Raman spectra of K2O-B2O3 glasses and melts

The structures of K2O-B2O3 glasses and melts have been studied by high-temperature Raman spectroscopy. With an increase in the K2O content and with increasing 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 glass/melt, the Raman spectra indicated a structural change in the borate species from B theta (4) tetrahedral units to metaborate, B theta O-2(-), triangular units with non-bridging oxygen with increasing temperature. The fraction of four-coordinated boron atoms, N-4, obtained from deconvolution of the Raman bands was gradually reduced above the glass transition temperature and converged to a constant value over 1400 K. This phenomenon could be explained by a thermodynamic process. (C) 2001 Elsevier Science B.V. All rights reserved.