Update: 3-Oct-2019


Title:
Magnetic ground state of the frustrated spin-1/2 chain compound beta-TeVO4 at high magnetic fields
Authors:
Pregelj, M; Zorko, A; Klanjsek, M; Zaharko, O; White, JS; Prokhnenko, O; Bartkowiak, M; Nojiri, H; Berger, H; Arcon, D Author Full Names: Pregelj, M.; Zorko, A.; Klanjsek, M.; Zaharko, O.; White, J. S.; Prokhnenko, O.; Bartkowiak, M.; Nojiri, H.; Berger, H.; Arcon, D.
Source:
PHYSICAL REVIEW B, 100 (9):10.1103/PhysRevB.100.094433 SEP 19 2019
Abstract:
Frustrated spin-1/2 chains, despite the apparent simplicity, exhibit a remarkably rich phase diagram comprising vector-chiral (VC), spin-density-wave (SDW), and multipolar/spin-nematic phases as a function of the magnetic field. Here we report a study of beta-TeVO4, an archetype of such compounds, based on magnetization and neutron diffraction measurements up to 25 T. We find the transition from the helical VC ground state to the SDW state at similar to 3 T for the magnetic field along the a and c crystal axes, and at similar to 9 T for the field along the b axis. The high-field (HF) state, existing above similar to 18 T, i.e., above similar to 1/2 of the saturated magnetization, is an incommensurate magnetically ordered state and not the spin-nematic state, as theoretically predicted for the isotropic frustrated spin-1/2 chain. The HF state is likely driven by sizable interchain interactions and symmetric intrachain anisotropies uncovered in previous studies. Consequently, the potential existence of the spin-nematic phase in beta-TeVO4 is limited to a narrow field range, i.e., a few tenths of a tesla bellow the saturation of the magnetization, as also found in other frustrated spin-1/2 chain compounds.

Title:
Metallic-mean quasicrystals as aperiodic approximants of periodic crystals
Authors:
Nakakura, J; Ziherl, P; Matsuzawa, J; Dotera, T Author Full Names: Nakakura, Joichiro; Ziherl, Primoz; Matsuzawa, Junichi; Dotera, Tomonari
Source:
NATURE COMMUNICATIONS, 10 10.1038/s41467-019-12147-z SEP 17 2019
Abstract:
Ever since the discovery of quasicrystals, periodic approximants of these aperiodic structures constitute a very useful experimental and theoretical device. Characterized by packing motifs typical for quasicrystals arranged in large unit cells, these approximants bridge the gap between periodic and aperiodic positional order. Here we propose a class of sequences of 2-D quasicrystals that consist of increasingly larger periodic domains and are marked by an ever more pronounced periodicity, thereby representing aperiodic approximants of a periodic crystal. Consisting of small and large triangles and rectangles, these tilings are based on the metallic means of multiples of 3, have a 6-fold rotational symmetry, and can be viewed as a projection of a non-cubic 4-D superspace lattice. Together with the non-metallic-mean three-tile hexagonal tilings, they provide a comprehensive theoretical framework for the complex structures seen, e.g., in some binary nanoparticles, oxide films, and intermetallic alloys.

Title:
High strain rate behaviour of nano-quasicrystalline Al93Fe3Cr2Ti2 alloy and composites
Authors:
Pedrazzini, S; Galano, M; Audebert, F; Siegkas, P; Gerlach, R; Tagarielli, VL; Smith, GDW Author Full Names: Pedrazzini, S.; Galano, M.; Audebert, F.; Siegkas, P.; Gerlach, R.; Tagarielli, V. L.; Smith, G. D. W.
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 764 10.1016/j.msea.2019.138201 SEP 9 2019
Abstract:
We demonstrate the outstanding dynamic strength of nano-quasicrystalline Al93Fe3Cr2Ti2 at.% alloy and composites. Unlike most crystalline Al alloys, this alloy exhibits substantial strain rate sensitivity and retains ductility at high strain rates. This opens new pathways for use in safety-critical materials requiring impact resistance.

Title:
How Accurate Do X-ray Data Need To Be To Obtain a Reliable Order of Stability for Polymorphs? The Case Study of p-Hydroxyacetophenone Polymorphs
Authors:
Sztylko, M; Malinska, M; Petricek, V; Gutmann, MJ; Hoser, AA Author Full Names: Sztylko, Marcin; Malinska, Maura; Petricek, Vaclav; Gutmann, Matthias J.; Hoser, Anna A.
Source:
CRYSTAL GROWTH & DESIGN, 19 (9):5132-5141; 10.1021/acs.cgd.9b00518 SEP 2019
Abstract:
Technical progress in crystallographic instruments allows contemporary crystallographers to more routinely conduct excellent quality low-temperature diffraction measurements. As a result, even crystal structures that have been extensively studied at ambient conditions start to reveal their more complex nature. The importance of low-temperature measurements is discussed based on the new, modulated structures found for polymorphs of 4'-hydroxyacetophenone (HAP). Diffraction data for this polymorphic system have been collected in the temperature range from 40 K to 330 K. At 123 K, form II of HAP appears to be a new, commensurately modulated structure with a modulation vector q = [0.4, 0.0, 0.0]. The structure can be solved and refined with 10 molecules in the asymmetric unit. A further decrease of temperature to 40 K resulted in the discovery of a new, incommensurately modulated phase with four independent molecules in the P2(1) monoclinic space group with the modulation vector q = [0.37, 0.17, 0.0]. Consequences of modulation for the relative stability of polymorphs will be discussed.

Update: 26-Sep-2019


Title:
Structural correlation of magneto-electric coupling in polycrystalline TbMnO3 at low temperature
Authors:
Agarwal, H; Yadav, P; Lalla, NP; Alonso, JA; Srivastava, ON; Shaz, MA Author Full Names: Agarwal, Harshit; Yadav, Poonam; Lalla, N. P.; Alonso, J. A.; Srivastava, O. N.; Shaz, M. A.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 806 510-519; 10.1016/j.jallcom.2019.07.228 OCT 25 2019
Abstract:
The present study is focused on the structural correlation of magneto-electric coupling that exists in polycrystalline TbMnO3. The X-ray diffraction patterns are collected at various conditions, which are (1) at 300 K without a magnetic field, (2) at 2 K without magnetic field and (3) at 2 K with 7 Tesla magnetic fields. The structural transition in TbMnO3 has been observed at 2 K and some lattice modulation after applying the magnetic field at 2 K. The Rietveld refinement of TbMnO3 confirms the orthorhombic phase with centrosymmetric space group Pnma at 300 K. We have observed that the inversion symmetry breaks at 2 K and the polycrystalline TbMnO3 has been refined using a non-centrosymmetric orthorhombic space group which can be either Pn2(1)a or P2(1)ma. This structural transition confirms the presence of a ferroelectric phase at 2 K. After the application of 7 Tesla magnetic field, the signature of an incommensurate phase has been observed in polycrystalline TbMnO3 at 2 K. The DC magnetization behaviour with temperature M(T) and field M(H) reveals the antiferromagnetic behaviour of polycrystalline TbMnO3 below 42 K. We have also measured magneto-dielectric property of polycrystalline TbMnO3 at the low temperature, which confirms the strong magneto-electric coupling in polycrystalline TbMnO3 below the transition temperature. (C) 2019 Elsevier B.V. All rights reserved.

Title:
Highly dispersive magnons with spin-gap-like features in the frustrated ferromagnetic S=1/2 chain compound Ca2Y2Cu5O10 detected by inelastic neutron scattering
Authors:
Matsuda, M; Ma, J; Garlea, VO; Ito, T; Yamaguchi, H; Oka, K; Drechsler, SL; Yadav, R; Hozoi, L; Rosner, H; Schumann, R; Kuzian, RO; Nishimoto, S Author Full Names: Matsuda, M.; Ma, J.; Garlea, V. O.; Ito, T.; Yamaguchi, H.; Oka, K.; Drechsler, S-L; Yadav, R.; Hozoi, L.; Rosner, H.; Schumann, R.; Kuzian, R. O.; Nishimoto, S.
Source:
PHYSICAL REVIEW B, 100 (10):10.1103/PhysRevB.100.104415 SEP 12 2019
Abstract:
We report inelastic neutron scattering experiments in Ca2Y2Cu5O10 and map out the full one-magnon dispersion which extends up to a record value of 53 meV for frustrated ferromagnetic (FM) edge-sharing CuO2 chain (FFESC) cuprates. A homogeneous spin-1/2 chain model with a FM nearest-neighbor (NN), an antiferromagnetic (AFM) next-nearest-neighbor (NNN) inchain, and two diagonal AFM interchain couplings (ICs) analyzed within linear spin-wave theory (LSWT) reproduces well the observed strong dispersion along the chains and a weak one perpendicularly. The ratio alpha = vertical bar J(a2)/J(a1)vertical bar fall of the FM NN and the AFM NNN couplings is found as similar to 0.23, close to the critical point alpha(c) = 1/4 which separates ferromagnetically and antiferromagnetically correlated spiral magnetic ground states in single chains, whereas alpha(c) > 0.25 for coupled chains is considerably upshifted even for relatively weak IC. Although the measured dispersion can be described by homogeneous LSWT, the scattering intensity appears to be considerably reduced at similar to 11.5 and similar to 28 meV. The gaplike feature at 11.5 meV is attributed to magnon-phonon coupling whereas based on density matrix renormalization group simulations of the dynamical structure factor the gap at 28 meV is considered to stem partly from quantum effects due to the AFM IC. Another contribution to that gap is ascribed to the intrinsic superstructure from the distorting incommensurate pattern of CaY cationic chains adjacent to the CuO2 ones. It gives rise to nonequivalent CuO4 units and Cu-O-Cu bond angles Phi and a resulting distribution of all exchange integrals. The J's fitted by homogeneous LSWT are regarded as average values. The record value of the FM NN integral J(1) = 24 meV among FFESC cuprates can be explained by a nonuniversal Phi(not equal 90 degrees) and Cu-O bond length dependent anisotropic mean direct FM Cu-O exchange (K) over bar (pd) similar to 120 meV, similar to a value of 105 meV for Li2CuO2, in accord with larger values for La2CuO4 and CuGeO3 (similar to 110 meV) reported by Braden et al. [Phys. Rev. B 54, 1105 (1996)] phenomenologically. Enhanced K-pd values are also needed to compensate a significant AFM J(dd) >= 6 meV from the dd channel, generic for FFESC cuprates but ignored so far.

Title:
Growth interactions between icosahedral quasicrystals
Authors:
Senabulya, N; Shahani, AJ Author Full Names: Senabulya, Nancy; Shahani, Ashwin J.
Source:
PHYSICAL REVIEW MATERIALS, 3 (9):10.1103/PhysRevMaterials.3.093403 SEP 11 2019
Abstract:
We investigate the solidification pathways of a population of icosahedral quasicrystals in a liquid through in situ synchrotron x-ray tomography. The wealth of three-dimensional space- and time-resolved data enables us to test the predictions of various models and theories of crystallization on a quasi-crystal-forming alloy. Remarkably, we find the general evolution equation-that accounts for the competing effects of growth, coalescence, and coarsening-fits well our experimental data on surface area concentration. Furthermore, we quantify the orientation selection, screening length, and coarsening rate of the dodecahedra, and compare these results to that of periodic crystals. The latter is a full order of magnitude smaller than that of elemental metal dendrites in the limit of zero volume fraction, a reflection of the low solid-liquid interfacial energy of the icosahedral phase. Our paper provides the critical input data for microstructural models used for integrated computational materials engineering of complex intermetallics, including quasicrystals.

Title:
Multiple charge density waves compete in ternary rare-earth nickel carbides, RNiC2 (R: Y, Dy, Ho, and Er)
Authors:
Maeda, H; Kondo, R; Nogami, Y Author Full Names: Maeda, Hiroyuki; Kondo, Ryusuke; Nogami, Yoshio
Source:
PHYSICAL REVIEW B, 100 (10):10.1103/PhysRevB.100.104107 SEP 9 2019
Abstract:
Single-crystal x-ray-diffraction experiments and electrical resistivity measurements were performed on intermetallic compounds of formula RNiC2 [rare earth (R): Y, Dy, Ho, and Er]. In the series of diffraction studies, we found three kinds of satellite reflections that had different wave vectors [incommensurate q(1)(ic):(0.5, 0.5 + eta, 0) and commensurate q(1)(c):(0.5, 0.5, 0) and q(2c):(0.5, 0.5, 0.5)] at temperatures where their resistivities show anomalies, such as a hump, a sharp increase, or a dent. Satellite reflections with nearly identical wave vectors have also been reported in RNiC2 composed of earlier lanthanide atoms (GdNiC2 and TbNiC2). These results indicate the formation of a charge density wave (CDW) also in RNiC2 studied in this paper. We found strong competition between the q(1ic) and the q(2c) CDWs in DyNiC2 and YNiC2, and that only the q(2c) CDW existed in HoNiC2 and ErNiC2. Based on the results obtained in the present paper and those of SmNiC2, GdNiC2, and TbNiC2 reported before, we discuss the CDW transitions in the RNiC2 family.

Title:
Formation of Incommensurate Charge Density Waves in Cuprates
Authors:
Miao, H; Fumagalli, R; Rossi, M; Lorenzana, J; Seibold, G; Yakhou-Harris, F; Kummer, K; Brookes, NB; Gu, GD; Braicovich, L; Ghiringhelli, G; Dean, MPM Author Full Names: Miao, H.; Fumagalli, R.; Rossi, M.; Lorenzana, J.; Seibold, G.; Yakhou-Harris, F.; Kummer, K.; Brookes, N. B.; Gu, G. D.; Braicovich, L.; Ghiringhelli, G.; Dean, M. P. M.
Source:
PHYSICAL REVIEW X, 9 (3):10.1103/PhysRevX.9.031042 SEP 6 2019
Abstract:
Although charge density waves (CDWs) are omnipresent in cuprate high-temperature superconductors, they occur at significantly different wave vectors, confounding efforts to understand their formation mechanism. Here, we use resonant inelastic x-ray scattering to investigate the doping- and temperature-dependent CDW evolution in La2-xBaxCuO4 (x = 0.115-0.155). We discover that the CDW develops in two stages with decreasing temperature. A precursor CDW with a quasicommensurate wave vector emerges first at high temperature. This doping-independent precursor CDW correlation originates from the CDW phase mode coupled with a phonon and "seeds" the low-temperature CDW with a strongly doping-dependent wave vector. Our observation reveals the precursor CDW and its phase mode as the building blocks of the highly intertwined electronic ground state in the cuprates.

Title:
Reply to comment on Couzi et al. (2018): a phenomenological model for structural phase transitions in incommensurate alkane/urea inclusion compounds
Authors:
Christensen, K; Williams, PA; Patterson, R; Palmer, BA; Couzi, M; Guillaume, F; Harris, KDM Author Full Names: Christensen, Kirsten; Williams, P. Andrew; Patterson, Rhian; Palmer, Benjamin A.; Couzi, Michel; Guillaume, Francois; Harris, Kenneth D. M.
Source:
ROYAL SOCIETY OPEN SCIENCE, 6 (8):10.1098/rsos.190518 AUG 2019
Abstract:
In a recentpaper (Couzi et al. 2018 R. Soc. open sci. 5, 180058. (doi: 10.1098/rsos.180058)), we proposed a new phenomenological model to account for the I <-> II <->"III" phase sequence in incommensurate n-alkane/urea inclusion compounds, which represents an alternative interpretation to that proposed in work of Toudic et al. In a Comment (Toudic et al. 2019 R. Soc. open sci. 6, 182073. (doi: 10.1098/rsos. 182073)), Toudic et al. have questioned our assignment of the superspace group of phase II of n-nonadecane/urea, which they have previously assigned, based on a (3 + 2)-dimensional superspace, as C222(1)(00 gamma)(10 delta). In this Reply, we present new results from a comprehensive synchrotron single-crystal X-ray diffraction study of n-nonadecane/urea, involving measurements as a detailed function of temperature across the I <-> II <->"III" phase transition sequence. Our results demonstrate conclusively that "main reflections" (h, k, l, 0) with h+k odd are observed in phase II of n-nonadecane/urea (including temperatures in phase II that are just below the transition from phase I to phase II), in full support of our assignment of the (3+ 1)-dimensional superspace group P212121(00.) to phase II. As our phenomenological model is based on phase II and phase '' III '' of this incommensurate material having the same (3+ 1)-dimensional superspace group P2(1)2(1)2(1)(00 gamma), it follows that the new X-ray diffraction results are in full support of our phenomenological model.

Title:
Comment on Couzi et al. (2018): a phenomenological model for structural transitions in incommensurate alkane/urea inclusion compounds
Authors:
Toudic, B; Guerin, L; Mariette, C; Frantsuzov, I; Rabiller, P; Ecolivet, C; Hollingsworth, MD Author Full Names: Toudic, B.; Guerin, L.; Mariette, C.; Frantsuzov, I.; Rabiller, P.; Ecolivet, C.; Hollingsworth, Mark D.
Source:
ROYAL SOCIETY OPEN SCIENCE, 6 (8):10.1098/rsos.182073 AUG 2019

Title:
Compression behavior of selected laser melted Al/quasicrystal composite lattice structure
Authors:
Kang, N; Lin, X; Xu, J; Joguet, D; Li, Q; Liao, HL; Huang, WD; Coddet, C Author Full Names: Kang, N.; Lin, X.; Xu, J.; Joguet, D.; Li, Q.; Liao, H. L.; Huang, W. D.; Coddet, C.
Source:
JOURNAL OF LASER APPLICATIONS, 31 (2):10.2351/1.5096152 MAY 2019
Abstract:
In this work, Al/quasicrystal (QC) composite lattice samples with several cellular sizes ranging from 1.5 to 5 mm were manufactured using selective laser melting (SLM). The porosity of all the designed lattice structure samples is fixed as 50%. The morphology of QC reinforcement on the top surface changes from micro desquamated to nano in situ reacted, as the cellular size increases. The result indicates that cellular size has a significant influence on the compressive behavior of SLM processed lattice samples. As the cellular size increases from 1.5 to 5 mm, the fractural mechanism changes from three stages of linear elastic-plateau-densification to two stages of elastic collapse. Moreover, both the first peak compressive strength and the strain at failure decrease, when the cellular size increases. Furthermore, the SLM processed lattice 3 sample, which possesses a large cellular size, broke into small fragments after the compression test.

Update: 18-Sep-2019


Title:
Supercell refinement: a cautionary tale
Authors:
Lovelace, J; Petricek, V; Murshudov, G; Borgstahl, GEO Author Full Names: Lovelace, Jeffrey; Petricek, Vaclav; Murshudov, Garib; Borgstahl, Gloria E. O.
Source:
ACTA CRYSTALLOGRAPHICA SECTION D-STRUCTURAL BIOLOGY, 75 852-860; 10.1107/S2059798319011082 9 SEP 2019
Abstract:
Theoretically, crystals with supercells exist at a unique crossroads where they can be considered as either a large unit cell with closely spaced reflections in reciprocal space or a higher dimensional superspace with a modulation that is commensurate with the supercell. In the latter case, the structure would be defined as an average structure with functions representing a modulation to determine the atomic location in 3D space. Here, a model protein structure and simulated diffraction data were used to investigate the possibility of solving a real incommensurately modulated protein crystal using a supercell approximation. In this way, the answer was known and the refinement method could be tested. Firstly, an average structure was solved by using the 'main' reflections, which represent the subset of the reflections that belong to the subcell and in general are more intense than the 'satellite' reflections. The average structure was then expanded to create a supercell and refined using all of the reflections. Surprisingly, the refined solution did not match the expected solution, even though the statistics were excellent. Interestingly, the corresponding superspace group had multiple 3D daughter supercell space groups as possibilities, and it was one of the alternate daughter space groups that the refinement locked in on. The lessons learned here will be applied to a real incommensurately modulated profilin-actin crystal that has the same superspace group.

Title:
Coordination shells and coordination numbers of the vertex graph of the Ammann-Beenker tiling
Authors:
Shutov, A; Maleev, A Author Full Names: Shutov, Anton; Maleev, Andrey
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 75 746-757; 10.1107/S2053273319008179 5 SEP 2019
Abstract:
The vertex graph of the Ammann-Beenker tiling is a well-known quasiperiodic graph with an eightfold rotational symmetry. The coordination sequence and coordination shells of this graph are studied. It is proved that there exists a limit growth form for the vertex graph of the Ammann-Beenker tiling. This growth form is an explicitly calculated regular octagon. Moreover, an asymptotic formula for the coordination numbers of the vertex graph of the Ammann-Beenker tiling is also proved.

Title:
Robust minimal matching rules for quasicrystals
Authors:
Kalugin, P; Katz, A Author Full Names: Kalugin, Pavel; Katz, Andre
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 75 669-693; 10.1107/S2053273319008180 5 SEP 2019
Abstract:
A unified framework is proposed for dealing with matching rules of quasiperiodic patterns, relevant for both tiling models and real-world quasicrystals. The approach is intended for extraction and validation of a minimal set of matching rules, directly from the phased diffraction data. The construction yields precise values for the spatial density of distinct atomic positions and tolerates the presence of defects in a robust way.

Title:
Twinning and incommensurate modulation in baumoite, Ba-0.5[(UO2)(3)O8Mo2(OH)(3)](H2O)(similar to 3), the first natural Ba uranyl molybdate
Authors:
Elliott, P; Plasil, J; Petricek, V; Cejka, J; Bindi, L Author Full Names: Elliott, Peter; Plasil, Jakub; Petricek, Vaclav; Cejka, Jiri; Bindi, Luca
Source:
MINERALOGICAL MAGAZINE, 83 (4):507-514; 10.1180/mgm.2019.20 AUG 2019
Abstract:
Baumoite, Ba-0.5[(UO2)(3)O8Mo2(OH)(3)](H2O)(similar to 3), is a new mineral found near Radium Hill, South Australia, where it occurs in a granite matrix associated with baryte, metatorbernite, phurcalite and kaolinite. Baumoite forms thin crusts of yellow to orange-yellow tabular to prismatic crystals. The mineral is translucent with a vitreous lustre and pale yellow streak. Crystals are brittle, the fracture is uneven and show one excellent cleavage. The Mohs hardness is similar to 21/2 . The calculated density is 4.61 g/cm(3). Optically, baumoite crystals are biaxial (-), with alpha = 1.716(4), beta= 1.761(4), gamma = 1.767(4) (white light); and 2V(calc) = 42.2 degrees. Electron microprobe analyses gave the empirical formula Ba0.87Ca0.03Al0.04U2.97Mo2.02P0.03O22H11.99, based on 22 O atoms per formula unit. The eight strongest lines in the powder X-ray diffraction pattern are [d(obs )angstrom (I) (hkl)]: 9.175(39)(12 (1) over bar), 7.450(100)(020), 3.554(20)(221), 3.365(31)(004, 202), 1255(31)(123, 30 (2) over bar), 3.209(28)(12 (4) over bar), 3.067(33)(30 (3) over bar, 222, 32 (2) over bar) and 2.977(20)(142). Single-crystal X-ray studies (R-1 = 5.85% for 1892 main reflections) indicate that baumoite is monoclinic, superspace group X2/m(a0g)0s with X = (0,1/2,0,1/2), with unit-cell parameters: a = 9.8337(3), b = 15.0436(5), c = 14.2055(6) angstrom, beta = 108.978(3)degrees, V= 1987.25(13) angstrom(3) and Z = 4. The crystal structure is twinned and incommensurately modulated and is based upon sheets of U6+ and Mo6+ polyhedra of unique topology. Four independent cationic sites partially occupied by Ba atoms are located between the sheets, together with H2O molecules.

Title:
Debye temperature of single-crystal Cr with incommensurate and commensurate magnetic structure
Authors:
Dubiel, SM; Zukrowski, J Author Full Names: Dubiel, Stanislaw M.; Zukrowski, Jan
Source:
EPL, 127 (2):10.1209/0295-5075/127/26002 JUL 2019
Abstract:
Single crystals of Cr and Cr3%Mn doped with similar to 0.2 at.% Sn-119 were studied by means of Sn-119-site Mossbauer spectroscopy. Mossbauer spectra recorded in the temperature range of 78-300 K were analyzed using a hyperfine field distribution method. Additionally, the spectra recorded on the Cr3%Mn sample were analyzed in terms of three sextets. Derived therefrom values of a center shift, CS, were fitted to the Debye model yielded values of the Debye temperature, T-D = 477(56) K for Cr and T-D = 282(16) :K for Cr3%Mn. The difference in the T-D-value can be regarded as evidence that a spin-phonon coupling is different for the incommensurate and commensurate antiferromagnetic magnetic structure of chromium. Copyright (C) EPLA, 2019

Update: 11-Sep-2019


Title:
Al-Cu-Fe quasicrystals as the anode for lithium ion batteries
Authors:
Lan, X; Wang, HJ; Sun, ZH; Jiang, XY Author Full Names: Lan, Xiao; Wang, Haijuan; Sun, Zhanhao; Jiang, Xunyong
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 805 942-946; 10.1016/j.jallcom.2019.07.148 OCT 15 2019
Abstract:
In this paper, Al-Cu-Fe quasicrystal alloy was used as the anode material for lithium-ion batteries. The first specific discharge capacity of quasicrystal was 204 mA h/g. Cyclic voltammetry showed that the oxidation peak of the Al-Cu-Fe quasicrystal was at about 1.4 V. The reduction peak was at 0.3 V. The Al-Cu-Fe quasicrystals had a higher Li-ion diffusion impedance and Warburg impedance in the first cycle. X-ray diffraction analysis demonstrated that Li atoms enter into the quasicrystal structure and can-not fully leave the quasicrystal during the first charge-discharge cycle, which induces an irreversible capacity. (C) 2019 Elsevier B.V. All rights reserved.

Title:
High-pressure structural change in the ferroelectric layered perovskite Sr2Nb2O7
Authors:
Alanis, J; Ojeda-Galvan, HJ; Rodriguez-Aranda, MC; Rodriguez, AG; Garcia, HM; Iniguez, J; Mendoza, ME; Navarro-Contreras, HR Author Full Names: Alanis, Javier; Joazet Ojeda-Galvan, Hiram; Rodriguez-Aranda, M. C.; Rodriguez, A. G.; Moreno Garcia, Harumi; Iniguez, Jorge; Eugenia Mendoza, Maria; Navarro-Contreras, Hugo R.
Source:
PHYSICAL REVIEW B, 100 (5):10.1103/PhysRevB.100.054110 AUG 26 2019
Abstract:
The structural changes of sintered powder samples of perovskite-slab layered polycrystalline Sr2Nb2O7 (SNO) ferroelectric compound subjected to high pressures are here investigated. The samples were prepared using a solid-state reaction in the presence (SNOE) or absence (SNO) of an applied electric field. Density functional theory (DFT) calculations including hydrostatic pressure indicate that SNO's ferroelectricity remains up to 25 GPa in the structure of space group Cmc2(1) derived from the condensation of one zone-center soft phonon. The predicted DFT theoretical structural changes are discussed and compared with the results of the experimental Raman spectra as a function of pressure. The pressure-dependent spectra were recorded from atmospheric pressure up to 11.5 and 13.5 GPa for SNOE and SNO, respectively. Both samples underwent a pressure induced phase transition from an incommensurate to a commensurate state at room temperature, SNO at Pi-c = 6.5 +/- 0.2 GPa, and SNOE at Pi-c = 6.9 +/- 0.3 GPa. The DFT calculations enable the identification of the change in phase to the orthorhombic structure with the space group Cmc2(1). The experimental values for Pi-c are in reasonably good agreement with the theoretical predicted value of similar to 7.3 GPa. After the critical pressures, the number of observable phonons decreases, that is, when the compound adopts a higher symmetry structure, several phonons vanish abruptly in both the SNO and SNOE samples, as expected. The Raman spectra for both samples show hysteresis effects, that is, after the pressure is removed, a few extra lines remain visible, as well as many relative intensity changes and broadenings for some phonon bands. The bulk moduli of the Sr2Nb2O7 before and after Pi-c are calculated resulting in 117.0 and 147.8 GPa, respectively. The Gruneisen parameters of the phonons observed are finally calculated and discussed.

Title:
Spin-Orbital Density Wave and a Mott Insulator in a Two-Orbital Hubbard Model on a Honeycomb Lattice
Authors:
Zhu, Z; Sheng, DN; Fu, L Author Full Names: Zhu, Zheng; Sheng, D. N.; Fu, Liang
Source:
PHYSICAL REVIEW LETTERS, 123 (8):10.1103/PhysRevLett.123.087602 AUG 23 2019
Abstract:
Inspired by the recent discovery of correlated insulating states in twisted bilayer graphene, we study a two-orbital Hubbard model on the honeycomb lattice with two electrons per unit cell. Based on the real-space density matrix renormalization group simulation, we identify a metal-insulator transition around U-c/t = 2.5-3. In the vicinity of U-c, we find strong spin-orbital density wave fluctuations at commensurate wave vectors, accompanied by weaker incommensurate charge density wave fluctuations. The spin-orbital density wave fluctuations are enhanced with increasing system sizes, suggesting the possible emergence of long-range order in the two-dimensional limit. At larger U, our calculations indicate a possible nonmagnetic Mott insulator phase without spin or orbital polarization. Our findings offer new insight into correlated electron phenomena in twisted bilayer graphene and other multiorbital honeycomb materials.

Title:
Pinched P-E hysteresis loops in Ba4Sm2Fe0.5Ti3Nb6.5O30 ceramic with tungsten bronze structure
Authors:
Li, C; Hong, JS; Huang, YH; Ma, X; Fu, MS; Li, J; Liu, XQ; Wu, YJ Author Full Names: Li, Cheng; Hong, Jiang Sheng; Huang, Yu Hui; Ma, Xiao; Fu, Mao Sen; Li, Juan; Liu, Xiao Qiang; Wu, Yong Jun
Source:
APPLIED PHYSICS LETTERS, 115 (8):10.1063/1.5111360 AUG 19 2019
Abstract:
In the present work, single-phase Ba4Sm2Fe0.5Ti3Nb6.5O30 ceramics with a tetragonal tungsten bronze structure (TTB) were synthesized. Pinched polarization-electric field (P-E) hysteresis loops are observed below the Curie temperature (T-c) in the as-synthesized ceramics. The origin of the loops was thoroughly studied using in situ TEM and XRD. The in situ selected area electron diffraction (SAED) patterns showed that the pinched loops originated from the coexistence of polar commensurate and nonpolar incommensurate superlattice reflections. In situ XRD results revealed increasing tetragonality with rising temperature, implying that the enhancement in octahedral tilting was closely related to the commensurate-incommensurate structural modulation.

Update: 5-Sep-2019


Title:
Low temperature magnetic and x-ray diffraction studies of YBa1-xSrxCuFeO5 (x=0, 0.5)
Authors:
Lai, S; Mukherjee, K; Yadav, CS Author Full Names: Lai, Surender; Mukherjee, K.; Yadav, C. S.
Source:
PHYSICA B-CONDENSED MATTER, 570 191-193; 10.1016/j.physb.2019.06.034 OCT 1 2019
Abstract:
We report low temperature magnetic and structural properties of Sr doped layered perovskite material YBaCuFeO5. YBaCuFeO5 is the antiferromagnetic compound with commensurate to incommensurate transition temperature at 200 K. Low temperature x-ray diffraction shows the lattice contraction effect with decreasing temperature. Below 15 K a strong bifurcation between the ZFC and FC curves has been observed in YBa0.5Sr0.5CuFeO5, which may arise due to lattice contraction effect which changes the interaction between the spin and the lattice.

Title:
Unique crystal structures and their applications as materials for Li1+x-yM1-x-3yTix+4yO3 (M = Nb or Ta, 0.07 <= x <= 0.33, 0 <= y <= 0.175)
Authors:
Nakano, H Author Full Names: Nakano, Hiromi
Source:
ADVANCED POWDER TECHNOLOGY, 30 (10):2003-2013; 10.1016/j.apt.2019.04.034 OCT 2019
Abstract:
In the Li2O-M2O5-TiO2 (M = Nb or Ta) system, Li1+x-yM1-x-3yTix+4yO3 (LMT) forms with a superstructure known as the M-phase, in which the periodical intergrowth layers are inserted in a matrix having a trigonal structure of LiMO3. We have been investigating this unique material focusing on its crystal structure, photoluminescence, and electrical properties. First, the formation area of the superstructure was compared between Nb- and Ta-systems and the difference was accurately analyzed. Second, to apply this unique material as a host material of phosphor, we synthesized new phosphors with various emission colors. Red phosphor, having a high PL intensity with an internal quantum efficiency of 98%, was successfully synthesized and used as a host material of the solid solution for the Ta system. Its high value was the result of the large centroid-to-cation distance of the Eu3+ position in the [(Li, Eu)O-12] polyhedral. Further still, toward application of the unique qualities of an electro-ceramic, we successfully fabricated oriented balk ceramics for the Nb system by slip casting in a strong magnetic field of 12 T. As a result, anisotropic electric properties were found along the c-axis, which were caused by the super-structure. We first clarified the mechanism showing that the anisotropic Qf value was due to anisotropic electron conductivity and anisotropic bonding strength within the superstructure. (C) 2019 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.

Title:
Structural, thermodynamic, thermal, and electron transport properties of single-crystalline LaPt2Si2
Authors:
Falkowski, M; Dolezal, P; Andreev, AV; Duverger-Nedellec, E; Havela, L Author Full Names: Falkowski, M.; Dolezal, P.; Andreev, A., V; Duverger-Nedellec, E.; Havela, L.
Source:
PHYSICAL REVIEW B, 100 (6):10.1103/PhysRevB.100.064103 AUG 20 2019
Abstract:
LaPt2Si2 in a single-crystalline form was subjected to structure, thermodynamic, thermal, and electron transport studies with a special emphasis on the structure phase transition appearing at T = 85 K. X-ray diffraction proves the noncentrosymmetric tetragonal structure of CaBe2Ge2-type (space group P4/nmm). The transition manifests as a small step of opposite sign in both lattice parameters, leaving almost no volume change. c decreases and a increases in the low-T phase, but the change of the c/a ratio does not exceed 0.1%. Additional periodicity, related to the supposed charge density wave (CDW) state, can be related to satellites corresponding to the wave vector q approximate to (0.36, 0, 0), which start to grow with temperature decreasing below 175 K and almost vanish (or relocate from the investigated ab plane) below the 85 K transition. Electrical resistivity reveals that the 85 K transition is hysteretic in temperature, with the difference between heating and cooling being almost 10 K, proving the first-order type of the transition. The transition dramatically enhances resistivity in the low-T state, pointing to a formation of a pseudogap. This, however, does allow a superconducting state, arising below T-c = 1.6 K. The temperature dependence up upper critical field is not compatible with the weak coupling BCS theory. Strong anisotropy of electronic structure and its dramatic changes at the structure transition are manifest also in thermal expansion and thermoelectric power. The Sommerfeld coefficient gamma = 7.8 mJ mol(-1) K-2 and Debye temperature of 205 K could be derived at low temperatures, but the specific heat has a strongly non-Debye like T dependence, which can be ascribed to a low-energy Einstein mode.

