Phase, Crystal Structure, and Thermoelectric Performance of Cubic Skinnerite Cu3Sb1-yFeyS3 Synthesized by Mechanical Alloying

Skinnerite (Cu₃SbS₃) has recently attracted attention as a promising thermoelectric material because of its low thermal conductivity. In this study, we performed the solid-state synthesis of Fe-doped skinnerite Cu₃Sb_1-yFe_yS₃ (y = 0.02−0.06) using mechanical alloying and hot pressing, and examined the samples’ thermoelectric properties relative to Fe doping content. All samples contained only a cubic skinnerite phase, as evidenced by X-ray diffraction. As the Fe content increased, the lattice constant decreased from 1.03370 to 1.03310 nm, indicating successful substitution of Fe at the Sb sites. The carrier concentration increased with the Fe doping level, resulting in increased electrical conductivity. The specimens with y = 0.02− 0.04 exhibited non-degenerate semiconductor behavior, where the electrical conductivity increased as the temperature increased. In contrast, a specimen with y = 0.06 changed conduction behavior to the degenerate state with minimal temperature dependence. As the Fe content increased, the Seebeck coefficient decreased, and Cu₃Sb_0.98Fe_0.02S₃ exhibited a maximum power factor of 1.16 mWm^-1K^-2 at 623 K. Thermal conductivity values for all specimens were lower than 1.20 Wm^-1K^-1 in the measured temperature range but were higher than undoped skinnerite. The highest thermoelectric performance was achieved by the Cu₃Sb_0.98Fe_0.02S₃ specimen, with a dimensionless figure of merit, ZT, of 0.9 obtained at 623 K.