Determination of the bond-angle distribution in vitreous B2O3 by B-11 double rotation (DOR) NMR spectroscopy

The B-O-B bond angle distributions for both ring and non-ring boron sites in vitreous B2O3 have been determined by B-11 double rotation (DOR) NMR and multiple-quantum (MQ) DOR NMR. The [B3O6] boroxol rings are observed to have a mean internal B-O-B angle of 120.0+/-0.7 degrees with a small standard deviation, sigma(R) = 3.2+/-0.4 degrees, indicating that the rings are near-perfect planar, hexagonal structures. The rings are linked predominantly by non-ring [BO3] units, which share oxygens with the boroxol ring, with a mean B-ring-O-Bnon-ring angle of 135.1+/-0.6 degrees and sigma(NR) = 6.7+/-0.4 degrees. In addition, the fraction of boron atoms, f, which reside in the boroxol rings has been measured for this sample as f = 0.73+/-0.01. (C) 2009 Elsevier Inc. All rights reserved