Effect of Bi-doping and Mg-excess on the thermoelectric properties of Mg2Si materials

•Bi-doped Mg2Si was synthesized by ball-milling, heating and hot pressing.•The maximum value of ZT for Mg2Si0.97Bi0.03 was found to be 0.68 at 810 K.•Mg excess compensates the lower Bi concentration and the materials present similar ZT.

In this work, Bi-doped magnesium silicide compounds were prepared by applying a combination of both, short-time ball milling and heating treatment. The effect of Mg excess was also studied, aiming towards further improvement in thermoelectric properties. The structural modifications of all materials were followed by Powder X-ray diffraction and Scanning Electron Microscopy. Highly dense pellets of Mg2Si1−xBix (0≤x≤0.035) and Mg2+δSi0.975Bi0.025 (δ=0.04, 0.06 and 0.12) were fabricated via hot pressing and studied in terms of Seebeck coefficient, electrical and thermal conductivities and free carrier concentration. Their thermoelectric performance, at high temperature range, is presented and the maximum value of the dimensionless-figure-of-merit (ZT) is found to be 0.68 at 810 K, for Mg2Si0.97Bi0.03.