Environment of Fe3+ ion and its influence on dielectric and spectroscopic properties of Pbo–Nb2O5–P2O5 glasses

PbO–Nb2O5–P2O5 glasses containing different concentrations of Fe2O3 (ranging from 0 to 3 mol%) were prepared. A number of studies viz., chemical durability, differential thermal analysis, spectroscopic (infrared, optical absorption ESR spectra) and dielectric studies (constant ε′, loss tan δ, AC conductivity σAC over a range of frequency and temperature) of these glasses have been carried out. The results of these studies have been analyzed in the light of different oxidation states of iron ions. The analysis indicates that the iron ions (when present in the concentration range, 0.2–1.0 mol%) exist mostly in trivalent state and occupy both tetrahedral and octahedral substitutional positions and are found to increase the rigidity of the glass network. However, in the concentration range of 1.0–2.5 mol%, the iron ions in the glass network seem to be existing by and large in Fe2+ state, occupying predominantly octahedral positions and are acting as modifiers.