Dielectric properties of carbon black-polyethylene composites below the percolation threshold

Changes in the dielectric properties, and their temperature dependence, related to the volume fraction of conducting filler for carbon black-polyethylene composites are discussed based on the effective medium approximation (EMA) theory. The composite satisfies the universal law of conductivity above the percolation threshold (p_c ) and gives a critical exponent of s=1 for the dielectric constant below p_c. The rate of the decrement of the % changes of relative dielectric constant and dielectric loss factor with temperature for the composites below p_c is enhanced by increasing the volume fraction. By incorporating the effect of thermal expansion into the EMA theory, the temperature dependence of relative dielectric constant and dielectric loss factor is successfully explained