Infinitely adaptive structure

In the shear stmctures discussed in the preceding sections, smaller compositional variations can be accommodated by changing the CS plane spacings. This, in 

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In the various intergrowth systems examined (see Table 5.3) there is no evidence for the presence of point defects. The origin of long-range periodicity in the complex recurrent intergrowth systems is, however, intriguing. The importance of elastic forces in the formation of polytypes, shear structures and infinitely adaptive structures was... 

For most, but not all, of the infinitely adaptive structures there may be a multiplicity of discrete, related, fully ordered structures for any one composition and, for certain compositions, the number of possible structures is potentially infinite. 

One of the prototypes of this behavior is the low-temperature form of tantalum pentoxide, L-Ta20s. The structure of this phase is ill defined, even though it is a stoichiometric oxide, and the room temperature stracture is a function of the prior thermal treatment temperature of the material. Reaction with other oxides, notably WO3, Zr02 and AI2O3, gives rise to solids with a broad oxygen nonstoichiometry. However, each composition appears to generate a uniquely ordered structure, which have been termed infinitely adaptive structures. 

IR-11.4.5 Defect clusters and use of quasi-chemical equations IR-11.5 Phase nomenclature IR-11.5.1 Introduction IR-11.5.2 Recommended notation IR-11.6 Non-stoichiometric phases IR-11.6.1 Introduction IR-11.6.2 Modulated structures IR-11.6.3 Crystallographic shear structures IR-11.6.4 Unit cell twinning or chemical twinning IR-11.6.5 Infinitely adaptive structures IR-11.6.6 Intercalation compounds IR-11.7 Polymorphism IR-11.7.1 Introduction IR-11.7.2 Use of crystal systems IR-11.8 Final remarks IR-11.9 References... 

Defects as described in Section 8.1 do not appear to form in these compounds. Each composition, no matter how close, chemically, it is to any other, appears to generate a unique and ordered structure, often with an enormous unit cell. Because of this, such structures are sometimes called infinitely adaptive structures . 

This rule is special to defect chemistry in crystalline solids, and requires special attention and some practice to avoid its pitfalls. As is discussed below, this rule does not apply to oxides with infinitely adaptive structures. 

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