The Pyroelectric Coefficient of Composites

The effective physical properties of composites are generally depending on the properties of the constituents, the volume ratio, and the shape and spatial arrangement of the components (e.g. the connectivity) in a quite complex way. This is the reason why problems like the dielectric constant of composites have kept scientists busy over more than a century. In the case of properties like the pyroelectric coefficient we have derived a simple relation which is of universal validity if only the following assumption is accepted: the dielectric constants of the constituents do not change under the influence of the electric field generated by the pyroelectric activity. This assumption holds usually very well in pyroelectric materials, as the electric field which results from the pyroelectric activity is much smaller than the electric field required to induce a significant variation of the dielectric constant. In this general relation, the pyroelectric coefficient of the composite is written as a function of the pyroelectric coefficients and dielectric constants of the constituents, the volume ratio and the effective dielectric constant of the composite material. Shape and spatial arrangement of the components are not directly involved in the relation, the influence of these is all included in the effective dielectric constant of the composite. Therefore, this relation gives a correct description for all kinds of connectivities and gives an easy access to the optimization of pyroelectric composites, e.g. by the specific introduction of some conductivity into the materials.