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

Semiconducting β-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 °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 κ is first introduced to predict the temperature-dependent multi-relaxation behavior intuitively. Combining the impedance matching theory, the relaxation factor κ can perfectly predict the best electromagnetic wave absorbing performance of S-CS (– 20.37 dB) both consideration of thickness and frequency at 800 °C, which is an effective way to characterize the electromagnetic absorbing performance at high temperature.