ChemInform Abstract: Synthesis, Structures, and Phase Transitions of Barium Bismuth Iridium Oxide Perovskites Ba2BiIrO6 and Ba3BiIr2O9

Autor: Brendan J. Kennedy, Chris D. Ling, Jarrah R. Spencer, Maxim Avdeev, Qingdi Zhou
Rok vydání: 2010
Předmět:
Zdroj: ChemInform. 41
ISSN: 1522-2667
0931-7597
DOI: 10.1002/chin.201024012
Popis: The Ba–Bi–Ir–O system is found to contain two distinct perovskite-type phases: a rock-salt ordered double perovskite Ba 2 BiIrO 6 ; and a 6H-type hexagonal perovskite Ba 3 BiIr 2 O 9 . Ba 2 BiIrO 6 undergoes a series of symmetry-lowering phase transitions on cooling Fm 3 ¯ m → R 3 ¯ c → 12 / m ( C 2 / m ) → I 1 ¯ ( P 1 ¯ ) , 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 300 K, making the room-temperature X-ray diffraction patterns extremely complex and potentially explaining why Ba 2 BiIrO 6 had not previously been identified and reported. A solid solution Ba 2 Bi 1+ x Ir 1− x O 6 , analogous to Ba 2 Bi 1+ x Ru 1− x O 6 , 0≤ x ≤2/3, was not observed. The 6H-type phase Ba 3 BiIr 2 O 9 undergoes a clean second-order phase transition P 6 3 / mmc → C 2/ c at 750 K, unlike 6H-type Ba 3 LaIr 2 O 9 , the P 6 3 / mmc structure of which is highly strained below ∼ 750 K but fails to distort coherently to the monoclinic phase.
Databáze: OpenAIRE
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