New insights into the structure of oxynitride NaPON phosphate glasses by 17-oxygen NMR
Résumé
Sodium metaphosphate oxynitride glasses with variable N/P ratio have been characterized by 17O and 31P Nuclear Magnetic Resonance. They were obtained by thermal treatment of 17O-enriched NaPO3 glass under ammonia flow for different durations. Owing to the small quantity of 17O-enriched glass available, the nitrogen content was evaluated by comparing their 31P NMR spectra with those of non-enriched glasses with known nitrogen content. 17O 3Q MAS-NMR enabled to distinguish bridging and non-bridging oxygens and, for the first time, we have got evidence for the presence of two different non-bridging oxygens, i.e. those in PO4 sites and those in nitrided PO3N or PO2N2 sites. An innovative treatment of NMR data that takes into account the distribution of NMR parameters enabled the quantification of the proportion of the two NBO sites. An extension of the nitridation model of phosphate glasses could be proposed, based on the bridging to non-bridging oxygens ratio, which could be calculated from the distribution of oxygen sites among the different structural groups.