Enhancing the Thermoelectric Performance of p-Type Mg₃Sb₂ via Codoping of Li and Cd

The Zintl compound Mg₃Sb₂ is a promising thermoelectric material with Earth-abundant components. Compared to its n-type counterpart, p-type Mg₃Sb₂ reveals lower dimensionless figure of merit (zT), principally due to the inferior electronic properties. Herein, p-type Mg₃Sb₂ materials codoped with Li and Cd have been synthesized via a ball milling plus hot pressing method, and their thermoelectric properties are systematically investigated within the temperature range 300-773 K. Li is found to be an effective hole dopant, which leads to a zT of 0.46 at 773 K in Mg_2.99Li_0.01Sb₂ that doubles the zT of Mg₃Sb₂. Additional Cd doping further increases carrier mobility ascribed to the weakened polar covalent bonding and diminishes the lattice thermal conductivity simultaneously due to the introduced atomic mass contrast between Cd and Mg. Eventually, the optimized power factor combined with the reduced thermal conductivity has significantly improved the thermoelectric performance of p-type Mg₃Sb₂, with Mg_2.69Li_0.01Cd_0.5Sb₂ achieving a maximum zT of ∼0.68 at 773 K and an average zT_ave of ∼0.32 over 300-773 K that compare very favorably to those of pristine Mg₃Sb₂. This study demonstrates that (Li, Cd) codoping is an effective strategy to enhance the thermoelectric properties of p-type Mg₃Sb₂ materials.