Influence of order-disorder transition on the mechanical and thermophysical properties of A2B2O7 high-entropy ceramics

Abstract

AbstractThe order-disorder transition (ODT) of A2B2O7 compounds obtained enormous attention owing to the potential application for thermal barrier coating (TBC) design. In this work, the influence of ODT on the mechanical and thermophysical properties of dual-phase A2B2O7 high-entropy ceramics was investigated by substituting Ce4+ and Hf4+ with different ionic radii on B-sites (Zr4+). The X-ray diffraction (XRD), Raman, and transmission electron microscopy (TEM) results show that $$r_{\rm{A}^{3+}}/r_{\rm{B}^{4+}}=1.47$$ r A 3 + / r B 4 + = 1.47 is the critical value of ODT phase boundary with different doping B-site ion contents, and the energy dispersive spectroscopy (EDS) results further indicate the uniform distribution of elements. Interestingly, owing to the high intrinsic disorder derived from high-entropy effect, the A2B2O7 high-entropy ceramics exhibit unreduced modulus (E0 ≈ 230 GPa) and enhanced mechanical properties (HV ≈ 10 GPa, KIC ≈ 2.3 MPa·m0.5). A2B2O7 high-entropy ceramics exhibit excellent thermal stability with relatively high thermal expansion coefficients (TECs) (Hf0.25, 11.20×10−6 K−1, 1000 °C). Moreover, the matching calculation implied that the ODT further enhances the phonon scattering coefficient, leading to a relatively lower thermal conductivity of (La0.25Eu0.25Gd0.25Yb0.25)2(Zr0.85Ce0.15)2O7 (1.48–1.51 W/(m·K), 100–500 °C) compared with other components. This present work provides a novel composition design principle for high-entropy ceramics, as well as a material selection rule for high-temperature insulation applications.