Lattice imperfections in organic solids. Part 1.—Anthracene

Dislocations in single crystals of melt-grown, solution-grown and vapour-grown anthracene have been characterized using the etch-pit technique and from an analysis of cleavage patterns. From the observed alignments of emergent dislocations (at (00l) faces) to form small-angle boundaries (of twist, tilt and mixed character), deductions are made concerning the planes and directions in which the dislocations move. The most widely occurring dislocations are those that glide in the (010) plane along the [001] direction. Dislocations that glide in the[100] direction in this plane are also feasible. Although less widely occurring, dislocations in the (100) plane exist, there being slight preference for those that glide along [010] to dominate, but those that move in the [001] direction definitely occur. The geometry of two kinds of emergent edge dislocations is outlined, and the relevance of lattice distortion at dislocation cores is considered in relation to the photodimerization of the solid.