Connectivities of Coordination Polyhedra in Phosphate Glasses from 31P Double-Quantum NMR Spectroscopy

High-resolution double-quantum nuclear magnetic resonance (NMR) spectroscopy in solids at a magnetic field of 11.75 T is applied to determine the structure of phosphate glasses. The connectivities between Q(n) coordination polyhedra, identified by their chemical shifts are established. Moreover, more extended structural features, such as rings or linear chains composed of Q(2) groups are resolved, since the chemical shift contains information about the local geometry, i.e. bond lengths and angles, which are in turn influenced by the surrounding Q(n) groups. From the study of two sodium phosphate glasses, containing 35 and 58 mol% of Na2O a motif involving sequences of at least three Q(2) groups could be identified in both compositions. Extensions of this new approach are discussed.