Investigation of A1-O-Si bond angle in glass by Al-27 3Q-MAS NMR and molecular dynamics

The Al-O-Si bond angles were investigated in sodium aluminosilicate glasses with variable calcium content by two complementary methods. We developed t he spectrum inversion for the Al-27 MQ-MAS to infer quantitative distributi ons of isotropic chemical shifts, enabling us to estimate an angular distri bution. The experimental data were then compared with molecular dynamics si mulations. In both cases, the Al-O-Si angle was observed to decrease as the calcium concentration increased. Structural analysis accounts for this eff ect by the gradually diminishing distance - and therefore the increasing in teraction - between the network modifiers and oxygen atoms near aluminum. A similar but less intense effect is predicted for the Si-O-Si angles. (C) 2 000 Elsevier Science B.V. All rights reserved.