Influence of electric field on the resistivity of a particulate layer

The measured resisitivity of a compacted layer of high-resistivity particulates descreases as the magnitude of the measuring electric field i s increased. This reduction in resistivity, which occurs for even quite moderate field intensities, is due to the particulate nature of the layer. High local electric fields are generated in the vicinity of the contact spots between particles. This reduces the bulk resistivity of the particle material. It also causes charge to be transferred across the small airgaps near the contact spots, thus increasing their effective area and reducing the effective resistivity of the layer. The electrical characteristics of the contacts are investigated experimentally by means of scaled up models, and these two effects of the high local fields are demonstrated experimentally. A semiempirical expression for the resistivity of a layer is developed that takes into account the particulate nature of the layer, particle material, bulk electrical properties, temperature and average electric-field intensity.