Effect of zirconium concentration and doping with Sr and Al on the sintering and electromechanical properties of lead zirconate titanate ceramics

The effect of small additions of Sr and Al on the dielectric and electromechanical properties of lead zirconate titanate (PZT) ceramics of different Zr/Ti ratios has been studied. Dielectric constants greater than 1200 and reached 1500 for polarised doped samples were obtained along with planar couplings of about 0.5. Variations of dielectric constant were found to be porosity dependent. Doping enhanced sintering, caused a shift in the morphotropic boundary toward the rhombohedral side, decreased the lattice distortion from cubic symmetry and caused grain growth inhibition. Anomalous density increase for Sr doped samples took place above 1150°C while samples doped with both Sr and Al showed such anomaly over all the investigated temperature range.The results were interpreted on the basis of the role played by crystal defects, the fluxing effects of the doping materials, and Coble's model of bulk diffusion of vacancies from pores to grain boundaries in relation to wall mobility.