Effects of composition on the vibrational properties of sodium silicate glasses

The vibrational modes and the calculated Raman spectra of computer generated models of sodium silicate glasses are presented and discussed. The localization of the vibrational modes on non-bridging oxygens (NBOs) increases linearly with increasing NBO/Si in all spectral ranges. Strongest localization is observed in the low-frequency range near the 225 and 320 cm−1 vibrational bands. The shape of the partial Raman spectra of SiO4 tetrahedra with different number of NBOs (Qn species) is complex and depends both on the glass composition and the connectivity of the Qn species. The estimated Qn scattering cross-sections increase with increasing the number of bridging oxygens.