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

Abstract

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 × 10¹⁹ 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 Mg_2.985Ag_0.015Sb₂ 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 Mg_2.985Ag_0.015Sb₂, which is superior to the previous report on Na-doped Mg₃Sb₂. Thus, Ag-doped Mg₃Sb₂ is a promising candidate for intermediate-temperature power generation.