▎ 摘　　要

As cutting-edge emerging electromagnetic (EM) wave-absorbing materials, the Achilles' heel of graphenes is vulnerable to oxidation under high temperature and oxygen atmosphere, particularly at temperatures more than 600 degrees C. Herein, a graphene@Fe3O4/siliconboron carbonitride (SiBCN) nanocomplex with a hierarchical A/B/C structure, in which SiBCN serves as a "shield" to protect graphene@Fe3O4 from undergoing high-temperature oxidation, was designed and tuned by polymer-derived ceramic route. The nanocomplexes are stable even at 1100-1400 degrees C in either argon or air atmosphere. Their minimum reflection coefficient (RCmin) and effective absorption bandwidth (EAB) are -43.78 dB and 3.4 GHz at ambient temperature, respectively. After oxidation at 600 degrees C, they exhibit much better EM wave absorption, where the RCmin decreases to 66.21 dB and EAB increases to 3.69 GHz in X-band. At a high temperature of 600 degrees C, they also possess excellent and promising EW wave absorption, for which EAB is 3.93 GHz, covering 93.6% range of X-band. In comparison to previous works on graphenes, either the EAB or the RCmin of these nanocomplexes is excellent at high-temperature oxidation. This novel nanomaterial technology may shed light on the downstream applications of graphenes in EM-wave-absorbing devices and smart structures worked in harsh environments.