Mg Compensating Design in the Melting-Sintering Method For High-Performance Mg₃ (Bi, Sb)₂ Thermoelectric Devices

N-type Mg₃ (Bi, Sb)₂ -based thermoelectric (TE) alloys show great promise for solid-state power generation and refrigeration, owing to their excellent figure-of-merit (ZT) and using cheap Mg. However, their rigorous preparation conditions and poor thermal stability limit their large-scale applications. Here, this work develops an Mg compensating strategy to realize n-type Mg₃ (Bi, Sb)₂ by a facile melting-sintering approach. "2D roadmaps" of TE parameters versus sintering temperature and time are plotted to understand the Mg-vacancy-formation and Mg-diffusion mechanisms. Under this guidance, high weight mobility of 347 cm²  V^-1  s^-1 and power factor of 34 µW cm^-1  K^-2 can be obtained for Mg_3.05 Bi_1.99 Te_0.01 , and a peak ZT≈1.55 at 723 K and average ZT≈1.25 within 323-723 K can be obtained for Mg_3.05 (Sb_0.75 Bi_0.25 )_1.99 Te_0.01 . Moreover, this Mg compensating strategy can also improve the interfacial connecting and thermal stability of corresponding Mg₃ (Bi, Sb)₂ /Fe TE legs. As a consequence, this work fabricates an 8-pair Mg₃ Sb₂ -GeTe-based power-generation device reaching an energy conversion efficiency of ≈5.0% at a temperature difference of 439 K, and a one-pair Mg₃ Sb₂ -Bi₂ Te₃ -based cooling device reaching -10.7 °C at the cold side. This work paves a facile way to obtain Mg₃ Sb₂ -based TE devices at low cost and also provides a guide to optimize the off-stoichiometric defects in other TE materials.