Synergistic Zn/Cu Co-doping Engineering for Concurrent Optimization of Carrier Transport and Lattice Thermal Conductivity in p-Type Mg₃Sb₂

p-Type Mg₃Sb₂ possesses strong thermoelectric potential, yet effective strategies to further enhance its performance remain underexplored. In this study, we investigated the p-type Zintl-phase compound Mg₃Sb₂ and proposed a Zn/Cu co-doping strategy to synergistically optimize carrier transport and lattice thermal conductivity. Mg_3.1−xZn_xSb₂ and Mg_2.3−yZn_0.8Cu_ySb₂ series samples were prepared via high-energy ball milling followed by hot pressing. First-principles calculations reveal that substituting Mg sites with Zn and Cu induces pronounced band-structure modulation, shifting the Fermi level into the valence band and narrowing the bandgap. These effects collectively increase hole concentration and enhance electrical conductivity. Meanwhile, the mass fluctuation and local lattice distortion introduced by co-doping intensify phonon scattering, resulting in a substantial reduction in lattice thermal conductivity. Experimentally, Zn/Cu co-doping delivers a well-balanced optimization of thermoelectric transport properties. The Mg_2.2Zn_0.8Cu_0.1Sb₂ sample achieves a power factor of 351.99 μW cm⁻¹ K⁻² and a peak ZT of 0.42 at 735 K, corresponding to a 147% improvement compared with the undoped sample. This work elucidates the synergistic effects of Zn/Cu co-doping in electronic band engineering and phonon modulation, offering a promising strategy for the rational design of high-performance p-type Mg₃Sb₂ and other Zintl-phase thermoelectric materials.