Thermoelectric performance improvement of p-type Mg₃Sb₂-based materials by Zn and Ag co-doping

Mg₃Sb₂-based Zintl compounds have attracted extensive attention as potential thermoelectric materials due to their earth-abundant elements. However, pure and intrinsic p-type Mg₃Sb₂ manifests a poor thermoelectric performance because of its high electrical resistivity. It is reported that Ag doping in Mg sites can increase the mobility and carrier concentration of p-type Mg₃Sb₂; however, high thermal conductivity still limits the improvement of the ZT value. In the present work, Zn and Ag co-doping in Mg sites was carried out to optimize the thermoelectric performance of p-type Mg₃Sb₂. Experimental results revealed that the carrier concentration and mobility of Mg₃Ag_0.01Sb₂ significantly increased after Zn doping, leading to an improvement of the power factor. Simultaneously, lattice thermal conductivity was significantly reduced due to the large mass difference between Zn and Mg. The Mg_2.39Zn_0.6Ag_0.01Sb₂ sample with an optimal doping concentration of 3.95 × 10¹⁹ cm⁻³ achieved a maximum ZT value of 0.84 at 773 K. Hence, Zn and Ag co-doping is an effective method to improve the thermoelectric performance of p-type Mg₃Sb₂.