High-pressure transformations of ilmenite to perovskite, and lithium niobate to perovskite in zinc germanate |
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| Authors: | Hitoshi Yusa Masaki Akaogi Nagayoshi Sata Hiroshi Kojitani Ryo Yamamoto Yasuo Ohishi |
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| Institution: | (1) Advanced Materials Laboratory, National Institute for Materials Science, 1-1 Namiki, Tsukuba, 305-0044 Ibaraki, Japan;(2) Department of Chemistry, Gakushuin University, 1-5-1 Mejiro, Toshima-ku, 171-8588 Tokyo, Japan;(3) Institute for Research on Earth Evolution, Japan Agency for Marine-Earth Science and Technology, 2–15, Natsushima-cho, Yokosuka, 237–0061 Kanagawa, Japan;(4) Japan Synchrotron Radiation Research Institute, 1–1-1 Kouto, Mikazuki-cho, Sayo-gun, 679–5198 Hyogo, Japan |
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| Abstract: | In-situ X-ray powder diffraction measurements conducted under high pressure confirmed the existence of an unquenchable orthorhombic perovskite in ZnGeO3. ZnGeO3 ilmenite transformed into perovskite at 30.0 GPa and 1300±150 K in a laser-heated diamond anvil cell. After releasing the pressure, the lithium niobate phase was recovered as a quenched product. The perovskite was also obtained by recompression of the lithium niobate phase at room temperature under a lower pressure than the equilibrium phase boundary of the ilmenite–perovskite transition. Bulk moduli of ilmenite, lithium niobate, and perovskite phases were calculated on the basis of the refined X-ray diffraction data. The structural relations among these phases are considered in terms of the rotation of GeO6 octahedra. A slight rotation of the octahedra plays an important role for the transition from lithium niobate to perovskite at ambient temperature. On the other hand, high temperature is needed to rearrange GeO6 octahedra in the ilmenite–perovskite transition. The correlation of quenchability with rotation angle of GeO6 octahedra for other germanate perovskites is also discussed. |
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| Keywords: | Perovskite Lithium niobate Ilmenite X-ray diffraction High-pressure phase transition |
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