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

• Published in: Physics and chemistry of minerals 2022-05, Vol.49 (5), Article 12
• Main Authors: Koemets, Iuliia, Ishii, Takayuki, Hanfland, Michael, Dubrovinsky, Leonid
• Format: Article
• Language: English
• Subjects: Crystallography and Scattering Methods; Crystals; Diamond anvil cells; Earth and Environmental Science; Earth Sciences; Equations of state; Experimental and Analytical Techniques at Extreme and Ambient Conditions; Extrasolar planets; Geochemistry; High pressure; Intermetallic compounds; Iron; Laser beam heating; Magnesium; Magnesium compounds; Mathematical analysis; Metal silicides; Mineral Resources; Mineralogy; Original Paper; Planetary interiors; Silicides; Silicon carbide; Single crystals; Thermal stability; X-ray diffraction
• ISSN: 0342-1791; 1432-2021
• DOI: 10.1007/s00269-022-01189-3

SiC and (Fe, Mg)-silicide are candidate phases forming under reducing conditions in the Earth and planetary interiors. However, structural studies of SiC and Mg 2 Si 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 β ʹ-Mg 2 Si 1.1 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 Mg 2 Si 7 phase upon laser heating β ʹ-Mg 2 Si 1.1 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) Å 3 ]. 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 Mg 2 Si 7 phase were detected upon releasing the pressure in the DAC, which suggests that this phase is unstable under ambient conditions.