Effect of alumina on the structure and properties of Li2O-B2O3-P2O5 glasses

The structure of glasses within the system Li2O-Al2O3-B2O3-P2O5 has been studied through P-31, B-11 and Al-27 Nuclear Magnetic Resonance, and the effect of Al2O3 substitution by B2O3 and P2O5 network formers on the structure and properties investigated for a constant Li2O content. Multinuclear NMR results reveal that substitution of Al2O3 for B2O3 and P2O5 network formers in a glass with composition 50Li(2)O.15B(2)O(3).35P(2)O(5) produces a change in boron environment from four-fold to three-fold coordination. Meanwhile aluminum can be present in four-, five- and six-fold coordinations a higher amount of Al(IV) groups is found for increasing alumina contents. The behavior of the glass transition temperature and electrical conductivity of the glasses has been interpreted as a function of the structural changes induced in the glass network when alumina is substituted for B2O3, P2O5 or both. Small additions of alumina produce a drastic increase in glass transition temperature, while it does not change for [Al2O3] greater than 3 mol.%. However, the electrical conductivity shows very different behavior depending on the type of substitution: it can remain constant when B2O3 content decreases or sharply decrease when P2O5 is substituted by Al2O3, which is attributed to a higher amount of BO3 and phase separation. (C) 2011 Elsevier B.V. All rights reserved.