THEORY OF FERROELECTRIC POLYMER-CERAMIC COMPOSITES

A model is proposed to establish the relevant constitutional parameters of ferroelectric composite materials such as shape, composition, and connectivity which determine the piezoelectric, dielectric, and elastic properties of the composite. A proper Monte Carlo method is used to calculate the active volumetric fraction of ceramic. An equivalent circuit is proposed to calculate the effective dielectric constant. The effective medium expressions for the dielectric constant, elastic constant, and local field coefficients (L E, LD, LS, LT) are generalized to include shape effect. These results are used to calculate the piezoelectric coefficients. Recently, some authors have proposed a model and claimed to have established the degree of heterogeneity, determined by the scaled average grain diameter, to be the important constitutional parameter of a composite. We argue that the important constitutional parameter is the volumetric fraction of the ceramic. Our model is simpler, uses fewer parameters and its predictions compare better with experiment. The simplicity of the model can be exploited for predictions of the properties and design of multi-phase ferroelectric composites.