Thermoelectric properties and oxidation behaviour of Magnesium Silicide

We study the oxidation behaviour of Mg2Si and the thermoelectric properties of Mg2Si composites. Above 723 K, Mg2Si reacts with O2 in air to yield MgO and Si. Using the Johnson-Mehl-Avrami (JMA) equation, the Avrami exponent (n) is equal to ~0.5, and it depends on the reaction temperature and time; this indicates that the oxidation is controlled by the diffusion-controlled reaction. In order to improve the oxidation-resistance of Mg2Si, β-FeSi2 films were fabricated on sintered Mg2Si samples by RF magnetron-sputtering deposition at RT followed by post-annealing at 873 K in vacuum. The β-FeSi2 layer effectively prevented the diffusion of oxygen at 873 K and improved the oxidation resistance of Mg2Si. The thermoelectric properties of impurity-doped Mg2Si composites fabricated using the reduction method of metal oxide / carbonate / hydroxide additives (Al2O3, Sb2O3, Bi2O3, Li2CO3, CuO, Ag2O, In2O3, La(OH)3, Ga2O3, Na2CO3, and Y2O3) have been characterized. The maximum values of ZT for impurity-doped Mg2Si composites fabricated using the reduction method of Al2O3, Bi2O3, Sb2O3, and La(OH)3 additives show 0.58 at 862 K, 0.68 at 864 K, 0.63 at 863 K, and 0.06 at 865 K, respectively.