Effects of Plastic Deformation on Ionic Conductivity

The principal effects of plastic deformation on the low-temperature conductivity of alkali halide crystals are summarised and interpreted as follows : 1. The high conductivity during deformation is due to the movement of charged dislocations under the forces exerted simultaneously by the stress and the applied electric field. 2. The increased conductivity following deformation which subsequently decays (Gyulai-Hartly effect) is most commonly due to the breaking-up of impurity-vacancy pairs or clusters. This is related to the sweep-up of charge by moving dislocations. 3. The final steady-state conductivity is less than that before deformation because vacancies are bound to dislocations and the dislocations are surrounded by compensating charge clouds which are regions of reduced conductivity. To account for the observations it is necessary to suppose that the effect is due not so much to normal dislocations as to dislocation debris.