Enhanced mechanical and thermoelectric properties enabled by hierarchical structure in medium-temperature Sb₂Te₃ based alloys

(Bi, Sb)₂Te₃ based materials have been commercially utilized in the field of solid refrigeration, but their application on power generation requires further improvement of thermoelectric and mechanical properties at elevated temperatures. This work reveals a kind of high-performance and robust Sb₂Te₃ based alloys operating above 550 K. Starting with the optimized composition In_0.1Sb_1.9Te₃, nanograins and nanotwins are constructed by high energy ball milling and some boron particles are added to impede the boundary softening caused by the grain refinement. On this basis, oversaturated copper (Cu) doping is employed to introduce both point defects and nanoprecipitates, further leading to a full-spectrum phonon scattering and extraordinary low lattice thermal conductivity. Besides, some Cu atoms replace Sb atoms to increase the carrier concentration and thus suppress the intrinsic excitation, while some others locate at twin boundaries as interstitials to accelerate the carrier migration between two adjacent twin variants, collectively contributing to significant improvement of power factor. Ultimately, the zT value of Cu_0.015B_0.05In_0.1Sb_1.885Te₃ is increased above 1.0 between 573 and 673 K. This material is very suitable for segmentation with optimized Bi_0.5Sb_1.5Te₃ alloys well operating at lower temperatures, leading to high device ZT exceeding 1.05 within 330–673 K, as well as high conversion efficiency up to 12.7% under temperature difference of 370 K.