Synergistic Optimization of Thermal and Mechanical Properties in Ce–Sc Co-Doped High-Entropy Fluorite Zirconates for Advanced Thermal Barrier Coatings

High-entropy zirconates represent one of the most promising thermal barrier coatings (TBCs) materials. In this work, high-entropy fluorite zirconates were synthesized via a reverse coprecipitation route, and their structural, mechanical, and thermal properties were systematically evaluated. All compositions crystallized into single-phase fluorite structure. Sc incorporation enhances hardness, while Ce enrichment promotes thermal expansion behavior. Notably, the Ce-Sc co-doped composition ( x = 0.1) achieves a synergistic optimization of properties, exhibiting low grain growth rate (0.0437 μm·h -1 ), high fracture toughness (1.64 MPa·m 1/2 ), a desirable thermal expansion coefficient (11.65 × 10 -6 K -1 , RT-1500 °C), and ultralow thermal conductivity (0.93 W·m -1 ·K -1 at 1500 °C). The markedly reduced thermal conductivity originates from enhanced phonon scattering induced by severe lattice distortion in the high-entropy fluorite lattice. These findings highlight Ce-Sc co-doping as an effective strategy to simultaneously optimize mechanical and thermal behavior, making the ceramic a strong candidate for advanced TBCs applications under extreme environments.