Revisiting phonon transport in perovskite SrTiO3: Anharmonic phonon renormalization and four-phonon scattering

We investigate the role of anharmonic phonon renormalization and four-phonon scattering in the thermal transport of cubic ${\mathrm{SrTiO}}_{3}$ from 200 to 800 K by constructing an accurate first-principles machine-learning potential with active learning. The anharmonic phonon dispersion relations show obvious low-frequency phonon hardening as temperature increases, implying potential importance of fourth order lattice anharmonicity in cubic ${\mathrm{SrTiO}}_{3}$. Under the perturbation theory and Boltzmann transport equation scheme, we find that phonon frequency renormalization can make a significant improvement in the calculations of thermal conductivity and its temperature dependence of cubic ${\mathrm{SrTiO}}_{3}$ compared to experimental data. Four-phonon scattering is usually important in strongly anharmonic materials with ultralow thermal conductivity and simple crystals featured by large acoustic-optical phonon band gaps. Nonetheless, we find that four-phonon scattering can make a considerable contribution to suppressing phonon transport in cubic ${\mathrm{SrTiO}}_{3}$ which has a moderate thermal conductivity. This study deepens the understanding of anharmonic phonon renormalization and four-phonon scattering in oxide perovskites.