The Effect of Excess PbO on Crystal Structure, Microstructure, Phase Transition and Dielectric Properties of (Pb0.75 Sr0.25)TiO3 Ceramics

This study investigated the effect of excess PbO on the crystal structure, microstructure, phase transition and dielectric properties of (Pb0.75Sr0.25)TiO3 (PST25) ceramics. The PST25 ceramics were synthesized by the solid-state reaction method with various excess PbO levels (0, 1, 3, 5 and 10 wt.%). The excess PbO was added to compensate for the lead loss from evaporation during calcination and sintering at 950 degrees C and 1150 degrees C. The X-ray characterization revealed that all samples had a tetragonal structure and impurity phases since PbO and PbO2 were detected in the calcined powders with higher than 3wt% of excess PbO. A pure perovskite phase was obtained in all ceramic samples. The c/a ratios tended to decrease with an increasing excess PbO in the calcined powders and sintered pellets. The average particle size and the average grain size of the PST tended to increase with an increase of PbO content. With 1 wt.% of excess PbO, the highest density and a broader dielectric peak were obtained. The dielectric spectrum was not present in the 3, 5 and 10 wt.% excess of PbO samples. The DSC results indicated that the Curie point shifted to a higher temperature with the increase in the excess of PbO until 3wt.%, then slightly decreased with higher excess PbO.