Fe3+ as the Main form of Iron Ions in Iron-Lead-Phosphate Glasses

Electron Paramagnetic Resonance EPR, hydrostatic density (ρ), molar volume (V), differential thermal analysis (DTA) and infrared spectroscopy measurements have been employed to investigate the effect of Fe2O3 content on the physical properties of a series of iron-lead-phosphate glasses in the system (100-2x)Fe2O3–xPbO-xP2O5 with x = 12.5, 15, 17.5 and 20 mol%. The samples have been prepared by melting the mixtures under normal atmosphere at 1300 ± 20° C. The EPR spectra, for all samples, reveal the presence of an intensive resonance peak at g ~ 2 which is attributed to Fe3+ ion located in a site with high symmetry. A monotonic increase in (ρ) value and a corresponding decrease of the (V) value are also detected with increasing Fe2O3. The increasing value of the glass transition temperature Tg with Fe2O3 content as detected by DTA indicates the increase of the degree of bridging. The increased (Tc-Tg) value reveals the stability of iron-rich phosphate glasses. The experimental IR absorption bands have been identified. The data have been discussed in terms of the formation of Fe3+ as the main form of iron ions in ironlead-phosphate glasses.