MULTICOMPONENT POLYMERIC COMPOSITES

New types of composite systems based on polymeric matrices (polystyren e, polyethylene) containing conductive (Pd, Ag, Ag alloys) and dielect ric (ferroelectric) components such as BaTiO3 or piezosonic powder wer e developed and investigated in bulk and as thick films. The latter we re prepared using a screen-printing technique applying the composite p aste on alumina, thermoset, enamelled steel and ceramic-coated Cu subs trates. In samples with a spatially homogeneous distribution of the me tal particles, as was the case with Pd, incorporation of the dielectri c component caused a marked decrease of the percolation threshold. The opposite was true when the particles were inhomogeneously distributed (Ag), namely, in thick films. Dielectric measurements showed that the real part of the complex permittivity increased substantially with th e content of both the dielectric additive and the metal component, esp ecially at high resistivity levels. Thick films are interesting becaus e the constant positive temperature coefficient of resistance can be u sed to make temperature sensors screen-printed on various substrates, for instance, on insulated metal.