Chapter 7 - Structural defects in crystals

Abstract

This chapter defines the distinction between a perfect and a real crystal. It focuses on the structural defects that are encountered in crystals. The atomic arrangement of a real crystal differs locally from the structure of a perfect crystal. The presence of defects in the crystalline structure considerably modifies the material properties. In monatomic crystals, such as metals, point defects are created in an independent manner. The chapter explains that it is possible to distinguish between Schottky defects, which are composed of an anionic vacancy and a cationic vacancy, and Frenkel defects, consisting of an arrangement of a vacancy and an interstitial ion. This chapter also explains that the real crystal deviates considerably from the perfect crystal model. It contains a large number of defects of which the smallest dimensions are generally of the order of an atomic diameter. These defects have a well-defined geometry. They can be point defects as vacancies or solute atoms, linear defects as in dislocations, or two-dimensional defects, such as grain boundaries, stacking faults, or twin boundaries.