Title:
Superconducting phase diagram and nontrivial band topology of structurally modulated Sn1-xSbx
Authors:
Liu, B; Xiao, CC; Zhu, QQ; Wu, JF; Cui, YW; Wang, HD; Wang, ZC; Lu, YH; Ren, Z; Cao, GH Author Full Names: Liu, Bin; Xiao, Chengcheng; Zhu, Qinqing; Wu, Jifeng; Cui, Yanwei; Wang, Hangdong; Wang, Zhicheng; Lu, Yunhao; Ren, Zhi; Cao, Guang-han
Source:
PHYSICAL REVIEW MATERIALS, 3 (8):10.1103/PhysRevMaterials.3.084603 AUG 19 2019
Abstract:
We report the discovery of superconductivity in binary alloy Sn1-xSbx with x in the range of 0.43 to 0.6, which possesses a modulated rhombohedral structure due to the incommensurate ordering of Sn and Sb layers along the c axis. The specific heat measurements indicate a weakly coupled, fully gapped superconducting state in this homogeneity range with a maximum bulk T-c of 1.58 K at x = 0.46, though the electronic specific heat and Hall coefficients remain nearly x independent. The nonmonotonic dependence of the bulk T-c is discussed in relation to the effects of Sb-layer intercalation between the [Sn4Sb3] seven-layer lamellae that are the essential building blocks for superconductivity. On the other hand, a zero-resistivity transition is found to take place well above the bulk superconducting transition, and the corresponding T-c increases monotonically with x from 2.06 K to 3.29 K. This contrast, together with the uniform elements distribution revealed by energy dispersive x-ray mapping, implies that the resistive transition is due to the strain effect at the grain boundary rather than the compositional inhomogeneity. The first-principles calculations on the representative composition Sn 4 Sb 3 (x = 0.43) indicate that it is topologically nontrivial similar to Sb, but with different Z(2) invariants (0;111). Our results not only identify a second superconducting region in the Sn-Sb phase diagram, but also provide a viable platform to study the interplay between structural modulation, nontrivial band topology, and superconductivity.

Title:
Depth dependent ferroelectric to incommensurate/commensurate antiferroelectric phase transition in epitaxial lanthanum modified lead zirconate titanate thin films
Authors:
Gao, M; Tang, X; Dai, S; Li, JF; Viehland, D Author Full Names: Gao, Min; Tang, Xiao; Dai, Steve; Li, Jiefang; Viehland, D.
Source:
APPLIED PHYSICS LETTERS, 115 (7):10.1063/1.5113720 AUG 12 2019
Abstract:
Transmission electron microscopy was used to investigate the coexistence of ferroelectricity (FE) and antiferroelectricity (AFE) in (001) and (011) (Pb0.97, La0.02) (Zr0.95, Ti0.05) O3 (PLZT) epitaxial thin films. The depth resolved selected area electron diffraction (SAED) results revealed that the AFE phase was located in the near interface region, whereas the FE phase was found in the near surface region. A thickness dependent lattice parameter distribution was calculated using the SAED data, and a decrease in the c/a ratio was found to correlate with the transition from AFE to FE stability. Additionally, commensurate and incommensurate modulations in AFE PLZT were identified based on the observation of various superlattice reflections.

Update: 28-Aug-2019


Title:
Significantly improved cycling stability for electrochemical hydrogen storage in Ti1.4V0.6Ni alloy with TiN
Authors:
Yu, L; Lin, J; Liang, F; Wang, LM; Chang, LM; Wang, FK; Li, N Author Full Names: Yu, Lu; Lin, Jing; Liang, Fei; Wang, Limin; Chang, Limin; Wang, Fangkuo; Li, Na
Source:
MATERIALS RESEARCH BULLETIN, 118 10.1016/j.materresbull.2019.110509 OCT 2019
Abstract:
Ti1.4V0.6Ni alloy contained icosahedral quasicrystals can be electrochemically charged and discharged with the maximum capacity of approximately 270 mAh g(-1), however this alloy shows poor cycling stability, making it difficult to develop the practical application. Here, new TiN-added Ti1.4V0.6Ni composites are prepared by ball-milling. The electrochemical performance of the composites as negative active ingredient of Nickel-metal hydride(Ni-MH) battery is compared with Ti1.4V0.6Ni. Benefiting from the excellent catalysts for HER, electrical conductivity and resistance to oxidation/corrosion of TiN, TiN-added Ti1.4V0.6Ni composites exhibit excellent cycling stability as well as charge retention(89.7% after 24 h relaxation). The cycling capacity retention rate for these electrodes is approximately 80% after a preliminarytest of 50 continuous cycles. But meanwhile, the maxium discharge capacity falls into about 250 g(-1), and the electrocatalytic activity improvement is hightly demanded. This work presents a practical method for using TiN as an additive for enhancing the cycling stability of hydrogen storage alloy.

Title:
Whirling spin order in the quasicrystal approximant Au72Al14Tb
Authors:
Sato, TJ; Ishikawa, A; Sakurai, A; Hattori, M; Avdeev, M; Tamura, R Author Full Names: Sato, Taku J.; Ishikawa, Asuka; Sakurai, Akira; Hattori, Masashi; Avdeev, Maxim; Tamura, Ryuji
Source:
PHYSICAL REVIEW B, 100 (5):10.1103/PhysRevB.100.054417 AUG 13 2019
Abstract:
A neutron powder diffraction experiment has been performed on the quasicrystal approximant Au72Al14Tb14, a body-centered-cubic crystal of icosahedral spin clusters. The long-range antiferromagnetic order was confirmed at the transition temperature T-N = 10.4 K. The magnetic structure consists of noncoplanar whirling spins on the icosahedral clusters, arranged in an antiferroic manner. A simple icosahedral spin-cluster model with uniaxial anisotropy accounts well the whirling spin order as well as the in-field metamagnetic transition, indicating that the icosahedral symmetry is essential.

Title:
Theory of quantum oscillations in quasicrystals: Quantizing spiral Fermi surfaces
Authors:
Spurrier, S; Cooper, NR Author Full Names: Spurrier, Stephen; Cooper, Nigel R.
Source:
PHYSICAL REVIEW B, 100 (8):10.1103/PhysRevB.100.081405 AUG 13 2019
Abstract:
We show that electronic materials with disallowed rotational symmetries that enforce quasiperiodic order can exhibit quantum oscillations and that these are generically associated with exotic "spiral Fermi surfaces." These Fermi surfaces are self-intersecting, and characterized by a winding number of their surface tangent-a topological invariant-that is larger than one. We compute the nature of the quantum oscillations in two experimentally relevant settings which give rise to spiral Fermi surfaces: a "nearly-free-electron" quasicrystal, and 30 degrees twisted bilayer graphene.

Title:
The incommensurately modulated structures of volcanic plagioclase: displacement, ordering and phase transition
Authors:
Jin, SY; Xu, HF; Wang, XP; Zhang, DO; Jacobs, R; Morgan, D Author Full Names: Jin, Shiyun; Xu, Huifang; Wang, Xiaoping; Zhang, Dongzho; Jacobs, Ryan; Morgan, Dane
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 75 643-656; SI 10.1107/S2052520619006243 4 AUG 2019
Abstract:
Four basaltic phenocryst samples of plagioclase, with compositions ranging from An(48) (andesine) to An(64) (labradorite), have been studied with single-crystal X-ray and neutron diffraction techniques. The samples were also subjected to a heating experiment at 1100 degrees C for two weeks in an effort to minimize the Al-Si ordering in their structures. The average and the modulated structures of the samples (before and after the heating experiment) were compared, in order to understand the mechanism of the phase transition from the disordered C (1) over bar structure to the e-plagioclase structure. A comparison between the structures from neutron and X-ray diffraction data shows that the < T-O > distance does not solely depend on the Al occupancy as previously thought. A dramatic decrease of the Al-Si ordering is observed after heating at 1100 degrees C for two weeks for all four samples, with an obvious change in the intensities of the satellite reflections (e-reflections) in the diffraction pattern. Evident changes in the modulation period were also observed for the more calcic samples. No obvious change in the Ca-Na ordering was observed after the heating experiment. An in situ heating X-ray diffraction experiment was carried out on the andesine sample (An(48)) to study the change in the satellite intensity at high temperature. A dramatic weakening of the satellite peaks was observed between 477 degrees C and 537 degrees C, which strongly supports the displacive nature of the initiation of e2 ordering. Rigid-Unit Mode (RUM) analysis of the plagioclase structure suggests the initial position of the e-reflections is determined by the anti-RUMs in the framework.

Title:
Daliranite, PbHgAs2S5: determination of the incommensurately modulated structure and revision of the chemical formula
Authors:
Lanza, AE; Gemmi, M; Bindi, L; Mugnaioli, E; Paar, WH Author Full Names: Lanza, Arianna E.; Gemmi, Mauro; Bindi, Luca; Mugnaioli, Enrico; Paar, Werner H.
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 75 711-716; SI 10.1107/S2052520619007340 4 AUG 2019
Abstract:
The incommensurately modulated crystal structure of the mineral daliranite has been determined using 3D electron diffraction data obtained on nanocrystalline domains. Daliranite is orthorhombic with a = 21, b = 4.3, c = 9.5 angstrom and shows modulation satellites along c. The solution of the average structure in the Pnma space group together with energy-dispersive X-ray spectroscopy data obtained on the same domains indicate a chemical formula of PbHgAs2S5, which has one S fewer than previously reported. The crystal structure of daliranite is built from columns of face-sharing PbS8 bicapped trigonal prisms laterally connected by Hg[2+4] polyhedra and (As23+S5)(4-) groups. The excellent quality of the electron diffraction data allows a structural model to be built for the modulated structure in superspace, which shows that the modulation is due to an alternated occupancy of a split As site.

Update: 22-Aug-2019


Title:
Comparison of quantum spin Hall states in quasicrystals and crystals
Authors:
Huang, HQ; Liu, F Author Full Names: Huang, Huaqing; Liu, Feng
Source:
PHYSICAL REVIEW B, 100 (8):10.1103/PhysRevB.100.085119 AUG 8 2019
Abstract:
We theoretically study the quantum spin Hall states in an Ammann-Beenker-type octagonal quasicrystal and a periodic snub-square crystal, both sharing the same basic building blocks. Although the bulk states show significant differences in localization and transport properties, the topological phases manifest similarly in the two systems. This indicates the robustness of the topological properties regardless of symmetry and periodicity. We characterize the topological nature of the two systems with a nonzero topological invariant (spin Bott index B-s and Z(2) invariant), robust metallic edge states, and quantized conductance. In spite of some quantitative differences, the topological phase diagram of the two systems also exhibits similar behaviors, indicating that the topological phase transition is mainly determined by similar interactions in the two systems regardless of their structural difference. This is also reflected by the observation that the transition point between the normal insulator and the quantum spin Hall state in both systems follows a universal linear scaling relation for topological phase transitions.

Title:
The origin of the modulated structure in Sr2CuO3+delta (delta=0.4): [CuO2] in-plane oxygen vacancy or apical oxygen vacancy?
Authors:
Shen, X; Cao, LP; Zhao, JF; Wang, WP; Liu, QQ; Yao, Y; Li, JJ; Gu, CZ; Chen, MW; Jin, CQ; Yu, RC Author Full Names: Shen, Xi; Cao, Li-Peng; Zhao, Jian-Fa; Wang, Wei-Peng; Liu, Qing-Qing; Yao, Yuan; Li, Jun-Jie; Gu, Chang-Zhi; Chen, Ming-Wei; Jin, Chang-Qing; Yu, Ri-Cheng
Source:
JOURNAL OF THE AMERICAN CERAMIC SOCIETY, 10.1111/jace.16662
Abstract:
We propose the question of the modulated structures of copper oxide is caused by the [CuO2] in-plane oxygen vacancy or apical oxygen vacancy. Sr2CuO3+delta single-crystal samples were prepared using high-temperature and high-pressure methods. The major phase of Sr2CuO3+delta (delta = 0.4) single-crystal system is found to be constituted by the 5 root 2 a modulated structure with the Fmmm space group, which originates from the [CuO2] in-plane oxygen vacancy appearing in octahedral Cu-O. Besides, the presence of the [CuO2] in-plane oxygen vacancy may obliterate the superconductivity of the system. Experimental results deduce that the oxygen vacancy may appear in the apical oxygen sites in high-temperature copper oxide superconductors.

Title:
Formation of an Intermediate Valence Icosahedral Quasicrystal in the Au-Sn-Yb System
Authors:
Yamada, T; Nakamura, Y; Watanuki, T; Machida, A; Mizumaki, M; Nitta, K; Sato, A; Matsushita, Y; Tsai, AP Author Full Names: Yamada, Tsunetomo; Nakamura, Yoko; Watanuki, Tetsu; Machida, Akihiko; Mizumaki, Masaichiro; Nitta, Kiyofumi; Sato, Akira; Matsushita, Yoshitaka; Tsai, An-Pang
Source:
INORGANIC CHEMISTRY, 58 (14):9181-9186; 10.1021/acs.inorgchem.9b00801 JUL 15 2019
Abstract:
We report on the formation of a new icosahedral quasicrystal (iQC) in the Au-Sn-Yb alloy system. This iQC has a primitive icosahedral lattice with a lattice constant a(ico) of 0.5447(7) nm and a composition that was determined to be Au60.0Sn26.7Yb13.3. X-ray absorption spectroscopy measurement of the near Yb L-3 edge demonstrates that the Yb valence in the iQC is an intermediate valence between divalent (4f(14)) and trivalent (4f(13)) at ambient pressure and was determined to be 2.18+. The results are compared to those for a corresponding 2/1 cubic approximant crystal. The formation of this new iQC is discussed in terms of the atomic size factor (delta) and the valence electron-to-atom ratio (e/a).

Update: 15-Aug-2019


Title:
V-51-NMR study on the S=1/2 square lattice antiferromagnet K2V3O8
Authors:
Takeda, H; Yasuoka, H; Yoshida, M; Takigawa, M; Ghimire, NJ; Mandrus, D; Sales, BC Author Full Names: Takeda, H.; Yasuoka, H.; Yoshida, M.; Takigawa, M.; Ghimire, N. J.; Mandrus, D.; Sales, B. C.
Source:
PHYSICAL REVIEW B, 100 (5):10.1103/PhysRevB.100.054406 AUG 5 2019
Abstract:
Static and dynamic properties of the quasi-two-dimensional antiferromagnet K2V3O8 have been investigated by V-51-NMR experiments on nonmagnetic V5+ sites. Above the structural transition temperature T-S = 115 K, NMR spectra are fully compatible with the P4bm space-group symmetry. The formation of superstructure below T-S causes splitting of the NMR lines, which get broadened at lower temperatures so that individual peaks are not well resolved. Evolution of NMR spectra with magnetic field along the c axis below the magnetic transition temperature T-N similar to 4 K is qualitatively consistent with a simple Neel order and a spin-flop transition. However, a broad feature of the spectra does not rule out possible incommensurate spin structure. The spin-lattice relaxation rate 1/T-1 below T-N shows huge enhancement for a certain range of magnetic field, which is independent of temperature and attributed to cross relaxation due to anomalously large nuclear spin-spin coupling between V5+ and magnetic V4+ sites. The results indicate strong gapless spin fluctuations, which could arise from incommensurate orders or complex spin textures.

Title:
Interpretation of diffuse scattering using superspace crystallography
Authors:
Schmidt, EM; Neder, RB Author Full Names: Schmidt, Ella Mara; Neder, Reinhard B.
Source:
PHYSICAL REVIEW B, 100 (5):10.1103/PhysRevB.100.054201 AUG 2 2019
Abstract:
Single-crystal diffuse scattering is generally interpreted using correlation parameters that describe probabilities for certain configurations on a local scale. In this paper we present an interpretation of diffuse maxima using a disordered superspace approach. In (D + d)-dimensional superspace two modulation functions are disordered along the superspace axis a(s,i) for i = 1, . . . , D, while the periodicity along the internal dimensions is maintained. This simple approach allows the generation of substitutionally disordered model structures that show diffuse maxima of any width at any position in reciprocal space. The extinction rules that are introduced by superspace symmetry are also fulfilled by the diffuse maxima from structures generated using the disordered superspace approach. In this paper we demonstrate the disordered superspace approach using a simple two-dimensional binary substitutionally disordered system. The extension of the approach to (3 + d)-dimensional superspace is trivial. The treatment of displacement and magnetic disorder as well as size-effect-like distortions in a similar manner is possible.

Title:
Conduction electrons in aperiodic versus periodic structures: An ESR study of quasicrystalline i-Y(Gd)-Cd and its approximant Y(Gd)Cd-6
Authors:
Cabrera-Baez, M; Avila, MA; Rettori, C Author Full Names: Cabrera-Baez, M.; Avila, M. A.; Rettori, C.
Source:
PHYSICAL REVIEW B, 100 (1):10.1103/PhysRevB.100.014207 JUL 31 2019
Abstract:
A formal description of collective electronic states in condensed-matter systems lacking long-range periodicity remains a theoretical challenge. To experimentally explore the differences in electronic and magnetic behavior between metallic quasicrystals (QCs) and their conventional crystalline analogs [quasicrystal approximants (QCAs)], we have grown single crystals of Y1-xGdx-Cd6 (QCA) together with their QC counterparts i-Y1-xGdx-Cd for x = 0.006, 0.01, 0.1, and 1.00, and we carried out comparative T-dependent electron spin resonance (ESR) measurements. On the high Gd concentration side, x = 1.00, we confirm that GdCd6 adopts an antiferromagnetic ground state below T-N similar to 22 K, whereas i-Gd-Cd presents spin-glass-like behavior showing similar local and dynamical properties from the point of view of ESR. For the diluted samples, our ESR experimental results show similar local conduction electron polarization behavior at the Gd3+ site in all QC/QCA pairs investigated, supporting the validity of using QCAs as periodic representations of QCs in terms of short-range electronic interactions. However, there is a measurable difference in the Korringa relaxation rate (spin-flip relaxation process between the localized Gd3+ 4f electron and the delocalized s-type conduction electrons at the Fermi surface) between the QC/QCA pairs probably associated with the lack of periodicity. We expect that our comparative ESR study may provide support and motivation for the development of new theoretical approaches toward a generalized band-structure theory, contemplating condensed-matter systems beyond the scope of traditional periodicity.

Update: 8-Aug-2019


Title:
Elastic Properties of a FeGe2 Single Crystal
Authors:
Zainullina, RI; Milyaev, MA Author Full Names: Zainullina, R. I.; Milyaev, M. A.
Source:
PHYSICS OF THE SOLID STATE, 61 (7):1278-1283; 10.1134/S1063783419070321 JUL 2019
Abstract:
The report presents the results of studying the temperature dependences of the velocities of propagation of longitudinal and torsion waves and the internal friction in a tetragonal FeGe2 single crystal along crystallographic axes [100], [110], and [001]. At temperatures of magnetic phase transitions of T-1 approximate to 263 K and T-2 approximate to 289 K an abrupt decrease of sound velocities is detected. A high anisotropy of the internal friction is observed in the region of existence of an incommensurate magnetic structure (T-1 <= T <= T-2).

Title:
Transition Kinetics of Self-Assembled Supramolecular Dodecagonal Quasicrystal and Frank-Kasper sigma Phases in AB(n) Dendron-Like Giant Molecules
Authors:
Feng, XY; Liu, GX; Guo, D; Lang, KN; Zhang, RM; Huang, JH; Su, ZB; Li, YW; Huang, MJ; Li, T; Cheng, SZD Author Full Names: Feng, Xueyan; Liu, Gengxin; Guo, Dong; Lang, Kening; Zhang, Ruimeng; Huang, Jiahao; Su, Zebin; Li, Yiwen; Huang, Mingjun; Li, Tao; Cheng, Stephen Z. D.
Source:
ACS MACRO LETTERS, 8 (7):875-881; 10.1021/acsmacrolett.9b00287 JUL 2019
Abstract:
A series of noncrystalline AB dendron-like giant molecules DPOSS MPOSSn (n = 2-6, DPOSS: hydrophilic polyhedral oligomeric silsesquioxane (POSS) cage; MPOSS: hydrophobic POSS cage) were synthesized. These samples present a thermodynamically stable phase formation sequence from the hexagonal cylinder phase (plane group of P6mm), to the Frank Kasper (F-K) A15 phase (space group of Pm (3) over barn), and further to the F-K sigma phase (space group of P4(2)/mnm), with increasing the number of MPOSS in a single molecule (n, from 2 to 6). Moreover, for DPOSS MPOSS5 and DPOSS-MPOSS6, an intriguing dodecagonal quasicrystal (DQC) structure has been identified and revealed as a kinetic favorable metastable phase at lower temperatures, while the thermodynamically stable phase is the a phase. The detailed investigation of the transition kinetics between the DQC and a phase in these samples makes it possible to identify how the self-assembly directs the phase transition in terms of molecular and supramolecular aspects.

Update: 1-Aug-2019


Title:
TEM study of incommensurate superstructure in Pb1-0.5xNbx((Zr0.52Sn0.48)(0.955)Ti-0.045)(1-x)O-3 ceramics with 0-1 switching characteristic strain and high energy storage density
Authors:
Lyu, CG; Liu, YF; Lyu, YN; Qian, H; Li, M; Chen, FJ; Xi, H Author Full Names: Lyu, Chongguang; Liu, Yunfei; Lyu, Yinong; Qian, Hao; Li, Min; Chen, Fujun; Xi, Hao
Source:
JOURNAL OF MATERIALS SCIENCE-MATERIALS IN ELECTRONICS, 30 (13):12375-12381; 10.1007/s10854-019-01595-4 JUL 2019
Abstract:
Pb1-0.5xNbx((Zr0.52Sn0.48)(0.955)Ti-0.045)(1-x)O-3(PNZST-100x (x=0.01, 0.02, 0.03, 0.04)) antiferroelectric (AFE) ceramics were prepared using a solid-state method. X-ray diffraction analysis indicates a structural evolution from the tetragonal phase to the pseudocubic phase. When x=0.02, the ceramic exhibits an enhanced energy storage density of 1.37J/cm(3), and a strain, with 0-1 switching characteristics, of 0.22%. Selected-area electron diffraction (SAED), high-resolution transmission electron microscopy imaging, and in-situ TEM analyses indicate that there are two kinds of superlattice reflections, including the 1/2(hkl) superlattice reflection (h, k, and l: all odd) and 1/6.67(a+b) one-dimensional incommensurate superlattice reflections. The origin of the 1/2(hkl) superlattice reflection was the tilting of a(-)a(-)a(-) oxygen octahedra. Therefore, the 1/2(hkl) reflections were no longer superlattice reflections, but fundamental reflections in the trigonal system; hence, the reciprocal vector was re-expressed as H, where h, k, and l are integers and (-h+k+l)=3n. The incommensurate structure of the PNZST-2 ceramic originated from the displacement of Pb2+.

Title:
Bridging the local configurations and crystalline counterparts of bulk metallic glass by nanocalorimetry
Authors:
Zhao, BG; Yang, B; Rodriguez-Viejo, J; Wu, MN; Schick, C; Zhai, QJ; Gao, YL Author Full Names: Zhao, Bingge; Yang, Bin; Rodriguez-Viejo, Javier; Wu, Mannan; Schick, Christoph; Zhai, Qijie; Gao, Yulai
Source:
JOURNAL OF MATERIALS RESEARCH AND TECHNOLOGY-JMR&T, 8 (4):3603-3611; 10.1016/j.jmrt.2019.05.023 JUL-AUG 2019
Abstract:
The structural understanding of crystallization in bulk metallic glasses (BMGs) has attracted much attention while rapid crystallization occurring under controllable conditions is less involved. In this study, a Ce68Al10Cu20Co2 (at.%) BMG was thermally devitrified by differential scanning calorimetry (DSC) and nanocalorimetry. At a heating rate of 10 K/min by DSC, AlCe3 and Ce are the major crystalline phases after devitrification while Al13Co4 quasicrystals and Ce are the dominant phases in the crystallization products at a heating rate of 5000 K/s by nanocalorimetry. Attributing to the covalent-like bond in Al-Co atom pairs, Al13Co4 quasicrystals precipitate in the primary crystallization and work as the precursors associating local atomic configurations in the glassy state with crystalline phases after crystallization. Attributing to the enhanced mobility of Cu atoms, compositional redistribution occurs in the as-cast sample. On nanocalorimetry heating, an unambiguous discrepancy in the nucleation and growth of the nano-sized Al13Co4 quasicrystals is thus triggered, contributing to an obvious difference in the crystal size. This research unveils the distinct crystallization behaviors of Ce-based BMG on rapid heating. The formation of quasicrystals demonstrates the multi-stage crystallization on rapid heating and bridges the structural gap between local atomic configurations of metallic glasses and crystalline phases. (C) 2019 The Authors. Published by Elsevier B.V.

Update: 25-Jul-2019


Title:
New stable icosahedral quasicrystal in the system Al-Cu-Co-Fe
Authors:
Klyueva, M; Shulyatev, D; Andreev, N; Tabachkova, N; Sviridova, T; Suslov, A Author Full Names: Klyueva, Maria; Shulyatev, Dmitry; Andreev, Nikolay; Tabachkova, Natalia; Sviridova, Tatiana; Suslov, Alexey
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 801 473-477; 10.1016/j.jallcom.2019.06.056 SEP 15 2019
Abstract:
Based on the conceptual Al-Cu-(Fe + Co) phase diagram we found an optimal initial composition and developed a method to grow Al-Cu-Fe-Co single-grain quasicrystals. Our original two-stage cooling process includes (i) fast cooling of the melt down to the quasicrystalline single phase region with rate of similar to 165 K/h to prevent growing of nonquasicrystalline phases in the melt, and (ii) slow cooling down with rate of similar to 2-3 K/h to grow large (mm-size) single-grain quasicrystals. As a result a new stable quaternary Al-based icosahedral quasicrystal has been obtained. The chemical composition of the grown quasicrystal determined by both the energy dispersive X-ray analysis and inductively coupled plasma mass spectrometry was Al64.36Cu22.20CO3.05Fe10.39. Powder XRD and selected area electron diffraction were carried out for the phase identification and confirmed the icosahedral structure. The temperature dependencies of the electrical resistance measured on the oriented samples in the temperature range of 1.4 K-300 K is typical for icosahedral quasicrystals. (C) 2019 Elsevier B.V. All rights reserved.

Title:
Direct observation of growth and stability of Al-Cu-Fe quasicrystal thin films
Authors:
Parsamehr, H; Yang, CL; Liu, WT; Chen, SW; Chang, SY; Chen, LJ; Tsai, AP; Lai, CH Author Full Names: Parsamehr, Hadi; Yang, Chun-Liang; Liu, Wei-Ting; Chen, Shi-Wei; Chang, Shou-Yi; Chen, Lih-Juann; Tsai, An Pang; Lai, Chih-Huang
Source:
ACTA MATERIALIA, 174 1-8; 10.1016/j.actamat.2019.05.024 AUG 1 2019
Abstract:
Al-Cu-Fe based quasicrystal thin films exhibit unique surface and mechanical properties. To better understand the formation of the quasicrystal thin films, we observe direct growth of quasicrystals, prepared in a multilayer Al-Cu-Fe thin films with subsequent heat treatment, by in-situ synchrotron x-ray diffraction and in-situ transmission electron microscopy during heating and cooling. Using these two methods, we show that the ternary phase is more thermodynamically stable compared to the binary phases at temperature higher than 470 degrees C during the heating process, and quasicrystal formation occurs during the cooling process, specifically at 660 degrees C, after the sample has reached a liquid state. To distinguish quasicrystal from approximant crystals in the obtained thin film samples, we use high resolution x-ray diffraction to analyze the sample at room temperature. We reveal that the peak broadening increases monotonically along the twofold, threefold, and fivefold high-symmetry directions with the physical scattering vector but does not have systematic dependence on the phason momentum, which suggests that the thin film sample is indeed a quasicrystal instead of approximant crystals and it is almost free of phason strain. Our study provides a complete understanding of the growth mechanism for thin film Al-Cu-Fe quasicrystals, which is of particular importance for developing versatile applications of quasicrystal thin films. (C) 2019 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Title:
Enhanced electrochemical hydrogen storage performance of Ti49Zr26Ni25 alloy by doping with Pd nanoparticles deposited MWCNTs
Authors:
Zhang, L; Zhang, YN; Lv, DF; Liu, H; Zhao, JX; Chen, P; Liu, WQ Author Full Names: Zhang, Lei; Zhang, Yinan; Lv, Dongfang; Liu, Heng; Zhao, Jianxun; Chen, Peng; Liu, Wanqiang
Source:
SOLID STATE SCIENCES, 94 138-144; 10.1016/j.solidstatesciences.2019.06.007 AUG 2019
Abstract:
Mechanical alloying and subsequent annealing are used to fabricate the Ti49Zr26Ni25 quasicrystal. A complexation-reduction method is employed to obtain the Pd deposited multiwall carbon nanotubes (Pd/MWCNTs). Composite of Ti49Zr26Ni25 mixed with Pd/MWCNTs is obtained via ball-milling. The composite alloy combines the characteristics of Pd in conjunction with the advantages of MWCNTs. Pd exhibits outstanding electrocatalytic activity and MWCNTs provide high conductivity and large specific surface area. The electrochemical performance and kinetics properties of the alloy electrodes for Ni/MH secondary batteries are studied. A maximum discharge capacity of 274.6 mAh/g is achieved for Ti49Zr26Ni25 + Pd/MWCNTs, remarkably higher than that for original Ti49Zr26Ni25 (208.9 mAh/g). In addition, the composite shows improved cyclic stability and high-rate dischargeability. The synergistic effect of Pd and MWCNTs can decrease charge-transfer resistance and accelerate the hydrogen transmission, thus improving the reaction kinetics and electrochemical activity of the electrode.

Title:
Conventional superconductivity in quasicrystals
Authors:
Araujo, RN; Andrade, EC Author Full Names: Araujo, Ronaldo N.; Andrade, Eric C.
Source:
PHYSICAL REVIEW B, 100 (1):10.1103/PhysRevB.100.014510 JUL 11 2019
Abstract:
Motivated by a recent experimental observation of superconductivity in the Al-Zn-Mg quasicrystal, we study the low-temperature behavior of electrons moving in the quasiperiodic potential of the Ammann-Beenker tiling in the presence of a local attraction. We employ the Bogoliubov-de Gennes approach for approximants of different sizes and determine the local pairing amplitude Delta(i) as well its spatial average, Delta(0), the superconducting order parameter. Due to the lack of periodicity of the octagonal tiling, the resulting superconducting state is inhomogeneous, but we find no evidence of the superconductivity islands, as observed in disordered systems, with Delta(i) -> 0 at T-c for all sites. In the weak-coupling regime, we find that the superconducting order parameter depends appreciably on the approximant size only if the Fermi energy sits at a pseudogap in the noninteracting density of states, with Delta(0) decreasing as the system size increases. These results are in line with the experimental observations for the Al-Zn-Mg quasicrystal, and they suggest that, despite their electronic structure, quasicrystals are prone to display conventional BCS-like superconductivity.

Title:
Tomonaga-Luttinger Liquid Spin Dynamics in the Quasi-One-Dimensional Ising-Like Antiferromagnet BaCo2V2O8
Authors:
Faure, Q; Takayoshi, S; Simonet, V; Grenier, B; Mansson, M; White, JS; Tucker, GS; Ruegg, C; Lejay, P; Giamarchi, T; Petit, S Author Full Names: Faure, Quentin; Takayoshi, Shintaro; Simonet, Virginie; Grenier, Beatrice; Mansson, Martin; White, Jonathan S.; Tucker, Gregory S.; Ruegg, Christian; Lejay, Pascal; Giamarchi, Thierry; Petit, Sylvain
Source:
PHYSICAL REVIEW LETTERS, 123 (2):10.1103/PhysRevLett.123.027204 JUL 10 2019
Abstract:
Combining inelastic neutron scattering and numerical simulations, we study the quasi-one-dimensional Ising anisotropic quantum antiferromagnet BaCo2V2O8 in a longitudinal magnetic field. This material shows a quantum phase transition from a Neel ordered phase at zero field to a longitudinal incommensurate spin density wave at a critical magnetic field of 3.8 T. Concomitantly, the excitation gap almost closes and a fundamental reconfiguration of the spin dynamics occurs. These experimental results are well described by the universal Tomonaga-Luttinger liquid theory developed for interacting spinless fermions in one dimension. We especially observe the rise of mainly longitudinal excitations, a hallmark of the unconventional low-field regime in Ising-like quantum antiferromagnetic chains.

Title:
Structural and electronic properties of the incommensurate host-guest Bi-III phase
Authors:
Kartoon, D; Makov, G Author Full Names: Kartoon, D.; Makov, G.
Source:
PHYSICAL REVIEW B, 100 (1):10.1103/PhysRevB.100.014104 JUL 9 2019
Abstract:
At high pressure, bismuth acquires a complex incommensurate host-guest structure, only recently discovered. Characterizing the structure and properties of this incommensurate phase from first principles is challenging owing to its nonperiodic nature. In this study we use large-scale density functional theory calculations to model commensurate approximants to the Bi-III phase, and in particular to describe the atomic modulations with respect to their ideal positions, shown here to strongly affect the electronic structure of the lattice and its stability. The equation of state and range of stability of Bi-III are reproduced in excellent agreement with experiment using a fully relativistic model. We demonstrate the importance of employing large unit cells for the accurate description of the geometric and electronic configuration of Bi-III. In contrast, accurate description of the equation of state of bismuth is found to be primarily sensitive to the choice of pseudopotential and exchange-correlation function, while almost completely insensitive to the commensurate approximation.

Title:
Effect of heat treatment on the microstructure and micromechanical properties of the rapidly solidified Mg61.7Zn34Gd4.3 alloy containing icosahedral phase
Authors:
Luo, WB; Xue, ZY; Mao, WM Author Full Names: Luo, Wen-bo; Xue, Zhi-yong; Mao, Wei-min
Source:
INTERNATIONAL JOURNAL OF MINERALS METALLURGY AND MATERIALS, 26 (7):869-877; 10.1007/s12613-019-1799-4 JUL 2019
Abstract:
In this paper, the microstructure evolution of the rapidly solidified (RS) Mg61.7Zn34Gd4.3 (at%, atomic ratio) alloy at high temperatures was investigated. The hardness and elastic modulus of the main precipitated phases were also analyzed and compared with those of the alpha-Mg matrix on the basis of nanoindentation tests. The results show that the RS alloy consists of either a petal-like icosahedral quasicrystal (IQC) phase (similar to 20 mu m) and block-shaped H1 phase (similar to 15 mu m) or IQC particles with an average grain size of similar to 107 nm as well as a small proportion of amorphous phase, which mainly depends on the holding time at the liquid temperature and the thickness of the ribbons. The IQC phase gradually transforms at 400 degrees C to a short-rod-shaped mu-phase (Mg28.6Zn63.8Gd7.7) with a hexagonal structure. The hardness of the IQC phase is higher than that of H1 phase, and both phases exhibit a higher hardness than the alpha-Mg matrix and the mu-phase. The elasticity of the H1 phase is superior to that of the alpha-Mg matrix. The IQC phase possesses a higher elastic modulus than H1 phase. The easily formed H1 phase exhibits the poorest plastic deformation capacity among these phases but a higher elastic modulus than the alpha-Mg matrix.

