Non-wetting crystal growth of Mg 2Si by vertical Bridgman method and thermoelectric characteristics

Abstract

Magnesium siliside (Mg 2Si) crystals have been grown using the vertical Bridgman method in a non-wetting growth environment, achieved by the use of an anti-adhesion coating on the crucible wall. The minimized adhesion of highly reactive molten magnesium (Mg), silicon (Si) and Mg 2Si permitted easy removal of the grown ingot from the crucible, and the external shape of the grown ingot followed the shape of inner wall of the crucible. The grown crystals were a single phase of polycrystalline Mg 2Si. X-ray analysis, such as Laue back-reflection and Lang transmission topographs revealed that grains obtained were single crystal in nature. Process induced contaminants were investigated by using grow discharge mass spectrometry (GDMS). The grown crystals exhibited n-type conductivity, which could result from the residual impurities in the Mg source material used and unintentional impurity incorporation during growth. Since Mg 2Si is a material candidate for thermal-to-electric energy-conversion, the thermoelectric properties such as Seebeck coefficient, S, electrical conductivity, σ, and thermal conductivity, κ, were measured as a function of temperature up to 873 K. Die-casting process induced characteristics of such thermoelectric properties are discussed. The maximum dimensionless figure-of-merit was estimated to be 0.17 at 656 K.