Design and thermophysical properties of disordered fluorite-structured high-entropy zirconate

To address the challenges of poor phase stability and insufficient sintering resistance in conventional yttria-stabilized zirconia (YSZ) thermal barrier coatings at high temperatures (>1473 K), this study proposes the development of novel rare-earth zirconates through a high-entropy strategy and structural design. A-site high-entropy zirconates (6RE)₂(Zr_1-xCex)₂O₇ with equimolar doping of six rare-earth elements (La, Lu, Yb, Tm, Er, Ho) were synthesized via solid-state reaction, yielding four disordered fluorite-structured samples (HZO, HZCO1, HZCO2, HZCO3) with varying Ce contents. Systematic characterization of their structural, thermophysical, and mechanical properties revealed that all samples formed single-phase disordered fluorite structures (space group Fm3m). Lattice distortion enhanced phonon scattering, while B-site Ce doping further reduced thermal conductivity to 1.29–1.63 W/m·K (400–1000 °C), representing 48 % reduction compared to YSZ (2.5–2.6 W/m∙K). The thermal expansion coefficients (10.0 × 10⁻⁶-12 × 10⁻⁶ K⁻¹, 800–1000 °C) demonstrated excellent compatibility with Ni/CoCrAlY bond coats. Notably, the materials exhibited superior damage tolerance, with a low brittleness index of 3.70 μm^−1/2. Analysis of mass and size disorder parameters elucidated structure-property correlations between disorder degree, thermal conductivity, and mechanical performance. This work provides experimental evidence and design principles for high-entropy zirconates in advanced thermal barrier coatings, highlighting their integrated advantages of ultralow thermal conductivity, high thermal expansion, and robust mechanical properties.