Correlation of network structure with devitrification mechanism in lithium and sodium diborate glasses

The intermediate-range structure of the network former in lithium and sodium diborate was studied using nuclear magnetic resonance spectroscopy. Specifically, 11B{10B} rotational-echo double resonance experiments were employed to determine the distribution of dipole couplings between these isotopes and in this way determine whether the intermediate range order of the borate network was the same in the glasses as in the crystal forms of these compounds. It was found that in the lithium diborate case the networks are in fact similar between glass and crystal, while in sodium diborate they differ substantially. Because lithium diborate shows homogeneous nucleation and growth on the laboratory time scale while sodium diborate does not, it was concluded that structural similarity between glass and crystal of the glass former correlates strongly with nucleation mechanism.