Ab initio lattice thermal conductivity of (Mg,Fe)O ferropericlase at the Earth's lower mantle pressure and temperature.

The effects of iron (Fe) incorporation on the lattice thermal conductivity (κlat) of MgO are investigated under the Earth's lower mantle pressure (P) and temperature (T) condition (P > ~20 GPa, T > ~2000 K) based on the density-functional theory combined with the anharmonic lattice dynamics theory. The κlat of ferropericlase (FP) is determined combining the internally consistent LDA+U method and self-consistent approach to solve the phonon Boltzmann transport equation. The calculated κlat are well fitted to the extended Slack model which is proposed in this study to represent κlat in a wide volume and T range. Results demonstrate that the κlat of MgO decreases strongly by Fe incorporation. This strong negative effect is found due to decreases in phonon group velocity and lifetime. Consequently, the κlat of MgO at the core-mantle boundary condition (P ~136 GPa, T ~4000 K) is substantially reduced from ~40 to ~10 Wm-1K-1 by the incorporation of Fe (12.5 mol%). The effect of Fe incorporation on the κlat of MgO is found to be insensitive to P and T, and at high T, the κlat of FP obeys a well-established T inverse relation unlike the experimental observations.