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J Kreisel - One of the best experts on this subject based on the ideXlab platform.

  • random local strain effects in homovalent substituted relaxor ferroelectrics a first principles study of bati0 74zr0 26o3
    Physical Review B, 2010
    Co-Authors: Claire Laulhe, A Pasturel, F Hippert, J Kreisel
    Abstract:

    We present first-principles superCell calculations on BaTi0.74Zr0.26O3, a prototype material for relaxors with a homovalent substitution. From a statistical analysis of relaxed structures, we give evidence for four types of Ti-atom polar displacements: along the , , or directions of the Cubic Unit Cell, or almost canCelled. The type of a Ti displacement is entirely determined by the Ti/Zr distribution in the adjacent Unit Cells. The underlying mechanism involves local strain effects that ensue from the difference in size between the Ti4+ and Zr4+ cations. These results shed light on the structural mechanisms that lead to disordered Ti displacements in BaTi(1-x)Zr(x)O3 relaxors, and probably in other BaTiO3-based relaxors with homovalent substitution.

J L Cohn - One of the best experts on this subject based on the ideXlab platform.

  • temperature dependent structural and transport properties of the type ii clathrates a8na16e136 a cs or rb and e ge or si
    Journal of Applied Physics, 2002
    Co-Authors: George S Nolas, Don Vanderveer, Angus P Wilkinson, J L Cohn
    Abstract:

    Variable temperature single-crystal structure analyses for Cs8Na16Si136, Rb8Na16Si136, Cs8Na16Ge136, and Rb8Na16Ge136 are reported along with electrical and thermal transport measurements on two polycrystalline specimens. The strong temperature dependence of the atomic displacement parameters for the alkali-metal atoms is indicative of significant disorder associated with the “rattling” alkali-metal atoms inside the two different polyhedra (sixteen dodecahedra and eight hexakaidecahedra per Cubic Unit Cell) that makeup the type II clathrate hydrate framework. This disorder can lead to low lattice thermal conductivities. Transport measurements show these compounds to be metallic. The potential of type II clathrates for thermoelectric applications is discussed.

Shirane - One of the best experts on this subject based on the ideXlab platform.

  • Anomalous phase in the relaxor ferroelectric Pb ( Zn 1/3 Nb 2/3 ) O 3
    Physical Review B, 2004
    Co-Authors: Z. Zhong, Y.-h. Bing, Chris Stock, Shirane
    Abstract:

    X-ray diffraction studies on a Pb(Zn$_{1/3}$Nb$_{2/3}$)O$_3$ (PZN) single crystal sample show the presence of two different structures. An outer-layer exists in the outer most $\sim$ 10 to 50~$\mu$m of the crystal, and undergoes a structural phase transition at the Curie temperature $T_C\approx410$ K. The inside phase is however, very different. The lattice inside the crystal maintains a Cubic Unit Cell, while ferroelectric polarization develops below $T_C$. The lattice parameter of the Cubic Unit Cell remains virtually a constant, i.e., much less variations compared to that of a typical relaxor ferroelectric, in a wide temperature range of 15 K to 750 K. On the other hand, broadening of Bragg peaks and change of Bragg profile line-shapes in both longitudinal and transverse directions at $T_C$ clearly indicate a structural phase transition occurring.

Claire Laulhe - One of the best experts on this subject based on the ideXlab platform.

  • random local strain effects in homovalent substituted relaxor ferroelectrics a first principles study of bati0 74zr0 26o3
    Physical Review B, 2010
    Co-Authors: Claire Laulhe, A Pasturel, F Hippert, J Kreisel
    Abstract:

    We present first-principles superCell calculations on BaTi0.74Zr0.26O3, a prototype material for relaxors with a homovalent substitution. From a statistical analysis of relaxed structures, we give evidence for four types of Ti-atom polar displacements: along the , , or directions of the Cubic Unit Cell, or almost canCelled. The type of a Ti displacement is entirely determined by the Ti/Zr distribution in the adjacent Unit Cells. The underlying mechanism involves local strain effects that ensue from the difference in size between the Ti4+ and Zr4+ cations. These results shed light on the structural mechanisms that lead to disordered Ti displacements in BaTi(1-x)Zr(x)O3 relaxors, and probably in other BaTiO3-based relaxors with homovalent substitution.

Robert Joseph Cava - One of the best experts on this subject based on the ideXlab platform.

  • Superconductivity in noncentrosymmetric Mg10Ir19B16
    Physical Review B, 2006
    Co-Authors: Tomasz Klimczuk, Emilia Morosan, Joe D. Thompson, H. W. Zandbergen, Robert Joseph Cava
    Abstract:

    Mg10Ir19B16, a previously unreported compound in the Mg-Ir-B chemical system, is found to be superconducting at temperatures near 5 K. The fact that the compound exhibits a range of superconducting temperatures between 4 and 5 K suggests that a range of stoichiometries is allowed, though no structural evidence for this is observed. The compound has a large, noncentrosymmetric, body centered Cubic Unit Cell with a=10.568 A, displaying a structure type for which no previous superconductors have been reported.