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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