L‘objectif de ce travail est de proposer une démarche, mettant en oeuvre les techniques de diffraction ainsi que les approches théoriques de la modélisation auto-cohérente, afin d'analyser et mieux comprendre le comportement mécanique de chaque phase d'un acier inoxydable austéno-ferritique laminé à chaud. L'étude expérimentale vise la caractérisation du comportement mécanique local des phases sous un chargement uniaxial. La diffraction des rayons X et la diffraction neutronique ont été utilisées dans cette optique. Les états de contrainte ont été déterminés par DRX dans les phases austénitique et ferritique chargées en traction. L'évolution des déformations élastiques dans chacune des phases a été mesurée par la diffraction des neutrons en utilisant la technique de « temps-de-vol » au cours d'essais de traction et de compression. Les constantes élastiques radiocristallographiques ont été déterminées en utilisant une procédure de calcul faisant appel au modèle auto-cohérent pour une déformation purement élastique. <br />Pour rendre compte du comportement mécanique du matériau étudié, le modèle micromécanique polycristallin auto-cohérent pour une déformation élastoplastique a été adapté et confronté aux expériences menées. La texture cristallographique et les contraintes résiduelles initiales ont été prises en compte dans cette analyse. Les cissions critiques et les paramètres d'écrouissage de chacune des phases de l'acier duplex étudié ont été identifiés. Les résultats de cette étude ont montré que la phase austénitique représente la phase la moins dure et la plus écrouissable. Lors du calcul, la prise en compte des contraintes résiduelles initiales dans l'échantillon non déformé a expliqué l'asymétrie du comportement mécanique des phases en traction et en compression. Il a été montré que les contraintes initiales modifient considérablement les valeurs des limites d'élasticité des phases. Une bonne correspondance a été notée en comparant les résultats obtenus par DRX à ceux obtenus par la diffraction neutronique. Le problème de la relaxation de la contrainte normale à la surface irradiée par les rayons X a été analysé et discuté. <br />En utilisant la DRX et la modélisation auto-cohérente, l'effet de la composition chimique de l'acier inoxydable austéno-ferritique ainsi que l'influence d'un vieillissement à 400°C pendant 1000h, sur le comportement mécanique de chacune des phases austénitique et ferritique, ont été mis en évidence.

The problem of zero order diffraction (ZOD) in the computer generated hologram (CGH) is a commonly reported issue in employing computer generated hologram (CGH) systems. Failing to remove the zero order diffraction in either far-field or near-field region limits the display region or even worse, can destroy the reconstructed image. Therefore, the elimination of the ZOD is higly desired. The proposed new techniques to suppress the ZOD are the backbone of this thesis. We investigated ZOD sources in two different CGH systems and suggested different methods to remove the ZOD in each system. Two types of spatial light modulator (SLM) were employed for different type of CGHs, including a phase-only SLM and a binary amplitude-only SLM. All the proposed methods were examined with either simulation and experimental tests. For amplitude-only experiments, the ZOD suppression reached a factor of 3. Image quality and diffraction efficiency were also investigated for the proposed methods. / text

Electron crystallography is powerful for determination of complex structures. The newly-developed 3D electron diffraction (ED) methods make structure determination from nano- and micron-sized crystals much easier than using other methods, for example X-ray diffraction. Almost complete 3D ED data can be collected easily and fast from crystals at any arbitrary orientations. Dynamical effects are largely reduced compared to zonal ED patterns. 3D ED is powerful for phase identification and structure solution from individual nano- and micron-sized crystals, while powder X-ray diffraction (PXRD) provides information from all phases present in the samples. 3D ED methods and PXRD are complementary and their combinations are promising for studying multiphasic samples and complicated crystal structures. In this thesis, the feasibility and capability of 3D ED methods, specifically rotation electron diffraction (RED), in phase identification and structure determination of different kinds of crystalline materials with nano- or submicrometer-sized crystals are investigated. Experimental conditions for RED data collection and data processing in relation to data quality, as well as the challenges in the applications of RED are discussed. RED was combined with PXRD to identify phases from as-synthesized samples and to characterize atomic structures of eleven crystalline compounds. It was shown to be possible to identify as many as four distinct compounds within one sample containing submicron-sized crystals in a Ni-Se-O-Cl system. RED was also used to determine unit cell and symmetry of isoreticular metal-organic frameworks (SUMOF-7) and solve five zeolite structures with new frameworks, ITQ-51, ITQ-53, ITQ-54, EMM-23 and EMM-25 and that of a metal-organic framework (MOF), SUMOF-7I. The structure of an open-framework germanate SU-77 was solved by combining RED with PXRD. The structures of the zeolites and SU-77 were confirmed by Rietveld refinement against PXRD. High-resolution transmission electron microscopy was used to confirm the structure models of ITQ-51, EMM-25 and SUMOF-7I. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Submitted. Paper 4: Accepted. Paper 6: Manuscript. Paper 7: Epub ahead of print. Paper 9: Manuscript. Paper 11: Manuscript.</p>

