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 BØ3 triangular units, were converted into pentaborate groups which consist of BØ4 tetrahedral (Ø=bridging oxygen atom) and BØ3 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 BØ4 tetrahedral units to metaborate, BØ2O−, triangular units with non-bridging oxygen with increasing temperature. The fraction of four-coordinated boron atoms, N4, 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.