ICT2014 Abstracts

　An important aspect of magnesium silicide (Mg₂Si) is its capability for being doped in order to modify its electrical conductivity, thermal conductivity and durability at elevated operating temperatures. Some features of Mg₂Si can broaden its application in the field of thermoelectric devices and encourage the development of a possible system for waste heat recovery.

　As a promising impurity in Mg₂Si, antimony (Sb) has been dominantly used in our previous experiments, enabling in practical terms an impeccable power factor of ~3.5x10^-3 W/mK² (600~900 K) and a ZT value of ~1.05 at 873 K. Sb-doping also provided satisfactory thermal durability, showing low and stable electrical resistivity characteristics at 873 K in atmosphere for up to 1000 h, though such samples were difficult to sinter to a high density with no cracking.

　To modify the fabrication process and the thermoelectric properties of Mg₂Si doped solely with Sb, an isoelectric impurity of zinc (Zn) was incorporated as a supplementary dopant. The concentrations of co-doped Sb and Zn were varied from 0.5 to 1.0 at%, respectively, and both elements were introduced into a congruent melt of Mg₂Si using the “All Molten Synthesis” method. The resultant polycrystalline Mg₂Si was pulverized and then sintered using a “Plasma Activated Sintering” (PAS) technique. Although material doped solely with Sb produced low yields in terms of specimens without cracks, almost all of the co-doped specimens typically had no cracks and a relative density of 98% or more, indicating that the reproducibility was better than that of simple Sb-doped samples. The 500 hours durability test at 873K in atmosphere exhibited no notable drop in electrical resistivity for all co-doped samples. The highest ZT value was 0.85 in an [Sb 1.0 at% + Zn 0.5 at%] co-doped sample. This value was higher than that of an [Sb 0.5 at%] sample.