Structural investigation of sodium borate glasses and melts by Raman spectroscopy. I. Quantitative evaluation of structural units

Short-range and intermediate range structures of the sodium borate glass system were investigated using Raman spectroscopy to quantify their dependence on Na2O concentration. High-resolution spectra were collected by Raman spectroscopy using the Q-switched, second-harmonic pulse of a Nd:YAG laser as an excitation source. The system was designed for measurement of the spectra of glasses and melts up to temperatures over 1000 degreesC with high signal to noise ratio. Use of polarized light and the simultaneous analysis of HH and VH spectra allowed deconvolution of Raman spectra into appropriate bands with high reproducibility. The deconvoluted bands in the high-frequency region of 1100-1600 cm(-1) could be assigned to the vibration modes due to the short-range structures of BO3 and BO2O- units in the glasses. The band intensity ratios showed a simple linear relationship with the molar ratio, symmetric BO3 triangle unit, N-3s, to asymmetric BO2O- triangle unit, N-3a, obtained from B-11-NMR results. These results allowed a quantitative measure for normalizing the spectra leading to a direct comparison of the band intensities. The ring-structures of intermediate range order, boroxol, pentaborate, tetraborate and diborate groups, could be quantified from the spectra in the middle-frequency region. Their trends with Na2O concentration showed a good consistency with B-10-NMR results and also Krogh-Moe's model. (C) 2003 Elsevier Science B.V. All rights reserved.