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Magnesium tin silicide based thermoelectrics contain earth abundant and non-toxic elements, and have the potential to replace established commercial thermoelectrics for energy conversion applications. In this work, porosity was used as a means to improve their thermoelectric properties. Compared to dense samples of Sb doped Mg2Si0.5Sn0.5 with a maximum zT of 1.39 at 663 K, porous samples (37% porosity) prepared by a pressure-less spark plasma sintering technique showed significantly lower thermal conductivity and higher Seebeck coefficient, resulting in an increased maximum zT of 1.63 at 615 K. The possible origins of the enhanced Seebeck coefficient can be attributed to a change of carrier concentration and modification of the band structure, produced by microstructural engineering of the surface composition and particle–particle contacts.

Spark plasma sintering (SPS) is a versatile and effective rapid processing technique to sinter nanostructured thermoelectric (TE) materials. This paper presents a combined experimental and modelling investigation of the Peltier effect during SPS processing of TE materials. The Peltier effect is related to the transport of heat by an electric current and produces a temperature gradient. This heat flow manifests itself at the junction between two dissimilar materials at which heat is evolved or absorbed. During SPS processing, the Peltier effect could manifest itself as a significant temperature gradient across the sample. The Peltier effect was found to produce a temperature gradient of 55 °C during the SPS processing of MgSi2 (ZT = 1.4, 3 mm sample thickness) and 60 °C for MnSi1.4 (ZT = 0.4, 3 mm sample thickness). The overall developed experimental and numerical methodology allowed us to confirm the existence of the Peltier effect and to quantify its magnitude. This enabled us to determine a correlation between the SPS process parameters and temperature gradient across the processed TE materials.