Basic defects and processes in solids

If you found a truth in the nature, put it into a book where it will be served even worth. (Wenn sie die Wahrheit in der Natur gefunden haben, so schmeiBen sie sie wieder in ein Buch, wo sie noch schlechter aufgehoben ist) 

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Basic defects and processes in solids Conduction band... 

A wide range of condensed matter properties including viscosity, ionic conductivity and mass transport belong to the class of thermally activated processes and are treated in terms of diffusion. Its theory seems to be quite well developed now [1-5] and was applied successfully to the study of radiation defects [6-8], dilute alloys and processes in highly defective solids [9-11]. Mobile particles or defects in solids inavoidably interact and thus participate in a series of diffusion-controlled reactions [12-18]. Three basic bimolecular reactions in solids and liquids are dissimilar particle (defect) recombination (annihilation), A + B —> 0 energy transfer from donors A to unsaturable sinks B, A + B —> B and exciton annihilation, A + A —> 0. 

Adsorption of water is thought to occur mainly at steps and defects and is very common on polycrystalline surfaces, and hence the metal oxides are frequently covered with hydroxyl groups. On prolonged exposure, hydroxide formation may proceed into the bulk of the solid in certain cases as with very basic oxides such as BaO. The adsorption of water may either be a dissociative or nondissociative process and has been investigated on surfaces such as MgO, CaO, TiOz, and SrTi03.16 These studies illustrate the fact that water molecules react dissociatively with defect sites at very low water-vapor pressures (< 10 9 torr) and then with terrace sites at water-vapor pressures that exceed a threshold pressure. Hydroxyl groups will be further discussed in the context of Bronsted acids and Lewis bases. 

In solid state physics, it is well known that many inorganic solids, e.g., the oxides and sulfides, can dissolve metals and nonmetals in excess, and that by this process electron and ion defects in the lattice will be formed. Wagner and co-workers (1) have developed the basic theory of... 

The underlying motivation of the work presented in this paper is to provide a theoretical understanding of basic physical and chemical properties and processes of relevance in photoelectrochemical devices based on nanostructured transition metal oxides. In this context, fundamental problems concerning the binding of adsorbed molecules to complex surfaces, electron transfer between adsorbate and solid, effects of intercalated ions and defects on electronic and geometric structure, etc., must be addressed, as well as methodological aspects, such as efficiency and reliability of different computational schemes, cluster models versus periodic ones, etc.. 

Photoconductivity in a solid is defined as an increase of conductivity caused by radiation. The phenomenon of photoconductivity involves the processes of absorption of radiation, photogeneration of charge carriers, their separation, diffusion and drift in an applied electric field, their temporary immobilization at sites known as trapping rites, release from traps and finally their recombination. The phenomenological relationships covering all these processes were primarily developed in connection with the study of crystalline covalent solids which dominated the early scientific literature on photoconductivity. Concurrent with the basic understanding of the phenomena was the development of several experimental techniques to study the fundamental processes and the specific identity of the defects and impurities that control these processes. 

Light-induced processes are described quite differently in molecular photochemistry and solid-state photophysics. In photochemistry one is used to an atomistic picture in which the arrangement of the atoms in the structure of a single molecule determines the electronic levels and thus the photochemical behavior. In contrast, the electronic levels of a solid are determined by the infinite periodicity of the atomic sequence in the crystal lattice. This leads to a basic concept according to which the solid can be treated as a dielectric continuum. Atomistic irregularities in the crystalline structure, such as lattice defects or impurities, are treated as perturbations of the spatially independent states in the energy bands. 

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