Effect of nanocomposite structure on the thermoelectric properties of 0.7-at% Bi-doped Mg₂Si nanocomposite

Nanocomposites offer a promising approach to the incorporation of nanostructured constituents into bulk thermoelectric materials. The 0.7-at% Bi-doped Mg₂Si nanocomposites are prepared by spark plasma sintering of the mixture of nanoscale and microsized 0.7-at% Bi-doped Mg₂Si powders. Microstructure analysis shows that the bulk material is composed of nano- and micrograins. Although the nanograin hinders electrical conduction, the nanocomposite structure is more helpful to reduce thermal conductivity and increase the Seebeck coefficient, hence improving thermoelectric performance. A dimensionless figure of merit of 0.8 is obtained for the 0.7-at% Bi-doped Mg₂Si nanocomposite with 50-wt % nanopowder, which is about twice larger than that of the sample without nanopowder.