Quantitative analysis of interstitial Mg in Mg2Si studied by single crystal X-ray diffraction

We investigate the existence of Mg at an interstitial (1/2 1/2 1/2) site of Mg-deficient Mg2Si samples, whose nominal composition is Mg2−xSi (x = 0, 0.095, 0.182, 0.260, and 0.333). Single-crystal X-ray diffraction measurements indicate that the interstitial Mg (Mgi) is contained in all samples, and its occupancy is around 0.5% regardless of x. This result is supported by the Hamilton test: a hypothesis that the Mgi exists in the Mg2−xSi samples is not rejected at the significant level below 0.10. On the other hand, the Mg occupancy at an (1/4 1/4 1/4) site tends to decrease with increasing x. The Seebeck coefficient and electrical conductivity of Mg2−xSi is discussed in terms of the x dependence of Mgi (1/2 1/2 1/2) and Mg (1/4 1/4 1/4) site occupancies.