Complex Permittivity and Microwave Absorbing Property of Si3N4–SiC Composite Ceramic

Si3N4—SiC composite ceramics were fabricated by chemical vapor infiltration using porous Si3N4 ceramic as preform. The average grain size of SiC was 30 nm. Relationship between SiC content and relative complex permittivity of Si3N4–SiC within the frequency range of 8.2–12.4 GHz (X-band) was investigated. The average real part of relative complex permittivity ɛ' of Si3N4–SiC increased from 3.7 to 14.9 and the relative imaginary part ɛ″ increased from 0.017 to 13.4 when the content of SiC increased from 0 to 10 vol.%. The Si3N4–SiC ceramic with 3 vol.% SiC achieved a reflection loss below −10 dB (90% absorption) at 8.6–11.4 GHz, and the minimum value was −27.1 dB at 9.8 GHz when the sample thickness was 2.5 mm. The excellent microwave absorbing abilities of Si3N4–SiC ceramic were attributed to the interfacial polarization at interface between Si3N4 and SiC and at grain boundary between SiC nanocrystals.