DC electrical conduction below the percolation Pc is due to a tunneling mechanism between finite clusters because of a non-ohmic behavior of current and an appearance of a current independent of frequency in ac conduction. The temperaturedependence of resistivityρ depending on applied field can be well explained with a tunneling model by incorporating the effect of thermal expansion on a tunneling gap in the model.In the region above Pc, on the other hand, the electrical conduction takes place on conducting pathways between electrodes. The temperature dependence of resistivity p above Pc is discussed with a model where the effects of thermal expansion on the number of conducting pathways and a thermally activated process in electrical conduction are taken into account.
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