[S-IT03] Structure and dynamics of Earth and Planetary deep interiors

[SIT03-18] Post-perovskite phase boundary of Fe- and Al-bearing MgSiO3

*Xianlong WANG¹, Taku TSUCHIYA¹ (1.GRC, Ehime University; ELSI, Tokyo Institute of Technology)

Keywords:First-principles method, internally consistent LSDA+U, post-perovskite, phase transition

The post-perovskite (PPv) phase transition of MgSiO₃ bridgmanite (Br) [1,2,3] occurs in the pressure (P) and temperature (T) conditions corresponding to the Earth's D? layer. Therefore, MgSiO₃ PPv is believed to be a key mineral to understanding the seismological properties in this layer. However, to date, it is still a challenging subject to determine the phase transition boundary preciously in the geophysically relevant Fe and Al-bearing compositions. Based on the first-principles methods combined with the internally consistent LSDA+U method and the lattice dynamics approach, the high-P and high-T thermodynamics of the MgSiO₃ phases are directly calculated with incorporation of 6.25 mol% of Fe²⁺, Fe³⁺Fe³⁺, Fe³⁺Al³⁺, and Al³⁺Al³⁺ [4,5]. Using calculated free energies, we determine the PPv phase boundaries for Fe and Al-bearing compositions. Our results show that at 2500 K, the Fe³⁺Al³⁺ and Fe³⁺Fe³⁺ incorporations span coexisting domains between Br and PPv significantly with lowering the transition pressure, in contrast to the Fe²⁺- and Al³⁺Al³⁺-bearing cases.

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