Sustainable dielectric relaxation across a broad temperature window remains a significant challenge for high-temperature electromagnetic-wave (EMW) absorption, particularly in extreme conditions where dissipation pathways are severely constrained. Herein, a porous ceramic embedded with high-entropy nanocrystals (P-HEN) was developed by leveraging the confinement effect of the SiOCN covalent network. The confined growth and effective phase separation of (FeNiCoAl)₃O₄ nanocrystals generate thermally stable dielectric-relaxation activation units within the SiOCN matrix. Furthermore, the random distribution of multi-metal cations in the nanocrystals, together with the multi-interfacial interactions between the nanocrystals and the matrix, generates strong polarization responses. Consequently, P-HEN achieves sustained dielectric relaxation and full-band effective absorption in the X-band over a wide temperature range from 25 to 700 °C, while also exhibiting excellent thermal insulation and ablation resistance. This work demonstrates a confinement-enabled mechanism for stabilizing dielectric-relaxation loss at elevated temperatures, providing a new strategy for designing wide-temperature-window EMW absorbers.

The limitations of conventional electromagnetic wave (EMW)-absorbing materials in terms of high-temperature resistance have stimulated interest in the development of high-temperature EMW-absorbing materials across various fields. However, owing to the temperature dependence of the permittivity, achieving effective EMW absorption across a wide temperature range remains a significant challenge for high-temperature EMW absorbing materials. Herein, a novel molecular-scale strategy is proposed for the in situ construction of multiple heterointerfaces during the polymer-derived ceramic (PDC) process, thereby achieving temperature-insensitive permittivity. The interfacial dipole polarization generated by multiple heterointerfaces effectively mitigates the dependence of the permittivity on conductivity, thereby reducing the temperature sensitivity of the overall permittivity. Moreover, the preparation of lightweight porous ceramics was further achieved via the self-sacrificing template method. As a proof-of-concept, multiheterointerface lightweight ceramics (MHLCs) that exhibit excellent thermal stability (up to 1000 °C), low density (1.03 g/cm³), low thermal conductivity (0.37 W/(m·K)), and high bending strength (33.55 MPa) have been designed and fabricated. These ceramics demonstrate excellent temperature-insensitive EMW absorption performance and thickness robustness, effectively absorbing X-band EMW across a temperature range from 25 to 900 °C at various thicknesses. This approach to developing temperature-insensitive dielectric ceramics significantly improves the performance and functionality of high-temperature EMW absorbing materials, thereby providing substantial guidance and reference value.

NiO, an anodic electrochromic material, has applications in energy-saving windows, intelligent displays, and military camouflage. However, its electrochromic mechanism and reasons for its performance degradation in alkaline aqueous electrolytes are complex and poorly understood, making it challenging to improve NiO thin films. We studied the phases and electrochemical characteristics of NiO films in different states (initial, colored, bleached and after 8000 cycles) and identified three main reasons for performance degradation. First, Ni(OH)₂ is generated during electrochromic cycling and deposited on the NiO film surface, gradually yielding a NiO@Ni(OH)₂ core–shell structure, isolating the internal NiO film from the electrolyte, and preventing ion transfer. Second, the core–shell structure causes the mode of electrical conduction to change from first- to second-order conduction, reducing the efficiency of ion transfer to the surface Ni(OH)₂ layer. Third, Ni(OH)₂ and NiOOH, which have similar crystal structures but different b-axis lattice parameters, are formed during electrochromic cycling, and large volume changes in the unit cell reduce the structural stability of the thin film. Finally, we clarified the mechanism of electrochromic performance degradation of NiO films in alkaline aqueous electrolytes and provide a route to activation of NiO films, which will promote the development of electrochromic technology.

Inorganic metal oxide electrochromic materials have good application prospects for energy-saving windows in buildings and smart display applications. Therefore, the development of electrochromic films with good cycling stabilities, fast color-change response times, and high coloring efficiencies has attracted considerable attention. In this study, nanoflake Li-doped NiO electrochromic films were prepared using a hydrothermal method, and the films exhibited superior electrochromic performances in the LiOH electrolyte. Li⁺ ions doping increased the ion transmission rates of the NiO films, and effectively promoted the transportation of ions from the electrolyte into NiO films. Meanwhile, the nanoflake microstructure caused the NiO films to have larger specific surface areas, providing more active sites for electrochemical reactions. It was determined that the NiO-Li20% film exhibited an ultra-fast response in the LiOH electrolyte (coloring and bleaching times reached 3 and 1.5 s, respectively). Additionally, the coloration efficiency was 62.1 cm² C⁻¹, and good cycling stability was maintained beyond 1500 cycles. Finally, the simulation calculation results showed that Li doping weakened the adsorption strengths of the NiO films to OH⁻, which reduced the generation and decomposition of NiOOH and helped to improve the cycling stabilities of the films. Therefore, the research presented in this article provides a strategy for designing electrochromic materials in the future.