Study on high-entropy rare-earth zirconate ceramics for thermal barrier coatings: High-temperature phase stability, thermophysical and mechanical properties

With the rapid development of aerospace technology, there is a growing demand for complex thermal barrier coatings (TBCs) with excellent high-temperature stability, thermophysical and mechanical properties. Based on the ionic radius size disorder as a guideline for component design, three high-entropy rare-earth zirconate ceramics were successfully designed and synthesized in this study: (Nd0.2Sm0.2Gd0.2Ho0.2Er0.2)2Zr2O7 (NSGHE), (La0.2Nd0.2Sm0.2Gd0.2Ho0.2)2Zr2O7 (LNSGH), and (La0.2Nd0.2Sm0.2Gd0.2Er0.2)2Zr2O7 (LNSGE). All samples exhibit dense and uniform grain structures with a relative density greater than 99%. After annealing at 1600 degrees C for 40 hours, the samples maintain a uniform microstructure and low grain growth rate, demonstrating superior anti-sintering ability. Due to the high-entropy effect and the impact of atomic size disorder, the NSGHE, LNSGH, and LNSGE ceramics exhibit high thermal expansion coefficients at 1200 degrees C (11.41 x 10-6 K-1, 11.20 x 10-6 K-1, and 11.69 x 10-6 K-1, respectively) and low thermal conductivities at room temperature (1.996 W center dot m-1 center dot K-1, 1.976 W center dot m-1 center dot K-1, and 1.745 W center dot m-1 center dot K-1, respectively). Additionally, NSGHE, LNSGH, and LNSGE exhibit excellent mechanical properties, with hardness values of 8.746 GPa, 9.639 GPa, and 11.259 GPa, respectively, and fracture toughness values of 0.990 MPa center dot m0.5, 1.196 MPa center dot m0.5, and 2.382 MPa center dot m0.5. From the thermal and mechanical property results, the significant effect of severe lattice distortion on the material properties is evident. Therefore, the degree of disorder in the ionic radius size should be suggested as an important reference index for designing complex thermal insulating ceramics. The findings of this study not only advance research on high-performance zirconate high-entropy ceramics but also provide important reference points for developing high-entropy oxides in TBC applications.