IR fundamental spectra and structure of pyrophosphate glasses along the 2ZnO center dot P2O5-2Me(2)O center dot P2O5 join (Me being Na and Li)

The IR reflection spectra of mixed zinc alkali pyrophosphate glasses in the broad frequency ranges are reported and the quantitative treatment of these with a version of the dispersion analysis method was conducted based on the specific analytical model of the complex dielectric constant of glasses. Numerical data on the optical constants, band frequencies, and band intensities are calculated. Results obtained are interpreted in terms of vibrations of the (PO3)(2-) and (PO2)(-) terminal groups, (PO4)(3-) anion, and P-O-P bridge. The presence of all these groups in the structures of glasses under study is confirmed and the formation of the (P3O9)(3-) ring metaphosphate anion rather than the chain polymeric phosphate anions is suggested. The gradual decrease in the width of the anion distribution toward the pyrophoshate anion with the Me(2)O for ZnO substitution is also confirmed. It is shown that this decrease determines the IR spectrum variations observed in the 0 to about 27 mol% Na2O composition range. The amounts of the (PO4)(3-) and (P3O9)(3-) anions are shown to become negligible in the structures of glasses with Na2O content greater than 30 mol%, and the IR spectrum variations observed in the 27-45 mol% Na2O composition range are shown to be mostly due to the intensity redistribution from the low-frequency component of the asymmetric stretch of the (PO3)(2-) terminal group to the high-frequency component of the same stretch.