Update: 17-Jul-2019


Title:
Comprehensive study of the magnetic phase transitions in Tb3Co combining thermal, magnetic and neutron diffraction measurements
Authors:
Herrero, A; Oleaga, A; Gubkin, AF; Frontzek, MD; Salazar, A; Baranov, NV Author Full Names: Herrero, A.; Oleaga, A.; Gubkin, A. F.; Frontzek, M. D.; Salazar, A.; Baranov, N., V
Source:
INTERMETALLICS, 111 10.1016/j.intermet.2019.106519 AUG 2019
Abstract:
A comprehensive study of the magnetic phase transitions in Tb3Co has been undertaken combining different techniques. Using single crystal neutron diffraction in the paramagnetic state a weak crystal structure distortion from the room temperature orthorhombic structure of the Fe3C type described with the Pnma space group toward structure with lower symmetry has been observed with cooling below 100 K. At 81 K there is a second order phase transition to an antiferromagnetic incommensurate phase with the propagation vector k = (0.155, 0, 0). As derived from thermal diffusivity measurements, the critical exponents for this transition are very close to the 3D-Heisenberg universality class, proving that the magnetic interactions are short-range but with a deviation from perfect isotropy due to crystal field effects. At T-2 approximate to 70 K there is another magnetic phase transition to a ferromagnetic state whose character is shown to be weakly first order. The low temperature magnetic state has a non-coplanar ferromagnetic structure with strong ferromagnetic components of Tb magnetic moments along the crystallographic c-axis. The application of an external magnetic field B = 2 T along the c crystallographic axis suppresses the incommensurate antiferromagnetic phase and gives rise to the ferromagnetic phase. The magnetic entropy peak change as well as the refrigerant capacity indicate that Tb3Co is a competitive magnetocaloric material in this temperature range.

Title:
Significantly improved plasticity of bulk metallic glasses by introducing quasicrystal within high energy glass matrix
Authors:
Liu, BC; Zhang, QD; Wang, HJ; Li, XY; Zu, FQ Author Full Names: Liu, Bao-Chuan; Zhang, Qi-Dong; Wang, Hui-Juan; Li, Xiao-Yun; Zu, Fang-Qiu
Source:
INTERMETALLICS, 111 10.1016/j.intermet.2019.106504 AUG 2019
Abstract:
Many studies consistently report that quasicrystal-BMG (bulk metallic glass) composites usually exhibit limited plasticity. In this work, however, we demonstrate that quasicrystal embedded in high energy glass matrix could remarkably improve the plasticity of BMGs. By the method, a Zr-based quasicrystal-BMG composite successfully exhibits > 50.0% compressive plasticity and > 6.6% bending strain, which is much higher than similar to 3.0% compressive plasticity in the monolithic as-cast BMG. After introducing quasicrystal within high energy glass matrix, the lower formation energy and difficulty to propagate of shear bands contribute to the enhanced plasticity. This work provides a new strategy to overcome the brittleness of BMGs and greatly promotes the practical value of quasicrystal in improving plasticity of BMGs.

Title:
Microstructural evolution and age-hardening behavior of quasicrystal-reinforced Mg-Dy-Zn alloy
Authors:
Bi, GL; Han, YX; Jiang, J; Jiang, CH; Li, YD; Ma, Y Author Full Names: Bi, Guang-Li; Han, Yu-Xiang; Jiang, Jing; Jiang, Chun-Hong; Li, Yuan-Dong; Ma, Ying
Source:
RARE METALS, 38 (8):739-745; 10.1007/s12598-018-1089-8 AUG 2019
Abstract:
Microstructural evolution and age-hardening behavior of Mg-2Dy-6Zn (at%) alloy during solid-solution and aging treatment were investigated. The microstructure of as-cast alloy is composed of -Mg, Mg3DyZn6 (I) phase, Mg3Dy2Zn3 (W) phase, Mg(Zn,Dy) phase and a small amount of Mg0.97Zn0.03 phases. After solid-solution treatment (480 degrees C, 12h), all the I phases and most W phases dissolve into -Mg matrix and the remainder W phases transform into Mg(Dy,Zn) phase and MgDy3 phase. During aging treatment, I phase and small amounts of W phases co-precipitate from -Mg matrix, respectively. The alloy exhibits a peak hardness of HV 77.5 at 200 degrees C for 8h. The excellent age-hardening behavior of alloy is mainly attributed to the co-precipitation strengthening of I and W phases.

Title:
Microstructure and mechanical properties of AZ31 magnesium alloy reinforced by I-phase
Authors:
Wu, HR; Du, WB; Li, SB; Liu, K; Wang, ZH Author Full Names: Wu, Hai-Rong; Du, Wen-Bo; Li, Shu-Bo; Liu, Ke; Wang, Zhao-Hui
Source:
RARE METALS, 38 (8):733-738; 10.1007/s12598-014-0390-4 AUG 2019
Abstract:
The particles of Mg-Zn-Gd icosahedral quasi-crystal master alloy were added into the AZ31 alloy by the repeated plastic working (RPW) process in order to improve the mechanical properties of the AZ31 alloy at room temperature. The microstructure and tensile properties of composites were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and tensile testing machine at room temperature. The results suggest that the RPW process can effectively refine the matrix and make the I-phase particles distribute uniformly. The ultimate tensile strength and the yield strength of the composites reach their maximum values of 362.3 and 330.5MPa, respectively, when the amount of I-phase particles added is 10%. Meanwhile, the elongation of the composites decreases sharply.

Title:
Disordered Jahn-Teller-Polaron States in the Simple Perovskite Manganite Ca(1-x)La(x)nO(3) with 0.15 <= x <= 0.28
Authors:
Endo, T; Goto, T; Inoue, Y; Koyama, Y Author Full Names: Endo, Tomoki; Goto, Takamasa; Inoue, Yasuhide; Koyama, Yasumasa
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 88 (7):10.7566/JPSJ.88.074708 JUL 15 2019
Abstract:
Among orbital-ordered states in manganites with strongly correlated electronic systems, both the C-type orbital-ordered (Ctype-OO) state and the charge- and orbital-ordered (COO) state have been reported in the simple perovskite Ca1-xLaxMnO3 (CLMO) with 0.15 <= x <= 0.28. To understand their formation from the disordered Pnma (DO) state with orthorhombic symmetry, the crystallographic features of prepared CLMO samples with 0.15 <= x <= 0.28 were examined mainly by transmission electron microscopy. When the temperature was lowered from the orthorhombic DO state for 0.15 <= x <= 0.23, referred to as Region I, the Ctype-OO state with monoclinic-P2(1)/m symmetry appeared via a disordered Jahn-Teller polaron (DJTP) state, which exhibited characteristic diffuse scattering around each DO reflection in electron diffraction patterns. For 0.23 <= x <= 0.28 as Region II, cooling from the DO state resulted in the appearance of the COO state via a similar DJTP state. In patterns obtained from the COO state, satellite reflections characterizing the state were confirmed to be due to both transverse and longitudinal lattice modulations. It was also found that the DJTP states in Regions I and II were present in T-N >= T >= T-Ct(yp)e-OO and T >= T-COO), respectively, and were identified as the precursor states, which appear prior to the formation of the Ctype-OO and COO states.

Title:
Emergent symmetries in block copolymer epitaxy
Authors:
Ding, Y; Gadelrab, KR; Rodriguez, KM; Huang, HJ; Ross, CA; Alexander-Katz, A Author Full Names: Ding, Yi; Gadelrab, Karim R.; Rodriguez, Katherine Mizrahi; Huang, Hejin; Ross, Caroline A.; Alexander-Katz, Alfredo
Source:
NATURE COMMUNICATIONS, 10 10.1038/s41467-019-10896-5 JUL 5 2019
Abstract:
The directed self-assembly (DSA) of block copolymers (BCPs) has shown promise in fabricating customized two-dimensional (2D) geometries at the nano- and meso-scale. Here, we discover spontaneous symmetry breaking and superlattice formation in DSA of BCP. We observe the emergence of low symmetry phases in high symmetry templates for BCPs that would otherwise not exhibit these phases in the bulk or thin films. The emergence phenomena are found to be a general behavior of BCP in various template layouts with square local geometry, such as 4(4) and 3(2)434 Archimedean tilings and octagonal quasicrystals. To elucidate the origin of this phenomenon and confirm the stability of the emergent phases, we implement self-consistent field theory (SCFT) simulations and a strong-stretching theory (SST)-based analytical model. Our work demonstrates an emergent behavior of soft matter and draws an intriguing connection between 2-dimensional soft matter self-assembly at the mesoscale and inorganic epitaxy at the atomic scale.

Title:
Magnetic phase diagram of the quantum spin chain compound SrCo2V2O8: a single-crystal neutron diffraction study
Authors:
Shen, L; Zaharko, O; Obirk, J; Jellyman, E; He, Z; Blackburn, E Author Full Names: Shen, L.; Zaharko, O.; Birk, J. O.; Jellyman, E.; He, Z.; Blackburn, E.
Source:
NEW JOURNAL OF PHYSICS, 21 10.1088/1367-2630/ab2b7a JUL 3 2019
Abstract:
We explore magnetic order in the quantum spin chain compound SrCo2V2O8 up to 14.9 T and down to 50 mK, using single-crystal neutron diffraction. Upon cooling in zero-field, commensurate antiferromagnetic (C-AFM) order with modulation vector k(C) = (0, 0, 1) develops below T-N similar or equal to 5.0 K. Applying an external magnetic field (H parallel to c axis) destabilizes this C-AFM order, leading to an order-disorder transition between T-N and similar to 1.5 K. Below 1.5 K, a commensurate to incommensurate (IC-AFM) transition occurs at 3.9 T, above which the magnetic reflections can be indexed by k(1C) = (0, 0,1 +/- delta l). The incommensurability N scales monotonically with H until the IC-AFM order disappears around 7.0 T. Magnetic reflections modulated by k(C) emerge again at higher fields. While the characters of the C-AFM, IC-AFM and the emergent AFM order in SrCo2V2O8 appear to fit the descriptions of the Neel, longitudinal spin density wave and transverse AFM order observed in the related compound BaCo2V2O8, our results also reveal several unique signatures that are not present in the latter, highlighting the inadequacy of mean-field theory in addressing the complex magnetic order in systems of this class.

Title:
X-ray magnetic diffraction under high pressure
Authors:
Wang, YS; Rosenbaum, TF; Feng, Y Author Full Names: Wang, Yishu; Rosenbaum, T. F.; Feng, Yejun
Source:
IUCRJ, 6 507-520; 10.1107/S2052252519007061 4 JUL 2019
Abstract:
Advances in both non-resonant and resonant X-ray magnetic diffraction since the 1980s have provided researchers with a powerful tool for exploring the spin, orbital and ion degrees of freedom in magnetic solids, as well as parsing their interplay. Here, we discuss key issues for performing X-ray magnetic diffraction on single-crystal samples under high pressure (above 40 GPa) and at cryogenic temperatures (4 K). We present case studies of both non-resonant and resonant X-ray magnetic diffraction under pressure for a spin-flip transition in an incommensurate spin-density-wave material and a continuous quantum phase transition of a commensurate all-in-all-out antiferromagnet. Both cases use diamond-anvil-cell technologies at third-generation synchrotron radiation sources. In addition to the exploration of the athermal emergence and evolution of antiferromagnetism discussed here, these techniques can be applied to the study of the pressure evolution of weak charge order such as charge-density waves, antiferro-type orbital order, the charge anisotropic tensor susceptibility and charge superlattices associated with either primary spin order or softened phonons.

Title:
Identification of Phase Transitions and Metastability in Dynamically Compressed Antimony Using Ultrafast X-Ray Diffraction
Authors:
Coleman, AL; Gorman, MG; Briggs, R; McWilliams, RS; McGonegle, D; Bolme, CA; Gleason, AE; Fratanduono, DE; Smith, RF; Galtier, E; Lee, HJ; Nagler, B; Granados, E; Collins, GW; Eggert, JH; Wark, JS; McMahon, MI Author Full Names: Coleman, A. L.; Gorman, M. G.; Briggs, R.; McWilliams, R. S.; McGonegle, D.; Bolme, C. A.; Gleason, A. E.; Fratanduono, D. E.; Smith, R. F.; Galtier, E.; Lee, H. J.; Nagler, B.; Granados, E.; Collins, G. W.; Eggert, J. H.; Wark, J. S.; McMahon, M. I.
Source:
PHYSICAL REVIEW LETTERS, 122 (25):10.1103/PhysRevLett.122.255704 JUN 28 2019
Abstract:
Ultrafast x-ray diffraction at the LCLS x-ray free electron laser has been used to resolve the structural behavior of antimony under shock compression to 59 GPa. Antimony is seen to transform to the incommensurate, host-guest phase Sb-II at similar to 11 GPa, which forms on nanosecond timescales with ordered guest-atom chains. The high-pressure bcc phase Sb-III is observed above similar to 15 GPa, some 8 GPa lower than in static compression studies, and mixed Sb-III/liquid diffraction are obtained between 38 and 59 GPa. An additional phase which does not exist under static compression, Sb-I', is also observed between 8 and 12 GPa, beyond the normal stability field of Sb-I, and resembles Sb-I with a resolved Peierls distortion. The incommensurate Sb-II high-pressure phase can be recovered metastably on release to ambient pressure, where it is stable for more than 10 ns.

Title:
Maximum supercooling studies in Ti39.5Zr39.5Ni21, Ti40Zr30Ni30, and Zr80Pt20 liquids-Connecting liquid structure and the nucleation barrier
Authors:
Sellers, ME; Van Hoesen, DC; Gangopadhyay, AK; Kelton, KF Author Full Names: Sellers, M. E.; Van Hoesen, D. C.; Gangopadhyay, A. K.; Kelton, K. F.
Source:
JOURNAL OF CHEMICAL PHYSICS, 150 (20):10.1063/1.5096188 MAY 28 2019
Abstract:
Almost three quarters of a century ago, Charles Frank proposed that the deep supercooling observed in metallic liquids is due to icosahedral short-range order (ISRO), which is incompatible with the long-range order of crystal phases. Some evidence in support of this hypothesis had been published previously. However, those studies were based on a small population of maximum supercooling measurements before the onset of crystallization. Here, the results of a systematic statistical study of several hundred maximum supercooling measurements on Ti39.5Zr39.5Ni21, Ti40Zr30Ni30, and Zr80Pt20 liquids are presented. Previous X-Ray and neutron scattering studies have shown that the structures of these liquid alloys contain significant amounts of ISRO. The results presented here show a small work of critical cluster formation (W* = 31-40 k(B)T) from the analysis of the supercooling data for the Ti39.5Zr39.5Ni21 liquid, which crystallizes to a metastable icosahedral quasicrystal. A much larger value (W* = 54-79 k(B)T and W* = 60-99 k(B)T) was obtained for the Ti40Zr30Ni30 and Zr80Pt20 liquids, respectively, which do not crystallize to an icosahedral quasicrystal. Taken together, these results significantly strengthen the validity of Frank's hypothesis. Published under license by AIP Publishing.

Title:
Chemical Bonding and Physical Properties in Quasicrystals and Their Related Approximant Phases: Known Facts and Current Perspectives
Authors:
Barber, EM Author Full Names: Macia Barber, Enrique
Source:
APPLIED SCIENCES-BASEL, 9 (10):10.3390/app9102132 MAY 2 2019
Abstract:
Quasicrystals are a class of ordered solids made of typical metallic atoms but they do not exhibit the physical properties that usually signal the presence of metallic bonding, and their electrical and thermal transport properties resemble a more semiconductor-like than metallic character. In this paper I first review a number of experimental results and numerical simulations suggesting that the origin of the unusual properties of these compounds can be traced back to two main features. For one thing, we have the formation of covalent bonds among certain atoms grouped into clusters at a local scale. Thus, the nature of chemical bonding among certain constituent atoms should play a significant role in the onset of non-metallic physical properties of quasicrystals bearing transition-metal elements. On the other hand, the self-similar symmetry of the underlying structure gives rise to the presence of an extended chemical bonding network due to a hierarchical nesting of clusters. This novel structural design leads to the existence of quite diverse wave functions, whose transmission characteristics range from extended to almost localized ones. Finally, the potential of quasicrystals as thermoelectric materials is discussed on the basis of their specific transport properties.

Title:
STATISTICAL DESCRIPTION OF DIFFRACTION PATTERN OF APERIODIC CRYSTALS
Authors:
Wolny, J; Buganski, I; Pytlik, L; Strzalka, R Author Full Names: Wolny, J.; Buganski, I; Pytlik, L.; Strzalka, R.
Source:
ARCHIVES OF METALLURGY AND MATERIALS, 64 (2):721-725; 10.24425/amm.2019.127604 2019
Abstract:
Modern crystallography faces a demanding challenge of describing atomic structure and diffraction pattern of quasicrystals, which, after 30 years of Shechtman's discovery, is still an open field of research. The classical approach based on the Braggs and Laue equations in three-dimensional space is useless, because the direct and the reciprocal lattices cannot be introduced for aperiodic systems. A standard solution to this problem, applied by number of scientists, is to retrieve periodicity in high dimensions. This is a purely mathematical approach with some difficulties from a point of view of physics. It is mathematically elegant, but not applicable to all aperiodic systems (e.g. Thue-Morse or Rudin-Shapiro sequences). It meets also a serious trouble in a proper description of structural defects, like phasons. In our opinion the most successful alternative to the multidimensional description is a statistical method of diffractional and structural analysis of aperiodic systems, also known as the average unit cell approach (AUC). In this work an application of the AUC method to selected aperiodic systems, including modulated structures, quasicrystals and covering clusters, is discussed in the form of a mini-review. A reader can find more details in the cited references.

Title:
Electronic properties of incommensurately modulated novel and complex materials
Authors:
Martino, E; Arakcheeva, A; Autes, G; Katrych, S; Yazyev, OV; Moll, PJW; Akrap, A; Forro, L Author Full Names: Martino, Edoardo; Arakcheeva, Alla; Autes, Gabriel; Katrych, Sergiv; Yazyev, Oleg V.; Moll, Philip J. W.; Akrap, Aim; Forro, Laszlo
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 74 E96-E96; S 10.1107/S2053273318093798 AUG 2018

Title:
Investigation of the structure of the modulated doubly ordered perovskite NaLaCoWO6 and its reversible phase transition with a colossal temperature hysteresis
Authors:
Cohn, CV; Zuo, P; Darie, C; Klein, H Author Full Names: Cohn, Claire V.; Zuo, Peng; Darie, Celine; Klein, Holger
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 74 E51-E51; S 10.1107/S2053273318094421 AUG 2018

Title:
Electron diffraction tomography of modulated minerals: the crystal structure of daliranite
Authors:
Gemmi, M; Lanza, A; Mugnaioli, E; Bindi, L; Paar, WH Author Full Names: Gemmi, Mauro; Lanza, Arianna; Mugnaioli, Enrico; Bindi, Luca; Paar, Werner H.
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 74 E321-E322; S 10.1107/S2053273318090356 AUG 2018

Title:
Application of the Generalized Penrose Tiling to the structure refinement of AICuRh decagonal quasicrystal
Authors:
Strzalka, R; Buganski, L; Chodyn, M; Wolny, J Author Full Names: Strzalka, Radoslaw; Buganski, Lreneusz; Chodyn, Maciej; Wolny, Janusz
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 74 E98-E98; S 10.1107/S2053273318093762 AUG 2018

Title:
Multidimensional crossed cube tilings
Authors:
Ben-Abraham, S Author Full Names: Ben-Abraham, Shelomo
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 74 E332-E332; S 10.1107/S2053273318090186 AUG 2018

Title:
Transitions toward complex electronic states and superperiodic structures in P4W16O56
Authors:
Duverger-Nedellec, E; Pautrat, A; Perez, O Author Full Names: Duverger-Nedellec, Elen; Pautrat, Alain; Perez, Olivier
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 74 E95-E95; S 10.1107/S2053273318093816 AUG 2018

Title:
Exploring modulation in molecular crystals at low temperatures
Authors:
Sztylko, M; Hoser, A Author Full Names: Sztylko, Marcin; Hoser, Anna
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 74 E327-E327; S 10.1107/S2053273318090289 AUG 2018

Title:
Aperidic structures and luminescent properties in the scheelite family
Authors:
Morozov, V; Abakumov, A; Hadermann, J; Khaikina, E; Deynekol, D; Lazoryak, B; Leonidov, I; Batuk, D; Batuk, M Author Full Names: Morozov, Vladimir; Abakumov, Artem; Hadermann, Joke; Khaikina, Elena; Deynekol, Dina; Lazoryak, Bogdan; Leonidov, Ivan; Batuk, Dmitry; Batuk, Maria
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 74 E94-E94; S 10.1107/S2053273318093828 AUG 2018

Title:
On the symmetry of incommensurate magnetic structures
Authors:
Perez-Mato, JM; Elcoro, L; Madariaga, G; Aroyo, MI Author Full Names: Manuel Perez-Mato, J.; Elcoro, Luis; Madariaga, Gotzon; Aroyo, Mois I.
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 74 E100-E101; S 10.1107/S2053273318093737 AUG 2018

Title:
AlCuRh decagonal quasicrystal - new techniques for the refinement
Authors:
Buganski, I; Strzalka, R; Wolny, J Author Full Names: Buganski, Ireneusz; Strzalka, Radoslaw; Wolny, Janusz
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 74 E328-E328; S 10.1107/S2053273318090265 AUG 2018

Title:
Clusters in the Al13TM4 quasicrystalline approximants : role on the surface structures and properties
Authors:
Gaudry, E Author Full Names: Gaudry, Emilie
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 74 E96-E97; S 10.1107/S2053273318093786 AUG 2018

Update: 11-Jul-2019


Title:
Low-temperature thermal conductivity and magnetic transitions of the kagome-staircase compound Ni3V2O8
Authors:
Zhao, ZY; Li, QJ; Liu, XG; Rao, X; Che, HL; Chu, LG; He, ZZ; Zhao, X; Sun, XF Author Full Names: Zhao, Z. Y.; Li, Q. J.; Liu, X. G.; Rao, X.; Che, H. L.; Chu, L. G.; He, Z. Z.; Zhao, X.; Sun, X. F.
Source:
PHYSICAL REVIEW B, 99 (22):10.1103/PhysRevB.99.224428 JUN 25 2019
Abstract:
The kagome-staircase compound Ni3V2O8 is an attractive multiferroic material exhibiting rich phase diagrams. However, the magnetic properties and magnetic transitions have been studied only above 1.3 K. In this work, we study the thermal conductivity kappa of Ni3V2O8 single crystals at low temperatures down to 0.3 K and in magnetic fields up to 14 T. In zero field, the magnetic transitions from the low-temperature incommensurate (LTI) phase to the commensurate phase (C) and then to a second commensurate phase (C' yield anomalies in kappa(T) curves at T-LC = 3.7 K and T-CC' = 2.0 K, respectively, which indicates a significant phonon scattering by the critical spin fluctuations. When the field is applied along the a axis, the field dependence of kappa displays four anomalies associated with different magnetic transitions and reveals an undetected magnetic state at subkelvin temperatures. In addition, the kappa(B) curves are found to depend not only on the history but also on the magnitude of the applied field. When the field is applied along the b axis, a high-field phase located above the LTI and high-temperature incommensurate phases is revealed.

Title:
Stacking sequence variations in vaterite resolved by precession electron diffraction tomography using a unified superspace model
Authors:
Steciuk, G; Palatinus, L; Rohlicek, J; Ouhenia, S; Chateigner, D Author Full Names: Steciuk, Gwladys; Palatinus, Lukas; Rohlicek, Jan; Ouhenia, Salim; Chateigner, Daniel
Source:
SCIENTIFIC REPORTS, 9 10.1038/s41598-019-45581-6 JUN 24 2019
Abstract:
As a metastable phase, vaterite is involved in the first step of crystallization of several carbonate-forming systems including the two stable polymorphs calcite and aragonite. Its complete structural determination would consequently shed important light to understand scaling formation and biomineralization processes. While vaterite's hexagonal substructure (a(0) similar to 4.1 angstrom and c(0) similar to 8.5 angstrom) and the organization of the carbonate groups within a single layer is known, conflicting interpretations regarding the stacking sequence remain and preclude the complete understanding of the structure. To resolve the ambiguities, we performed precession electron diffraction tomography (PEDT) to collect single crystal data from 100 K to the ambient temperature. The structure was solved ab initio and described over all the temperature range using a unified modulated structure model in the superspace group C12/c1(alpha 0 gamma)00 with a = a(0) = 4.086(3) angstrom, b = root 3a(0) = 7.089(9) angstrom, c = c(0) = 8.439(9) angstrom, alpha=beta=gamma=90 degrees and q = 2/3a* + gamma c*. At 100 K the model presents a pure 4-layer stacking sequence with gamma = 1/2 whereas at the ambient temperature, ordered stacking faults are introduced leading to gamma < 1/2. The model was refined against PEDT data using the dynamical refinement procedure including modulation and twinning as well as against x-ray powder data by the Rietveld refinement.

Title:
Effect of exchange interaction on electronic instabilities in the honeycomb lattice: A functional renormalization group study
Authors:
O, SJ; Kim, YH; Rim, HY; Pak, HC; Im, SJ Author Full Names: O, Song-Jin; Kim, Yong-Hwan; Rim, Ho-Yong; Pak, Hak-Chol; Im, Song-Jin
Source:
PHYSICAL REVIEW B, 99 (24):10.1103/PhysRevB.99.245140 JUN 21 2019
Abstract:
The impact of local and nonlocal density-density interactions on the electronic instabilities in the honeycomb lattice is widely investigated. Some early studies proposed the emergence of interaction-induced topologically nontrivial phases, but recently, it was denied in several works including renormalization group calculations with refined momentum resolution. We use the truncated unity functional renormalization group to study the many-body instabilities of electrons on the half-filled honeycomb lattice, focusing on the effect of the exchange interaction. We show that varying the next-nearest-neighbor repulsion and nearest-neighbor exchange integral can lead to diverse ordered phases, namely, the quantum spin Hall, the spin-Kekule, and some spin- and charge-density-wave phases. The quantum spin Hall phase can be induced by a combination of the ferromagnetic exchange and pair hopping interactions. Another exotic phase, the spin-Kekule phase, develops in a very small region of the parameter space considered. We encounter the three-sublattice charge-density-wave phase in a large part of the parameter space. It is replaced by the incommensurate charge density wave when increasing the exchange integral. In order to reduce the computational effort, we derive the explicit symmetry relations for the bosonic propagators of the effective interaction and propose a linear-response-based approach for identifying the form factor of order parameter. Their efficiencies are confirmed by numerical calculations in our work.

Title:
Suppression of charge density wave order by disorder in Pd-intercalated ErTe3
Authors:
Straquadine, JAW; Weber, F; Rosenkranz, S; Said, AH; Fisher, AIR Author Full Names: Straquadine, J. A. W.; Weber, F.; Rosenkranz, S.; Said, A. H.; Fisher, And I. R.
Source:
PHYSICAL REVIEW B, 99 (23):10.1103/PhysRevB.99.235138 JUN 19 2019
Abstract:
Disorder is generically anticipated to suppress long range charge density wave (CDW) order. We report transport, thermodynamic, and scattering experiments on PdxErTe3, a model CDW system with disorder induced by intercalation. The pristine parent compound (x = 0) shows two separate, mutually perpendicular, incommensurate unidirectional CDW phases setting in at 270 K and 165 K. In this work we present measurements on a finely-spaced series of single crystal samples, in which we track the suppression of signatures corresponding to these two parent transitions as the Pd concentration increases. At the largest values of x, we observe complete suppression of long range CDW order in favor of superconductivity. We also report evidence from electron and x-ray diffraction which suggests a tendency toward short-range ordering along both wave vectors which persists even well above the crossover temperature and comment on the origin and consequences of this effect. Based on this work, PdxErTe3 appears to provide a promising model system for the study of the interrelation of charge order and superconductivity in the presence of quenched disorder, for pseudotetragonal materials.

Title:
Commensurate Nb2Zr5O15: Accessible Within the Field Nb2ZrxO2x+5 After All
Authors:
Wiedemann, D; Orthmann, S; Muhlbauer, MJ; Lerch, M Author Full Names: Wiedemann, Dennis; Orthmann, Steven; Muehlbauer, Martin J.; Lerch, Martin
Source:
CHEMISTRYOPEN, 8 (4):447-450; 10.1002/open.201900043 APR 2019
Abstract:
Doped niobium zirconium oxides are applied in field-effect transistors and as special-purpose coatings. Whereas their material properties are sufficiently known, their crystal structures remain widely uncharacterized. Herein, we report on the comparably mild sol-gel synthesis of Nb2Zr5O15 and the elucidation of its commensurately modulated structure via neutron diffraction. We describe the structure using the most appropriate superspace as well as the convenient supercell approach. It is part of an -PbO2-homeotypic field with the formula Nb2ZrxO2x+5, which has previously been reported only for x5.1, and is closely related to the structure of Hf3Ta2O11. The results, supported by X-ray diffraction and additional synthesis experiments, are contextualized within the existing literature. Via the sol-gel route, metastable Nb-Zr-O compounds and their heavier congeners are accessible that shed light on possible structures of these commercially utilized materials.

Update: 27-Jun-2019


Title:
Growth of layered Lu(2)Fe(3)O(7 )and Lu3Fe4O10 single crystals exhibiting long-range charge order via the optical floating-zone method
Authors:
Hammouda, SS; Angst, M Author Full Names: Hammouda, S. S.; Angst, M.
Source:
JOURNAL OF CRYSTAL GROWTH, 521 50-54; 10.1016/j.jcrysgro.2019.06.003 SEP 1 2019
Abstract:
We report the controlled growth of single crystals of intercalated layered Lu1+n Fe2+nO4+3n-delta(n = 1,2) with different oxygen stoichiometries delta. For the first time crystals sufficiently stoichiometric to exhibit superstructure reflections in X-ray diffraction attributable to charge ordering were obtained. The estimated correlation lengths tend to be smaller than for not intercalated LuFe2O4. For Lu2Fe3O7, two different superstructures were observed, one an incommensurate zigzag pattern similar to previous observations by electron diffraction, the other an apparently commensurate pattern with (1/31/30) propagation. Implications for the possible charge order in the bilayers are discussed. Magnetization measurements suggest reduced magnetic correlations and the absence of an antiferromagnetic phase.

Title:
Synthesis and characterization of Sn reinforced Al-Cu-Fe quasicrystalline matrix nanocomposite by mechanical milling
Authors:
Shadangi, Y; Shivam, V; Singh, MK; Chattopadhyay, K; Basu, J; Mukhopadhyay, NK Author Full Names: Shadangi, Yagnesh; Shivam, Vikas; Singh, Manish Kumar; Chattopadhyay, Kausik; Basu, Joysurya; Mukhopadhyay, N. K.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 797 1280-1287; 10.1016/j.jallcom.2019.05.128 AUG 15 2019
Abstract:
The influence of mechanical milling (MM), primarily on microstructure and phase evolution in Al62.5Cu25Fe12.5 (at%) quasicrystalline (IQC) matrix reinforced with varying volume fraction of Sn has been investigated by means of X-ray diffraction (XRD), scanning & transmission electron microscopy (SEM and TEM) and differential scanning calorimetry (DSC) methods. It was observed that with increasing the milling duration, the IQC phase transforms to crystalline B2 phase [Al (Cu, Fe) and Pm3m, a = 0.29 nm]. In SEM and TEM analysis, it was found that both IQC and Sn particles are refined during MM. The XRD and TEM results confirm the formation nanostructured matrix consisting of nanocrystalline B2 phase along with minor IQC phase reinforced with ultrafine grained Sn particles after 40 h of MM. The STEM-EDS results show a homogenous distribution of elements (Al, Cu, Fe). The Sn particles were immiscible in a matrix consisting of B2 and IQC phase as indicated by XRD and TEM investigations. (C) 2019 Elsevier B.V. All rights reserved.

Title:
Comprehensive magnetic phase diagrams of the polar metal Ca-3(Ru0.95Fe0.05)(2)O-7
Authors:
Lei, SM; Chikara, S; Puggioni, D; Peng, J; Zhu, MZ; Gu, MQ; Zhao, WW; Wang, Y; Yuan, YK; Akamatsu, H; Chan, MHW; Ke, XL; Mao, ZQ; Rondinelli, JM; Jaime, M; Singleton, J; Weickert, F; Zapf, VS; Gopalan, V Author Full Names: Lei, Shiming; Chikara, Shalinee; Puggioni, Danilo; Peng, Jin; Zhu, Mengze; Gu, Mingqiang; Zhao, Weiwei; Wang, Yu; Yuan, Yakun; Akamatsu, Hirofumi; Chan, Moses H. W.; Ke, Xianglin; Mao, Zhiqiang; Rondinelli, James M.; Jaime, Marcelo; Singleton, John; Weickert, Franziska; Zapf, Vivien S.; Gopalan, Venkatraman
Source:
PHYSICAL REVIEW B, 99 (22):10.1103/PhysRevB.99.224411 JUN 10 2019
Abstract:
Polar metals exist as a rather unique class of materials as they combine two seemingly mutually exclusive properties (polar order and metallicity) in one system. So far only a few polar metals have been unambiguously identified; the magnetic ones are exceptionally rare. Here we investigate a 5% Fe-doped polar metal Ca3Ru2O7, via electrical transport, magnetization, microstrain, and optical second-harmonic generation measurements. We report the full magnetic phase diagrams (in the field-temperature space) for magnetic field H parallel to a and H parallel to b, which exhibit distinct field-dependent magnetizations behavior. In particular, for H parallel to a we found a ferromagnetic incommensurate spin structure, which is absent in the pure Ca3Ru2O7. We propose a microscopic spin model to understand this behavior, highlighting the role of Fe doping in tipping the delicate balance of the underlying exchange-interaction energy in this system.

