Enhanced thermoelectric performance of AgBi₃S₅ by antimony doping

AgBi₃S₅ is a promising n-type thermoelectric material with low lattice thermal conductivity. In this paper, polycrystalline bulk samples of n-type Ag_1−xSb_xBi₃S₅ (x = 0–0.03) were prepared by high-temperature reaction and pressed by spark plasma sintering (SPS). Electrical conductivity of AgBi₃S₅ is enhanced significantly due to the increased carrier concentration. There is a remarkable enhancement of power factor from ~ 2.1 μW·cm⁻¹·K⁻² for undoped AgBi₃S₅ to ~ 3.3 μW·cm⁻¹·K⁻² for Ag_0.97Sb_0.03Bi₃S₅. The Sb lone pair electrons, as indicated from density functional theory (DFT) calculation results, contribute to the Fermi energy and enhance the carrier effective mass. In addition, the point defects enhance phonon scattering and decrease the lattice thermal conductivity. Owing to the enhanced power factor and reduced thermal conductivity, the thermoelectric figure of merit (ZT) at 800 K for Ag_0.97Sb_0.03Bi₃S₅ reaches 0.53, which is 70% higher than that of the pristine AgBi₃S₅.