title: Postperovskite phase transition of ZnGeO3: comparative crystal chemistry of postperovskite phase transition from germanate perovskites.
abstract: The postperovskite phase of ZnGeO3 was confirmed by laser heating experiments of the perovskite phase under 110-130 GPa at high temperature. Ab initio calculations indicated that the phase transition occurs at 133 GPa at 0 K. This postperovskite transition pressure is significantly higher than those reported for other germanates, such as MnGeO3 and MgGeO3. The comparative crystal chemistry of the perovskite-to-postperovskite transition suggests that a relatively elongated b-axis in the low-pressure range resulted in the delay in the transition to the postperovskite phase. Similar to most GdFeO3-type perovskites that transform to the CaIrO3-type postperovskite phase, ZnGeO3 perovskite eventually transformed to the CaIrO3-type postperovskite phase at a critical rotational angle of the GeO6 octahedron. The formation of the postperovskite structure at a very low critical rotational angle for MnGeO3 suggests that relatively large divalent cations likely break down the corner-sharing GeO6 frameworks without a large rotation of GeO6 to form the postperovskite phase.
authors.affiliation: National Institute for Materials Science (NIMS) , 1-1, Namiki, Tsukuba, Ibaraki 305-0044, Japan.
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Yusa
authors.forename: Taku
authors.initials: T
authors.lastname: Tsuchiya
authors.forename: Masaki
authors.initials: M
authors.lastname: Akaogi
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Kojitani
authors.forename: Daisuke
authors.initials: D
authors.lastname: Yamazaki
authors.forename: Naohisa
authors.initials: N
authors.lastname: Hirao
authors.forename: Yasuo
authors.initials: Y
authors.lastname: Ohishi
authors.forename: Takumi
authors.initials: T
authors.lastname: Kikegawa