Structural characterization of glassy phases in the system Na2O-Ga2O3-P2O5by MAS and solution NMR and vibrational spectroscopy. II. Structure of thephosphate network

The structure of the phosphate network of glasses in the system Na2O-Ga2O3- P2O5 has been investigated as a function of the Na/Ga molar ratio and the p hosphate composition corresponding to a mono, di, tri, tetra and meta phosp hate stoichiometry. The glass is made of phosphate molecular groups of diff erent lengths linked by the cations with rather ionic (Na) or more covalent (Ga) bonds except in the case of the orthophosphate composition for which we only found isolated PO43- ions. The vibrational spectra are sensitive to composition variations but the band width and the couplings between the di fferent groups prevent any quantitative determination. P-31 MAS-NMR gives a n in-situ information on the P environment in the glass but the signals are often large and ill defined so that the assignment is not at all straightf orward. On the other hand, P-31 solution NMR gives sharper signals, allowin g more quantitative determinations but the dissolution process always intro duces some indeterminacy on the real glass structure which can be minimized by a careful preparation of the solution. (C) 2000 Elsevier Science B.V. A ll rights reserved.