Thermal Transport and Thermoelectric Properties of Rb2PdX6 (X=Cl, Br) from First‐principles Study

Abstract Vacancy‐ordered double perovskites are characterized by stable structure, non‐toxicity, low thermal conductivity, and large Seebeck coefficient, which are potential thermoelectric materials. In this work, the thermal transport and thermoelectric properties of Rb 2 PdX 6 (X=Cl, Br) are theoretically investigated. We find that the calculated thermal conductivity is underestimated from the phonon Boltzmann transport equation (PBTE) since the mean free path of a large number of phonons is less than the Ioffe‐Regel limit. The room‐temperature thermal conductivities of Rb 2 PdCl 6 and Rb 2 PdBr 6 are 0.42 W m −1 K −1 and 0.22 W m −1 K −1 based on two‐channel phonon transport mode, respectively. The thermal conductivity of Rb 2 PdBr 6 is almost unchanged with the temperature. Rb 2 PdX 6 (X=Cl, Br) have large Seebeck coefficient for p‐type doping due to triple degeneracy in the VBM and the thermoelectric property of p‐type doping is better than that for n‐type doping. The ab initio scattering and transport program (AMSET) is used to calculate the electron scattering rate. At 700 K, the maximum ZT of p‐type doping Rb 2 PdCl 6 and Rb 2 PdBr 6 can reach to 0.51 and 1.31, respectively. Replacement of Cl by Br results in lower thermal conductivity and smaller bandgap, and thus larger the maximum ZT value. This work demonstrates that Rb 2 PdBr 6 is a potential high‐performance p‐type thermoelectric perovskite material.