SURFACE PHENOMENA AND DISLOCATIONS IN ALKALI HALIDES

By means of a decoration method with Au and electron microscopy, we have studied some surface phenomena and imperfections in alkali halide single crystals. We have found that the formation energy of kinks in LiF, NaF, KF, NaCl and KBr is 1 20 the energy of evaporation of the crystal. The crystals have been heated at various temperatures between R.T. and 350°C, and we have found that the spiral polygonization does not depend on the temperature but on the step height. The figures that were previously considered to be produced by thermal etching are now believed to be due to the variation of the cleavage plane with temperature. We propose a mechanism to account for the interaction of dislocations with Burgers vectors 1 2a 〈110〉, and we find in our experiments that interaction is possible by thermal activation corresponding to temperatures of 200 °C and 270 °C for NaCl and KBr respectively. We give a kinematic interpretation to the decoration figure which had been previously ascribed to an edge dislocation. We have also found some decoration figures which we associate with twist grain boundaries, on the {110} planes, the average angle of rotation being 41' in NaCl. © 1968.