Solids defect chemistry

Solid state chemistry is controlled by defects, and the highly defective, shock-compressed solid provides the optimal condition for chemical change. 

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. 

Van Gool, W., Principles of Defect Chemistry of Crystalline Solids, Academic Press, London and New York (1966)... 

J. Maier, Solids - defects and function Principles in the Physical Chemistry of solid state chemistry, B.G. Teubner Verlag (2000). 

Before we proceed to analyze defect reactions by a mathematical approach, let us consider an applications of solid state chemistry. In this example, the effect of a defect on the properties of the solid is described. 

Note that the cheurged vacancy diffuses as one of the reacting species to form the defect compound. This situation is quite common in the solid state chemistry of compounds conteiining multivalent cations. The trivalent Ni3+ also gives rise to a new compound, N1A104. Yet the same... 

Defects are often deliberately introduced into a solid in order to modify physical or chemical properties. However, defects do not occur in the balance of reactants expressed in traditional chemical equations, and so these important components are lost to the chemical accounting system that the equations represent. Fortunately, traditional chemical equations can be easily modified so as to include defect formation. The incorporation of defects into normal chemical equations allows a strict account of these important entities to be kept and at the same time facilitates the application of chemical thermodynamics to the system. In this sense it is possible to build up a defect chemistry in which the defects play a role analogous to that of the chemical atoms themselves. The Kroger-Vink notation allows this to be done provided the normal mles that apply to balanced chemical equations are preserved. 

The first four chapters introduce basic concepts that are developed to build up a framework for understanding defect chemistry and physics. Thereafter, chapters focus rather more on properties related to applications. Chapter 5 describes diffusion in solids Chapter 6, ionic conductivity Chapters 7 and 8 the important topics of electronic conductivity, both intrinsic (Chapter 7) and extrinsic (Chapter 8). The final chapter gives a selected account of magnetic and optical defects. 

This type of defect equilibrium treatment has been used extensively to model the defect chemistry and non-stoichiometry of inorganic substances and has the great advantage that it easily takes several simultaneous defect equilibria into account [22], On the other hand, the way the mass action laws are normally used they are focused on partial thermodynamic properties and not on the integral Gibbs energy. The latter is often preferred in other types of thermodynamic analyses. In such cases the following solid solution approach is an alternative. 

Boroomand F, Wessel E, Bausinger H, and Hilpert K. Correlation between defect chemistry and expansion during reduction of doped LaCr03 interconnects for SOFCs. Solid State Ionics 2000 129 251-258. 

Driessens F. C. M. (1968). Thermodynamics and defect chemistry of some oxide solid solutions. Parts I and II. Ber. Buns. Phys. Chem., 72 754-772. 

Morlotti R. and Ottonello G. (1982). Solution of rare earth elements in silicate solid phases Henry s law revisited in light of defect chemistry. Phys. Chem. Minerals, 8 87-97. 

It is now well established that surface defects and imperfections determine the chemical reactivity of solid surfaces, making defect engineering an important branch of modern solid state chemistry and physics. However, this reactivity can in turn be responsible for the toxicity of different silicate dusts. A number of interesting studies have appeared which correlate the surface properties of different silicates to their genotoxicity and potential health hazards.190 192 In particular the potential of a surface to generate and release free radicals via the... 

One of the exceptions was the discovery of high ionic conductivity in appropriately doped FaGa03.128 129 As in the other oxide ion conductors, its ionic conductivity depends on both the dopant level as well as on the nature of the dopant. A major difference to ceria and zirconia is the presence of two cations that can be substituted the detailed defect chemistry of such solid solutions is far from being fully understood. Co-doping of Sr on A sites and Mg on B-sites leads to an ionic conductivity of ca. 0.12—0.17 S cm 1 at 800°C,130-133 which is similar to doped ceria but considerably exceeds the value of YSZ (ca. 0.03 S cm 1 at 800°C80 81). The activation energy also varies with composition and can be as low as ca. 0.6 eV.130 131 At about 600-700°C, the... 

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. 

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