Point defect: also aggregation

Two point defects may aggregate to give a defect pair (such as when the two vacanc that constitute a Schottky defect come from neighbouring sites). Ousters of defects ( also form. These defect clusters may ultimately give rise to a new periodic structure oi an extended defect such as a dislocation. Increasing disorder may alternatively give j to a random, amorphous solid. As the properties of a material may be dramatically alte by the presence of defects it is obviously of great interest to be able to imderstand th relationships and ultimately predict them. However, we will restrict our discussion small concentrations of defects. 

Formation of point defects as the result of aggregation-based growth is more difficult to establish because of the difficulty in detecting such features in nanoparticles. However, it seems probable that aggregation based growth involving nanoparticles with surface-adsorbed ions will result in impurity sequestration (Banfield et al. 2000 also see Furer 1993). The chemistry of some natural nanomaterials supports this inference (Fowle et al. 2000 Fowle et al., in prep.). However, the validity of this hypothesis awaits experimental confirmation. 

In addition to a vacancy-driven process, diffusion under irradiation may also be enhanced by the formation and diffusion of other point defects, such as selfinterstitials, divacancies, and other defect aggregates, which are not present under equilibrium conditions. A general statement for the atomic diffusion coefficient can be written in terms of the various point defects as... 

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