Dielectric properties of barium titanate prepared by hot isostatic pressing

Densification behavior and grain size of BaTiO3 as a function of temperature were compared between hot isostatic pressing (HIP) and pressureless-sintering in air. The HIP-treatment under a pressure of 160 MPa lowered the densification temperature by 250 degrees C compared to pressureless-sintering for the achievement of relative density above 90%, Grain growth occurred faster in the HIP-treatment than in pressureless-sintering at a similar heating temperature. The decrease of grain size from 3 to 0.5 mu m resulted in the change of crystal structure from tetragonal to cubic. The dielectric constant at room temperature showed a maximum at a grain size of 1.4 mu m, independent of the density of BaTiO3. Porosity significantly affected the dielectric loss (tan delta) of BaTiO3. Decrease of porosity in the early stage of sintering drastically reduced the dielectric loss, The dielectric loss of BaTiO3 in the final stage of sintering correlated with the volume of closed pores.