X-ray absorption is not only element specific, but atom specific: two atoms of the same element in different states or in different neighbourhoods will have slightly different absorption characteristics. These energy dependent atomic form factors are carried over to the diffraction intensities. The atomic form factors are sensitive not only to the the energy of the X-ray but also the diffraction criteria; providing individual local physical data at different ratios in various diffractions. This process is referred to as site selectivity, it is unique to Diffraction Spectroscopy, and is achieved only when the sample is in crystal form. Through this work, a technique has been devised to site-separate two atoms of iron from within a protein, that builds on prior small unit cell Diffraction Anomalous Fine Structure experiments and harnesses the collection and processing software commonly used in large unit cell crystallography. A technique (dev + PCA) has been developed to retrieve the small signals from individual atom-labels out of the large and noisy background of real diffraction taken across a spectrum. The intensity of the diffractions are calculated by integrating over multiple images, profiling spots, merging datasets, and scaling across the whole spectrum. This thesis explores how Diffraction Spectroscopy can be used effectively on large unit cells, namely those of proteins. Site-selective absorption experiments were conducted on large unit cell crystals at a 3rd generation beamline, exclusively using existing equipment. The spectra generated were limited in scope but are an adequate proof of concept.

This project proposes a reactor-based instrument, which retains most of the above advantages of spallation source engineering instruments, while maintaining the advantages inherent to steady-state instruments. The main idea is to allow the entire white beam from the reactor onto the sample---no monochromation. Diffraction is then allowed at a fixed angle, and information from two sample directions can be obtained simultaneously. Since a white beam is incident onto the sample, the diffraction condition is satisfied for multiple sample planes in the fixed angle of diffraction. Multiple analyzer/detector pairs are placed downstream from the sample and tuned to scatter only one of the diffracted wavelength bands. Monte Carlo methods were used to create models of both a standard two-axis engineering diffractometer, found on current reactor sources, and the proposed white beam instrument. There models were validated by experiments performed on a standard two-axis instrument, which was also modified to operate in a white beam configuration, in which the position of the sample and monochromator were interchanged. Both the models and the experiments of the white beam instrument showed proof of concept for this design and identified areas of concern that required special attention. Upon a comparison on the results from the standard two-axis instrument to the results from the white beam instrument (both simulation and experimental), it was found that the standard diffractometer showed a better performance in all aspects. However, this project proposes numerous areas where the white beam design can be improved upon in order to enhance its performance as an engineering instrument. The most important of these is the design of an appropriate analyzer/detector system, as the results overwhelmingly show this to be the area of greatest concern. Ideas for a few such designs are also given. / Thesis (Master, Physics, Engineering Physics and Astronomy) -- Queen's University, 2009-04-23 17:46:59.419

Over the last decade progress towards step-wise structural transformations in solid state chemistry has been made using metal hydride reductants. Alkali and alkali-earth metal hydrides can effectively reduce transition metal oxides resulting frequently in novel oxygen defect structures. This provides access to control over cation oxidation states and magnetic exchange pathways, and thus electronic and magnetic properties. The goal for this research was to investigate a representative system that could be used both for exploration of novel oxygen defect phases and for investigating the fundamental parameters governing successful solid state reductions. The systems chosen for investigation were Sr2-xCaxMnO4 (0<x<2) and Sr2-xBaxMnO4 (x< 0.04). Detailed analysis of metal hydride reactivity with Sr2MnO4 is presented in addition to proof of the solid state reduction mechanism. As a result a number of novel oxygen defect phases have been produced, Sr2MnO4-x (0<x<0.37). The potential for producing novel lithium doped Sr2MnO4-x phases using a reduction/insertion approach with LiH has also been identified. Lastly as a test of application for metal hydrides as reductants the ability to topotactically reduce ScVO4 has been investigated.

