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

Abstract The relative entropic contributions of correlated vs. uncorrelated Si O bond length and Si O Si 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 Si O vs. Si O Si 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 Si O distances and Si O Si 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.