Control of the Thermoelectric Properties of Mg2Sn Single Crystals via Point-Defect Engineering

Mg2Sn is a potential thermoelectric (TE) material that can directly convert waste heat into electricity. In this study, Mg2Sn 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 Mg2Sn 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) x 10(-2) is realised for the Mg2Sn single-crystal ingot by introducing V-Mg. These results demonstrate that the TE properties of Mg2Sn can be optimised via point-defect engineering.