Influence of four-phonon scattering and wavelike phonon tunneling effects on the thermal transport properties of TlBiSe2

TlBiSe₂ is considered a potential thermoelectric material due to its ultralow lattice thermal conductivity κL and excellent electrical properties. However, previous studies on the thermal properties of TlBiSe₂ only considered the effects of three-phonon scattering, which resulted in significant differences between theoretical and experimental values. In this material, four-phonon scattering processes mainly reduce the thermal transport of acoustic phonons, resulting in an approximate 28% reduction in particlelike thermal conductivity κₚ at 300 K. The high-frequency optical branches are dense and the phonon lifetime is short, making it easy to generate wavelike phonon tunneling. After considering wavelike thermal conductivity κc, κL along the in-plane direction is in good agreement with the experimental values. A nonstandard κL∝T^-0.36 dependence is revealed in the cross-plane direction. At high temperatures, κc in the cross-plane direction is greater than κₚ and κc dominates the thermal transport with 61% of κL at 700 K. In addition to the frequency difference of the phonon pairs, the interbranch phonon group velocity also has an important effect on κc. Our work improves the calculational accuracy of thermal conductivity for TlBiSe₂ and broadens the field for application of ternary-layered thallium-based semiconductors.