Thermoelectric performance of n-type Mg(2)Ge

Magnesium-based thermoelectric materials (Mg(2)X, X = Si, Ge, Sn) have received considerable attention due to their availability, low toxicity, and reasonably good thermoelectric performance. The synthesis of these materials with high purity is challenging, however, due to the reactive nature and high vapour pressure of magnesium. In the current study, high purity single phase n-type Mg(2)Ge has been fabricated through a one-step reaction of MgH(2) and elemental Ge, using spark plasma sintering (SPS) to reduce the formation of magnesium oxides due to the liberation of hydrogen. We have found that Bi has a very limited solubility in Mg(2)Ge and results in the precipitation of Mg(2)Bi(3). Bismuth doping increases the electrical conductivity of Mg(2)Ge up to its solubility limit, beyond which the variation is minimal. The main improvement in the thermoelectric performance is originated from the significant phonon scattering achieved by the Mg(2)Bi(3) precipitates located mainly at grain boundaries. This reduces the lattice thermal conductivity by ~50% and increases the maximum zT for n-type Mg(2)Ge to 0.32, compared to previously reported maximum value of 0.2 for Sb-doped Mg(2)Ge.