Raman spectroscopic study of nitrate glasses

Raman spectra have been measured on five series of glass compositions between the nitrates of calcium, cadmium, and magnesium and the nitrates of sodium and potassium. The composition dependence of the spectra can be broadly interpreted in terms of the structure of the glasses. Further, it is observed that for any given divalent cation–degenerate ν3 and ν4 modes tends to remain at constant frequency regardless of composition, while the higher frequency component shifts to higher values as the concentration of divalent cation is increased. A theoretical model is developed which includes both fixed and stochastic perturbations. Two exact theorems about the effect of perturbations on the vibrations of the nitrate anion are proved. Using these theorems as a guide it is shown how the results of some model calculations permit an explanation of the observed band splitting and the frequency dependence of the bands. The observed frequency trends both in glass and molten salt spectra, are largely independent of the detailed geometry of the model.