Anisotropic structures characterized

The structural features of most niobium oxychlorides known to-date are summarized in Table 6.1. The use of a combination of chloride and oxide hgands leads to compounds with unique structure types [41], characterized by a remarkable variety of cluster frameworks, ranging from discrete cluster units to chains, layers, and three-dimensional nets, some topologies of which are unprecedented in compounds containing octahedral clusters. Most of the niobium oxychlorides known to date have anisotropic structures (the exceptions are Cs2LuNb,5Cli70 and PbLusNbsClisOg). 

We have overviewed some strategies for the surface-mediated fabrication of metal and alloy nanoscale wires and particles in mesoporous space, and their structural characterization and catalytic performances. Extension of the present approaches for metal/alloy nanowires may lead to the realization of the prospechve tailored design of super active, selective and stable catalysts applicable in industrial processes. The organometallic clusters and nanowires offer exciting and prospechve opportunities for the creahon of new catalysts for industry. Various metal/ alloy nanowires and nanoparhcles in the anisotropic arrangement in porous supports would help in understanding the unexpected electronic and optic properties due to the quantum effect, which are relevant to the rational design of advanced electronic and optic devices. 

The cell density (number of cells per unit cross-section area or volume) is also used to characterize the coarseness or fineness of foam. Foamed products can feature a deliberately created inhomogeneous (nonuniform) morphology. An example is when a foamed core is sandwiched between solid skins as in so-called structural foams, or in elastomeric products with so-called integral skins. With cells elongated in the direction of foam rise or melt flow, the process will give an anisotropic structure and properties (Chapter 15). 

The group of J.P. Costes was the first to report on the use of rare-earth ions as the anisotropic source to design single-chain magnet systems [75]. Slow relaxation of the magnetization was observed in a Cu VTb heterometal-lic complex unfortunately not structurally characterized but formulated (LCu)2Tb(N03) on the basis of elemental analysis (with H3L 2-hydroxy-M- 2-[2-hydroxyethyl-amino]ethyl benzamide). Frequency dependence of the ac susceptibility was observed below 5 K (for frequencies ranging from 1 to 1000 Hz). From these data, the relaxation time of the magnetization was extracted and found to follow an activated behavior with = 28.5 K and... 

We have only described here the mineral mesophases that have been fully and unambiguously characterized. This review article is therefore not exhaustive. Other less well-documented examples can be found in the literature, in particular in another review article [127,128]. Nevertheless, the diversity of examples described here should draw the attention of the reader to the fact that suspensions based on anisotropic structural units may be liquid crystalline, a feature that could be used to obtain a better understanding/optimization of materials synthesis and processing conditions. Thus, the existence of a nematic domain in the phase diagram together with the possibility of growing reproducibly oriented single domains on the centimeter scale could be used, for instance, in the field of pillared materials to produce better structured materials. 

As a further complication the data previously discussed was reported for bulk materials and takes no account of the anisotropic structure of the K2Nip4 materials. It has been well documented that the oxygen interstitial in these types of oxides is located in the rocksalt layers and that the most likely conduction path for interstitial mobility is through the ab plane [30-32]. Hence it is likely that the attractive diffusion performance reported for the nickelate based materials could be further improved through the orientation of the cathode layer. In order to characterize the anisotropy of both diffusion and surface exchange, Bassat et al [19] have investigated isotopic exchanges... 

M. Malta, G. Louam, N. Errien, and R. M. Torresi, Nanofibers composite vanadium oxide/ polyaniline synthesis and characterization of an electroactive anisotropic structure, Electrochem. Commun., 5, 1011-1015 (2003). 

The structural model for tosylate-doped PEDOT presented a contribution to the structural characterization of PEDOT by using de Leeuw s chemical method extended to a surface-confined polymerization. Thin PEDOT films were formed that were subsequently studied with grazing incidence X-ray diffraction using synchrotron radiation. From these studies it was concluded that the material is very anisotropic and these thin films exhibit a limited crystalline order. 

We have tried to characterize the structure by any statistic information, and found that the pair correlation function can be extracted layer-by-layer, even for this kind of strongly anisotropic structure of molecules. Figure 4 shows the in-plane pair correlation function for the contacting layer, which demonstrates that the structure at the higher temperature is rather liquid-like with random nature. On the other hand a decrease in teinierature down to 185 K brings almost perfect hexagonal order, which is typically demonstrated by the first minimum reaching down to zero, and by the sprit of the second peak. 

Isotropic carbon is obtained by the pyrolysis of a hydrocarbon, usually methane, at high temperature (1200-1500°C) in a fluidized bed on a graphite substrate.Under these conditions, a turbostratic structure is obtained which is characterized by very little ordering and an essentially random orientation of small crystallites. In contrast to graphite which is highly anisotropic, such a structure has isotropic properties (see Ch. 7). Isotropic carbon is completely inert biologically. Its properties are compared to alumina, another common implant material, in Table 17.8. Notable is its high strain to failure. 

Liquid crystals (LCs) are organic liquids with long-range ordered structures. They have anisotropic optical and physical behaviors and are similar to crystal in electric field. They can be characterized by the long-range order of their molecular orientation. According to the shape and molecular direction, LCs can be sorted as four types nematic LC, smectic LC, cholesteric LC, and discotic LC, and their ideal models are shown in Fig. 23 [52,55]. 

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