Lattice thermal conductivities of two SiO$_2$ polymorphs by first-principles calculation and phonon Boltzmann transport equation

TL;DR

This study uses first-principles calculations and phonon Boltzmann transport equations to analyze and compare the lattice thermal conductivities of two SiO$_2$ polymorphs, revealing differences in phonon dynamics and anisotropy.

Contribution

It provides a detailed first-principles analysis of phonon properties and thermal conductivities in two SiO$_2$ polymorphs, highlighting the role of phonon scattering and interactions.

Findings

Different anisotropies in thermal conductivities due to phonon velocity and lifetime variations.

Phonon lifetimes are governed by energy and momentum conservation in three-phonon processes.

Phonon-phonon interaction strengths influence thermal conductivity distributions.

Abstract

Lattice thermal conductivities of two SiO$_2$ polymorphs, i.e., $\alpha$-quartz (low) and $\alpha$-cristobalite (low), were studied using first-principles anharmonic phonon calculation and linearized phonon Boltzmann transport equation. Although $\alpha$-quartz and $\alpha$-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 $\alpha$-quartz and $\alpha$-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.