Elastic properties of the post-perovskite phase of Fe2O3 and implications for ultra-low velocity zones

The properties of the post-perovskite phase of Fe2O3 have been investigated using both the generalized gradient approximation (GGA) and GGA + U methods. The low-spin post-perovskite phase is found to have monoclinic symmetry. While GGA and GGA + U predict very different spin transition pressures, bulk elastic properties are found to be similar. Linear mixing of the elastic properties of the post-perovskite phase of Fe2O3 with those previously calculated for the MgSiO3 phase shows that the properties of ferric-iron-enriched post-perovskite are compatible with seismic constraints for ultra-low velocity zones. Agreement with observations for ultra-low velocity zones is further increased if they are presumed to be hotter than normal mantle.