Ab initio investigation on the high‐temperature thermodynamic properties of Fe3+‐bearing MgSiO3 perovskite

Abstract

High‐pressure (P) and high‐temperature (T) thermodynamics and spin transition of Fe3+‐bearing MgSiO3 perovskite (Pv) are investigated by means of the internally consistent LDA + U method combined with the lattice dynamics method. Fe3+ is found to contribute mainly to the low frequency phonons. The spin transition of iron in the B site occurs at 55 GPa at 300 K and from ~75 to ~90 GPa at lower mantle temperatures. Although high‐spin Fe3+ expands the volume of Pv, most of the bulk thermodynamic properties of Pv are insensitive to Fe3+ incorporation at least at XFe2O3 = 0.0625, with the exception of the Grüneisen parameter. The calculated properties are in good agreement with room temperature experimental data, but a significant increase suggested in the isothermal bulk modulus is not predicted. Results clearly demonstrate that Fe3+‐bearing perovskite alone does not reproduce the density and the bulk sound velocity of the Earth's lower mantle simultaneously.