Thermal Conductivity Of Caf2 At High Pressure

We study the thermal transport properties of three CaF2 polymorphs up to a pressure of 30 GPa using first-principles calculations and an interatomic potential based on machine learning. The lattice thermal conductivity kappa is computed by iteratively solving the linearized Boltzmann transport equation and by taking into account three-phonon scattering. Overall,. increases nearly linearly with pressure, and we show that the recently discovered delta-phase with P62m symmetry and the previously known gamma-CaF2 high-pressure phase have significantly lower lattice thermal conductivities than the ambient-thermodynamic cubic fluorite (Fm3m) structure. We argue that the lower kappa of these two high-pressure phases stems mainly due to a lower contribution of acoustic modes to. as a result of their small group velocities. We further show that the phonon mean free paths are very short for the P62m and Pnma structures at high temperatures, and we use the Cahill-Pohl model to assess the lower limit of thermal conductivity in these domains.