Iron phosphate glass from Fe4(P2O7)3: A new approach

Iron phosphate glass of composition 40 mol% Fe2O3–60 mol% P2O5 is generally prepared by melt quench technique using a mixture of Fe2O3 and NH4H2PO4 at 1423 K (labelled as IPG-A). Though the starting material contains only Fe3+ ions, the resultant glass is found to contain different concentrations of Fe2+ ions depending on the conditions of preparation. Hence an attempt was made to synthesize iron phosphate glass (labelled as IPG-D) from Fe3+ containing crystalline compound, Fe4(P2O7)3 (synthesized through solution route) whose composition is the same as that of IPG-A. IPG-D could be quenched at 1323 K, which is 100 K less than the normal pouring temperature of IPG-A. Synthesized IPG-D was investigated for its phase purity and structure by XRD, Mössbauer and Raman spectroscopy. No phase separation was observed during the investigation. Importantly we report the formation of IPG-D with almost all Fe ions in 3+ valence state for the first time. The advantage of using a crystalline compound for the formation of iron phosphate glass is presented.