Kinetics of densification/phase transformation and transport properties of Mg-Sn cubic/trigonal composites

Abstract

The Mg-Sn materials are interesting because of useful semiconducting properties and particularly because of their earth abundant, environmentally friendly constituent elements. The cubic Mg2Sn phase appears in the equilibrium phase diagram and has been extensively studied, while the transport properties of the trigonal phase—that does not appear in the phase diagram—have not been reported. We produced dense composites composed of cubic (stable) and trigonal (metastable) phases using a combination of high energy ball milling and current activated pressure assisted densification (CAPAD). We present a kinetic study of the densification and cubic to trigonal phase transformation. In addition, we present transport property measurements of cubic/trigonal composites. We determine densification rates and observe distinct densification regimes, attributed to the cubic-to-tetragonal phase transformation as well as porosity removal. Transport property measurements reveal that altering the amount of metastable phase in the composites changes both the electrical and thermal properties. The electrical conductivity significantly increases with increasing trigonal phase fraction. The thermal conductivities are similar for all compositions, which is likely due to the nanocrystalline character of the composites.