Effect of Synthesis and Sintering Conditions on the Thermoelectric Properties of n-Doped Mg2Si

Magnesium silicide (Mg2Si)-based alloys are promising candidates for thermoelectric (TE) energy conversion in the middle-high temperature range. The detrimental effect of the presence of MgO on the TE properties of Mg2Si based materials is widely known. For this reason, the conditions used for synthesis and sintering were optimized to limit oxygen contamination. The effect of Bi doping on the TE performance of dense Mg2Si materials was also investigated. Synthesis was performed by ball milling in an inert atmosphere starting from commercial Mg2Si powder and Bi powder. The samples were consolidated, by spark plasma sintering, to a density > 95%. The morphology, and the composition and crystal structure of samples were characterized by field-emission scanning electronic microscopy and x-ray diffraction, respectively. Moreover, determination of Seebeck coefficients and measurement of electrical and thermal conductivity were performed for all the samples. Mg2Si with 0.1 mol% Bi doping had a ZT value of 0.81, indicative of the potential of this method for fabrication of n-type bulk material with good TE performance.