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Equation of state of the high-pressure polymorph of FeSi to 67 GPa

¹ Institute for Research on Earth Evolution, Japan Agency for Marine-Earth Science and Technology, 2–15 Natsushima-cho, Yokosuka-shi, Kanagawa 237–0061, Japan
² High Energy Acceleration Research Organization, 1–1 Oho, Tsukuba, Ibaraki 305–0801, Japan
³ Japan Synchrotron Radiation Research Institute, 1–1-1, Kouto, Sayo-cho, Sayo-gun, Hyogo 679–5198, Japan

^* Corresponding author, e-mail: shigeaki.ono{at}ucl.ac.uk

The compressibility of high-pressure phase FeSi was investigated by in situ high-pressure X-ray powder diffraction. Pressure up to 67 GPa was generated using the diamond anvil cell technique. FeSi transformed to a B2-type structure during laser heating, and remained stable up to the maximum pressure. This first-order phase transformation showed a volume reduction of 4 % at 25 GPa. The fit of a Birch-Murnaghan equation-of-state to the pressure-volume data resulted in V₀ = 21.32 (3) ų and K₀ = 225 (2) GPa when K₀’ was fixed at 4. Our results are in good agreement with those of previous numerical studies using a GGA method employing ab initio calculations. This indicates that a small amount of B2-type FeSi phase may contribute to the decrease in seismic velocity at the base of the lower mantle.

Key-words: compressibility measurement: FeSi, phase transition, high pressure phase: iron silicide, diamond anvil cell.