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The multifunctional metastable SiBOCN system ceramics (including SiBN, SiCN, SiON, SiBC, SiBCN, SiBON, SiBOCN, etc.) are a new type of advanced structure-function integrated materials with unique structure and adjustable dielectric properties for high-temperature applications in thermal protection, communications, precise guidance, and microwaveabsorption stealthy. These metastable materials generally require the rational co-design of multiscale structure and chemical composition to achieve desirable dielectric properties which induce interaction with incident electromagnetic wave. Herein, this review presents the latest development of metastable SiBOCN system ceramics, with the intent of summarising key findings, uncovering major trends and providing guidance for future efforts. Major themes in this assessment focus on the main processing routes, basic mechanisms for microwave transmission and absorption, scientific basis for material selection in specific background, principles for multiscale structure design and chemistry optimisation, tunable microwave transparent or absorbing properties, and future challenges and prospects in this active research filed.

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Lightweight SiBCN ceramic nanofibers were prepared by a combination of electrostatic spinning and high-temperature annealing techniques, showing tunable electromagnetic wave absorption. By controlling the annealing temperature, the nanoscale architectures and atomic bonding structures of as-prepared nanofibers could be well regulated. The resulting SiBCN nanofibers ∼300 nm in diameter, which were composed of an amorphous matrix, β-SiC, and free carbon nanocrystals, were defect-free after annealing at 1600 °C. SiBCN nanofibers annealed at 1600 °C exhibited good microwave absorption, obtaining a minimum reflection coefficient of −56.9 dB at 10.56 GHz, a sample thickness of 2.6 mm with a maximum effective absorption bandwidth of 3.45 GHz, and a maximum dielectric constant of 0.44. Owing to the optimized A + B + C microstructure, SiBCN ceramic nanofibers with satisfying microwave absorption properties endowed the nanofibers with the potential to be used as lightweight, ultrastrong radar wave absorbers applied in military and the commercial market.