Diffraction from Dislocations

Abstract

WILSON¹ has calculated the nature of the diffraction from a cylindrical crystal with a single axial screw dislocation. Diffraction from an edge dislocation is more difficult to treat theoretically, because of the more complex nature of the elastic field surrounding the dislocation. An approximate treatment has been given by Wilson², who assumed that the displacements of the atoms were parallel to the Burgers vector. We have succeeded in solving the diffraction problem for a cylindrical crystal with an axial edge dislocation, in which the displacements correspond to isotropic elastic theory. Two independent methods were used : straightforward calculation (by T. S.), and direct observation in a Lipson diffractometer of the optical diffraction pattern of a two-dimensional grating representing the crystal (B. T. M. W.). In Fig. 1 we reproduce the optical diffraction pattern given by a grating representing (a) a perfect crystal (no dislocation) and (b) a simple-cubic crystal with an edge dislocation normal to the plane corresponding to the plane of the grating.