Analysis of frequency dependence of complex impedance and electrical characterization of Fe2O3/kaolin ceramics for civil engineering applications

The complex impedance spectroscopy (CIS) method is usually used in order to analyze the electrical response of different semiconducting disordered materials as a function of frequency at different temperatures. The real and imaginary parts of the complex impedance can show different semicircles in the complex plane that give evidence for the presence of both bulk and grain boundary contributions. Many parameters can be deduced from the analysis of CIS data, such as relaxation times and activation energies. There are some literature data concerning electrical properties of clays and (semiconductor, sand, cement,…)/clay mixtures. Most of the published works are related to the AC conductivity of rocks with the effect of water or oil content but there are no similar studies on the characterization of the microstructure of individual clays as ceramic materials by analyzing their temperature and frequency dependence of their electrical conductivities. Hence, this paper presents an analysis of electric complex impedance of the Fe2O3/Kaolin composite in the high temperature range up to 740 °C. Sinusoidal voltage with frequency in the range [100 Hz, 1 MHz] is applied to the material in order to measure the electrical conductivity for various concentrations of Fe2O3 from zero to 100 %. The activation energies for the conduction and for the relaxation processes are determined and their dependence on the density of Fe2O3 analyzed. Furthermore, let's found that Fe2O3 have the effect to increase the electrical conductivity in our samples. From the Nyquist diagrams, only one semi-circle related to the contribution of the grains to the total electrical conduction is identified for all investigated samples