Improved Thermoelectric Performance of Cu3Sb1−x−ySnxInySe4 Permingeatites Double-Doped with Sn and In

Abstract

Cu–Sb–Se ternary chalcogenide compounds composed of earth-abundant low-toxicity elements are attracting attention as economical and ecofriendly semiconductors. Among them, permingeatite (Cu₃SbSe₄) is a potential thermoelectric material with high Seebeck coefficient and low lattice thermal conductivity. However, it is necessary to improve its thermoelectric properties through doping, as it has low electrical conductivity due to its low intrinsic carrier concentration. In this study, samples of Cu₃Sb_1−x−ySn_xIn_ySe₄ (0.02 ≤ x ≤ 0.08 and 0.04 ≤ y ≤ 0.06) double-doped with In (group 13 element) and Sn (group 14 element) at the Sb (group 15 element) sites of permingeatite were synthesized and their thermoelectric performances were evaluated. All samples exhibited a single phase of permingeatite with tetragonal structure, and high relative densities of 97.4–98.9%. The lattice constants of the a- and c-axes were 0.5651–0.5654 and 1.1249–1.1257 nm, respectively, owing to the successful substitution of Sn and In at the Sb sites. As the doping concentrations of Sn and In increased, the carrier (hole) concentration increased. Thus, the Seebeck coefficient decreased, while the electrical and thermal conductivities increased. Sn doping was found to be more effective than In doping. Because Cu₃Sb_0.96−xSn_xIn_0.04Se₄ exhibits higher Seebeck coefficients than Cu₃Sb_0.94−xSn_xIn_0.06Se₄, larger power factors and higher dimensionless figures of merit (ZTs) were achieved for the Cu₃Sb_0.96−xSn_xIn_0.04Se₄ specimens. Cu₃Sb_0.92Sn_0.04In_0.04Se₄ achieved a maximum ZT of 0.59 at 623 K, based on its Seebeck coefficient of 161 µVK⁻¹, electrical conductivity of 4.69 × 10⁴ Sm⁻¹, thermal conductivity of 0.77 Wm⁻¹K⁻¹, and power factor of 1.22 mWm⁻¹K⁻².