Gradient Nanotwins and Enhanced Weighted Mobility Synergistically Upgrade Bi_0.5Sb_1.5Te₃ Thermoelectric and Mechanical Performance

Bi2Te3-based alloys have historically dominated the commercial realm of near room-temperature thermoelectric (TE) materials. However, the more widespread application is currently constrained by its mediocre TE performance and inferior mechanical properties resulting from intrinsic hierarchical structure. Herein, microstructure modulation and carrier transport optimization strategies are employed to efficiently balance the electro-thermal transport performance. Specifically, the weighted mobility increases by 24%, while the lattice thermal conductivity decreases by 31% at 350 K compared to the matrix. Consequently, the Bi0.5Sb1.496Cu0.004Te2.98 sample attains a peak ZT of 1.45 at 350 K and an average ZT of 1.20 (300-500 K). Moreover, intricated microstructure design, exemplified by the gradient twin structure, significantly enhances the mechanical performance metrics, including Vickers hardness, compressive strength, and bending strength, to notable levels of 0.94 GPa, 224 MPa, and 58 MPa, respectively. Consequently, the constructed 17-pair TE modules demonstrate a maximum conversion efficiency of 6.5% at Delta T = 200 K, surpassing the majority of reported Bi2Te3-based modules. This study provides novel insights into the synergistic enhancement of TE and mechanical properties in Bi2Te3-based materials, with potential applicability to other TE systems.