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One of the most promising applications of high entropy ceramics is their use as high temperature protective materials. Due to the additional entropic stabilization of the crystal structure, four- and five-element high entropy ceramics exhibit enhanced thermal and mechanical properties. For these applications, one of the most promising high entropy protective oxides are ZrO2- and HfO2-based protective HEOs. In this article, we study the HfO2–ZrO2–Y2O3–CeO2 equimolar system with the addition of MgO as a fifth component. We found that the HfZrCeY(Mg)O system maintains a single FCC crystalline structure up to the MgO concentration = 31.9 mol.%. Additionally, we determined that an addition of MgO at the close-to-equimolar HfZrCeY(Mg)O composition enhances the thermal properties of HEO, but reduces the mechanical properties such as hardness and resistance to crack formation. The minimum weight loss at the heating from RT up to 1450 °C was measured for the close-to-equimolar HfZrCeY(Mg)O composition at 18.4 mol.% MgO. The hardness of such composition was around 18 GPa. Due to the combination of these properties, the synthesized coating can be used as a protective material for high temperature applications, such as the protection of turbine parts. [ABSTRACT FROM AUTHOR]

The limited efficiency of traditional trial-and-error experiments has impeded the development and application of high-entropy fluorite oxides in thermal insulation coatings. To solve this problem, a novel entropy descriptor based on first principles is presented to help select candidate components for synthesizing high-entropy fluorite structure oxides. Results show that the compatibilities of 10 single-phase high-entropy fluorite oxides can be accurately predicted based on entropy formation ability. In the studied (Zr, Hf, Pr, La, X) O 2-δ system, a correlation between thermal characteristics and size/mass differences was established by designing the size and mass of X. Specifically, we found that the thermal conductivity is more strongly correlated with the difference in atomic mass, while the coefficient of thermal expansion is strongly correlated with the difference in atomic size. X-ray photoelectron spectroscopy (XPS) analysis shows that the concentration of oxygen vacancy can effectively reduce the thermal conductivity of high-entropy fluorite oxides. In addition, the values of hardness, elastic modulus and thermal conductivity of five single-phase fluorite oxides are successfully predicted by first principles calculation, and the differences between these values and the experimental results are small, which provides a prospective significance for the performance prediction of high-entropy fluorite oxides. Our findings provide a strategy for customizing high-entropy fluorite single-phase oxides with suitable properties to meet the performance requirements of thermal barrier coatings (TBCs). • The DFT calculation provides an entropy descriptor to evaluate the comfiability of high-entropy single-phase fluorite oxides based on their entropy formation capacity. • The hardness, elastic modulus and thermal conductivity of the studied sample are obtained by DFT calculation, and the difference between them and the experimental values is small. • In the (Zr, Hf, Pr, La, X)O 2-δ system, the atomic size difference and atomic mass difference of five single-phase samples were quantified, and their thermal conductivity and thermal expansion values were correlated. [ABSTRACT FROM AUTHOR]

The effects of substituting the B cation in A3BO7 ceramics on their thermal physical properties were investigated by applying a large mass difference. Y3(Nb1‐xTax)O7 (x = 0, 0.1, 0.2, 0.3, 0.4, and 0.5) ceramics were synthesized, and their structural characteristics were determined. All the fabricated Y3(Nb1‐xTax)O7 ceramics showed defective fluorite structures and glass‐like low thermal conductivity (1.18−2.04 W/m∙K at 25°C) because of the highly distorted crystal structure and significant mass difference. Substitution with Ta5+ enhanced the sintering resistance, leading to superior thermal‐insulating performance via grain boundary scattering. Furthermore, the ceramics exhibited excellent coefficients of thermal expansion, implying the promising applicability of Y3(Nb1‐xTax)O7 as new thermal barrier materials. The effect of mass difference on the thermomechanical properties of the ceramics was examined, suggesting a simple strategy for engineering the chemical composition of new thermal barrier materials. [ABSTRACT FROM AUTHOR]

In this study, a high-entropy approach was employed to design a new single-phase A 2 B 2 O 7 oxide for thermal insulation applications. Multicomponent high-entropy oxides, containing up to seven different cations, were successfully synthesized in a single defective fluorite structure. We observed that the incorporation of the functional cation, Zn2+, effectively blocked the heat radiation phenomenon by reducing the photon mean free path, and further reduced the high-temperature thermal conductivity owing to the larger free carrier concentration originated from the large number of oxygen vacancies. Although a large concentration of Zn2+ caused a slight reduction in thermal expansion, this study suggests that functional cations can be easily incorporated; thus, expanding the material diversity beyond the typical doping levels to develop new thermal barrier materials. [ABSTRACT FROM AUTHOR]

• A novel high entropy ceramic with hybrid mixing of Si and metal atoms was proposed. • Hf 0.25 Zr 0.25 Ce 0.25 Y 0.125 Si 0.125 O 2-δ was synthesized and its single phase was confirmed. • This Si-stabilized fluorite oxide has high thermal stability, good mechanical, and thermal properties, promising for aerospace applications. We design and synthesise a new high-entropy ceramic Hf 0.25 Zr 0.25 Ce 0.25 Y 0.125 Si 0.125 O 2-δ through a hybrid mixing of non-metal and metal atoms. First-principles calculations predict the thermal stability of the single-crystal phase at high temperatures. XRD and EDS mapping confirm a single cubic fluorite phase with a uniform elemental distribution. In-situ high-temperature XRD shows that the phase is stable with no phase separation or secondary phases. The measured mechanical and thermal properties are comparable with reported high-entropy fluorite oxides. Our results add to the compositional space of high-entropy ceramics for a wide range of applications from thermal insulators to electronics. [ABSTRACT FROM AUTHOR]