Structural Studies of NaPO3-AlF3 Glasses by High-Resolution Double-Resonance Nuclear Magnetic Resonance Spectroscopy

The local structure of the model glasses (NaPO3)1-x-(AlF3)x (0 ≤ x ≤ 0.4), prepared by standard melt-cooling, was extensively investigated by high-resolution solid state NMR including advanced double resonance techniques. This glass system offers the opportunity of studying five different heteronuclear distance correlations (Na-F, Na-P, P-F, Al-F, P-Al) by ten distinct double resonance experiments, involving all of the constituent elements present. 27Al MAS-NMR data indicate that aluminum is predominantly six-coordinated. According to 27Al{31P} and 27Al{19F} rotational echo double resonance (REDOR) spectroscopic results, two to three Al-F and three to four Al-O-P linkages occur in these glasses, independent of composition x. 19F MAS-NMR spectra show the presence of terminal P-bound and Al-bound fluorine species. A small amount of fluorine bridging to two aluminum octahedra, which could be assigned based on 19F{27Al} and 19F{31P} REDOR experiments, was also detected. 19F{23Na} REDOR experiments indicate that the Al-bound terminal F atoms interact significantly more strongly with sodium ions than the P-bonded terminal F atoms, which is consistent with local charge considerations. Based on the detailed quantitative dipole-dipole coupling information obtained, a comprehensive structural model for these glasses is presented.

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Recommended citation: H. Bradtmüller, L. Zhang, C.C. de Araujo, H. Eckert, D. Möncke, D. Ehrt, “Structural Studies of NaPO3-AlF3 Glasses by High-Resolution Double-Resonance Nuclear Magnetic Resonance Spectroscopy”, Journal of Physical Chemistry C, 2018, 122, 21579−21588.