Thermal Stability of Mg₂Si_0.6Sn_0.4 under Oxidation Conditions

The use of Mg₂Si_0.6Sn_0.4 under air in thermoelectric modules in the mid-temperature range of 400-600 °C is linked to its ability to resist oxidation. In this study, oxidation experiments performed at 400 °C under air evidenced the stability of the material, either under static conditions (up to 100 h) or under severe heating-cooling cyclic conditions (up to 400 cycles), showing its ability to be used in a reliable way at this temperature. By combining thermogravimetry, scanning electron microscopy, temperature X-ray diffraction analysis, and mechanical and thermodynamic considerations, a mechanism is proposed explaining how Mg₂Si_0.6Sn_0.4 further undergoes decomposition with time under air when treated above 500 °C. The presence of Sn and the formation of various oxides are the key parameters of the material's degradation.