Dielectric Constant Anomaly in PZT/Ag Functional Composites

The PZT/Ag composites were fabricated via conventional powder processing at 1200℃ by using PZT and Ag powders as the starting materials. Although the sintering temperature being higher than melting point of Ag, the pure Ag particles were homogeneously dispersed in the PZT matrix with sound PZT/Ag interfaces, and no metallic alloys between Ag and Pb were formed. At the same time, a small quantity of Ag was found to diffuse into the Pb-lattice. In the range of 0-15vol% Ag, the dielectric properties of the PZT/Ag composites were investigated. The results show that the relative dielectric constant er first decreases when Ag concentration is 1vol%, and then increases gradually up to 15vol%. This dielectric constant anomaly was explained on the basis of A-site cation substitution of perovskite structure as well as the percolation theory. In the lower Ag concentrations, the Ag+ substitutes Pb2+ and decreases the dielectric constant and this is the dominant mechanism; with the increase in Ag concentration, the effective dielectric field is established to increase the dielectric constant and it gradually becomes the dominant mechanism.