Effect of Impurity Doping on Thermoelectric Properties of Melt-Grown Mg₂Sn Crystals

Abstract

We investigated the thermoelectric properties of melt-grown Mg₂Sn crystals doped with various impurities such as Al, Bi, Sb, P, In, Ag, Au, W, and Mo; a large difference in the carrier concentration was observed for each impurity. The Bi- and Sb-doped Mg₂Sn crystals showed n-type conductivity and had enough electron concentrations in the order of 10¹⁹ cm^-3 by doping, and the maximum figure of merit (ZT) of 0.35 was observed in the crystal doped with 1.5 at% of Bi at 550 K. The Ag-, P-, In-, Au-, W-, and Mo-doped materials exhibited p-type conductivity. The Ag-doped samples had sufficient hole concentrations of more than 10¹⁹ cm^-3, and the ZT reached 0.25 in the sample doped with 1.0 at% of Ag at 450 K. The P- and Sb-doped Mg₂Sn crystals became dark gray powder within 1–2 weeks, but the crystals doped with the other impurities did not. This result suggested that the oxidation resistance of Mg₂Sn crystals varied greatly depending on the type of dopant impurity.