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^- Ca^2+-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. (author)