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Unquenchable hexagonal perovskite in high-pressure polymorphs of strontium silicates

¹ Advanced Materials Laboratory, National Institute for Materials Science, 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan
² Department of Chemistry, Gakushuin University, 1-5-1 Mejiro, Toshima-ku, Tokyo 171-8588, Japan
³ Institute for Research on Earth Evolution, Japan Agency for Marine-Earth Science and Technology, 2-15, Natsushima-cho, Yokosuka, Kanagawa 237-0061, Japan
⁴ Japan Synchrotron Radiation Research Institute, 1-1-1 Kouto, Mikazuki-cho, Sayo-gun, Hyogo 679-5198, Japan

Correspondence: ^* E-mail: yusa.hitoshi{at}nims.go.jp

The presence of hexagonal silicate perovskite (6H-BaTiO₃ type) was confirmed in the SrSiO₃ compound by in-situ angle dispersive X-ray diffraction at high pressure. The perovskite was crystallized from pressure-induced amorphous SrSiO₃ in a diamond anvil cell by laser heating at 35 GPa. On releasing the pressure, the perovskite also changed into an amorphous state as does CaSiO₃ perovskite. This SrSiO₃ perovskite, with a tolerance factor greater than unity, forms a face-sharing SiO₆ octahedron, which leads to a structure with hexagonal symmetry. Incorporation of Sr into CaSiO₃ perovskite in the early stage of the differentiation in the Earth’s mantle might have influenced the symmetry of CaSiO₃ perovskite in the present lower mantle. As far as we know, this is the first report suggesting the existence of hexagonal perovskite in silicates.

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