Enhanced Thermoelectric Performance of Mg-Doped AgSbTe₂ by Inhibiting the Formation of Ag₂Te

The existence of Ag₂Te has always been an obstacle for p-type thermoelectric material AgSbTe₂ to improve its thermoelectric performance. In this work, AgSb_1-xMg_xTe₂ samples are synthesized by melting-slow-cooling and then spark plasma sintering (SPS). Through increasing the solubility of Ag₂Te in the AgSbTe₂ matrix by Mg doping, the formation of Ag₂Te is inhibited. Density functional theory calculations confirm more valence bands are involved in electrical transport due to Mg doping. Therefore, the electrical conductivity of AgSb_1-xMg_xTe₂ samples has been greatly improved due to the reduction of Ag₂Te with n-type electrical conductivity. Moreover, the downward trend of ZT, which is caused by the structural transition of Ag₂Te at about 418 K, disappears. Meanwhile, lattice defects form in the AgSb_0.98Mg_0.02Te₂ sample, and Mg doping improves the configurational entropy change, resulting in a decrease in lattice thermal conductivity over the entire temperature range of measurement. Finally, a high ZT value of 1.31 at 523 K is achieved for the AgSb_0.98Mg_0.02Te₂ sample. This study demonstrates that Mg doping can effectively improve AgSbTe₂ thermoelectric performance by inhibiting the formation of the Ag₂Te impurity phase.