NMR studies of the structure of non-metallic glasses

Boron-11 NMR spectroscopy has been used for 25 years to determine for borate glasses and crystalline compounds the fractions of borons in BO4 (N4) and BO3 (N3) configurations, and the fractions of BO3 units having all bridging (N35) and one or more non-bridging (Nsub(3A)) oxygens. Iron lead borate glasses containingFto 15.3 mol% Fe2O3 are found to have the iron ions distributed uniformly throughout the glasses, and the iron oxide influences the borate network only up to 4.64 mol% Fe2O3. Recent studies of glasses in the systems LiX-Li2O-B2O3 where X = F, Cl reveal that N4 is determined solely by the oxygen available as Li2O in these superionic conducting glasses. The greater sensitivity of boron-10 NMR spectra to structural details has now permitted identification in glasses of structural groupings found in the crystalline compounds of borate glassforming systems, and quantitative determination of the amount of each unit. Spectra for alkali borate glasses have permitted construction of quantitative models for these glasses at all compositions. Oxygen-17 NMR spectra for vitreous B2O3 and SiO2 yield bonding and structural information confirm models for these glasses. Silicon-29 NMR spectra for glasses in the system K2O-SiO2 show agreement with the spectra for the crystalline compounds at compositions for which compounds exist, and differ significantly from compound to compound. (orig.)