Enhancing cryogenic thermoelectric performance of BiSb alloys by La induced charge density localization and band convergence

BiSb alloys are promising thermoelectric materials for Cryogenic power generation with an optimal operating temperature range of 60 ∼ 300 K. Although the thermoelectric properties of n-type BiSb polycrystalline materials doped with metallic elements are generally enhanced, but the mechanisms underlying these improvements remain incompletely understood. Motivated by the high valence-electron activity and large atomic radius of La, we investigate the thermoelectric properties of La doped polycrystalline Bi 85 Sb 15-x La x (x = 0 ∼ 0.5), supplemented by density functional theory (DFT) calculations. The results indicate that La doping slightly increases the band gap and promotes conduction-band convergence, thereby optimizing the electronic structure. Consequently, the Bi 85 Sb 14.6 La 0.4 sample exhibits a high power factor of 3315 μW m −1  K −2 at 213 K. The higher Seebeck coefficient is attributed to an increased density of states effective mass induced by La doping. The enhanced electrical conductivity primarily results from La induced optimization of the electronic structure and grain-growth driven increases in carrier mobility. In addition, the accompanying lattice strain and microscopic morphological defects of La doping effectively suppress the lattice thermal conductivity to ∼0.79 W m −1  K −1 at 273 K. Consequently, this a peak ZT of ∼0.40 at 243 K and an average ZT of ∼0.34 in the range of 153 K ∼ 303 K. Our work offers a promising route to improving the thermoelectric performance of BiSb materials and extending their effective operating range at low temperatures.