Inter-tetrahedra bond angle of permanently densified silicas extracted from their Ramanspectra

Abstract

Relative Raman scattering intensities are obtained in three samples of vitreous silica ofincreasing density. The variation of the intensity upon densification is very different forbending and stretching modes. For the former we find a Raman coupling-to-light coefficient. A comparative intensity and frequency dependence of the Raman spectral lines inthe three glasses is performed. Provided the Raman spectra are normalized byCB, there exists a simple relation between the Si–O–Si bond angle andthe frequency of all O-bending motions, including those of fourfold (n = 4) andthreefold (n = 3) rings. For 20% densification we find a reduction of∼5.7° of the maximum of the network angle distribution, a value in very closeagreement with previous NMR experiments. The threefold and fourfold ringsare weakly perturbed by the densification, with a bond angle reduction of∼0.5° for the former.