Solid-State Synthesis and Thermoelectric Performance of Cu3Sb1−yBIII ySe4 (BIII = Al, In) Permingeatites

Permingeatite (Cu₃SbSe₄) is a promising thermoelectric material with narrow bandgap energy and large carrier effective mass. However, doping is required to improve its electrical conductivity and thermoelectric properties. In this study, Cu₃Sb_1−y(Al/In)_ySe₄ doped with B^III-group elements (Al or In) at the Sb sites was synthesized using mechanical alloying followed by sintering through hot pressing. The resulting Cu₃Sb_1−y(Al/In)_ySe₄ contained a single phase of permingeatite with a tetragonal structure and therefore achieved a high relative density of 97.5–99.2%. The substitution of Al/In at the Sb sites produced lattice constants of a = 0.5652–0.5654 nm and c = 1.1249–1.1254 nm. As the Al/In doping content increased, the carrier (hole) concentration increased, reducing the Seebeck coefficient and increasing the electrical and thermal conductivities. Substituting Al³⁺ or In³⁺ at the Sb⁵⁺ site can generate additional carriers, resulting in a high electrical conductivity of (1.4–1.1) × 10⁴ Sm⁻¹ at 323–623 K for Cu₃Sb_0.92In_0.08Se₄. Cu₃Sb_0.96Al_0.04Se₄ exhibited a maximum power factor of 0.51 mWm⁻¹K⁻² at 623 K and a minimum thermal conductivity of 0.74 Wm⁻¹K⁻¹, resulting in a maximum dimensionless figure of merit, ZT, of 0.42 at 623 K. Cu₃Sb_0.96In_0.04Se₄ obtains a ZT of 0.47 at 623 K, indicating a high power factor of 0.65 mWm⁻¹K⁻² at 623 K and low thermal conductivity of 0.84 Wm⁻¹K⁻¹ at 523 K.