Discovery of high-performance low-cost n-type Mg 3 Sb 2 -based thermoelectric materials with multi-valley conduction bands.

Widespread application of thermoelectric devices for waste heat recovery requires low-cost high-performance materials. The currently available n-type thermoelectric materials are limited either by their low efficiencies or by being based on expensive, scarce or toxic elements. Here we report a low-cost n-type material, Te-doped Mg3 Sb1.5 Bi0.5 , that exhibits a very high figure of merit zT ranging from 0.56 to 1.65 at 300-725 K. Using combined theoretical prediction and experimental validation, we show that the high thermoelectric performance originates from the significantly enhanced power factor because of the multi-valley band behaviour dominated by a unique near-edge conduction band with a sixfold valley degeneracy. This makes Te-doped Mg3 Sb1.5 Bi0.5 a promising candidate for the low- and intermediate-temperature thermoelectric applications.