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Perovskite-to-postperovskite transitions in NaNiF3 and NaCoF3 and disproportionation of NaCoF3 postperovskite under high pressure and high temperature.

Authors
  • Yusa, Hitoshi
  • Shirako, Yuichi
  • Akaogi, Masaki
  • Kojitani, Hiroshi
  • Hirao, Naohisa
  • Ohishi, Yasuo
  • Kikegawa, Takumi
Type
Published Article
Journal
Inorganic Chemistry
Publisher
American Chemical Society (ACS)
Publication Date
Jun 18, 2012
Volume
51
Issue
12
Pages
6559–6566
Identifiers
DOI: 10.1021/ic300118d
PMID: 22656193
Source
Medline
License
Unknown

Abstract

High-pressure structural phase transitions in NaNiF(3) and NaCoF(3) were investigated by conducting in situ synchrotron powder X-ray diffraction experiments using a diamond anvil cell. The perovskite phases (GdFeO(3) type) started to transform into postperovskite phases (CaIrO(3) type) at about 11-14 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 NaCoF(3) 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 NaCoF(3). Elemental analysis of the recovered amorphous samples indicated that the NaCoF(3) postperovskite disproportionated into two phases. This kind of disproportionation was not evident in NaNiF(3) even after laser heating at 54 GPa. In contrast to the single postpostperovskite phase reported in NaMgF(3), such a postpostperovskite phase was not found in the present compounds.

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