Porous amorphous ceramics enable confined growth of high-entropy spinel for high-temperature electromagnetic wave attenuation

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.