Comparison of ultra-low lattice thermal conductivity of the full-Heusler compound Li2Rb(Cs)Bi after considering strong quartic anharmonicity

This paper conducts a detailed study on the thermal transport and thermoelectric properties of Li 2Rb(Cs)Bi and analyzes the optical phonon frequency shift caused by considering anharmonicity. We mainly focus on studying the microscopic mechanism of the difference in lattice thermal conductivity ( κ L) of the two materials. By calculating the group velocity, scattering rate, scattering phase space and scattering sub-process, it is concluded that κ L is mainly dominated by the acoustic branch. Due to its small group velocity and large scattering rate, Li 2CsBi has a low κ L, which is 0.60 W m − 1K − 1 at 300 K. Research results show that n-type Li 2CsBi has a higher ZT value of about 2.1 at T = 900 K, while p-type Li 2RbBi has a higher ZT value of about 1.5 at the same temperature. These results provide an important theoretical basis for the application of Li 2Rb(Cs)Bi in the field of thermoelectric conversion.