On the symmetry and structure of (001) twist boundaries in f.c.c. metals

Abstract

In a paper published recently Bristowe and Crocker (1978) discuss the structure of (001) twist boundaries in f.c.c. metals. Computer simulation methods were used to investigate boundary structures between Coincidence related crystals. Mechanically stable structures were obtained by allowing relative displacements of the adjacent crystals as a whole and relaxation of individual atoms. Structures of the type studied are necessarily periodic, having two non-colinear translation axes in the interface plane, but Bristowe and Crocker found that favourable structures also possess rotation and screw axes. Clearly, a system of space-group classification would be very helpful for discussions of the symmetry of these and other bicrystals. The 230 conventional space groups for single crystals are inappropriate because single crystals possess three non-colinear translation axes. However, other space-group systems have been devised for objects containing one or two non-colinear translation axes and a unique plane, and these systems are ideally suited for classification of bicrystal symmetry. The purpose of this paper is to demonstrate the use of these space groups by considering the symmetry of the, bicrystals studied by Bristowe and Crocker.