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

We investigated the synthesis protocols of the pure and Pb-doped bulk polycrystalline Cu3Sb1-xPbxSe4 (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 I42m for all studied compositions. The electrical resistivity [rho(T)] demonstrated a degenerate semiconducting behavior for pure as well as doped samples. The overall rho(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, Cu3Sb0.99Pb0.01Se4. The thermoelectric compatibility factor decreased with doping, and a maximum value (1.14 V-1) was found for the pristine sample at 250 K.