High-entropy rare-earth oxide ceramics for next-generation thermal and environmental barrier coatings: A comprehensive review

As turbine-inlet temperatures in advanced aero-engines and heavy-duty gas turbines continue to rise, conventional thermal and environmental barrier coatings (TBCs/EBCs) are increasingly confronted with critical operational bottlenecks. They are increasingly plagued by deleterious high-temperature phase transformations, thermal expansion mismatch with substrates, and catastrophic degradation induced by molten calcium-magnesium-aluminosilicate (CMAS) and water-vapor corrosion. To decisively break these inherent limitations, high-entropy rare-earth oxides (HEREOs) have rapidly emerged as a revolutionary materials paradigm. Driven by configurational entropy stabilization, severe lattice distortion, and sluggish diffusion effects, HEREOs uniquely synchronize ultra-low thermal conductivity, tailorable thermal expansion coefficients, and exceptional chemical inertness within a single crystal lattice. This comprehensive review systematically navigates the cutting-edge advancements of HEREOs for next-generation hot-section protection. It first demystifies the intricate process–microstructure relationships during coating deposition, highlighting non-equilibrium phase evolution induced by thermal spraying. Subsequently, it critically dissects high-temperature phase stability, multiscale defect-engineered thermophysical properties, and intricate failure mechanisms under CMAS and water-vapor attacks. Notably, to counteract the intrinsic brittleness and improve the inferior fracture toughness of HEREOs, advanced structural engineering—incorporating multiphase synergistic toughening and gradient architectures—is highlighted as a crucial strategy for enhancing thermal shock durability. Finally, transitioning from empirical trial-and-error to a predictive framework, this review envisions a machine learning-empowered inverse design paradigm, offering a data-driven roadmap for the multi-objective optimization and lifetime prediction of highly robust HEREO coatings. This contribution also statistically outlines the latest research trends, offering researchers forward-looking guidance and evidence-based references.