Perovskite-to-Postperovskite Transitions in NaNiF3 and NaCoF3 and Disproportionation of NaCoF3 Postperovskite under High Pressure and High Temperature

详细信息    查看全文

• 作者：Hitoshi Yusa ; Yuichi Shirako ; Masaki Akaogi ; Hiroshi Kojitani ; Naohisa Hirao ; Yasuo Ohishi ; Takumi Kikegawa
• 刊名：Inorganic Chemistry
• 出版年：2012
• 出版时间：June 18, 2012
• 年：2012
• 卷：51
• 期：12
• 页码：6559-6566
• 全文大小：400K
• 年卷期：v.51,no.12(June 18, 2012)
• ISSN：1520-510X

文摘

High-pressure structural phase transitions in NaNiF₃ and NaCoF₃ were investigated by conducting in situ synchrotron powder X-ray diffraction experiments using a diamond anvil cell. The perovskite phases (GdFeO₃ type) started to transform into postperovskite phases (CaIrO₃ type) at about 11鈥?4 GPa, even at room temperature. The transition pressure is much lower than those of oxide perovskites. The anisotropic compression behavior led to heavily tilted octahedra that triggered the transition. Unlike oxide postperovskites, fluoropostperovskites remained after decompression to 1 atm. The postperovskite phase in NaCoF₃ broke down into a mixture of unknown phases after laser heating above 26 GPa, and the phases changed into amorphous ones when the pressure was released. High-pressure and high-temperature experiments using a multianvil apparatus were also conducted to elucidate the phase relations in NaCoF₃. Elemental analysis of the recovered amorphous samples indicated that the NaCoF₃ postperovskite disproportionated into two phases. This kind of disproportionation was not evident in NaNiF₃ even after laser heating at 54 GPa. In contrast to the single postpostperovskite phase reported in NaMgF₃, such a postpostperovskite phase was not found in the present compounds.