Enhancement of low-temperature thermoelectric performance via Pb doping in Cu₃SbSe₄

We investigated the synthesis protocols of the pure and Pb-doped bulk polycrystalline Cu₃Sb_1-xPb_xSe₄ (0 ≤ x ≤ 0.04) system and studied their crystallographic and thermoelectric properties intending to reach a high figure of merit (ZT). The solid-state reaction method under a 10⁻⁵ Torr vacuum was employed to synthesize the pristine and doped samples. The Rietveld analysis of room-temperature X-ray diffraction confirmed tetragonal structure with space group I4‾2m for all studied compositions. The electrical resistivity [ρ(T)] demonstrated a degenerate semiconducting behavior for pure as well as doped samples. The overall ρ(T) increased with increasing Pb content. The positive values of Seebeck coefficient [S(T)] data in the investigated temperature range for all the studied compositions revealed that holes played a major role in the conduction mechanism. The S(T) values rose with increased temperature, a characteristic of degenerate semiconductors. The temperature-dependent Seebeck coefficient data analysis revealed a narrow bandgap behavior for all studied samples. The analysis suggests that the electronic thermal conductivity only contributed up to 1% to the total thermal conductivity, and the remaining 99% was contributed by lattice thermal conductivity. The estimated ZT values showed as much as 20% enhancement at 380 K for a 1% doped sample, Cu₃Sb_0.99Pb_0.01Se₄. The thermoelectric compatibility factor decreased with doping, and a maximum value (1.14 V⁻¹) was found for the pristine sample at 250 K.