Gibbs Adsorption and Zener Pinning Enable Mechanically Robust High-Performance Bi₂ Te₃ -Based Thermoelectric Devices

Bi₂ Te₃ -based alloys have great market demand in miniaturized thermoelectric (TE) devices for solid-state refrigeration and power generation. However, their poor mechanical properties increase the fabrication cost and decrease the service durability. Here, this work reports on strengthened mechanical robustness in Bi₂ Te₃ -based alloys due to thermodynamic Gibbs adsorption and kinetic Zener pinning at grain boundaries enabled by MgB₂ decomposition. These effects result in much-refined grain size and twofold enhancement of the compressive strength and Vickers hardness in (Bi_0.5 Sb_1.5 Te₃ )_0.97 (MgB₂ )_0.03 compared with that of traditional powder-metallurgy-derived Bi_0.5 Sb_1.5 Te₃ . High mechanical properties enable excellent cutting machinability in the MgB₂ -added samples, showing no missing corners or cracks. Moreover, adding MgB₂ facilitates the simultaneous optimization of electron and phonon transport for enhancing the TE figure of merit (ZT). By further optimizing the Bi/Sb ratio, the sample (Bi_0.4 Sb_1.6 Te₃ )_0.97 (MgB₂ )_0.03 shows a maximum ZT of ≈1.3 at 350 K and an average ZT of 1.1 within 300-473 K. As a consequence, robust TE devices with an energy conversion efficiency of 4.2% at a temperature difference of 215 K are fabricated. This work paves a new way for enhancing the machinability and durability of TE materials, which is especially promising for miniature devices.