Realizing high conversion efficiency of Mg3Sb2-based thermoelectric materials

Mg3Sb2-based thermoelectric materials have drawn much attention in the last couple of years due to their high peak figure of merit, ZT. However, there have yet been no reports focused on fabricating Mg3Sb2-based thermoelectric devices and measuring their conversion efficiencies. Here we report the successful production of contact layers on the recently reported Mg3Sb2-based thermoelectric material using a one-step hot-press technique to achieve good bonding strength and low electrical contact resistance between the thermoelectric material and the contact layers, which are both very important for real applications. The conversion efficiency is measured to be up to 10.6% at a temperature difference of 400 °C from 100 to 500 °C, suggesting that Mg3Sb2-based thermoelectric materials have a good potential for mid-temperature heat conversion, which is supported by the conversion efficiency extracted from the finite difference method. Although a high average ZT, (ZT)avg of 0.96 is measured, we further experimentally demonstrate engineering ZT, (ZT)eng, is more accurate than (ZT)avg, in predicting conversion efficiency. Another recently reported half-Heusler material ZrCoBi0.65Sb0.15Sn0.2, with high peak ZT is also tested to verify this assertion. •Good contact layers on the Mg3Sb2-based thermoelectric material were made.•An ultrahigh conversion efficiency was measured to be ∼10.6% at ∼400 °C.•Uncertainties in the measurement were eliminated by all means.•(ZT)eng is more effective than (ZT)avg to predict conversion efficiency.