| Abstrakt: |
In a recent paper, Vignarooban et al [Europhys. Lett., 2014, 108, 56001] claim to have identified the first realisation of a flexible ⇌ rigid transition driven by dimensional crossover, and to have established the existence of a so-called "intermediate phase" in the lithium and sodium borate glass-forming systems. It is demonstrated, however, that these authors appear to have conflated the dimensionality of the superstructural unit species, which dominate the glass structure, with that of the vitreous network into which they are incorporated, and that the distributions of (super)structural unit species they predict for both systems are incompatible with those expected on the basis of the corresponding crystalline phases. An alternative model for predicting the rigidity of oxide networks is presented, which explains the variation of the glass transition temperature, Tg, for Li2O-B2O3 and Na2O-B2O3 glasses, as a function of the network modifier fraction, xM, and it is concluded that the so-called "intermediate phase" is not a phase at all, but merely coincides with the region of maximum network connectivity. [ABSTRACT FROM AUTHOR] |
