Solid state defects

Four Challenges in IVIoSecula Modelling Free Energies, Solvation, Reactions and Solid-state Defects... 

In solid state chemistry the limited atomic mobility in the solid state controls chemical changes and leads to explicit consideration of the relative location of potential reactants (the configuration) and solid state reactivity as controlled by solid state defects. The same factors dominate shock-induced solid state chemistry. 

Several different types of species, including various solid state defects, diffuse and form a phase boimdaty of reaction, which may further react to form specific compositions. 

Attenuation in solids due to viscosity may be treated by a similar analysis. There may well be other damping mechanisms, such as heat conduction (i.e. imperfectly adiabatic conditions) which also gives an f2 law, and other phenomena associated with solid state defects that may have more complicated frequency and temperature dependence. In polycrystalline solids, especially metals and alloys and also ceramics, elastic grain scattering may cause much greater attenuation than any inelastic damping (Papadakis 1968 Stanke and Kino 1984). 

Our work has applied these techniques to the study of the binary insulating materials including the fluorites, alkali halides, alkaline earth oxides, and perovskites. Many of these are simple materials that are commonly used as models for all solid state defect equilibria. Our work has had the goal of determining at the microscopic level the defect equilibria and dynamics that are important in understanding solid state chemistry as well as developing new tools for the studies of solid materials. 

Site selective laser spectroscopy is a very powerful tool for studying the local environments that are present in samples. We have shown that defect structures in solids are determined by its previous history and that these structures can be measured with site selective spectroscopy. There has been no application of such techniques to geologically important questions since our work has concentrated on understanding fundamental questions about solid state defect chemistry. Our work suggests though that site selective laser spectroscopy could have important application in geological studies if it were used in the hands of people with that background. 

So far in this chapter, we have assumed implicitly that all the pure substances considered have ideal lattices in which every site is occupied by the correct type of atom or ion. This state appertains only at OK, and above this temperature, lattice defects are always present the energy required to create a defect is more than compensated for by the resulting increase in entropy of the structure. There are various types of lattice defects, but we shall introduce only the Schottky and Erenkel defects. Solid state defects are discussed further in Chapter... 

John D. Bak and John C. Wright Site-Selective Spectroscopy of the Solid-State Defect Chemistry in Erbium-Doped Barium Titanate J. Phys. Chem. B 2005,109, 18391-18399... 

It is well known that defects play an important role in determining material properties. Point defects play a major role in all macroscopic material properties that are related to atomic diffusion mechanisms and to electronic properties in semiconductors. Line defects, or dislocations, are unquestionably recognized as the basic elements that lead to plasticity and fracture (Fig. 20.1). Although the study of individual solid-state defects has reached an advanced level, investigations into the collective behavior of defects under nonequilibrium conditions remain in their infancy. Nonetheless, significant progress has been made in dislocation dynamics and plastic instabilities over the past several years, and the importance of nonlinear phenomena has also been assessed in this field. Dislocation structures have been observed experimentally. 

Solid-state defect structures, (a) Schottky defect, (b) Frenkel defect, (c) Nonstoichiometric Feo sO. (d) An... 

In this case, the g tensor is characterized by gxx = gyy = gzz = giso and a single symmetrical line is observed. This simple situation is not very often encountered in powders except for some solid state defects and transition metal ions in highly symmetric environments such as or T. ... 

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