Evaluation of dielectric models for ceramic/polymer composites : effect of filler size and concentration

Abstract

The main theoretical models for evaluation of the dielectric constant of ceramic/polymer composites are summarized and applied to PZT/poly(vinylidene fluoride) and BaTiO3/poly(vinylidene fluoride) composites with varying filler concentration and size in order to evaluate the suitability of the models and the main interactions that are responsible for the composite dielectric behavior . All models predict an increase in dielectric constant with increasing filler content. On the other hand, this increase is different for different models, showing the relative importance of the different interactions. Experimentally, the size of the inclusions plays an important role in determining the dielectric behaviour of a composite, especially at the nanoscale. Effects occurring at the interface between the filler particles and the matrix become important as the relative surface area at the interface increases. Models not including fitting parameters do not properly represent the increase in dielectric constant with increasing filler content and none of them seems to properly represent the dielectric behavior of nanocomposites. In this way, the effects contemplated by the models – interactions between the particles, interactions with the field, depolarization factor or shape parameter – are not sufficient to account for the variations of the dielectric behavior related to the sizes of the particles.