Complex Permittivity and Microwave Absorbing Property of Si ₃N ₄-SiC Composite Ceramic

Si ₃N ₄-SiC composite ceramics were fabricated by chemical vapor infiltration using porous Si ₃N ₄ ceramic as preform. The average grain size of SiC was 30 nm. Relationship between SiC content and relative complex permittivity of Si ₃N ₄-SiC within the frequency range of 8.2-12.4 GHz (X-band) was investigated. The average real part of relative complex permittivity e{open}' of Si ₃N ₄-SiC increased from 3.7 to 14.9 and the relative imaginary part e{open}' increased from 0.017 to 13.4 when the content of SiC increased from 0 to 10 vol.%. The Si ₃N ₄-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 Si ₃N ₄-SiC ceramic were attributed to the interfacial polarization at interface between Si ₃N ₄ and SiC and at grain boundary between SiC nanocrystals.