Defects in materials

Abstract

For diffusion to occur in ceramics it is essential to state that the mechanism of diffusion must proceed by point defects exchange with atoms. The reason for this is that ceramics are characterized either by covalent or ionic bonding and relatively high energy is required to tear such bonds before an oscillating step can cause the actual motion of an atom by the above mechanisms without involving some defect. Spatial considerations also play a key role in this process. Point defects, such as vacancies and interstitials, are involved in atomic diffusion mechanisms. These defects disturb lattice periodicity and perfect crystals without them exist only at absolute zero temperature. Point defects are a thermodynamic feature and their concentration is in thermodynamic equilibrium. The concentration of vacancies is calculated. Schematic illustrations of vacancies, interstitials and their mixture are presented in this chapter. The methods of generating vacancies by quenching, plastic deformation and radiation are considered.