Browsing by Author "Yamaura, K"

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    A layered wide-gap oxyhalide semiconductor with an infinite ZnO2 square planar sheet: Sr2ZnO2Cl2
    (Royal Society of Chemistry, 2017-03-13) Su, Y; Tsujimoto, Y; Miura, A; Asai, S; Avdeev, M; Ogino, H; Ako, M; Belik, AA; Masuda, T; Uchikoshi, T; Yamaura, K
    A new square-planar zinc oxyhalide, Sr2ZnO2Cl2, was successfully synthesized using a high-pressure method. Absorption spectroscopy revealed an indirect band gap of 3.66 eV. Electronic structure calculations indicated a strong hybridization between Zn 3dx2−y2 and O 2p orbitals, which is distinct from tetrahedrally coordinated ZnO. © Royal Society of Chemistry 2021
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    Magnetic and structural studies of Sc containing ruthenate double perovskites A2ScRuO6 (A = Ba, Sr)
    (American Chemical Society, 2017-07-10) Kayser, P; Injac, S; Ranjbar, B; Kennedy, BJ; Avdeev, M; Yamaura, K
    Ruthenium-containing double perovskites A2ScRuO6 have been synthesized as polycrystalline powders and structurally characterized using a combination of synchrotron X-ray and neutron powder diffraction methods. When A = Ba, a hexagonal 6L perovskite structure is obtained if the synthesis is conducted at ambient pressure and a rock-salt ordered cubic structure is obtained if the sample is quenched from high pressures. The Sr oxide Sr2ScRuO6 is obtained with a rock-salt ordered corner sharing topology. Heat capacity and bulk magnetic susceptibility measurements show that the three oxides are antiferromagnets. Cubic Ba2ScRuO6 undergoes a metal–insulator transition near 270 K and hexagonal Ba2ScRuO6 is a semiconductor with an activation energy of 0.207 eV. The magnetic structures of the two rock-salt ordered double perovskites were established using powder neutron diffraction and are described by k = (0,0,1) and k = (0,0,0) for the Ba and Sr oxides, respectively, corresponding to type I antiferromagnetic structures, with ferromagnetic layers stacked antiferromagnetically. The ambient-pressure hexagonal polymorph of Ba2ScRuO6 has partial Sc-Ru ordering at both the face-sharing B2O9 dimer and corner-sharing BO6 sites. The magnetic structure is described by k = (1/2,0,0) with the basis vector belonging to the irreducible representation Γ3. © 2017 American Chemical Society
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    Phase transitions in strontium perovskites. Studies of SrOsO3 compared to other 4d and 5d perovksites
    (Elsevier, 2016-05-01) Kennedy, BJ; Avdeev, M; Feng, HL; Yamaura, K
    The structure of a polycrystalline sample of SrOsO3 has been investigated using powder neutron diffraction from 5 to 300K, and powder synchrotron X-ray diffraction from 80 to 870K. At low temperatures SrOsO3 is orthorhombic in Pbnm and heating results in a sequence of phase transition transitions Pbnm→Imma→I4/mcm→Pm3̅m. This behavior is compared to that of other Sr containing perovskites. Comparison of the transition temperatures in SrBO3 perovskites shows that the tolerance factor alone does not determine the temperature at which the cubic phase is stabilized but rather the electronic configuration of the B-site cation appears to be significant. © 2016 Elsevier Inc.