Significant Anharmonicity of Thermal Transport in Amorphous Silica at High Temperature

The anharmonicity of thermal transport in amorphous solids is underappreciated and inadequately understood, although considerable attention is paid to that of crystals. Herein, the anharmonic effects on the heat conduction of amorphous silica are investigated by combining the normal mode decomposition method with the Wigner transport equation. The existence of significant anharmonicity in amorphous silica, including temperature‐dependent linewidths and frequency shifts of the vibrational modes, is demonstrated. By considering the anharmonic effects, the predicted temperature dependence of thermal conductivities at high temperatures agrees well with the increasing trend observed in experiments. The underlying mechanisms are further revealed. The anharmonic frequency shifts notably affect the strength of coupling between pairs of vibrational modes and dictate the positive temperature dependence, whereas the increasing linewidths with increasing temperature are of minor importance. This work contributes to the understanding of the anharmonicity of thermal vibrations and heat conduction in amorphous materials.