The role of Sb5+ in the structure of Sb2O3-B2O3 binary glasses -: an NMR and Mossbauer spectroscopy study

Glasses of general formula xSb(2)O(3) (1-x)B2O3 (0 less than or equal to x less than or equal to 0.8) have been prepared by conventional melt- quenching. Mossbauer spectroscopy shows that a fraction of the Sb3+ is converted to Sb5+ and this fraction increases with x. High-field B-11 MAS NMR gives well-resolved resonances from boron atoms which are 3- and 4-coordinated to oxygen. The fraction of 4-coordinated boron, N-4, goes through a maximum value of 0.12 +/- 0.01 at x = 0.5. The position of the maximum in N-4 is consistent with the cation potential for Sb3+, as observed for other systems. However, the low value of N-4 at this maximum is not so readily explained. The values are similar to those predicted if [BO4](-) were stabilised by [SbO4](+) but the trends with composition are different. (C) 2004 Elsevier Inc. All rights reserved.