Evaluation of Third‐Order Elastic Constants and Pressure Dependence of Second‐Order Elastic Constants of Ionic Crystals

Abstract

AbstractThe third order elastic constants and the pressure dependence of second‐order elastic constants are evaluated for alkali halides with NaCl and CsCl structures, and for alkaline earth oxides with NaCl structure on the basis of the Löwdin‐Lundqvist three‐body potential theory for ionic solids. The potential parameters are derived from the knowledge of the overlap integrals. An exponential form suggested by Cochran is used for the variation of the three‐body overlap parameter. It is considered that the second‐neighbour repulsive as well as the van der Waals interactions contribute to the short‐range energy. The analysis presented uses only two parameters and determines six third‐order elastic constants, three pressure derivatives of second‐order elastic constants, and the cohesive energy of 22 crystals. The results obtained are in good agreement with experimental data.