Browsing by Author "Miyake, M"

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    Crystal structures and phase transition in (Sr0.8Ce0.2)(Mn(1-y)Coy)O-3 (y=0 and 0.2): the influence of Jahn-Teller distortion
    (Institute of Physics, 2009-03-25) Zhang, Z; Howard, CJ; Kennedy, BJ; Matsuda, M; Miyake, M
    We have studied the crystal structures of (Sr0.8Ce0.2)(Mn1-yCoy)O-3 (y = 0 and 0.2) using neutron diffraction. Both (Sr0.8Ce0.2)MnO3 and (Sr0.8Ce0.2)(Mn0.8Co0.2)O-3 have a tetragonal structure in space group I4/mcm at room temperature, and the octahedral tilt angle around the c-axis is nearly the same. The only significant difference is the shape of the Mn(Co)O-6 octahedron: it is elongated in (Sr0.8Ce0.2)MnO3 due to the cooperative Jahn-Teller (JT) effect, but essentially regular in (Sr0.8Ce0.2)(Mn0.8Co0.2) O3 due to the absence of JT-active Mn3+ ions. With increasing temperature, both compounds undergo a continuous phase transition at around 400°C to a cubic structure in Pm (3) over barm, with no indication of a distinct transition in (Sr0.8Ce0.2) MnO3 from the removal of the static JT distortion. In addition, the temperature dependence of the octahedral tilt angle is very similar in the two samples, implying that the JT distortion has minimal effect on the octahedral tilting and the phase transition to cubic. X-ray absorption near-edge structure (XANES) analysis indicates that the Ce oxidation state is predominantly 4+ in both samples. The electrical conductivity is higher in (Sr0.8Ce0.2)MnO3 than in (Sr0.8Ce0.2)(Mn0.8Co0.2)O-3 in the temperature range studied (100-900°C). © 2009, Institute of Physics
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    Structural and electronic phase transitions in Sr1-xCexMnO3 perovskites
    (Elsevier, 2008-10-01) Kennedy, BJ; Saines, PJ; Zhou, QD; Zhang, Z; Matsuda, M; Miyake, M
    The structures of eight members of the series Sr1-xCexMnO3 with 0.075≤x≤0.4 have been established using synchrotron X-ray powder diffraction. Unusual peak broadening due to domainwall scattering is observed near the composition-induced first-order cubic–tetragonal transition. The temperature dependence of the structures for three examples x = 0.1, 0.2 and 0.35 is described. For the x = 0.1 and 0.35 samples evidence for a first-order loss of the orbital ordering associated with a cooperative Jahn–Teller distortion is presented. The onset of the orbitally disordered state is accompanied by a discontinuous reduction in cell volume. © 2008, Elsevier Ltd.
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    Structural characterisation of the perovskite series Sr0.9-xCaxCe0.1MnO3: influence of the Jahn-Teller effect
    (Elsevier, 2009-04) Kennedy, BJ; Ting, J; Zhou, QD; Zhang, Z; Matsuda, M; Miyake, M
    Fifteen perovskite-type compounds Sr0.9−xCaxCe0.1MnO3, x=0–0.9 in steps as fine as 0.05, have been synthesised by solid state methods, and the room temperature structures characterised using X-ray synchrotron powder diffraction. At low Ca contents (x≤0.45) the structures are tetragonal in space group I4/mcm and at high Ca contents (x≥0.55) the compounds are orthorhombic in space group Pbnm. At room temperature these two phases co-exist in the compound with x=0.5. XANES measurements show the Ce to be present as Ce4+ in all the oxides. High temperature structures are reported for selected members. © 2009, Elsevier Ltd.