Title:
Experimental realization of a semiconducting quasicrystalline approximant in Al-Si-Ru system by band engineering
Authors:
Iwasaki, Y; Kitahara, K; Kimura, K Author Full Names: Iwasaki, Yutaka; Kitahara, Koichi; Kimura, Kaoru
Source:
PHYSICAL REVIEW MATERIALS, 3 (6):10.1103/PhysRevMaterials.3.061601 JUN 7 2019
Abstract:
We found that an Al-Si-Ru cubic quasicrystalline approximant has a semiconducting band structure by performing an orbital analysis based on density functional theory. These semiconducting transport properties have been confirmed in an experimentally synthesized sample. The temperature dependences of the electrical conductivity and the Seebeck coefficient were consistent with the trends of an intrinsic semiconductor with a band gap of 0.15 eV above 350 K. The lattice thermal conductivity had a low value of approximately 1.0 W m(-1) K-1 above 400 K, which is close to the theoretical minimum.

Title:
Incommensurate magnetism in K2MnS2-xSex and prospects for tunable frustration in a triangular lattice of pseudo-1D spin chains
Authors:
Bhutani, A; Behera, P; McAuliffe, RD; Cao, HB; Huq, A; Kirkham, MJ; dela Cruz, CR; Woods, T; Shoemaker, DP Author Full Names: Bhutani, Ankita; Behera, Piush; McAuliffe, Rebecca D.; Cao, Huibo; Huq, Ashfia; Kirkham, Melanie J.; dela Cruz, Clarina R.; Woods, Toby; Shoemaker, Daniel P.
Source:
PHYSICAL REVIEW MATERIALS, 3 (6):10.1103/PhysRevMaterials.3.064404 JUN 5 2019
Abstract:
We report a detailed investigation of K2MnS2 and K2MnSe2 from the K2MnS2 structure type and their magnetic solid solution K2MnS2-xSex and find that compounds of this structure type consist of strongly coupled pseudo-one-dimensional antiferromagnetic chains that collectively represent a frustrated two-dimensional triangular antiferromagnet. Bulk samples of K2MnS2-xSex with 0 <= x <= 2 are characterized using x-ray diffraction, neutron diffraction, magnetization, and heat-capacity measurements. An incommensurate cycloid magnetic structure with a magnetic propagation vector k = [0.58 0 1] is observed for all samples in K2MnS2-xSex, and the ordering is robust despite a 12% increase in cell volume. Geometric frustration of chains results in incommensurability along a and a two-step magnetic transition. The varying geometries accessible in compounds of this structure type are presented as promising avenues to tune frustration.

Title:
Emergent localization in dodecagonal bilayer quasicrystals
Authors:
Park, MJ; Kim, HS; Lee, S Author Full Names: Park, Moon Jip; Kim, Hee Seung; Lee, SungBin
Source:
PHYSICAL REVIEW B, 99 (24):10.1103/PhysRevB.99.245401 JUN 4 2019
Abstract:
Long range order in the absence of translational symmetry gives rise to drastic revolution of our common knowledge in condensed-matter physics. Quasicrystals, as such an unconventional system, became a plethora to test our insights and to find exotic states of matter. In particular, electronic properties in quasicrystals have gotten lots of attention along with their experimental realization and controllability in twisted bilayer systems. In this work, we study how quasicrystalline order in bilayer systems can induce unique localization of electrons without any extrinsic disorders. We focus on the dodecagonal quasicrystal that has been demonstrated in twisted bilayer graphene system in recent experiments. In the presence of a small gap, we show the localization generically occurs due to the nonperiodic nature of quasicrystals, which is evidenced by the inverse participation ratio and the energy-level statistics. We understand the origin of such localization by approximating the dodecagonal quasicrystals as an impurity scattering problem.

Title:
Study of Penrose Tiling Using Parameterization Method
Authors:
Shutov, AV; Maleev, AV Author Full Names: Shutov, A. V.; Maleev, A. V.
Source:
CRYSTALLOGRAPHY REPORTS, 64 (3):376-385; 10.1134/S1063774519030234 MAY 2019
Abstract:
A new description of Penrose tiling, based on parameterization of tiling rhombuses, has been obtained. A method making it possible to describe clusters and coordination environments in Penrose tiling in terms of parameters is developed. The parameters of all possible types of the first coordination environments in Penrose tiling are found. A new proof is obtained that the form of layer-by-layer growth of Penrose tiling is a regular decagon, and the vertices of this decagon are calculated.

Update: 19-Jun-2019


Title:
Control of wave propagation response using quasi crystals: A formulation based on spectral finite element
Authors:
Chellappan, V; Gopalakrishnan, S; Mani, V Author Full Names: Chellappan, Vinita; Gopalakrishnan, S.; Mani, V
Source:
MECHANICS OF ADVANCED MATERIALS AND STRUCTURES, 26 (7):579-600; 10.1080/15376494.2017.1410901 APR 3 2019
Abstract:
This paper presents wave propagation studies in quasi crystal structures and quasi crystal reinforced aluminium structures. The analysis is performed using frequency domain spectral finite element formulation. The analysis considers different 2-D decagonal and 3-D icosahedral quasi crystals. First, wave propagation analysis of quasi crystal structure alone is performed and the propagation of phonon and phason modes for different quasi crystals are studied. The study includes the propagation of axial and transverse wave responses in these quasi crystals. The study has found that the amplitude of the phason modes is very small compared to the phonon modes and the increase of the phason mode content (through increase in R) increases the phason mode amplitude, without affecting the phonon mode amplitudes. It is shown that the dominant axial phonon mode is non-dispersive and the dominant flexural phonon mode is dispersive. In the next study, the aluminium beam structure is reinforced with different quasi crystals in different configurations and the wave propagation of axial and transverse responses are studied. For all the combinations of quasi crystal aluminium beam combination, there is substantial suppression of responses both for the axial and the bending responses. Unsymmetrical configuration produces substantial non-dominant phonon modes which propagate dispersively. It is found that for a symmetric bi-morph configuration, the response is reduced significantly, about 68% and 75% for axial loading and 80% and 78% for flexural loading, respectively, for the 2-D decagonal quasi crystal and the 3-D icosahedral quasi crystal.

Title:
Microstructure and mechanical behavior of Al92Fe3Cr2X3 (X = Ce, Mn, Ti, and V) alloys processed by centrifugal force casting
Authors:
Koga, GY; Silva, AMBE; Wolf, W; Kiminami, CS; Bolfarini, C; Botta, WJ Author Full Names: Koga, Guilherme Yuuki; Branquinho e Silva, Ana Martha; Wolf, Witor; Kiminami, Claudio Shyinti; Bolfarini, Claudemiro; Botta, Walter Jose
Source:
JOURNAL OF MATERIALS RESEARCH AND TECHNOLOGY-JMR&T, 8 (2):2092-2097; 10.1016/j.jmrt.2018.12.022 APR 2019
Abstract:
Microstructural and mechanical characterization of Al92Fe3Cr2X3 (X = Ce, Mn, Ti, and V) alloys were performed. The alloys were processed by a method that uses centrifugal force to cast the samples into a rotating copper mold. Microstructural characterization was carried out by means of x-ray diffraction, scanning electron microscopy, and differential scanning calorimetry. Compressive tests at room and at 300 degrees C were performed in selected samples to evaluate their mechanical properties. Microstructural characterization showed the formation of quasicrystalline phases as well as other intermetallic phases embedded within an Al-FCC matrix. The Ce-containing alloy exhibited promising results regarding quasicrystalline phase formation and stability as well as with respect to its mechanical properties at high temperatures. The quasicrystalline phase of this alloy appears to be stable up to 545 degrees C when the DSC reveals an exothermic transformation. In addition, the presence of a eutectic structure surrounding the Al-FCC grains enhanced the mechanical strength of this alloy. At 300 degrees C, the Ce-containing alloy showed yield strength and ultimate tensile strength of 180 MPa and 360 MPa, respectively. If compared to a commercial aluminum alloy 2024 at the T6 condition, close to 300 degrees C, the alloy studied here showed an increase of more than 4 times in the yield strength, and almost 7 times in the ultimate tensile strength. The high thermal stability and mechanical properties at high temperatures of this alloy open interesting possibilities for further studies and future applications of this Al-Fe-Cr-Ce alloy. (C) 2019 Published by Elsevier Editora Ltda. on behalf of Brazilian Metallurgical, Materials and Mining Association.

Title:
Effect of I(Mg3YZn6)-, W(Mg3Y2Zn3)- and LPSO(Mg12ZnY)- phases on tensile work-hardening and fracture behaviors of rolled Mg-Y-Zn alloys
Authors:
Yang, JY; Kim, WJ Author Full Names: Yang, Jun Yeong; Kim, Woo Jin
Source:
JOURNAL OF MATERIALS RESEARCH AND TECHNOLOGY-JMR&T, 8 (2):2316-2325; 10.1016/j.jmrt.2019.04.016 APR 2019
Abstract:
The effects of secondary phases (W,Mg3Y2Zn3), long-period stacking-ordered (LPSO, Mg12ZnY) and icosahedral (I, Mg3YZn6) phases on the tensile properties and work- hardening behavior of Mg-Y-Zn alloys (Mg-1.32Zn-1.79Y, ZW12; Mg-4.4Zn-2.2Y, ZW42; and microstructures were studied at room temperature. The volume fractions of LPSO, W and I-phase in ZW12, ZW42 and ZW51 were 4.7, 6.3 and 4.8%, respectively. The rolled alloys exhibited a similar level of yield strength but different work hardening characteristics and tensile fracture behavior. The rolled ZW51 with I-phase particles exhibited the highest work-hardening rate and the largest tensile elongation (with ductile fracture). The ZW42 with W-phase particles exhibited a work-hardening rate slightly lower than that of the rolled ZW51, despite having the larger amount of secondary phase, and premature fracture occurred far before neck formation in ZW42, while fracture occured after neck formation occurred far before neck formation in ZW42, while fracture occured after neck formation in ZW51. The fractured surface showed that the coherent interface between the I-phase and Mg matrix phase is significantly more resistant to cracking than is the incoherent interface between the W-phase and Mg matrix phase. The rolled ZW12 with LPSO-phase, forming a coherent interface with the Mg matrix phase, exhibited a considerably lower work hardening rate than the rolled ZW51, though they had the similar amounts of secondary phase. Thus, the uniform strain of the rolled ZW12 was quite small compared with that of the rolled ZW51, though fracture occurred after necking in both alloys. The same work-hardening and tensile elongation behaviors were retained after annealing treatment on the rolled alloys. (C) 2019 The Authors. Published by Elsevier B.V.

Title:
Synthesis and Investigation of Quaternary Quasi-Crystalline Phase in Al - Cu - Fe - Cr Alloys
Authors:
Wang, YF; Hou, H; Zhao, YH; Tian, JZ Author Full Names: Wang, Yifan; Hou, Hua; Zhao, Yuhong; Tian, Jinzhong
Source:
METAL SCIENCE AND HEAT TREATMENT, 60 (11-12):770-776; 10.1007/s11041-019-00354-w MAR 2019
Abstract:
Formation of a quasi-crystalline phase under rapid solidification and heat treatment of alloys of the Al - Cu - Fe - Cr system is studied. The study is performed by x-ray diffractometry, optical, scanning and transmission electron microscopy and differential scanning calorimetry. It is shown that the quasi-crystalline Al65Cu20Fe10Cr5 phase is a mixture of icosahedral and decagonal phases. The substitution of iron with chromium destabilizes the icosahedral I-phase and promotes formation of a decagonal d-phase. After quenching from 880 degrees C, the Al64Cu24Fe10Cr2 alloy acquires a pure I-phase, and the Al64Cu24Fe8Cr4 alloy acquires a d-phase.

Update: 13-Jun-2019


Title:
Charge density wave and lock-in transitions of CuV2S4
Authors:
Ramakrishnan, S; Schonleber, A; Hubschle, CB; Eisele, C; Schaller, AM; Rekis, T; Bui, NHA; Feulner, F; van Smaalen, S; Bag, B; Ramakrishnan, S; Tolkiehn, M; Paulmann, C Author Full Names: Ramakrishnan, Sitaram; Schoenleber, Andreas; Huebschle, Christian B.; Eisele, Claudio; Schaller, Achim M.; Rekis, Toms; Nguyen Hai An Bui; Feulner, Florian; van Smaalen, Sander; Bag, Biplab; Ramakrishnan, Srinivasan; Tolkiehn, Martin; Paulmann, Carsten
Source:
PHYSICAL REVIEW B, 99 (19):10.1103/PhysRevB.99.195140 MAY 23 2019
Abstract:
The three-dimensional charge density wave (CDW) compound CuV2S4 is known to undergo phase transitions at similar to 91 and similar to 50 K. Employing single-crystal x-ray diffraction on an annealed crystal, we confirm the formation of an incommensurate CDW at T-CDW approximate to 91 K, and we establish the nature of the transition at Tlock-in approximate to 50 K as a lock-in transition toward a threefold superstructure. As-grown crystals develop the same incommensurate CDW as the annealed crystal does, but they fail to go through the lock-in transition. Instead, the length of the modulation wave vector continues to decrease down to low temperatures in as-grown crystals. These findings are corroborated by distinct temperature dependencies of the electrical resistivity, magnetic susceptibility, and specific heat measured on as-grown and annealed crystals. A superspace model for the crystal structure of the incommensurate CDW suggests that the formation of extended vanadium clusters is at the origin of the CDW. In the lock-in phase, short and long V-V distances persist, but clusters now percolate the entire crystal. The lowering toward orthorhombic symmetry appears to be responsible for the precise pattern of short and long V-V distances. However, the orthorhombic lattice distortion is nearly zero for the annealed crystal, while it is visible for the as-grown material, again suggesting the role of lattice defects in the latter.

Title:
Magnons in a Quasicrystal: Propagation, Extinction, and Localization of Spin Waves in Fibonacci Structures
Authors:
Lisiecki, F; Rychly, J; Kuswik, P; Glowinski, H; Klos, JW; Gross, F; Trager, N; Bykova, I; Weigand, M; Zelent, M; Goering, EJ; Schutz, G; Krawczyk, M; Stobiecki, F; Dubowik, J; Grafe, J Author Full Names: Lisiecki, Filip; Rychly, Justyna; Kuswik, Piotr; Glowinski, Hubert; Klos, Jaroslaw W.; Gross, Felix; Traeger, Nick; Bykova, Iuliia; Weigand, Markus; Zelent, Mateusz; Goering, Eberhard J.; Schuetz, Gislea; Krawczyk, Maciej; Stobiecki, Feliks; Dubowik, Janusz; Graefe, Joachim
Source:
PHYSICAL REVIEW APPLIED, 11 (5):10.1103/PhysRevApplied.11.054061 MAY 22 2019
Abstract:
Magnonic quasicrystals exceed the possibilities of spin-wave (SW) manipulation offered by regular magnonic crystals, because of their more complex SW spectra with fractal characteristics. Here, we report the direct x-ray microscopic observation of propagating SWs in a magnonic quasicrystal, consisting of dipolar coupled permalloy nanowires arranged in a one-dimensional Fibonacci sequence. SWs from the first and second band as well as evanescent waves from the band gap between them are imaged. Moreover, additional mini band gaps in the spectrum are demonstrated, directly indicating an influence of the quasiperiodicity of the system. Finally, the localization of SW modes within the Fibonacci crystal is shown. The experimental results are interpreted using numerical calculations and we deduce a simple model to estimate the frequency position of the magnonic gaps in quasiperiodic structures. The demonstrated features of SW spectra in one-dimensional magnonic quasicrystals allow utilizing this class of metamaterials for magnonics and make them an ideal basis for future applications.

Title:
Changes in spin and lattice dynamics induced by magnetic and structural phase transitions in multiferroic SrMn7O12
Authors:
Kamba, S; Goian, V; Kadlec, F; Nuzhnyy, D; Kadlec, C; Vit, J; Borodavka, F; Glazkova, IS; Belik, AA Author Full Names: Kamba, Stanislav; Goian, Veronica; Kadlec, Filip; Nuzhnyy, Dmitry; Kadlec, Christelle; Vit, Jakub; Borodavka, Fedir; Glazkova, Iana S.; Belik, Alexei A.
Source:
PHYSICAL REVIEW B, 99 (18):10.1103/PhysRevB.99.184108 MAY 20 2019
Abstract:
SrMn7O12 is a recently synthesized homolog of multiferroic CaMn7O12. Upon cooling, SrMn7O12 undergoes a series of structural and magnetic phase transitions from cubic to rhombohedral symmetry, and to an incommensurately modulated crystal structure, which is connected with charge and orbital ordering of the Mn cations. We report infrared, terahertz, and Raman spectra of SrMn7O12 ceramics reflecting corresponding changes in phonon selection rules, including new phonons appearing in spin-order-induced ferroelectric phases. The observed phonon activities are compared with the predictions from the factor-group analysis. In the high-temperature phase, more phonons are observed than the number predicted for the cubic symmetry. This is explained by the presence of rhombohedral clusters in the cubic phase. The strongest variations occur in THz spectra near the two magnetic phase transitions, at T-N1 = 87 K and T-N2 = 63 K. These activate new modes in the spectra, with resonance frequencies and intensities changing with temperature and magnetic field. Below T-N2, we observed a transfer of oscillator strengths from low-frequency phonons to these excitations, which we assign to electromagnons.

Title:
Microstructure and Mechanical Properties of Extruded Mg-7Sn-5Zn-xAl (x=0, 1, 2 and 3 wt.%) Alloy
Authors:
Jiang, J; Li, TQ; Bi, GL; Yan, FY; Cao, C; Li, YD; Ma, Y Author Full Names: Jiang, Jing; Li, Tingqu; Bi, Guang-Li; Yan, Feng-Yun; Cao, Chi; Li, Yuan-Dong; Ma, Ying
Source:
JOURNAL OF MATERIALS ENGINEERING AND PERFORMANCE, 28 (5):2672-2680; 10.1007/s11665-019-04053-8 MAY 2019
Abstract:
Microstructure and mechanical properties of extruded Mg-7Sn-5Zn-xAl (x=0, 1, 2 and 3 wt.%) alloy were investigated. The as-cast Mg-7Sn-5Zn alloy mainly comprised alpha-Mg dendrites, Mg2Sn and nanosized Mg-Zn phases in a Mg matrix, whereas the quasicrystal (icosahedral (I)) phase precipitated with the addition of Al. After extrusion, the grain size decreased due to dynamic recrystallization and the resulting particles were crushed and distributed along the extrusion direction. The highest tensile strength was exhibited by the extruded Mg-7Sn-5Zn-2Al alloy, which had a yield strength, ultimate tensile strength and elongation to failure of 198, 343 MPa and 18.7%, respectively. The high tensile strength was mainly attributed to grain refinement and precipitation strengthening of the Mg2Sn and icosahedral phases.

Update: 6-Jun-2019


Title:
The influence of the incommensurately modulated structure on the physical properties of Fe1.35Ge
Authors:
Jacimovic, J; Popcevic, P; Arakcheeva, A; Pattison, P; Pisoni, A; Katrych, S; Prsa, K; Berger, H; Smontara, A; Forro, L Author Full Names: Jacimovic, J.; Popcevic, P.; Arakcheeva, A.; Pattison, P.; Pisoni, A.; Katrych, S.; Prsa, K.; Berger, H.; Smontara, A.; Forro, L.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 794 108-113; 10.1016/j.jallcom.2019.04.159 JUL 25 2019
Abstract:
Single crystal growth by chemical vapour transport has resulted samples with Fe1.35Ge stoichiometry. Structural study has shown that the large number of vacancies introduces an incommensuately modulated structure. The electrical resistivity is in the 200 mu Omega cm range at room temperature, and although the ferromagnetic transition temperature at 425 K is clearly visible, it hardly varies down to 4.2 K. It is suggested that the large number of vacancies (and the incommensurate modulation) introduce a strong backscattering, and the system is at the brink of a Mooij correlation. The thermal conductivity and Seebeck coefficient carry also the consequences of the high concentration of vacancies. (c) 2019 Elsevier B.V. All rights reserved.

Title:
Annealing induced precipitation of nanoscale icosahedral quasicrystals in aluminum based alloy
Authors:
Mochugovskiy, A; Tabachkova, N; Mikhaylovskaya, A Author Full Names: Mochugovskiy, Andrey; Tabachkova, Natalia; Mikhaylovskaya, Anastasia
Source:
MATERIALS LETTERS, 247 200-203; 10.1016/j.matlet.2019.03.126 JUL 15 2019
Abstract:
This study analyzes the precipitation phenomenon in the Al-3%Mg-1%Mn alloy and shows that low-temperature annealing at 360 degrees C enables the decomposition of an as-cast Mn-enriched supersaturated solid solution and precipitation of the quasicrystalline icosahedral phase. Icosahedrons are predominantly formed heterogeneously on the dislocations and dislocation walls. Precipitates with quasicrystalline structure contain Al and Mn, free of Si, and their size varies in a range of 17-71 nm. The Ashby-Brown contrast and the ordered positions of the precipitate and matrix reflections in the SAED and in high-resolution TEM images suggest partial coherency of the quasicrystalline precipitates and aluminum matrix. (C) 2019 Elsevier B.V. All rights reserved.

Title:
Incommensurate Magnetism Near Quantum Criticality in CeNiAsO
Authors:
Wu, S; Phelan, WA; Liu, L; Morey, JR; Tutmaher, JA; Neuefeind, JC; Huq, A; Stone, MB; Feygenson, M; Tam, DW; Frandsen, BA; Trump, B; Wan, C; Dunsiger, SR; McQueen, TM; Uemura, YJ; Broholm, CL Author Full Names: Wu, Shan; Phelan, W. A.; Liu, L.; Morey, J. R.; Tutmaher, J. A.; Neuefeind, J. C.; Huq, Ashfia; Stone, Matthew B.; Feygenson, M.; Tam, David W.; Frandsen, Benjamin A.; Trump, Benjamin; Wan, Cheng; Dunsiger, S. R.; McQueen, T. M.; Uemura, Y. J.; Broholm, C. L.
Source:
PHYSICAL REVIEW LETTERS, 122 (19):10.1103/PhysRevLett.122.197203 MAY 15 2019
Abstract:
We report the discovery of incommensurate magnetism near quantum criticality in CeNiAsO through neutron scattering and zero field muon spin rotation. For T < T-N1 = 8.7(3) K, a second order phase transition yields an incommensurate spin density with a wave vector k = (0.44(4), 0, 0). For T < T-N2 = 7.6(3) K, we find coplanar commensurate order with a moment of 0.37(5)mu(B), reduced to 30% of the saturation moment of the vertical bar +/- 1/2 > Kramers doublet ground state, which we establish through inelastic neutron scattering. Muon spin rotation in CeNiAs1-xPxO shows the commensurate order only exists for x <= 0.1 so we infer the transition at x(c) = 0.4(1) is between an incommensurate longitudinal spin density wave and a paramagnetic Fermi liquid.

Title:
Magnetic Phase Transitions to an Incommensurate Magnetic Structure in FeGe2 Compound
Authors:
Men'shenin, VV Author Full Names: Men'shenin, V. V.
Source:
PHYSICS OF THE SOLID STATE, 61 (3):421-432; 10.1134/S1063783419030211 MAR 2019
Abstract:
A symmetry analysis of possible magnetic structures in an incommensurate magnetic phase in FeGe2 compound, resulted from phase transitions from the paramagnetic phase, was performed based on a phenomenological consideration. It is shown that two possible approaches to a such an analysis, the first of which uses the magnetic representation of the space group, and the second one is based on the expansion of the magnetic moment in basis functions of irreducible representations of the space group of the paramagnetic phase, yield the same results. Space group irreducible representations are determined, according to which the transition to an incommensurate structure can occur. The set of these representations appears identical in both approaches. Ginzburg-Landau functionals for analyzing the transitions according to these representations are written. A renormalization group analysis of the second-order phase transitions from the paramagnetic state to the incommensurate magnetic structure is performed. It is shown that a helical magnetic structure can arise in the incommensurate phase as a result of two second-order phase transitions at the transitions temperature.

Update: 29-May-2019


Title:
Preparation of bulk metallic glasses by modifying local structure of icosahedral quasicrystals
Authors:
Li, ZJ; Pan, SP; Zhang, SH; Feng, SD; Li, MZ; Liu, RP; Tian, YJ; Wang, LM Author Full Names: Li, Zijing; Pan, Shaopeng; Zhang, Suhong; Feng, Shidong; Li, Maozhi; Liu, Riping; Tian, Yongjun; Wang, Li-min
Source:
INTERMETALLICS, 109 97-104; 10.1016/j.intermet.2019.03.007 JUN 2019
Abstract:
An attempt is carried out to design metallic glasses by modifying the local structure of icosahedral quasicrystals. A series of metallic glasses are prepared by introducing beryllium to the quasicrystal former, Zr40Ti40Ni20, and the maximum diameter of the glasses reaches 20 mm. A phase transformation diagram is constructed for the alloys of (Zr40Ti40Ni20)(100-x)Be-x, revealing the transition from stable crystal to quasicrystal and then to metallic glasses with the increased Be content. This study shows a connection between the formation of metallic glasses and the specific thermodynamics of the initially precipitated quasicrystals. Interestingly, both improvements in the forming ability for glasses and quasicrystals are observed over a wide composition range. Ab initio molecular dynamic simulations show the evolution of the structural features of the metallic melts for the optimised glass forming region, which guarantee the primary precipitation of quasicrystal.

Title:
Formation and stability of complex metallic phases including quasicrystals explored through combinatorial methods
Authors:
Wolf, W; Kube, SA; Sohn, S; Xie, YJ; Cha, JJ; Scanley, BE; Kiminami, CS; Bolfarini, C; Botta, WJ; Schroers, J Author Full Names: Wolf, Witor; Kube, Sebastian A.; Sohn, Sungwoo; Xie, Yujun; Cha, Judy J.; Ellen Scanley, B.; Kiminami, Claudio S.; Bolfarini, Claudemiro; Botta, Walter J.; Schroers, Jan
Source:
SCIENTIFIC REPORTS, 9 10.1038/s41598-019-43666-w MAY 9 2019
Abstract:
Aluminum-based quasicrystals typically form across narrow composition ranges within binary to quaternary alloys, which makes their fabrication and characterization challenging. Here, we use combinatorial approaches together with fast characterization techniques to study a wide compositional range including known quasicrystal forming compositions. Specifically, we use magnetron cosputtering to fabricate libraries of similar to 140 Al-Cu-Fe and similar to 300 Al-Cu-Fe-Cr alloys. The alloys compositions are measured through automated energy dispersive X-ray spectroscopy. Phase formation and thermal stability are investigated for different thermal processing conditions (as-sputtered and annealed at 400 degrees C, 520 degrees C and 600 degrees C for Al-Cu-Fe libraries; annealed at 600 degrees C for Al-Cu-Fe-Cr libraries) using automated X-ray diffraction and transmission electron microscopy. In both systems the compositional regions across which the quasicrystalline phase forms are identified. In particular, we demonstrate that the quasicrystalline phase forms across an unusually broad composition range in the Al-Cu-Fe-Cr system. Additionally, some of the considered alloys vitrify during sputtering, which also allows us to study their nucleation behavior. We find that phases with polytetrahedral symmetry, such as the icosahedral quasicrystal and the lambda-Al13Fe4 phase, exhibit higher nucleation rates but lower growth rates, as compared to other phases with a lower degree of polytetrahedral order. Altogether, the here used combinatorial approach is powerful to identify compositional regions of quasicrystals.

Title:
Lattice Discontinuities of 1T-TaS2 across First Order Charge Density Wave Phase Transitions
Authors:
Wang, W; Dietzel, D; Schirmeisen, A Author Full Names: Wang, Wen; Dietzel, Dirk; Schirmeisen, Andre
Source:
SCIENTIFIC REPORTS, 9 10.1038/s41598-019-43307-2 MAY 8 2019
Abstract:
Transition metal dichalcogenides are lamellar materials which can exhibit unique and remarkable electronic behavior due to effects of electron-electron and electron-phonon coupling. Among these materials, 1T-tantalum disulfide (1T-TaS2) has spurred considerable interest, due to its multiple first order phase transitions between different charge density wave (CDW) states. In general, the basic effects of charge density wave formation in 1T-TaS2 can be attributed to in plane re-orientation of Ta-atoms during the phase transitions. Only in recent years, an increasing number of studies has also emphasized the role of interlayer interaction and stacking order as a crucial aspect to understand the specific electronic behavior of 1T-TaS2, especially for technological systems with a finite number of layers. Obviously, continuously monitoring the out of plane expansion of the sample can provide direct inside into the rearrangement of the layer structure during the phase transition. In this letter, we therefore investigate the c-axis lattice discontinuities of 1T-TaS2 by atomic force microscopy (AFM) method under ultra-high vacuum conditions. We find that the c-axis lattice experiences a sudden contraction across the nearly-commensurate CDW (NC-CDW) phase to commensurate CDW (C-CDW) phase transition during cooling, while an expansion is found during the transition from the C-CDW phase to a triclinic CDW phase during heating. Thereby our measurements reveal, how higher order C-CDW phase can favor a more dense stacking. Additionally, our measurements also show subtler effects like e.g. two expansion peaks at the start of the transitions, which can provide further insight into the mechanisms at the onset of CDW phase transitions.

Title:
Crystal Structure and Photoluminescence Properties of an Incommensurate Phase in EuO- and P2O5-Doped Ca2SiO4
Authors:
Hiramatsu, Y; Michiue, Y; Funahashi, S; Hirosaki, N; Banno, H; Urushihara, D; Asaka, T; Fukuda, K Author Full Names: Hiramatsu, Yuya; Michiue, Yuichi; Funahashi, Shiro; Hirosaki, Naoto; Banno, Hiroki; Urushihara, Daisuke; Asaka, Toru; Fukuda, Koichiro
Source:
INORGANIC CHEMISTRY, 58 (9):6155-6160; 10.1021/acs.inorgchem.9b00408 MAY 6 2019
Abstract:
We have for the first time clarified the incommensurately modulated crystal structure as well as the photoluminescence properties of Eu2+ -activated Ca2SiO4 solid solution, the chemical formula of which is (Ca1.88Eu0.012+square(0.11))-(Si0.78P0.22)O-4, where square denotes vacancies in Ca sites with the replacement of Si4+ by P5+. The emission spectrum upon the 335 nm excitation showed a relatively broad band centered at ca. 490 nm and a full width at half-maximum of ca. 80 nm. The crystal structure was made up of the four types of beta-Ca2SiO4-like layers with one type of interlayer. The incommensurate modulation with superspace group Pnma(0 beta 0)00s was induced by the long-range stacking order of these layers. The modulation wavevector was 0.27404(2) x b*, with the basic unit-cell dimensions being a = 0.68355(2) nm, b = 0.54227(2) nm, and c = 0.93840(3) nm (Z = 4). The basic structure contained two nonequivalent Ca sites. One site was fully occupied by Ca2+ and free from Eu2+ in the overall incommensurate structure. The occupational modulation at the other site was so significant that the sum of site occupation factors for Ca2+ and Eu2+ as low as 0.5 was seen at the interlayer. This site was too large for accommodation of Ca2+ but was suitable for Eu2+. Thus, the Eu2+ ions would exclusively concentrate at the relevant site, which would cause the emission peak of the incommensurate phase to be shifted to the shorter wavelength ranges as compared with those of the other commensurate phases such as beta and alpha'(L).

Title:
Synthesis and Atomic Structure of the Yb-Ga-Au 1/1 Quasicrystal Approximant
Authors:
Yamada, T; Kurihara, T; Prots, Y; Sato, A; Matsushita, Y; Grin, Y; Tsai, AP Author Full Names: Yamada, Tsunetomo; Kurihara, Takuya; Prots, Yurii; Sato, Akira; Matsushita, Yoshitaka; Grin, Yuri; Tsai, An Pang
Source:
INORGANIC CHEMISTRY, 58 (9):6320-6327; 10.1021/acs.inorgchem.9b00513 MAY 6 2019
Abstract:
The Yb-Ga-Au 1/1 quasicrystal approximant (AP) composition ranges from Yb14.0Ga20.6Au65.4 to Yb-14.8Ga46.3Au38.9, and single crystals of the 1/1 AP having the composition Yb13.8Ga26.1Au60.1 were obtained by the self-flux technique. X-ray structural analysis demonstrated that the atomic structure [space group Im (3) over bar; a = 14.6889(9) angstrom] can be described by the body-centered packing of Tsai-type rhombic triacontahedron (RTH) clusters. The positional disorder in these clusters, interpreted as the average of an orientationally disordered tetrahedron and triangle, results in positional disorder in the outer shells. The elemental distributions and positions of mixtures of Au and Ga atoms in the RTH clusters correspond to those in the isostructural Yb15Al36Au49 1/1 AP.

Title:
Na3Sm(PO4)(2):(3+1)-dimensional commensurately modulated structure model and photoluminescence properties
Authors:
Zhang, RJ; Zhao, D; Zhong, Q; Xue, YL; Huang, GX Author Full Names: Zhang, Rui-Juan; Zhao, Dan; Zhong, Qiu; Xue, Ya-Li; Huang, Guang-Xu
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE-CRYSTALLINE MATERIALS, 234 (5):281-289; 10.1515/zkri-2018-2095 MAY 2019
Abstract:
For the first time, we determined the detailed crystal structure of Na3Sm(PO4)(2) using single crystal X-ray diffraction and established the commensurately modulated structure model using the superspace formalism. The structure adopts a (3+1)-dimensional superspace group Pca2(1)(0 beta 0)000 with the modulation vector q=1/3b*. At the same time, the photoluminescent properties of Na3Sm(PO4)(2) sintered at different temperatures between 800 and 1200 degrees C were studied. Under near-UV excitation (402 nm), Na3Sm(PO4)(2) shows intense characteristic emission bands of Sm3+ (561, 596, 642 nm) with the CIE coordinate of (0.5709, 0.4282), corresponding to orange color. The excitation spectrum covers a wide range from 350 nm to 470 nm, which indicates that Na3Sm(PO4)(2) can be efficiently activated by near-UV or visuable LED ship.

Title:
Influence of Ni Alloying on the Precipitation of Quasicrystal Phase in As-Cast Mg96.5Zn1Y1.5Mn1 Alloy
Authors:
Zhu, W; Liu, W; Zhang, YG; Ma, QQ; Zhang, JS; Xu, CX Author Full Names: Zhu, Wei; Liu, Wei; Zhang, Yong Gang; Ma, Qiang Qiang; Zhang, Jinshan; Xu, Chunxiang
Source:
ADVANCED ENGINEERING MATERIALS, 21 (4):10.1002/adem.201801238 APR 2019
Abstract:
Ni alloying is first adopted to explore the precipitation of quasicrystal phase (I phase) in Mg96.5Zn1Y1.5Mn1 alloy containing LPSO structure and W phase during solidification. Results show the component of I phase is Mg-3(Zn, Ni)(6)Y-1 which mainly distributes near the W phase. Besides, during the formation of I phase, Ni acts as Zn to participate in the precipitation process of I phase, making up for the deficiency of Zn. Meanwhile, an excellent strength-ductility balance with ultimate tensile strength (210MPa) and elongation (9.5%) is greatly optimized.

