Temperature dependence of resistivity of carbon black-polyethlene composites below and above the percolation threshold

Temperature dependence of resistivity /spl rho/ of carbon black (CB)-polyethylene composites with volume fraction /spl rho/ below and above percolation threshold /spl rho//sub c/ is studied based on the electrical conduction mechanism. The temperature dependence of /spl rho/ of the composites with /spl rho/ below /spl rho//sub c/ can be explained with a tunneling conduction model by incorporating the effect of thermal expansion of the composites into a tunneling gap. On the other hand, the temperature dependence of /spl rho/ of the composites with /spl rho/ above /spl rho//sub c/ shows a negative TCR in low temperatures and the absolute value of TCR is getting larger with more CB loading. By assuming that the electrical conduction through percolating paths is a thermally activated process and incorporating the effect of thermal expansion into /spl rho/, the temperature dependence of /spl rho/ above /spl rho//sub c/ has been well explained and the apparent activation energy is estimated at 0.14 eV.