Thermoelectric transport properties of polycrystalline SnSe alloyed with PbSe

Single-crystal SnSe has been found to exhibit exceptional thermoelectric performance, but the efficiency of polycrystalline samples is still far from satisfactory. In this work, with an intention to effectively suppress heat conduction and minimally affect hole transport, we alloyed p-type polycrystalline SnSe with PbSe. Single-phase Sn_1−xPb_xSe solid solutions were formed up to x ≈ 0.12. The lattice thermal conductivity was reduced from 1.4 to 0.85 W m⁻¹ K⁻¹ by 12 at. % PbSe alloying due to strain and mass fluctuations. Interestingly, the Seebeck coefficient and carrier concentration were nearly unchanged by Pb substitution, indicating a constant effective mass and an undisrupted valence band maximum. A peak figure of merit (ZT) of 0.85 at 800 K was obtained in the x = 0 sample, and relatively high performance was also achieved in solid solutions. A concise model was developed involving multiple carrier scattering mechanisms, capturing the dependence of the mobility on composition and temperature.