Electronic Orbital Alignment and Hierarchical Phonon Scattering Enabling High Thermoelectric Performance p-Type...

Environmentally friendly Mg₃Sb₂-based materials have drawn intensive attention owing to their promising thermoelectric performance. In this work, the electrical properties of p-type Mg₃Sb₂ are dramatically optimized by the regulation of Mg deficiency. Then, we, for the first time, found that Zn substitution at the Mg2 site leads to the alignment of p and p orbital, resulting in a high band degeneracy and the dramatically enhanced Seebeck coefficient, demonstrated by the DFT calculations and electronic properties measurement. Moreover, Zn alloying decreases Mg1 (Zn) vacancies formation energy and in turn increases Mg (Zn) vacancies and optimizes the carrier concentration. Simultaneously, the Mg/Zn substitutions, Mg vacancies, and porosity structure suppress the phonon transport in a broader frequency range, leading to a low lattice thermal conductivity of ~0.47 W m^-1 K^-1 at 773 K. Finally, a high ZT of ~0.87 at 773 K was obtained for Mg_1.95Na_0.01Zn₁Sb₂, exceeding most of the previously reported p-type Mg₃Sb₂ compounds. Our results further demonstrate the promising prospects of p-type Mg₃Sb₂-based material in the field of mid-temperature heat recovery.