HR: 1340h
AN: MR23A-0183    [Abstracts]
TI: Stability of Post-Perovskite Phase in Analogue Materials to MgSiO$_{3}$
AU: * Tateno, S
EM: stateno@geo.titech.ac.jp
AF: Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Ookayama,Meguro, Tokyo, 152-8551 Japan
AU: Hirose, K
EM: Kei@geo.titech.ac.jp
AF: Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Ookayama,Meguro, Tokyo, 152-8551 Japan
AU: Sata, N
EM: sata@jamstec.go.jp
AF: Institute for Frontier Research on Earth Evolution, Japan Agency for Marine-Earth Science and Technology, Natsushima-cho, Yokosuka, Kanagawa, 237-0061 Japan
AU: Ohishi, Y
EM: ohishi@spring8.or.jp
AF: Japan Synchrotron Radiation Research Institute, Mikazuki-cho, Sayo-gun, Hyogo, 679-5198 Japan
AB: Recent high-pressure experiments by Murakami et al. (2004) showed a novel phase transition from perovskite to a CaIrO$_{3}$-type post-perovskite phase (space group: {\it Cmcm}) in MgSiO$_{3}$ above 125 GPa and 2500 K. It is well known that a wide range of chemical compositions has perovskite structure at high pressures. In order to know the chemical variation that adopts CaIrO$_{3}$-type post-perovskite structure, we examined the phase transition of perovskite structure in germinates (MgGeO$_{3}$, MnGeO$_{3}$ and CdGeO$_{3}$) and titanates (MnTiO$_{3}$ and CdTiO$_{3}$) with increasing pressure at high temperature. Experiments were made at BL10XU of SPring-8 by a combination of laser-heated diamond-anvil cell (LHDAC) techniques and synchrotron X-ray diffraction measurements. Results demonstrate that both MnGeO$_{3}$ and MgGeO$_{3}$ perovskites undergo phase transition to the CaIrO$_{3}$-type post-perovskite structure similarly to the MgSiO$_{3}$ perovskite. The transition pressures are 58 GPa and 63 GPa at 1600 K, respectively, that are much lower than that in MgSiO$_{3}$. The molar volumes of these post-perovskite phases are smaller by 1.5 % than those of perovskite at equivalent pressure. In contrast, structure of CdGeO$_{3}$ perovskite becomes less distorted from ideal cubic structure with increasing pressure, and perovskite phase is stable at least to 110 GPa at 2000 K. Post-perovskite phase transition is, therefore, unlikely to occur in CdGeO$_{3}$ with further compression. Perovskite phase is stable also in MnTiO$_{3}$ and CdTiO$_{3}$ up to 50 GPa at 1700 K and 70 GPa at 2500 K, respectively. However, the structural distortion of both MnTiO$_{3}$ and CdTiO$_{3}$ perovskite increases with pressure. This observation suggests that post-perovskite phase transition may occur in both the compositions at higher pressures.
DE: 3620 Crystal chemistry
DE: 3630 Experimental mineralogy and petrology
DE: 3924 High-pressure behavior
DE: 3954 X ray, neutron, and electron spectroscopy and diffraction
DE: 1213 Earth's interior--dynamics (8115, 8120)
SC: Mineral and Rock Physics [MR]
MN: 2004 AGU Fall Meeting