RAMAN STUDY OF THE STRUCTURE OF K_2O-B_2O_3 GLASSES AND MELTS

摘要

The structure of alkali borate glasses and melts with 10, 20 and 30 mol% K_2O have been studied by high-temperature Raman spectroscopy. Not only with an increase of K_2O content but also with increasing temperature, boroxol rings in the potassium borate glass/melt have converted to pentaborate groups which consist of BO_4~- tetrahedra (O = bridging oxygen atom) and metaborate, BO_2O~-, triangular units. Furthermore, Raman spectra have indicated a structural change of borate species from BO_4 tetrahedral units to BO_3 triangles with non-bridging oxygen with increasing temperature in 30 mol% K_2O-B_2O_3 glass. The fraction of four-coordinated boron atoms, N_4, was obtained and found to exhibit a gradual reduction above the glass transition temperature in this glass.