High-entropy ceramic dual-phase evolution mechanisms and their influence on the thermophysical performance of thermal barrier coatings

High-entropy rare-earth oxide ceramics offer great potential for thermal barrier coatings (TBCs) due to their tunable thermal expansion coefficients (TECs) and low thermal conductivities. In this study, a series of high-entropy rare-earth zirconia-ceria ceramics, (La_0.2Nd_0.2Gd_0.2Ho_0.2Y_0.2)₂(Zr_1-xCe_x)₂O₇ (x = 0, 0.125, 0.25), were synthesized and characterized. The samples are denoted as 5RZ (x = 0), 5RZC1 (x = 0.125), and 5RZC2 (x = 0.25), where "5 R" refers to the five rare-earth elements, "Z" to Zr, and "C" to Ce. The research systematically investigates both the evolution of the phase structure and its influence on physical properties. The study found that the 5RZ sample with appropriate dual-phase ratios inhibits grain growth by clamping the grain boundaries, thus maintaining the fine grain structure. Owing to this property, 5RZ displays a low thermal conductivity of 1.730 W·m⁻¹·K⁻¹ at 800 °C. While in the fluorite phase dominated 5RZC1 and 5RZC2, the phonon scattering and defect scattering effects bring about a reduction in thermal conductivity to 2.216 W·m⁻¹·K⁻¹, and 1.599 W·m⁻¹·K⁻¹, respectively. Meanwhile, the TECs decrease gradually with the increase in the proportion of the fluorite phase, from 11.52 × 10⁻⁶ K⁻¹ for 5RZ to 11.10 × 10⁻⁶ K⁻¹ for 5RZC2. Additionally, 5RZ, 5RZC1, and 5RZC2 also exhibited higher hardness (10.52 ∼ 12.05 GPa) and fracture toughness (1.46 ∼ 1.50 MPa·m^1/2). The research results reveal the evolution and regulation mechanisms of the dual-phase structure, providing both theoretical basis and practical guidance for the tunable design of thermophysical and mechanical properties in TBCs.