B1-to-B2 Structural Transitions in Rock Salt Intergrowth Structures

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• 作者：Takafumi Yamamoto ; Yoji Kobayashi ; Taku Okada ; Takehiko Yagi ; Takateru Kawakami ; C茅dric Tassel ; Shota Kawasaki ; Naoyuki Abe ; Ken Niwa ; Takumi Kikegawa ; Naohisa Hirao ; Mikio Takano ; Hiroshi Kageyama
• 刊名：Inorganic Chemistry
• 出版年：2011
• 出版时间：November 21, 2011
• 年：2011
• 卷：50
• 期：22
• 页码：11787-11794
• 全文大小：455K
• 年卷期：v.50,no.22(November 21, 2011)
• ISSN：1520-510X

文摘

The rock salt (B1) structure of binary oxides or chalcogenides transforms to the CsCl (B2) structure under high pressure, with critical pressures P_s depending on the cation to anion size ratio (R_c/R_a). We investigated structural changes of A₂MO₃ (A = Sr, Ca; M = Cu, Pd) comprising alternate 7-fold B1 AO blocks and corner-shared MO₂ square-planar chains under pressure. All of the examined compounds exhibit a structural transition at P_s = 29鈥?1 GPa involving a change in the A-site geometry to an 8-fold B2 coordination. This observation demonstrates, together with the high pressure study on the structurally related Sr₃Fe₂O₅, that the B1-to-B2 transition generally occurs in these intergrowth structures. An empirical relation of P_s and the R_c/R_a ratio for the binary system holds well for the intergrowth structure also, which means that P_s is predominantly determined by the rock salt blocks. However, a large deviation from the relation is found in LaSrNiO_3.4, where oxygen atoms partially occupy the apical site of the MO₄ square plane. We predict furthermore the occurrence of the same structural transition for Ruddlesden鈥揚opper-type layered perovskite oxides (AO)(AMO₃)_n, under higher pressures. For investigating the effect on the physical properties, an electrical resistivity of Sr₂CuO₃ is studied.