Solid-State Synthesis and Thermoelectric Performance of Cu3Sb1-yBIIIySe4 (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, Cu3Sb1-y(Al/In)ySe4 doped with BIII-group elements (Al or In) at the Sb sites was synthesized using mechanical alloying followed by sintering through hot pressing. The resulting Cu3Sb1-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) x 104 Sm-1 at 323-623 K for Cu3Sb0.92In0.08Se4. Cu3Sb0.96Al0.04Se4 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. Cu3Sb0.96In0.04Se4 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.