The Effect of Ge on Mg2Si0.6−x Sn0.4Ge x Materials

Abstract

In this work, we investigate the influence of the introduction of Ge on the thermoelectric properties of Bi-doped quaternary Mg2Si0.6−x Sn0.4Ge x alloys. Mg2Si0.58−x Sn0.4Bi0.02Ge x materials were fabricated by a low temperature reaction method, followed by hot pressing. Structure and phase composition of the obtained hot-pressed pellets were observed by x-ray diffraction. Morphology and chemical composition were monitored by scanning electron microscopy equipped with energy-dispersive x-ray spectroscopy. The results indicate a natural tendency of the material to phase separate into Si-rich, Sn-rich, and Ge-rich regions, which seem to become finer in size with Ge concentration. The compounds have been characterized by electrical conductivity, Seebeck coefficient, and thermal conductivity measurements in the temperature range of 300–823 K. The effect of Ge in the lattice thermal conductivity is discussed in terms of solid solution formation as well as effective medium theory.