Enhanced low‐frequency microwave absorption via polarization loss in nanodomain‐rich SiCN

Abstract Polymer‐derived ceramics (PDCs), known for their exceptional thermal stability and adjustable dielectric characteristics, show great promise in electromagnetic wave absorption applications under extreme temperature conditions. Their multiphase and multi‐heterointerface structures also enable effective low‐frequency absorption for 5G applications, a crucial yet underexplored capability. In this study, nickel‐modified SiCN (SiCN/Ni) ceramics were synthesized through coordination crosslinking of trace amounts of nickel‐based metal‐organic framework (Ni‐MOF) with polysilazane precursor, followed by high‐temperature pyrolysis. The investigation reveals that Ni‐MOF enables the formation of both dielectric and magnetic loss components, specifically SiC nanocrystals, free carbon, and Ni 2 Si nanocrystals, during the synthesis process at reduced temperature conditions. The coexistence of electromagnetic‐transparent and absorbing phases enhances impedance matching. The heterogeneous nanodomains create multiple interfaces, induce significant lattice strain, and produce abundant structural defects, which together enhance interfacial and dipole polarization effects. Notably, the optimized SiCN/Ni ceramic exhibits exceptional microwave absorption performance at low frequency, achieving a minimum reflection loss of –46.1 dB at 5.28 GHz. The low‐frequency absorption bandwidths reach 0.76 and 1.0 GHz at thicknesses of 4.0 and 5.0 mm, fully covering both the n 78 band (3.3–3.8 GHz) and n 79 band (4.4–5.0 GHz) used in 5G communications. These findings present new opportunities for developing advanced lower‐frequency absorbers based on dielectric PDCs.