A Raman Study of Iron-Phosphate Crystalline Compounds and Glasses

Ferrous and ferric phosphate crystalline compounds and glasses were studied using Raman spectroscopy. A comparison of the spectra from crystalline and glassy ortho-, pyro-, and metaphosphates indicates that similar phosphate anions constitute the structures of the respective materials, and some information about the compositional dependence of the phosphate-site distributions in the glasses can be gleaned from relative peak intensities. A correlation exists between the average P-O bond distance and the Raman peak frequencies in the crystalline compounds, and this correlation is used to provide information about the structures of the iron phosphate glasses. For example, the average P-O bond distance is estimated to decrease from about 1.57 angstrom for iron metaphosphate glasses (O/P similar to 3.0) to 1.54 angstrom for iron orthophosphate glasses (O/P similar to 4.0). These bond distances are in good agreement with those reported from diffraction studies of similar glasses.