Investigating low-frequency dielectric properties of a composite using the distribution of relaxation times technique

Abstract

The distribution of relaxation times approach, a less frequently employed dielectric data analysis technique, is utilized to better understand the relaxation characteristics of composites consisting of metal-coated, hollow glass spheres dispersed in a paraffin wax matrix. The dielectric properties of the composite samples are measured by means of impedance spectroscopy in the frequency range 0.1 mHz to 10 MHz. The application of a mixture law is not appropriate for the analysis of the frequency-dependent properties of the considered system on this broad frequency range. However, utilization of the distribution of relaxation times procedure to study the dielectric behaviour shows clear trends in the mixtures’ relaxation spectra. Relaxation processes of the paraffin wax and those specific to the composites are found from the extracted distribution of relaxation times spectra. The influence of the filler concentration, q, on the dielectric properties is examined; a relaxation with a narrow distribution at intermediate frequencies becomes broad with the addition of the filler. This relaxation, in the form of the low-frequency-dispersions (also known as constant phase angle) phenomenon, dominates the dielectric properties of the composites with high bead concentration, q>0.15. The variation in dielectric properties of individual samples whose bead concentrations q are nominally the same is discussed in terms of possible microstructural variations.

Acknowledgment

Enis Tuncer is sponsored by the US Department of Energy, Office of Electricity Delivery and Energy Reliability, Superconductivity Program for Electric Power Systems, under contract No. DE-AC05-00OR22725 with UT-Battelle, LLC. Nicola Bowler's work was performed at the Center for NDE at Iowa state university with funding from the Air Force Research Laboratory through S&K Technologies, Inc. on delivery order number 5007-I0WA-001 of the prime contract F09650-00-D-0018.