Enhancing the thermoelectric efficiency in p-type Mg3Sb2via Mg site co-doping

Mg3Sb2 based Zintl compounds are promising thermoelectric materials due to the abundance of magnesium and antimony in nature. However, the main hindrance in realizing the full potential of Mg3Sb2 compounds for thermoelectric applications is the low figure of merit (zT) of p-type Mg3Sb2, in comparison with its n-type counterpart. We report here the enhancement of the thermoelectric properties of p-type Cu and Ag co-doped Mg3Sb2 processed by a solid-state synthesis route. The samples contain α-Mg3Sb2 as a major phase along with elemental Sb as a minor phase. The doped Mg3Sb2 compounds are thermally stable up to 773 K, irrespective of the presence of a small amount of Sb. The co-doping of Ag and Cu in Mg3Sb2 is found to enhance the power factor to 0.8 mW mK−2 and the thermoelectric figure of merit to 0.76 at 673 K. This is the highest figure of merit among doped p-type Mg3Sb2 compounds reported to date. The rattling of the heavy atoms in co-doped Mg3Sb2 is found to significantly reduce the lattice thermal conductivity, which enhances the thermoelectric figure of merit. This work proposes an effective strategy to enhance the zT of p-type Mg3Sb2via Cu–Ag co-doping at Mg sites.