Electrical conduction mechanism in lead borate and lead silicate glasses containing Fe ions

The electrical conductivity σ/sub DC/ is measured of the glasses in the system (x Fe2O3PbO / 2 B2O3) where x, in moles, varies from 0.1 to 0.6. The conductivity in the temperature region 100 to 350 K follows an expected Arrhenius type behaviour with a slight curvature in ln σ vs. 1/T curves for glasses with x <= 0.4. The novel feature is that Moessbauer spectra for the glasses x <= 0.4 do not show the presence of Fe2+ ions and therefore conduction must be assumed as thermally activated hopping on the distribution of Fe3+ over octahedral and tetrahedral sites. The glasses with higher concentrations of Fe show two activation energies and this is attributed to the presence of crystalline phase of αFe2O3 in these glasses. The existence of crystalline phase is confirmed by Moessbauer spectra. αFe2O3 is a semiconductor but neither of the two activation energies agrees with the reported bandgap. The conduction in these glasses is therefore probably a mixture of hopping over the sites and extended state conduction through islands of αFe2O3 with defects. A detailed quantitative model is under study. (author)