Effects of pore structures on the dielectric properties of silicon nitride-based ceramics

The pore structures are invariably ignored when evaluating the dielectric properties of silicon nitride (Si3N4) ceramics. In this work, the effects of pore structures on the dielectric properties were revealed using both theoretical models and experimental evaluation. Theoretical models illustrate that the pore geometry and average pore radius are the determinants of dielectric properties when porosity remains constant. Experimentally, Si3N4-based ceramics with different pore structures were achieved via adding different amounts of beta-Si3N4 whiskers. Then the correlations between dielectric properties and pore structures were investigated. The marked variation between experimental dielectric constants and three homogeneous isometrical sphere models reveals that the pore structures have conspicuous effects on the dielectric properties, as well as the consistent loss tangents.