The Elastic Field of Point Defects
Unlike dislocations, which are linear defects of the crystal lattice, point defects are lattice imperfections having all dimensions of the order of one atomic spacing. The point defect may be a vacant site in the atomic lattice, called a vacancy, a foreig
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THE ELASTIC FIELD OF POINT DEFECTS
Unlike dislocations, which are linear defects of the crystal lattice, point defects are lattice imperfections having all dimensions of the order of one atomic spacing. The point defect may be a vacant site in the atomic lattice, called a vacancy, a foreign atom replacing one atom of the lattice, called a substitutional atom, or an atom situated between the normal sites of the lattice, called an interstitial atom. An interstitial atom is said to be intrinsic or extrinsic, according as it is of the same nature or of different nature with the atoms of the host lattice. Sometimes, two or more point defects can build characteristic arrangements which are thermodynamically stable, i.e. their self-energies are smaller than the sum of the self-energies of the individual point defects. The collective motion of point defects produces viscous effects at a macroscopic scale, which are of great importance for many processes taking place in crystals (see, e.g. Seeger [286], Hirth and Lothe [162], Nowik and Berry [455], chapters 7 and 8). Like dislocations, however, each point defect moves in an almost good crystal, which may be considered to a large extent as an elastic medium. Moreover, the interaction of a point defect with other crystal defects is mostly of elastic nature. That is why we will devote this chapter to elastic models of point defects and to various methods for calculating the elastic interaction of a point defect with dislocations or other point defects.
21. Modelling of point defects as
spherical inclusions in elastic media
The simplest model of a point defect is given by a spherical rigid or elastic inclusion in an infinite isotropic medium. In both cases the elastic state possesses spherical symmetry with respect to the centre of the inclusion. By using spherical co-ordinates T, e,
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