ABSTRACT
This chapter discusses the diffusion of atoms in a random fashion throughout the crystal lattice. In many processes it is necessary to be able to estimate the distance that atoms can diffuse in a given time. When diffusion occurs atoms are migrating through the crystal structure. Diffusion of an atom in a solid is not a truly random process and it is reasonable to suppose that in many circumstances a given jump direction may depend on the direction of the previous jump. In exchange diffusion an impurity swaps places with a neighbouring normal atom while in ring diffusion cooperation between several atoms is needed to make the exchange. The process of self-diffusion involves the movement of atoms in a random fashion through a crystal. In order to link the idea with the magnitude of the self-diffusion coefficient it is necessary to return to the basic equations of diffusion theory, Fick’s laws.
