Electrical properties and structure of lead-borate glass containing iron ions

Abstract

The ac and dc conductivity in iron–lead-borate glass samples was investigated in the frequency range from 1mHz to 1MHz and in the temperature range from 153K to 423K. The structure was investigated by the means of atomic force microscopy (AFM) and the crystalline phases (if present) were identified by the means of X-ray diffractometry. Two types of ac electrical behaviour were observed. The first group of glass samples which contain up to 31% mol Fe2O3 shows singular flattened semicircle in the impedance spectra. The second group of glass with over 25% mol Fe2O3 shows two distinguishable semicircles indicating two relaxation processes.The results of structure investigation show that glass samples containing more than 2.5% mol Fe2O3 contain ball-shaped nanostructures. They have average size of an order of magnitude 100nm. In XRD patterns for glass containing less than 19% mol Fe2O3 there are no diffraction peaks while in the patterns for samples with a larger amount of iron oxide some small peaks are present which indicate that some crystalline phases exist in these samples. In glass containing up to 19% iron oxide one process is responsible for conduction mechanism, small-polaron hopping. In the glass samples containing more of iron oxide, two dielectric relaxation processes were found. The second process may be caused by interface effect or conductivity process in the granules.