This thesis primarily focuses on the systematic understanding of structure – reactivity relationships in two representative systems: bixbyite and related structures as well as indium doped CeO2. Topotactic reaction routes have gained significant attention over the past two decades due to their potential to access kinetically controlled metastable materials. This has contributed substantially to the understanding of solid state reaction pathways and provided first insights into mechanisms. Contrary to the widely used ex-situ methods, in – situ techniques including powder x-ray diffraction and thermogravimetric – differential thermal analysis have been employed extensively throughout this work in order to follow the reaction pathways in real time. Detailed analysis of the AVO3 (A = In, Sc) bixbyite reactivity under oxidative conditions has been carried out and a variety of novel metastable oxygen defect phases have been identified and characterized. The novel metastable materials have oxygen deficient fluorite structures and consequently are potential ion conductors. Structural aspects of the topotactic vs. reconstructive transformations are illustrated with this model system. The structure – reactivity study of AVO3 phases was extended to AVO3 perovskite family. Based on the research methodologies and results from AVO3 bixbyite reactivity studies a generalized mechanistic oxidation pathway has been established with a non-vanadium phase, ScTiO3 bixbyite. However, there is stark contrast in terms of structural stability and features beyond this stability limit during AVO3 and ScTiO3 bixbyite reaction pathways. A series of complex reaction sequences including phase separation and phase transitions were identified during the investigation of ScTiO3 reactivity. The two-step formation pathway for the fluorite – type oxide ion conductor Ce1-xInxO2-δ (0 ≤ x ≤ 0.3) is being reported. The formation of the BaCe1-xInxO3-δ perovskites and the subsequent CO2-capture reaction with the formation of Ce1-xInxO2-δ (0 ≤ x ≤ 0.3) has been investigated in detail. The two-step formation pathway is contrasted with the unsuccessful direct method. The stability and the extent of In – doping for the CeO2 fluorite phases that can be achieved through this CO2 – capture method are reported. The necessity and strategies for the selection of appropriate intermediate precursors for the preparation of doped CeO2 are also reported.

Over the last decade progress towards step-wise structural transformations in solid state chemistry has been made using metal hydride reductants. Alkali and alkali-earth metal hydrides can effectively reduce transition metal oxides resulting frequently in novel oxygen defect structures. This provides access to control over cation oxidation states and magnetic exchange pathways, and thus electronic and magnetic properties. The goal for this research was to investigate a representative system that could be used both for exploration of novel oxygen defect phases and for investigating the fundamental parameters governing successful solid state reductions. The systems chosen for investigation were Sr2-xCaxMnO4 (0<x<2) and Sr2-xBaxMnO4 (x< 0.04). Detailed analysis of metal hydride reactivity with Sr2MnO4 is presented in addition to proof of the solid state reduction mechanism. As a result a number of novel oxygen defect phases have been produced, Sr2MnO4-x (0<x<0.37). The potential for producing novel lithium doped Sr2MnO4-x phases using a reduction/insertion approach with LiH has also been identified. Lastly as a test of application for metal hydrides as reductants the ability to topotactically reduce ScVO4 has been investigated.

The simple cubic ReO₃-type framework has all of the key features required for negative thermal expansion (NTE) arising from the transverse thermal motion of bridging atoms and rotation of rigid polyhedra. Although ReO₃ itself only displays low NTE below ambient temperature, there is a potentially large family of isostructural fluorides and oxyfluorides that could display NTE. However, the coefficients of thermal expansion (CTE) of ReO₃-type materials range from strongly positive to strongly negative. Through extensive use of in situ synchrotron diffraction, this thesis examines the thermal expansion of several ReO₃-type fluorides and oxyfluorides, demonstrating the effects on CTE and related properties of both cation and anion substitution and the disorder produced by these structural changes.

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