Synergistic effects of Mg vacancy and Ag doping on thermoelectric transport properties of p-type Mg3Sb2

Abstract

The defect formation energy and the electronic structures of Ag-doped Mg3-x-yAgySb2 alloys were accurately determined by carrying out first-principles calculations. The relevant crystals were prepared by using the directional solidification method and their thermoelectric properties were thoroughly investigated. From the calculated outcomes, it was demonstrated that Mg1 sites tend to form a vacancy, while Mg2 sites are preferentially substituted by the Ag atoms. The top values of the electrical conductivity and the power factor of the Mg2.95Ag0.025Sb2 alloy were improved by 25% and 10%, respectively. The increased point defect content is beneficial for enhancing the phonon scattering. In addition, the maximum ZT value of the Mg2.95Ag0.025Sb2 alloy was 1.1 – 1.45 times higher than that of the previously reported Ag-doped crystals. In the medium temperature range, the ZT values remained above 0.5, which is also considered a significant improvement compared with other types of p-type Mg3Sb2 alloys reported in the literature.