The Structure of Aluminosilicate Glasses: High-Resolution 17O and 27Al MAS and 3QMAS NMR Study

Abstract

We investigate short-range order and local atomic configuration in charge-balanced aluminosilicate glasses as functions of composition, using 17O and 27Al MAS and triple-quantum magic angle spinning (3QMAS) NMR spectroscopy. Enhanced resolution in 17O and 27Al 3QMAS spectra, compared to MAS NMR, allows the quantification of the spectra and the extent of disorder using a semiempirical function relating 3QMAS efficiency to a quadrupolar coupling constant (Cq). The variations with the Si/Al ratio (R) in peak positions and widths in the isotropic dimension of 27Al 3QMAS NMR spectra in both Na- and Ca-aluminosilicate glasses can be ascribed to variations in the populations of Al sites with varying numbers of Al vs Si neighbors with composition. In the 17O 3QMAS spectra, variations of populations of three clearly resolved oxygen sites (Al−O−Al, Si−O−Al, and Si−O−Si) with R and cation field strength are consistent with the predictions given in our previous results from 29Si MAS NMR. The quadrupolar coupling prod...