Mechanochemical synthesis and thermoelectric properties of high quality magnesium silicide

Magnesium silicide and related alloys are attractive for thermoelectric applications due to their low toxicity, thermal stability, low density, relative abundance and low cost of production. Earlier work on the synthesis of Mg2Si via high energy ball milling resulted in incomplete product formation, oxide impurities, and contamination from milling media. Here we present an improved solid-state synthesis of n-type magnesium silicide using the mechanochemical technique of high energy ball milling of the elements followed by high pressure sintering using hot uniaxial compaction. This robust synthetic method permits a detailed investigation of thermoelectric properties as a function of Bi doping. The thermoelectric properties of Mg2Si1-xBix (0 <= x <= 0.021) samples are characterized from 300 K to 775 K. These results are analyzed within a single parabolic band (SPB) model to determine the effective conduction band parameters and identify regimes of non-SPB behavior.