Correlation of rattlers with thermal transport and thermoelectric performance

The presence of rattlers in the host-guest structure has sparked great interest in the field of thermoelectrics, as it allows for the suppression of thermal transport in materials through vigorous anharmonic vibrations. This work predicts a ternary half-Heusler compound, LiAgTe, with good thermoelectric properties and high-temperature stability, which possesses a host-guest structure. Furthermore, it provides a detailed analysis of the role of rattlers in the transport process. By microscopically exploring rattlers, we have revealed that rattlers (Ag atoms), while suppressing the thermal transport properties of the host framework, provide a significant enhancement of the electronic transport capability through the provision of nearly free weakly bound electrons. Using self-consistent phonon theory combined with compressive sensing lattice dynamics method, we captured the exact lattice thermal conductivity considering quartic anharmonicity and four-phonon scattering, and obtained the electronic transport parameters through the calculation of τ_e, which includes full anisotropic acoustic deformation potential scattering, polar optical phonon scattering, and ionized impurity scattering. We systematically dissected the role of rattlers in the host-guest structure by combining methods such as electron local function, Bader charge density, and Vibration visualization. The anharmonic vibrations of rattlers enhance the temperature response of scattering, resulting in rapid deterioration of thermal transport at high temperatures. Moreover, the extended d-orbital electrons of the rattlers, together with the p-orbital electrons of the Te atom in the host framework, result in the coexistence of maximum degeneracy and high dispersion bands in the valence band, which greatly enhances the electronic transport properties.