2021 Volume 62 Issue 6 Pages 871-879
Improving the oxidation resistance of Mg2Si is important for its practical use in thermoelectric devices. The oxidation behavior of Sb-doped Mg2Si with and without added Al2O3 or Al under heating from 293 K to 1023 K in a 200 Pa water vapor atmosphere was observed by using an environmental scanning electron microscope (E-SEM). Compositional analysis before and after in situ oxidation in the E-SEM was performed by energy-dispersive X-ray analysis (EDX). The depth profile of the samples after thermal oxidation in the E-SEM was evaluated by X-ray photoelectron spectroscopy (XPS). The dimensionless figure of merit of Sb-doped Mg2Si with added Al2O3 or Al was also evaluated. The oxidation onset temperature was 603 K for Mg2Si, and 747 K to 793 K for Mg2Si with 0.8 to 4.5 mol% Al2O3 added or 4.0 at% Al added. The O concentration after oxidation at 873 K as measured by EDX (accelerating voltage: 3 kV) was 35.85 at% without Al2O3 or Al addition, but 11.55 at% to 13.80 at% with Al2O3 or Al addition. The Si concentration after oxidation at 873 K as measured by EDX (accelerating voltage: 3 kV) was 0.30 at% when no Al2O3 or Al was added to the Mg2Si, but 15.32 to 20.97 at% with Al2O3 or Al addition. Evaluation by XPS revealed a layer with a relatively high concentration of aluminum oxide or aluminum at a depth of about 20 nm from the surface of the Mg2Si sample with added Al2O3 or Al, respectively. This layer appears to suppress Mg2Si oxidation. The addition of Al2O3 or Al had a slightly positive effect on the thermoelectric properties of Mg2Si.