Title:
The Effect of Composition on the Formation of a BCC Approximant in Ti-Cr-Al-Si-O Alloys
Authors:
Firstov, SA; Gorban, VF; Karpets, MV; Krapivka, MO; Rokytska, OA; Samelyuk, AV Author Full Names: Firstov, S. A.; Gorban, V. F.; Karpets, M. V.; Krapivka, M. O.; Rokytska, O. A.; Samelyuk, A. V.
Source:
POWDER METALLURGY AND METAL CERAMICS, 57 (11-12):731-739; 10.1007/s11106-019-00038-3 MAR 2019
Abstract:
The microstructure, phase composition, and mechanical properties of Ti-Cr-Al-Si-O alloys in ascast state and after annealing at 800 degrees C have been studied. The as-cast alloys with 50 and 60 at.% Ti have two phases: a 1/1 (TiCrSi) cubic approximant of the quasicrystalline phase and an intermetallic Cr2Ti(C14) Laves phase in different ratios. The as-cast alloy with a high titanium amount (72 at.%) contains three phases: a 1/1(TiCrSi) approximant and two -Ti and -Ti solid solutions. The effect of annealing on the phase composition of the alloys has been studied. After annealing, the alloys with the lowest (50 at.%) and highest (72 at.%) Ti contents change their phase composition with the formation of Ti5Si3 silicide, while the alloy with 60 at.% Ti exhibits high thermal stabilityits phase composition remains unchanged. The changes in hardness of the starting and annealed alloys have been examined by automatic indentation. The highest hardness, 11.7 GPa, is shown by the as-cast Ti72Cr20Al2Si2(SiO2)(4) alloy. The hardness of the annealed Ti50Cr30Al13Si2(SiO2)(5) alloy increases to 14.8 GPa.

Update: 22-May-2019


Title:
Formation and crystallographic orientation study of quasicrystal, 2/1 and 1/1 approximants in Cd-Mg-Y system using electron backscatter diffraction (EBSD)
Authors:
Labib, F; Ohhashi, S; Tsai, AP Author Full Names: Labib, Farid; Ohhashi, Satoshi; Tsai, An-Pang
Source:
PHILOSOPHICAL MAGAZINE, 99 (12):1528-1550; 10.1080/14786435.2019.1585589 JUN 18 2019
Abstract:
A partial isothermal ternary phase diagram of the Cd-Mg-Y system including icosahedral quasicrystal (i-QC) and 1/1 approximant (APP) was obtained at 673 K. The stability of the i-QC and APPs in terms of composition and temperature was studied, as a result of which the 2/1 APP phase was discovered at 773 K. Moreover, the i-QC phase was found to be stable at lower Y concentrations of similar to 12-13 at.%, as compared to the 1/1 APP, which showed similar to 15-16 at.% Y. Single i-QC, 2/1 and 1/1 APP grains were also synthesized applying centrifuging system. Electron backscatter diffraction (EBSD) characterization of the obtained i-QC and APPs revealed almost the same Kikuchi patterns for the i-QC and 2/1 APP, indicating high resemblance of their structures. However, the Kikuchi pattern acquired from the 1/1 APP was distinguishable from the one obtained from the i-QC as it showed split bands. The occurrence of the split bands was associated with significant deviation from a perfect icosahedral symmetry. This was also confirmed by analysing calculated electron diffraction and Kikuchi patterns along pseudo-five-fold axes of the 2/1 and 1/1 APPs. Finally, orientation relationships between the i-QC, 1/1 APP and alpha-Mg were investigated by analysing acquired EBSD Kikuchi patterns from the respective domains. Accordingly, three perpendicular two-fold axes of the i-QC and {100} axes of the 1/1 APP occur along three mutually orthogonal {0001}, {10-10} and {11-20} axes of the alpha-Mg.

Title:
Effect of Ca Doping on Modulated Structures in Multiferroic Bi1-xCaxFeO3
Authors:
Hiroyama, T; Hirata, A; Inoue, Y; Horibe, Y; Koyama, Y Author Full Names: Hiroyama, Takumi; Hirata, Akihiko; Inoue, Yasuhide; Horibe, Yoichi; Koyama, Yasumasa
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 88 (5):10.7566/JPSJ.88.054601 MAY 15 2019
Abstract:
The crystallographic features of Bi1-xCaxFeO3 samples with x = 0.10, 0.15, 0.20, and 0.30 compositions are investigated by transmission electron microscopy. Perovskite-based modulated structures are found in all the samples except for the x = 0.10 sample where a rhombohedral R3c BiFeO3-type structure is observed at room temperature. The in situ heating experiment indicates that the modulated structure appears even in the x = 0.10 sample at 673K or higher. At room temperature, the modulation direction is found to change at approximately x = 0.20. The models of the modulated structures are constructed by introducing periodic antiphase boundaries in terms of the M-3-type rotational displacements of the FeO6 octahedra. The electron diffraction patterns simulated from the models are in good agreement with the experimental results. The composition dependence of the modulated structures is also discussed.

Title:
Preparation and electro-catalytic activity of nanoporous palladium by dealloying rapidly-quenched Al70Pd17Fe13 quasicrystalline alloy
Authors:
Liu, XY; Wang, YM; Qiang, JB; Wang, BL; Ma, DG; Zhang, W; Dong, C Author Full Names: Liu, Xin-yi; Wang, Ying-min; Qiang, Jian-bing; Wang, Bao-lin; Ma, Dian-guo; Zhang, Wei; Dong, Chuang
Source:
TRANSACTIONS OF NONFERROUS METALS SOCIETY OF CHINA, 29 (4):785-790; 10.1016/S1003-6326(19)64988-5 APR 2019
Abstract:
The formation of nanoporous Pd was studied by electro-chemical dealloying a rapidly-quenched Al70Pd17Fe13 quasicrystal alloy in dilute NaCl aqueous solution, and the electro-catalytic activity of the nanoporous Pd towards methanol electro-oxidation was evaluated by cyclic voltammetry in 1 mol/L KOH solution. XRD and TEM analyses revealed that nano-decomposition of quasicrystal grains occurred in the initial stage of dealloying, and the fully dealloyed sample was composed of FCC-Pd phase. Scanning electron microscopy observation indicated that a maze-like nanoporous pattern was formed in the dealloyed sample, consisting of percolated pores of 5-20 nm in diameter in a skeleton of randomly-orientated Pd nano-ligaments with a uniform thickness of similar to 5 nm. A retention of similar to 12 at.% Al in the Pd nano-ligments was determined by energy dispersive X-ray spectroscopy (EDS). The nanoporous Pd demonstrated obvious electro-catalytic activity towards methanol electro-oxidation in alkaline environment.

Title:
Analytic Solutions to Two-Dimensional Decagonal Quasicrystals with Defects Using Complex Potential Theory
Authors:
Cao, HB; Shi, YQ; Li, W Author Full Names: Cao, Haobai; Shi, Yiqing; Li, Wu
Source:
CRYSTALS, 9 (4):10.3390/cryst9040209 APR 2019
Abstract:
An analytical treatment for two-dimensional point group 10 mm decagonal quasicrystals with defects was suggested based on the complex potential method. On the basis of the assumption of linear elasticity, two new conformal maps were applied to two examples: the first was an arc with an elliptic notch inner surface in a decagonal quasicrystal, where the complex potentials could be exactly obtained; and the second was concerned with a decagonal point group 10 mm quasicrystalline strip weakened by a Griffith crack, which was subjected to a pair of uniform static pressures. Using the basic idea underlying crack theory, the extent of the stress intensity factors was analytically estimated. If the height was allowed to approach infinity, these results can be turned into the known results of an ordinary crystal with only phonon elastic parameters when the phason and phonon-phason elastic constants are eliminated.

Title:
Y3Ru2-x-A Representative of a Composite Modulated Family of Intermetallics
Authors:
Lidin, S; Folkers, L Author Full Names: Lidin, Sven; Folkers, Laura
Source:
CRYSTALS, 9 (4):10.3390/cryst9040189 APR 2019
Abstract:
The compound Y3Ru2-x was synthesized from the elements and the structure was solved from single crystal synchrotron data. The high quality of the data allowed the determination of the incommensurate ordering of the compound, previously reported as disordered, with respect to the second subsystem. The compound crystallizes in the super space group X-3(00)0 with the q-vector axial along c*, q = 00, = 0.4276(7) and the centering vectors (1/3 2/3 0 1/3), (2/3 1/3 0 2/3).

Title:
Formation of ethylene-vinyl acetate composites filled with Al-Cu-Fe and Al-Cu-Cr quasicrystallline particles
Authors:
Tcherdyntsev, VV; Stepashkin, AA; Chukov, DI; Olifirov, LK; Senatov, FS Author Full Names: Tcherdyntsev, Victor V.; Stepashkin, Andrey A.; Chukov, Dilyus, I; Olifirov, Leonid K.; Senatov, Fedor S.
Source:
JOURNAL OF MATERIALS RESEARCH AND TECHNOLOGY-JMR&T, 18 (1):572-589; 10.1016/j.jmrt.2018.05.008 JAN-MAR 2019
Abstract:
Icosahedral Al65Cu23Fe12 and decagonal Al73Cu11Cr16 quasicrystalline powders were synthesized by the mechanical alloying and subsequent annealing. Morphology evolution at mechanical alloying of Al-based powders was found to be determined by competition between cold welding and fracture mechanisms. Mechanical alloying results in formation of coarse agglomerates consisting of fine particles. The chemical binding between the polymer matrix and quasicrystals, destruction of agglomerated at extrusion, and the uniform distribution of quasicrystals over the polymer melt were provided by surface treatment of quasicrystalline particles with silanes. The highly filled (up to 60 wt%) ethylene-vinyl acetate/quasicrystals composites were obtained, and their rheological characteristics were studied. It was shown that the fluidity of the melt is retained at a high level providing uniform distribution of quasicrystalline particles over the polymer. (C) 2018 Brazilian Metallurgical, Materials and Mining Association. Published by Elsevier Editora Ltda.

Title:
Study of the surface properties of the epoxy/quasicrystal composite
Authors:
Barros, TPD; Cavalcante, DGD; de Oliveira, DF; Caluete, RE; de Lima, SJG Author Full Names: dos Santos Barros, Thayza Pacheco; de Lima Cavalcante, Danielle Guedes; de Oliveira, Danniel Ferreira; Caluete, Rafael Evaristo; Guedes de Lima, Severino Jackson
Source:
JOURNAL OF MATERIALS RESEARCH AND TECHNOLOGY-JMR&T, 18 (1):590-598; 10.1016/j.jmrt.2018.04.015 JAN-MAR 2019
Abstract:
This work consists of the study of the surface and Hardness properties of epoxy/quasicrystal (QC) composites. The composites had volumetric proportions of 1%, 10%, 20% and 30%, where the comparison was made between the composites and the pure epoxy resin. Techniques of Shore D Hardness, Thermogravimetric Analysis Techniques, Roughness Test, Contact Angle Analysis and Scanning Electron Microscopy (SEM) were used. Wettability test allowed to analyze the surface of the composite under the influence of two liquids: saline water and paraffinic oil. Regarding the composite and the pure resin, the contact angle increased when the liquid used in the test was saline water and decreased when exposed to paraffinic oil. It could be ensured that this small variation of the contact angles in relation to the increase of the composition occurred due to the influence of the roughness. In relation to saline water, the roughness has operated in order to prevent the liquid from spreading on the composite. As for paraffinic oil, it influenced in an opposite way, absorbing the oil and reducing the angle formed. When analyzing the pure quasicrystal, the effect was contrary to that of the composite: when it was exposed to saline water the contact angle decreased, on the other hand when exposed to paraffinic oil the resulting angle increased. This effect is related to the low polarity of the Quasicrystal, which when exposed to an apolar liquid tends to repel, thus forming a greater contact angle. Through this study it is concluded that it was possible to obtain a composite QC/Epoxy with greater hardness and still maintain its surface characteristics. (C) 2018 Published by Elsevier Editora Ltda. on behalf of Brazilian Metallurgical, Materials and Mining Association.

Update: 15-May-2019


Title:
Density Wave Probes Cuprate Quantum Phase Transition
Authors:
Webb, TA; Boyer, MC; Yin, Y; Chowdhury, D; He, Y; Kondo, T; Takeuchi, T; Ikuta, H; Hudson, EW; Hoffman, JE; Hamidian, MH Author Full Names: Webb, Tatiana A.; Boyer, Michael C.; Yin, Yi; Chowdhury, Debanjan; He, Yang; Kondo, Takeshi; Takeuchi, T.; Ikuta, H.; Hudson, Eric W.; Hoffman, Jennifer E.; Hamidian, Mohammad H.
Source:
PHYSICAL REVIEW X, 9 (2):10.1103/PhysRevX.9.021021 MAY 1 2019
Abstract:
In cuprates, the strong correlations in proximity to the antiferromagnetic Mott insulating state give rise to an array of unconventional phenomena beyond high-temperature superconductivity. Developing a complete description of the ground-state evolution is crucial to decoding the complex phase diagram. Here we use the structure of broken translational symmetry, namely, d-form factor charge modulations in (Bi, Pb)(2) (Sr, La)(2)CuO6+delta as a probe of the ground-state reorganization that occurs at the transition from truncated Fermi arcs to a large Fermi surface. We use real space imaging of nanoscale electronic inhomogeneity as a tool to access a range of dopings within each sample, and we definitively validate the spectral gap Delta as a proxy for local hole doping. From the Delta dependence of the charge modulation wave vector, we discover a commensurate-to-incommensurate transition that is coincident with the Fermi-surface transition from arcs to large hole pocket, demonstrating the qualitatively distinct nature of the electronic correlations governing the two sides of this quantum phase transition. Furthermore, the doping dependence of the incommensurate wave vector on the overdoped side is at odds with a simple Fermi-surface-driven instability.

Title:
Reprogrammability and Scalability of Magnonic Fibonacci Quasicrystals
Authors:
Lisiecki, F; Rychly, J; Kuswik, P; Glowinski, H; Klos, JW; Gross, F; Bykova, I; Weigand, M; Zelent, M; Goering, EJ; Schutz, G; Gubbiotti, G; Krawczyk, M; Stobiecki, F; Dubowik, J; Grafe, J Author Full Names: Lisiecki, Filip; Rychly, Justyna; Kuswik, Piotr; Glowinski, Hubert; Klos, Jaroslaw W.; Gross, Felix; Bykova, Iuliia; Weigand, Markus; Zelent, Mateusz; Goering, Eberhard J.; Schuetz, Gisela; Gubbiotti, Gianluca; Krawczyk, Maciej; Stobiecki, Feliks; Dubowik, Janusz; Graefe, Joachim
Source:
PHYSICAL REVIEW APPLIED, 11 (5):10.1103/PhysRevApplied.11.054003 MAY 1 2019
Abstract:
Magnonic crystals are systems that can be used to design and tune the dynamic properties of magnetization. Here, we focus on one-dimensional Fibonacci magnonic quasicrystals. We confirm the existence of collective spin waves propagating through the structure as well as dispersionless modes; the reprogammability of the resonance frequencies, dependent on the magnetization order; and dynamic spin-wave interactions. With the fundamental understanding of these properties, we lay a foundation for the scalable and advanced design of spin-wave band structures for spintronic, microwave, and magnonic applications.

Title:
Incommensurate 2k(F) density wave quantum criticality in two-dimensional metals
Authors:
Halbinger, J; Pimenov, D; Punk, M Author Full Names: Halbinger, Johannes; Pimenov, Dimitri; Punk, Matthias
Source:
PHYSICAL REVIEW B, 99 (19):10.1103/PhysRevB.99.195102 MAY 1 2019
Abstract:
We revisit the problem of two-dimensional metals in the vicinity of a quantum phase transition to incommensurate Q = 2k(F) charge-density-wave order, where the order-parameter wave vector Q connects two hot spots on the Fermi surface with parallel tangents. Earlier theoretical works argued that such critical points are potentially unstable, if the Fermi surface at the hot spots is not sufficiently flat. Here we perform a controlled, perturbative renormalization-group analysis and find a stable fixed point corresponding to a continuous quantum phase transition, which exhibits a strong dynamical nesting of the Fermi surface at the hot spots. We derive scaling forms of correlation functions at the critical point and discuss potential implications for experiments with transition-metal dichalcogenides and rare-earth tellurides.

Title:
Quasicrystalline electronic states in 30 degrees rotated twisted bilayer graphene
Authors:
Moon, P; Koshino, M; Son, YW Author Full Names: Moon, Pilkyung; Koshino, Mikito; Son, Young-Woo
Source:
PHYSICAL REVIEW B, 99 (16):10.1103/PhysRevB.99.165430 APR 29 2019
Abstract:
The recently realized bilayer graphene system with a twist angle of 30 degrees offers a new type of quasicrystal which unites the dodecagonal quasicrystalline nature and graphene's relativistic properties. Here, we introduce a concise theoretical framework that fully respects both the dodecagonal rotational symmetry and the massless Dirac nature, to describe the electronic states of the system. We find that the electronic spectrum consists of resonant states labeled by 12-fold quantized angular momentum, together with the extended relativistic states. The resulting quasiband structure is composed of the nearly flat bands with spiky peaks in the density of states, where the wave functions exhibit characteristic patterns which fit to the fractal inflations of the quasicrystal tiling. We also demonstrate that the 12-fold resonant states appear as spatially localized states in a finite-size geometry, which is another hallmark of quasicrystal. The theoretical method introduced here is applicable to a broad class of "extrinsic quasicrystals" composed of a pair of two-dimensional crystals overlaid on top of the other with incommensurate configurations.

Update: 8-May-2019


Title:
Effect of thermal treatment upon the structure incommensurability and magnetism of the spin chain oxide Sr3CaMn2CoO9+delta
Authors:
Seikh, MM; Caignaert, V; Sakly, N; Perez, O; Raveau, B; Hardy, V Author Full Names: Seikh, Md. Motin; Caignaert, Vincent; Sakly, Nahed; Perez, Olivier; Raveau, Bernard; Hardy, Vincent
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 790 572-576; 10.1016/j.jallcom.2019.03.183 JUN 25 2019
Abstract:
Spin chain oxides with different incommensurate hexagonal composite structures have been obtained for a same cationic composition according to the formula Sr3CaMn2CoO9+delta by varying the thermal treatments in air. The cell parameters of these oxides, a-9.5 angstrom, c(1)similar to 2.5 angstrom and c(2)similar to 3.8 angstrom, decrease as the deviation from commensurability increases, i.e. as gamma = c(1)/c(2) decreases and falls away from 2/3. All the investigated samples exhibit a signature typical of single-ion magnet (SIM), as well as a competition between single-chain magnet (SCM) and short-range ordering (SRO) responses. The balance between the latter two features turns out to be clearly affected by the thermal treatment. The sample quenched at 1450 degrees C, which structure is almost commensurate (gamma = 0.6659, close to 2/3), exhibits a SCM behavior without sizeable indication of SRO, whereas, for the samples annealed at 1300 degrees C or furnace cooled from 1400 degrees C with an incommensurate structure (gamma = 0.6622-0.6631), the SRO character is strongly reinforced. These changes in the magnetic response are assumed to originate from incorporation of extra oxygen into the commensurate stoichiometric Sr3CaMn2CoO9 oxide, leading to the replacement of some trimeric units built up of two octahedra and one trigonal prism (Oh(2)Tp) by tetrameric units (Oh(3)Tp) containing one additional octahedron, with a concomitant appearance of cationic vacancies in the trigonal prismatic sites. (C) 2019 Elsevier B.V. All rights reserved.

Title:
Many-beam dynamical scattering simulations for scanning and transmission electron microscopy modalities for 2D and 3D quasicrystals
Authors:
Singh, S; Lenthe, WC; De Graef, M Author Full Names: Singh, Saransh; Lenthe, William C.; De Graef, Marc
Source:
PHILOSOPHICAL MAGAZINE, 10.1080/14786435.2019.1605217
Abstract:
We present a general theory of electron scattering from both 2D and 3D quasicrystals, applicable to both transmission (forescatter) and scanning (backscatter) geometries. Specifically, simulations of conventional zone axis diffraction patterns, convergent beam diffraction patterns and electron backscatter diffraction for decagonal AlNiCo are presented. As expected, the geometry of the diffraction pattern is similar to kinematical patterns, but the intensity distributions show strong dynamical effects in all the modalities. Experimental electron backscatter diffraction patterns for AlNiCo are compared to simulated patterns for this 2D quasicrystalline structure as well as one of its crystalline monoclinic approximant phases, CoAl. While the simulated patterns from the quasicrystalline and approximant phases are very similar to the experimental patterns, direct comparison shows a better agreement with the decagonal phase.

Title:
Looking for alternatives to the superspace description of icosahedral quasicrystals
Authors:
Madison, AE; Madison, PA Author Full Names: Madison, A. E.; Madison, P. A.
Source:
PROCEEDINGS OF THE ROYAL SOCIETY A-MATHEMATICAL PHYSICAL AND ENGINEERING SCIENCES, 475 (2221):10.1098/rspa.2018.0667 JAN 2019
Abstract:
A multiple-cell approach is discussed as a possible alternative to the higher dimensional crystallography of icosahedral quasicrystals. It is based on the Socolar-Steinhardt tiling combined with the quasi-unit cell model. Quasi-unit cells fill the space without gaps and overlappings similar to those in periodic crystals. Similarly, the atoms can occupy general and special positions. The alloy stoichiometry and the packing density can be calculated through the relative tile frequencies, which in turn are determined as the components of the Perron-Frobenius eigenvector of the corresponding substitution matrix. The calculation of the diffraction pattern reduces to the Perron projection of a special matrix, the entries of which reflect the contribution of each type of quasi-unit cell to the coherent scattering.

Update: 2-May-2019


Title:
Characterization of aluminium matrix compositesreinforced by Al-Cu-Fe-Cr quasicrystalline particles
Authors:
Yuan, Y; Hou, H; Zhao, YH; Yan, F Author Full Names: Yuan, Ye; Hou, Hua; Zhao, Yuhong; Yan, Feng
Source:
MATERIALS RESEARCH EXPRESS, 6 (7):10.1088/2053-1591/ab15a4 JUL 2019
Abstract:
The Al63Cu25Fe9Cr3 quasicrystalline was prepared by conventional casting method. The microstructures and phase composition of Al63Cu25Fe12 quasi-crystalline and Al65Cu20Fe10Cr5 phases were characterized by XRD and SEM. Aluminium based composites was fabricated by using the Al63Cu25Fe9Cr3 quasicrystalline particles as the reinforcing phase and ZL101 as matrix with mechanical stirring. The effects of quasicrystals content, on the microstructure and mechanical properties of the obtained composite, were investigated. The results show that the as-cast quasicrystalline material is composed of d-phase(Al65Cu20Fe10Cr5), I-phase(Al63Cu25Fe12), lambda-Al3Fe, beta-AlFe3 and a small amount of eta-AlCu, theta-Al2Cu phases. After heat treatment, the quasicrystalline intermediate alloy composition tends to quasicrystal phase. In the composite material, the diffusion between the quasicrystalline and the matrix alloy caused the decomposition of the structure of quasicrystalline phase. With the increase of quasicrystalline content, the tensile strength of the composites increases. However, addition of the Cr element changes the acicular beta-Fe(Al80-85Fe6-9Si10-15) phase into a manlike or bone-like alpha-Fe(Al80-85Fe4-8Si6-8Cr3-5) phase which increases the elongation of the composite. The best comprehensive mechanical properties corresponded to the 7 wt% quasicrystalline particles. Strengthening mechanism of quasicrystal reinforced aluminum matrix composites, a model that model considers the dislocation strengthening mechanism and the effect of load transfers mechanism on the tensile strength of composites. This theory calculates the tensile strength of quasicrystalline reinforced aluminum matrix composites and verifies the effectiveness of the model through experiments.

Title:
Effect of selective post-aging treatment on subsurface damage of quasicrystal reinforced Al composite manufactured by selective laser melting
Authors:
Kang, N; El Mansori, M; Lu, JL; Lin, X; Huang, WD Author Full Names: Kang, N.; El Mansori, M.; Lu, J. L.; Lin, X.; Huang, W. D.
Source:
WEAR, 426 934-941; 10.1016/j.wear.2018.12.048 B APR 30 2019
Abstract:
In this work, Al-Fe-Cr quasicrystal reinforced Al matrix composite was in-situ prepared by using selective laser melting from powder mixture of Al-Cu-Fe-Cr quasicrystal and pure Al. The effect of selective post-aging treatment on microstructure and mechanical properties were determined with focus on the metastable phases. The microstructural analysis, which was determined by X-ray diffraction and scanning electron microscopy, indicates that the Al-based intermetallic is precipitated from supersaturated alpha-Al after the aging process. Moreover, the compression tests were performed on the samples in form of dense and lattice structures (50% porosity). The elastic modules of dense and lattice structural samples reduce from 21.3 GPa and 4.4-14.6 GPa and 3.6 GPa by using a low cooling-rated aging process. After aging process, the compressive deformation behavior of dense part changes from elastic-plastic-fracture mode to elastic-plastic-densification mode. On the other hand, the failure mechanism of lattice structural sample changes from rapid-single-stage to slow-double-stage with an improvement of the strain at failure.

Title:
Unconventional Charge Density Wave Order in the Pnictide Superconductor Ba(Ni1-xCox)(2)As-2
Authors:
Lee, S; de la Pena, G; Sun, SXL; Mitrano, M; Fang, YZ; Jang, HY; Lee, JS; Eckberg, C; Campbell, D; Collini, J; Paglione, J; de Groot, FMF; Abbamonte, P Author Full Names: Lee, Sangjun; de la Pena, Gilberto; Sun, Stella X-L; Mitrano, Matteo; Fang, Yizhi; Jang, Hoyoung; Lee, Jun-Sik; Eckberg, Chris; Campbell, Daniel; Collini, John; Paglione, Johnpierre; de Groot, F. M. F.; Abbamonte, Peter
Source:
PHYSICAL REVIEW LETTERS, 122 (14):10.1103/PhysRevLett.122.147601 APR 12 2019
Abstract:
Ba(Ni1-xCox)(2)As-2 is a structural homologue of the pnictide high temperature superconductor, Ba(Fe1-xCox)(2)As-2, in which the Fe atoms are replaced by Ni. Superconductivity is highly suppressed in this system, reaching a maximum T-c = 2.3 K, compared to 24 K in its iron-based cousin, and the origin of this T-c suppression is not known. Using x-ray scattering, we show that Ba(Ni1-xCox)(2)As-2 exhibits a unidirectional charge density wave (CDW) at its triclinic phase transition. The CDW is incommensurate, exhibits a sizable lattice distortion, and is accompanied by the appearance of alpha Fermi surface pockets in photoemission [B. Zhou et al., Phys. Rev. B 83, 035110 (2011)], suggesting it forms by an unconventional mechanism. Co doping suppresses the CDW, paralleling the behavior of antiferromagnetism in iron-based superconductors. Our study demonstrates that pnictide superconductors can exhibit competing CDW order, which may be the origin of T-c suppression in this system.

Title:
Electron diffraction study of crystal structures of (Sr1-xBax)(2)Nb2O7
Authors:
Aryal, B; Morikawa, D; Tsuda, K; Tsukada, S; Akishige, Y; Terauchi, M Author Full Names: Aryal, Bikas; Morikawa, Daisuke; Tsuda, Kenji; Tsukada, Shinya; Akishige, Yukikuni; Terauchi, Masami
Source:
PHYSICAL REVIEW MATERIALS, 3 (4):10.1103/PhysRevMaterials.3.044405 APR 12 2019
Abstract:
Selected-area electron diffraction and convergent-beam electron diffraction (CBED) techniques are used to reveal the Ba doping effect on the crystal structure of (Sr1-xBax)(2)Nb2O7 [SBN(x)] in the temperature range from 293 to 693 K. Ba doping of Sr2Nb2O7 (SN) causes weakening of the incommensurate modulation and deviation from the C-centered lattice. On the other hand, symmetries of fundamental reflections in CBED patterns of SBN(x) are seen to be the same as those of SN, showing a small structural deviation from Cmc2(1). Crystal symmetries above and below the temperature of a relaxorlike dielectric anomaly in SBN (x = 0.32) at 465 K remain unchanged. CBED experiments with a nanometer-sized electron probe do not show any indication of the presence of a nanodomain around this temperature. However, the presence of a few-micron-sized polar-inversion domains is found at around 573 K in SBN (x = 0.32). The origin of the reported relaxorlike dielectric anomaly in SBN (x = 0.32) is discussed on the basis of the experimental results of CBED.

Update: 25-Apr-2019


Title:
Influence of Ir Additions and Icosahedral Short Range Order (ISRO) on Nucleation and Growth Kinetics in Au-20.5Wt Pct Cu-4.5Wt PctAg Alloy
Authors:
Zollinger, J; Rouat, B; Guyon, J; Pillai, SK; Rappaz, M Author Full Names: Zollinger, J.; Rouat, B.; Guyon, J.; Pillai, S. K.; Rappaz, M.
Source:
METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE, 50A (5):2279-2288; 10.1007/s11661-019-05176-2 MAY 2019
Abstract:
Based on detailed EBSD analyses, Kurtuldu et al. (Acta Mater. 70:240-248, 2014) have explained the grain refinement of Au-12.5 wt pctCu-12.5 wt pctAg (yellow gold) by the addition of minute amounts of Ir in terms of icosahedral quasicrystal (iQC)-mediated nucleation, i.e., Ir induced the formation of Icosahedral short range order (ISRO) of atoms in the liquid, leading to the formation of iQC on which the fcc-phase forms. In the present contribution, we show that: (i) this mechanism is also responsible of the grain refinement in Au-20.5 wt pctCu-4.5 wt pctAg (pink gold) with Ir addition; (ii) ISRO also influences the morphology and growth kinetics of the fcc phase: at solidification rate of a few mm/s, 100 dendrites are replaced by a cellular-type morphology growing along 111 when 100 wt ppm of Ir is added to the melt; (iii) iQC-mediated nucleation is accompanied by a spinodal decomposition of the liquid, which is revealed at high cooling rate by the formation of Cu-rich particles or dendrites, some of them being also twinned, in parallel to iQC-mediated grain refinement and twin formation. (C) The Minerals, Metals & Materials Society and ASM International 2019

Title:
Structural evolution of La2Ti2O7 at elevated temperatures
Authors:
Ishizawa, N; Ninomiya, K; Wang, J Author Full Names: Ishizawa, Nobuo; Ninomiya, Keisuke; Wang, Jun
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 75 10.1107/S2052520619002105 2 APR 2019
Abstract:
Structural evolution of a La2Ti2O7 ferroelectric compound possessing perovskite-type slabs at elevated temperatures was investigated using the single-crystal X-ray diffraction technique. The monoclinic low-temperature phase (L) transformed into the orthorhombic high-temperature phase (H) via an incommensurately modulated phase (IC) between similar to 989 and similar to 1080 K. The L-IC transition was considered to be of the first order, with the L+IC two-phase co-existing region between similar to 989 and similar to 1027 K. The structure of IC was determined from the (3+1)-dimensional superspace representation with a modulation vector q = alpha a(o) (alpha similar or equal to 0.49), where a o is the a-axis vector of the basic cell. The structural modulation originated from the variation of the tilt angle of the TiO6 octahedra in the perovskite-type slab in association with small positional displacements of La atoms. The IC-H transition took place at -1080 K and was close to the second order. During the IC-H transition, nanoscale flat plate domains having either a cell twin of the L-type structural modules or a cell twin of the alternating H- and L-type structural modules began to appear in the approximant structure of IC. The thickness of the flat plate domains then grew rapidly along the modulation vector in proportion to (1/2-alpha)(-1) as alpha approached 1/2 with decreasing temperature. In the two-phase L+IC co-existing region, the IC phase consisting of the two types of cell twins was gradually replaced with the low-temperature monoclinic phase L, which is not cell twinned but rather twinned macroscopically by the L-type structural modules.

Update: 17-Apr-2019


Title:
Distortion analysis of crystalline and locally quasicrystalline 2D photonic structures with grazing-incidence small-angle X-ray scattering
Authors:
Pfluger, M; Soltwisch, V; Xavier, J; Probst, J; Scholze, F; Becker, C; Krumrey, M Author Full Names: Pflueger, Mika; Soltwisch, Victor; Xavier, Jolly; Probst, Juergen; Scholze, Frank; Becker, Christiane; Krumrey, Michael
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY, 52 322-331; 10.1107/S1600576719001080 2 APR 2019
Abstract:
In this study, grazing-incidence small-angle X-ray scattering (GISAXS) is used to collect statistical information on dimensional parameters in an area of 20 x 15 mm on photonic structures produced by nanoimprint lithography. The photonic structures are composed of crystalline and locally quasicrystalline two-dimensional patterns with structure sizes between about 100 nm and 10 mu m to enable broadband visible light absorption for use in solar-energy harvesting. These first GISAXS measurements on locally quasicrystalline samples demonstrate that GISAXS is capable of showing the locally quasicrystalline nature of the samples while at the same time revealing the long-range periodicity introduced by the lattice design. The scattering is described qualitatively in the framework of the distorted-wave Born approximation using a hierarchical model mirroring the sample design, which consists of a rectangular and locally quasicrystalline supercell that is repeated periodically to fill the whole surface. The nanoimprinted samples are compared with a sample manufactured using electron-beam lithography and the distortions of the periodic and locally quasiperiodic samples are quantified statistically. Owing to the high sensitivity of GISAXS to deviations from the perfect lattice, the misalignment of the crystallographic axes was measured with a resolution of 0.015 degrees, showing distortions of up to +/- 0.15 degrees in the investigated samples.

Title:
Effects of semisolid treatment and ECAP on the microstructure and mechanical properties of Mg-6.52Zn-0.95Y alloy with icosahedral phase
Authors:
Li, KN; Zhang, YB; Zeng, Q; Huang, GH; Ji, B; Yin, DD Author Full Names: Li, K. N.; Zhang, Y. B.; Zeng, Q.; Huang, G. H.; Ji, B.; Yin, D. D.
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 751 283-291; 10.1016/j.msea.2019.02.083 MAR 28 2019
Abstract:
The microstructure evolutions and mechanical properties of Mg-6.52Zn-0.95Y (wt%) alloy with icosahedral phase (I-phase) by semisolid treatment and equal channel angular processing (ECAP) were systematically investigated. After semisolid treatment, lamellar ultra-fine eutectic phases with spacing of 100 +/- 19 nm formed at the grain boundaries. After subsequent 4 passes ECAP, fine grains (2.9 +/- 0.4 gm) were obtained and the lamellar eutectic phases were fragmented into 50-500 nm granular particles. The best comprehensive mechanical properties with ultimate tensile strength (UTS) of 385 +/- 18 MPa, tensile yield strength (TYS) of 290 +/- 3 MPa and elongation to failure (EL) of 22.0 +/- 1.6% were obtained by the combination of semisolid treatment and subsequent 2 passes ECAP at 300 degrees C followed by 2 passes ECAP at 200 degrees C, compared with that by the initial alloy. The improvement of mechanical properties results from combined effects of the grain refinement, dispersion of nanoscale I-phase particles and weakened basal texture. In addition, the I-phase particles contributed to the grain refinement during dynamic recrystallization by particle stimulated nucleation (PSN), which contributed to both strength and ductility. The average Schmid factor (SF) of basal slip increased from 0.2 to 0.4 after semisolid treatment and ECAP processing, which benefit the ductility.

