Atomic properties binary

Solid solutions are very common among structurally related compounds. Just as metallic elements of similar structure and atomic properties form alloys, certain chemical compounds can be combined to produce derivative solid solutions, which may permit realization of properties not found in either of the precursors. The combinations of binary compounds with common anion or common cation element, such as the isovalent alloys of IV-VI, III-V, II-VI, or I-VII members, are of considerable scientific and technological interest as their solid-state properties (e.g., electric and optical such as type of conductivity, current carrier density, band gap) modulate regularly over a wide range through variations in composition. A general descriptive scheme for such alloys is as follows [41]. 

By using a systematic procedure to find the relevant element properties representing the alloying behaviour of binary systems, Villars (1983, 1985) defined three expressions for atomic properties which enable systems that form compounds to be separated from those that do not. 

A similar procedure was also used by Villars to find atomic property expressions which could be used to distinguish the crystal structures of intermetallic compounds 182 sets of tabulated physical properties and calculated atomic properties were considered. These were combined, for binary phases, according to the modulus sums, differences and ratios. The best separations were obtained by using three-dimensional maps, which, for a binary AVB,., x [Pg.309]

For materials in the condensed phase, the orbital implementation of the KT -when based on an atomistic description - overestimates in general the values of Se relative to experiment in the low and intermediate projectile velocity region. Since the KT is based on the binary encounter approach, this result is expected since the electronic states in a solid are mainly of a collective character and cannot be fully described by local atomic properties. However, the orbital implementation of the KT may be adapted for sohd targets by introducing band states instead of atomic states. 

The term surface alloy is somewhat generic and may refer to a variety of different systems. Here, we apply it to those systems where ultra-thin metal layers (i.e. a few atomic layers thick) are deposited on a bulk metal surface and where the system is subsequently annealed in vacuum in order to obtain alloying in a surface region a few atoms thick. In these conditions it is possible to obtain single atomic layer binary phases, or multilayer surface alloy phases (also termed epitaxial alloys (for a general discussion of these surface alloys, see [5]. Relatively to the subject of the present paper, two Pt-Sn systems have been studied Sn-Pt(l 11) and Sn-Pt(lOO). The behavior and the structural properties of these systems will be discussed in detail in the following. 

In addition to the estimated properties, we measured the thermochemistry of several important vapor species. These measurements were conducted in a Knudsen effusion cell using special line-of-sight vaporization under subambient pressures with flowing O2 and H2O vapor mixtures [4]. The gaseous species over silica [5], manganese oxide [6], lanthana, alumina, and palladium metal were detected and relative partial pressures measured as a function of temperature. These vapor pressure measurements were calibrated by using the known metal atom or binary metal oxide volatility as a calibration source. Oxide species concentrations were measured relative to that of a reference compound, e.g., metal atom. The identification of oxide and hydroxide compounds was facilitated by Ae technique of threshold electron ionization [7]. These data were then evaluated using estimated entropy functions and the third law temperatures. 

The enzyme vanillyl-alcohol oxidase (VAO, E.C. 1.1.3.38) was examined in detail with respect to mechanism, structural properties, and biotechnological applications by van Berkel and coworkers, giving an excellent example of how detailed biochemical studies provide a basis for preparative biocatalytic applications (for recent reviews see[1, 21). The homooctamer with a monomer mass of 65 kDa was isolated and purified from Penicillium simplicissimum. The catalytic mechanism of VAO-catalyzed oxidation of para-alkyl phenols was studied in detail[3-5 After initial hydride abstraction from the Ca atom, a binary complex of the intermediate para-quinone methide and reduced FAD reacts with molecular oxygen, regenerating the... 

The magnetic properties of an alloy can be studied as a function of the temperature and concentration of the constituent metals. Order-disorder phenomena can be measured directly and compared with the thermal history and mechanical properties of the alloy. The statistical occupation of the first coordination sphere round the resonant atoms in binary alloys can be derived from magnetic spectra. 

Reyes-Nava et al performed molecular-dynamics simulations on Pt-Au, Pt-Pd, and Pt Ni nanoalloys in order to study the ordering in binary, metallic clusters. They used approximate descriptions of the interatomic interactions similar to the studies we just mentioned. Reyes-Nava et al predicted that the trends in the most stable chemieal ordering are determined by the differences in the atomic properties of its constituents. Thus, for adjacent elements in the periodic table, the element with the lower valence-electron density will be found in the surface region. For alloys for... 

Temary and quaternary semiconductors are theoretically described by the virtual crystal approximation (VGA) [7], Within the VGA, ternary alloys with the composition AB are considered to contain two sublattices. One of them is occupied only by atoms A, the other is occupied by atoms B or G. The second sublattice consists of virtual atoms, represented by a weighted average of atoms B and G. Many physical properties of ternary alloys are then expressed as weighted linear combinations of the corresponding properties of the two binary compounds. For example, the lattice constant d dependence on composition is written as ... 

The program uses two ASCII input files for the SCF and properties stages of the calculation. There is a text output file as well as a number of binary or ASCII data files that can be created. The geometry is entered in fractional coordinates for periodic dimensions and Cartesian coordinates for nonperiodic dimensions. The user must specify the symmetry of the system. The input geometry must be oriented according to the symmetry axes and only the symmetry-unique atoms are listed. Some aspects of the input are cumbersome, such as the basis set specification. However, the input format is documented in detail. 

Many other properties have been found to show periodic variations and these can be displayed graphically or by circles of varying size on a periodic table, e.g. melting points of the elements, boiling points, heats of fusion, heats of vaporization, energies of atomization, etc. Similarly, the properties of simple binary... 

The thermodynamic and other physical properties of binary oxides (e.g. A//f, AGf, mp, etc.) show characteristic trends and variations when plotted as a function of atomic number, and the preparation of such plots using readily available compilations of data can be a revealing and rewarding exercise. 

For all the olefins studied, alkyl-, fluoro-, or chloro-substituted, three binary, mononuclear species were observed. It now seems that it is a general property of Ni and Pd atom-olefin reactions at cryogenic temperatures to form complexes that have a maximum coordination of three olefin molecules per metal atom, regardless of the electronic or steric attributes of the substituent(s). As intimated previously, the absence of higher stoichiometry species, even for unsubstituted ethylene, is, most probably, the result of steric interactions (54). 

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