Synthesis, processing and transport properties of cubic and trigonal solid solutions in the Mg-Si-Sn system

Mg-Si-Sn solid solutions have interesting and useful semiconducting properties particularly for thermoelectric applications. While cubic solid solutions have been prepared by a variety of methods, solid solutions with a trigonal crystal structure have not been reported. We employed a combination of high energy ball milling and current activated pressure assisted densification (CAPAD) to induce and complete phase transformation from cubic to trigonal phase, forming dense trigonal composites. This is the first successful preparation of the trigonal phase in Mg-Si-Sn system. In addition, we report the transport properties of both the cubic and trigonal composites measured in the 160-400 K range. The electrical conductivity of the trigonal composites was several times higher compared to the cubic counterparts while thermal conductivity is lower but in the range of previously reported Mg-Si-Sn materials. The Seebeck coefficient of the trigonal composites is lower compared to the cubic samples, leading to low ZT values. The ZT of the cubic samples, however is higher than previously reported for un-doped Mg-Si-Sn solid solutions which is promising for thermoelectric applications.