Defect chemistry

The topic of mixed conduction in nonstoichiometric oxides was reviewed by Tuller [24], and his comprehensive paper is recommended to the reader interested in more detail concerning the role of multivalent dopants on the defect chemistry of fluorite and fluorite-related oxides, and corresponding transport properties. Equations which express the oxygen flux in solid solutions of, e.g.. 

In addition to the defect reactions given in Section 10.4.2.1, one extra reaction needs to be considered, i.e. the ionization of the multivalent cation. On using the general notation N for the multivalent cation one may write. 

Electroneutrality relation Eq. (10.31) must be rewritten to include the charged species Nm  

With the aid of experimentally derived equilibrium constants, Eqs. (10.42)-(10.45) may be used to construct the Kroger-Vink defect diagram, from which expressions for the partial conductivities of the mobile ionic and electronic defects can be derived [24]. 

Electrical properties of solid solutions Zr02-Ce02-Y203 have been investi- 

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

Note that we have written two defect reactions for the case of vacancy formation in Table 3-2. Pyrophosphate is an insulator and the formation of a positively-charged vacancy is much less likely than the vacancy plus a free positive charge. This brings us to a rule found in defect chemistry that seems to be universal, namely ... 

In the real world of defect chemistry, we find that in addition to the simple defects, other types of defects can also appear, depending upon the type of crystal we are dealing with. These may be summarized as shown in the following, given as 3.7.1. on the next page. 

In the non-stoichiometric case where ionization of defects is the norm, the mathematics become too complicated so that the equations are not solvable. However, we can use a thermodynamic method to obtain the results we want. We will present here the case of silver bromide whose use in photographic film highlights the use of defect chemistry for practical purposes. 

Binsma, J. J. M. Giling, L. J. Bloem, J. 1982. Luminescence of copper (I) indium sulfide. I. The broad band emission and its dependence on the defect chemistry. 

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. 

Expansion and further explanation with respect to defects and defect chemistry and physics will be found in ... 

D. M. Smyth The Defect Chemistry of Metal Oxides, Oxford University Press, Oxford, United Kingdom, 2000. 

There are large numbers of anion excess fluorite-related structures known, a small number of which are listed in Table 4.4. The defect chemistry of these phases is enormously complex, deserving of far more space than can be allocated here. The defect structures can be roughly divided into three categories random interstitials, which in... 

As in the previous chapter, most work has been carried out on oxides, and these figure prominently here. As the literature on oxides alone is not only vast but is also rapidly increasing, this chapter focuses upon a number of representative structure types to explain the broad principles upon which the defect chemistry depends. However, despite considerable research, the defect chemistry and physics of doped crystals is still open to considerable uncertainty, and even well-investigated simple oxides such as lithium-doped nickel oxide, Li Nij- O, appear to have more complex defect structures than thought some years ago. 

Despite the many investigations of the defect chemistry of lithium-oxide-doped nickel oxide, the real nature of the defect structure still remains uncertain. For many years the holes were regarded as being localized on Ni2+ ions to form Ni3+, written Mi - ... 

The formal defect chemistry description of these processes has already described (Sections 4.3.3 and 8.5.1). 

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. 

Analyses of the defect chemistry and thermodynamics of non-stoichiometric phases that are predominately ionic in nature (i.e. halides and oxides) are most often made using quasi-chemical reactions. The concentrations of the point defects are considered to be low, and defect-defect interactions as such are most often disregarded, although defect clusters often are incorporated. The resulting mass action equations give the relationship between the concentrations of point defects and partial pressure or chemical activity of the species involved in the defect reactions. 

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. 

The defect chemistry of La, xSrxMn03l(5 under cathodic polarization conditions has been subjected to intensive studies due to its importance in the fundamental understanding of the 02 reduction mechanism and electrocatalytic activity. Yasumoto... 

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. 

Larsen PH, Hendriksen PV, and Mogensen M. Dimensional stabihty and defect chemistry of doped lanthanum chromites. J. Thermal Analysis 1997 49 1263-1275. 

The organization of this book follows the various states of aggregation of the earth s materials, in an order that reflects their relative importance in geology. Five chapters deal with the crystalline state. The first chapter is preparatory, the second and third are operative. The fourth summarizes some concepts of defect chemistry, the role of which in geochemistry is becoming more and more important as studies on kinetics and trace element applications advance. The fifth chapter is a (necessarily concise) state-of-the-art appraisal of the major silicate minerals. 

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