Résumé
We have shown in a previous study that the Raman spectra of aluminosilicate glasses were sensitive to vibrations of network-modifiers cations. On the contrary, the contribution steaming from charge compensator cations is very weak providing thereby an experimental contrast to differentiate these two structural cation environments [1]. Complementary experiments have been performed in borosilicate glasses and lead to the same conclusions. Sodo-silicate and borosilicate glass models have also been obtained using ab-initio numerical simulations and the atomic vibrations have been calculated. The simulations show that two vibrational contributions of network-modifier cations are expected at frequency between ~150cm-1 and 380cm-1, in very close agreement with the experimental observations. A vibrational analysis performed in a series of sodosilicate glasses reveals that these modes originate from dangling and stretching motion of the cation relative to its nearest non-bridging oxygen. The same type of analysis is in progress for borosilicate systems.