Mapping aluminum/phosphorus connectivities in aluminophosphate glasses

Two-dimensional Al-27/P-31 cross-polarization magic-angle spinning (CPMAS) NMR experiments are performed on sodium aluminophosphate glasses in the xNa AlO(2) (1 - x)NaPO3 compositional range; providing direct detection of part icular aluminum species connected to specific phosphorus species. In partic ular, the spectral-editing capabilities of two-dimensional experiments allo w the elucidation of phosphorus resonances that are strongly correlated to four-, five-and six-coordinate aluminum species. Results from two-dimension al contour plots and projections of spectra along the P-31 dimension allow the assignment of phosphate structures that cannot be directly assigned fro m one-dimensional P-31 MAS spectra. Q(1)(0), Q(3)(0) and Q(2)(1) species ha ve all been identified in these aluminophosphate glasses and tetrahedral al uminum species are bonded to each of these phosphate moieties. Changes in t he phosphate/aluminate ordering are also monitored by inspection of the pho sphorus subspectra of the two-dimensional CPMAS experiments, demonstrating a change in aluminum/phosphorus connectivity correlated to changes in molar composition. (C) 2000 Elsevier Science B.V. All rights reserved.