Crystalline Electron Phases

The phase stability of crystalline electron phases or Hume-Rothery (HR) phases has been explained by the afore-mentioned band-structure effects. For this purpose, the k- as well as r-space representation have been used successfully [5.45,46]. Crystalline HR-phases are well documented and excellent text books or reviews exist in this field [5.13,14, 35]. In the present section, only a few facts are mentioned in order to show how glassy metals belong to this class of phases. 

Under equilibrium conditions, the alloys considered in this paper show several crystalline HR-phases between Z = 1 e/a and approximately Z = 1.8-2.0 e/a (Table 1 a - e). 

Although the composition, which depends on the valence of the polyvalent element, might be quite different, structurally similar phases exist for different alloys in similar Z-regions. In the lower part of Fig. 5.6, this is shown for some Cu10o- Mx alloys with M = Zn, Be, Al, Sn chosen for the different valencies. Such a scaling behaviour of physical properties with Z is the most characteristic feature of HR-phases. As an additional indication, effects on the DOS have often been observed experimentally and minima are well established [5.35, 47], 

Whereas fee contains 4 and bcc 2 atoms per unit cell, y-brass is rather complex with 52 atoms per cell. Z became close to 1.8 e/a, and the Jones zone is 

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The different classes of Ru-based catalysts, including crystalline Chevrel-phase chalcogenides, nanostructured Ru, and Ru-Se clusters, and also Ru-N chelate compounds (RuNj), have been reviewed recently by Lee and Popov [29] in terms of the activity and selectivity toward the four-electron oxygen reduction to water. The conclusion was drawn that selenium is a critical element controlling the catalytic properties of Ru clusters as it directly modifies the electronic structure of the catalytic reaction center and increases the resistance to electrochemical oxidation of interfacial Ru atoms in acidic environments. 

Although the elemental analysis indicates an enrichment in Al, no crystalline Al phase was observed in any of the sediment samples. Neither XRD nor electron diffraction showed a separate Al hydroxide phase. 

Fig. 2 Scheme depicting the radiological behavior of the waters of hydration in DNA. For the first nine waters, ESR evidence suggests that both holes and electrons efficiently transfer to the DNA. For samples with additional waters from F=9 to F=21 (F is defined as the number of water molecules per nucleotide), holes form hydroxyl radicals with ESR parameters characteristic of a glassy environment and electrons efficiently transfer to the DNA. For samples with F>21, a crystalline ice phase forms holes in the ice phase form hydroxyl radicals with parameters characteristic of a crystalline ice environment. There is no ESR evidence that electrons from this phase transfer to the DNA. For samples with F>21, the glassy phase is reduced to about 14 waters per nucleotide with the remainder ice phase [3c]... 

The structure, crystallinity and phase of the films were studied by X-ray diffraction (Cu Ka filtered radiation) and by reflection and transmission high energy electron diffraction (RHEED and THEED), with 50 keV incident electron beams. The composition and the purity of the films was determined by Auger electron spectroscopy (AES). A cylindrical mirror analyser with a coaxial electron gun was placed at 30° with respect to the normal surface. 

Takeuchi etal. (1985) have examined the HDS catalyst deposits in detail with XPS, ESR, x-ray diffraction, and electron microscopy. X-ray diffraction revealed the presence of the crystalline V3S4 phase, a nonstoichiomet-ric, polycrystalline solid with sulfur-to-vanadium ratios of 1.2 to 1.5. This polycrystalline material was observed by microscopy as 10-/um-long, rod-shaped crystals on the outer surface of the catalyst and about 0.1 /urn in length within the catalyst pores. The x-ray diffraction technique will not reveal any amorphous phases present. Electron spin resonance spectra revealed the presence of a vanadyl on the surface that was coordinated with 4S and distinctly different from the 4N coordination of the crude oil... 

When the manganese concentration exceeds 25 a/o, the amorphous phase is gradually replaced by a crystalline bcc phase [129, 146-150], Although the x-ray diffraction pattern suggests the structure to be W-type (Figure 28(a)), it was determined by electron diffraction that the x-ray pattern only showed the third order reflections of a y-brass related D8i 3 structure [148]. It was concluded that the electro-deposited phase was a cubic variant of Mru Ah with a lattice parameter of 0.9012 nm. It was further suggested to be the high temperature y 1 phase, which has a com-... 

