Abstract
By comparing the available structural parameters of silicate glasses and crystals of the same composition, the correlations between the nucleation behaviour of a glass and its short and middle range order, specially the coordination of the modifier cations, are discussed. There are glass systems which nucleate homogeneously (Li2O · SiO2, Na2O · SiO2, CaO · SiO2, Li2O · 2SiO2, BaO · 2SiO2, CaO · A12O3 · 2 SiO2) and systems which nucleate only heterogeneously (PbO · SiO2, CaO · MgO · 2SiO2, Na2O · 2SiO2, Na2O · A12O3 · 6SiO2). It is demonstrated that changes in the cation coordination during the formation of the long range order play an important role for nucleation behaviour.