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

11 B and 27 Al 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 27 Al 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 27 Al chemical shifts for a wide range of boroaluminate glass compositions.