P. R. Sarode

Valence fluctuation in some Yb intermetallics by X-ray photoemission and X-ray absorption

The valence state of Yb in some of its intermetallics, YbNi2Ge2, YbCu2Si2 and YbPd2Si2 has been investigated by LIII(Yb) absorption edges and X-ray pnotoelectron spectra in the 4f and 4d regions. These studies establish the presence of mixed valence in all three systems and illustrate the utility of 4f and 4d spectra in the study of mixed valence in Yb compounds.

Relation between effective atomic charge and chemical shifts in X-ray absorption spectra of transition-metal compounds

Chemical shifts of K absorption discontinuities, Delta E, of several manganese, iron and cobalt oxides with the metal in the formal oxidation states between +2 and +4, have been measured. These data, together with data in the literature on other compounds of these metals, can be fitted into the expression Delta E=aq+bq2, where q is the effective atomic charge on the metal. Theoretical considerations also support this functional relationship between Delta E and q.

High-temperature superconductivity in YBa2Cu3O7 and related perovskite oxides: Some aspects of solid state chemistry☆

Thermogravimetry and Cu K-absorption edge measurements show that the superconducting YBa/sub 2/Cu/sub 3/O/sub 7/ sample (annealed in O/sub 2/) contains more oxygen than the nonsuperconducting sample annealed in N/sub 2/, the former has a less distorted structure with the actual composition not far from the ideal one. Oxides of the formula Y/sub 1-x/Ba/sub 2/Cu/sub 3/O/sub 7/ (x = 0.05, 0.10 and 0.15) annealed in oxygen also possess the perovskite structure and show high-T/sub c/ superconductivity. The superconducting transition temperature seems to generally increase with the nominal Cu/sup 3+//Cu/sup 2+/ ratio in the superconducting copper oxides. Control of the Cu/sup 3+//Cu/sup 2+/ ratio (and hence the density of states at the metal-nonmetal transition in the non-superconducting state) through the oxygen stoichiometry or an appropriate cation substitution seems to provide a basis for synthesizing high-T/sub c/ copper oxides.

A XANES study of mixed-valence transition-metal oxides and rare-earth alloys

Energies of the 1s → 3d. 1s → 4s and 1s → 4p transitions of Mn, Fe and Co in a series of oxides have been obtained from X-ray absorption near-edge structure (XANES). Bivalent metal oxides do not show separate features in XANES due to the two oxidation states of the metal, but the spectroscopic transition energies.

Study of As2(Se,Te)3 glasses by X-ray absorption and photoelectron spectroscopy

E_\gamma

Charge transfer in chevrel phases

: as well as the 3d-4s and 3d-4p energy differences.

Copper binding by Pseudomonas aeruginosa

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An EXAFS study of amorphous selenium

E, increase smoothly with the oxidation number of the metal or its effective atomic charge, q. The variation of transition energies as well as

XPS and x-ray absorption-edge studies of the surface and bulk valence states of cerium in ceco2

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Transition metal oxide perovskites by photoelectron and x-ray absorption spectroscopy*

E values with q is best described by the parabolic relation.