Intergrowth ordered

When tripropylamine or tributylamine is used instead of the corresponding Alk N salt, ZSM-5/11 mixed phases (intergrowths ) are formed, suggesting that the Alk N species are less efficient in directing a specific structure. Unexpectedly, Bu N yields essentially a ZSM-5-rich phase while ZSM-11-rich phases are preferentially obtained with Pr N (XRD data). When an organic molecule acts as template towards (alumino)silicate species to form an ordered zeolitic framework, the latter is supposed to organize itself around the host organic species in such a way that a complete... 

In the brownmillerite structure, the oxygen vacancies order in such a way that half the iron of CaFe02.5 are octahedrally coordinated and half are tetrahedrally coordinated. This ordering is an expression of the tetrahedral-site stability of Fe ions. In a system like Lai yCayFe03 x < y/2, there is a tendency to form intergrowths of perovskite and brownmillerite structures the oxygen vacancies do not remain randomly distributed. Mossbauer spectra at 4.2 K for this complex system exhibit three sextets they have been interpreted in terms of 2 Fe and one Fe " ", or of an Fe and the disproportiona-... 

Sibieude has reported the occurrence of several ordered or partly ordered W structures at high temperatures in these systems. The evidence is from X-ray powder-diffraction and electron microscopy. In the light of our earlier discussion of B1, C1 and A-La2C>3 it is not surprising that these ternaries are also intergrowths of 111 layers of the first two - or the last two. 

Nb02.5 and this was described in detail in elegant papers by Anderson (1970, 1973). Ordered phases are based on shear structures, with parallel CS planes (double crystallographic shear) separating the blocks of the ReOs lattice. Ternary and intergrowth block structures have been discovered by extensive HRTEM... 

Figure 11.4 shows the various Habitus of calcite crystals observed in nature. To demonstrate Habitus changes at different orders of crystallization, or those depending on crystallization temperatures, three examples of intergrowths of two different Habitus of calcite are shown in Fig. 11.5 [3], see also Fig. 7.10. Figure 11.5(a) shows that later-grown calcite crystals on earlier-formed prismatic crystals of calcite show a different prismatic to a dog-tooth Habitus from the host crystal. 

Figure 5.12 (a) Ordered defects in monoclinic TiOfTij gOj g) (b) ordered defects in (orthorhombic) nonstoichiometric TiOj l (c) coherent intergrowth of (a) and (b) along the (120) planes of rocksalt structure. Lines indicate unit cell faces of the superstructures. (After Anderson, 1984.)... 

Perovskites constitute an important class of inorganic solids and it would be instructive to survey the variety of defect structures exhibited by oxides of this family. Nonstoichiometry in perovskite oxides can arise from cation deficiency (in A or B site), oxygen deficiency or oxygen excess. Some intergrowth structures formed by oxides of perovskite and related structures were mentioned in the previous section and in this section we shall be mainly concerned with defect ordering and superstructures exhibited by these oxides. 

OTOOTOTOOT Other ordered intergrowth phases reported are Ca7Fe6TiO,8... 

Fig. 2.78 Lattice image of an intergrowth structure [(3, 2 ), (3, 2 ) ] in clinohumite (3, 2 )ccp On the right (b) is shown the high-resolution lattice image of clinohumite, in the top left (a) the diffraction pattern and in the bottom left (a) the lattice image at low magnification. An ordered intergrowth of (3, 2 ) in every four clinohumite (3, 2 ) is seen, i.e. [(3, 2 ), (3,2 ) ].

Thus, it has been confirmed that there are many phases on the line MY of Fig. 2.83, which originate from the ordered stacking of M and Y blocks along the c-axis. As is clear, infinite discrete compounds can exist between the M and Y phases in principle. This is a typical example of the intergrowth structure. 

This approach is extremely powerful and endowed with the ability to reach near-atomic resolution. But it is a difficult one to apply in routine analyses because it demands electron microscopic expertise of a high order. It is also a destructive procedure, and not easily adapted for rapid detection and characterization of intergrowths in as-prepared zeolites in general. 

---