Effects of vacancy defects on Fe properties incorporated in MgO

Distributions of Fe in MgO containing Mg vacancy, O vacancy, and Schottky defect are investigated based on the density functional theory (DFT). Our results show that since Mg vacancy will remove electrons from MgO, Fe tends to get close to Mg vacancy but far from O vacancy. The Mg vacancy can decrease the magnetic moment of iron and change its valence state from 2+  to 3+, which leads to ~5% decrease of Fe-O bond length comparable to the effect of 30 GPa external pressure. Furthermore, iron incorporation can increase the Schottky defect concentration of MgO especially in the environment of the Earth's lower mantle, where ~20 mol% Fe-bearing MgO locates at extreme high temperature conditions.