Thermoelectric properties of p-type Mg2Si0.3Sn0.7 doped with silver and gallium

Abstract

Structure, composition, and transport properties of Mg2−xAgx(Si0.3Sn0.7)1−yGay (x = {0, 0.02}, y = {0, 0.02, 0.04, 0.06}) solid solutions produced by melting followed by spark plasma sintering are investigated. The preparation method is adjusted to control sample stoichiometry and phase composition. Doping with two types of dopants at different sites, while employing synthesis methods which generate a small amount of secondary phase, is an uncommon approach in this materials, expected to enhance their thermoelectric performance. An enhanced carrier concentration but diminished mobility is observed in the samples with higher amounts of dopant, which leads to the highest values of the power factor, for Mg1.98Ag0.02Si0.27Sn0.67Ga0.06 in a narrow temperature range (575–675 K) around the peak value, of 9.10−4 Wm−1 K−2 at 625 K. The two types of dopants have opposing effects on the thermal conductivity, with Ag promoting strong phonon scattering and decreasing its values while Ga increases them because of its enhanced carrier concentration. The rather high thermal conductivity values of the double doped compounds produce low values of the ZT without exceeding 0.29 at 627 K for Mg1.98Ag0.02Si0.3Sn0.7 sample.