Inhomogeneities and Effective Mass in Doped Mg2Si

Abstract

Magnesium silicide (Mg2Si)-based materials are promising candidates as thermoelectric components for mid-temperature range (500–900 K) energy conversion. Many different approaches for determining the parabolicity of the conduction band have been suggested in the literature, while the values of the effective mass m* dL reported, lie between 0.46 and 1.1 m0. The aim of this work is to contribute in elucidating the discrepancy observed in the effective mass values of the lower conduction band of highly doped Mg2Si and examine whether this discrepancy could be attributed to the method of determination or to the sample’s characteristics. We present the results of effective mass calculations at room temperature (RT) by applying different experimental methods and models (parabolic and non-parabolic) in two different groups of samples; one yielding profound inhomogeneities (Sb-doped) and one yielding homogeneous (Bi-doped) samples. Concluding this analysis, it seems that the lower conduction band of Mg2Si is more likely described as non-parabolic. Comparing the two groups of samples, our analysis indicated that the effective mass may be significantly underestimated for samples with dopant and content-modulated composition.