Vibrational anharmonicity results in decreased thermal conductivity of amorphous HfO2 at high temperature

While the high-temperature thermal transport in crystalline materials has been recently carefully addressed, it is much less explored for amorphous materials. Most of the existing studies have focused on the low-/mid-temperature range and have generally found the increasing trend of thermal conductivity with temperature and converging to a constant value, mainly due to the temperature dependence of heat capacity. In this work, we investigate the temperature-dependent thermal conductivity of amorphous ${\mathrm{HfO}}_{2}$ with three different methods, including molecular dynamics, the Allen-Feldman theory, and the quasiharmonic Green-Kubo method, with the forces extracted from a machine-learning potential parametrized from first principles. While the Allen-Feldman theory and the quasiharmonic Green-Kubo method show the same temperature dependence trend as the previous expectation even at high temperatures, molecular dynamics simulations show a clear decreasing trend of thermal conductivity at high temperatures. By comparing the results from these approaches, we identify that two anharmonic effects, i.e., thermal expansion and vibrational mode softening, are the mechanisms of the decreased thermal conductivity of amorphous ${\mathrm{HfO}}_{2}$ at high temperatures.