Fraction of boroxol rings in vitreous boron trioxide

Abstract

The structure of vitreous boron trioxide (${\mathrm{B}}_{2}$${\mathrm{O}}_{3}$) has been investigated by reverse Monte Carlo modeling using reported neutron and x-ray diffraction data. Structural models with different amounts of borons in boroxol rings were created using coordination and bonding constraints. The structure factors and the corresponding pair correlation functions of the models are generally in good agreement with the experimental neutron and x-ray data. However, the models containing large amounts of boroxol rings show significantly larger deviations from the experimental data than those with small fractions. Furthermore, features of the bond angle and dihedral angle distributions as well as visual inspection of the boroxol-rich models show that most of the rings in these models are seriously distorted from planarity. It is evident that it is not possible to reproduce the experimental neutron structure factor with a high fraction (g30%) of borons in planar boroxol rings. Rather, the results indicate that the structure of vitreous ${\mathrm{B}}_{2}$${\mathrm{O}}_{3}$ contains less than 20% borons in boroxol rings.