Reduction of thermal conductivity and improved mechanical properties by incorporating high-entropy carbides into p-type Bi0.5Sb1.5Te3 alloy

Abstract

High-entropy alloys have attracted considerable attention in thermoelectrics due to their severe lattice distortions and complex microstructures, which effectively reduce thermal conductivity. In this study, for the first time, high-entropy carbides (HECs) (Hf-Ta-Zr-Ti-Nb)C were introduced into water-atomized p-type Bi_0.5Sb_1.5Te₃ (BST) powder to fabricate BST + x wt% HEC (x = 0, 1, 2, 3) composites via high-energy ball milling, and their microstructural changes, thermoelectric, and mechanical properties were systematically investigated. HEC additions caused a monotonic reduction in particle size, while maintaining the rhombohedral (BiSb)₂Te₃ phase with minor peak shifts. The carrier effective mass (m∗) increased marginally from 0.9 to 1.0m_d in BST+2 wt% HEC, accompanied by a minor decrease in power factor (S²σ). On the other hand, BST+3 wt% HEC exhibited a reduced thermal conductivity (κ) of 1.04 W/m. K. at 350 K, attributed to multiple alloy disorder and misfit dislocations at coherent BST-HEC interfaces. Despite it, a large power factor (S²σ) of pristine BST led to a maximum figure of merit, ZT_max of 1.05 at 400 K, with an average ZT_avg of 0.87. A higher Vickers hardness of 223 Hv was obtained for BST+3 wt% HEC, attributed to the grain refinement induced by the HEC additions. This study demonstrates that high-entropy carbide doping is a promising strategy for reducing the thermal conductivity in thermoelectric alloys, offering potential for large-scale commercialization.