Dielectric spectroscopy of polymer-metal composites across the percolation threshold

Polymer (polar/nonpolar)/metal composites (PMC) were prepared under different process conditions. In polar PMC, dipolar relaxation plays a predominant role below percolation threshold (f(c)) and anomalous low frequency dispersion (ALFD) becomes dominant above fc while ALFD is the only likely possibility for nonpolar PMC above f(c). The magnitude of relaxation exponents m, p and n, evaluated from the experimental results using Jonscher's universal dielectric response (JUDR) laws, falls within the universal limit similar to [ 0, 1] with additional feature of strong dependence on volume fraction of conductor (f(con)). The decrease in the relaxation exponent m with an increase of fcon is directly linked with decrease in the number of dipoles of the polymer in the composite and is accompanied by a distribution of relaxation time due to increased heterogeneity of the system. The magnitude of the relaxation exponent n decreases at f(c), due to the prevalence of Maxwell-Wagner-Sillar polarization contributed by uncorrelated electrons.