New insights into oxygen environments generated during phosphate glass alteration: a combined O-17 MAS and MQMAS NMR and first principles calculations study

In the present study, we used a combination of O-17 NMR methods at a high magnetic field with first-principles calculations in order to characterize the oxygen sites in a series of hydroxylated sodium phosphate compounds, namely the hydrogen pyrophosphate Na2H2P2O7 and the hydrogen orthophosphates NaH2PO4, NaH2PO4 center dot H2O and NaH2PO4 center dot 2H(2)O. The chemical shifts and quadrupolar parameters of these compounds were interpreted in terms of local and semi-local environment, i.e., the chemical composition of the immediate surroundings and the nature of the bonds, e. g. hydrogen bonding. The magnitude of the quadrupolar interaction and its asymmetry were revealed to be a precise indicator of the local structure in sodium hydrogen phosphates. Our O-17 NMR experimental and computing approach allowed for identification and quantification of the different crystalline phases involved in the weathering mechanism of a sodium phosphate glass, even in small amount.