Highly thermally stable epitaxial high-entropy fluorite oxide thin films

While high-entropy fluorite oxides have shown promise for applications in extreme environments, achieving epitaxial integration with high thermal stability and structural coherence remains a significant challenge. Here, we report the synthesis of an epitaxial chemically disordered single-phase fluorite oxide thin film, (HfZrCeGdCa)O2, on a yttria-stabilized zirconia (YSZ) (100) substrate via pulsed laser deposition. Structural characterization by x-ray diffraction (XRD) and atomic-resolution scanning transmission electron microscopy imaging and energy-dispersive x-ray spectroscopy confirm the high crystalline quality and uniform elemental distribution of the film, validating its chemically disordered single-phase character. In situ temperature-dependent XRD shows the high thermal stability without phase separation and secondary phase formation up to 1200 °C. Reciprocal space mapping and strain analysis indicate coherent in-plane lattice matching with the YSZ substrate, accompanied larger out-of-plane lattice constant. Local lattice tilting, rotation, and interfacial dislocations are observed, suggesting partial strain relaxation close to the interface. These results underscore the structural integrity and thermal stability of the chemically disordered single-phase fluorite oxide films, supporting their potential use in advanced functional coatings for extreme environments.