Insights into the structure of Bi2O3-B2O3 glasses as predicted from density correlations

A model has been presented to correlate both the density and molar volume of Bi2O3-B2O3 glasses with the structure. The model makes use of the available data of the fraction of four coordinated boron to get the concentration of all structural units. The concentration of BO4 units shows a maximum at similar to 31 mol% Bi2O3. There is a nonlinear decrease in the concentration of symmetric BO3 units and an increase in the concentration of BiO6 units. Asymmetric BO3 units start forming for Bi2O3 >42 mol%. It is deduced that in BiO6 units, oxygen atoms are four coordinated with Bi atoms. The model is able to fit the calculated and experimental density and molar volume and explains the minimum in the molar volume at 22 mol%Bi2O3. (C) 2014 Elsevier B.V. All rights reserved.