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Abstract
Composite materials made from Calcium modified Lead Titanate grains embedded in a copolymer matrix of poly(vinyledene fluoride trifluorethylene) have been produced in order to optimise their pyroelectric and piezoelectric properties.
The resulting coefficients are dependent both on the electrical, mechanical and thermal properties of the constituents materials and the morphology of the composite (i.e. connectivity, grain size of the ceramic).
However in order to predict the properties of these composites one must take into account the degree of poling of the ferroelectric ceramic grains. This is specially so in composites with 0-3 connectivity as opposed for instance to the 1-3 connectivity pattern in which the poling voltage will be appear both across the polymer and the ceramic phases making the estimation of the poling of the ceramic easier. The materials we fabricated can be thought of as a mixed 0-3 and 1-3 connectivity composite. This will depend on the grain size of the ceramic used (relative to the thickness to the sample) and on the ceramic loading which can be as high as 65%.
In this paper we study the poling behaviour of 0-3 composites taking into account the resistivity and dielectric constant mismatch of the polymer/ceramic system as a function of temperature. Here we point out that the polymer used has a ferroelectric phase transition at 127°C so that a better dielectric matching is achieved at these temperatures. Ferroelectric hysteresis measurements is also reported as a function of the temperature and frequency.
