Thermoelectric Properties of Mg 2 Si 1-x-y Ge x Sb y Prepared by Spark Plasma Sintering

The magnesium compound Mg2Si and its solid solutions are expected as n-type thermoelectric (TE) material because they are non-toxic, have a large Clarke number, and are light weight. In this study, we improved TE performance by doping Ge into Sb-doped Mg2Si to cause phonon scattering and increase carrier concentration. A bulk of Sb-doped Si-Ge alloy as the raw material was fabricated using an arc-melting method. A high-purity Mg2Si was synthesized from metal Mg and Sb-doped Si-Ge alloy using spark plasma sintering equipment. For the samples with the same Sb concentration, the electrical conductivity was equivalent. On the other hand, the Seebeck coefficient was dependent on Ge concentration. Due to phonon scattering, thermal conductivity decreased by a small amount of Ge doping and κ ph dominated for thermal conduction. The minimum thermal conductivity of Mg2Si0.90Ge0.10 was 2.25 W/mK (κ ph : 2.06 W/mK, κ el : 0.19 W/mK). The dimensionless figure of merit (ZT) for the Mg2Si0.945Ge0.05Sb0.005 sample was higher than that of the others due to reducing thermal conductivity and increasing carrier concentration. The maximum ZT was 0.47 at 713 K.