Thermal Conductivity of MgSiO3 Perovskite: Insights from Phonon Quasiparticles

Abstract:

Compared to electronic and photonic transports, heat transport is less well understood for many materials. At high temperature, thermal conductivity often displays a saturated behavior deviating from the well-known 1/T scaling. The understanding relies on a minimal mean free path phenomenology, additionally implemented to phonon gas model and often used for practical investigations. Unfortunately, a validity check of this minimal mean free path phenomenology against the underlying microscopic behavior is missing. In this work, we investigate lattice thermal conductivity of MgSiO3 perovskite within the framework of phonon gas model. Such study is possible due to a recent theoretical advance – a hybrid approach of first principle molecular dynamics fused with lattice dynamics. MgSiO3 perovskite, the most abundant component of Earth minerals existing in the Earth lower mantle, provides an excellent test bed for studying thermal conduction under high temperature conditions. Surprisingly, the calculated phonon mean free paths do not have the prescribed minima even at extremely high temperature, and neither does the lattice thermal conductivity. The obtained lattice thermal conductivity is in good agreement with the measured values from ambient pressure to lower mantle pressures at room temperature and obeys the typical linear dependence on pressure as revealed by experiments.

Research supported by NSF/EAR and Chinese Academy of Sciences.