Migration of defects

The steps do not necessarily, however, proceed as simply as indicated but may also involve the formation of additional intermediates, such as adsorbed O", 02, etc., and/or the generation and migration of defects at a surface, interface or in the bulk. 

Mechanical activation of mixtures involves the dispersion of solids and their plastic deformation. These processes cause the generation of defects in solids they also accelerate the migration of defects in the bulk, increase the number of contacts between particles, and renew the contacts. All these factors provide chemical interaction between solids initiated by mechanical loading. These factors are the subject of investigations in one of the fields of solid state chemistry, namely, the mechanochemistry of inorganic substances, which is intensively developed. In particular, a large... 

Dielectric polarizabilities are useful for prediction of dielectric constants of new materials and compounds whose dielectric constants have not been measured, and in calculations of energies of the formation and migration of defects. In addition, deviations from the polarizability additivity rule are useful in understanding certain physical properties such as thermodynamic functions and ionic and electronic conductivity." ... 

Figure 5 The basic concept of P.G. De Gennes reptation of a chain trapped in a tube-like region by migration of "defects" along the nhain.

Diffusion of crystal compounds mainly depends on the movement of defect in lattice, e.g., relying on the migration of defects between the crunodes or electrons. Therefore, there are similar defects in the lattice of active component. 

Ionic transport in crystals usually involves migration of defects (vacancies, interstitial ions, interstitial pairs). Haven and Verkerk [46] argued that when the ionic motion involves defect mechanisms the experimental difihision coefficient, D, is different (because of correlation effects) from the calculated one, D, which obeys the Nemst-Einstein equation... 

Atomic diffusion has been extensively studied in some of the cubic carbides in the disordered state (see review by Davis, 1987). Both atom species (metal and carbon) diffuse by independent, random migration of defects on the respective sublattice of each component. For carbon, owing to the large concentrations of carbon vacancies, the activation energy for self-diffusion is a pure migration energy to 4eV) in TiCj, ... 

Fig. 5.39 The local (free) energy balance for the conduction process. Formation and migration of defects [176]. More precisely Agi should be replaced by the term Agj - Vj and AgAg by AgAg - V g.

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