Comparative Al-27 NMR and LAXS studies on rapidly quenched aluminosilicateglasses

Aluminium site occupancies deduced from Al-27 NMR measurements of several a luminosilicate glasses of composition 35-60 mol% Al2O3 were used to calcula te the mean coordination number, assuming two polyhedral models. In the mod els the 30 ppm Al NMR resonance was assigned to fivefold coordinated Al or to distorted tetrahedral units, respectively. Comparison of these mean coor dination numbers with those derived from pair distribution functions (PDF) from X-ray scattering data of these glasses support the model in which the 30 ppm Al NMR peak is assigned to distorted tetrahedral units. This conclus ion is also supported by simulations of the PDF line profiles using the NMR site occupancies and mean polyhedral bond lengths. (C) 1998 Elsevier Scien ce Limited. All rights reserved.