Influence of impurities and electric fields on the kinetic characteristics of the expansion of dislocation half-loops in NaCl:2236; Ca2+ crystals

The effect of the concentration (C) of Ca²⁺ impurity ions and electric fields up to 50 kV/cm on the kinetic characteristics of the expansion of edge and screw dislocation half-loops in annealed and quenched NaCl crystals is studied. It is confirmed that 1) the concentration dependence of the rate v of expansion of screw half-loops takes the form v = v^* exp (-AC^1/2); 2) with increasing field strength E the velocity v increases linearly in pure NaCl crystals'; in impure crystals for E>5 kV/cm the rate of expansion of the edge half-loops increases and that of the screw half-loops diminishes as exp (E). The extent of the latter effect depends on the concentration of Ca²⁺ impurity ions in the crystals and also on their heat treatment. The exponential change in v with field E is apparently a consequence of the reorientation of the Ca²⁺ ion-cation vacancy dipoles in the electric field. The activation energy for the reorientation of the dipoles is estimated. The linear increase in the rate of expansion of the half-loops is explained as being due to the reduction in the number of steps in the dislocation under the influence of the electric field.Translated from Izvestlya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 35–40, April, 1976.