Laboratoire Charles Coulomb UMR 5221 CNRS/UM2 (L2C)


Accueil > La Recherche > Axes & Equipes > Matière Molle & Verres > Equipe : Physique des Verres > Thème : Structure, vibration, relaxations dans les systèmes désordonnés

Small ring density and inter-tetrahedra bond angle of permanently densified silicas : Femtosecond and Raman spectroscopy study

par Sébastien LAYSSAC - publié le , mis à jour le

Involved researchers : B. Hehlen, M. Foret

(Collaboration with P. Langot, J. Burgin, and F. Vallée, CPMOH-Bordeaux)

Normal and permanently densified silica glasses (SiO2) have been investigated using a time resolved pump-probe technique and spontaneous Raman spectroscopy. Comparison of the amplitudes of the time- and frequency-domain responses reveals a much larger increase in concentration of three-membered rings as compared to four-membered ones upon densification. The variation of the intensity upon densification is also very different for bending and stretching modes. For the former we find a Raman coupling-to-light coefficient CB µ w2. We performed a comparative intensity and frequency dependence of the Raman spectral lines in the three glasses. Provided the Raman spectra are normalized by CB, there exists a simple relation between the Si-O-Si bond-angle and the frequency of all O-bending motions, including those of fourfold (n=4) and threefold (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 close agreement with previous NMR experiments. The threefold and fourfold rings are weakly perturbed by the densification, with a bond-angle reduction of ~ 0.5° for the former.