Synergistic strategy for enhancing the thermoelectric properties of Mg2+-Zn2+ co-doped high-entropy fluorite-structured oxide ceramics

The inherent contradiction between electrical and thermal transport has restricted the development of thermoelectric materials. However, high-entropy ceramics with complex structures exhibit unique properties and are expected to overcome this limitation. Herein, the thermoelectric properties of high-entropy fluorite oxides (Zr 0.194 Ce 0.194 Pr 0.194 Y 0.194 Ho 0.194 Mg x Zn 0.03-x )O 2-δ (0 ≤ x ≤ 0.03) are systematically tuned through the Mg-Zn co-doping strategy. The optimal composition (x=0.015) achieves a ZT of 0.46 at 773   K, which was approximately 119% higher than the undoped sample, and about 58% and 41% over Mg-only and Zn-only doped samples. This enhancement results from Zn increasing electrical conductivity as a charge donor while Mg reduces thermal conductivity through point defect scattering, enabling the synergistic optimization of electrical/thermal performance. First-principles calculations reveal Zn induces band convergence and gap contraction, increasing the density-of-states effective mass and promoting electron delocalization. This work validates high-entropy design combined with defect engineering as an effective strategy for developing high-performance thermoelectric materials.