Determination of the bond-angle distribution in vitreous B 2O 3 by 11B double rotation (DOR) NMR spectroscopy
The B-O-B bond angle distributions for both ring and non-ring boron sites in vitreous B 2O 3 have been determined by 11B double rotation (DOR) NMR and multiple-quantum (MQ) DOR NMR. The [B 3O 6] boroxol rings are observed to have a mean internal B-O-B angle of 120.0±0.7° with a small standard deviation, σR=3.2±0.4°, indicating that the rings are near-perfect planar, hexagonal structures. The rings are linked predominantly by non-ring [BO 3] units, which share oxygens with the boroxol ring, with a mean B ring-O-B non-ring angle of 135.1±0.6° and σNR=6.7±0.4°. 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.