of crystal chemistry and of data banks. Diffuse scattering from disordered structures without and with partial long-range order allows determination of short-range order. Neutron and electron scattering and diffraction are also mentioned.
Title:
Direct Preparation of Nano-Quasicrystals via a Water-Cooled Wedge-Shaped Copper Mould
Authors:
Wang, ZF; Zhao, WM; Qin, CL; Cui, Y; Fan, SL; Jia, JQ Author Full Names: Wang, Zhifeng; Zhao, Weimin; Qin, Chunling; Cui, Yan; Fan, Shenglei; Jia, Junqing
Source:
JOURNAL OF NANOMATERIALS, 10.1155/2012/708240 2012
Abstract:
We have successfully synthesized multicomponent Mg-based nano-quasicrystals (nano-QCs) through a simple route by using a water-cooled wedge-shaped copper mould. Nanoscale QCs are prepared directly on tip of wedge-shaped castings. The further study shows that nano-QCs in the Mg(71)Zn(26)Y(2)Cu(1) alloy show well microhardness of greater than HV450. Electrochemical properties of three kinds of quasicrystal alloys are investigated in simulated seawater. The Mg(71)Zn(26)Y(2)Cu(1) nano-QC alloy presents the best corrosion resistance in this study for the formation of well-distributed nano-QC phases (1 similar to 5 nm) and polygonal Mg(2)(Cu,Y) nanophases (40 similar to 50 nm).
Title:
Potts Model with the Simplest Modulated Phase
Authors:
Ganikhodjaev, N; Temir, S; Akin, H; Uguz, S Author Full Names: Ganikhodjaev, Nasir; Temir, Seyit; Akin, Hasan; Uguz, Selman
Source:
JOURNAL OF THE KOREAN PHYSICAL SOCIETY, 59 (5):2971-2979; 10.3938/jkps.59.2971 NOV 2011
Abstract:
We study the phase diagrams for the Potts model on the Bethe lattice with competing nearest-neighbor interactions J(1) and ternary interactions J(p) and J(t). At vanishing temperature, the phase diagram is fully determined for all values and signs of J(p)/J(1) and J(t)/J(1); in particular, we show that the phase diagrams contain ferromagnetic, paramagnetic and < 2 > phases only; i.e., the set of modulated phases consists of the < 2 > phase only for J(1) > 0 and J(p)/J(1) < 0. We verify that values of T/J(1) in the very narrow strip -0.11 < T/J(1) < 0 with -J(p)/J(1) < 0 favor the modulated phase, which is either a commensurate phase with a very large period or an incommensurate phase. The transition lines are obtained from stability conditions, and characteristic points in the phase diagram are analyzed by using numerical iterations. Also the wavevectors versus temperature are plotted for some critical points in the modulated phases.
Title:
Materials Researcher Dan Shechtman receives Nobel Prize for discovery of quasicrystals
Authors:
[Anonymous] Author Full Names: [Anonymous]
Source:
MRS BULLETIN, 36 (11):849-849; 10.1557/mrs.2011.284 NOV 2011

Update: 25-Jan-2012

Title:
Microstructure evolution of Zr(65)Al(7.5)Cu(12.5)Ni(10)Ag(5) bulk metallic glass due to rolling and its influence on the thermal stability
Authors:
Yan, ZJ; Yan, J; Hu, Y; Hao, WX Author Full Names: Yan, Z. J.; Yan, J.; Hu, Y.; Hao, W. X.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 513 75-79; 10.1016/j.jallcom.2011.09.083 FEB 5 2012
Abstract:
X-ray diffraction (XRD), differential scanning calorimetry (DSC) and high-resolution transmission electron microscopy (HRTEM) are employed to investigate the microstructure evolution of Zr(65)Al(7.5)Cu(12.5)Ni(10)Ag(5) bulk metallic glass subjected to rolling at room temperature. The strain rates are controlled to be 10(-4)-10(-3) s(-1). The results show that the plastic deformation during rolling behaves as an inhomogeneous mode with the characteristic of shear bands, which results in the two-state characteristic of atomic movement from competition between the ordering and disordering processes. The icosahedron-like clusters precipitate in the transition regions between the shear bands and the amorphous matrix, and they tend to aggregate into nano-sized orders. The results of DSC indicate that the onset precipitation temperature of I-phase during heating of the metallic glass obviously decreases due to rolling. However, the time window for the completion of amorphous-to-icosahedral phase transformation is evidently lengthened. The microstructure evolution during rolling and its influence on the thermal stability are discussed. (C) 2011 Elsevier B.V. All rights reserved.
