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

Abstract

The 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.

Influence of size disorder parameter on the thermophysical properties of rare‐earth‐zirconate medium‐entropy ceramics

“…At low temperature (100–500°C), the thermal diffusivity decreases as the temperature rises, whereas in the high‐temperature section (500–1000°C), it tends to increase. La 2 Zr 2 O 7 ceramics also have the same phenomenon 34,40,41 . This is because as the temperature increases, the total energy radiated by the object increases.…”

“…La 2 Zr 2 O 7 ceramics also have the same phenomenon. 34,40,41 This is because as the temperature increases, the total energy radiated by the object increases. The laser flash analyzer we used (LFA1000, Linseis, Germany) is a model…”

Fast grain growth phenomenon in high-entropy ceramics: A case study in rare-earth hexaaluminates

“…Following the metallic high-entropy alloys (HEAs) which have been extensively studied since 2004 [1,2], high-entropy ceramics including oxides [3][4][5][6][7][8][9][10], borides [11][12][13][14][15], carbides [16][17][18][19], and silicides [20,21] have been developed and studied intensively in recent years. High-entropy ceramics generally exhibit special physical and chemical properties, which are generally resulted from their complex composition, severe lattice distortion, and the sluggish diffusion effect [22][23][24].…”

Gateway toward efficient and miniaturized A2B2O7-type fluorite structure-based energy storage devices

“… 13 In addition, the crystallographic visualization also helps to distinguish these two structures based on occupancy of Wyckoff positions by cations and anions in three different ways, 14 (i) the A and B -site cations in pyrochlore structure occupy 16 c and 16 d sites, respectively while in the fluorite structure both A and B -site cations occupy a single 4 a site, (ii) the oxygen anions in pyrochlore structure lie at 48 f site with coordinates ( x , 1/8,1/8) while in fluorite structure, it lies at 8 c site with coordinates (1/4,1/4,1/4), and (iii) the oxygen anion which lies at 8 b site in pyrochlore structure moves to 4 a site in fluorite structure. 15 Due to these differences, the A and B -site cations are surrounded by 8 and 6 anions, respectively, in pyrochlore structure which transforms to an average of 7 coordinates in fluorite structure. This structural flexibility of AB O-type materials makes them prominent to be utilized in photoluminescence, anti-erosion applications, thermal barrier coating, magnetic devices, nuclear waste management, electrical device, gas sensors, and high-temperature catalysts.…”