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Complex compositions and structural designs severely restrict the practical application of high-temperature microwave-infrared compatible stealth coatings. To address this issue, high-temperature microwave-infrared compatible stealth coatings of a single 8 wt% yttria-stabilized zirconia (8YSZ) component are proposed for the first time. Originating from conductive, interfacial and dipole polarization losses, 8YSZ coating presents superior microwave absorbing properties at 900 °C, including strong absorption (minimum reflection loss (RLmin) of −50 dB), a thin thickness of 1.5 mm, and a better effective absorption bandwidth (EAB) of 2 GHz. Moreover, it maintains low infrared emissivity (ε < 0.3) in the infrared bands of 3–5 μm compared with traditional materials. In contrast to the conventional strategy in which microwave-infrared compatible stealth materials are explored in the pool of “complex” multiple-component or metamaterial, this work reveals an avenue to look into materials with simple compositions realizing microwave-infrared compatible stealth simultaneously, which would be of both scientific and technological significance in the fields of stealth technology. Moreover, the present work reveals new applications of 8YSZ coatings in the field of high-temperature stealth technology.

Abstract The critical requirements for the environmental barrier coating (EBC) materials of silicon-based ceramic matrix composites (CMCs) include good tolerance to harsh environments, thermal expansion matches with the interlayer mullite, good high-temperature phase stability, and low thermal conductivity. Cuspidine-structured rare-earth aluminates RE4Al2O9 have been considered as candidates of EBCs for their superior mechanical and thermal properties, but the phase transition at high temperatures is a notable drawback of these materials. To suppress the phase transition and improve the phase stability, a novel cuspidine-structured rare-earth aluminate solid solution (Nd0.2Sm0.2Eu0.2Y0.2Yb0.2)4Al2O9 was designed and successfully synthesized inspired by entropy stabilization effect of high-entropy ceramics (HECs). The as-synthesized HE (Nd0.2Sm0.2Eu0.2Y0.2Yb0.2)4Al2O9 exhibits a close thermal expansion coefficient (6.96×10-6 K-1 at 300–1473 K) to that of mullite, good phase stability from 300 to 1473 K, and low thermal conductivity (1.50 W·m–1·K–1 at room temperature). In addition, strong anisotropic thermal expansion has been observed compared to Y4Al2O9 and Yb4Al2O9. The mechanism for low thermal conductivity is attributed to the lattice distortion and mass difference of the constituent atoms, and the anisotropic thermal expansion is due to the anisotropic chemical bonding enhanced by the large size rare-earth cations.

Abstract Rare-earth tantalates and niobates (RE3TaO7 and RE3NbO7) have been considered as promising candidate thermal barrier coating (TBC) materials in next generation gas-turbine engines due to their ultra-low thermal conductivity and better thermal stability than yttria-stabilized zirconia (YSZ). However, the low Vickers hardness and toughness are the main shortcomings of RE3TaO7 and RE3NbO7 that limit their applications as TBC materials. To increase the hardness, high entropy (Y1/3Yb1/3Er1/3)3TaO7, (Y1/3Yb1/3Er1/3)3NbO7, and (Sm1/6Eu1/6Y1/6Yb1/6Lu1/6Er1/6)3(Nb1/2Ta1/2)O7 are designed and synthesized in this study. These high entropy ceramics exhibit high Vickers hardness (10.9–12.0 GPa), close thermal expansion coefficients to that of single-principal-component RE3TaO7 and RE3NbO7 (7.9×10−6-10.8×10−6C−1 at room temperature), good phase stability, and good chemical compatibility with thermally grown Al2O3, which make them promising for applications as candidate TBC materials.