Avoidance of a continuous-random-network in vitreous silica: Entropic and energetic consequences

The relative entropic contributions of correlated vs. uncorrelated SiO bond length and SiOSi bond angle distributions in the corner-shared tetrahedral network of vitreous silica are estimated semi-quantitatively using the concept of differential entropy. The results suggest that a positively correlated SiO vs. SiOSi distribution will be entropically stabilized in a glass structure over a negatively correlated distribution, which is typical of crystalline polymorphs of silica. This hypothesis lends support to the recent experimental observation of a positively correlated joint distribution of SiO distances and SiOSi angles in vitreous silica by 17O nuclear magnetic resonance spectroscopy. On the other hand, an estimation of the relative effect of these distributions on the ring strain energy suggests that the glass structure avoids a random or uncorrelated joint distribution of these structural parameters as in a continuous random network, due to the high strain energy associated with such a distribution.