∼100% enhancement of cryogenic thermoelectric performance of Bi80Sb20 alloys by incorporation of Fe3O4 nanoparticles

Abstract

Bi₈₀Sb₂₀-based alloys are promising candidates for thermoelectric applications below room temperature. However, their inherently low thermoelectric performance, characterized by a limited power factor and high lattice thermal conductivity, severely hinders practical utilization. To address this challenge, we introduce Fe₃O₄ nanoparticles as a second phase to construct Bi₈₀Sb₂₀/Fe₃O₄ nanocomposites via a high-efficiency mechanical alloying process, assisted by stearic acid dispersion, followed by spark plasma sintering. The incorporation of nano-Fe₃O₄ leads to enhanced carrier mobility and intensified phonon scattering at nanoparticle interfaces, resulting in a remarkable threefold increase in the power factor and a 20–40% reduction in lattice thermal conductivity. As a result, the optimized composite with 0.4 vol% Fe₃O₄ achieves a peak zT of 0.31 at 242 K – representing nearly a 100% improvement over the pristine matrix – and an average zT of 0.29 in the range of 150–300 K. In addition to the thermoelectric enhancements, the Vickers hardness of the composites is also significantly improved. These findings demonstrate the potential of superparamagnetic Fe₃O₄ nanoparticle incorporation as an effective strategy for the simultaneous enhancement of both thermoelectric and mechanical properties in Bi₈₀Sb₂₀-based alloys, offering a viable pathway for low-temperature power generation and refrigeration applications.