Title:
Influence of cobalt substitution on the magnetism of NiBr2
Authors:
Rai, BK; Christianson, AD; Mandrus, D; May, AF Author Full Names: Rai, Binod K.; Christianson, Andrew D.; Mandrus, David; May, Andrew F.
Source:
PHYSICAL REVIEW MATERIALS, 3 (3):10.1103/PhysRevMaterials.3.034005 MAR 25 2019
Abstract:
Co-substituted Ni1-xCoxBr2 (0 <= x <= 1) single crystals were synthesized using vapor transport. The physical properties of the crystals were characterized by x-ray powder diffraction, magnetization, and specific-heat measurements. Room-temperature x-ray powder diffraction data indicate that a change from the CdCl2 structure type to the CdI2 structure type occurs within 0.56 < x < 0.76. NiBr2 has a commensurate antiferromagnetic phase below TN approximate to 46 K and an incommensurate magnetic ground state below TIC approximate to 20 K. Both magnetic transitions are affected by cobalt substitution, and the incommensurate phase transition is present up to at least x = 0.56. The evolution of magnetism has been studied as a function of cobalt content and is summarized in the temperature-composition phase diagram.

Title:
A neutron diffraction demonstration of long-range magnetic order in the quasicrystal approximant DyCd6
Authors:
Ryan, DH; Cadogan, JM; Kong, T; Canfield, PC; Goldman, AI; Kreyssig, A Author Full Names: Ryan, D. H.; Cadogan, J. M.; Kong, T.; Canfield, P. C.; Goldman, A. I.; Kreyssig, A.
Source:
AIP ADVANCES, 9 (3):10.1063/1.5079991 MAR 2019
Abstract:
We have used neutron powder diffraction to demonstrate the existence of long-range antiferromagnetic order of Ising-like Dy moments in the DyCd6 quasicrystal approximant phase. This cubic compound undergoes a slight distortion to a monoclinic cell at low temperatures. The Neel temperature is 18.0(2) K and the magnetic order of the Dy sublattice may be described in the parent cubic Im (3) over bar structure using a combination of two propagation vectors, k(1) = [0 0 0] and k(2) = [1/2 0 1/2], yielding 'anti-I' order. Alternatively, when referred to the monoclinic C2/c cell, the magnetic structure may be described by a single propagation vector: k = [1 0 0]. (C) 2019 Author(s).

Title:
Modulated magnetic structure in Fe-57 doped orthorhombic YbMnO3: A Mossbauer study
Authors:
Duttine, M; Wattiaux, A; Balima, F; Decorse, C; Moutaabbid, H; Ryan, DH; Bonville, P Author Full Names: Duttine, Mathieu; Wattiaux, Alain; Balima, Felix; Decorse, Claudia; Moutaabbid, Hicham; Ryan, D. H.; Bonville, Pierre
Source:
AIP ADVANCES, 9 (3):10.1063/1.5077005 MAR 2019
Abstract:
In the orthorhombic manganites o-RMnO3, where R is a heavy rare earth (R = Gd-Yb), the Mn3+ sublattice is known to undergo two magnetic transitions. The low temperature phase has an antiferromagnetic structure (collinear or elliptical), which has been well characterized by neutron diffraction in most of these compounds. The intermediate phase, occurring in a narrow temperature range (a few K), is documented for R = Gd-Ho as a collinear modulated structure, incommensurate with the lattice spacings. We report here on a Fe-57 Mossbauer study of 2% Fe-57 doped o-YbMnO3, where the spin only Fe3+ ion plays the role of a magnetic probe. From the analysis of the shape of the magnetic hyperfine Mossbauer spectra, we show that the magnetic structure of the intermediate phase in o-YbMnO3 (38.0 K < T < 41.5 K) is also modulated and incommensurate. (C) 2019 Author(s).

Update: 10-Apr-2019


Title:
Relaxing Kondo-screened Kramers doublets in CeRhSi3
Authors:
Pasztorova, J; Howell, A; Songvilay, M; Sarte, PM; Rodriguez-Rivera, JA; Arevalo-Lopez, AM; Schmalzl, K; Schneidewind, A; Dunsiger, SR; Singh, DK; Petrovic, C; Hu, R; Stock, C Author Full Names: Pasztorova, J.; Howell, A.; Songvilay, M.; Sarte, P. M.; Rodriguez-Rivera, J. A.; Arevalo-Lopez, A. M.; Schmalzl, K.; Schneidewind, A.; Dunsiger, S. R.; Singh, D. K.; Petrovic, C.; Hu, R.; Stock, C.
Source:
PHYSICAL REVIEW B, 99 (12):10.1103/PhysRevB.99.125144 MAR 25 2019
Abstract:
CeRhSi3 is a superconductor under pressure coexisting with a weakly antiferromagnetic phase characterized by a Bragg peak at (q) over right arrow (0) = (similar to 0.2, 0, 0.5) [N. Aso et al., J. Magn. Magn. Mater. 310, 602 (2007)]. The compound is also a heavy-fermion material with a large specific heat coefficient gamma = 110 mJ mol(-1) K-2 and a high Kondo temperature of T-K = 50 K, indicating CeRhSi3 is in a strongly Kondo screened state. We apply high-resolution neutron spectroscopy to investigate the magnetic fluctuations in the normal phase, at ambient pressures, and at low temperatures. We measure a commensurate dynamic response centered around the (Q) over right arrow = (0, 0, 2) position that gradually evolves to H similar to 0.2 with decreasing temperature and/or energy transfers. The response is broadened both in momentum and energy and is not reminiscent of sharp spin wave excitations found in insulating magnets where the electrons are localized. We parametrize the excitation spectrum and temperature dependence using a heuristic model utilizing the random-phase approximation to couple relaxing Ce3+ ground-state Kramers doublets with a Kondo-like dynamic response. With a Ruderman-Kittel-Kasuya-Yosida exchange interaction within the ab plane and an increasing single-site susceptibility, we can qualitatively reproduce the neutron spectroscopic results in CeRhSi3 and, namely, the trade-off between scattering at commensurate and incommensurate positions. We suggest that the antiferromagnetic phase in CeRhSi3 is driven by weakly correlated relaxing localized Kramers doublets and that CeRhSi3 at ambient pressures is on the border between a Rudderman-Kittel-Yosida antiferromagnetic state and a Kondo-screened phase where static magnetism is predominately absent.

Update: 4-Apr-2019


Title:
Analysis solution method for 3D planar crack problems of two-dimensional hexagonal quasicrystals with thermal effects
Authors:
Li, Y; Zhao, MH; Qin, QH; Fan, CY Author Full Names: Li, Yuan; Zhao, MingHao; Qin, Qing-Hua; Fan, CuiYing
Source:
APPLIED MATHEMATICAL MODELLING, 69 648-664; 10.1016/j.apm.2019.01.004 MAY 2019
Abstract:
An analysis solution method (ASM) is proposed for analyzing arbitrarily shaped planar cracks in two-dimensional (2D) hexagonal quasicrystal (QC) media. The extended displacement discontinuity (EDD) boundary integral equations governing three-dimensional (3D) crack problems are transferred to simplified integral-differential forms by introducing some complex quantities. The proposed ASM is based on the analogy between these EDD boundary equations for 3D planar cracks problems of 2D hexagonal QCs and those in isotropic thermoelastic materials. Mixed model crack problems under combined normal, tangential and thermal loadings are considered in 2D hexagonal QC media. By virtue of ASM, the solutions to 3D planar crack problems under various types of loadings for 2D hexagonal QCs are formulated through comparison to the corresponding solutions of isotropic thermoelastic materials which have been studied intensively and extensively. As an application, analytical solutions of a penny-shaped crack subjected uniform distributed combined loadings are obtained. Especially, the analytical solutions to a penny-shaped crack subjected to the anti-symmetric uniform thermal loading are first derived for 2D hexagonal QCs. Numerical solutions obtained by EDD boundary element method provide a way to verify the validity of the presented formulation. The influences of phonon-phason coupling effect on fracture parameters of 2D hexagonal QCs are assessed. (C) 2019 Elsevier Inc. All rights reserved.

Title:
Rational Design and Self-Assembly of Two-Dimensional, Dodecagonal DNA Quasicrystals
Authors:
Liu, LF; Li, Z; Li, YL; Mao, CD Author Full Names: Liu, Longfei; Li, Zhe; Li, Yulin; Mao, Chengde
Source:
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 141 (10):4248-4251; 10.1021/jacs.9b00843 MAR 13 2019
Abstract:
Quasicrystals are a class of materials with long-range order but no translational periodicity. Though many quasicrystals have been discovered, rational design and engineering of quasicrystals remain a great challenge. Herein, we have developed a rational strategy to assemble two-dimensional (2D), dodecagonal quasicrystals from branched DNA nanomotifs. The key of our strategy is to balance the rigidity and flexibility of the motifs, which is controlled by the introduction of interbranch "bridges". By fine-tuning the experimental conditions, we are able to predictably produce either 2D quasicrystals or conventional crystals. This study presents a rational design, prediction and realization of quasicrystal formation.

Update: 27-Mar-2019


Title:
Spinodal decomposition in a melt-spun Cu-15Ni-8Sn alloy
Authors:
Kondo, S; Nakashima, H; Morimura, T Author Full Names: Kondo, Shin-ichiro; Nakashima, Hiromichi; Morimura, Takao
Source:
PHYSICA B-CONDENSED MATTER, 560 244-254; 10.1016/j.physb.2019.01.030 MAY 1 2019
Abstract:
We investigate the spinodal decomposition process in a melt-spun Cu-15Ni-8Sn alloy using X-ray diffraction (XRD), transmission electron microscopy (TEM), and electron diffraction analyses. In the XRD measurements, an aging treatment of more than 300 min at 350 degrees C was required to obtain the (200) sidebands. TEM observations of the melt-spun samples aged at 350 degrees C for 40, 60, and 300 min showed a modulated structure with a wavelength too small to be detected by TEM and aging for about 1200 min was required for the clear appearance of a modulated structure. The electron diffraction patterns showed only the disordered fcc phase with no satellite structures in the sample aged for 20 min at 350 degrees C, which implied that no spinodal decomposition occurred. Aging for 40 min at 350 degrees C was required before the super-lattice reflection of DO22 was observed. These experimental results indicate that the decomposition process in the melt-spun alloy was slow initially.

Title:
Analytical and numerical investigations of noncollinear magnetic ordering in the frustrated delafossite CuCrO2
Authors:
Albaalbaky, A; Kvashnin, Y; Patte, R; Ledue, D Author Full Names: Albaalbaky, Ahmed; Kvashnin, Yaroslav; Patte, Renaud; Ledue, Denis
Source:
PHYSICAL REVIEW B, 99 (10):10.1103/PhysRevB.99.104415 MAR 12 2019
Abstract:
The magnetic propagation vector in delafossite CuCrO2 with classical Heisenberg spins is calculated analytically as a function of exchange interactions up to fourth-nearest neighbors. Exchange interactions are estimated by a series of density functional theory calculations for several values of lattice distortion. Our calculations show that the magnetic propagation vector is directly affected by the considered distortions providing different stable commensurate or incommensurate magnetic configurations. A realistic set of exchange interactions corresponding to a 0.1% lattice distortion yields the experimental ground state with an incommensurate propagation vector q similar to (0.329, 0.329, 0). We find that a very weak antiferromagnetic interlayer interaction favors an incommensurate ordering even in the absence of lattice distortion. Moreover, the exchange energy of a magnetic configuration of a finite crystal of CuCrO2 with periodic boundary conditions is derived analytically. Based on that, highly accurate Monte Carlo simulations performed on CuCrO2 confirm both the proposed analytical calculations and the density functional theory estimations, where we obtain excellent convergence toward the experimental ground state with a magnetic propagation vector q = (0.3288, 0.3288, 0).

Title:
Size effect of soft phonon dispersion in nanosized ferroics
Authors:
Morozovska, AN; Eliseev, EA Author Full Names: Morozovska, Anna N.; Eliseev, Eugene A.
Source:
PHYSICAL REVIEW B, 99 (11):10.1103/PhysRevB.99.115412 MAR 11 2019
Abstract:
Using Landau-Ginsburg-Devonshire theory, we derive and analyze analytical expressions for the frequency dispersion of soft phonon modes in nanosized ferroics and perform numerical calculations for a thin SrTiO3 film. We revealed the pronounced "true" size effect in the dependence of soft phonon spatial dispersion on the film thickness and predict that it can lead to the "apparent" or "false" size effect of dynamic flexoelectric coupling constants. Also, we derived analytical expressions describing the influence of finite size effect on the appearance and properties of the incommensurate spatial modulation induced by the static flexoelectric effect in ferroic thin films. To verify the theoretical predictions experimental measurements of the soft phonon dispersion in nanosized ferroics seem urgent.

Title:
Magnetic-field-induced incommensurate to collinear spin order transition in NiBr2
Authors:
Babu, S; Prokes, K; Huang, YK; Radu, F; Mishra, SK Author Full Names: Babu, S.; Prokes, K.; Huang, Y. K.; Radu, F.; Mishra, S. K.
Source:
JOURNAL OF APPLIED PHYSICS, 125 (9):10.1063/1.5066625 MAR 7 2019
Abstract:
The triangular spin lattice of NiBr2 is a canonical example of the frustrated helimagnet that shows a collinear commensurate antiferromagnetic to an incommensurate spin helix phase transition on cooling. Herein, we have studied a self-flux grown NiBr2 single crystal by neutron diffraction and low temperature magnetization measurements at fields up to 14 T. Experimental findings enable the deduction of the driving force responsible for the spin spiral ordering. The neutron diffraction data reveal satellite peaks representing characteristic features of an incommensurate magnetic state. The satellites develop symmetrically below T-N = 44.0(1) K, replacing the main magnetic reflections. Interestingly, a field-induced incommensurate to commensurate spin phase transition has been successfully demonstrated, which enforces the spin helix to restore the high temperature compensated antiferromagnetic structure. This reorientation can be described by a spin-flop in the (a-b) basal plane of a triangular spin lattice system. The findings offer a novel way for spin helix control of incommensurate phases, having immense scientific and technological implications in the next generation data storage devices.

Update: 20-Mar-2019


Title:
Isothermal section of Ga-Co-Cu phase diagram at 830 degrees C and its peculiarities
Authors:
Priputen, P; Drienovsky, M; Noga, P; Kusy, M; Cernickova, I; Janovec, J Author Full Names: Priputen, P.; Drienovsky, M.; Noga, P.; Kusy, M.; Cernickova, I; Janovec, J.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 785 1173-1179; 10.1016/j.jallcom.2019.01.288 MAY 15 2019
Abstract:
Recently, the Ga-based ternary alloys have gained interest for the possibility of finding new quasicrystals. Inspired by the previously reported decagonal and icosahedral quasicrystals identified in the Ga50Co25Cu25 alloy at 830 degrees C, the phase equilibria of 27 alloys of various composition were investigated in this work. Based on the obtained results, an isothermal section of the Ga-Co-Cu phase diagram at 830 degrees C was proposed. However, neither decagonal nor icosahedral quasicrystals were found to be stable at 830 degrees C, but instead of that, a superalloy-like structure was found in the Ga35Co25Cu40 alloy consisting of beta-GaCo and beta-GaCug-GaCu. (C) 2019 Elsevier B.V. All rights reserved.

Title:
Band gap closure, incommensurability and molecular dissociation of dense chlorine
Authors:
Dalladay-Simpson, P; Binns, J; Pena-Alvarez, M; Donnelly, ME; Greenberg, E; Prakapenka, V; Chen, XJ; Gregoryanz, E; Howie, RT Author Full Names: Dalladay-Simpson, Philip; Binns, Jack; Pena-Alvarez, Miriam; Donnelly, Mary-Ellen; Greenberg, Eran; Prakapenka, Vitali; Chen, Xiao-Jia; Gregoryanz, Eugene; Howie, Ross T.
Source:
NATURE COMMUNICATIONS, 10 10.1038/s41467-019-09108-x MAR 8 2019
Abstract:
Diatomic elemental solids are highly compressible due to the weak interactions between molecules. However, as the density increases the intra-and intermolecular distances become comparable, leading to a range of phenomena, such as structural transformation, molecular dissociation, amorphization, and metallisation. Here we report, following the crystallization of chlorine at 1.15(30) GPa into an ordered orthorhombic structure (oC8), the existence of a mixed-molecular structure (mC8, 130(10)-241(10) GPa) and the concomitant observation of a continuous band gap closure, indicative of a transformation into a metallic molecular form around 200(10) GPa. The onset of dissociation of chlorine is identified by the observation of the incommensurate structure (i-oF4) above 200(10) GPa, before finally adopting a monatomic form (oI2) above 256(10) GPa.

Title:
Resonantly hybridized excitons in moire superlattices in van der Waals heterostructures
Authors:
Alexeev, EM; Ruiz-Tijerina, DA; Danovich, M; Hamer, MJ; Terry, DJ; Nayak, PK; Ahn, S; Pak, S; Lee, J; Sohn, JI; Molas, MR; Koperski, M; Watanabe, K; Taniguchi, T; Novoselov, KS; Gorbachev, RV; Shin, HS; Fal'ko, VI; Tartakovskii, AI Author Full Names: Alexeev, Evgeny M.; Ruiz-Tijerina, David A.; Danovich, Mark; Hamer, Matthew J.; Terry, Daniel J.; Nayak, Pramoda K.; Ahn, Seongjoon; Pak, Sangyeon; Lee, Juwon; Sohn, Jung Inn; Molas, Maciej R.; Koperski, Maciej; Watanabe, Kenji; Taniguchi, Takashi; Novoselov, Kostya S.; Gorbachev, Roman V.; Shin, Hyeon Suk; Fal'ko, Vladimir I.; Tartakovskii, Alexander I.
Source:
NATURE, 567 (7746):81-+; 10.1038/s41586-019-0986-9 MAR 7 2019
Abstract:
Atomically thin layers of two-dimensional materials can be assembled in vertical stacks that are held together by relatively weak van der Waals forces, enabling coupling between monolayer crystals with incommensurate lattices and arbitrary mutual rotation(1,2). Consequently, an overarching periodicity emerges in the local atomic registry of the constituent crystal structures, which is known as a moire superlattice(3). In graphene/hexagonal boron nitride structures(4), the presence of a moire superlattice can lead to the observation of electronic minibands(5-7), whereas in twisted graphene bilayers its effects are enhanced by interlayer resonant conditions, resulting in a superconductor-insulator transition at magic twist angles(8). Here, using semiconducting heterostructures assembled from incommensurate molybdenum diselenide (MoSe2) and tungsten disulfide (WS2) monolayers, we demonstrate that excitonic bands can hybridize, resulting in a resonant enhancement of moire superlattice effects. MoSe2 and WS2 were chosen for the near-degeneracy of their conduction-band edges, in order to promote the hybridization of intra- and interlayer excitons. Hybridization manifests through a pronounced exciton energy shift as a periodic function of the interlayer rotation angle, which occurs as hybridized excitons are formed by holes that reside in MoSe2 binding to a twist-dependent superposition of electron states in the adjacent monolayers. For heterostructures in which the monolayer pairs are nearly aligned, resonant mixing of the electron states leads to pronounced effects of the geometrical moire pattern of the heterostructure on the dispersion and optical spectra of the hybridized excitons. Our findings underpin strategies for bandstructure engineering in semiconductor devices based on van der Waals heterostructures(9).

Title:
Redox behaviour and solid solubility of cerium ortho-niobates
Authors:
Harris, CM; Skinner, SJ Author Full Names: Harris, Cassandra M.; Skinner, Stephen J.
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 271 135-143; 10.1016/j.jssc.2018.12.042 MAR 2019
Abstract:
Using Ce L-III edge X-ray absorption near edge spectroscopy (XANES), it is shown that acceptor dopants introduced to cerium members of the rare earth ortho-niobate series, Ce1-xSrxNbO4 +/- delta and Ce1-xSrxNbO4 +/- delta, are charge compensated by the formation of holes on the cerium sublattice. These spectroscopic studies are complemented by structural studies, using X-ray and neutron powder diffraction, determining that the solubility limit of the strontium and calcium dopants within the CeNbO4+delta structure is similar to 10% and similar to 30% respectively. Under oxidising conditions, the Ce3+/Ce4+ redox couple facilitates reversible redox processes, and it is observed that the Ce1-xSrxNbO4 +/- delta and Ce1-xSrxNbO4 +/- delta materials form commensurate and incommensurately modulated oxygen hyperstoichiometric phases as a function of temperature. Under reducing atmospheres, this redox activity is suppressed, and charge-compensating Ce4+ holes are annihilated.

Title:
Kinetics of a Phonon-Mediated Laser-Driven Structural Phase Transition in Sn2P2Se6
Authors:
Kubli, M; Savoini, M; Abreu, E; Burganov, B; Lantz, G; Huber, L; Neugebauer, MJ; Boie, L; Esposito, V; Bothschafter, EM; Parchenko, S; Grubel, S; Porer, M; Rittmann, J; Beaud, P; Staub, U; Yabashi, M; Tanaka, Y; Katayama, T; Togashi, T; Kohutych, AA; Vysochanskii, YM; Johnson, SL Author Full Names: Kubli, Martin; Savoini, Matteo; Abreu, Elsa; Burganov, Bulat; Lantz, Gabriel; Huber, Lucas; Neugebauer, Martin J.; Boie, Larissa; Esposito, Vincent; Bothschafter, Elisabeth M.; Parchenko, Sergii; Gruebel, Sebastian; Porer, Michael; Rittmann, Jochen; Beaud, Paul; Staub, Urs; Yabashi, Makina; Tanaka, Yoshikazu; Katayama, Tetsuo; Togashi, Tadashi; Kohutych, Anton A.; Vysochanskii, Yulian M.; Johnson, Steven L.
Source:
APPLIED SCIENCES-BASEL, 9 (3):10.3390/app9030525 FEB 1 2019
Abstract:
We investigate the structural dynamics of the incommensurately modulated phase of Sn2P2Se6 by means of time-resolved X-ray diffraction following excitation by an optical pump. Tracking the incommensurable distortion in the time domain enables us to identify the transport effects leading to a complete disappearance of the incommensurate phase over the course of 100 ns. These observations suggest that a thin surface layer of the high-temperature phase forms quickly after photo-excitation and then propagates into the material with a constant velocity of 3.7 m/s. Complementary static structural measurements reveal previously unreported higher-order satellite reflection in the incommensurate phase. These higher-order reflections are attributed to cubic vibrational terms in the Hamiltonian.

Title:
Wood-Derived Dietary Fibers Promote Beneficial Human Gut Microbiota
Authors:
La Rosa, SL; Kachrimanidou, V; Buffetto, F; Pope, PB; Pudlo, NA; Martens, EC; Rastall, RA; Gibson, GR; Westereng, B Author Full Names: La Rosa, Sabina Leanti; Kachrimanidou, Vasiliki; Buffetto, Fanny; Pope, Phillip B.; Pudlo, Nicholas A.; Martens, Eric C.; Rastall, Robert A.; Gibson, Glenn R.; Westereng, Bjerge
Source:
MSPHERE, 4 (1):10.1128/mSphere.00554-18 JAN-FEB 2019
Abstract:
Woody biomass is a sustainable and virtually unlimited source of hemicellulosic polysaccharides. The predominant hemicelluloses in softwood and hardwood are galactoglucomannan (GGM) and arabinoglucuronoxylan (AGX), respectively. Based on the structure similarity with common dietary fibers, GGM and AGX may be postulated to have prebiotic properties, conferring a health benefit on the host through specific modulation of the gut microbiota. In this study, we evaluated the prebiotic potential of acetylated GGM (AcGGM) and highly acetylated AGX (AcAGX) obtained from Norwegian lignocellulosic feedstocks in vitro. In pure culture, both substrates selectively promoted the growth of Bifidobacterium, Lactobacillus, and Bacteroides species in a manner consistent with the presence of genetic loci for the utilization of beta-manno-oligosaccharides/beta-mannans and xylo-oligosaccharides/ xylans. The prebiotic potential of AcGGM and AcAGX was further assessed in a pH-controlled batch culture fermentation system inoculated with healthy adult human feces. Results were compared with those obtained with a commercial fructo-oligosaccharide (FOS) mixture. Similarly to FOS, both substrates significantly increased (P < 0.05) the Bifidobacterium population. Other bacterial groups enumerated were unaffected with the exception of an increase in the growth of members of the Bacteroides-Prevotella group, Faecalibacterium prausnitzii, and clostridial cluster IX (P < 0.05). Compared to the other substrates, AcGGM promoted butyrogenic fermentation whereas AcAGX was more propiogenic. Although further in vivo confirmation is necessary, these results demonstrate that both AcGGM and AcAGX from lignocellulosic feedstocks can be used to direct the promotion of beneficial bacteria, thus exhibiting a promising prebiotic ability to improve or restore gut health. IMPORTANCE The architecture of the gut bacterial ecosystem has a profound effect on the physiology and well-being of the host. Modulation of the gut microbiota and the intestinal microenvironment via administration of prebiotics represents a valuable strategy to promote host health. This work provides insights into the ability of two novel wood-derived preparations, AcGGM and AcAGX, to influence human gut microbiota composition and activity. These compounds were selectively fermented by commensal bacteria such as Bifidobacterium, Bacteroides-Prevotella, F. prausnitzii, and clostridial cluster IX spp. This promoted the microbial synthesis of acetate, propionate, and butyrate, which are beneficial to the microbial ecosystem and host colonic epithelial cells. Thus, our results demonstrate potential prebiotic properties for both AcGGM and AcAGX from lignocellulosic feedstocks. These findings represent pivotal requirements for rationally designing intervention strategies based on the dietary supplementation of AcGGM and AcAGX to improve or restore gut health.

Update: 13-Mar-2019


Title:
Mechanics of dislocations and metadislocations in quasicrystals and their approximants: power invariance and balance
Authors:
Mariano, PM Author Full Names: Mariano, Paolo Maria
Source:
CONTINUUM MECHANICS AND THERMODYNAMICS, 31 (2):373-399; 10.1007/s00161-018-0690-2 MAR 2019
Abstract:
We discuss the mechanics of a single dislocation in quasicrystals. We account for dislocation's core by means of a non-constant line energy. Above all, we focus attention on the origin of the balance equations involving the pertinent bulk and line actions. We derive all balances, including those of configurational actions along the dislocation line,from a unique invariance requirement for the so-called relative power; it is an axiom that furnishes also the action-reaction principle for the standard traction and the phason one, as well as the standard Cauchy theorem and, in addition, the existence of phason stress and self-action. The theoretical scheme presented here includes the description of the large core of metadislocations in quasicrystal's approximants (complex metallic alloys). Each metadislocation features thousands of atoms per unit thickness in the direct vicinity of the core, a circumstance suggesting to consider it as a sort of micro-rod, a view adopted in the present paper. In fact, from an abstract point of view, the results presented here describe the motion of a rod within a body with vectorial microstructure.

Title:
Principles of weakly ordered domains in intermetallics: the cooperative effects of atomic packing and electronics in Fe2Al5
Authors:
Vinokur, AI; Hilleke, KP; Fredrickson, DC Author Full Names: Vinokur, Anastasiya, I; Hilleke, Katerina P.; Fredrickson, Daniel C.
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 75 297-306; 10.1107/S2053273318017461 2 MAR 2019
Abstract:
Many complex intermetallic structures feature a curious juxtaposition of domains with strict 3D periodicity and regions of much weaker order or incommensurability. This article explores the basic principles leading to such arrangements through an investigation of the weakly ordered channels of Fe2Al5. It starts by experimentally confirming the earlier crystallographic model of the high-temperature form, in which nearly continuous columns of electron density corresponding to disordered Al atoms emerge. Then electronic structure calculations on ordered models are used to determine the factors leading to the formation of these columns. These calculations reveal electronic pseudogaps near 16 electrons/Fe atom, an electron concentration close to the Al-rich side of the phase's homogeneity range. Through a reversed approximation Molecular Orbital (raMO) analysis, these pseudogaps are correlated with the filling of 18-electron configurations on the Fe atoms with the support of isolobal sigma Fe-Fe bonds. The resulting preference for 16 electrons/Fe requires a fractional number of Al atoms in the Fe2Al5 unit cell. Density functional theory-chemical pressure (DFT-CP) analysis is then applied to investigate how this nonstoichiometry is accommodated. The CP schemes reveal strong quadrupolar distributions on the Al atoms of the channels, suggestive of soft atomic motions along the undulating electron density observed in the Fourier map that allow the Al positions to shift easily in response to compositional changes. Such a combination of preferred electron counts tied to stoichiometry and continuous paths of CP quadrupoles could provide predictive indicators for the emergence of channels of disordered or incommensurately spaced atoms in intermetallic structures.

Title:
Ted Janssen and aperiodic crystals
Authors:
de Boissieu, M Author Full Names: de Boissieu, Marc
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 75 273-280; 10.1107/S2053273318016765 2 MAR 2019
Abstract:
This article reviews some of Ted Janssen's (1936-2017) major contributions to the field of aperiodic crystals. Aperiodic crystals are long-range ordered structures without 3D lattice translations and encompass incommensurately modulated phases, incommensurate composites and quasicrystals. Together with Pim de Wolff and Aloysio Janner, Ted Janssen invented the very elegant theory of superspace crystallography that, by adding a supplementary dimension to the usual 3D space, allows for a deeper understanding of the atomic structure of aperiodic crystals. He also made important contributions to the understanding of the stability and dynamics of aperiodic crystals, exploring their fascinating physical properties. He constantly interacted and collaborated with experimentalists, always ready to share and explain his detailed understanding of aperiodic crystals.

Title:
A side-by-side comparison of the solidification dynamics of quasicrystalline and approximant phases in the Al-Co-Ni system
Authors:
Han, I; Xiao, XH; Sun, HP; Shahani, AJ Author Full Names: Han, Insung; Xiao, Xianghui; Sun, Haiping; Shahani, Ashwin J.
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 75 281-296; 10.1107/S2053273318017114 2 MAR 2019
Abstract:
Quasicrystals and their approximants have triggered widespread interest due to the challenge of solving their complex crystal structures as well as their possibly exceptional properties. The structural motifs of approximants are similar to those of the corresponding quasicrystals, but to what extent are their crystallization pathways the same? Unfortunately, there have been very few in situ experimental investigations to answer this question. Here, by leveraging the high penetrating power of hard X-rays, synchrotron-based X-ray tomography was conducted in order to capture the nucleation and growth of a decagonal quasicrystal and its related approximant. The combination of data-driven computational analysis with new thermodynamic databases allowed the characterization, with high precision, of the constitutional and kinetic driving forces for crystallization. The experimental results prove that the growth of both crystals from a liquid is dominated by first-order kinetics. Nevertheless, and somewhat surprisingly, significant differences were observed in their rates of nucleation and growth. The reasons for such divergent behaviours are discussed in light of contemporary theories of intermetallic crystallization.

Title:
Phason-flips refinement of and multiple-scattering correction for the d-AlCuRh quasicrystal
Authors:
Ruganski, I; Strzalka, R; Wolny, J Author Full Names: Ruganski, Ireneusz; Strzalka, Radoslaw; Wolny, Janusz
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 75 352-361; 10.1107/S2053273318017254 2 MAR 2019
Abstract:
The origin of the characteristic bias observed in a logarithmic plot of the calculated and measured intensities of diffraction peaks for quasicrystals has not yet been established. Structure refinement requires the inclusion of weak reflections; however, no structural model can properly describe their intensities. For this reason, detailed information about the atomic structure is not available. In this article, a possible cause for the characteristic bias, namely the lattice phason flip, is investigated. The derivation of the structure factor for a tiling with inherent phason flips is given and is tested for the AlCuRh decagonal quasicrystal. Although an improvement of the model is reported, the bias remains. A simple correction term involving a redistribution of the intensities of the peaks was tested, and successfully removed the bias from the diffraction data. This new correction is purely empirical and only mimics the effect of multiple scattering. A comprehensive study of multiple scattering requires detailed knowledge of the diffraction experiment geometry.

Title:
Aperiodic order coming of age: from inorganic materials to dynamic protein superstructures
Authors:
Borgstahl, G; Goldman, AI; Thiel, PA Author Full Names: Borgstahl, Gloria; Goldman, Alan I.; Thiel, Patricia A.
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 75 212-213; 10.1107/S2053273319001165 2 MAR 2019

Title:
Full real-space analysis of a dodecagonal quasicrystal
Authors:
Schenk, S; Zollner, EM; Krahn, O; Schreck, B; Hammer, R; Forster, S; Widdra, W Author Full Names: Schenk, Sebastian; Zollner, Eva Maria; Krahn, Oliver; Schreck, Berit; Hammer, Rene; Foerster, Stefan; Widdra, Wolf
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 75 307-313; 10.1107/S2053273319000056 2 MAR 2019
Abstract:
The atomically resolved real-space structure of a long-range-ordered dodecagonal quasicrystal is determined based on scanning tunnelling microscopy. For the BaTiO3-derived oxide quasicrystal which spontaneously forms on a Pt(111) surface, 8100 atomic positions have been determined and are compared with an ideal Niizeki-Gahler tiling. Although the Niizeki-Gahler tiling has a complex three-element structure, the abundance of the triangle, square and rhomb tiling elements in the experimental data closely resembles the ideal frequencies. Similarly, the frequencies of all possible next-neighbour tiling combinations are, within the experimental uncertainty, identical to the ideal tiling. The angular and orientational distributions of all individual tiling elements show the characteristics of the dodecagonal quasicrystal. In contrast, the analysis of the orientation of characteristic and more complex tiling combinations indicates the partial decomposition of the quasicrystal into small patches with locally reduced symmetry. These, however, preserve the long-range quasicrystal coherence. The symmetry reduction from dodecagonal to sixfold is assigned to local interaction with the threefold substrate. It leads to atomic flips which preserve the number of quasicrystal tiling elements.

