Solubility of FeO in (Mg,Fe)SiO3 perovskite and the post-perovskite phase transition

Phase relations in Mg0.5Fe0.5SiO3 and Mg0.25Fe0.75SiO3 were investigated in a pressure range from 72 to 123 GPa on the basis of synchrotron X-ray diffraction measurements in situ at high-pressure and -temperature in a laser-heated diamond-anvil cell (LHDAC). Results demonstrate that Mg0.5Fe0.5SiO3 perovskite is formed as a single phase at 85–108 GPa and 1800–2330 K, indicating a high solubility of FeO in (Mg,Fe)SiO3 perovskite at high pressures. Post-perovskite appears coexisting with perovskite in Mg0.5Fe0.5SiO3 above 106 GPa at 1410 K, the condition very close to the post-perovskite phase transition boundary in pure MgSiO3. The coexistence of perovskite and post-perovskite was observed to 123 GPa. In addition, post-perovskite was formed coexisting with perovskite also in Mg0.25Fe0.75SiO3 bulk composition at 106–123 GPa. In contrast to earlier experimental and theoretical studies, these results show that incorporation of FeO stabilizes perovskite at higher pressures. This could be due to a larger ionic radius of Fe2+ ion, which is incompatible with a small Mg2+ site in the post-perovskite phase.