Browsing by Author "Moriyoshi, C"

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    Ground state of (Pb0.94Sr0.06)(Zr0.530Ti0.470)O3 in the morphotropic phase boundary region: evidence for a monoclinic Cc space group
    (American Physical Society, 2011-10-24) Solanki, RS; Singh, AK; Mishra, SK; Kennedy, SJ; Suzuki, T; Kuroiwa, Y; Moriyoshi, C; Pandey, D
    The antiferrodistortive (AFD) phase transition for a pseudotetragonal composition of Pb(Zr(0.530)Ti(0.470))O(3) doped with 6% Sr has been investigated using sound velocity (4-320 K), high-resolution synchrotron x-ray powder diffraction (100-800 K), and high-resolution as well as high-flux neutron powder diffraction measurements (4 K) to settle the existing controversies about the true ground state of Pb(Zr(x)Ti(1-x))O(3) (PZT) in the morphotropic phase boundary (MPB) region. The multiplet character of the neutron diffraction profiles of (3/2 1/2 1/2)(pc) (pseudocubic or pc indices) and (3/2 3/2 1/2)(pc) superlattice peaks, appearing below the AFD transition temperature, rules out the rhombohedral R3c space group. The true ground state is confirmed to be monoclinic in the Cc space group, in agreement with the predictions of the first-principles calculations and earlier findings for pure PZT in the MPB region. Here, 6% Sr(2+) substitution and the use of high-wavelength (lambda = 2.44 angstrom) neutrons have played a key role in settling the existing controversies about the true ground state of PZT in the MPB region. © 2011, American Physical Society
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    Hydrothermal synthesis, crystal structure, and superconductivity of a double-perovskite Bi oxide
    (American Chemical Society, 2015-12-23) Rubel, MHK; Takei, T; Kumada, N; Ali, MM; Miura, A; Tadanaga, K; Oka, K; Azuma, M; Yashima, M; Fujii, K; Magome, E; Moriyoshi, C; Kuroiwa, Y; Hester, JR; Avdeev, M
    Double-perovskite Bi oxides are a new series of superconducting materials, and their crystal structure and superconducting properties are under investigation. In this paper, we describe the synthesis and characterization of a new double-perovskite material that has an increased superconductive transition temperature of 31.5 K. The structure of the material was examined using powder neutron diffraction (ND), synchrotron X-ray diffraction (SXRD), and transmission electron microscopy (TEM). Rietveld refinement of the sample based on ND and SXRD data confirmed an A-site-ordered (K1.00)(Ba1.00)3(Bi0.89Na0.11)4O12 double-perovskite-type structure with the space group Im3̅m (No. 229). This structural analysis revealed the incorporation of Na with Bi in the structure and a bent bond between (Na, Bi)–O–(Na, Bi). TEM analyses also confirmed a cubic double-perovskite structure. This hydrothermally synthesized compound exhibited a large shielding volume fraction, exceeding 100%, with onset of superconductivity at ∼31.5 K. Its electrical resistivity dropped near onset at ∼28 K, and zero resistivity was confirmed below 13 K. The calculated band structure revealed that the metallicity of the compound and the flatness of the conduction bands near the Fermi level (EF) are important for the appearance of superconductivity. © 2015 American Chemical Society