Dielectric relaxation and a.c. conduction phenomena of PbO-PbF2-B2O3 glasses doped with FeO

PbO-PbF₂-B₂O₃ glasses containing different concentrations of FeO have been prepared. The glasses are characterized by X-ray diffraction and differential thermal analysis. The dielectric properties viz., dielectric constant, loss, conductivity, over a moderately wide range of frequency and temperature and dielectric breakdown strength have been investigated. The results of these studies have been analyzed in the light of different oxidation states of iron with the aid of the data on IR, ESR, optical absorption and magnetic susceptibility measurements. The analysis shows that iron ions exist mainly in Fe³⁺ state, occupy tetrahedral positions and increase the insulating strength of the glass if FeO is present in smaller concentrations. However, if FeO is present in higher concentrations in the glass matrix, (i) the dielectric relaxation intensity has been observed to increase, (ii) the intensity and the half width of the ESR signal has been observed to decrease and (iii) the value of magnetic moment (evaluated from magnetic susceptibility) has been observed to drop to a value of 4.6 μ_B from 5.7 μ_B. From these results it has been concluded that in this concentration range, iron ions exist mainly in divalent state.