Transport properties of conducting amorphous carbon-poly(vinyl chloride) composite

The dc electrical conductivity of composites of poly(vinyl chloride) filled with amorphous carbon (a-C) flakes has been studied from room temperature to 1.2 K. The dc conductivity shows percolative behavior and as a function of a-C content, follows the scaling law sigma alpha(p - p(c))(t) where p(c) is percolation threshold and t the critical exponent with values 0.0165 and 3.1, respectively. The value of t shows evidence for non-universal value of critical exponent. In the temperature range 1.2 K to 50 K-60 K all the samples show the thermal fluctuation induced tunneling of the charge carriers through the insulating layer of polymer separating amorphous carbon aggregates. At high temperatures the differential thermal expansion of PVC and amorphous carbon plays a crucial role in conduction mechanism that leads to positive temperature coefficient of resistivity near to room temperature. (C) 2005 Elsevier Ltd. All rights reserved.