Structural Determinations for Sodium Borate Glasses Using B10 and B11 NMR
In earlier NMR studies of structure and bonding in borate glasses (1–7), the central transition (m=1/2 ↔ 1/2) of the B-11 isotope has been employed almost exclusively. Aside from its usefulness in the determination of N4, the fraction of four coordinated boron atoms, B-11 NMR has been of limited value in determining the coupling constant (Qcc) and the asymmetry parameter (n) found in the glass. This limitation is due primarily to the importance of dipolar broadening and the existence of distributions in Qcc and n. B-10 NMR, on the other hand, affords 3 advantages over the use of the central transition of B-11 NMR: 1) dipolar broadening is much less important (8); 2) the distribution of Qcc is directly obtainable from a part of the B-10 NMR spectrum (8); and 3) there exists another part of the B-10 NMR experimental spectrum that is sensitive to the distributions of n, but insensitive to distributions of Qcc (9). These features of the B-10 NMR spectrum are employed in this work for the study of glasses in the sodium borate system.
KeywordsBoron Atom Borate Glass Sodium Borate Lever Rule Sodium Oxide
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