Complex ac conductivity of a carbon black composite as a function of frequency, composition, and temperature

The complex conductivities between 10 mHz and 1 MHz of a series of disordered carbon-black-polymer composites have been measured. The carbon black volume fractions span the percolation threshold, with de conductivities ranging from 10(-18) to 10(-6) (Omega cm)(-1). The room temperature results are similar to previous measurements on other percolation systems. Conductivity measurements as a function of temperature on a composite sample, slightly above the room-temperature percolation threshold, are consistent with the percolation threshold increasing with temperature and becoming equal to the actual volume fraction at about 130 degrees C. The real conductivity at different temperatures is shown to scale onto a single curve. An anomalous peak in the real dielectric constant as a function of composition close to the percolation threshold is also observed. [S0163-1829(99)13441-6].