Our 17O Dynamic-Angle Spinning (DAS) result on silica glass is quite significant because it revealed an unexpected result that both the distributions Si-O distance and Si-O-Si in silica glass are considerably narrower than all previous diffraction studies, i.e., revealing a more ordered structure than previously thought. Even more arresting, however, is our finding of a strong positive correlation between Si-O-Si angle and Si-O distance, i.e., Si-O distance decreasing with decreasing Si-O-Si angle.
This trend would seem counter-intuitive to many in terms of steric effects (local energetics), and also because it runs opposite to trends generally found in crystalline silica polymorphs. On the basis of variable temperature and pressure structural studies of quartz, however, we speculate that this behavior may result from the disequilibrium nature of the glass. Such results will certainly lead to revisions of a number of currently popular structural models, and could provide the impetus to develop new models.
Other References and Related Resources from our Lab
Correlated Structural Distributions in Silica Glass
T. M. Clark, P. J. Grandinetti, P. Florian, and J. F. Stebbins
Dependence of bridging oxygen 17O quadrupolar coupling parameters on Si-O distance and Si-O-Si angle,
T. M. Clark and P. J. Grandinetti