Title:
Incommensurate magnetic order in TbTe(3)
Authors:
Pfuner, F; Gvasaliya, SN; Zaharko, O; Keller, L; Mesot, J; Pomjakushin, V; Chu, JH; Fisher, IR; Degiorgi, L Author Full Names: Pfuner, F.; Gvasaliya, S. N.; Zaharko, O.; Keller, L.; Mesot, J.; Pomjakushin, V.; Chu, J-H; Fisher, I. R.; Degiorgi, L.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 24 (3):10.1088/0953-8984/24/3/036001 JAN 25 2012
Abstract:
We report a neutron diffraction study of the magnetic phase transitions in the charge-density wave (CDW) TbTe(3) compound. We discover that in the paramagnetic phase there are strong 2D-like magnetic correlations, consistent with the pronounced anisotropy of the chemical structure. A long-range incommensurate magnetic order emerges in TbTe(3) at T(mag1) = 5.78 K as a result of continuous phase transitions. We observe that near the temperature T(mag1) the magnetic Bragg peaks appear around the position (0, 0, 0.24) (or its rational multiples), that is fairly close to the propagation vector. 0; 0; 0 : 29 associated with the CDW phase transition in TbTe(3). This suggests that correlations leading to the long-range magnetic order in TbTe(3) are linked to the modulations that occur in the CDW state.
Title:
Magnetic properties of sigma- and hexagonal-Mn(76)Si(18)Cr(6) approximant phases of a dodecagonal quasicrystal
Authors:
Kashimoto, S; Kocjan, A; Jaglicic, Z; Jazbec, S; Iga, H; Ishimasa, T; Dolinsek, J Author Full Names: Kashimoto, S.; Kocjan, A.; Jaglicic, Z.; Jazbec, S.; Iga, H.; Ishimasa, T.; Dolinsek, J.
Source:
PHYSICAL REVIEW B, 84 (22):10.1103/PhysRevB.84.224201 DEC 19 2011
Abstract:
The tetragonal sigma phase and the hexagonal (hex) phase in the Mn-Si-V(Cr) transition-metal-alloy systems are stable approximant phases of a dodecagonal (12-fold) quasicrystal that can be prepared in bulk quantities. We have synthesized samples of the sigma and hex phases of composition Mn(76)Si(18)Cr(6) and determined their magnetic properties. In the sigma-Mn(76)Si(18)Cr(6), a spin-freezing transition to a canonical spin-glass phase was detected below T(f) approximate to 8 K, characterized by a maximum in the zero-field-cooled susceptibility, a frequency-dependent cusp in the ac susceptibility, M(H) hysteresis, and ultraslow time decay of the thermoremanent magnetization. In contrast, no spin-glass transition was observed in the hex-Mn(76)Si(18)Cr(6) phase down to the lowest investigated temperature of 2 K. The analysis of the susceptibility has shown that the coupling of spins in both phases is antiferromagnetic (AFM), but the coupling strength is considerably stronger in the sigma phase. Since both phases are structurally described by the triangle-square tiling scheme related to that of the dodecagonal quasicrystal, which imposes geometric frustration of the AFM-coupled spins on triangles, the absence of spin-glass transition in the hex-Mn(76)Si(18)Cr(6) could be due to shifting of this transition below the lowest temperature of our experimental setup, as a consequence of weaker spin coupling and smaller moment sizes in the hex phase. In both investigated samples, tiny Mn(3)O(4) inclusions that undergo a transition to a ferrimagnetic phase at T(C) approximate to 42 K were detected in the magnetic signal. Geometric frustration of interactions between the AFM-coupled spins placed at the vertices of the triangle-square tiling should be a general feature of dodecagonal quasicrystals and their approximants, so that spin-glass-type ordering is expected to occur quite commonly in the dodecagonal phases.
