Copper Chalcogenide-Copper Tetrahedrite Composites-A New Concept for Stable Thermoelectric Materials Based on the Chalcogenide System.

For the first time, an alternative way of improving the stability of Cu-based thermoelectric materials is proposed, with the investigation of two different copper chalcogenide-copper tetrahedrite composites, rich in sulfur and selenium anions, respectively. Based on the preliminary DFT results, which indicate the instability of Sb-doped copper chalcogenide, the CuS-CuSbS and CuSe-CuSbSe composites are obtained using melt-solidification techniques, with the tetrahedrite phase concentration varying from 1 to 10 wt.%. Room temperature structural analysis (XRD, SEM) indicates the two-phase structure of the materials, with ternary phase precipitates embed within the copper chalcogenide matrix. The proposed solution allows for successful blocking of excessive Cu migration, with stable electrical conductivity and Seebeck coefficient values over subsequent thermal cycles. The materials exhibit a p-type, semimetallic character with high stability, represented by a near-constant power factor (PF)-temperature dependences between individual cycles. Finally, the thermoelectric figure-of-merit ZT parameter reaches about 0.26 (623 K) for the CuS-CuSbS system, in which case increasing content of tetrahedrite is a beneficial effect, and about 0.44 (623 K) for the CuSe-CuSbSe system, where increasing the content of CuSbSe negatively influences the thermoelectric performance.