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Enhancing the Thermoelectric Performance of p-Type Mg3Sb2 via Co-doping of Li and Cd.

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 co-doped 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 of 300-773 K. Li is found to be an effective hole dopant, which leads to a zT of 0.46 at 773 K in Mg2.99Li0.01Sb2 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 Mg2.69Li0.01Cd0.5Sb2 achieving a maximum zT of ~0.68 at 773 K and an average zTave of ~0.32 over 300-773 K that compare very favorably to pristine Mg3Sb2. This study demonstrates that (Li, Cd) co-doping is an effective strategy to enhance the thermoelectric properties of p-type Mg3Sb2 materials.