Title:
Deformed triangular lattice antiferromagnets in a magnetic field: Role of spatial anisotropy and Dzyaloshinskii-Moriya interactions
Authors:
Griset, C; Head, S; Alicea, J; Starykh, OA Author Full Names: Griset, Christian; Head, Shane; Alicea, Jason; Starykh, Oleg A.
Source:
PHYSICAL REVIEW B, 84 (24):10.1103/PhysRevB.84.245108 DEC 12 2011
Abstract:
Recent experiments on the anisotropic spin-1/2 triangular antiferromagnet Cs(2)CuBr(4) have revealed a remarkably rich phase diagram in applied magnetic fields, consisting of an unexpectedly large number of ordered phases. Motivated by this finding, we study the role of three ingredients-spatial anisotropy, Dzyaloshinskii-Moriya interactions, and quantum fluctuations-on the magnetization process of a triangular antiferromagnet, coming from the semiclassical limit. The richness of the problem stems from two key facts: (1) the classical isotropic model with a magnetic field exhibits a large accidental ground-state degeneracy and (2) these three ingredients compete with one another and split this degeneracy in opposing ways. Using a variety of complementary approaches, including extensive Monte Carlo numerics, spin-wave theory, and an analysis of Bose-Einstein condensation of magnons at high fields, we find that their interplay gives rise to a complex phase diagram consisting of numerous incommensurate and commensurate phases. Our results shed light on the observed phase diagram for Cs(2)CuBr(4) and suggest a number of future theoretical and experimental directions that will be useful for obtaining a complete understanding of this material's interesting phenomenology.
Title:
Structure and Morphology of Induction-Melted Higher Manganese Silicide
Authors:
Zhou, AJ; Cui, HG; Li, JZ; Zhao, XB Author Full Names: Zhou Ai-Jun; Cui Heng-Guan; Li Jing-Ze; Zhao Xin-Bing
Source:
ACTA PHYSICO-CHIMICA SINICA, 27 (12):2915-2919; 10.3866/PKU.WHXB20112915 DEC 2011
Abstract:
Field emission scanning microscopy (FESEM) and energy-dispersive X-ray spectroscopy (EDXS) were used to study the morphology and composition of secondary phase precipitations in induction-melted higher manganese silicide (HMS). Striations of the secondary phase were observed in individual HMS crystals with an average interval of 5-30 pm and a thickness of similar to 30 nm. The chemical composition of the striations was examined and found to be MnSi, which was observed as an amorphous phase by high resolution transmission electron microscopy (HRTEM). The crystal structure of HMS was determined by selective area electron diffraction (SAED) and the results indicated a single Mn(4)Si(7) phase in the as-prepared material and no other incommensurate HMS phases were found. After ball milling and hot pressing many defects and stress fields were observed in the HMS by transmission electron microscope (TEM), which differentiated substantially from the morphology of the as-melted HMS.
Title:
Phase diagram of hard tetrahedra
Authors:
Haji-Akbari, A; Engel, M; Glotzer, SC Author Full Names: Haji-Akbari, Amir; Engel, Michael; Glotzer, Sharon C.
