Role of alloying in the phonon and thermal transport of SnS-SnSe across the phase transition?

Abstract

Atomic-level investigations of the underlying phonon and thermal transports of strongly anharmonic alloy-based thermoelectric materials and their structural phase transitions are yet to be fully explored. Herein, we system-atically investigate the anharmonic lattice dynamics and thermal transport of SnS0.75Se0.25 using perturbation theory up to quartic anharmonicity and molecular dynamics simulations with the first-principles-based machine-learning potential. We find the non-monotonic temperature dependence of the phonon linewidths and fre-quencies of the gamma(4) and Y-1 modes. This work demonstrates an apparent kappa L reduction from SnS to SnS0.75Se0.25, mainly attributed to the enhanced scattering rates of the middle-frequency phonons and the decreased group velocities of the high-frequency phonons. We also find that the effects of the quartic anharmonicity on the thermal transport of SnS and SnS0.75Se0.25 are significant, and the phonon coherence contributions are non-negligible in describing the thermal transport. Moreover, we reveal a decrease of kappa L in SnS0.75Se0.25 by randomizing Se atoms, which can be ascribed to an additional phonon scattering arising from sublattice mass disorder.