Short-range structure of alkaline-earth borate glasses by pulsed neutron diffraction and molecular dynamics simulation

The structure of vitreous MO . nB(2)O(3) (M = Ca and Ba; n = 2, 3 and 4) ha s been studied by pulsed neutron diffraction measurement with the help of m olecular dynamics (MD) simulation. The first and second peaks assigned to t he nearest-neighbor B-O and O-O correlations, respectively, in the obtained total pair distribution functions shifted little with increasing MO conten t, while the asymmetry of the first peak increased significantly with MO co ntent, these results are different from those for potassium borate glasses. It was inferred that the BO3 and BO4 units are better defined in these alk aline-earth borate glasses than those in the potassium borate glasses. Both the full-width at half maximum (FWHM) of the first peak and the average co -ordination number of O around B clearly increased as MO content increased which is the same behavior with alkali borate glasses. The fraction of four -co-ordinated B showed a larger deviation from x/(1 - x) for CaO-B2O3 glass es than that for BaO-B2O3 glasses which shows a different dependence of the deviation on cation size from that in alkali borate glasses, and is in goo d agreement with the results from MID simulation. (C) 2001 Elsevier Science B.V. All rights reserved.