A unique hollow porous bowl-like nitrogen-doped cobalt/carbon nanocomposite (HBN-Co/C) composed of Co nanoparticles anchored in N-doped porous carbon was designed for enhancing electromagnetic microwave absorption (EMA). The inner cavities of the HBN-Co/C could be regulated to match the impedance and permittivity between the absorber and air, leading to a precise adjustment of the EMA performance. More importantly, the existence of inner cavities decreases the extra multi-interface promoted interfacial polarization and overall density. The synergetic effects of the multicomponents, multiple reflections, and scatterings promoted strong interfacial polarization and facilitated impedance matching. As a result, the HBN-Co/C nanocomposites displayed excellent EMA performance, for which the minimum reflection loss was −42.3 dB at 13.3 GHz with a thickness of only 1.9 mm. The effective absorption bandwidth below −10 dB was up to 5.1 GHz (12.9−18.0 GHz) when the thickness was 1.7 mm. This work provides a facile design and synthesis strategy of novel lightweight electromagnetic wave absorbers with broadband and strong absorption.

Quaternary siliconboron carbonitride (SiBCN) ceramics show excellent hightemperature stability and oxidation resistance, indicating great potential as hightemperature electromagnetic (EM) wave absorbing materials. In this contribution, an efficient and facile method was developed to prepare bulk iron-containing SiBCN (Fe-SiBCN) ceramics with remarkable EM wave absorption at high temperature by pyrolyzing boron and iron containing precursors (PSZV-B-Fe). The introduction of boron and iron not only improves the high-temperature stability but also influences the complex permittivity and EM wave absorption. The minimum reflection coefficient (RC min ) is −61.05 dB, and the effective bandwidth absorption (EAB) is 3.35 GHz (9.05-12.4 GHz). The RC min will be decreased to −52.3 dB at 600°C as well as the EAB covers more than 67% of the X band (2.8 GHz). The high-temperature stable Fe-SiBCN ceramics with adjustable dielectric properties can be utilized as high-performance EM wave-absorbing materials in high-temperature and harsh environments.