Raman spectra of K2O-B2O3 glasses and melts

The structures of K2O-B2O3 glasses and melts have been studied by high-temp erature Raman spectroscopy. With an increase in the K2O content and with in creasing temperature, the boroxol rings, which only consist of B theta (3) triangular units, were converted into pentaborate groups which consist of B theta (4) tetrahedral (theta = bridging oxygen atom) and B theta (3) units in the 10 and 20 mol% K2O-B2O3 glasses/melts. In the 30 mol% K2O-B2O3 glas s/melt, the Raman spectra indicated a structural change in the borate speci es from B theta (4) tetrahedral units to metaborate, B theta O-2(-), triang ular units with non-bridging oxygen with increasing temperature. The fracti on of four-coordinated boron atoms, N-4, obtained from deconvolution of the Raman bands was gradually reduced above the glass transition temperature a nd converged to a constant value over 1400 K. This phenomenon could be expl ained by a thermodynamic process. (C) 2001 Elsevier Science B.V. All rights reserved.