Simultaneously enhanced thermoelectric and mechanical properties of the Cu3SbSe4 system through a multi-element co-doping strategy

Cu 3 SbSe 4 is a promising thermoelectric material due to its intrinsically low lattice thermal conductivity and non-toxic, earth-abundant composition; however, its inherently low carrier concentration limits electrical conductivity and the thermoelectric figure of merit ( ZT ). In this study, a series of Cu 3 Sb 1-3 x (BiGeSn) x Se 4 ( x  = 0, 0.02, 0.06, 0.08, and 0.10) ceramic samples were fabricated through a three-step process comprising vacuum melting, subsequent annealing, and hot-press sintering. At 323 K, the electrical conductivity increases from 16.2 to 121.1 S cm −1 upon Bi–Ge–Sn co-doping, representing a 647% enhancement. The power factor of the Cu 3 Sb 0.76 (BiGeSn) 0.08 Se 4 attained a value of 567.6 μW m −1 K −2  at 623 K, approximately 1.86 times higher than that of the undoped Cu 3 SbSe 4 (305 μW m −1 K −2 ). Substitutional co-doping of Bi (isovalent), Ge, and Sn (acceptor-like) introduces lattice-scale defects into the Cu 3 SbSe 4 matrix, leading to grain refinement and enhanced phonon scattering. Consequently, lattice thermal conductivity is markedly suppressed, enabling a peak ZT value of 0.75 for Cu 3 Sb 0.82 (BiGeSn) 0.06 Se 4 —threefold that of pristine Cu 3 SbSe 4 (0.25). Concurrently, mechanical properties are improved, Vickers hardness rises to 329.01 H V (+12.9% relative to the undoped sample), and the Young's modulus reaches 72.58 GPa (+24.2%). These results demonstrate that multi-element co-doping is an effective strategy for the simultaneous optimization of thermoelectric and mechanical performance. The observed enhancements are attributed to the combined effects of multiple dopant species on carrier concentration modulation, phonon scattering intensification, and microstructural refinement.