Iron redox equilibrium, structure and properties of zinc iron phosphate glasses

Iron redox equilibrium, structure and properties were investigated for the 10ZnO–30Fe2O3–60P2O5 (mol%) glasses melted at different temperatures. The structure and valence states of the iron ions in these glasses were investigated using Mössbauer spectroscopy, Raman spectroscopy and differential thermal analysis. Mössbauer spectroscopy indicated that the concentration of Fe2+ ions increased in the 10ZnO–30Fe2O3–60P2O5 (mol%) glass with increasing melting temperature. The Fe2+/(Fe2+ + Fe3+) ratio increased from 0.18 to 0.38 as the melting temperature increased from 1100 to 1300 °C. The measured isomer shifts showed that both Fe2+ and Fe3+ ions are in octahedral coordination. It was shown that the dc conductivity strongly depended on Fe2+/(Fe2+ + Fe3+) ratio in glasses. The dc conductivity increases with the increasing Fe2+ ion content in these glasses. The conductivity arises from the polaron hopping between Fe2+ and Fe3+ ions which suggests that the conduction is electronic in nature in zinc iron phosphate glasses.