Isothermal equation of state and phase stability of Fe 5 Si 3 up to 96 GPa and 3000 K

The composition of Earth's core has first‐order implications for understanding the thermal and chemical history of the deep Earth. The present work measures the pressure‐volume equation of state of Fe 5 Si 3 to 96 GPa in a diamond anvil cell using noble gas pressure media and demonstrates that Fe 5 Si 3 is not stable at high temperature and pressure but reappears during thermal quench. The isothermal equation of state at ambient temperature of Fe 5 Si 3 is given by the bulk modulus K T ,0  = 167 (8) and K T ,0 ′ = 5.1 (2), with V 0  = 56.29 cm  3  mol −1 . At high temperatures and pressures we observed the disappearance of hexagonal Fe 5 Si 3 diffraction peaks and the appearance of peaks corresponding to cubic FeSi and Fe 3 Si structures at 18 GPa and at the lowest measurable temperature (~1300 K), indicating that Fe 5 Si 3 is not stable at high temperature. Upon temperature quench diffraction peaks corresponding to Fe 5 Si 3 reappear, confirming its stability at ambient temperature and high pressure.