Abstract
This article reviews the transport of atoms through crystalline solids under the influence of external electric fields, chemical and isotopic concentration gradients and thermal gradients. The main emphasis is on the statistical and thermodynamic description of these phenomena via the theory of mobile lattice imperfections - vacancies and interstitial atoms. In discussing the various phenomena in detail (§ 5) extensive use is made of non-equilibrium thermodynamics as providing a convenient general formalism. Particular attention is given wherever possible to the physical interpretation of the descriptions provided by this formalism.An introductory survey of the properties of vacancies and interstitials in relation to diffusion phenomena is given in § 2. This includes a summary of the various defect models applicable to different solids - metals, ionic solids, semiconductors and insulators. Section 3 deals in greater detail with certain necessary aspects of the statistical thermodynamics of solids containing defects. Section 4 briefly summarizes the basic theory of non-equilibrium thermodynamics, oriented towards matter transport in crystalline solids; attention is drawn to several pitfalls in this approach. Finally, § 5 is the main object of the review; it applies the material developed in §§ 3 and 4. This section deals with (i) isothermal diffusion in metal alloys, including chemical diffusion, and isotopic tracer diffusion, particular attention being given to dilute systems, (ii) electrolytic conductivity, ionic mobility and both solute and solvent diffusion in ionic solids, special attention being given to the relation between these quantities and to a generalized form of the Nernst-Einstein relation, (iii) the Soret effect and thermal diffusion, especially in metals and dilute alloys, and (iv) thermoelectric phenomena in ionic solids. The article does not deal with grain boundary or surface diffusion and does not specifically discuss diffusion-controlled chemical reactions, sintering or creep. Discussions of these aspects of the subject are given in the works listed in the bibliography.
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