Electronic spin transitions in iron-bearing MgSiO3 perovskite

The electronic spin state of iron in perovskites with the chemical composition Mg_0.9375Fe_0.0625SiO₃, Mg_0.8750Fe_0.1250SiO₃ and Mg_0.9375Fe_0.0625Si_0.9375Fe_0.0625O₃, have been determined at 0 K and various pressures between 40–160 GPa, using ab initio methods. The results indicate that ferric iron exhibits a wide range of spin transition pressures between about 60–160 GPa, while ferrous iron has a much narrower span, between about 130–145 GPa. In general, the lowest spin transition pressures are associated with the most energetically favorable substitution configurations, where iron atoms are closest together. The effect of spin state on calculated elastic properties is found to be small.