Simultaneous enhancement of mechanical and thermoelectric properties via precipitation engineering in Mg₃(Sb, Bi)₂

Precipitation strengthening is a well-established mechanism for enhancing mechanical properties in metals. As for thermoelectric materials, however, research on precipitates has primarily focused on their role in decoupling electron and phonon transport, with their potential for improving mechanical properties receiving limited attention. Herein, we systematically investigate the synergistic effects of V-rich nanoscale precipitates on both the thermoelectric and mechanical properties of Mg₃(Sb, Bi)₂. These precipitates promote grain growth and donate electrons to the matrix, leading to a high electrical conductivity of 6.3 × 10⁴ S·m^-1 at 323 K. Their uniform dispersion also effectively enhances phonon scattering, yielding an average figure of merit ( zT ) of 1.2 over 323-723 K. More importantly, we discover that deformation triggers dynamic precipitation in polycrystalline Mg₃(Sb, Bi)₂. Applied stress generates a high density of dislocations and sub-grain boundaries, which serve as fast diffusion pathways facilitating the reprecipitation of Mg-rich and Bi-rich phases, thereby simultaneously strengthening and toughening the material. Consequently, the optimized Mg_3.19V_0.01Sb_1.5Bi_0.49Te_0.01 demonstrates a compressive strain of 47 % together with a compressive strength of 550 MPa. This work elucidates the dual role of nano-precipitates in governing both thermoelectric transport and mechanical reliability, offering new insights and an effective strategy for strengthening Mg₃(Sb, Bi)₂-based thermoelectrics.