Lattice thermal conductivity calculations of α-quartz and α-cristobalite

Lattice thermal conductivities of two SiO₂ polymorphs, α-quartz and α-cristobalite, were studied using first-principles anharmonic phonon calculation and linearized phonon Boltzmann transport equation¹. Although α-quartz and α-cristobalite have similar phonon densities of states, phonon frequency dependencies of phonon group velocities and lifetimes are dissimilar, which results in largely different anisotropies of the lattice thermal conductivities. For α-quartz and α-cristobalite, distributions of the phonon lifetimes effective to determine the lattice thermal conductivities are well described by energy and momentum conservations of three phonon scatterings weighted by phonon occupation numbers and one parameter that represents the phonon-phonon interaction strengths.
[1] K. Mizokami et al, Phys. Rev. B 97, 224306 (2018)