Raman spectroscopic investigation of the structure of silicate glasses. III. Raman intensities and structural units in sodium silicate glasses

摘要

The Raman scattering intensity of the 1100 cmminus;1polarized band, which appears on the addition of Na2O to SiO2glass, reaches a maximum at the disilicate composition. The intensity of the polarized band at 950 cmminus;1increases sharply as the Na2O concentration increases above 30 molethinsp;percnt;. These data were interpreted by normal mode calculations and by IR and Raman intensity calculations for the silicate anion structural units: SiO4isolated tetrahedra, Si2O7dimers, Si2O6chain links, Si2O5sheet units, and Si2O4framework units. According to these simplified models, the polarized high frequency band is due to symmetric stretching of Sindash;Ominus;nonbridging bonds and the frequency increases with degree of polymerization of the tetrahedra. The previous assignments of the 1100 cmminus;1band to the symmetric stretch of tetrahedra containing one nonbridging oxygen and of the 950 cmminus;1band to the symmetric stretch of tetrahedra containing two nonbridging oxygens were confirmed. The other main feature of the alkali silicate glasses, an intense polarized band in the range of 400ndash;600 cmminus;1, was shown to be a mixed stretching bending mode of the Sindash;Ondash;Si bridging bond. The model also accounts for the loss of intensity of the high frequency band with increasing degree of silica polymerization.