Influence of the synthesis parameters on the transport properties of Mg2Si0.4Sn0.6 solid solutions produced by melting and spark plasma sintering

In this work, the influence of the preparation route on the structural, morphological, and thermoelectric properties of the Mg2Si0.4Sn0.6 solid solutions is investigated. The synthesis based on melting the constituent elements in a closed graphite crucible followed by spark plasma sintering allows mixing elements with a large difference of their melting temperatures and a good control of sample stoichiometry. The optimized synthesis route is validated by the doped V and Sb samples, which yield good thermoelectric performance. The n-type doping leads to two orders of magnitude increase of the carrier concentration, and thus a subsequent increase of the electrical conductivity, which, in turn, augments greatly the power factor of the Mg1.98V0.02Si0.385Sn0.6Sb0.015 to 42.61 x10−4 Wm−1K−2 at 650K. Although doping slightly enlarges the thermal conductivity, a peak value of the figure of merit ZT∼1.15 is obtained at 723K, which is 20 times higher than the ZT of un-doped material.