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 Rb-2(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 ( kappa (L)) of the two materials. By calculating the group velocity, scattering rate, scattering phase space and scattering sub-process, it is concluded that kappa (L )is mainly dominated by the acoustic branch. Due to its small group velocity and large scattering rate, Li 2CsBi has a low kappa (L), which is 0.60 W m K-- 1( - 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 Rb-2(Cs)Bi in the field of thermoelectric conversion.