Strain-Engineered Thermoelectric Performance in Superatomic Semiconductor Re₆Se₈Cl₂: The Role of Four-Phonon Scattering and Coherent Phonons

Strain engineering is an effective strategy to enhance the thermoelectric performance of materials by tuning their phonon and electron transport properties. We investigate the thermoelectric properties of the van der Waals superatomic semiconductor Re₆Se₈Cl₂ under compressive and tensile strain, focusing on its phonon dynamics and thermal transport mechanisms. Through first-principles calculations and self-consistent phonon theory, we reveal the critical role of anharmonic phonon interactions, achieving a remarkably low lattice thermal conductivity of 0.36 W/(m K) at 300 K by incorporating four-phonon scattering and coherent phonon contributions. Compressive strain enhances coherent phonon effects, revealing a complex interplay between diffusive and wave-like thermal transport. For <i>p</i>-type doping, strain-induced changes in carrier effective mass and scattering mechanisms significantly improve carrier mobility and the Seebeck coefficient, achieving a thermoelectric figure of merit (<i>ZT</i>) of 2.12 at 600 K. This study underscores the potential of strain engineering and coherent phonons in designing high-performance thermoelectric materials.