Modelling glass transition temperatures of chalcogenide glasses. Applied to phase-change optical recording materials

A model is presented for estimating the glass transition temperature of covalent amorphous materials from their enthalpy of atomisation. The enthalpy of atomisation is calculated by summing all individual bond enthalpies taking account of the coordination numbers of the constituting elements. A consistent set of bond enthalpies has been derived from the enthalpies of atomisation of stoichiometric compounds. The model is applicable to covalent amorphous materials consisting of the elements from group IB–VIB and for which the average number of valence electrons is no less than 4. It is shown that the model can be used for the development of phase-change materials for rewritable optical recording. Since the glass transition temperature is a lower limit for the crystallisation temperature, the model can predict the stability against spontaneous crystallisation of amorphous phase-change materials.