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 Mg 2 Ge is synthesized using a solid-state technique, fully characterized, and compared with Mg 2 Ge fabricated through different processes. We have found that Bi is an ineffective dopant in Mg 2 Ge and precipitates into Mg 2 Bi 3 . 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 Mg 2 Ge. This work highlights the impact of the fabrication technique on the thermoelectric performance of Mg-based compounds.

Suppression of magnetism and Seebeck effect in Na0.875CoO2 induced by SbCo dopants

“…In Mg 3 Sb 2 , interstitial doping with Li, Zn, Cu, and Be is found to be ineffective for n-type doping; however, Li is identified as a good p-type dopant [69]. Bi is an ineffective dopant in Mg 2 Ge and precipitates into Mg 2 Bi 3 [70]. Boron is ineffective as dopant in α-MgAgSb [71].…”

Order and disorder in the modulated phase hp‐Mg9Ge5.1

“…This has stimulated renewed recent interest in the compound as magnesiumbased thermoelectric material. [8][9][10][11] Early experiments evidenced that application of high-pressure induces a phase transformation into a new phase, which has been described as related to cotunnite, PbCl 2 . [12,13] The exact nature of the crystal structure remained a long standing enigma [14][15][16] and the apparent shortcomings of commensurate descriptions triggered repeated attempts to resolve the issue.…”

“…The germanium variety Mg 2 Ge exhibits semiconducting electrical properties in accordance with its electron‐precise character. This has stimulated renewed recent interest in the compound as magnesium‐based thermoelectric material [8–11] . Early experiments evidenced that application of high‐pressure induces a phase transformation into a new phase, which has been described as related to cotunnite, PbCl 2 [12,13] .…”