Thermoelectric properties and electronic structure of p-type Mg 2Si and Mg 2Si 0.6Ge 0.4 compounds doped with Ga

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Mg 2Si:Ga x and Mg 2Si 0.6Ge 0.4:Ga x ( x = 0.4% and 0.8%) solid solutions have been synthesized by direct melting in tantalum crucibles and hot pressing. The effect of Ga doping on the thermoelectric properties has also been investigated by measurements of thermopower, electrical resistivity, Hall coefficient and thermal conductivity in temperature range from 300 to 850 K. All samples exhibit a p-type conductivity evidenced by positive sign of both thermopower and Hall coefficient in the investigated temperatures. The maximum value of the dimensionless figure of merit ZT was reached for the Mg 2Si 0.6Ge 0.4:Ga(0.8%) compound at 625 K (ZT ∼ 0.36). The p-type character of thermoelectric behaviours of Ga-doped Mg 2Si and Mg 2Si 0.6Ge 0.4 compounds well corroborates with the results of electronic structure calculations performed by the Korringa–Kohn–Rostoker method and the coherent potential approximation (KKR-CPA), since Ga diluted in Mg 2Si and Mg 2Si 0.6Ge 0.4 (on Si/Ge site) behaves as hole donor due to the Fermi level shifted to the valence band edge. The onset of large peak of DOS from Ga impurity at the valence band edge, well corroborates with high Seebeck coefficient measured in Ga-doped samples.