Simultaneous improvement of power factor and thermal conductivity via Ag doping in p-type Mg3Sb2 thermoelectric materials

Mg3Sb2-based Zintl compounds are potential thermoelectric materials for power generation due to their earth-abundant component elements. Pure Mg3Sb2, however, exhibits an intrinsically low p-type carrier concentration at room temperature. Density functional theory calculations of p-type Mg3Sb2 suggest that the carrier density can be tuned by doping at the Mg sites without significant modification of the valence bands, and the optimal doping concentration is predicted to be 4.0 x 10(19) cm(-3). Herein we have successfully synthesized Ag-doped Mg3Sb2 samples by a one-step spark plasma sintering method. All Ag-doped samples display an increased carrier concentration and enhanced Hall mobility relative to the undoped sample, leading to a significant decrease in the electrical resistivity. As a result of simultaneous improvements in the power factor and thermal conductivity, the zT values of the Ag-doped samples are strongly enhanced; an optimum value of 0.51 at 725 K in Mg2.985Ag0.015Sb2 is achieved, which is a factor of 2.4 larger than that of the undoped sample. The average zT is estimated to be 0.21 in Mg2.985Ag0.015Sb2, which is superior to the previous report on Na-doped Mg3Sb2. Thus, Ag-doped Mg3Sb2 is a promising candidate for intermediate-temperature power generation.