Valence States (valence + states)

Distribution by Scientific Domains

Selected Abstracts

Valence state partitioning of V between pyroxene-melt: Effects of pyroxene and melt composition, and direct determination of V valence states by XANES.

Application to Martian basalt QUE 94201 composition
This increase is due to the increased availability of elements for coupled substitution with the V3+ or V4+ ions, namely A1 and Na. For this bulk composition, both A1 and Na are higher in concentration in augite compared with pigeonite; therefore more V can enter augite than pigeonite. Direct valence state determination by XANES shows that the V3+ and V4+ are the main V species in the melt at fO2 conditions of IW-1 to IW+3.5, whereas pyroxene grains at IW-1, IW, and IW+1 contain mostly V3+. This confirms the idea that V3+ is more compatible in pyroxene than V4+. The XANES data also indicates that a small percentage of V2+ may exist in melt and pyroxene at IW-1. The similar valence of V in glass and pyroxene at IW-1 suggests that V2+ and V3+ may have similar compatibilities in pyroxene. [source]

Magnetoresistivity model and ionization-energy approximation for ferromagnets

Andrew Das Arulsamy
Abstract The evolution of resistivity versus temperature (, (T)) curve for different doping elements, and in the presence of various defects and clustering are explained for both diluted magnetic semiconductors (DMS) and manganites. Here, we provide unambiguous evidence that the concept of ionization energy (EI) which is explicitly associated with the atomic energy levels, can be related quantitatively to transport measurements. The proposed ionization energy model is used to understand how the valence states of ions affect the evolution of , (T) curves for different doping elements. We also explain how the , (T) curves evolve in the presence of, and in the absence of defects and clustering. The model also complements the results obtained from first-principles calculations. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Lattice dynamics of CuAlO2 under high pressure from ab initio calculations

P. Rodríguez-Hernández
Abstract The density functional perturbation theory is employed to study the vibrational properties of CuAlO2 under pressure. The calculations are preformed using the pseudopotential wave method and the local density approximation for the exchange-correlation (XC) potential. The d electrons of Cu are treated as valence states. We present the phonon dispersion curves. Our results are in good agreement with the available experimental Raman scattering experiments. Ab initio calculations show the presence of a dynamical instability, possibly related with the experimentally observed phase transition. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Conformational Effects on Circular Dichroism in the Photoelectron Angular Distribution

CHEMPHYSCHEM, Issue 4 2006
Devis Di Tommaso Dr.
Abstract The B-spline density-functional method has been applied to the conformers of the (1R,,2R)-1,2-dibromo-1,2-dichloro-1,2-difluoroethane molecule. The cross section, asymmetry, and dichroic parameters relative to core and valence orbitals, which do not change their nature along the conformational curve, have been systematically studied. While the cross section and the asymmetry parameter are weakly affected, the dichroic parameter appears to be rather sensitive to the particular conformer of the molecule, suggesting that this dynamical property could be a useful tool for conformational analysis. The computational method has also been applied to methyl rotation in methyloxirane. Unexpected and dramatic sensitivity of the dichroic-parameter profile to the methyl rotation, both in the core and valence states, has been found. Boltzmann averaging over the conformers reproduces quite closely the profiles previously obtained for the minimum-energy conformation, which is in good agreement with the experimental results. [source]