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

Abstract N‐type Mg 3 (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 Mg 3 (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 cm 2 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 Mg 3 (Bi, Sb) 2 /Fe TE legs. As a consequence, this work fabricates an 8‐pair Mg 3 Sb 2 ‐GeTe‐based power‐generation device reaching an energy conversion efficiency of ≈5.0% at a temperature difference of 439 K, and a one‐pair Mg 3 Sb 2 ‐Bi 2 Te 3 ‐based cooling device reaching −10.7 °C at the cold side. This work paves a facile way to obtain Mg 3 Sb 2 ‐based TE devices at low cost and also provides a guide to optimize the off‐stoichiometric defects in other TE materials.