Anomalously dominating four-phonon scattering in pressure-dependent thermal transport in beryllium oxide

Rocksalt beryllium oxide (BeO) exhibits a unique combination of a large bandgap and high dielectric constant, but it is stable only at high pressures. While ambient-pressure wurtzite BeO plays a crucial role in various applications, its thermal transport properties under pressure remain largely unexplored. Here, we employ the first-principles phonon Boltzmann transport theory to investigate the pressure-dependent thermal transport in BeO. Our results reveal a nonmonotonic pressure dependence of thermal conductivity, characterized by a significant drop upon the wurtzite–rock salt phase transition. Furthermore, we demonstrate a crucial role for four-phonon scattering processes, which are typically neglected in conventional calculations. Neglecting four-phonon scattering leads to a substantial overestimation of thermal conductivity. This anomalous dominance of four-phonon scattering can be attributed to the exceptionally large anharmonicity, driven by the strong pressure-dependent repulsive interactions between oxygen atoms, which exhibit a 1/d4 dependence on interatomic distance. Our findings emphasize the critical importance of considering higher-order phonon scattering processes in pressure-dependent systems. These insights have significant implications for understanding and manipulating thermal transport in materials subjected to extreme pressures.