Effect of porous structure on the dielectric properties of silicon nitride ceramics

Two different series of porous silicon nitride ceramics, whose volume fractions of porosity are from 0 to 0.6, were fabricated using two different preparation routes: (i) the addition of pore-forming agent, and (ii) freeze-drying processing. Effects of the amount of pore-forming agent and the concentration of water-based slurry on porosity were investigated. In order to predict and understand experimental dielectric properties-porosity relationships, porosity, porous structure and dielectric properties were evaluated separately for each series of materials. The results showed that besides the volume fraction porosity, the geometrical nature was also a major factor that influences the dielectric properties of the samples.