Synthesis, structures, and phase transitions of barium bismuth iridium oxide perovskites Ba2BiIrO6 and Ba3BiIr2O9
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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.
Perovskite, X-ray diffraction, Iridium oxides, Phase transformations, Synchrotrons, Neutron diffraction
Ling, C. D., Kennedy, B. J., Zhou, Q. D., Spencer, J. R., & Avdeev, M. (2010). Synthesis, structures, and phase transitions of barium bismuth iridium oxide perovskites Ba2BiIrO6 and Ba3BiIr2O9. Journal of Solid State Chemistry, 183(3), 727-735. doi:10.1016/j.jssc.2010.01.017