Multiple dielectric behavior of Cf-SiCNFs/Si3N4 ceramic composite at high temperatures

Semiconducting beta-SiC nanofibers coated carbon fibers were introduced to reinforce Si3N4 ceramics, giving rise to forming hierarchical microstructure and excellent microwave absorbing performance. Dielectric properties of C-f-SiCNFs/Si3N4 ceramic composite (denoted as S-CS) has been investigated in the X-band (8.2-12.4 GHz) at elevated temperatures (from room temperature to 800 degrees C). The temperature-dependent dielectric of S-CS exhibits a multi-relaxation characteristic, which is related to the hierarchical structure, complex component, and electromagnetic frequency. The thermal dielectric behavior is discussed by Debye theory, and the relaxation factor kappa is first introduced to predict the temperature-dependent multi-relaxation behavior intuitively. Combining the impedance matching theory, the relaxation factor kappa can perfectly predict the best electromagnetic wave absorbing performance of S-CS (- 20.37 dB) both consideration of thickness and frequency at 800 degrees C, which is an effective way to characterize the electromagnetic absorbing performance at high temperature.