  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 stem. In addition, we report the
transport properties of both the cubic and trigonal composites measured in the
160 to 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.