Source:
JOURNAL OF CHEMICAL PHYSICS, 135 (19):10.1063/1.3651370 NOV 21 2011
Abstract:
Advancements in the synthesis of faceted nanoparticles and colloids have spurred interest in the phase behavior of polyhedral shapes. Regular tetrahedra have attracted particular attention because they prefer local symmetries that are incompatible with periodicity. Two dense phases of regular tetrahedra have been reported recently. The densest known tetrahedron packing is achieved in a crystal of triangular bipyramids (dimers) with a packing density of 4000/4671 approximate to 85.63%. In simulation a dodecagonal quasicrystal is observed; its approximant, with periodic tiling (3.4.3(2).4), can be compressed to a packing fraction of 85.03%. Here, we show that the quasicrystal approximant is more stable than the dimer crystal for packing densities below 84% using Monte Carlo computer simulations and free energy calculations. To carry out the free energy calculations, we use a variation of the Frenkel-Ladd method for anisotropic shapes and thermodynamic integ ration. The enhanced stability of the approximant can be attributed to a network substructure, which maximizes the free volume (and hence the wiggle room) available to the particles and facilitates correlated motion of particles, which further contributes to entropy and leads to diffusion for packing densities below 65%. The existence of a solid-solid transition between structurally distinct phases not related by symmetry breaking - the approximant and the dimer crystal - is unusual for hard particle systems. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3651370]
Title:
Formation of Icosahedral Quasicrystals and 1/1 Crystal Approximants in Al-Pd-RE (RE: Rare Earth Metals) Systems
Authors:
So, YG; Yoshikawa, T; Saruhashi, F; Edagawa, K; Tamura, R Author Full Names: So, Yeong-Gi; Yoshikawa, Takuro; Saruhashi, Fukuaki; Edagawa, Keiichi; Tamura, Ryuji
Source:
MATERIALS TRANSACTIONS, 52 (11):2011-2015; 10.2320/matertrans.M2011162 NOV 2011
Abstract:
We have investigated the formation of an icosahedral quasicrystal (i-phase) and its 1/1-crystal approximant (1/1-phase) in the (Al, Ga)-Pd-RE (Rare earth metals) systems. Consequently, the Ga-Pd-Sc 1/1-phase, the Al-Pd-RE (RE = Yb, Tin and Er) 1/1-phase and the Al-Pd-Yb i-phase have been newly found by the substitution of Al for Ga, or Sc for other RE in the constituent elements of the Al(54)Pd(30)Sc(16) i-phase previously reported. For the i- and the 1/1-phases studied in this work, the number of valence electrons per atom (e/a) ratio is 2.10 and the atomic radius ratio of the rare earth element to that of the other base elements is in the range 1.15-1.24, which fulfilled the formation conditions previously reported for other Tsai-type i-phases. On the other hand, the stability of the i-phases becomes lower with increasing the atomic radii of the RE elements, which indicates that the atomic radius ratio plays important role in the formation of the Al-Pd-RE i- and 1/1-phases. [doi:10.2320/matertrans.M2011162]
Title:
Ti/Pr(0.7)Ca(0.3)MnO(3)/La(0.67)Sr(0.33)MnO(3)/Pt heterostructures
Authors:
Wang, ZW; Zhang, J; Li, HW; Dong, CY; Zhao, J; Zhao, X; Chen, W Author Full Names: Wang Zhong-Wei; Zhang Jian; Li Hong-Wei; Dong Chun-Ying; Zhao Jing; Zhao Xu; Chen Wei
Source:
ACTA PHYSICA SINICA, 60 (11):NOV 2011
Abstract:
Ti/Pr(0.7)Ca(0.3)MnO(3)/Pt and Ti/Pr(0.7)Ca(0.3)MnO(3)/La(0.67)Sr(0.33)MnO(3)/Pt heterostructures are prepared using a pulsed laser deposition (PLD) technique, and the resistive switching of the heterostructures is investigated. The Ti/Pr(0.7)Ca(0.3)MnO(3)/La(0.67)Sr(0.33)MnO(3)/Pt heterostructure, which has a La(0.67)Sro(0.33)MnO(3) modulation layer, shows superior characteristics of resistive switching. In particular, the switching ratio and the fatigue properties are improved greatly in this heterostructure. The mechanism of resistive switching in Ti/Pr(0.7)Ca(0.3)MnO(3)/La(0.67)Sr(0.33)MnO(3)/Pt heterostructure is also discussed in this paper.

