Local Structure of Alkaline‐Earth Boroaluminate Crystals and Glasses: II, 11B and 27Al MAS NMR Spectroscopy of Alkaline‐Earth Boroaluminate Glasses

Abstract
11B and 27Al magic angle spinning nuclear magnetic resonance (MAS NMR) spectra of alkaline‐earth boroaluminate glasses show that the structure of these glasses are far more complicated than previously thought. The relative concentrations of 3‐ and 4‐coordinated boron vary as found by previous investigators using continuous‐wave NMR methods, but the 27Al NMR spectra indicate the presence of Al in 4‐, 5‐, and 6‐fold coordination, in contrast to previous assignments. Analysis of the data based on local charge balance considerations provides a qualitative model that correctly predicts compositional variations of the NMR peak intensities and 27Al chemical shifts for a wide range of boroaluminate glass compositions.

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