Microwave synthesis of Al-doped SiC powders and study of their dielectric properties

To improve the dielectric properties of β-SiC powders, microwave synthesis was applied to produce SiC powders doped with different amounts of Al from fine powders of Si, C and Al under Ar atmosphere. The dielectric properties of the as-synthesized Al-doped SiC powders were investigated, and the mechanism of dielectric loss by doping has been discussed. The presence of Al influenced the formation of secondary phases (α-SiC and Al₄SiC₄) and the microstructure of the resultant powders. The produced powders form Al-SiC solid-solutions, which seemingly favor defect polarization loss effect in the high frequency region. This is consistent with the measurements of dielectric properties, which showed that doping of SiC with Al causes increase of permittivity, both real and imaginary parts, and loss tangent, within 8.2-12.4 GHz. The results show that SiC doped with 30% Al has the highest real part ε′ and imaginary part ε″ of permittivity and also loss tangent.