Anharmonic Thermodynamics and Lattice Thermal Conductivity across the Post-Perovskite Transition in MgSiO3
Abstract
MgSiO3 perovskite (Pv) is the most abundant mineral in the Earth's lower mantle (LM), composing about 75 vol% of this region. It undergoes a structural phase transition to post-perovskite (PPv) under the lowermost mantle conditions, i.e., above ~125 GPa and ~2500 K. To address lattice anharmonicity across the phase transition under such extreme conditions, we conduct calculations using the phonon quasiparticle (PHQ) approach. The PHQ is based on ab initio molecular dynamics and, in principle, captures full anharmonicity. Free energies in the thermodynamic limit are computed using temperature-dependent quasiparticle dispersions within the phonon gas model. Systematic results on anharmonic thermodynamic properties and phase boundary are reported. By comparing the thermodynamics and phase boundary obtained by the PHQ and those by the quasiharmonic approximation (QHA), anharmonic effects are demonstrated, and the inadequacy of the QHA is indicated. Lattice thermal conductivities (κ) are computed using the quasiparticle lifetimes at the level of relaxation-time approximation. Systematic pressure and temperature dependence of κ are reported, and κ along the typical geotherm is modeled. The Pv-PPv phase transition is associated with a ~25% increase in κ. Such change resulting from structural change and phonon velocity increase is illustrated.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2022
- Bibcode:
- 2022AGUFMMR25A..03Z