Disruption of the periodicity of a crystal lattice
A crystallographic defect is an interruption of the regular patterns of arrangement of atoms or molecules in crystalline solids. The positions and orientations of particles, which are repeating at fixed distances determined by the unit cell parameters in crystals, exhibit a periodic crystal structure, but this is usually imperfect.[2][3][4][5] Several types of defects are often characterized: point defects, line defects, planar defects, bulk defects. Topological homotopy establishes a mathematical method of characterization.
^Siegel, R. W. (1982) Atomic Defects and Diffusion in Metals, in Point Defects and Defect Interactions in Metals, J.-I. Takamura (ED.), p. 783, North Holland, Amsterdam
^Crawford, J. H.; Slifkin, L. M., eds. (1975). Point Defects in Solids. New York: Plenum Press.
^Watkins, G. D. (1997) "Native defects and their interactions with impurities in silicon", p. 139 in Defects and Diffusion in Silicon Processing, T. Diaz de la Rubia, S. Coffa, P. A. Stolk, and C. S. Rafferty (eds), vol. 469 of MRS Symposium Proceedings, Materials Research Society, Pittsburgh, ISBN1-55899-373-8