Elastic anisotropy of FeSiO3 end‐members of the perovskite and post‐perovskite phases

The athermal elastic constants of the perovskite and post‐perovskite polymorphs of pure end‐member FeSiO3 were calculated from ab initio calculations. We predict that incorporating ten mole percent FeSiO3 together with four mole percent Al2O3 into MgSiO3 reduces the perovskite to post‐perovskite phase transition pressure by 5 GPa. Small changes in the seismic properties of the post‐perovskite phase due to the incorporation of iron and alumina are compatible with observations for the lower mantle. MgSiO3 post‐perovskite enriched in fifty percent or more iron may be responsible for ultra‐low velocity zones at the base of the mantle.