Thermoelectric properties of mechanically alloyed Cu₃Sb_1–y(Al/In)_yS₄ famatinites

Cu₃Sb_1–y(Al/In)_yS₄ (0 ≤ y ≤ 0.08) famatinite compounds were synthesized, and phase analysis was conducted based on the Al or In doping level, followed by an examination of charge transport and thermoelectric properties. All specimens exhibited a tetragonal famatinite phase and demonstrated high-relative densities ranging from 97.2 to 99.5%. Al doping notably decreases the a-axis (0.5228–0.5231 nm) and marginally increases the c-axis (1.0764–1.0770 nm), whereas In doping marginally decreases the a-axis (0.5377–0.5380 nm) and significantly increases the c-axis (1.0781–1.0791 nm). The carrier concentration rose with increasing Al/In content, leading to an increase in electrical conductivity (σ), while the Seebeck coefficient (α) declined. The electrical conductivity increased to 450–1130 Sm⁻¹ for Cu₃Sb_0.94Al_0.06S₄ and 250–1110 Sm⁻¹ for Cu₃Sb_0.94In_0.06S₄ at 323–623 K. However, the Seebeck coefficient decreased to 105–243 μVK⁻¹ for Cu₃Sb_0.94Al_0.06S₄ and 334–406 μVK⁻¹ for Cu₃Sb_0.94In_0.06S₄ at 323–623 K. Consequently, the highest power factor of 0.18 mWm⁻¹ K⁻² was obtained at 623 K for Cu₃Sb_0.94In_0.06S₄. Cu₃Sb_0.96Al_0.04S₄ demonstrated the lowest thermal conductivity (κ), while Cu₃Sb_0.94In_0.06S₄ achieved the highest thermoelectric figure of merit (ZT = 0.16) at 623 K.