Solid-State Synthesis of Thermoelectric Materials in Mg–Si–Ge System

Solid solution Mg 2 Si 1 - x Ge x for various concentration of germanium, x, is successfully prepared in single phase by the bulk mechanical alloying (BMA) and the hot pressing (HP). Both BMA and HP process conditions were optimized to yield high dense samples with fine, homogeneous microstructure. The electrical conductivity, the Seebeck coefficient and the thermal conductivity are measured from room temperature up to about 700 K. The Seebeck coefficient is much sensitive to the germanium content, x in Mg 2 Si 1 - x Ge x . The pn-transition takes place at x = 0.35 where the Seebeck coefficient drastically changes its sign. The measured band gap of Mg 2 Si 1 - x Ge x decreases with x from 0.71 to 0.54 eV. The figure of merit at 613 K of Mg 2 Si 0 . 6 Ge 0 . 4 reaches 0.34 x 10 - 3 K - 1 in the case of BMA for N = 600 and HP at 773 K by 1 GPa for 3.6 ks.