Dislocation

In materials science, a dislocation or Taylor's dislocation is a crystallographic defect or irregularity within a crystal structure. The presence of dislocations strongly influences many of the properties of materials.Etch Pits formed on the ends of Dislocations in silicon, orientation 100Etch Pits formed on the ends of Dislocations in silicon, orientation 111Etch Pits formed on the ends of Dislocation in silicon, orientation 111Dislocation source (schematic)LiF irradiated with gamma. The slip plane is visible as a diagonal line, with compressive forces showing green and tensile forces showing red. In materials science, a dislocation or Taylor's dislocation is a crystallographic defect or irregularity within a crystal structure. The presence of dislocations strongly influences many of the properties of materials. The theory describing the elastic fields of the defects was originally developed by Vito Volterra in 1907. The term 'dislocation' referring to a defect on the atomic scale was coined by G. I. Taylor in 1934. Some types of dislocations can be visualized as being caused by the termination of a plane of atoms in the middle of a crystal. In such a case, the surrounding planes are not straight, but instead they bend around the edge of the terminating plane so that the crystal structure is perfectly ordered on either side. This phenomenon is analogous to the following situation related to a stack of paper: If half of a piece of paper is inserted into a stack of paper, the defect in the stack is noticeable only at the edge of the half sheet. The two primary types of dislocations are edge dislocations and screw dislocations. Mixed dislocations are intermediate between these. Mathematically, dislocations are a type of topological defect, sometimes called a soliton. Dislocations behave as stable particles: they can move around, but maintain their identity. Two dislocations of opposite orientation can cancel when brought together, but a single dislocation typically cannot 'disappear' on its own. Two main types of dislocations exist: edge and screw. Dislocations found in real materials are typically mixed, meaning that they have characteristics of both.