Hierarchically Porous Multiphase Si‐Based Ceramics with Synergistic Electromagnetic Wave Absorption Mechanisms

A novel multiphase Si‐based ceramic material with hierarchical porosity is devised via one‐step etching activation of carbon‐rich polycarbosilane ceramics. Integrating free carbon, SiC crystals, amorphous SiOC, and engineered porosity, the material surprisingly achieves exceptional electromagnetic absorption performance, offering new insights into the synergistic design of multiphase ceramics and porous architectures. Abstract The development of high‐performance electromagnetic wave absorbers is critical for mitigating electromagnetic pollution in modern electronic and communication systems. Here, a scalable strategy is developed to fabricate hierarchically porous, multiphase Si‐based ceramics (Six‐Oy‐Cz) via one‐step activation of carbon‐rich polycarbosilane precursors. The resulting material integrates β‐SiC crystals, amorphous SiOC, and conductive carbon within a tunable porous architecture. This combination creates abundant heterogeneous interfaces, defect structures, and enhanced impedance matching. The optimized sample achieves a minimum reflection loss of −70.44 dB at just 1.79 mm thickness and a broad 4.32 GHz bandwidth at a matching thickness of 1.86 mm. Structural, dielectric, and radar simulation analyses reveal that interfacial polarization, dipolar polarization, conduction loss, and pore‐induced scattering work synergistically to dissipate electromagnetic energy. This work offers a simple, cost‐effective approach to engineer next‐generation ceramic EMW absorbers. A novel multiphase Si-based ceramic material with hierarchical porosity is devised via one-step etching activation of carbon-rich polycarbosilane ceramics. Integrating free carbon, SiC crystals, amorphous SiOC, and engineered porosity, the material surprisingly achieves exceptional electromagnetic absorption performance, offering new insights into the synergistic design of multiphase ceramics and porous architectures. Abstract The development of high-performance electromagnetic wave absorbers is critical for mitigating electromagnetic pollution in modern electronic and communication systems. Here, a scalable strategy is developed to fabricate hierarchically porous, multiphase Si-based ceramics (Si x -O y -C z ) via one-step activation of carbon-rich polycarbosilane precursors. The resulting material integrates β-SiC crystals, amorphous SiOC, and conductive carbon within a tunable porous architecture. This combination creates abundant heterogeneous interfaces, defect structures, and enhanced impedance matching. The optimized sample achieves a minimum reflection loss of −70.44 dB at just 1.79 mm thickness and a broad 4.32 GHz bandwidth at a matching thickness of 1.86 mm. Structural, dielectric, and radar simulation analyses reveal that interfacial polarization, dipolar polarization, conduction loss, and pore-induced scattering work synergistically to dissipate electromagnetic energy. This work offers a simple, cost-effective approach to engineer next-generation ceramic EMW absorbers. Advanced Science, Volume 12, Issue 42, November 13, 2025.