Intergrowth disordered

In contrast, ZSM-48 forms only in basic synthesis media. It is the only zeosil that has so far been obtained with the simple cobalticinium cation as SDA. The depiction of the channel structure in Fig 4, in which one-dimensional channels are lined by ten [Si04/2] tetrahedra, is an idealized one, however. ZSM-48 type zeosils and zeolites typically exhibit intergrowth disorder. This is also true of the compound synthesized with the cobalticinium cation. An X-ray powder diffraction pattern clearly shows disorder-induced broadening of some reflections. The synthesis, which is not easily reproduced, gives ZSM-48 as bundles of tiny yellow needles [47]. 

The first analytical tool to assess tire quality of a zeolite is powder x-ray diffraction. A collection of simulated powder XRD patterns of zeolites and some disordered intergrowths togetlier witli crystallographic data is available from tlie IZA [4o]. Phase purity and x-ray crystallinity, which is arbitrarily defined as tlie ratio of tlie intensity of... 

A) A stacking disorder (De Wolff disorder intergrowth of ramsdellite- and pyrolusite- type units, as already described above). This kind of disorder can be quantified by two parameters ... 

Figure 3. Schematic illustration of the disposition of chains made up of cornersharing SiOk tetrahedra in the triclinic and monoclinic forms of wollastonite, (The Ca2+ ions have been omitted for clarity) (top), and (hOl) and (hll) x-ray diffraction patterns that signify that the specimen in question is disordered and made up of intergrowths of the triclinic and monoclinic forms (bottom).

Additional information on disordered intergrowths can be found in the Catalog of Disordered Zeolite Structures, which is available electronically at http //www.iza-structure.org/databases/. 

Disordered intergrowths of chlorites, micas, 0.7-nm sheet silicates, and layer-hydroxides have also been observed (e.g., 18-21). 

Plate 6—Lattice image of Ca,La,, FeOi, showing disordered intergrowth. B stands for brownmillerite structure and G stands for... 

Plate 12 Disordered intergrowth of Aurivillius phases as illustrated in the case of Bi,Ti3Fe50i- (from ref 91... 

It is truly remarkable that in none of the ordered or disordered intergrowth phases do we see any evidence of vacancies or other point defects. Nonstoichiometry is however present in all systems showing disordered intergrowth of two or more phases. 

Ca2Fe205 and oxides of the CaMn03 v family are good examples of such vacancy-ordered structures. Complex intergrowth phases (ordered as well as disordered) involving brownmillerite and other related phases are commonly found in some of the anion-deficient oxides. Some of them also show polytypism due to different modes of stacking of the hexagonal and cubic layers. 

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