Effect of aluminum doping on microwave permittivity of silicon carbide powders

The permittivity and structure of commercial SiC powders before and after thermal diffusion of aluminum were explored in this study. The X-ray diffraction analysis and permittivity results show that heat treatment at 2000°C for 1 h has no influence not only on the structure of the SiC powders but also on the permittivity. Thermal diffusion of aluminum at 1800°, 1900°, and 2000°C was carried out for 1 h at 5 Pa in Ar atmospheres, respectively. A graphite die with two chambers was used during the experiment to separate the aluminum powders from the SiC powders. Aluminum vapor at high temperatures passes to the upper chamber through holes and diffuses into the SiC powders. The permittivities of the as-received SiC powders at 8.2-12.4 GHz were measured, and the results indicate that the real and imaginary parts of permittivity are improved much more than those of the original SiC powder. Both the real and the imaginary parts of the doped SiC increase with the diffusion temperatures, which could be attributed to defects from thermal diffusion of aluminum.