Gibbs Adsorption and Zener Pinning Enable Mechanically Robust High‐Performance Bi(2)Te(3)‐Based Thermoelectric Devices

Bi(2)Te(3)‐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 Bi(2)Te(3)‐based alloys due to thermodynamic Gibbs adsorption and kinetic Zener pinning at grain boundaries enabled by MgB(2) 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)Te(3))(0.97)(MgB(2))(0.03) compared with that of traditional powder‐metallurgy‐derived Bi(0.5)Sb(1.5)Te(3). High mechanical properties enable excellent cutting machinability in the MgB(2)‐added samples, showing no missing corners or cracks. Moreover, adding MgB(2) 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)Te(3))(0.97)(MgB(2))(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.