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Polymer‐derived ceramics (PDCs) have become promising candidates for electromagnetic wave (EMW) absorption due to their high thermal stability, design flexibility, and versatile functionality. However, the inevitable porous structure formed during pyrolysis greatly limits its mechanical performance. In this work, Ni–Fe–C/HfO2/SiCN ceramic was prepared by simultaneously doping nickel and iron‐containing metal‐organic framework (Ni–Fe–MOF) nanoparticles and hafnium dioxide (HfO2) nanoparticles into the ceramic precursor, thereby improving its intrinsic brittle structure while granting it extraordinary EMW absorption performance. The flexural strength, flexural modulus, and Vickers hardness of Ni–Fe–C/HfO2/SiCN ceramic were 101.06 MPa, 40.19 GPa, and 13.31 GPa, respectively. These values were 1 132%, 749%, and 191% higher than those of the initial SiCN ceramics. In addition, by optimizing the content of Ni–Fe–MOF, the Ni–Fe–C/HfO2/SiCN ceramic demonstrated satisfying EMW absorption performance from 25°C to 500°C. At 25°C, the minimum reflection loss (RLmin) and effective absorption bandwidth (EAB) were −54.07 dB and 3.95 GHz, covering 94% of the X‐band at a thickness of 2.27 mm. At 500°C, the RLmin and EAB were −33.72 dB and 1.82 GHz, still covering 43% of the X‐band at a thickness of only 1.65 mm. This work provides valuable insight into the integration of mechanical and EMW absorbing functions of PDC materials. [ABSTRACT FROM AUTHOR]

Quaternary siliconboron carbonitride (SiBCN) ceramics show excellent high‐temperature stability and oxidation resistance, indicating great potential as high‐temperature 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 (RCmin) is −61.05 dB, and the effective bandwidth absorption (EAB) is 3.35 GHz (9.05–12.4 GHz). The RCmin 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. [ABSTRACT FROM AUTHOR]