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Letter |
1 Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Ookayama, Meguro, Tokyo 152-8551, Japan
2 Japan Synchrotron Radiation Research Institute, Mikazuki-cho, Sayo-gun, Hyogo 679-5198, Japan
3 Institute for Research on Earth Evolution, Japan Agency for Marine-Earth Science and Technology, Natsushima-cho, Yokosuka, Kanagawa 237-0061, Japan
Correspondence: * E-mail: kei{at}geo.titech.ac.jp
A phase transition of MgGeO3 perovskite was examined at high-pressure and -temperature using synchrotron X-ray diffraction measurements. The results demonstrate that it transforms to a CaIrO3-type post-perovskite phase above 63 GPa at 1800 K. The density increase is 1.5% at the transition pressure. These observations confirm that MgGeO3 is a low-pressure analogue to MgSiO3, for which a similar phase transition was recently found above 125 GPa and 2500 K. The unit-cell parameters of MgGeO3 post-perovskite phase obtained at 300 K during decompression from 79 to 6 GPa show that the b-axis is significantly more compressible than are the a- and c-axes, which could be due to the GeO6-octahedral sheet stacking structure along b. The bulk modulus was determined to be K0 = 192(±5) GPa with a fixed pressure derivative of the bulk modulus, K', of 4.
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