Spin-State Crossover of Iron in Lower-Mantle Minerals: Results of DFT+U Investigations

The lower mantle is the largest layer of the Earth. Pressures and temperatures there vary from 23 GPa to 135 GPa and ~1,900 K to 4,000 K. Aluminous perovskite, Al-Mg_1−xFe_xSiO₃, and ferropericlase, Mg_1−xFe_xO, are the most important phases of the Earth’s lower mantle, comprising ~62 vol% and ~35 vol% of this region, respectively. The remaining consists of CaSiO₃-perovskite, according to the pyrolitic compositional model (Ringwood 1982). Silicate perovskite transforms into another polymorph, post-perovskite, at conditions expected to occur near the D″ discontinuity in the...