Failure Of Theoretically Expecting Glass Structure From Composition

The constitution of glasses has been predicted in terms of compositions, but it sometimes fails. Complicated behaviour of lead oxyfluorosilicate glasses was first presented where the prediction was valid only in a limited range of composition represented by the molar ratio PbO/SiO2. Several examples of the failure to theoretically expect the glass structure were collected from the literature, from which the factors to consider were proposed.