Lossy AlN–SiC composites fabricated by spark plasma sintering

Dense lossy AlN–SiC composites doped with Y₂O₃ were fabricated by spark plasma sintering (SPS). Both the microstructure and the dielectric properties are different from those of hot-pressed samples. Microstructure analysis reveals little solid solution (AlN)_x(SiC)_1-x is formed. Scanning evanescent microwave microscopy images show that the materials by SPS exhibit large contrast in dielectric permittivity, whereas the hot-pressed materials show very mild fluctuation in dielectric permittivity over the samples. The results indicate that AlN–SiC composites fabricated by SPS can be treated approximately as a mechanical mixture of AlN and SiC when estimating complex permittivity of the composite in the microwave range. The complex permittivity of the composites with different SiC contents can be phenomenologically predicted by effective medium approximation.