Thermoelectric Properties of p-Type Mg2Si0.25Sn0.75 Doped with Sodium Acetate and Metallic Sodium

Abstract

We have investigated the thermoelectric properties of p-type Na-doped Mg2 Si0.25Sn0.75 solid solutions prepared by liquid–solid reaction and hot-pressing methods. Na was introduced into Mg2Si0.25Sn0.75 by using either sodium acetate (CH3COONa) or metallic sodium (2 N). The samples doped with sodium acetate consisted of phases with antifluorite structure and a small amount of MgO as revealed by x-ray diffraction, whereas the sample doped with metallic sodium contained the Sn, MgO, and Mg2SiSn phases. The hole concentrations of Mg1.975Na0.025Si0.25Sn0.75 doped by sodium acetate and metallic sodium were 1.84 × 1025 m−3 and 1.22 × 1025 m−3, respectively, resulting in resistivities of 4.96 × 10−5 Ω m (sodium acetate) and 1.09 × 10−5 Ω m (metallic sodium). The Seebeck coefficients were 198 μV K−1 (sodium acetate) and 241 μV K−1 (metallic sodium). The figures of merit for Mg1.975Na0.025Si0.25Sn0.75 were 0.40 × 10−3 K−1 (sodium acetate) and 0.25 × 10−3 K−1 (metallic sodium) at 400 K. Thus, sodium acetate is a suitable Na dopant for Mg2Si1−xSnx.