High-Temperature Stable and Metal-Free Electromagnetic Wave-Absorbing SiBCN Ceramics Derived from Carbon-Rich Hyperbranched Polyborosilazanes

High-temperature stable and metal-free siliconboron carbonitride ceramics with high electromagnetic (EM) wave-absorbing efficiency were achieved through the structural design and pyrolysis of carbon-rich hyperbranched polyborosilazane precursors with pendent phenyl groups. The introduction of benzene rings into the precursors dramatically changes the microstructure and the EM wave-absorbing property of ceramics. It reveals that the ceramics pyrolyzed from the benzene ring-containing preceramic precursors have a higher carbon content and a larger number of sp2 carbons and generate crystalline carbons (graphitic carbons and tubular carbons) in situ, which lead to excellent EM wave-absorbing properties. The EM wave absorption efficiency and effective absorption bandwidth (EAB, reflection coefficient (RC) below ？10 dB) can be tuned via annealing of the ceramics. The ceramics stable at 1320 °C exhibit their optimized EM wave-absorbing performance with a minimum RC (RCmin) of ？71.80 dB and an EAB of 3.65 GHz (8.2–11.85 GHz). We believe that the research extends the design strategy of advanced EM wave-absorbing functional materials, which have great potential as promising absorbers in commercial or military applications