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

Abstract

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.