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- Title
NMR AND NQR STUDIES OF BORATES AND BORIDES.
- Authors
BRAY, Philip J.
- Abstract
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-coordinated borons on the basis of the larger 11B quadrupole interactions for the BO3 configuration (2⋅4-2⋅9 MHz) and the smaller values for the BO4 (less than 0·90 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, as previously thought, due to the destruction of BO4 with added alkali oxide above 15-20 mol%. Advances in experiment and theory then permitted clear distinctions between the NMR spectra for symmetric and asymmetric BO3 units (e.g. a BO3 with all bridging or all non-bridging oxygens (NBO) and one with 1 or 2 NBO.) The NMR data for many binary and ternary borate glass systems are consistent with the Krogh-Moe model in which the glasses consist of mixtures of structural groupings from the crystalline compounds of the glassforming oxides. More recent uses of zero-field NMR, or pure nuclear quadrupole resonance (NQR) spectroscopy, have yielded major improvement in the resolution of the 11B responses from the various boron--oxygen bonding configurations. (As an example: the NQR spectra clearly display responses from two boron sites in vitreous B2O3.) Extension of the NQR studies to the 10B isotope has yielded improvements by two or three significant figures in the parameters of the quadrupole interaction. These developments have greatly increased the ability to identify with high accuracy and relative certainty the type and amount of each boron site in a solid, and should allow clear identification of the structural groupings in glasses. The high accuracy in the quadrupolar parameters, and their sensitivity to minor changes in charge distribution and structure, make these parameters sensitive tools for comparison with calculated values and for monitoring compositional variations, radiation damage, stress, thermal histories, and other aspects of boron-containing solids.
- Subjects
NUCLEAR quadrupole resonance; BORATE glass; BORATES; BORIDES; AREA measurement; NUCLEAR magnetic resonance spectroscopy; BINARY mixtures
- Publication
Physics & Chemistry of Glasses: European Journal of Glass Science & Technology Part B, 2022, Vol 63, Issue 4, p119
- ISSN
1753-3562
- Publication type
Article