Network structure of multi-component sodium borosilicate glasses by neutron diffraction

Neutron diffraction structure study has been performed on multi-component sodium borosilicate based waste glasses with the composition of (65 - x)SiO_2. · xB₂O₃ · 25Na₂O · 5BaO · 5ZrO₂, x = 5-15 mol%. The maximum momentum transfer of the experimental structure factor was 30 Å^-1, which made available to determine the distribution function with high r-space resolution. Reverse Monte Carlo modelling was applied to calculate several partial atomic pair correlation functions, nearest neighbor distances and coordination numbers have been revealed. The characteristic features of Si-O and Si-Si distributions are similar for all glassy samples, suggesting that the Si-O network consisting of tetrahedral SiO₄ units is highly stable even in the multi-component glasses. The B-O correlations proved to be fairly complex, two distinct first neighbor distances are present at 1.40 Å and 1.60 Å, the latter equals the Si-O distance. Coordination number distribution analyzes has revealed 3 and four-coordinated boron atoms. The O-O distribution suggests a network configuration consisting of boron rich and silicon rich regions. Our findings are consistent with a structure model where the boron rich network contains mostly trigonal BO₃ units, and the silicon rich network is formed by a mixed continuous network of ^[4]Si-O-Si^[4] with several different ^[4]B-O-Si^[4] and ^[3]B-O-Si^[4] linkages.