Evolution of Davidson-Cole relaxation behavior in random conductor-insulator composites

The evolution of the frequency-dependent, complex dielectric permittivity of three-dimensional, random conductor-insulator composites as a function of conductive inclusion concentration is explored by numerical simulation. A smooth transition from Debye behavior at low inclusion concentrations to a non-Debye, Davidson-Cole relaxation structure at higher concentrations is typically observed below the percolation threshold. The prevalence of the Davidson-Cole behavior and variations in relaxation parameters with respect to clustering statistics are explored through a survey of random networks. The dielectric response in denser composites is also explored, in both a standard randomly filled, percolating configuration and in a different type of random filling in which percolation has been deliberately prevented. In both cases, the relaxation component continues to exhibit a Davidson-Cole functional form. The passage through percolation does not strongly affect the Davidson-Cole exponent in the standard filling case, but in the percolation-prevention case a strong increase in exponent with inclusion concentration is observed. (C) 2003 American Institute of Physics.