Nmr And Nqr Studies Of Borates And Borides

A 1958 paper by Silver & Bray introduced the use of nuclear magnetic resonance (NMR) spectra for 11B to study structure and bonding in glasses. The NMR spectra clearly distinguished between 3-coordinated and 4-coordianted borons on the basis of the larger 11B quadruple interactions for the BO3 configuration (2.4-2.9 MHz) and the smaller values for the BO4 (less than 0.09 MHz). Quantitative measurements of the area under the narrow resonance (BO4) and broad response (BO3) allowed the fraction, N4, of 4-coordinated borons to be established. It was soon found that the "borate anomaly" in binary alkali borate glasses was not, are previously thought, due to the destruction of BO4 with added alkali oxide above 15-20 mol%.