Effect of four-phonon scattering on strain-dependent thermal and thermoelectric transport of ferroelectric α-In2Se3 monolayer

Abstract

Understanding and controlling thermal transport in thermoelectric materials is crucial for enhancing their efficiency. This study investigates the effect of four-phonon scattering on the strain-dependent lattice thermal conductivity of ferroelectric α-In2Se3 monolayers using first-principles calculations and the phonon Boltzmann transport equation. The results show that four-phonon scattering reduces thermal conductivity, with its influence increasing under tensile strain. Strain leads to a decrease in the phonon group velocity and an increase in the four-phonon scattering phase space, which enhances phonon scattering and shortens phonon lifetimes. At 4% strain, the inclusion of four-phonon scattering reduces thermal conductivity by about 33% compared to three-phonon-only calculations. Further analysis shows that redistribution (+−) and splitting (−−) processes become more significant under strain, while combination (++) processes decrease. The strain-induced enhancement of four-phonon phase space is notably stronger than that of three-phonon processes due to the higher combinatorial flexibility and sensitivity of four-phonon channels to phonon dispersion changes. In addition, the calculated electronic transport properties indicate that tensile strain improves the power factor, and the resulting thermoelectric figure of merit (ZT) increases from 0.17 (unstrained) to 0.42 at 4% strain when including four-phonon scattering. These results suggest that four-phonon scattering should be considered when modeling both thermal and thermoelectric transport in strained ferroelectric materials.