Crystal Defects

Abstract

Crystals are never free of defects. This is a fundamental consequence of equilibrium thermodynamics, as we will show in Section 3.2.2. Real crystals even have a defect structure far from thermodynamic equilibrium, due to the lack of mechanisms to establish thermodynamic equilibrium. We distinguish different kinds of crystal defects which are most easily classified according to their dimension; vacancies and interstitials (zero dimensional point defects), dislocations (one dimensional line defects), and grain and phase boundaries (two dimensional planar defects). Sometimes different phases are considered as three dimensional defects. However, these phases are constituents of the thermodynamic equilibrium and the real defect, the interface boundary, can be subsumed under the category of two dimensional defects.