Multi-component polymeric composites

New types of composite systems based on polymeric matrices (polystyrene, polyethylene) containing conductive (Pd, Ag, Ag alloys) and dielectric (ferroelectric) components such as as BaTiO 3 or piezosonic powder were developed and investigated in bulk and as thick films. The latter were prepared using a screen-printing technique applying the composite paste on alumina, thermoset, enamelled steel and ceramic-coated Cu substrates. In samples with a spatially homogeneous distribution of the metal particles, as was the case with Pd, incorporation of the dielectric 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 the content of both the dielectric additive and the metal component, especially at high resistivity levels. Thick films are interesting because the constant positive temperature coefficient of resistance can be used to make temperature sensors screen-printed on various substrates, for instance, on insulated metal.