Distribution of species in Na2O–CaO–B2O3 glasses as probed by FTIR

• This work explores the structural units in xCaO–Na2O–B2O3 glasses.
• IR spectra have been used to get the fraction N4 of four coordinated boron.
• A simple technique has been used to analyze the change of N4.
• The glasses are looked as mixture of corresponding Na2O–B2O3 and CaO–B2O3 glasses.
• CaO has a greater tendency to form asymmetric BO3 units.

The article presents a simple method that can be used to get the concentration of various species in mixed-modifier borate glasses. By using the fraction of four coordinated boron in xCaO (30 − x)Na2O70B2O3 (0 ≤ x ≤ 27.5 mol%) and xCaO(40 − x)Na2O60B2O3 glasses (10 ≤ x ≤ 40 mol%), the concentration of BO4− and asymmetric BO3 units related to each modifier oxide could be determined. CaO has a greater tendency to form asymmetric BO3 units in the first glass series, while Na2O has the ability to form BO4 units to a greater extent. In xCaO(40 − x)Na2O60B2O3 glasses, BO4− and asymmetric BO3 units are formed at the same rate from Na2O and CaO. The fraction of four coordinated boron, can be predicted by treating the studied glasses as if they are mixtures of Na2O–B2O3 and CaO–B2O3 matrices. The change in N4 is due to change in the relative concentration of these matrices.