Comment on ‘Bond volumes in crystals and glasses and a study of the germanate anomaly’ by H.-J. Weber [J. Non-Cryst. Solids 243 (1999) 220]

A recent paper [J. Non-Cryst. Solids 243 (1999) 220] introduced the concept of bond volume Vb=V0+α∗d3/N, where d is bond length, N is coordination number, and V0 is free volume. It was found empirically that α∗=12.25±0.25 for compact structures. The concept of bond volume was used to analyse free volume in germanate glasses, and hence investigate the germanate anomaly. The present comment gives an explicit derivation for the value of α∗ in common binary compounds. The common feature of structures with α∗≈12 is not that they have space-filling by coordination polyhedra, but rather that they have a dense packing of anions.