Microwave permittivity of SiC-Al₂O₃ composite powder prepared by sol-gel and carbothermal reduction

SiC-Al₂O₃ composite powder was prepared by sol-gel and carbothermal reduction method. The powder synthesized was characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) to confirm the phase formation, and the thermodynamic analysis was performed systematically. Moreover, the variation of its microwave permittivity with different atomic ratio of Al/Si was investigated in the frequency range of 8.2-12.4 GHz. The results show that, the powder obtained consists of spherical particles of 300-400 nm in diameter, which are composed of SiC and Al₂O₃ microcrystal with the grain size of approximately 45 nm. The results of XRD accord with those of the thermodynamic analysis. It is impossible for Al atoms to dissolve in the lattice of SiC during the carbothermal reduction process. Along with the increase of atomic ratio of Al/Si in the xerogel, the amount of Al₂O₃ in the powder synthesized increases, which reduces both ε′, the real part of complex permittivity, and tgδελ(ε″/ε′), the dissipation factor, where ε″ is the imaginary part of complex permittivity.