High-entropy perovskite RETa₃O₉ ceramics for high-temperature environmental/thermal barrier coatings

Four high-entropy perovskite (HEP) RETa₃O₉ samples were fabricated via a spark plasma sintering (SPS) method, and the corresponding thermophysical properties and underlying mechanisms were investigated for environmental/thermal barrier coating (E/TBC) applications. The prepared samples maintained low thermal conductivity (1.50 W·m⁻¹·K⁻¹), high hardness (10 GPa), and an appropriate Young’s modulus (180 GPa), while the fracture toughness increased to 2.5 MPa·m^1/2. Nanoindentation results showed the HEP ceramics had excellent mechanical properties and good component homogeneity. We analysed the influence of different parameters (the disorder parameters of the electronegativity, ionic radius, and atomic mass, as well as the tolerance factor) of A-site atoms on the thermal conductivity. Enhanced thermal expansion coefficients, combined with a high melting point and extraordinary phase stability, expanded the applications of the HEP RETa₃O₉. The results of this study had motivated a follow-up study on tantalate high-entropy ceramics with desirable properties.