Burgess, Ayrton;
(2025)
Development and Applications of Diffraction Anomalous Fine Structure: Extracting Site-Specific X-ray Absorption Spectra of Functional Oxides.
Doctoral thesis (Ph.D), UCL (University College London).
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Abstract
This thesis presents the development and applications of the Diffraction Anomalous Fine Structure (DAFS) technique for determining the site-specific structural properties of a given metal ion. A graphical user interface has been developed to extract anomalous scattering factors f’ and f” from powder samples, based on an iterative Kramers-Kronig algorithm described in the literature [ ¨ 1], [2], to improve DAFS ’user-friendliness’. XAS extracted from DAFS are further processed using typical XAS analysis software [3]. In the first instance, the optimal XRD data collection procedure was investigated using different detector systems, across a given absorption edge and data collected using the Pilatus detector was found to be superior. Fe3O4, which has both tetrahedral and octahedral environments located in different crystallographic sites, was used to test the validity of the DAFS measurement. The investigation showed that the conventional XAS data could be represented by a linear combination of the individual site contributions extracted from DAFS. Further studies on ZnFe2O4 revealed the presence of Zn2+ ions in both crystallographic sites, with the tetrahedral site dominating the sample. Zn2+ ions doped in ZrO2, a prominent CO2 hydrogenation catalyst, was investigated by collecting diffraction data across the Zn K-edge to understand the nature of Zn incorporation. Reflections in the XRD pattern of tetragonal ZrO2 were used to extract the DAFS, and it clearly shows that Zn2+ ions are substituted into Zr4+ sites. Further XANES simulations using oxygen-deficient structures support the presence of oxygen vacancies. Finally, directional anisotropy in the growth of nanocrystalline ZnO prepared from the decomposition of Zinc peroxide was investigated using two prominent reflections in the XRD data, and extracted DAFS was again analysed via conventional XAS analysis procedures. This project has established a method to simplify the DAFS measurement at a conventional XAS beamline. Furthermore, the computational analysis procedures generated as part of this work are also presented with the hope that DAFS will become a more widely utilised structural technique in synchrotron light sources worldwide
| Type: | Thesis (Doctoral) |
|---|---|
| Qualification: | Ph.D |
| Title: | Development and Applications of Diffraction Anomalous Fine Structure: Extracting Site-Specific X-ray Absorption Spectra of Functional Oxides |
| Open access status: | An open access version is available from UCL Discovery |
| Language: | English |
| Additional information: | Copyright © The Author 2025. Original content in this thesis is licensed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International (CC BY-NC 4.0) Licence (https://creativecommons.org/licenses/by-nc/4.0/). Any third-party copyright material present remains the property of its respective owner(s) and is licensed under its existing terms. Access may initially be restricted at the author’s request. |
| Keywords: | Materials Science, Chemistry, Diffraction Anomalous Fine Structure, X-ray Absorption, X-ray diffraction |
| UCL classification: | UCL UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Chemistry |
| URI: | https://discovery.ucl.ac.uk/id/eprint/10205179 |
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