Title:
Characterizing modulated structures with first-principles calculations: a unified superspace scheme of ordering in mullite
Authors:
Klar, PB; Etxebarria, I; Madariaga, G Author Full Names: Klar, Paul Benjamin; Etxebarria, Inigo; Madariaga, Gotzon
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 75 260-272; 10.1107/S2053273319000846 2 MAR 2019
Abstract:
The benefit of computational methods applying density functional theory for the description and understanding of modulated crystal structures is investigated. A method is presented which allows one to establish, improve and test superspace models including displacive and occupational modulation functions from firstprinciples calculations on commensurate structures. The total energies of different configurations allow one to distinguish stable and less stable structure models. The study is based on a series of geometrically optimized superstructures of mullite (A(l4+2x)Si(2-2x)O(10-x)) derived from the superspace group Pham(alpha 01/2)0ss. Despite the disordered and structurally complex nature of mullite, the calculations on ordered superstructures are very useful for determining the ideal Al/Si ordering in mullite, extracting atomic modulation functions as well as understanding the SiO2-Al2O3 phase diagram. The results are compared with experimentally established models which confirm the validity and utility of the presented method.

Title:
Phase diagram of the Kondo model on the zigzag ladder
Authors:
Peschke, M; Woelk, LM; Potthoff, M Author Full Names: Peschke, Matthias; Woelk, Lena-Marie; Potthoff, Michael
Source:
PHYSICAL REVIEW B, 99 (8):10.1103/PhysRevB.99.085140 FEB 27 2019
Abstract:
The effect of next-nearest-neighbor hopping t(2) on the ground-state phase diagram of the one-dimensional Kondo lattice is studied with density-matrix renormalization-group techniques and by comparing with the phase diagram of the classical-spin variant of the same model. For a finite t(2), i.e., for a zigzag-ladder geometry, indirect antiferromagnetic interactions between the localized spins are geometrically frustrated. We demonstrate that t(2) at the same time triggers several magnetic phases which are absent in the model with nearest-neighbor hopping only. For strong J, we find a transition from antiferromagnetic to incommensurate magnetic short-range order, which can be understood entirely in the classical-spin picture. For weaker J, a spin-dimerized phase emerges, which spontaneously breaks the discrete translation symmetry. The phase is not accessible to perturbative means but is explained, on a qualitative level, by the classical-spin model as well. Spin dimerization alleviates magnetic frustration and is interpreted as a key to understand the emergence of quasi-long-range spiral magnetic order, which is found at weaker couplings. The phase diagram at weak J, with gapless quasi-long-range order on top of the twofold degenerate spin-dimerized ground state, competing with a nondegenerate phase with gapped spin (and charge) excitations, is unconventional and eludes an effective low-energy spin-only theory.

Title:
Gauge theory for the cuprates near optimal doping
Authors:
Sachdev, S; Scammell, HD; Scheurer, MS; Tarnopolsky, G Author Full Names: Sachdev, Subir; Scammell, Harley D.; Scheurer, Mathias S.; Tarnopolsky, Grigory
Source:
PHYSICAL REVIEW B, 99 (5):10.1103/PhysRevB.99.054516 FEB 25 2019
Abstract:
We describe the phase diagram of a 2+1-dimensional SU(2) gauge theory of fluctuating incommensurate spin density waves for the hole-doped cuprates. Our primary assumption is that all low-energy fermionic excitations are gauge neutral and electron-like, while the spin density wave order is fractionalized into Higgs fields transforming as adjoints of the gauge SU(2). The confining phase of the gauge theory is a conventional Fermi liquid with a large Fermi surface (and its associated d-wave superconductor). There is a quantum phase transition to a Higgs phase describing the "pseudogap" at lower doping. Depending on the quartic terms in the Higgs potential, the Higgs phase exhibits one or more of charge density wave, Ising-nematic, time-reversal odd scalar spin chirality, and Z(2) topological orders. It is notable that the emergent broken symmetries in our theory of fluctuating spin density waves coincide with those observed in diverse experiments. For the electron-doped cuprates, the spin density wave fluctuations are at wave vector (pi, pi), and then the corresponding SU(2) gauge theory only has a crossover between the confining and Higgs regimes, with an exponentially large confinement scale deep in the Higgs regime. On the Higgs side, for both the electron- and hole-doped cases, and at scales shorter than the confinement scale (which can be infinite when Z(2) topological order is present), the electron spectral function has a "fractionalized Fermi liquid" form with small Fermi surfaces. We also describe the deconfined quantum criticality of the Higgs transition in the limit of a large number of Higgs flavors, and perturbatively discuss its coupling to fermionic excitations.

Title:
Spin dynamics and field-induced magnetic phase transition in the honeycomb Kitaev magnet alpha-Li2IrO3
Authors:
Choi, S; Manni, S; Singleton, J; Topping, CV; Lancaster, T; Blundell, SJ; Adroja, DT; Zapf, V; Gegenwart, P; Coldea, R Author Full Names: Choi, Sungkyun; Manni, S.; Singleton, J.; Topping, C., V; Lancaster, T.; Blundell, S. J.; Adroja, D. T.; Zapf, V; Gegenwart, P.; Coldea, R.
Source:
PHYSICAL REVIEW B, 99 (5):10.1103/PhysRevB.99.054426 FEB 25 2019
Abstract:
The layered honeycomb iridate alpha-Li2IrO3 displays an incommensurate magnetic structure with counter-rotating moments on nearest-neighbor sites, proposed to be stabilized by strongly frustrated anisotropic Kitaev interactions between spin-orbit entangled Ir4+ magnetic moments. Here we report powder inelastic neutron scattering measurements that observe sharply dispersive low-energy magnetic excitations centered at the magnetic ordering wave vector, attributed to Goldstone excitations of the incommensurate order, as well as an additional intense mode above a gap Delta similar or equal to 2.3 meV. Zero-field muon-spin relaxation measurements show clear oscillations in the muon polarization below the Ned temperature T-N similar or equal to 15 K with a time-dependent profile consistent with bulk incommensurate long-range magnetism. Pulsed-field magnetization measurements observe that only about half the saturation magnetization value is reached at the maximum field of 64 T. A clear anomaly near 25 T indicates a transition to a phase with reduced susceptibility. The transition field has a Zeeman energy comparable to the zero-field gapped mode, suggesting gap suppression as a possible mechanism for the field-induced transition.

Title:
Static response of functionally graded multilayered one-dimensional hexagonal piezoelectric quasicrystal plates using the state vector approach
Authors:
Huang, YZ; Li, Y; Yang, LZ; Gao, Y Author Full Names: Huang, Yun-zhi; Li, Yang; Yang, Lian-zhi; Gao, Yang
Source:
JOURNAL OF ZHEJIANG UNIVERSITY-SCIENCE A, 20 (2):133-147; 10.1631/jzus.A1800472 FEB 2019
Abstract:
The effect of the non-homogeneity of material properties has been considered the important variation mechanism in the static responses of quasicrystal structures, but the existing theoretical model for it is unable to simulate the material change format beyond the exponential function. In this paper, we create a new model of functionally graded multilayered 1D piezoelectric quasicrystal plates using the state vector approach, in which varying functionally graded electro-elastic properties can be extended from exponential to linear and higher order in the thickness direction. Based on the state equations, an analytical solution for a single plate has been derived, and the result for the corresponding multilayered case is obtained utilizing the propagator matrix method. The present study shows, in particular, that coefficient orders of two varying functions (the power function and the exponential function) of the material gradient provide the ability to tailor the mechanical behaviors in the system's phonon, phason, and electric fields. Moreover, the insensitive points of phonon stress and electric potential under functionally graded effects in the quasicrystal layer are observed. In addition, the influences of stacking sequences and discontinuity of horizontal stress are explored in the simulation by the new model. The results are very useful for the design and understanding of the characterization of functionally graded piezoelectric quasicrystal materials in their applications to multilayered systems.

Title:
Elasto-hydrodynamics of quasicrystals with a crack under sudden impacts
Authors:
Zhou, YB; Li, XF Author Full Names: Zhou, Y. -B.; Li, X. -F.
Source:
PHILOSOPHICAL MAGAZINE LETTERS, 98 (10):419-436; 10.1080/09500839.2019.1566796 2018
Abstract:
In this paper, a mode-III crack in one-dimensional (1D) hexagonal quasicrystals subjected to anti-plane impact loading is analyzed. The elasto-hydrodynamics of quasicrystals is adopted, where the phonon field obeys wave equation, and the phason field obeys diffusion equation. By introducing a new auxiliary function, the coupled wave-diffusion equations are converted to a single higher-order partial differential equation. With the aid of the Laplace transform, an associated mixed initial-boundary value problem is reduced to two sets of dual integral equations, and then transformed into two coupled Fredholm integral equations of the second kind. Numerical results of transient phonon and phason stress intensity factors and crack-centre displacement jump are obtained through the numerical inversion of the Laplace transform and are presented graphically to show the influences of the phason.

Update: 7-Mar-2019


Title:
Neutron diffraction study of a metallic kagome lattice, Tb3Ru4Al12
Authors:
Rayaprol, S; Hoser, A; Iyer, KK; Upadhyay, SK; Sampathkumaran, EV Author Full Names: Rayaprol, Sudhindra; Hoser, Andreas; Iyer, Kartik K.; Upadhyay, Sanjay K.; Sampathkumaran, E. V.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 477 83-87; 10.1016/j.jmmm.2018.12.104 MAY 1 2019
Abstract:
We present the results of neutron diffraction studies on polycrystals of a metallic kagome lattice, Tb3Ru4Al12, reported recently to undergo reentrant magnetism, with the onset of long range antiferromagnetic order below (T-N = 22 K) and spin-glass features below about 17 K. The present results reveal long-range antiferromagnetic order of an incommensurate type with the moments oriented along c-axis at all temperatures below T-N. There are however notable changes in the T-dependence of propagation vector along b-axis across 17 K. An observation of interest is that there is no decrease of intensity of magnetic Bragg peaks on entrance into the glassy phase (that is, below 17 K). This finding suggests that the magnetism of this compound is an exotic one.

Title:
Charge orbital and spin ordering transitions in La1-xSrxMnO3+delta(x=0.67 & 0.71)
Authors:
Shahee, A; Kaushik, SD; Lalla, NP Author Full Names: Shahee, Aga; Kaushik, S. D.; Lalla, N. P.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 782 277-287; 10.1016/j.jallcom.2018.11.404 APR 25 2019
Abstract:
Structural and magnetic phase-transitions in La1-xSrxMnO3+delta (x = 0.67 & 0.71) have been studied employing x-ray diffraction, neutron diffraction and transmission electron microscopy (TEM) in conjunction with electrical-transport and magnetic studies. These studies reveal a cubic to incommensurate (IC) charge-ordered (CO) tetragonal phase-transition in both the samples with k-vector varying with temperature and thus indicates charge density wave-like nature. Followed by magnetic transition from paramagnetic phase to incommensurate antiferromagnetic phase. The nearly equal expansion of the a,b axes in the ab plane and the contraction of the c-axis (i.e. type-I Jahn-Teller distortion (JTD)) indicate that the CO is accompanied by a planer ferro-ordering of 3d(x2-y2) orbitals in the ab plan, which is different from haring-bone type ordering of 3d(3x2-r2)/3d(3y2-r2) orbitals, commonly observed in narrow bandwidth CO manganites. For x = 0.71, a second phase-transition from type-I JTD-CO phase (c < a) to charge disorder type-II JTD tetragonal phase (c > a) was observed. Through EDAX analysis in TEM, a nanoscale marginal composition difference has been observed to lead to nanoscale phase-coexistence. These studies have revealed first microscopic evidence of CO and nano-scale multiphase coexistence in La1-xSrxMnO3+delta with x = 0.67 & 0.71. (C) 2018 Elsevier B.V. All rights reserved.

Title:
Negative refraction in quasicrystalline multilayered metamaterials
Authors:
Morini, L; Eyzat, Y; Gei, M Author Full Names: Morini, Lorenzo; Eyzat, Yoann; Gei, Massimiliano
Source:
JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS, 124 282-298; 10.1016/j.jmps.2018.10.016 MAR 2019
Abstract:
Inspired by some recent results in elastodynamics of layered composites, we address here the problem of an antiplane elastic wave obliquely incident at the interface between a substrate and a periodic laminate with a quasicrystalline structure (generated by the Fibonacci substitution rule). The angles of refraction of the transmitted modes are computed by combining the transfer matrix method with the normal mode decomposition and evaluating the direction of the average Poynting vector. It is shown that, with respect to a periodic classical bilayer, on the one hand, beyond a certain frequency threshold, high order Fibonacci laminates can provide negative refraction for a wider range of angles of incidence, on the other, they allow negative wave refraction at lower frequencies. The outcome strongly relies on the Floquet-Bloch dynamic analysis of this class of laminates that is performed thoroughly. It is revealed that the corresponding spectra have a self-similar character linked to the specialisation of the Kohmoto's invariant, a function of the frequency that was recently studied by the authors for periodic one-dimensional quasicrystalline-generated waveguides. This function is able to explain two types of scaling occurring in dispersion diagrams. The attained results represent an important advancement towards the realisation of multilayered quasicrystalline metamaterials with the aim to control negatively refracted elastic waves. (C) 2018 Elsevier Ltd. All rights reserved.

Title:
Excess specific heat from the gapped sliding phonon modes in the incommensurate composite crystal Sr14Cu24O41
Authors:
Bag, R; Hazra, S; Kini, RN; Singh, S Author Full Names: Bag, Rabindranath; Hazra, Soumitra; Kini, Rajeev N.; Singh, Surjeet
Source:
PHYSICAL REVIEW B, 99 (5):10.1103/PhysRevB.99.054305 FEB 13 2019
Abstract:
We show that the low-temperature specific heat (C-p) of the incommensurate chain-ladder system {CuO2}(alpha){Sr2Cu2O3} = Sr14Cu24O41 (for alpha = 10/7) shows a rather large excess contribution of nonmagnetic origin. Diluted Al doping at the Cu site or annealing the crystal in an O-2 atmosphere suppresses this feature considerably. Using THz time-domain spectroscopy, we relate the occurrence of excess specific heat to the presence of very low-energy (similar to 1 meV) gapped phonon modes that originate from the sliding motion of oppositely charged {CuO2} chain and {Sr2Cu2O3} ladder sheets past each other.

Title:
Critical Properties of the Anisotropic Ising Model with Competitive Interactions in the Region of a Phase Transition from the Modulated Phase to the Paramagnetic One
Authors:
Murtazaev, AK; Ibaev, ZG Author Full Names: Murtazaev, A. K.; Ibaev, Zh. G.
Source:
JOURNAL OF EXPERIMENTAL AND THEORETICAL PHYSICS, 127 (6):1040-1045; 10.1134/S106377611812021X DEC 2018
Abstract:
Monte Carlo methods are used to study the anisotropic Ising model with competing interactions in the region of the phase transition from the modulated to the paramagnetic phase. Using histogram analysis of Monte Carlo data and the theory of finite-size scaling, it is shown that the transition from the modulated state to the paramagnetic one is a second-order phase transition. The critical parameters and temperatures of phase transitions in this region are calculated. It is shown that the modulated-paramagnetic phase transition cannot be described within the framework of the known universality classes of critical behavior.

Update: 27-Feb-2019


Title:
Microstructure and mechanical properties of an aluminum alloy reinforced by Al-Ni-Co-Mn quasi-crystalline
Authors:
Yuan, Y; Hou, H; Zhao, YH; Yan, F; Zhang, Y Author Full Names: Yuan, Ye; Hou, Hua; Zhao, Yu Hong; Yan, Feng; Zhang, Yu
Source:
MATERIALS RESEARCH EXPRESS, 6 (5):10.1088/2053-1591/ab014c MAY 2019
Abstract:
The Al72Ni13Co10Mn5 quasi-crystalline was prepared by conventional casting method. The microstructures and the phase composition of Al72Ni12Co16 quasi-crystalline, Al70Ni11Co12Mn7 and Al2Ni phases were characterized by XRD, SEM and DSC. The (Al72Ni13Co10Mn5)p/ZL101A aluminium based composite was fabricated by using the Al72Ni13Co10Mn5 quasicrystals particles as the reinforcing phase and ZL101A as the matrix with electromagnetic stirring. The results showed that the Al72Ni13Co10Mn5 is a QC(quasi-crystalline) phase and the hardness of Al72Ni13Co10Mn5 is higher than d-Al72Ni12Co16; the as-cast (Al72Ni13Co10Mn5)p/ZL101A composites are composed of alpha-Al, eutectic Si, theta, gamma and phi phase. With the increase of reinforcing particle fraction, the changed order for the morphology of coralline Si as follows: coral distribution -> partially converted into strips strip -> or thick sheet. The changes of mechanical properties were studied by tensile test and the resulting crystalline phase gamma and phi phases contribute to the improvement of the mechanical properties of the composite. After adding 4%wt% quasicrystalline particles, the tensile strength increased by 20.3%. However, when additional increased to 7 wt% will cause agglomeration and clusters of the theta phase, which leads to the decrease of the mechanical properties.

Title:
Analysis of migration maps and features of magnetic properties of LiNi0.9M0.1PO4 (M = Co, Mn) single crystals
Authors:
Urusova, N; Semkin, M; Kratochvilova, M; Barykina, J; Volegov, A; Park, JG; Lee, S; Pirogov, A Author Full Names: Urusova, N.; Semkin, M.; Kratochvilova, M.; Barykina, J.; Volegov, A.; Park, J. -G.; Lee, S.; Pirogov, A.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 781 571-581; 10.1016/j.jallcom.2018.12.089 APR 15 2019
Abstract:
Lithium orthophosphates of the LiMPO4 type (M = Ni, Co, Fe, and Mn) gain intensive development due to the potential applications as electrodes for lithium-ion batteries. The other remarkable property of LiMPO4 is the multiferroicity. We present a study of the crystal structure and magnetic properties, refined anisotropic thermal coefficients and Li-ion migration maps of the LiNi0.9M0.1PO4(M = Co, Mn) single crystals and compared results for the undoped LiNiPO4 and LiMnPO4 ones. All samples have been synthesized by the flux method. In LiNi0.9M0.1PO4(M = Co, Mn), doping increases the lattice constants, unit cell volume, valence bonds, and the anisotropic thermal coefficients. By means of X-ray diffraction and the program package TOPOS, the Li-cation migration maps were obtained. The Li-ions move along the [010] direction which can be clearly visualized in the mixed-metal LiNi0.9 M0.1PO4(M = Co, Mn) single crystals. It was found that the 10% doping of LiNiPO4 by cobalt ions leads to a decrease in the formation temperature and to the suppression of the incommensurate phase. The 10% doping of manganese ions increases the transition temperature, while the temperature range of the incommensurate phase narrows. (C) 2018 Elsevier B.V. All rights reserved.

Title:
Magnetic properties of RCuAl3 (R = Pr and Nd) compounds
Authors:
Klicpera, M; Fikacek, J; Vlaskova, K; Puente-Orench, I; Divis, M; Javorsky, P Author Full Names: Klicpera, Milan; Fikacek, Jan; Vlaskova, Kristina; Puente-Orench, Ines; Divis, Martin; Javorsky, Pavel
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 781 1189-1197; 10.1016/j.jallcom.2018.12.077 APR 15 2019
Abstract:
( )Magnetic properties of PrCuAl3 and NdCuAl3 single crystals, adopting the tetragonal BaNiSn3 -structure-type, are reported. Our magnetization and specific heat measurements revealed no magnetic ordering in PrCuAl3, while NdCuAl3 orders antiferromagnetically below T-N = 2.45 K. The paramagnetic regime was investigated for both analogues revealing (i) the a-axis as the easy direction of magnetization with (ii) a relatively high uniaxial anisotropy energy of 13.2 meV for PrCuAl3 compared to a smaller value of 4.7 meV for NdCuAl3. The measured data are well explained by rare-earth ground state multiplet splitting in crystal electric field. A powder neutron diffraction experiment confirmed PrCuAl3 to remain paramagnetic down to 1.5 K. On the other hand, NdCuAl3 orders antiferromagnetically below T-N with an incommensurate magnetic structure described by two propagation vectors k(1) = (1/3 - delta(1), 0, 0) and k(2) = (1/7 - delta 2 , 1/7 - delta(2) , 0), where delta(1) = 0.035(1) and delta(2) = 0.007(1). The magnetic moments (of both magnetic modulations) are arranged within the basal plane with a small z-component moment allowed by the symmetry. Our results are discussed with respect to other RCuAl3 compounds. (C) 2018 Elsevier B.V. All rights reserved.

Title:
Spontaneous and induced magnetic phase transitions in Tb0.9Er0.1Ni5
Authors:
Lee, HJ; Choi, YN; Lukoyanov, AV; Gerasimov, EG; Pirogov, AN Author Full Names: Lee, H-J; Choi, Y-N; Lukoyanov, A., V; Gerasimov, E. G.; Pirogov, A. N.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 475 593-601; 10.1016/j.jmmm.2018.12.004 APR 1 2019
Abstract:
Magnetic and neutron powder diffraction measurements have been carried out on Tb0.9Er0.1Ni5 intermetallic compound. The intermetallide crystallizes in the hexagonal CaCu5-type structure and possesses a long-range magnetic order at temperatures below 22 K. A fan-like magnetic structure is described by two propagation vectors: k(1) = 0 and k(2) = 2 pi/c(0, 0, 0.036), at 20 K. The total Tb-ion magnetic moment has the ferromagnetic and modulated components. The latter is a transverse spin wave. When the sample is cooled at a temperature below 8 K, the module of the k(2) vector does not change and is equal to k(2) = 2 pi/c(0, 0, 0.027). An "in-commensurate - lock-in" magnetic transition takes place at 8 K. The k(2) vector exhibits a temperature hysteresis of about (5-6) K, whereas the intensities of Bragg reflections and satellites do not show up appreciable changes. When an external magnetic field is applied to the sample, the satellites and the module of the k(2) vector decrease, while the Bragg intensities increase. The sample becomes a ferromagnetic at a field of similar to 2 kOe, and the Tb-ion magnetic moment is equal to 8.3 mu(B). A general notion of the Tb0.9Er0.1Ni5 magnetic state evolution with an external field is given using the field dependence of the background intensity in diffraction patterns. First principle calculations for TbNi5 and Tb0.9Er0.1Ni5 are performed including the 4f states into the orbital basis and accounting for strong electronic correlations and spin-orbital coupling. This allowed obtaining both spin and orbital moments of the effective Tb-ion moment and estimating also the value of Tb-Tb exchange interaction.

Title:
Direct observation of incommensurate magnetism in Hubbard chains (vol 565, pg 56, 2018)
Authors:
Salomon, G; Koepsell, J; Vijayan, J; Hilker, TA; Nespolo, J; Pollet, L; Bloch, I; Gross, C Author Full Names: Salomon, Guillaume; Koepsell, Joannis; Vijayan, Jayadev; Hilker, Timon A.; Nespolo, Jacopo; Pollet, Lode; Bloch, Immanuel; Gross, Christian
Source:
NATURE, 566 (7743):E5-E5; 10.1038/s41586-019-0906-z FEB 14 2019

Title:
Honeycomb lattice type charge density wave associated with interlayer Cu ions ordering in 1T-CuxTiSe2
Authors:
Kitou, S; Kobayashi, S; Kaneko, T; Katayama, N; Yunoki, S; Nakamura, T; Sawa, H Author Full Names: Kitou, Shunsuke; Kobayashi, Shintaro; Kaneko, Tatsuya; Katayama, Naoyuki; Yunoki, Seiji; Nakamura, Toshikazu; Sawa, Hiroshi
Source:
PHYSICAL REVIEW B, 99 (8):10.1103/PhysRevB.99.081111 FEB 11 2019
Abstract:
The phase transition phenomenon in a semimetallic 1T-TiSe2. has attracted attention as an excitonic insulator. However, as the phase transition accompanying superlattice peaks has the q vector connecting the Fermi surfaces of the three-dimensional shape of hole and electron pockets, it also assumes the charge density wave (CDW) state owing to the electron-phonon interaction. To understand the electronic state at the low temperature, control of the chemical potential was attempted by electronic doping through Cu+ intercalation. Physical properties measurements and synchrotron x-ray diffraction experiments in CuxTiSe2 (x = 0-0.35) were performed. The phase transition was determined to occur as a cooperative phenomenon between the honeycomb lattice type CDW corresponding to the nesting vector and the ordered state of the Cu+ ions between TiSe2 layers at a specific doping amount (x = 1/3). The behavior of Cu+ ions in highly doped regions suggests the occurrence of a two-dimensional liquid-solid state transition based on the temperature dependence of the x-ray diffuse scattering.

Title:
Crystallographic Relationship between the nu (Mn82Si18) and H (Mn7Si2V) Phases in the Mn-Si-V Alloy System
Authors:
Nakayama, K; Kurihara, D; Koyama, Y Author Full Names: Nakayama, Kei; Kurihara, Daichi; Koyama, Yasumasa
Source:
MATERIALS TRANSACTIONS, 59 (7):1051-1056; 10.2320/matertrans.MD201712 2018
Abstract:
There are the intermetallic-compound nu (Mn82Si18) and H (Mn7Si2V) phases in the Mn-Si-V alloy system. These two phases can be regarded as approximant phases of the dodecagonal quasicrystal, and their crystal structures involve similar structural hierarchies consisting of dodecagonal atomic columns and giant dodecagonal structural units. To understand the crystallographic relationship between these approximant phases, we examined their crystallographic features mainly by transmission electron microscopy. It was found that there is a simple orientation relationship of N(001)(nu)//N(0001)(H) and N(010)(nu)//N(01<(1)overbar>0)(H) between the nu and H structures. In addition, H-structure regions have an antiphase boundary with a pi phase shift along a column axis as a structural defect. A notable feature of the antiphase boundary is that it consists of decagonal columns, not dodecagonal columns present in the H structure, where both 11 dodecagonal columns and eight decagonal columns form one dodecagonal unit in the nu structure. The nu structure can thus be produced in the following two steps. First, eight outer dodecagonal columns in each dodecagonal unit in the H structure are replaced by eight decagonal columns. The second step is the periodic introduction of antiphase boundaries, consisting of decagonal columns present in the replacement.

Update: 20-Feb-2019


Title:
Benefits of intermediate-layer formation at the interface of Nb/Cu and Ta/Cu explosive clads
Authors:
Parchuri, P; Kotegawa, S; Yamamoto, H; Ito, K; Mori, A; Hokamoto, K Author Full Names: Parchuri, PradeepK.; Kotegawa, Shota; Yamamoto, Hajime; Ito, Kazuhiro; Mori, Akihisa; Hokamoto, Kazuyuki
Source:
MATERIALS & DESIGN, 166 10.1016/j.matdes.2019.107610 MAR 15 2019
Abstract:
A systematic, comparative study was carried out to quantitatively characterize the bending strength of wavy interfaces with and without an intermediate layer (IL) in Nb/Cu and Ta/Cu explosive clads. The clads having wavy interfaces with and without an IL were obtained at horizontal high and low collision velocities (HCV and LCV) in the explosive welding, respectively. The stress-strain curves of all the clads were similar in three-point bending tests, but the clads with an IL exhibited higher bending stress than those without an IL. Moreover, cracks were observed in the Nb plate of Nb/Cu clads without an IL, but nocracks in that with an IL. TEM observation confirmed coexistence of ultrafine refractory metal and Cu phases in the ILs. In addition, the Ta-Cu-based intermetallic compound or dodecagonal quasicrystal, which is a non-equilibrium phase, were also observed along with coexistence of Ta and Cu phases in the ILs of Ta/Cu interface. Cladding at HCV and a lower collision angle assisted in resultant less strain in refractory metal plates near the joint interfaces than those at LCV, due to IL formation. The ILs assisted in obtainment of interfaces of higher hardness, leading to higher bending-stress clads without losing large elongation. (C) 2019 Elsevier Ltd. This is an open access article under the CC BY-NC-ND license.

Title:
Formation and temporal evolution of modulated structure in high Nb-containing lamellar gamma-TiAl alloy
Authors:
Ren, GD; Dai, CR; Mei, W; Sun, J; Lu, S; Vitos, L Author Full Names: Ren, Guo-dong; Dai, Cheng-ren; Mei, Wei; Sun, Jian; Lu, Song; Vitos, Levente
Source:
ACTA MATERIALIA, 165 215-227; 10.1016/j.actamat.2018.11.041 FEB 15 2019
Abstract:
The formation and temporal evolution of the modulated structure in a lamellar gamma-based Ti-45Al-8.5Nb alloy have been investigated by transmission electron microscopy (TEM) in combination with first-principles theory in this work. The results show that the Nb-rich O phase as a constituent of the modulated structure is thermodynamically stable below 650 degrees C in the alpha(2) lamellae. The morphology of the O phase variants changes from thin plate-like shape with a low volume fraction at initial annealing to rectangle/square shape with a high volume fraction after a prolonged annealing, and the retransformed alpha(2), named as alpha(2-II) hereafter, emerges at intersections of the variants with two orthogonal habit planes due to their elastic interactions. The partitioning coefficient of Nb between the O phase and alpha(2) is about 2 at 600 degrees C. The diffusion coefficient of Nb derived from growth kinetics of the O phase is about (1.3 +/- 0.2) x 10(-22) m(2)s(-1) in the alpha(2) lamellae. Significant precipitation hardening effect of the O phase has been revealed for the alpha(2) lamellae and gamma/(alpha(2)+O) lamellar microstructure, which is supposed to be attributed to refining the alpha(2) lamellae associated with elastic strain energy from the alpha(2) -> O phase transformation and introducing the interface between the modulated lamella and adjacent gamma phase. (C) 2018 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Title:
Room temperature structure and transport properties of the incommensurate modulated LaNb0.88W0.12O4.06
Authors:
Li, C; Pramana, SS; Skinner, SJ Author Full Names: Li, Cheng; Pramana, Stevin S.; Skinner, Stephen J.
Source:
DALTON TRANSACTIONS, 48 (5):1633-1646; 10.1039/c8dt03958e FEB 7 2019
Abstract:
The crystal structure of a (3 + 2)D incommensurate modulated LaNb0.88W0.12O4.06 phase, a novel oxygen ionic conductor, is refined using a combination of synchrotron X-ray diffraction and electron diffraction data. The superspace group I2/c(alpha(1)0(gamma 1))00(alpha(2)0(gamma 2))00 (a = 5.4131(1) angstrom, b = 11.6432(2) degrees, c = 5.2963(1) angstrom, beta = 91.540(1)degrees, q(1) = 0.2847(5)a* + 0.1098(9)c* and q(2) = -0.1266(9)a* + 0.2953(1)c*) was chosen for the refinement. Similar to other scheelite type modulated structures, the modulation of LaNb0.88W0.12O4.06 stems from the cation occupancy ordering in the xz plane. To facilitate the modulated cation sub-lattice, and to compensate for the difference in their size and charge, the B site polyhedra are distorted by stretching the B-O bond lengths. Consequently, an extension in the B site coordination number from 6 to 8 is observed in the modulated phase. An interconnected 3D network of BOx polyhedra, similar to that of modulated CeNbO4.25, is obtained as a result of the structure modulation, which is not available in the unmodulated parent structure. Tracer diffusivity measurements indicate that the composition is an oxygen ion conductor, which relies on an intersticalcy conduction mechanism. Oxygen tracer diffusivity of 2.46 x 10(-9) cm(2) s(-1), at 750 degrees C is reported.

Title:
In-Situ observation of local atomic structure of Al-Cu-Fe quasicrystal formation
Authors:
Parsamehr, H; Lu, YJ; Lin, TY; Tsai, AP; Lai, CH Author Full Names: Parsamehr, Hadi; Lu, Ying-Jiu; Lin, Tzu-Ying; Tsai, An-Pang; Lai, Chih-Huang
Source:
SCIENTIFIC REPORTS, 9 10.1038/s41598-018-37644-x FEB 4 2019
Abstract:
The phase and local environment, neighbouring atoms and coordination numbers (CN), for an Al-Cu-Fe multilayer were studied during heating (to 800 degrees C) and cooling (to room temperature) processes using in-situ X-Ray diffraction (XRD) and in-situ X-ray absorption spectroscopy (XAS) techniques to investigate the formation of Al-Cu-Fe quasicrystals (QCs). In-situ XRD clarified the transition of the omega-Al7Cu2Fe phase to a liquid state at the high temperature which transformed into the QC phase during cooling. The in-situ XAS showed a relatively small shift in distance between Cu-Al and Fe-Al during the phase evolution from RT to 700 degrees C. The distance between Cu-Cu, however, showed a significant increase from omega-phase at 700 degrees C to the liquid state at 800 degrees C, and this distance was maintained after QC formation. Furthermore, the CN of Fe-Al was changed to N = 9 during cooling. Through our observations of changes in CN, atomic distances and the atomic environment, we propose the local structural ordering of the quasicrystalline phase originated from a liquid state via omega-phase. In this study, we give a clear picture of the atomic environment from the crystalline to the quasicrystalline phase during the phase transitions, which provides a better understanding of the synthesis of functional QC nanomaterials.

Title:
Enhancing Morphology and Separation Performance of Polyamide 6,6 Membranes By Minimal Incorporation of Silver Decorated Graphene Oxide Nanoparticles
Authors:
Mahmoudi, E; Ng, LY; Ang, WL; Chung, YT; Rohani, R; Mohammad, AW Author Full Names: Mahmoudi, Ebrahim; Ng, Law Yong; Ang, Wei Lun; Chung, Ying Tao; Rohani, Rosiah; Mohammad, Abdul Wahab
Source:
SCIENTIFIC REPORTS, 9 10.1038/s41598-018-38060-x FEB 4 2019
Abstract:
Nanomaterials can be incorporated in the synthesis of membrane to obtain mixed-matrix membrane with marked improvement in properties and performance. However, stability and dispersion of the nanomaterials in the membrane matrix, as well as the need to use high ratio of nanomaterials for obvious improvement of membrane properties, remain a major hurdle for commercialization. Hence, this study aims to investigate the improvement of polyamide 6,6 membrane properties with the incorporation of silver nanoparticles decorated on graphene oxide (Ag-GO) nanoplates and at the same time focus is given to the issues above. Graphene oxide nanoplates were synthesized using the modified Hummers' method and decorated with silver before embedded into the polyamide 6,6 matrix. Physicochemical characterizations were conducted on both nanoplates and the mixed-matrix Ag-GO polyamide 6,6 membrane. The issues of Ag agglomeration and leaching were not observed, which could be attributed to the decoration of Ag on GO that helped to disperse the nanomaterials and provided a better anchor point for the attachment of Ag nanoparticles. The synthesized membrane showed marked improvement regarding flux (135% increment) and antifouling (40% lower irreversible fouling), which could be ascribed to the more negative charge of membrane surface (-14 +/- 6 to -31 +/- 3.8 mV) and hydrophilicity (46% enhancement) of the membranes. With minimal embedment of Ag nanoparticles, the membrane showed superior antibacterial property where the E. coli bacteria could not form a single colony on the membrane surface. Overall, the decoration of Ag on GO nanoplates could be a promising approach to resolve the agglomeration and leaching issues as well as reduce the amount of precious Ag in the synthesis of Ag-GO polyamide 6,6 membrane.

