Effects of Fe and Al distributions on the Pv–PPv phase transition pressure of MgSiO3

Abstract

SUMMARY Based on the first-principles method combined with Special Quasi-random Structures package, we investigated the effects of impurities distributions on the perovskite (Pv)–post-perovskite (PPv) phase transition pressures of Fe- and Al-bearing MgSiO3. 61 different distribution configurations were calculated. The results show that the distribution has marginal effect on the Pv–PPv phase transition pressure of Fe2+-bearing MgSiO3. However, the separate of Al3+Al3+ ions can significantly increase the Pv–PPv phase transition pressure to that higher than the core–mantle boundary (CMB) pressure. In the most disordered structures of Al3+Al3+-bearing case constructed by SQS, the Pv–PPv phase transition pressure is higher than 400 GPa. Based on our previous result, we proposed that only Fe2+-bearing MgSiO3 can induce the discontinuous increase in shear wave velocity at the CMB, while Al3+Al3+-, Fe3+Al3+- and Fe3+Fe3+-bearing MgSiO3 cannot.