ALTERNATING-CURRENT ELECTRICAL-PROPERTIES OF RANDOM METAL-INSULATOR COMPOSITES

The complex a.c. impedance of three different random metal-insulator composites near their percolation threshold has been studied. These three metal-insulator systems include different shapes of nickel particles (filamentary and nodular shapes) in a matrix of polypropylene and silver particles in the matrix of potassium chloride. By using different metal-insulator structures and phases it is possible to elucidate the effect of different metal particle shapes and types of insulator phase on the electrical properties of these composites near their percolation threshold. Electrical properties, including d.c. conductivity, a.c. conductance, capacitance and dielectric loss tangent, of these metal-insulator composites as a function of metal volume fraction and frequency (5 Hz to 13 MHz) are presented. The results are correlated with structural characterization of these composites and are used to examine the applicability of different electrical transport models on these composite materials. The effect of different metal particle shapes on the percolation threshold and the power-law dependent percolation phenomenon is also discussed.