Surface tension of the {100} face of alkali halide crystals

Abstract

In this paper, the distinction between the surface free energy (or surface energy at 0°K) and surface tension is re-examined. The change in the state of stress in a crystal associated with the presence of the surface is represented by the surface stress tensor. The mechanical definition which is adopted for this tensor, is similar to that used in the theory of the surface tension of liquids. The surface tension is a scalar quantity related to the trace of the surface stress tensor. Results of calculations of surface tensions are reported for the |100) face of all the alkali halides with the NaCl structure. The model used is the same as that employed in previous calculations of the surface energies of these crystals, and includes a consideration of distortion effects (displacement and polarization of the ions) occurring in the surface region. Positive surface tensions were found for all of the alkali halides investigated.