Structural parallelism

FIG. 1 Schematic of two atomically structured, parallel surface planes (from Ref. 134). 

The growth of vanadium oxide overlayers on Rh(l 11) converges after a number of intermediate stages to the formation of a three-dimensional bulk-like epitaxial V203 film [90], which is oriented with the (0 0 01) plane of its corundum structure parallel to the Rh(l 1 1) substrate surface. The V203 phase is the thermodynamically stable... 

Fig. 4. Transmission electron micrograph (TEM) of a CdTe deposit formed using 200 cycle of CdTe via EC-ALE. The regular layered structure, parallel with the substrate Au lattice planes, suggests the epitaxial nature of the deposit. Reproduced by permission from ref. [114].

A perfect surface is obtained by cutting the infinite lattice in a plane that contains certain lattice points, a lattice plane. The resulting surface forms a two-dimensional sublattice, and we want to classify the possible surface structures. Parallel lattice planes are equivalent in the sense that they contain identical two-dimensional sublattices, and give the same surface structure. Hence we need only specify the direction of the normal to the surface plane. Since the length of this normal is not important, one commonly specifies a normal vector with simple, integral components, and this uniquely specifies the surface structure. 

When an electric field is applied to an ER fluid, it responds by forming fibrous or chain structures parallel to the applied field. These structures gready increase the viscosity of the fluid, by a factor of 105 in some cases. At low shear stress the material behaves like a solid. The material has a yield stress, above which it will flow, but with a high viscosity. The force necessary to shear the fluid is proportional to the square of the electric field (116). 

The simplest alkyne complexes, the metal acetylenes, resemble those of ethylene. For example, there are analogues of Zeise s salt in which an acetylene molecule ts bound to platinum(l)) and occupies a position like that of ethylene in Zeise s salt. In addition, there are L,Pt(RC=CR) complexes that have structures paralleling that of LjWHjC CHj) (Fig. 15.24). For both of these PtfO) complexes, an approximate square planar arrangement around the metal is found. Alkynes are more electronegative than ulkenes and are therefore better it acceptors. Thus it is appropriate to view them as metal lacyclopropenes 79... 

This synthesis of hydrazoic acid, said D. I. Mendeleeff, marks one of the most important achievements of the year 1890. This remarkable acid has no structural parallel among the inorganic acids, and in that respect it occupies an isolated position. The phenyl derivative of this acid, CflHg.N3, was discovered by J. P. Griess in 1867. 

A possible mechanism for the conversion of a ccp structure to bcc for a metal involves compression. Metals are more compressible than solids such as salts, and metals are much more malleable and ductile than most other solids. In Figure 4.4, on the left side, we view a ccp structure parallel to the packing layers. The ccp structure is viewed from an angle so that A, B, and C positions are staggered. No attempt has been made to distinguish the distance of the atoms in each layer from the viewer. As drawn the distances from the viewer are shortest for A and longest for C (this is an arbitrary choice of sites one could choose C positions closer than either A or B). In the figure the layers are compressed so that layers are converted as follows ... 

Fig. 1—(a) Ideal perovskite structure (b) layer sequence in the perovskite structure parallel to (001) and (c) GdFeOj structure. 

A yellow form of the pentacyanocobaltate(II) ion has been observed in DMF solution. Various monomeric (NR4)3[Co(CN)5] complexes have been crystallized26 and a structural study on one shows the anion to possess a truly five-coordinate square-pyramidal geometry.27 Electron irradiation of solid K3[Co(CN)6] gives a presumed pentacyanocobaltate(II) ion,28 the visible spectrum of which is virtually identical with that of [Co(CN)5]3a ). The structural parallels between the green and yellow forms of [Co(CN)5]3 and isoelectronic [Co(CNR)5]2+ ions indicate that all the green forms observed both in the solid state and in solution are weakly coordinated in the sixth axial position. 

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