Ab initio predictions of potassium partitioning between Fe and Al-bearing MgSiO3 perovskite and post-perovskite

Ab initio quantum mechanical computations suggest that potassium (K) preferentially partitions into MgSiO3 perovskite (pv) over post-perovskite (ppv) under lower mantle conditions when charge coupled with trivalent cations of aluminum (Al3+) or iron (Fe3+). In an Al-bearing MgSiO3, the equilibrium constant KD increases with pressure, leveling off at ∼33 at ∼100 GPa and 3000 K. For an Fe-bearing MgSiO3, KD slowly increases with pressure reaching a value of ∼8 at core-mantle boundary (CMB) pressures and 3000 K. Our results imply that a potassium-enriched lowermost mantle layer based on the stability of ppv is unlikely.