Intergrowth coherent

III.C.4. Intergrowths in Zeolite Catalysts Coherent, Recurrent, and Random... 

One of the earliest direct bonuses of imaging zeolitic catalysts by HRTEM was the discovery (10) that the nominally phase-pure ZSM-5 (structure code MFI) contained sub-unit-cell coherent intergrowths of ZSM-11 (MEL). It soon became apparent (46) that, depending on the mode of synthesis of these and other pentasil (zeolitic) catalysts, some specimens of ZSM-5 contained recurrent (regular) intergrowths of ZSM-11. It also emerged that intergrowths of offretite and erionite are features of both nominally phase-pure erionite and of pure offretite and of many members of the so-called ABC-6 family of zeolites (47). 

Figure 18 (a) HREM lattice image of TlBa2Ca4Cu6013 (1245) with SADP inset. The unit cell is outlined, (b) Coherently intergrown 4 layer intergrowths (arrowed) of 1234 structure in 1245. 

Figure 1.18, An HRTEM image of coherent intergrowths in TlBa2Ca4Cu50i3 (1245), a high-temperature superconductor (HTSC) with five Cu-O layers. Four Cu-O layers (arrowed) of the 1234 HTSC phase are intergrown in the five Cu-O layer compound. (After Gai 1992.)...

Between n = 4 and 4.5, a large number of coherent intergrowth phases with long periodicities are known in this system (Portier et al, 1975). 

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.)... 

Figure 36 Electron micrograph of a crystal fragment of the mineral chloritoid. The crystal is mainly composed of one polytypic stacking sequence, but three others, labelled Al, A2, and A3, are also present and exist as coherent intergrowths in the parent matrix (Reproduced by permission from Proc. R. Soc. London, Ser. A, 1978, 36, 399)...

Third, the notion (and reality) of such structural infractions as twins and coherent intergrowths - as is seen by Yacaman et al. in a 923-atom nanoalloy of AuPd [35] - is meaningless in our molecular bimetallic nanoparticles. In the nanoaUoys of Yacaman et al. [35, 42] and others [43], one may discern directly, by aberration-corrected electronic microscopy, thin bands of hexagonal close-packed and face-centered cubic packed sheets. In a typical molecular nanoparticle of the kind that we have studied (also by aberration-corrected electron microscopy [39]), it is directly established (in line with theoretical predictions [44]) that a single bimetallic cluster of RUj Pt does indeed possess molecular character. Furthermore, when six or more such clusters coalesce into larger entities containing ca 200 atoms they adopt the regular crystalline, and faceted state of a bulk metal. 

Penn and Banfield (1998b, 1999) and Banfield et al. (2000) demonstrated that twins and structurally distinct slabs are generated when oriented aggregation involves an interface for which coherence can be obtained in more than one orientation. Multiple aggregation events, perhaps in combination with screw dislocation-based growth, can generate complex polytypes and structural intergrowths (Penn and Banfield 1998). 

Intergrowth tungsten bronzes exist when hexagonal tungsten bronzes coherently intergrow with the parent WO3 stmcture (Figs. 4.14 and 4.15). 

Figure 2. Example of coherent intergrowth with extended defects (A) Lamellae of H-Nb O. (blocks 5x3 and 4x3) in 25%2 Details of Nb O (circle in a))...

Colorless BeSiN, is a stoichiometric compound which crystallizes with a wurtzite superstructure [100] each nitrogen atom is surrounded by two Be and two Si atoms as shown in Fig. 11 tetrahedra tilled with like atoms form zigzag chains. Electron microscopy revealed coherent intergrowths of l-Bc,N, and BeSiN, [101]. 

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