Modeling for high-temperature dielectric behavior of multilayer Cf/Si3 N4 composites in X-band

The high-temperature dielectric behavior of multilayer C-f/Si-3 N-4 composites fabricated by gelcasting and pressuureless sintering was intensively investigated at temperatures coverage up to 800 degrees C in X-band (8.2-12.4 GHz). Experimental results have shown the permittivity of Si-3 N-4 matrix exhibits excellent thermo-stability with temperature coefficient lower than 10(-3) C-1. Besides, both the real and imaginary parts of permittivity of multilayer Cf/Si-3 N-4 composites exhibit positive temperature coefficient characteristic which attributed to the enhancement of space charge polarization. Furthermore, temperature-dependent permittivity of Cf/Si-3 N-4 composites is demonstrated to be well distributed on circular arcs with centers actually keep around the real (epsilon') axis in Cole-Cole plane. Finally, the relaxation time for multilayer Cf/Si-3 N-4 composites gradually increases from 216.1 ps to 250.2 ps when heated from room temperature to 800 degrees C, and is almost twice as much as a single cycle for electromagnetic wave in X-band which leads to continuous decrease in permittivity with frequency. (C) 2016 Elsevier Ltd. All rights reserved.