Application and Extension of the Short-Range Order Configuration, SROC, Model in Bismuth Borate Glasses

The quantification of the short-range order (SRO) of glassy materials remains an open challenge over the years. In particular, in borate glasses this task is further complicated by the change in the B coordination number from 3 to 4 and by the formation of superstructural units. Nevertheless, in two recent articles of our group, the SRO structure of bismuth, xBi2O3-(1-x)B2O3, and zinc, xZnO-(1-x)B2O3, borate glasses was completely resolved by two completely independent methods. The first one, for Bi-borates, involved the analysis of infrared absorption coefficient spectra into Gaussian component bands whereas the second one, for Zn-borates, the application of the Short-Range Order Configuration model (SROC), an extension of the well-known lever rule. In this article, we extend the application of the SROC model in bismuth borate glasses, in the range where Bi cations were found to act predominantly as modifiers, i.e. 0.20 ≤ x ≤ 0.40. Our extension results in a modification of the originally proposed SROC model, by adding an additional node, and by defining the prerequisites for any augmented version of the model. The molar fractions of the borate units for the calculated SRO structure, in a continuous way throughout the range investigated, are in excellent agreement with existing literature data. Moreover, it is highlighted how the onset of disproportionation reactions, between borate units, can be handled in the framework of the introduced Augmented Short-Range Order Configuration model, ASROC.