Effect of the Fabrication Technique on the Thermoelectric Performance of Mg-Based Compounds - A Case Study of n-Type Mg2Ge

Abstract

High performance, low cost, and low toxicity have been the main characteristics associated with magnesium-based thermoelectric materials. Nevertheless, the high volatility of magnesium creates challenges in the synthesis of these materials. In this work, n-type Mg2Ge is synthesized using a solid-state technique, fully characterized, and compared with Mg2Ge fabricated through different processes. We have found that Bi is an ineffective dopant in Mg2Ge and precipitates into Mg2Bi3. Regardless of the technique used, the loss of Mg by evaporation and formation of precipitates in Bi-doped samples resulted in a low charge carrier concentration and, consequently, a low power factor. The precipitates significantly reduced the lattice thermal conductivity, however, leading to a figure-of-merit, zT, of 0.4 at 725 K, improving the previously reported figure-of-merit, zT, of 0.2 for Sb-doped Mg2Ge. This work highlights the impact of the fabrication technique on the thermoelectric performance of Mg-based compounds.