Update: 19-Jan-2012

Title:
Evolution of the commensurate and incommensurate magnetic phases of the S=3/2 kagome staircase Co(3)V(2)O(8) in an applied field
Authors:
Helton, JS; Chen, Y; Bychkov, GL; Barilo, SN; Rogado, N; Cava, RJ; Lynn, JW Author Full Names: Helton, Joel S.; Chen, Ying; Bychkov, Georgii L.; Barilo, Sergei N.; Rogado, Nyrissa; Cava, Robert J.; Lynn, Jeffrey W.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 24 (1):10.1088/0953-8984/24/1/016003 JAN 11 2012
Abstract:
Single crystal neutron diffraction studies have been performed on the S = 3/2 kagome staircase compound Co(3)V(2)O(8) with a magnetic field applied along the magnetization easy-axis ((H) over right arrow parallel to(a) over right arrow). Previous zero- field measurements (Chen Y et al 2006 Phys. Rev. B 74 014430) reported a rich variety of magnetic phases, with a ferromagnetic ground state as well as incommensurate, transversely polarized spin density wave (SDW) phases (with a propagation vector of (k) over right arrow = (0 delta 0)) interspersed with multiple commensurate lock-in transitions. The magnetic phase diagram with ((H) over right arrow parallel to(a) over right arrow) adds further complexity. For small applied fields, mu(0)H approximate to 0.05 T, the commensurate lock-in phases are destabilized in favor of the incommensurate SDW ones, while slightly larger applied fields restore the commensurate lock-in phase with delta = 1/2 and yield a new commensurate phase with delta = 2/5. For measurements in an applied field, higher-order scattering is observed that corresponds to the second harmonic.
Title:
Microstructures and mechanical properties of quasicrystal reinforced AZ31 matrix composites
Authors:
Wang, XD; Du, WB; Wang, ZH; Liu, K; Li, SB Author Full Names: Wang, Xudong; Du, Wenbo; Wang, Zhaohui; Liu, Ke; Li, Shubo
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 530 446-451; 10.1016/j.msea.2011.09.110 DEC 15 2011
Abstract:
In order to improve the mechanical properties of AZ31 alloys, the repeated plastic working process was employed to fabricate the AZ31-based composites reinforced with stable icosahedral quasicrystal particles. The microstructure of the composites has been investigated by XRD, SEM, TEM and HREM, and their mechanical properties have also been studied. The results showed that the RPW process reduced the grain size significantly, and the average grain size was only about 500 nm after 200 cycles of RPW. A good metallurgical bond interface between the quasicrystal particles and the Mg matrix was found in their crystallographic orientation relationship of (1 0 (1) over bar 0)(mg)//2-f. The composites exhibited the maximum yield tensile strength of 334 MPa and the maximum ultimate tensile strength of 372 MPa at room temperature, respectively. The enhanced mechanical properties were attributed to the strengthening effect of quasicrystal particles and the refined microstructure. (C) 2011 Elsevier B.V. All rights reserved.
Title:
Effects of the commensurability and disorder on friction for the system Xe/Cu
Authors:
Franchini, A; Bortolani, V; Santoro, G; Xheka, K Author Full Names: Franchini, A.; Bortolani, V.; Santoro, G.; Xheka, K.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 23 (48):10.1088/0953-8984/23/48/484004 DEC 7 2011
Abstract:
We present molecular dynamics simulations of static friction for a monolayer of Xe deposited on a thick slab of Cu for two different geometries. The interaction potential between Xe and Cu has been derived from DFT calculations. The first geometry is the commensurate adsorption geometry (root 3 x root 3)R30 degrees suggested by LEED, corresponding to a coverage 1/3, where all Xe atoms are on top positions. The second one corresponds to a coverage 0.36 and is characterized by a large surface unit cell, containing 9 Xe atoms in different disordered positions. This large unit cell mimics an incommensurate case. Our analysis points out the effect of the order/disorder in tribological properties of a realistic three-dimensional system.
Title:
Resonant tunneling in GaAs/Al(x)Ga(1-x)As superlattices with aperiodic potential profiles
Authors:
Djelti, R; Aziz, Z; Bentata, S; Besbes, A Author Full Names: Djelti, R.; Aziz, Z.; Bentata, S.; Besbes, A.
Source:
SUPERLATTICES AND MICROSTRUCTURES, 50 (6):659-666; 10.1016/j.spmi.2011.09.007 DEC 2011
Abstract:
Using the exact Airy function formalism and the transfer-matrix technique, we have numerically investigated in this paper the effect of intentional correlations in spatial disorder on transmission properties of one-dimensional superlattices. Such systems consist of two different structures randomly distributed along the growth direction, with the additional constraint that barriers (wells) of one kind always appear in triply. It is shown that the intentional correlations in disorder and superlattices structural parameters are responsible to obtain resonant tunneling in aperiodic structure. (C) 2011 Elsevier Ltd. All rights reserved.
