Junction Line Disclinations: Characterisation and Observations

Experimental observations obtained using high resolution transmission electron microscopy (HREM) of junctions between two or more interfaces are analysed to determine whether they exhibit disclination character. The method of analysis used is circuit mapping, and the advantage of using rotation and mirror symmetry operations in the present context, rather than translation operations as is done conventionally, is demonstrated. This technique is applied to micrographs of junctions selected from published literature, and includes junctions in homophase and heterophase materials. It is concluded that few observations currently provide unequivocal evidence of junction line disclination character. This situation may be due in part to the special crystallographic constraints on the applicability of HREM to studies of junction lines. The examples which have been identified all arise at intersections where favourable interfaces, such as epitaxial and twin boundaries, intersect. Moreover, such juncions occur either in pairs, in the form of disclination dipoles, or in small particles.