Mechanical and thermoelectric properties of the RbSnX3 (X = F, Cl) compounds

The dimensionless figures of merit (bp-ZTs) with the bipolar effect of RbSnX3 (X = F, Cl) are evaluated. The carrier-type dependent Seebeck (Sn/Sp) coefficient, electric conductivity (σn/σp), and electronic thermal conductivity (κen/κep) of RbSnX3 at 300–900 K are obtained via solving the Boltzmann transport equation on the basis of the first principles band alignments and intrinsic carrier concentrations. Then, the corresponding values with bipolar effect (Sbp, σbp, and κbp) are evaluated. The bp-ZTs are determined with the obtained Sbp, σbp, and κbp and the calculated lattice thermal conductivity of RbSnX3. The results demonstrate that the maximum bp-ZTs can reach 3.17 for RbSnF3 and 1.66 for RbSnCl3 at 900 K, indicating that the two compounds are promising thermoelectric materials. To understand the mechanism of the thermoelectric performance, we also examine the relationship between the thermoelectric properties (ZT/Sn/Sp/σn/σp/κen/κep) and carrier concentration. Comparing the bp-ZTs with the dimensionless figures of merit obtained from the direct summation of the ones for the n-type and p-type carriers without bipolar effect, we find the bipolar effects are trivial in all the considered temperatures.