Title:
Energy-dispersive Laue experiments with X-ray tube and PILATUS detector: precise determination of lattice constants
Authors:
Kurdzesau, F Author Full Names: Kurdzesau, Fiodar
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY, 52 72-93; 10.1107/S1600576718017193 1 FEB 2019
Abstract:
A PILATUS detector in combination with a conventional sealed X-ray tube was used for the development of the energy-dispersive Laue diffraction technique, which can be applied for precise measurements of single-crystal lattice constants in transmission and reflection modes without moving the sample. Exploiting the ability of PILATUS detectors to suppress counting of X-ray photons below a certain energy threshold allows one to recover the wavelength of diffracted Bragg reflections, reconstruct the three-dimensional reciprocal-space pattern, index X-ray diffraction peaks, and find the orientation and lattice parameters of the crystal without any a priori information about the sample. By making some geometrical assumptions and using a set of fast in situ calibration procedures, it is possible to simultaneously refine lattice constants and hardware correction factors, which simplifies the sample preparation and measurement strategies. Several samples [silicon, quartz, fluorite (CaF2), o-Al13Co4 quasicrystal approximant, Laves (MgZn2) and Bergman (Mg-32(Al,Zn)(49)) phases] were studied with the developed technique, and 0.01 angstrom and 0.1 degrees precisions were routinely reached for lattice vector lengths and angles, respectively. The use of the developed methods is only limited by the energy resolution of the PILATUS detector, where lattice vectors with >27 angstrom length cannot be reliably resolved.

Title:
Damping Properties of As-Cast Mg-Zn-Y Alloy with / Phase
Authors:
Wan, DQ; Hu, YL; Li, ZM; Ye, ST Author Full Names: Wan Diqing; Hu Yinglin; Li Zhumin; Ye Shuting
Source:
RARE METAL MATERIALS AND ENGINEERING, 48 (1):71-76; JAN 2019
Abstract:
A conventional casting method was adopted to fabricate the alloys of Mg-Zn-Y, in which the dendritic morphology and its relation to the damping properties of as-cast Mg-Zn-Y alloy were studied based on the typical Mg93Zn6Y1 alloy containing icosahedral quasicrystal phase. By controlling the pouring temperature, the stirring speed and stirring time, the dendritic morphology with different parameters was obtained. The results show that the microstructure of the as-cast Mg93Zn6Y1 mainly consists of alpha-Mg dendritic crystal and icosahedral quasicrystal phase. After stirring, the primary alpha-Mg dendritic gradually have fractal characteristics in faith, and its size changes, affecting the damping capacity. The mechanism was discussed.

Title:
Porous Al63Cu25Fe12 quasicrystals covered with (Al11.5Fe13.9Cu19.7)O-54.9 nanosheets
Authors:
Zhang, F; Guo, HJ; Wang, LL; Ma, HK; Li, H; Zhang, L; He, ZB Author Full Names: Zhang, Fan; Guo, Huijie; Wang, Leilei; Ma, Haikun; Li, Hua; Zhang, Lei; He, Zhangbing
Source:
MATERIALS CHARACTERIZATION, 147 165-172; 10.1016/j.matchar.2018.10.026 JAN 2019
Abstract:
Porous Al63Cu25Fe12 quasicrystal alloys with the surfaces and the wall of pores covered with abundant (Al11.5Fe13.9Cu19.7)O-54.9 nanosheets were successfully fabricated through the combination of powder metallurgy and dealloying in NaOH solutions. Their compositions, microscopic morphology, and crystal structures were investigated using energy-dispersive X-ray spectroscopy, scanning electron microscopy, X-ray diffraction, and transmission electron microscopy. We found that the composite of porous Al63Cu25Fe12 quasicrystal alloys and (Al11.5Fe13.9Cu19.7)O-54.9 nanosheets shows high catalytic performances in hydrogen production by methanol steam reforming at relatively low temperatures. X-ray photoelectron spectroscopy was used to analyze the catalytic mechanisms, and Cu was found to be the key element in this catalytic reaction.

Update: 13-Feb-2019


Title:
Helical Ordering of Spin Trimers in a Distorted Kagome Lattice of Gd3Ru4Al12 Studied by Resonant X-ray Diffraction
Authors:
Matsumura, T; Ozono, Y; Nakamura, S; Kabeya, N; Ochiai, A Author Full Names: Matsumura, Takeshi; Ozono, Yusaku; Nakamura, Shintaro; Kabeya, Noriyuki; Ochiai, Akira
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 88 (2):10.7566/JPSJ.88.023704 FEB 15 2019
Abstract:
Successive magnetic phase transitions at T-1 = 17.5 K and T-2 = 18.5 K in Gd3Ru4Al12, with a distorted kagome lattice of Gd ions, is studied using resonant X-ray diffraction with polarization analysis. It has been suggested that in this compound the S = 7/2 spins on the nearest-neighbor Gd-triangle form a ferromagnetic trimer and the Gd lattice can be effectively considered as an antiferromagnetic triangular lattice of S = 21/2 spin trimers [S. Nakamura et al., Phys. Rev. B 98, 054410 (2018)]. We show that the magnetic order in this system is described by an incommensurate wave vector q similar to (0.27,0, 0), which varies slightly with temperature. In the low temperature phase below T-1, the experimental results are well explained by considering that the spin timers form a helical order with both the c-axis and c-plane components. In the intermediate phase above T-1 the c-axis component vanishes, resulting in a sinusoical structure within the c-plane. The sinusoidal-helical transition at T-1, can be regarded as an ordering of chiral degree of freedom, which is degenerate in the intermediate phase.

Title:
Long-period structural modulation on the global length scale as the characteristic feature of the morphotropic phase boundaries in the Na0.5Bi0.5TiO3 based lead-free piezoelectrics
Authors:
Das Adhikary, G; Khatua, DK; Senyshyn, A; Ranjan, R Author Full Names: Das Adhikary, Gobinda; Khatua, Dipak Kumar; Senyshyn, Anatoliy; Ranjan, Rajeev
Source:
ACTA MATERIALIA, 164 749-760; 10.1016/j.actamat.2018.11.016 FEB 1 2019
Abstract:
The inherent structural disorder has a profound effect on the dielectric, ferroelectric and the electromechanical response of the Na0.5Bi0.5TiO3 (NBT) based lead-free piezoelectrics. While analogous to the lead-based classical morphotropic phase boundary (MPB) systems the existence of MPB has been recognized in some derivatives of NBT displaying enhanced electromechanical response, there is a lack of clarity on the structural state of the MPB compositions on NBT-based systems on the global length scale. We have examined this issue on the well known MPB system (1-x)Na0.5Bi0.5TiO3-(x)K0.5Bi0.5TiO3(NBT-KBT) by carrying out structural investigations on local and global length scales using Eu+3 photoluminiscence and high-resolution neutron powder diffraction techniques, respectively. Our study reveals that the MPB of this system is characterized by the onset of a long-period modulated structure with a periodicity of similar to 40 angstrom on the global scale. Temperature depedent neutron diffraction study revealed that the intermediate temperature P4bm phase which appears in NBT is suppressed for the MPB composition. The MPB composition rather develops a long-period modulated phase on cooling from the cubic phase. The ergodic-nonergodic relaxor ferroelectric transition occurs within this long-period modulated phase. In the non-ergodic regime, however, strong electric field irreversibly transforms the long-period modulated phase to the rhombohedral ferroelectric (R3c). We demonstrate that thermal depolarization of this system is a distinct structural event characterized by the system losing its field-induced long range rhombohedral (R3c) coherence and transforming back to the long-period modulated phase. Our study suggests that the long-period modulated phase is the primary structural feature of the MPB compositions in NBT-based piezoelectrics. (C) 2018 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Title:
Symmetry-changing commensurate-incommensurate solid transition in the He-4 monolayer on 6,6,12-graphyne
Authors:
Ahn, J; You, M; Lee, G; Volkoff, T; Kwon, Y Author Full Names: Ahn, Jeonghwan; You, Mujin; Lee, Gwangyoung; Volkoff, Tyler; Kwon, Yongkyung
Source:
PHYSICAL REVIEW B, 99 (2):10.1103/PhysRevB.99.024113 JAN 30 2019
Abstract:
Path-integral Monte Carlo calculations have been carried out to investigate physical properties of a He-4 monolayer adsorbed on a single 6,6,12-graphyne sheet, which is one of the graphyne families possessing a rectangular symmetry. To characterize elusive quantum phases of an adsorbed He-4 monolayer on 6,6,12-graphyne, we model the He-4-graphyne interaction by the pairwise sum of empirical He-4-C interatomic potentials. At partially filled He-4 coverages, we identify three commensurate solids of the C-3/4, C-4/4, and C-6/4 structures from the two-dimensional density distribution. These solids show the rectangular symmetry inherited from the symmetry of 6,6,12-graphyne, which were confirmed with the analysis of their static structure factors. At high helium coverages near its completion, the He-4 monolayer is predicted to exhibit a transition from a rectangular commensurate structure to a triangular incommensurate structure, after going through inhomogeneous structures mixed with domains of triangular and rectangular orderings. This symmetry-changing transition has not been observed in He-4 monolayers adsorbed on other carbon substrates.

Title:
Microstructure, texture evolution and tensile properties of extruded Mg-4.58Zn-2.6Gd-0.16Zr alloy
Authors:
Xiao, L; Yang, GY; Chen, JM; Luo, SF; Li, JH; Jie, WQ Author Full Names: Xiao, Lei; Yang, Guangyu; Chen, Jieming; Luo, Shifeng; Li, Jiehua; Jie, Wanqi
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 744 277-289; 10.1016/j.msea.2018.11.142 JAN 28 2019
Abstract:
Microstructure, texture evolution and mechanical properties of extruded Mg-4.58Zn-2.6Gd-0.18Zr alloy were investigated at extrusion temperatures of 260 degrees C, 280 degrees C and 300 degrees C, extrusion ratios of 10, 15 and 30, and ram speeds of 3 mm s(-1) and 6 mm s(-1), respectively. The results indicated that the as-cast experimental alloy was composed of alpha-Mg matrix, coarse alpha-Mg + W(Mg3Zn3Gd2) eutectic and icosahedral quasicrystalline I(Mg3Zn6Gd) phase. A small amount of undissolved W phases were detected after the homogenization treatment at 505 degrees C up to 16 h, while most I phase dissolved into the alpha-Mg matrix. The initial crystallites before extrusion were randomly oriented, and showed a typical random texture. After extrusions, all samples exhibited a bimodal microstructure consisting of fine Dynamic recrystallization (DRX) grains and coarse elongated un-DRX grains, and the formation of ultra-fine DRX grains only occurred in the sample with an extrusion ratio of 10 at 260 degrees C, 3 mm s(-1), which was caused by the solute segregation in homogenized billets and non-uniformly distributed W phase during the extrusion process. A fiber texture with {0002} planes and < 1210 > directions paralleled to the extrusion direction was observed to be dominant in all the extruded samples. Furthermore, the increase of extrusion ratio was found to be beneficial for the DRX process and refinement of grain size, and the maximum texture intensity was accordingly weakened, which resulted in a decrease of tensile yield strength but an increase of elongation. With increasing the extrusion temperature or ram speed, both the grain size and DRX fraction gradually increased. Consequently, the texture was randomized and the maximum texture intensity decreased, which led to a reduction of the elongation and tensile yield strength. The tensile failure behaviors under different extrusion conditions were found to be related with the contraction twin lamellas formed in the un-DRX grains and the string-like W phases.

Title:
Comparing the anomalous Hall effect and the magneto-optical Kerr effect through antiferromagnetic phase transitions in Mn3Sn
Authors:
Balk, AL; Sung, NH; Thomas, SM; Rosa, PFS; McDonald, RD; Thompson, JD; Bauer, ED; Ronning, F; Crooker, SA Author Full Names: Balk, A. L.; Sung, N. H.; Thomas, S. M.; Rosa, P. F. S.; McDonald, R. D.; Thompson, J. D.; Bauer, E. D.; Ronning, F.; Crooker, S. A.
Source:
APPLIED PHYSICS LETTERS, 114 (3):10.1063/1.5066557 JAN 21 2019
Abstract:
In the non-collinear antiferromagnet Mn3Sn, we compare simultaneous measurements of the anomalous Hall effect (AHE) and the magneto-optical Kerr effect (MOKE) through two magnetic phase transitions: the high-temperature paramagnetic/antiferromagnetic (AF) phase transition at the Neel temperature (T-N approximate to 420 K) and a lower-temperature incommensurate magnetic ordering at T-1 approximate to 270 K. While both the AHE and MOKE are sensitive to the same underlying symmetries of the AF non-collinear spin order, we find that the transition temperatures measured by these two techniques unexpectedly differ by approximately 10 K. Moreover, the applied magnetic field at which the AF order reverses is significantly larger when measured by MOKE than when measured by AHE. These results point to a difference between the bulk and surface magnetic properties of Mn3Sn. Published under license by AIP Publishing.

Title:
Quasicrystal nucleation and Z module twin growth in an intermetallic glass-forming system
Authors:
Hornfeck, W; Kobold, R; Kolbe, M; Conrad, M; Herlach, D Author Full Names: Hornfeck, Wolfgang; Kobold, Raphael; Kolbe, Matthias; Conrad, Matthias; Herlach, Dieter
Source:
NATURE COMMUNICATIONS, 9 10.1038/s41467-018-06597-0 OCT 3 2018
Abstract:
While quasicrystals possess long-range orientational order they lack translation periodicity. Considerable advancements in the elucidation of their structures and formative principles contrast with comparatively uncharted interrelations, as studies bridging the spatial scales from atoms to the macroscale are scarce. Here, we report on the homogeneous nucleation of a single quasicrystalline seed from the undercooled melt of glass-forming NiZr and its continuous growth into a tenfold twinned dendritic microstructure. Observing a series of crystallization events on electrostatically levitated NiZr confirms homogeneous nucleation. Mapping the microstructure with electron backscatter diffraction suggests a unique, distortion-free structure merging a common structure type of binary alloys with a spiral growth mechanism resembling phyllotaxis. A general geometric description, relating all atomic loci, observed by atomic resolution electron microscopy, to a pentagonal Z module, explains how the seed's decagonal long-range orientational order is conserved throughout the symmetry breaking steps of twinning and dendritic growth.

Title:
Waves in one-dimensional quasicrystalline structures: dynamical trace mapping, scaling and self-similarity of the spectrum
Authors:
Morini, L; Gei, M Author Full Names: Morini, Lorenzo; Gei, Massimiliano
Source:
JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS, 119 83-103; 10.1016/j.jmps.2018.06.007 OCT 2018
Abstract:
Harmonic axial waves in quasiperiodic-generated structured rods are investigated. The focus is on infinite bars composed of repeated elementary cells designed by adopting generalised Fibonacci substitution rules, some of which represent examples of one-dimensional quasicrystals. Their dispersive features and stop/pass band spectra are computed and analysed by imposing Floquet-Bloch conditions and exploiting the invariance properties of the trace of the relevant transfer matrices. We show that for a family of generalised Fibonacci substitution rules, corresponding to the so-called precious means, an invariant function of the circular frequency, the Kohmoto's invariant, governs self-similarity and scaling of the stop/pass band layout within defined ranges of frequencies at increasing generation index. Other parts of the spectrum are instead occupied by almost constant ultrawide band gaps. The Kohmoto's invariant also explains the existence of particular frequencies, named canonical frequencies, associated with closed orbits on the geometrical three-dimensional representation of the invariant. The developed theory represents an important advancement towards the realisation of elastic quasicrystalline metamaterials. (C) 2018 Elsevier Ltd. All rights reserved.

Update: 6-Feb-2019


Title:
Observation of the nesting and defect-driven 1D incommensurate charge density waves phase in the 2D system
Authors:
Matetskiy, AV; Denisov, NV; Hsing, CR; Wei, CM; Zotov, AV; Saranin, AA Author Full Names: Matetskiy, A., V; Denisov, N., V; Hsing, C. R.; Wei, C. M.; Zotov, A., V; Saranin, A. A.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 31 (11):10.1088/1361-648X/aaf9ea MAR 20 2019
Abstract:
We report on the low-temperature scanning tunneling microscopy/spectroscopy (STM/STS) study of the (Bi, Na)/Si(111) root 3 x root 3 reconstruction that is known to possess Fermi surface with apparently good nesting. We found that defects on this surface produce a one-dimensional-like pattern with the periodicity of 8.2 +/- 0.4 angstrom that is incommensurate with the root 3 x root 3 lattice period. The dI/dV mapping analysis reveals an occurrence of the k-dependent branch associated with quasi-particle interference and the k-independent branch associated with the nesting vector connecting the parallel segments of the (Bi,Na)/Si(111) root 3 x root 3 Fermi surface, the fingerprint of the charge-density-wave (CDW) phase. The STS data demonstrates that development of the CDW phase leads to reducing electron density of states at the Fermi level.

Title:
Coherent photo-induced phonon emission in the charge-density-wave state of K0.3MoO3
Authors:
Rabia, K; Meng, F; Thomson, MD; Bykov, M; Merlin, R; van Smaalen, S; Roskos, HG Author Full Names: Rabia, K.; Meng, F.; Thomson, M. D.; Bykov, M.; Merlin, R.; van Smaalen, S.; Roskos, H. G.
Source:
NEW JOURNAL OF PHYSICS, 21 10.1088/1367-2630/aaf81f JAN 18 2019
Abstract:
We report on the observation of coherent terahertz (THz) emission from the quasi-one-dimensional charge-density wave (CDW) system, blue bronze (K0.3MoO3), upon photo-excitation with ultrashort near-infrared optical pulses. The emission contains a broadband, low-frequency component due to the photo-Dember effect, which is present over the whole temperature range studied (30-300 K), as well as a narrow-band doublet centered at 1.5 THz, which is only observed in the CDW state and results from the generation of coherent transverse-optical phonons polarized perpendicular to the incommensurate CDW b-axis. As K0.3MoO3 is centrosymmetric, the lowest-order generation mechanism which can account for the polarization dependence of the phonon emission involves either a static surface field or quadrupolar terms due to the optical field gradients at the surface. This phonon signature is also present in the ground-state conductivity, and decays in strength with increasing temperature to vanish above T similar to 100 K, i.e. significantly below the CDW transition temperature. The temporal behavior of the phonon emission can be well described by a simple model with two coupled modes, which initially oscillate with opposite polarity.

Update: 23-Jan-2019


Title:
On the Characterization of a Hitherto Unreported Icosahedral Quasicrystal Phase in Additively Manufactured Aluminum Alloy AA7075
Authors:
Kairy, SK; Gharbi, O; Nicklaus, J; Jiang, D; Hutchinson, CR; Birbilis, N Author Full Names: Kairy, S. K.; Gharbi, O.; Nicklaus, J.; Jiang, D.; Hutchinson, C. R.; Birbilis, N.
Source:
METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE, 50A (2):529-533; 10.1007/s11661-018-5025-1 FEB 2019
Abstract:
Aluminum alloy AA7075 (Al-Zn-Mg-Cu) specimens were prepared using selective laser melting, also known as powder bed fusion additive manufacturing. In the as-manufactured state, which represents a locally rapidly solidified condition, the prevalence of a previously unreported icosahedral quasicrystal with 5-fold symmetry was observed. The icosahedral quasicrystal, which has been termed -phase (nu-phase), was comprised of Zn, Cu, and Mg.

Title:
Topological Landscape of Competing Charge Density Waves in 2H-NbSe2
Authors:
Gye, G; Oh, E; Yeom, HW Author Full Names: Gye, Gyeongcheol; Oh, Eunseok; Yeom, Han Woong
Source:
PHYSICAL REVIEW LETTERS, 122 (1):10.1103/PhysRevLett.122.016403 JAN 9 2019
Abstract:
Despite decades of studies of the charge density wave (CDW) of 2H-NbSe2, the origin of its incommensurate CDW ground state has not been understood. We discover that the CDW of 2H-NbSe2 is composed of two different, energetically competing, structures. The lateral heterostructures of two CDWs are entangled as topological excitations, which give rise to a CDW phase shift and the incommensuration without a conventional domain wall. A partially melted network of topological excitations and their vertices explain an unusual landscape of domains. The unconventional topological role of competing phases disclosed here can be widely applied to various incommensuration or phase coexistence phenomena in materials.

Update: 17-Jan-2019


Title:
Anisotropic transient thermoelasticity analysis in a two-dimensional decagonal quasicrystal using meshless local Petrov-Galerkin (MLPG) method
Authors:
Hosseini, SM; Sladek, J; Sladek, V Author Full Names: Hosseini, Seyed Mahmoud; Sladek, Jan; Sladek, Vladimir
Source:
APPLIED MATHEMATICAL MODELLING, 66 275-295; 10.1016/j.apm.2018.09.024 FEB 2019
Abstract:
The meshless local Petrov-Galerkin (MLPG) method is employed for anisotropic transient thermoelasticity analysis of 2D decagonal quasicrystals (QCs) subjected to transient thermal and mechanical shock loadings. The wave type model and the elasto-hydrodynamic model are applied to derive the phonon and phason governing equations, respectively. The temperature affects only the phonon field. To find the temperature distributions on the assumed 2D domain, the anisotropic heat conduction problem is solved using the MLPG method. Also, the MLPG method is successfully employed to obtain the transient behaviors of both phonon and phason displacements by solving the governing equations in local integral equations (LIEs) forms. Making use a unit step function as the test functions in the local weak-form of governing equations, we derived the local integral equations (LIEs) considered on small subdomains identical with support domains of test functions around each node. The radial basis functions are used for approximation of the spatial variation of field variables. The Laplace-transform technique is utilized to discretize the time variations. (C) 2018 Elsevier Inc. All rights reserved.

Title:
Direct observation of incommensurate magnetism in Hubbard chains
Authors:
Salomon, G; Koepsell, J; Vijayan, J; Hilker, TA; Nespolo, J; Pollet, L; Bloch, I; Gross, C Author Full Names: Salomon, Guillaume; Koepsell, Joannis; Vijayan, Jayadev; Hilker, Timon A.; Nespolo, Jacopo; Pollet, Lode; Bloch, Immanuel; Gross, Christian
Source:
NATURE, 565 (7737):56-+; 10.1038/s41586-018-0778-7 JAN 3 2019
Abstract:
The interplay between magnetism and doping is at the origin of exotic strongly correlated electronic phases and can lead to novel forms of magnetic ordering. One example is the emergence of incommensurate spin-density waves, which have wavevectors that do not belong to the reciprocal lattice. In one dimension this effect is a hallmark of Luttinger liquid theory, which also describes the low-energy physics of the Hubbard model(1). Here we use a quantum simulator that uses ultracold fermions in an optical lattice(2-8) to directly observe such incommensurate spin correlations in doped and spin-imbalanced Hubbard chains using fully spin- and density-resolved quantum gas microscopy. Doping is found to induce a linear change in the spin-density wavevector, in excellent agreement with predictions from Luttinger theory. For non-zero polarization we observe a reduction in the wavevector with magnetization, as expected from the antiferromagnetic Heisenberg model in a magnetic field. We trace the microscopic-scale origin of these incommensurate correlations to holes, doublons (double occupancies) and excess spins, which act as delocalized domain walls for the antiferromagnetic order. In addition, by inducing interchain coupling we observe fundamentally different spin correlations around doublons and suppression of incommensurate magnetism at finite (low) temperature in the two-dimensional regime(9). Our results demonstrate how access to the full counting statistics of all local degrees of freedom can be used to study fundamental phenomena in strongly correlated many-body physics.

Title:
Crystal structure of the high-temperature form of the trisulfide Cs2S3 and the (3+1)D modulated structure of the telluride K37Te28
Authors:
Stuble, P; Berroth, A; Wortelkamp, F; Rohr, C Author Full Names: Stueble, Pirmin; Berroth, Angela; Wortelkamp, Fritz; Roehr, Caroline
Source:
ZEITSCHRIFT FUR NATURFORSCHUNG SECTION B-A JOURNAL OF CHEMICAL SCIENCES, 74 (1):33-47; SI 10.1515/znb-2018-0168 JAN 2019
Abstract:
The high-temperature polymorph of the trisulfide Cs2S3, which has been synthesized from Cs2S2 and elemental sulfur, crystallizes in a new structure type (monoclinic, space group P2(1)/c, a = 999.97(4), b = 1029.30(5), c = 2642.07(12) pm, beta = 90.083(2)degrees, Z = 16, R1 = 0.0324). The structure contains four crystallographically independent angled S-3(2-) trisulfide ions with S-S distances of 205.7-208.3 pm. The distorted b.c.c. packing of the anions and their insertion in the five-membered rings of 3.5(3) + 3.5.3.5. (1:1) Cs nets are similarly found in the r.t. form (Cmc2(1), K2S3-type structure) and the two polymorphs differ mainly in the orientation of the S-3 groups. The second title compound, K37Te28, was synthesized from stoichiometric melts of the elements. It forms a complex (3 + 1)D modulated tetragonal structure (space group I4(1)/amd (00 sigma(3))s0s0, q=(0, 0, 0.5143), a = 1923.22(2), c = 2626.66(4) pm, Z = 4, R1(all) = 0.0837). According to K37Te28 = K-37[Te(1X)](8)[Te(2X)(2)](6)[Te(3X)(8)] the structure contains three different types of Te anions: The two crystallographically different isolated telluride anions [Te(1X)](2-) are coordinated by 9/10 K+ cations. Three [Te(2X)(2)](2-) dumbbells (d(Te-Te) = 277.9/286.4 pm) are arranged to 'hexamers'. The Te(31) and Te(32) atoms are located in columns of face-sharing K square antiprisms. Their z position modulation, which is accompanied by a smaller shift of the surrounding K+ cations, results in the decomposition of the [Te(3X)(8)](2) chain in a sequence vertical bar:Te-3-Te-2-Te-2-Te-3-Te-2-Te-2-Te-2:vertical bar of dumbbells Te-2(2-) (d(Te-Te) = 304 pm) and hypervalent linear trimers Te-3(4- )(d(Te-Te) = 325 pm).

Title:
A Yoffe-type moving crack in one-dimensional hexagonal piezoelectric quasicrystals
Authors:
Zhou, YB; Li, XF Author Full Names: Zhou, Y. -B.; Li, X. -F.
Source:
APPLIED MATHEMATICAL MODELLING, 65 148-163; 10.1016/j.apm.2018.08.005 JAN 2019
Abstract:
A Yoffe-type moving crack in one-dimensional hexagonal piezoelectric quasicrystals is considered. The Fourier transform technique is used to solve a moving crack problem under the action of antiplane shear and inplane electric field. Full elastic stresses of phonon and phason fields and electric fields are derived for a crack running with constant speed in the periodic plane. Obtained results show that the coupled elastic fields inside piezoelectric quasicrystals depend on the speed of crack propagation, and exhibit the usual square-root singularity at the moving crack tip. Electric field and phason stresses do not have singularity and electric displacement and phonon stresses have the inverse square-root singularity at the crack tip for a permeable crack. The field intensity factors and energy release rates are obtained in closed form. The crack velocity does not affect the field intensity factors, but alters the dynamic energy release rate. Bifurcation angle of a moving crack in a 1D hexagonal piezoelectric quasicrystal is evaluated from the viewpoint of energy balance. Obtained results are helpful to better understanding crack advance in piezoelectric quasicrystals. (C) 2018 Elsevier Inc. All rights reserved.

Title:
The origin of the polar symmetry in huebnerite-type multiferroics
Authors:
Park, SH; Behal, D; Pedersen, B Author Full Names: Park, So-Hyun; Behal, David; Pedersen, Bjoern
Source:
PHYSICA B-CONDENSED MATTER, 551 118-121; 10.1016/j.physb.2017.11.034 DEC 15 2018
Abstract:
The magnetic structure of the multiferroic phase AF2 of huebnerite (MnWO4) has been re-investigated based on the polar space group P2, instead of P2/c widely accepted in literature. The site character between two independent sites for Mn2+, Mn-a and Mn-b, fairly differs from each other in terms of bond valence sums. This hidden intrinsic dipole moment is the true origin of the chiral magnetic order in AF2 in the polar superspace group P2.1' (alpha, 1/2, gamma)0s. From structure refinements using single crystal neutron diffraction data at 10 K the ellipticity of the spin helix could be determined to be 0.92 and 0.77 at Mn-a and Mn-b, respectively. The different contributions of two chiral spin-textures to electric polarisation microscopically measurable in the b axis (P-b) could be estimated with P-b (Mn-a) = 22.8 mu Cm-2 and P-b (Mn-b) = 12.2 mu Cm-2.

Update: 9-Jan-2019


Title:
Lattice Modulation and Structural Phase Transition in the Antiferromagnet EuAl4
Authors:
Shimomura, S; Murao, H; Tsutsui, S; Nakao, H; Nakamura, A; Hedo, M; Nakama, T; Onuki, Y Author Full Names: Shimomura, Susumu; Murao, Hiroki; Tsutsui, Satoshi; Nakao, Hironori; Nakamura, Ai; Hedo, Masato; Nakama, Takao; Onuki, Yoshichika
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 88 (1):10.7566/JPSJ.88.014602 JAN 15 2019
Abstract:
X-ray diffraction measurements on the antiferromagnet EuAl4 using synchrotron radiation have revealed that satellite peaks characterized by an incommensurate wave vector (0, 0, zeta) with zeta approximate to 0.18 appear below 145.1 K, suggesting the formation of a charge density wave. The value of zeta shows an inflection at an antiferromagnetic transition temperature of 15.4K, and it changes discontinuously at lower antiferromagnetic transition temperatures of 12.2 and 10.0K. The antiferromagnetic transition at 12.2 K is accompanied by a structural transition from the modulated structure on a tetragonal lattice to that on a lattice with lower symmetry such as an orthorhombic one.

Title:
Unique Helical Magnetic Order and Field-Induced Phase in Trillium Lattice Antiferromagnet EuPtSi
Authors:
Kaneko, K; Frontzek, MD; Matsuda, M; Nakao, A; Munakata, K; Ohhara, T; Kakihana, M; Haga, Y; Hedo, M; Nakama, T; Onuki, Y Author Full Names: Kaneko, Koji; Frontzek, Matthias D.; Matsuda, Masaaki; Nakao, Akiko; Munakata, Koji; Ohhara, Takashi; Kakihana, Masashi; Haga, Yoshinori; Hedo, Masato; Nakama, Takao; Onuki, Yoshichika
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 88 (1):10.7566/JPSJ.88.013702 JAN 15 2019
Abstract:
Magnetic transition phenomena in cubic chiral antiferromagnet EuPtSi with T-N = 4.0 K were investigated by means of single crystal neutron diffraction. At 0.3 K in the ground state, magnetic peaks emerge at positions represented by an ordering vector q(1) = (0.2, 0.3, 0) and its cyclic permutation. Upon heating, an additional magnetic peak splitting with hysteresis was uncovered at around T-N* similar to 2.5 K, indicating the presence of a first-order commensurate incommensurate transition with q(1)* = (0.2, 0.3, delta) (delta(max) similar or equal to 0.04) at T-N*. A half-polarized neutron scattering experiment for polarization parallel to the scattering vector revealed that polarization antiparallel to the scattering vector has stronger intensity in both magnetic phases. This feature clarifies the single chiral character of the helical structure with moments lying perpendicular to the ordering vector in both ordered states. Under a vertical magnetic field of 1.2 T for B parallel to [1, 1, 1] at 1.9 K entering into the so-called A phase, magnetic peaks form characteristic hexagonal patterns in the equatorial scattering plane around nuclear peaks. An ordering vector q(A) similar or equal to (+/- 0.09, +/- 0.20, -/+ 0.28) of the A-phase has similar periodic length as q(1), and could be the hallmark of a formation of skyrmion lattice in EuPtSi.

Title:
Hyperuniformity and anti-hyperuniformity in one-dimensional substitution tilings
Authors:
Oguz, EC; Socolar, JES; Steinhardt, PJ; Torquato, S Author Full Names: Oguz, Erdal C.; Socolar, Joshua E. S.; Steinhardt, Paul J.; Torquato, Salvatore
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 75 3-13; 10.1107/S2053273318015528 1 JAN 2019
Abstract:
This work considers the scaling properties characterizing the hyperuniformity (or anti-hyperuniformity) of long-wavelength fluctuations in a broad class of one-dimensional substitution tilings. A simple argument is presented which predicts the exponent alpha governing the scaling of Fourier intensities at small wavenumbers, tilings with alpha > 0 being hyperuniform, and numerical computations confirm that the predictions are accurate for quasiperiodic tilings, tilings with singular continuous spectra and limit-periodic tilings. Quasiperiodic or singular continuous cases can be constructed with alpha arbitrarily close to any given value between -1 and 3. Limit-periodic tilings can be constructed with alpha between -1 and 1 or with Fourier intensities that approach zero faster than any power law.

Title:
k-eIsocoronal tilings
Authors:
Taganap, E; De Las Penas, MLA Author Full Names: Taganap, Eduard; Antonette De Las Penas, Ma. Louise
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 75 94-106; 10.1107/S2053273318013992 1 JAN 2019
Abstract:
In this article, a framework is presented that allows the systematic derivation of planar edge-to-edge k-isocoronal tilings from tile-s-transitive tilings, s <= k. A tiling T is k-isocoronal if its vertex coronae form k orbits or k transitivity classes under the action of its symmetry group. The vertex corona of a vertex x of T is used to refer to the tiles that are incident to x. The k-isocoronal tilings include the vertex-k-transitive tilings (k-isogonal) and k-uniform tilings. In a vertex-k-transitive tiling, the vertices form k transitivity classes under its symmetry group. If this tiling consists of regular polygons then it is k-uniform. This article also presents the classification of isocoronal tilings in the Euclidean plane.

Update: 4-Jan-2019


Title:
Spatially localized quasicrystalline structures
Authors:
Subramanian, P; Archer, AJ; Knobloch, E; Rucklidge, AM Author Full Names: Subramanian, P.; Archer, A. J.; Knobloch, E.; Rucklidge, A. M.
Source:
NEW JOURNAL OF PHYSICS, 20 10.1088/1367-2630/aaf3bd DEC 14 2018
Abstract:
Soft matter systems have been observed to self-assemble, over a range of system parameters, into quasicrystalline structures. The resulting quasicrystals (QCs) may minimize the free energy, and be in thermodynamic coexistence with the liquid state. At such state points, the likelihood of finding the presence of spatially localized states with quasicrystalline structure within the liquid is increased. Here we report the first examples of metastable spatially localized QCs of varying sizes in both two and three dimensions. Implications of these results for the nucleation of quasicrystalline structures are discussed. Our conclusions apply to a broad class of soft matter systems and more generally to continuum systems exhibiting quasipatterns.


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