Anomalous pressure effect on the thermal conductivity of ZnO, GaN, and AlN from first-principles calculations

Abstract

In this paper, the lattice thermal conductivities of bulk ZnO, GaN, and AlN in the normal-pressure wurtzite phase and high-pressure rocksalt phase at room temperature are investigated by solving the phonon Boltzmann transport equation based on first-principles calculations. The results show that the thermal conductivities of the rocksalt ZnO, GaN, and AlN close to the phase-transition pressure are reduced by 73%, 91%, and 34%, respectively, compared to that of corresponding normal-pressure wurtzite structures. Additionally, the thermal conductivity of wurtzite ZnO and GaN exhibits unexpectedly nonmonotonic dependence on pressure; however, for wurtzite and rocksalt AlN the thermal conductivity increases monotonically with the increase of pressure. Detailed phonon mode analysis reveals that the enhanced lattice anharmonicity is responsible for the depressed thermal conductivity of the rocksalt phase. By evaluating the relative contributions of dominant factors affecting lattice thermal conductivity, we find that the nonmonotonic response of thermal conductivity to pressure in wurtzite ZnO and GaN is attributed to the interplay of group velocity and phonon relaxation time. This study provides quantitative understanding of lattice thermal conductivity of ZnO, GaN, and AlN considering the pressure-induced phase transition and highlights the importance of pressure in manipulating lattice thermal conductivity.