Gravity-induced gradients in thermoelectric Mg2Si0.9925-xSnxSb0.0075

Ten samples of high-efficiency thermoelectric materials with nominal compositions Mg2.2Si0.3925Sn0.6Sb0.0075 and Mg2.2Si0.5925Sn0.4Sb0.0075 were prepared by induction melting, ball milling and spark plasma sintering (SPS). After SPS processing, all pellets were investigated for a potential compositional gradient in Si/Sn content by employing spatially resolved Seebeck coefficient measurements and X-ray powder diffraction including subsequent Rietveld refinement. The samples have gradients, with the Mg2Sn-rich phase being consistently in the bottom of all samples. Energy dispersive X-ray spectroscopy confirmed the results. The large difference in densities between the Mg2Sn-rich and the Mg2Si-rich phases is responsible for the creation of the gradient. The results propose a new way to utilize SPS processing in fabrication of functionally graded materials. Additionally, the Seebeck coefficient, thermal conductivity, electrical resistivity, and Hall carrier concentration are measured on two samples from each batch from room temperature to 400 degrees C. (c) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.