Bi and Sn Co-doping Enhanced Thermoelectric Properties of Cu₃SbS₄ Materials with Excellent Thermal Stability

Cu₃SbS₄-based materials composed of nontoxic, low-cost, and earth-abundant elements potentially exhibit favorable thermoelectric performance. However, some key transport parameters and thermal stability have not been reported. In this work, the effects of Bi and Sn co-doping on thermoelectric properties and the thermal stability of Cu₃SbS₄ were studied by experiment and theoretical validation. Bi and Sn doping can effectively tune the electrical properties and the electronic band structure. The Bi and Sn doping leads to an increased carrier concentration from 6.4 × 10¹⁷ to 7.4 × 10²⁰ cm^-3 and a decreased optical band gap from 0.85 to 0.73 eV. The effective mass was increased from ∼3.0 m_e for Bi-doped samples to ∼4.0 m_e for Bi and Sn co-doped samples. An enhanced power factor of 1398 μW m^-1 K^-2 at 623 K was obtained for Cu₃Sb_1-BiSnS₄ (x = 0.06, y = 0.09). The measurements of elastic properties exhibited a large Grüneisen parameter (γ ∼2) for Cu₃SbS₄-based materials. Finally, a maximum zT of 0.76 ± 0.02 at 623 K was achieved for Cu₃Sb_1-BiSnS₄ (x = 0.06, y = 0.05) sample. In addition, Cu₃SbS₄ materials possess excellent thermal stability after thermal treatment in vacuum at 573 K for totally 500 h and dozens of heating-cooling thermal cycles (300-623-300 K). It indicates that Cu₃SbS₄ is a robust alternative for Te-free thermoelectric materials at an intermediate temperature range. This work provides feasible guidance to survey the thermal stability of chalcogenides.