Abstract. Nanopowders of nonstoichiometric tungsten oxides were synthesized by method of electric explosion of conductors (EEC). Their electronic and atomic structures were explored by XPS and TEM methods. It was determined that mean size of nanoparticles is d=10-35 nm, their composition corresponds to protonated nonstoichiometric hydrous tungsten oxide W02.9i (OH)o.o9, there is crystalline hydrate phase on the nanoparticles surface. After anneal a content of OH-groups on the surface of nonstoichiometric samples is higher than on the stoichiometric ones. High sensitivity of the hydrogen sensor based on WO2.9r(OH)0.09 at 293 K can be connected with forming of proton conductivity mechanism. 

The variety in properties of different produced carbon materials is conditioned by the electronic structure of a carbon atom. The redistribution of electron density, the formation of electronic clouds of different modifications around the atoms, the hybridization of orbitals (sp3-, sp2-, sp- hybridization) are responsible for the existence of different crystalline allotropic phases and their modifications. 

Several research approaches are pursued in the quest for more efficient and active photocatalysts for water splitting (i) to find new single-phase materials, (ii) to tune the band-gap energy of TJV-active photocatalysts (band-gap engineering), and (iii) to modify the surface of photocatalysts by deposition of cocatalysts to reduce the activation energy for gas evolution. Obviously, the previous strategies must be combined with the control of the s)mthesis of materials to customize the crystallinity, electronic structure, and morphology of materials at nanometric scale, as these properties have a major impact on photoactivity. 

Hoppe H, Drees M, Schwinger W, Schaffler F, Sariciftci NS (2005) Nano-crystalline fullerene phases in polymer/fullerene bulk-heterojunction solar cells a transmission electron microscopy study. Synth Met 152 117... 

In this chapter we present a survey of our current understanding of interrelations between the electronic and ionic structure in late-transition-polyvalent-element metallic glasses. Evidence of a strong influence of conduction electrons on the ionic structure, and vice versa, of the ionic structure on the conduction electrons, is presented. We discuss as well the consequences to phase stability, the electronic density of states, dynamic properties, electronic transport, and magnetism. A scaling behaviour of many properties versus Z, the mean electron number per atom, is the most characteristic feature of these alloys. Crystalline alloys which are also strongly dominated by the conduction electrons are often called electron phases or Hume-Rothery phases. The amorphous alloys under consideration are consequently described as an Electron Phase or Hume-Rothery Phase with Amorphous Structure. Similar theoretical concepts as applied to crystalline Hume-Rothery alloys are used for the present amorphous samples. 

The electronic model for phase stability has been extrapolated from the region of the crystalline HR-phases to the amorphous state considered here, indicating the latter as a limiting case of the crystalline Hume-Rothery phases for Z 1.8 e/a. The scaling behaviour with Z of all properties is explained along these lines. 

Very little is known about the motions of lipid bilayers at elevated pressures. Of particular interest would be the effect of pressure on lateral diffusion, which is related to biological functions such as electron transport and some hormone-receptor interactions. Pressure effects on lateral diffusion of pme lipid molecules and of other membrane components have yet to be carefully studied, however. Figure 9 shows the pressure effects on the lateral self diffusion coefficient of sonicated DPPC and POPC vesicles [86]. The lateral diffusion coefficient of DPPC in the liquid-crystalline (LC) phase decreases, almost exponentially, with increasing pressure from 1 to 300 bar at 50 °C. A sharp decrease in the D-value occurs at the LC to GI phase transition pressure. From 500 bar to 800 bar in the GI phase, the values of the lateral diffusion coefficient ( IT0 cm s ) are approximately constant. There is another sharp decrease in the value of the lateral diffusion coefficient at the GI-Gi phase transition pressure. In the Gi phase, the values of the lateral diffusion coefficient ( 1-10"" cm s ) are again approximately constant. 

When an X-ray beam falls on alums iwo processes may occur. The beam may be scaltcrcd or the beam may be absorbed with an ejection of electrons from an atom. In the case of a crystalline material the scattering of X-rays is used to determine the structure of the solid phase and the chemist applies this method to the proof of the structure of new compounds very often. But even when a regular crystalline arrangement does not exist, as in liquids or amorphous solids, scattering patterns are produced. I.ike in the crystalline solid phase the scattering of X-rays on disordered systems can be used to determine the probability of distribution of atoms in the environment of any reference atom, or in other words the frequency with which interatomic distances occur. 

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