Ab initio predictions of potassium partitioning between Fe and Al-bearing MgSiO 3 perovskite and post-perovskite

Ab initio quantum mechanical computations suggest that potassium (K) preferentially partitions into MgSiO ₃ perovskite (pv) over post-perovskite (ppv) under lower mantle conditions when charge coupled with trivalent cations of aluminum (Al ³⁺) or iron (Fe ³⁺). In an Al-bearing MgSiO ₃, the equilibrium constant K_D increases with pressure, leveling off at ∼33 at ∼100 GPa and 3000 K. For an Fe-bearing MgSiO ₃, K_D 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.