Enhanced Thermoelectric Performances Driven by High-Pressure Phase Transition of Mg2Sn Compound

The ground state properties of the Mg2Sn compound under seven different crystal structures were studied using a first principles approach based on the full-potential augmented plane wave method FP-LAPW within the GGA-PBEsol approximation. We fixed the cubic structure of CaF2-type as zero pressure phase and we have considered the orthorhombic PbCl2-type, hexagonal Ni2In-type, tetragonal Al2Cu-type, cubic MgCu2-type, hexagonal MgZn2-type and dihexagonal MgNi2-type as candidates structures for the high-pressure phases. We used Gibbs' equation to examine these high-pressure structures and compare their enthalpies. Thus, it appears that the Mg2Sn compound undergoes three pressure-induced phase transitions. First, it is a transition from the CaF2-type cubic structure to the orthorhombic PbCl2-type structure; second, the transition from the PbCl2-type structure to the hexagonal Ni2In-type structure; and third, the transition will take place toward the cubic structure MgCu2-type which should be stable. In addition, to further examine the thermoelectric performances of each stable phase, we combined the results calculated for the electronic properties by the TB-mBJ approximation with the semi-classical Boltzmann theory using the BoltzTraP code. Our key result is that Mg2Sn compound with cubic MgCu2-type structure has a high value of figure of merit (ZT(e)) compared to the cubic CaF2-type structure, which could promise it as an excellent candidate for potential thermoelectric applications at high pressure.