Two-stage dissociation in MgSiO3 post-perovskite

The fate of MgSiO3 post-perovskite under TPa pressures is key information for understanding and modeling interiors of super-Earths-type exoplanets and solar giantsʹ cores. Here, we report a dissociation of MgSiO3 post-perovskite into CsCl-type MgO and P21/c-type MgSi2O5 at ~ 0.9 TPa obtained by first principles calculations. P21/c-type MgSi2O5 should dissociate further into CsCl-type MgO and Fe2P-type SiO2 at ~ 2.1 TPa. The first dissociation should occur in all solar giants and heavy super-Earths, while the second one should occur only in Jupiter and larger exoplanets. Both dissociations are endothermic and have large negative Clapeyron slopes. If the first dissociation should occur in the middle of a silicate mantle, it could promote mantle layering. We provide essential thermodynamic properties of P21/c-type MgSi2O5 for modeling interiors of super-Earths.