Revealing the Thermophysical Behavior of Fluorite-Type High-Entropy Ceramics for Advanced Thermal Barrier Coating Applications

Taking advantage of the ionic size and mass disorder as component design criteria, three novel high-entropy rare-earth zirconate ceramics, including (Sm0.2Gd0.2Dy0.2Er0.2Tm0.2)2Zr2O7, (Gd0.2Dy0.2Ho0.2Er0.2Tm0.2)2Zr2O7 and (Gd0.2Dy0.2Ho0.2Er0.2Yb0.2)2Zr2O7, with single-phase fluorite structure were successfully synthesized. All compositions exhibited enhanced mechanical properties, with Vickers hardness and fracture toughness increasing as the grain size decreased. (Gd0.2Dy0.2Ho0.2Er0.2Yb0.2)2Zr2O7 demonstrated superior mechanical performance, achieving values of 11.41 ± 0.40 GPa and 1.78 ± 0.12 MPa·m1/2, respectively. The thermal expansion coefficients at 1000 °C ranged from 10.80 × 10−6 K−1 to 11.39 × 10−6 K−1, which is proportional to the average ionic bond length. Notably, (Sm0.2Gd0.2Dy0.2Er0.2Tm0.2)2Zr2O7 exhibited low room-temperature thermal conductivity (1.58 W·m−1·K−1) due to pronounced size and mass disorder, without compromising structural stiffness. These findings highlight the potential of high-entropy design for advanced thermal barrier coatings.