Thermal conductivity of MgO:Fe at high pressure and the spin transition via ab initio calculations.

In this work we elucidate the effect of the spin transition on the thermal transport in ferropericlase (Mg_xFe_1-xO) from ab-initio calculations. Ferropericlase is expected to be one the components of the Earth’s mantle and at the high-pressure conditions of the lower mantle, iron atoms substituted into the MgO rocksalt lattice experience transition from a high spin state to a low spin state. Recent experimental study has demonstrated a substantial decrease of the thermal conductivity in MgO:Fe at pressures that correspond to the onset of the spin transition, and the latter has been implicated as the cause of the former. Here, we consider possible mechanisms that affect the thermal conductivity as a function of pressure across the spin transition. Those include phonon scattering on the electronic states of iron atoms as well as volume collapse which accompanies spin transition. We report our results for the lattice thermal conductivity in ferropericlase from the accurate solution of the Boltzmann Transport Equation for phonons using DFT calculations as an input. We account for impurity scattering via Virtual Crystal Approximations and take into account the effect of the electron-phonon interactions across the spin transition.