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The development of high‐performance microwave absorption materials in harsh environment is highly desirable but challenging. Herein, lightweight silicon oxycarbonitride (SiOCN) ceramic aerogels were fabricated by the pyrolysis of bridged polysilsesquioxane aerogels, which was presynthesized by a sol–gel method followed by vacuum drying. The structural order and content of free carbon phase determined by pyrolysis temperature play a critical role in modulating the impedance matching and attenuation capacity. The as‐prepared SiOCN aerogel pyrolyzed at 1000°C achieves a minimal reflection loss of −64.2 dB at 8.96 GHz and a broad bandwidth of 5.4 GHz at a low thickness of 2.15 mm. The hierarchical pore structure, abundant heterogeneous amorphous SiOCN/free carbon interfaces, and conductive free carbon phase benefit the superior absorption performance by forming good impedance matching, multiple scattering, interface polarization, and conduction losses. This work provides an insight for the rational design of polymer‐derived ceramic aerogel‐based microwave absorption materials for potential application under extreme conditions such as high‐temperature and oxidation environments.

Dielectric genes regulation has already been regarded an effective strategy to manipulate electromagnetic wave response of two-dimensional graphene-based absorbers. However, there is still lacking of elaborate understanding and precise tailoring...

Heterointerface engineering for different identifiable length scales has emerged as a key research area for obtaining materials capable of high‐performance electromagnetic wave absorption; however, achieving controllable architectural and compositional complexity in nanomaterials with environmental and thermal stabilities remains challenging. Herein, metal‐containing silicon carbonitride (SiCN/M) nanocomposite ceramics with multiphase heterointerfaces were in situ synthesized via coordination crosslinking, catalytic graphitization, and phase separation processes using trace amounts of metal–organic frameworks (MOFs). The results reveal that the regulation of dielectric genes by MOFs can yield considerable lattice strain and abundant lattice defects, contributing to strong interfacial and dipole polarizations. The as‐prepared SiCN/M ceramics demonstrate excellent microwave absorption performance: the minimum reflection loss (RLmin) is −72.6 dB at a thickness of only 1.5 mm and −54.1 dB at an ultralow frequency of 3.56 GHz for the SiCN/Fe ceramics and the RLmin is −55.1 dB with a broad bandwidth of 3.4 GHz at an ultralow thickness of 1.2 mm for the SiCN/CoFe ceramic. The results are expected to provide guidance for the design of future dielectric microwave absorption materials based on heterointerface engineering while offering a paradigm for developing MOF‐modified SiCN nanocomposite ceramics with desirable properties.

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