Raman Spectroscopy of Calcium Phosphate Glasses with Varying CaO Modifier Concentrations

Raman spectroscopy has been performed on a series of calcium phosphate glasses prepared from calcium dihydrogenphosphate and CaO in which the CaO content is varied from that of the metaphosphate stoichiometry, in which the mole ratio of CaO to P₂O₅ is 1.00, to a stoichiometry in which the mole ratio is 1.49. Investigation of the vibrational behavior provides insight into the effects of the CaO modifier on the depolymerization processes occurring in these phosphate glasses. Curve-fitting procedures are used to accurately identify peak positions and resolve overlapped bands in the spectra. Depolymerization of the phosphate chains is clearly observed in the vibrational spectra as indicated by shifts in the v_s(POP), v_s(PO₂), and v_as(PO₂) vibrations. At the largest CaO modifier concentrations, distinct crystalline phases of α- and γ-Ca₂P₂O₇ are observed. Analysis of the Raman spectra for these systems suggests that crystallization occurs from the short chain regions of the glass.