Bimodal distribution of Si-O-Si angles in sodo-silicate glasses

Polarized Raman scattering is performed in a series of sodo-silicate glasses. The Si-O-Si inter-tetrahedral angle and its distribution are extracted using a model developed previously for densified silica, and the result are compared to ab initio atomistic calculations. The two techniques reveal a reduction of the most probable angle of about 0.30°/mol% of Na2O, but the shape of the angular distributions are different. The results suggest that Raman scattering enhances a specific angular distribution of Si-O-Si bridges, likely those close to sodium atoms, highlighting local angular heterogeneities.