B-11 NMR-STUDIES IN BARIUM BERATE GLASSES WITH LOW FE2O3 CONTENT

Ten glass samples in the system xFe(2)O(3).(20-x)BaO.80B(2)O(3)(0.0 le ss than or equal to x less than or equal to 2.0 mol%) were fabricated, and pulsed NMR measurements were performed at room temperature as fol lows: (1) a B-11 NMR spectrum was obtained for each sample; and (2) N- 4, the fraction of 4-coordinated borons, was determined by integrating the area of the narrow line and broad line spectra. N-4 values were a nalyzed in terms of changes in the boron-oxygen configuration. A two-r egion behavior was exhibited by the N-4; that is, N-4 values in the fi rst region (0.5 mol% Fe2O3 and below) increased, but N-4 values in the second region (above 0.5 mol% Fe2O3) decreased with increasing Fe2O3. In this study, it was found that, in the first region, our glasses ha d only the symmetric structures and, in the second region, symmetric a nd asymmetric structures. However, the number of asymmetric structures was too small to be observed by B-11 NMR. The asymmetry parameter eta and the quadrupole coupling constant Q(cc), of pure B2O3 glass were a pproximately 0.26 and 2.94 MHz, respectively, and these values are a b it higher than the values of CW-NMR measurements, eta similar to 0.13 and Q(cc)similar to 2.6 MHz. However,slightly higher values of the asy mmetry parameter are expected in pulsed NMR measurements at a high res onance frequency of 64.19 MHz.