Title:
Structure, electrical and magnetic property investigations on dense Fe-doped hexagonal BaTiO(3)
Authors:
Wei, XK; Su, YT; Sui, Y; Zhang, QH; Yao, Y; Jin, CQ; Yu, RC Author Full Names: Wei, X. K.; Su, Y. T.; Sui, Y.; Zhang, Q. H.; Yao, Y.; Jin, C. Q.; Yu, R. C.
Source:
JOURNAL OF APPLIED PHYSICS, 110 (11):10.1063/1.3658813 DEC 1 2011
Abstract:
Hexagonal Ba(Ti(1-x)Fe(x))O(3-delta) (x = 1/6, 1/3) ceramics treated with post annealing are specifically synthesized to explore the origin mechanism of the unusual ferromagnetism in the doped system. X-ray diffraction refinements and transmission electron microscope experiments reveal that their structures are incommensurately modulated owing to simultaneous oxygen vacancies at both O1 and O2 sites. Consequently, coexisting weak ferrielectricity and weak ferromagnetism are presented at room temperature. Analysis on their leakage current plot reveals that their conduction follows trap-filled limit model. In combination with the magnetism studies on 5 mol% Fe-doped crystals [Phys. Rev. B 83, 144407 (2011)], the reduction of ferromagnetism with an increase of conductivity suggests that dynamic exchanges of trapped electrons among the bound magnetic polarons attribute to the intrinsic ferromagnetism. (C) 2011 American Institute of Physics. [doi:10.1063/1.3658813]
Title:
Analytic solutions to a finite width strip with a single edge crack of two-dimensional quasicrystals
Authors:
Li, W Author Full Names: Li Wu
Source:
CHINESE PHYSICS B, 20 (11):10.1088/1674-1056/20/11/116201 NOV 2011
Abstract:
In this paper, we investigate the well-known problem of a finite width strip with a single edge crack, which is useful in basic engineering and material science. By extending the configuration to a two-dimensional decagonal quasicrystal, we obtain the analytic solutions of modes I and II using the transcendental function conformal mapping technique. Our calculation results provide an accurate estimate of the stress intensity factors K(I) and K(II), which can be expressed in a quite simple form and are essential in the fracture theory of quasicrystals. Meanwhile, we suggest a generalized cohesive force model for the configuration to a two-dimensional decagonal quasicrystal. The results may provide theoretical guidance for the fracture theory of two-dimensional decagonal quasicrystals.
Title:
On a Realistic Growth Mechanism for Quasicrystals
Authors:
Steurer, W Author Full Names: Steurer, Walter
Source:
ZEITSCHRIFT FUR ANORGANISCHE UND ALLGEMEINE CHEMIE, 637 (13):1943-1947; SI 10.1002/zaac.201100210 NOV 2011
Abstract:
Simple rules are discussed that can guide under realistic conditions the growth of quasicrystals. We propose a two-step mechanism where the well-known overlap rules for the fundamental atomic clusters are complemented by the new layer-continuation rule. This rule demands that the sets of atomic layers, crisscrossing each atomic cluster according to its eigensymmetry, have to be continued across all other clusters formed during the growth process. On one hand, this combined growth rule is local because each fundamental cluster already defines the overlap rules as well as the basic set of atomic layers. On the other hand, it is global because the framework of atomic layers originating locally from each cluster extends infinitely. The layer-continuation rule guides the attachment of atoms to the growing quasicrystal and assists the overlap rules, which are at the high temperatures, where crystal growth takes place, only weakly supported by specific atomic arrangements in the shared cluster volumes.
Title:
Proton NMR study of the organic metal kappa-(BETS)(2)Mn[N(CN)(2)](3)
Authors:
Vyaselev, OM; Kushch, ND; Yagubskii, EB Author Full Names: Vyaselev, O. M.; Kushch, N. D.; Yagubskii, E. B.
