Effects of Sn Doping on Charge Transport and Thermoelectric Performance of Wittichenite

Abstract

Wittichenite Cu3BiS3 is a promising thermoelectric material with intrinsically low thermal conductivity owing to its complex crystal structure and strong lattice anharmonicity; however, its thermoelectric performance is limited by low carrier concentration and insufficient electrical conductivity. In this study, Cu3Bi1−xSnxS3 (x = 0.02–0.06) compositions were designed by substituting Sn4+ for Bi3+ sites, and dense single-phase bulk specimens were prepared using mechanical alloying followed by hot pressing. The effects of Sn doping on charge transport and thermoelectric properties were then systematically examined. Structural analysis confirmed that Sn was successfully incorporated into the Cu3BiS3 lattice without secondary phase formation, accompanied by anisotropic lattice contraction associated with the difference in ionic radii between Sn4+ and Bi3+. With increasing Sn content, the carrier concentration increased from approximately 1016 cm−3 to the 1017 cm−3 level, whereas the Hall mobility remained nearly unchanged, resulting in a substantial enhancement in electrical conductivity. Although the Seebeck coefficient decreased with increasing carrier concentration, the reduction was moderate, leading to an improved power factor of 0.10 mW·m−1·K−2 at 673 K. The thermal conductivity remained low, approximately 0.30–0.40 W·m−1·K−1, across the entire composition range, and the electronic contribution was less than 1%, indicating that heat transport was predominantly governed by the lattice contribution. These results demonstrate that Sn doping effectively improves the electrical transport properties while preserving the intrinsically low lattice thermal conductivity of Cu3BiS3. Consequently, a maximum ZT of 0.18 was achieved at 673 K, corresponding to a 64% improvement compared with the undoped specimen. Therefore, this study suggests that carrier concentration control via aliovalent doping is an effective strategy for enhancing the thermoelectric performance of wittichenite.