Neu 2D NMR experiments for determining the structure of phosphate glasses:a review

Double quantum nuclear magnetic resonance measurements exploiting the dipol e coupling between the phosphorus atoms as well as a novel two-dimensional exchange experiment using the scalar coupling are described for measuring t he connectivities of phosphate tetrahedra in glasses. It is shown that bond ing scenarios of up to four connected tetrahedra can be determined in phosp hates and phosphate glasses and that estimations of the chain length distri butions are possible in glasses having shorter chain fragments. Nuclear mag netic resonance (NMR) is also capable of measuring local order in extruded phosphate glasses using rotorsynchronized excitation in combination with ma gic angle sample spinning. Finally, we show that the relative orientations of chemical shift tensors can be determined by two-dimensional nuclear magn etic resonance. This determination provides an additional verification of c onnectivities and can possibly enable access to bonding angle data in the f uture. (C) 2000 Elsevier Science B.V. All rights reserved.