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 xNaAlO(2) (1 - x)NaPO3 compositional range; providing direct detection of particular aluminum species connected to specific phosphorus species. In particular, the spectral-editing capabilities of two-dimensional experiments allow the elucidation of phosphorus resonances that are strongly correlated to four-, five-and six-coordinate aluminum species. Results from two-dimensional contour plots and projections of spectra along the P-31 dimension allow the assignment of phosphate structures that cannot be directly assigned from one-dimensional P-31 MAS spectra. Q(1)(0), Q(3)(0) and Q(2)(1) species have all been identified in these aluminophosphate glasses and tetrahedral aluminum species are bonded to each of these phosphate moieties. Changes in the phosphate/aluminate ordering are also monitored by inspection of the phosphorus 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.