Electrical, Thermal, and Thermoelectric Transport Properties of Se-doped Polycrystalline Re₂Te₅

Re₂Te₅ is considered a potential thermoelectric material because of its intrinsically low thermal conductivity, due to its complex crystal structure. Herein, a series of Se-doped Re₂Te₅ (Re₂Te_5-xSe_x, x = 0, 0.2, 1, and 2) samples were synthesized, and their electrical and thermal transport properties were investigated. Pure orthorhombic Re₂Te₅ phases were successfully synthesized without any impurities for all compositions, and the continuous decrease in the calculated lattice parameters confirmed the substitution of Se atoms at the Te sites. A maximum power factor of 0.135 mW/mK² was achieved for the sample with x = 0.2 at 880 K, mainly due to the increase in carrier concentration and electrical conductivity. The lattice thermal conductivity significantly decreased for all doped samples, which was attributed to the point defect phonon scattering caused by Se doping. The thermoelectric figure of merit, zT reached a maximum value of 0.20 at 880 K for Re₂Te_4.8Se_0.2 (x = 0.2) sample, which was approximately 22% higher than that of the pristine Re₂Te₅ sample. The weighted mobility, quality factor, and expected zT were calculated to evaluate the optimization of the power factor and zT.