Finite-temperature force constants are essential for accurately predicting the thermal conductivity of rutile TiO2

Abstract

Phonon transport in rutile $\mathrm{Ti}{\mathrm{O}}_{2}$ between temperatures of 100 and 900 K is investigated using lattice dynamics calculations and the Boltzmann transport equation. Zero- and finite-temperature force constants are extracted from density functional theory calculations to examine the effects of finite temperature on phonon properties and thermal conductivity. Using the zero-temperature force constants leads to thermal conductivity predictions along the $a$ and $c$ axes that are 50% lower than experimental measurements at a temperature of 300 K. The underprediction increases as the temperature is further increased. Using temperature-specific force constants, however, leads to thermal conductivity predictions that fall within the uncertainty bounds of multiple sets of experimental measurements. Phonon mode analysis reveals that the thermal conductivity underprediction from the zero-temperature force constants is a result of an underprediction of phonon lifetimes. The lifetime underprediction results from the temperature dependence of (i) the second-order force constants, which set the phonon frequencies and thus the three-phonon scattering phase space, and (ii) the third-order force constants, which influence the intrinsic scattering rates. Our results emphasize the importance of including finite-temperature effects when studying phonon transport in oxides and inform how nanostructuring impacts the thermal conductivity of rutile $\mathrm{Ti}{\mathrm{O}}_{2}$.