Ceramic samples of La, -,Sr,Ni, -,Fe,O, + d , designed to model the ICI Hydecat catalyst, have been prepared via precipitation followed by high temperature annealing. The samples are characterized by X-ray diffraction, EDAX and atomic absorption spectrometry. The small changes in electronic structure as a function of x and y have been probed using photoemission.This reveals a progressive shift of the valence-band edge towards the Fermi level as a function of Sr-doping level, consistent with the approach to a metal to non-metal transition. Resonant photoemission at the Fe and Ni 3p thresholds is used to identify the transition metal contributions to the valence band density of states, and confirms a valence state of 33.0 for Fe. High resolution ESCA is used to quantify the surface composition of the samples, revealing Sr segregation consistent with that found in related perovskites and layered perovskites. Adsorption of CO onto the surfaces of these materials is seen to give rise to the ready production of a carbonate species. Water adsorption studies, which test the potential stability of the materials for possible applications in aqueous solution, are also presented.

Synchrotron-excited resonant-photoemission measurements at rare-earth 4d ~ 4fand transition-metal 3p ~ 3d thresholds have been carried out using a variety of complex cuprates and nickelates on stations 6.1 (grazing-incidence monochromator) and 6.2 (toroidal-grating monochromator) at the SRS CLRC Daresbury Laboratory. The systems studied are Nd2Nil _xCuxO4, La2_xSrxNil _yFeyO4 + 6 and Bi2Sr/Cal_xYxCu208 + 6. A combination of EDC and constant-initial-state data is used to examine the 4f and 3d contributions to the valence-band density of states and their binding-energy positions relative to the Fermi energy. This allows the study of the valence states of the transitionmetal ions and their modulation on doping. For La2_ xSrxNii _ yFeyO4 + 6, this approach is used to infer a valence state of _> 3.0 for Fe. In the case of Bi2Sr2Cal _ xYxCuz08 + 6, the effect of Cu valence modulation on the 3p resonance is observed as x is varied. This is discussed in the light of controversy surrounding shifts in core-level photoemission with doping for this system.

EXAFS is used to study changes in local structure which occur on doping at the B site in two related perovskite oxides,. In the case of the stannate, data is taken at the Sr K, Sb K and Sn K edges. A combination of near-edge XAS and EXAFS measurements show that Sb dopes into the material as SbV . In the case of the bismuthate, data is taken at the low-intensity Bi L I and Pb L II edges, with the aim of resolving controversy surrounding the interpretation of EXAFS data taken at the overlapping L III edges. In BaBiO 3 , two BiMO bond lengths are observed, suggesting the presence of a charge density wave. In this material, equal proportions of these two bond lengths are present. However, as Pb is doped into the material, the proportion of oxygen bonded to Bi at the shorter of the two distances increases progressively.

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