Fate of MgSiO3 Post-Perovskite at Terapascal Pressures*

Understanding the fate of MgSiO$_{\mathrm{3}}$ post-perovskite (ppv) under TPa pressures should provide insights into the nature of the interiors of Super-Earths-type exoplanets. The prediction that ppv should dissociate into the elementary oxides MgO and SiO$_{\mathrm{2}}$ at TPa pressures has been confirmed by all ab initio computational studies so far. The most recent high pressure and high temperature (PT) studies agree that at \textasciitilde 2.2 TPa the dissociation process should be completed. These studies also agree that the final dissociation phase boundary has a negative Clapeyron slope, irrespective of the dissociation paths, suggesting a barrier to whole mantle convection possibly leading to chemical stratification in the deep mantle of these planets. The dissociation paths identified more recently involve partial dissociation into MgO, SiO$_{\mathrm{2}}$, and Mg- and Si-rich intermediate compounds whose compositions are temperature dependent. Here we re-investigate the high PT phase diagram of the MgO-SiO$_{\mathrm{2}}$ system and identify novel phase fields and dissociation paths that push the final dissociation boundary to \textasciitilde 3 TPa.