Extremely strong four-phonon scattering and ultra-low lattice thermal conductivity due to quartic anharmonicity in fluoride perovskites XHgF3 (X = K, Rb)

Abstract

Using high-throughput first-principles calculations, combined with self-consistent phonon theory and Boltzmann transport equations, the lattice thermal transport properties of fluoride perovskites XHgF3 (X = K, Rb) with strong anharmonicity are investigated. After considering the quartic anharmonic renormalization, the imaginary frequency in the phonon spectrum disappears and the low-lying modes soften, resulting in a low group velocity of the acoustic phonons. The strong quartic anharmonicity also causes extremely strong four-phonon scattering, which is even greater than three-phonon scattering in the low frequency phonon mode. The results show that the lattice thermal conductivity κL of XHgF3 (X = K, Rb) is ultra-low and the temperature dependence is unusually weak. The κL of KHgF3 at 300 K is only 0.18 Wm−1K−1, which is one-fifth of the classical low thermal conductivity material, quartz glass. Our study points the way to addressing the thermal transport properties of materials with strong anharmonicity and demonstrates that XHgF3 (X = K, Rb) can not only serve as a good thermal insulation material but also has potential applications in the thermoelectric field.