Nanotwins Strengthening High Thermoelectric Performance Bismuth Antimony Telluride Alloys

Bi₂ Te₃ based thermoelectric alloys have been commercialized in solid-state refrigeration, but the poor mechanical properties restrict their further application. Nanotwins have been theoretically proven to effectively strengthen these alloys and could be sometimes constructed by strong deformation during synthesis. However, the obscure underlying formation mechanism restricts the feasibility of twin boundary engineering on Bi₂ Te₃ based materials. Herein, thorough microstructure characterizations are employed on a series of Bi_0.4 Sb_1.6 Te_{3+ δ} alloys to systematically investigate the twins' formation mechanism. The results show that the twins belong to the annealing type formed in the sintering process, which is sensitive to Te deficiency, rather than the deformation one. The Te deficiency combined with mechanical deformation is prerequisite for constructing dense nanotwins. By reducing the δ below -0.01 and undergoing strong deformation, samples with a high density of nanotwins are obtained and exhibit an ultrahigh compressive strength over 250 MPa, nearly twice as strong as the previous record reported in hierarchical nanostructured (Bi, Sb)₂ Te₃ alloy. Moreover, benefitting from the suppressed intrinsic excitation, the average zT value of this robust material could reach near 1.1 within 30-250 °C. This work opens a new pathway to design high-performance and mechanically stable Bi₂ Te₃ based alloys for miniature device development.