Thermal expansion in insulating materials

A model of thermal expansion in terms of the Morse potential which was developed earlier for low temperatures is extended to high temperatures and applied to a semiempirical calculation of thermal expansion in insulating materials. In this model, the localized quantum mechanical solutions of the Morse potential are combined with the Debye model to give a localized-continuum description of thermal expansion. A set of empirical rules is developed for characterizing the interatomic potential in terms of the Morse potential. These are then applied to the quantitative calculation of thermal expansion in the alkali halide crystals and a group of binary high temperature materials with the aid of the known crystal structures, compressibilities, and Debye temperatures of these materials. Good agreement between calculated and experimental values is obtained for temperatures ranging between 0 K to values near the melting points. A discussion of the underlying basis of the empirical rules is given as well as their likely applicability to a wide range of insulating materials.