With the development of hypersonic vehicle technology, ceramic-based radome materials are highly demanded due to their high operating temperatures, good dielectric properties, and high mechanical properties. Although α-SiAlON is an ideal material for radome applications, its intrinsic low transmittance and high thermal conductivity limit its applications. Herein, we prepared Y–α-SiAlON porous ceramics through tert-butanol (TBA) gel-casting using the self-synthesized α-SiAlON powder. The Y–α-SiAlON porous ceramics exhibited a uniform micron-level connected pore structure with the porosity (P) of 44.2%–58.6%. The real part of permittivity ( ${\epsilon }^{\prime }$) was 3.13–4.18 (8.2–12.4 GHz), which decreased significantly with the increasing porosity. The wave transmittance ( $|T{|}^2$) of the sample with porosity of 58.6% could exceed 80% in the thickness range of 6–10 mm. The thermal conductivity was maintained at a low level of 1.38–2.25 W·m⁻¹·K⁻¹ owing to the introduction of the pore structure. The flexural strength was 44.73–88.33 MPa, which may be increased by rod-like α-SiAlON grains. The results indicate that the prepared Y–α-SiAlON porous ceramics meet the requirements of high-temperature wave-transmitting materials for radome applications.

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_A3+/r_B4+ = 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, K_IC ≈ 2.3 MPa·m^0.5). A₂B₂O₇ high-entropy ceramics exhibit excellent thermal stability with relatively high thermal expansion coefficients (TECs) (Hf0.25, 11.20×10^-6 K^-1, 1000 ℃). Moreover, the matching calculation implied that the ODT further enhances the phonon scattering coefficient, leading to a relatively lower thermal conductivity of (La_0.25Eu_0.25Gd_0.25Yb_0.25)₂(Zr_0.85Ce_0.15)₂O₇ (1.48-1.51 W/(m·K), 100-500 ℃) 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.

Reversible luminescence modulation behavior upon the photochromic effect endows the photochromic ceramics with great potential in anti-counterfeiting and data storage applications. Here, Sm³⁺-doped KSr₂Nb₅O₁₅ photochromic ceramics exhibit superior anti-counterfeiting ability: good covertness and considerable modulation ratio of luminescent emission intensity after photochromic reaction. The results show that the photochromism originated from oxygen and cation vacancies, which were directly identified by electron paramagnetic resonance and positron annihilation lifetime spectra. Unexpectedly, oxygen vacancies work more effectively than cation vacancies during photochromic reactions. Moreover, the extraordinary anti-counterfeiting ability was attributed to the high energy transfer rate, which was particularly caused by the short mean distance below 1 nm between the Sm³⁺ and vacancies. The work here has provided atomic-scale structural evidence and made a progress in understanding the photochromic origins and mechanism in color-center theory.