Thermoelectric Properties of Al-doped Mg2Si Compounds Prepared via Three Kinds of Process for Grain Refinement

Abstract

ABSTRACTDimagnesium silicide is an eco-friendly thermoelectric compound whose constituent elements of both Mg and Si are non-toxic and exist in abundance on the earth. In this study, we attempted to control the thermal conductivity of Al-doped Mg2Si by grain refinement. Three types of Si powders, i.e., commercial coarse powder, its pulverized powder and commercial fine powder were prepared for synthesizing the Al-doped Mg2Si. Mg powder and one of the Si powders were weighed with Mg/Si mole ratio of 67/33, and mixed with Al powder with amount of 0.1 at.%. The Al-doped Mg2Si compounds were synthesized using three different Si powders via a liquid-solid phase reaction process under unified synthesizing conditions. A part of the synthesized Mg2Si powder using the coarse Si powder was pulverized. Four kinds of Mg2Si powders were sintered by pulse discharge sintering method under unified sintering conditions. The sintered samples of the synthesized Mg2Si powders made from the fine and the milled Si powders and of the milled Mg2Si powder had the grain-refined microstructure. Especially, the sintered sample of the milled Mg2Si powder was effective for grain refinement and for reduction of thermal conductivity, and had the best thermoelectric performance of ZT = 1.15 at 873 K.