Source:
JOURNAL OF EXPERIMENTAL AND THEORETICAL PHYSICS, 113 (5):835-841; 10.1134/S106377611114010X NOV 2011
Abstract:
Magnetic properties of the organic conductor kappa-(BETS)(2)Mn[N(CN)(2)](3) above and below the temperature of the metal-insulator transition that occurs at T (MI) a parts per thousand 25 K are studied by (1)H NMR. The proton spectrum is shown to be determined by the static dipolar fields from Mn(2+) localized moments, while the (1)H spin-lattice relaxation is dominated by fluctuating fields from Mn(2+) electrons. The NMR data, both static (the spectra) and dynamic (the spin-lattice relaxation), indicate the freezing of Mn(2+) moments into a short-range or an incommensurate long-range antiferromagnetic order below T (MI).
Title:
A Study of the Formation of Ln(2+x)Me(2-x)O(7-x/2) (Ln = Gd, Dy; Me = Zr, Hf) Nanocrystals
Authors:
Popov, VV; Zubavichus, YV; Petrunin, VF; Menushenkov, AP; Kashurnikova, OV; Korovin, SA; Chernikov, RV; Yaroslavtsev, AA Author Full Names: Popov, V. V.; Zubavichus, Ya. V.; Petrunin, V. F.; Menushenkov, A. P.; Kashurnikova, O. V.; Korovin, S. A.; Chernikov, R. V.; Yaroslavtsev, A. A.
Source:
GLASS PHYSICS AND CHEMISTRY, 37 (5):512-520; 10.1134/S1087659611050117 OCT 2011
Abstract:
It has been established that the process of producing the Ln(2+x)Me(2-x)O(7-x/2) (Ln = Gd, Dy; Me = Zr, Hf) nanocrystals by calcination of hydroxides, which, in turn, have been produced by coprecipitation of metal salts, includes several stages. At the beginning, the X-ray amorphous structure of the precursors remains unchanged during dehydration; during subsequent heating to 600-700 degrees C, nanocrystals with a disordered fluorite structure begin to be formed. An increase in the temperature above 700 degrees C leads to an increase in the size of crystallites (coherent scattering regions). This process is accompanied by changes occurring in their local structure. In the nanocrystalline powders of Cd(2)Hf(2)O(7) and Gd(2)Zr(2)O(7) synthesized at 1200 degrees C (6 h), the pyrochlore-type superstructure with the lattice parameters doubled relative to fluorite has been revealed. It has also been found that, possibly, the Dy(2)HfO(5) sample at 1600 degrees C (3 h) has a modulated structure.

Update: 11-Jan-2012

Title:
Ordered fluorite phases in the Bi(2)O(3)-Ta(2)O(5) system: A structural and electrical investigation
Authors:
Struzik, M; Malys, M; Wrobel, W; Abrahams, I; Krok, F; Dygas, JR Author Full Names: Struzik, M.; Malys, M.; Wrobel, W.; Abrahams, I.; Krok, F.; Dygas, J. R.
Source:
SOLID STATE IONICS, 202 (1):22-29; 10.1016/j.ssi.2011.08.009 NOV 2 2011
Abstract:
Structure and electrical behaviour are reported for the system Bi(1-x)Ta(x)O(1.5+x) (0.167 <= x <= 0.250). In the compositional range 0.200 < x <= 0.250 an incommensurately modulated pseudo-cubic phase (type II) is observed, with the appearance of a larger pseudo-cubic phase in the region 0.167 <= x <= 0.200. Structural analysis of the type II phases by neutron diffraction reveals subtle changes in the oxide ion distribution with temperature, associated with changes in the incommensurate modulation parameter. Analysis of the defect structure of the type II phase reveals chains of tantalate octahedra as a likely structural motif. It is proposed that these chains facilitate an electronic contribution to total conductivity at low temperatures through electron hopping along the chains. Changes in oxide ion vacancy ordering may explain the observed non-linear behaviour in the thermal expansion of lattice parameter and Arrhenius plots of total conductivity. (C) 2011 Elsevier B.V. A! ll rights reserved.

Update: 4-Jan-2012

Title:
Nobel Prize in Chemistry honors the discovery of quasicrystals
Authors:
Smart, AG Author Full Names: Smart, Ashley G.
Source:
PHYSICS TODAY, 64 (12):17-20; DEC 2011

M.D.

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