Dislocations in Solids. Plastic Relaxation.

Dislocations are responsible for the plastic deformation of crystalline materials such as metals, and play a role in a number of other properties of crystals, such as crystal growth, electrical properties of semiconductors, radiation damage through their interaction with point defects, and so on. Their theoretical discovery dates back to the years just before the second World War, and their visualization by various techniques, essentially electron microscopy, to the 1950s. They are an essential ingredient of physical metallurgy. They carry internal stresses and are "topologically" related to the symmetries of the crystal. It is this double character that makes them act as sources of plastic deformation. Their topological properties were fully appreciated with the appearance of a general classification of topological defects in ordered media, which comprehends superfluids, magnetic systems, and liquid crystals. Although defects and their textures in liquid crystals were observed (by optical microscopy) long before defects and their textures in solids, it is only in the last 10 years that investigations on the role of structure and texture on the rheological properties have been developed. A good knowledge of the bases of the physics of defects in solids cannot but help to progress in the investigation of rheological properties and instabilities of mesomorphic materials. [ABSTRACT FROM AUTHOR]