MODELLING OF THE BEHAVIOUR OF HOPPING CONDUCTIVITY IN A SOLID EXHIBITING A SEMICONDUCTOR-INSULATOR TRANSITION, AS A FUNCTION OF FREQUENCY

We propose a model which explains the evolution of the frequency dependent conductivity while an organized structure appears in an initially amorphous system. We assume that the cristalline organization is connected with the existence of an anisotropy. An anisotropy parameter is calculated. An "a priori" calculation of the conductivity is developped, which correctly accounts for the experimental results obtained on "low temperature" carbons

Measurements of radiation induced defects in quartz material by Dielectric Relaxation Spectroscopy

International audienc

Comparison between thermally-stimulated current and complex impedance spectroscopy measurements on a dehydrated Ca-montmorillonite

International audienc

Complex Impedance Spectroscopy of alkali impurities in as-grown, irradiated and annealed quartz

This work compares the dielectric relaxation properties of different crystalline quartz materials, according to their source (natural or synthetics). It is shown that these relaxation properties are due to a hopping process of alkaline (Li+, Na+ and K+) impurities, located near [Al-O4]5- tetrahedra. A detailed analysis, in terms of the distribution function of the dielectric loss peak, allowed us to perfectly distinguish the different types of as-grown quartz. We show that i) the natural quartz has less stable M+ charge carriers than the synthetic materials and that ii) the homogeneity of the M+ trapping sites, created by the [Al-O4]5- tetrahedra, strongly depends on the crystal growth conditions. These features were then studied using quartz samples with different treatment conditions: as-grown, irradiated or annealed at high temperature. We propose that the irradiation greatly facilitates the M+ relaxation, by creating additional low energy M+ hosting sites, whose number depends on the source of the quartz crystals. We also show that for 100kRad irradiation, the saturation state of the defects is already reached for all the materials under consideration. Finally, we propose that irradiation followed by annealing at 450°C improve the M+ stability and homogeneity in quartz materials, compared with the as-grown materials, this trend being much more relevant for the natural than for the synthetic quartz