Enhancing the Thermoelectric Performance of Mg₂Sn Single Crystals via Point Defect Engineering and Sb Doping

Mg₂Sn is a potential thermoelectric (TE) material that exhibits environmental compatibility. In this study, we fabricated Sb-doped Mg₂Sn (Mg₂Sn_1-Sb) single-crystal ingots and demonstrated the enhancement of TE performance via point defect engineering and Sb doping. The Mg₂Sn_1-Sb single-crystal ingots exhibited considerably enhanced electrical conductivity because of the donor-doping effect in addition to high carrier mobility. Moreover, the Mg₂Sn_1-Sb single-crystal ingots contained Mg vacancy (V_Mg) as a point defect. The introduced V_Mg and doped Sb atoms formed nanostructures, both acting as phonon-scattering centers. Consequently, lower lattice thermal conductivity was achieved for the Mg₂Sn_1-Sb single-crystal ingots compared with polycrystalline counterparts. Owing to the significant enhancement in the electrical conductivity and the reduction in the lattice thermal conductivity, the maximum power factor of 5.1(4) × 10^-3 W/(K² m) and the maximum dimensionless figure of merit of 0.72(5) were achieved for the Mg₂Sn_0.99Sb_0.01 single-crystal ingot, which are higher than those of single-phase Mg₂Sn_1-Sb polycrystals.