Martis, V; (2012) Synchrotron radiation studies of multicomponent metal oxides. Doctoral thesis (PhD), UCL (University College London).

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Abstract

The work described in this thesis is focused on the development of characterization methods for determining the structure of multicomponent metal oxides using synchrotron radiation techniques, in particular, X-ray Absorption Fine Structure (XAFS) and Energy Resolved Electron Yield X-ray Absorption Spectroscopy (EREY– XAS). XAFS is a superior technique for determining the local structure of, for example, transition metals that are used as dopants in very low concentrations. It also provides information on early stages of crystallization processes before a material develops sufficient long range order. Energy resolved XAS was developed as an alternative to conventional transmission and fluorescence techniques which probe mainly the bulk of materials. This techniques yield information about the local structure from the near surface region of materials. The other complementary techniques used for characterization of materials were XRD, Raman spectroscopy, X-ray Photoelectron Spectroscopy (XPS) and Scanning Electron Microscopy (SEM). New insights about formation of Bi2MoO6 crystallites from an amorphous gel below 200oC were obtained with a novel in situ setup, in which XAFS and XRD was combined with RAMAN spectroscopy in a single experiment. Combined XRD/XAFS technique was used for determining the growth mechanism of Bi2MoO6 formed under hydrothermal conditions from an amorphous gel. The reaction kinetics was quantified by using the Avrami-Erofe’ev formalism. The surface sensitive of EREY–XAS was performed on several materials in particular chromium doped Fe2O3 catalysts and cobalt substituted aluminophosphates such as CoAlPO-18 and CoAlPO-34. The sensitivity of technique was assessed by comparison with conventional XAS techniques and XPS. Finally, the interactions of a synchrotron X-ray beam with a sample were studied. In particular, the effects of exposure to a monochromatic 10 keV X-ray beam on thermally induced crystallization of lithium disilicate glass were investigated.

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