Dependence of N 4 upon alkali modifier in binary borate glasses

In this paper we re-examine the alkali dependence of the fraction of four-coordinated borons (N4) in two series of glasses: alkali borates (0·4M2O.B2O3) and mixed lithium caesium borates (0·4(xLi2O+(1-x)Cs2O). B2O3). High field B MAS-NMR experiments were performed to maximise the accuracy of the present results. We found no evidence for an alkali dependence on N4 in either system. In each case N4 closely followed the relation N4=R where R is the molar ratio of alkali to boron.