NONLINEAR CURRENT-VOLTAGE CHARACTERISTICS IN ANISOTROPIC EPOXY-RESIN GRAPHITE FLAKE COMPOSITES

The conductivity of an isotropic composite materials constituted of si ngle-crystal graphite flakes in an epoxy resin and subjected to a vari able d.c. electric field has been studied. Non-linearities in the curr ent-voltage characteristics have been found and are discussed with in the framework of two theoretical models, the non-linear random resisto r network and the dynamic random resistor network. We show that our ma terials can be modelled by the non-linear random resistor network, whi ch, to our knowledge, is the first time that the predictions of this m odel seem so well supported in a real, three-dimensional composite.