Biaxial Strain Enhanced Thermoelectric Properties of Nanolayered TlCuS: Critical Role of Four-Phonon Scattering

Abstract Strain is an effective approach to enhance the thermoelectric performance of materials. The nanolayered copper-based chalcogenide TlCuS, characterized by its small band gap and ultralow lattice thermal conductivity (κL), has been synthesized and demonstrates potential as a high-performance thermoelectric material. This study systematically investigates the transport properties of TlCuS through biaxial tensile strain modulation based on first-principles calculations combined with Boltzmann transport theory. The results indicate that strain induces band convergence in TlCuS compounds, leading to an enhanced Seebeck coefficient. When four-phonon (4ph) scattering is considered, the calculated results show good agreement with experimental data, indicating strong high-order anharmonicity in TlCuS, with 4ph scattering being the dominant process. Furthermore, the softening of phonon frequencies in strained TlCuS leads to a reduction in κL, which is beneficial for achieving high-performance thermoelectric materials. At 300 K, with just a 2% biaxial tensile strain, the κL value sharply decreased from 0.551 to 0.453 W m−1 K−1. Under a 3% biaxial tensile strain, the p-type TlCuS compound achieves an optimal ZT value of 3.00 at 700 K. Our findings not only elucidate the physical mechanisms governing the transport properties of strained TlCuS, but also provide valuable insights for the application of nanolayered copper-based chalcogenides in the field of thermoelectrics.