Studies of structure of calcium–iron phosphate glasses by infrared, Raman and UV–Vis spectroscopies

Glasses in the ternary CaO–Fe2O3–P2O5 system were prepared and studied by means of density, differential scanning calorimetry, infrared, Raman and UV–Vis spectroscopies. The results showed that density and molar volume in the glass system decreased with increasing substitution of CaO for Fe2O3. The variation of glass transition temperature and thermal stability was strictly related to the nature of bonding in the vitreous network. Spectroscopic analysis showed that substitution of CaO for Fe2O3 induced an evolution of structural units from pyrophosphate to metaphosphate species indicating the polymerization of phosphate chains and the decrease of non-bridging oxygen concentrations. With increasing substitution of CaO for Fe2O3 The P–O–Ca linkage and (P–O− Ca2+ −O–P) chains participated in the glass network by replacing P–O–Fe bonds. The absorption band of the P–O–Ca stretching mode in the glasses with high CaO content (≥32 mol%) was assigned at around 1084 cm−1. The absorption edge would fall in the region between 332 and 420 nm which are the absorption bands of Fe3+ ions.