The boroxol ring fraction in boron trioxide glass

The intermediate range order in boron trioxide glass continues to be of int erest and controversy as the Second International Conference on Berate Glas ses, Crystals and Melts showed In order to investigate this order we perfor med a new experiment which is sensitive to the dihedral angle distribution of neighbouring structural units. This experiment consists of correlating t he NMR frequencies of neighbouring boron nuclei which are identical if the boron oxide polyhedra containing the two boron atoms are coplanar, as found in ring systems but differ for noncoplanar geometries, Through the rate of growth of signal intensity arising from the non-coplanar case, as compared to that obtained in a boron trioxide crystal of known structure, we de the fraction of boron atoms contained in boroxol rings in the glass to be 0.66 +/-0.02.