Equations of state of α-SiC (6H) and βʹ-Mg₂Si₁.₁ from single-crystal X-ray diffraction data and novel high-pressure magnesium silicide Mg₂Si₇

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Koemets, Iuliia ; Ishii, Takayuki ; Hanfland, Michael ; Dubrovinsky, Leonid:
Equations of state of α-SiC (6H) and βʹ-Mg₂Si₁.₁ from single-crystal X-ray diffraction data and novel high-pressure magnesium silicide Mg₂Si₇.
In: Physics and Chemistry of Minerals. Bd. 49 (2022) Heft 5 . - 12.
ISSN 1432-2021
DOI: https://doi.org/10.1007/s00269-022-01189-3

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Abstract

SiC and (Fe, Mg)-silicide are candidate phases forming under reducing conditions in the Earth and planetary interiors. However, structural studies of SiC and Mg₂Si at high pressure and their thermal stability are presently lacking. In this work, we applied single-crystal X-ray diffraction in a diamond anvil cell at high pressure and determined the equations of state of α-SiC (6H) and βʹ-Mg₂Si₁.₁ up to 60 and 40 GPa, respectively, yielding bulk moduli of 226.0(4) and 56(1) GPa. We also report the formation of a novel orthorhombic Mg₂Si₇ phase upon laser heating βʹ-Mg₂Si₁.₁ at ~ 45 GPa and 2000 °C [Pbam, a = 7.16(1) Å, b = 12.490(3) Å, c = 2.6545(3) Å, V = 237.5(3) Å3]. The structure of this compound contains layers formed by irregular 12-member silicon rings, which are arranged in channels filled with both Mg and Si atoms. No signs of the Mg₂Si₇ phase were detected upon releasing the pressure in the DAC, which suggests that this phase is unstable under ambient conditions.