Ordering of defects

Table 14.15 Intermediate phases formed by ordering of defects in the praseodymium-oxygen system...

In spite of several investigations of defect perovskite systems in the last few years, there is much scope for study in this interesting aspect of solid state inorganic chemistry. The nature of defects as well as the ordering of defects in many systems are yet to be studied. For example, not much is known about the defect... 

Defect equilibria in intermetallic compounds are inferred from measured changes of vapor pressure with composition and from other experimental information. Equilibria analogous to those in aqueous solution are found in dissociation, com-plexing, and random solution other equilibria connected with the ordering of defects show a distinctly intermetallic flavor. Techniques for calculating the equilibria are described. Cerium-cadmium phase information is collected. 

When the defect interaction energy is much larger than the thermal energy, it can lead to an ordering of defects into superlattice structures and to the appearance of phases having ordered arrays of defects. Other interactions may also become important as the spin-dependent interactions between the d electrons in the Fj gS system (24). We shall not consider these order-disorder phenomena, since they are discussed by Wadsley (30). Some of the structural-consequences of ordering are considered below. 

Lambeck, P.V and Jonker, G.H. (1978) Ferroelectric domain stabilization in BaTiOs by bulk ordering of defects. Ferroelectrics, 22, 729-731. 

Despite very clear structural motifs based on four-connected atoms within the frameworks, the clathrates seldom have completely ordered crystal structures. Different kinds of crystallographic disorder appear including defects in the framework and in the cages, mixed occupation by different elements, and positional disorder of the so-formed sub-sites. The resulting defect or substitution variants tend to form superstructures by ordering of defects or different atoms on the substitution positions. Most of these effects have already been studied on representatives of the clathrate-I type, thus some such examples are given below. 

Chebotin VN, Mezrin VA (1985) Ordering of defects, thermodynamic and transput properties of solid oxide electrolytes with fluorite structure. Phys Status Solid A 89 199-211... 

Association of defects to form clusters and ordering of defects, a subject which has been mentioned in the introduction, reduce the formation energy per defect. Clustering and ordering of point defects will be discussed in later sections. 

Product failures in the field sometimes occur at very low levels, on the order of defects per million. The determination of the failure mechanism in these cases is often very difficult because more than one factor leads to the failure. In many cases, two distinct situations have to occur simultaneously for the failure to occur. And in some cases, three or more factors need to coincide. In this paper, we describe the failure analysis of a solution container which was found to have panel leaks. In a future paper, we hope to outline how the failure mechanism was used to troubleshoot the product manufacturing process and solve the problem in the field. 

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