Thermoelectric properties of zinc-doped CuSnSe and CuSnTe

High-performance thermoelectric materials are currently being sought after to recycle waste heat. Copper chalcogenides in general are materials of great interest because of their naturally low thermal conductivity and readily modifiable electronic properties. The compounds Cu 5 Sn 2 Q 7 were previously reported to have metal-like properties, which is not a desirable characteristic for thermoelectric materials. The aim of this study was to reduce the carrier concentration of these materials by Zn-doping, and then investigate the electronic and thermoelectric properties of the doped materials in comparison to the undoped ones. The compounds were synthesized using both the traditional solid-state tube method and ball-milling. The crystal structures were characterized using powder X-ray diffraction, which confirmed that all materials crystallize in the monoclinic system with the space group C 2. With the partial substitution of zinc for copper atoms, the compounds exhibited an overall improvement in their thermoelectric properties. Figure of merit values were determined to be 0.20 for Cu 4 ZnSn 2 Se 7 at 615 K and 0.05 for Cu 4 ZnSn 2 Te 7 at 575 K. The incorporation of Zn in Cu 5 Sn 2 Q 7 adds one additional electron per formula unit, which results in a narrow band gap semiconductor with improved thermoelectric properties.