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

Abstract

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 Mg3.05Bi1.99Te0.01, and a peak ZT≈1.55 at 723 K and average ZT≈1.25 within 323–723 K can be obtained for Mg3.05(Sb0.75Bi0.25)1.99Te0.01. 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 Mg3Sb2-GeTe-based power-generation device reaching an energy conversion efficiency of ≈5.0% at a temperature difference of 439 K, and a one-pair Mg3Sb2-Bi2Te3-based cooling device reaching −10.7 °C at the cold side. This work paves a facile way to obtain Mg3Sb2-based TE devices at low cost and also provides a guide to optimize the off-stoichiometric defects in other TE materials.