Gradient Impedance All-Ceramic Aerogels: Resolving the Trade-Off Between Broadband and Strong Microwave Absorption

Balancing superb impedance matching and strong attenuation capacity still remains a critical challenge in the development of microwave-absorbing materials (MAM). Here, we report a multiscale design strategy to fabricate gradient impedance all-ceramic aerogels, achieving both excellent impedance matching and enhanced attenuation. The composite aerogel, composed of hybrid SiC/Si₃N₄ nanowire networks, features a multilayer gradient impedance structure that ensures a smooth electromagnetic wave transition from free space to the material, minimizing reflection while enabling efficient wave attenuation. Benefiting from this design, the aerogel exhibits ultralow density (15 mg/cm³), an outstanding effective absorption bandwidth (EAB) of 11.2 GHz, and a minimum reflection loss (RL_min) of -46.2 dB at room temperature. The superior absorption performance originates from the synergistic effect of gradient impedance matching and multiple electromagnetic wave loss mechanisms, including conduction loss, polarization loss, and multiple scattering and reflections. Furthermore, the inherent thermal stability of ceramics allows the aerogel to retain remarkable absorption performance after oxidation at 1300 °C, with an EAB of 9.52 GHz and RL_min of -43.4 dB. This work not only demonstrates the potential of gradient impedance aerogels for extreme environments but also provides a strategy for the design of a high-performance MAM.