Elastic Interaction between Dislocations and Tetragonal Defects in Anisotropic Sodium Chloride

Abstract

The elastic interaction energies between a calcium-cation vacancy pair and both a screw and an edge dislocation in a sodium chloride lattice are calculated using isotropic, semi-anisotropic, and anisotropic elasticity theory. The defect pairs considered have their axes along the 〈100〉 directions, the cation vacancy occupying a next-nearest neighbor position to the calcium impurity. They produce a tetragonal strain field in the lattice which interacts elastically with the stress field of both kinds of dislocations. The semi-anisotropic method introduces the single-crystal elastic constants by considering the defect pair as a force dipole. The interaction of the stress arising from this force dipole with the strain field of a dislocation as determined by isotropic elasticity theory is then calculated. For the other two methods of calculation the stress field of a dislocation in an isotropic and in an anisotropic medium are used. Dislocations in sodium chloride lie along certain high-symmetry directions thus enabling closed-form solutions for their stress fields in anisotropic materials to be obtained. Results of the calculations indicate good agreement between the isotropic and anisotropic cases and poor agreement between these two cases and the semi-anisotropic case. A comparison is made between the results of these calculations and the analogous situation of the interaction of dislocations with carbon interstitials in iron for which calculations have been made previously using isotropic and semi-anisotropic elasticity theories.