Control of the Thermoelectric Properties of Mg(2)Sn Single Crystals via Point-Defect Engineering

Mg(2)Sn is a potential thermoelectric (TE) material that can directly convert waste heat into electricity. In this study, Mg(2)Sn single-crystal ingots are prepared by melting under an Ar atmosphere. The prepared ingots contain Mg vacancies (V(Mg)) as point defects, which results in the formation of two regions: an Mg(2)Sn single-crystal region without V(Mg) (denoted as the single-crystal region) and a region containing V(Mg) (denoted as the V(Mg) region). The V(Mg) region is embedded in the matrix of the single-crystal region. The interface between the V(Mg) region and the single-crystal region is semi-coherent, which does not prevent electron carrier conduction but does increase phonon scattering. Furthermore, electron carrier concentration depends on the fraction of V(Mg), reflecting the acceptor characteristics of V(Mg). The maximum figure of merit zT(max) of 1.4(1) × 10(−2) is realised for the Mg(2)Sn single-crystal ingot by introducing V(Mg). These results demonstrate that the TE properties of Mg(2)Sn can be optimised via point-defect engineering.