No abstract

We have utilized X-ray absorption fine structure (XAFS) spectroscopy to investigate the local atomic and electronic structure of iron incorporated into electrodeposited nickel hydroxide films. We found that cathodic codeposition from a solution containing Fe(II) and Ni(II) ions results in iron occupying Ni lattice sites in R-Ni(OH) 2 . The X-ray absorption near edge structure (XANES) shows that Fe is present as Fe(III) ions in the cathodically codeposited film. Analysis of the extended X-ray absorption fine structure (EXAFS) shows that Fe is coordinated to oxygen at ∼2.00 Å and to Ni at ∼3.11 Å. This Fe-O bond length is smaller than the Fe(II)-O bond distance found in Fe(OH) 2 (∼2.10 Å) but is in good agreement with the average Fe-(III)-O bond distance found in FeOOH (R, γ). The Fe-Ni bond distance is in agreement with that of the Ni(II)-Ni(II) bond distance found in R-Ni(OH) 2 . Moreover, the radial structure function (RSF) around Fe shows a distinct peak at ∼5.8 Å, which is a fingerprint of the brucite (R-Ni(OH) 2 ) structure. On anodic oxidation of the codeposited film in KOH, we found that the Fe ions occupied Ni lattice sites in γ-NiOOH.The XANES shows that the Fe edge shifts to higher energy values, indicating an increase in the oxidation state of Fe on charging. Analysis of the EXAFS data shows that Fe is coordinated to oxygen at ∼1.94 Å and to Ni at ∼2.84 Å. The latter value is in good agreement with the Ni(IV)-Ni(IV) bond length found in γ-NiOOH. The RSF around Fe in the oxidized film shows a distinct peak at ∼5.4 Å, just as in the RSF of Ni in γ-NiOOH. The Fe-O bond distance of ∼1.94 Å is in good agreement with the Fe(IV)-O bond distance found in SrFeO 3 . Our results strongly suggest that the Fe ions in the oxidized film is nominally tetravalent but with the Fe-O bond possessing a high degree of covalency.

No abstract

We discuss the properties of superconducting derivatives of the RuSr2GdCu2O8 (1212-type) ruthenocuprate, for which heterovalent doping has been achieved through partial substitution of Cu ions into the RuO2 planes (Ru1-xSr2GdCu2+xO8-d, 0Ru doping achieved in these phases is found to decrease the temperature for magnetic ordering as well the volume fraction of the magnetic phase.Comment: Proceedings of the 3rd Polish-US Workshop on Magnetism and Superconductivity of Advanced Materials, July 14-19, 2002, Ladek Zdroj (Poland) to appear in Physica