Browsing by Author "Spencer, JR"

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    Corrigendum to “Synthesis, structures, and phase transitions of barium bismuth iridium oxide perovskites Ba2BiIrO6 and Ba3BiIr2O9” [J. Solid State Chem. 183 (2010) 727–735]
    (Elsevier, 2010-11-01) Ling, CD; Kennedy, BJ; Zhou, Q; Spencer, JR; Avdeev, M
    The authors wish to draw the reader’s attention to an unfortunate series of typographical errors in this article. The space group of Ba2BiIrO6 at room temperature was incorrectly referred to throughout the text as R3 , The correct space group is R3c . which was used for all the Rietveld-refinements and to generate all the relevant tables and figures. © 2010 Elsevier Inc.
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    Structures and crystal chemistry of the double perovskites Ba(2)LnB'O6 (Ln = lanthanide B'=Nb5+ and Ta5+), Part I - investigation of Ba(2)LnTaO(6) using synchrotron x-ray and neutron powder diffraction
    (Elsevier, 2007-11) Saines, PJ; Spencer, JR; Kennedy, BJ; Avdeev, M
    The structure of 14 compounds in the series Ba(2)LnTaO(6) have been examined using synchrotron X-ray diffraction and found to undergo a sequence of phase transitions from I2/m monoclinic to I4/m tetragonal to Fm (3) over barm cubic symmetry with decreasing ionic radii of the lanthanides. Ba2LaTaO6 is an exception to this with variable temperature neutron diffraction being used to establish that the full series of phases adopted over the range of 15-500 K is P2(1)/n monoclinic to I2/m monoclinic to R (3) over bar rhombohedral. The chemical environments of these compounds have also been investigated and the overbonding to the lanthanide cations is due to the unusually large size for the B-site in these perovskites. © 2007, Elsevier Ltd.
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    Synthesis, structures, and phase transitions of barium bismuth iridium oxide perovskites Ba2BiIrO6 and Ba3BiIr2O9
    (Elsevier, 2010-03) Ling, CD; Kennedy, BJ; Zhou, QD; Spencer, JR; Avdeev, M
    The Ba-Bi-Ir-O system is found to contain two distinct perovskite-type phases a rock-salt ordered double perovskite Ba2BiIrO6, and a 6H-type hexagonal perovskite Ba3BiIr2O9 Ba2BiIrO6 undergoes a series of symmetry-lowering phase transitions on cooling Fm (3) over barm -> R (3) over barc -> 12/m(C2/m)->/(1) over bar (P (1) over bar), all of which are second order except the rhombohedral monoclinic one, which is first order The monoclinic phase is only observed in a 2-phase rhombohedral+monoclinic regime. The transition and 2-phase region lie very close to 300K, making the room-temperature X-ray diffraction patterns extremely complex and potentially explaining why Ba2BiIrO6 had not previously been identified and reported A solid solution Ba2Bi1+xIr1-xO6, analogous to Ba2Bi1+xRu1-xO6, 0 <= x <= 2/3, was not observed The 6H-type phase Ba3BiIr2O9 undergoes a clean second-order phase transition P6(3)/mmc -> C2/c at 750K, unlike 6H-type Ba3LaIr2O9, the P6(3)/mmc structure of which is highly strained below similar to 750K but fails to distort coherently to the monoclinic phase. © 2010, Elsevier Ltd.