TABLE OF CONTENTS It is generally agreed that the lattice vacancy is the predominant type of point defect in simple metals and rare gas solids. Direct and indirect measurements of the vacancy concentration as a function of temperature exist that support this contention. The concentration of point defects other than vacancies is relatively low in close-packed hexagonal and face-centered cubic structures because their formation requires large lattice distortions. In more open structures, however, such as body-centered cubic and the diamond structure characteristic of semiconductors, interstitials may be important.
Point defects have a number of important effects on crystal properties. They often control the mechanisms of diffusion, they contribute to electrical and thermal resistivity, they play a role in the growth of voids during plastic deformation, and they affect the conductivity of semiconductors. Through their interaction with dislocations and other internal stress sources, they have an effect on the mechanical properties of metals and on microstructure. Also, because of their critical role in diffusion, they are important in the properties of nucleation, growth, and phase transformations. In ionic crystals, they are responsible for the electrical conductivity.
In this chapter, the statistical mechanical theory of a pure monatomic crystal containing vacant lattice sites and atoms in interstitial positions is developed. We first treat crystals in which the monovacancy is the only defect. This allows us to present the theory in its most transparent form. The theory of crystals with more complex point defect systems is a simple extension of this and...
