Rozprawy doktorskie na temat „Synchrotron Diffraction Studies”

The structural evolution of cosmic dust analogues has been investigated using in situ synchrotron X-ray powder diffraction (SXPD) at the Diamond Light Source. Amorphous Mg/Ca silicates are produced as analogues of cosmic dust using a modified sol-gel method. They are studied under non-ambient temperature and pressure conditions using in situ powder diffraction, complemented by FTIR and Raman spectroscopy. The solid-state mineralisation of amorphous grains is observed by thermal annealing and the results of this allow the environmental conditions leading to the formation of crystalline dust grains in astrophysical environments to be constrained. The solid-gas carbonation of amorphous Ca-rich silicates is studied using in situ SXPD and analysed using full-profile fitting techniques, while the effect of ex situ carbonation on the short range ordering of amorphous grains is investigated using high energy SXPD and Pair Distribution Function (PDF) analysis. The formation of a metastable calcium carbonate phase (vaterite) is observed and the importance of this in relation to astrophysical environments is discussed. In situ Raman and SXPD data of CO2 clathrate hydrates are presented and the importance of the Raman data obtained here with relevance to future remote sensing missions to Solar System bodies is discussed. This work indicates the importance of laboratory work to the field of astrophysics and provides novel experimental approaches to aid our understanding of astrophysical processes.

The technique of single crystal synchrotron X-ray diffraction is applied in the study of solid state proton transfer processes in hydrogen bonded molecular complexes. Proton transfer processes are of interest where they are responsible for a number of physical and chemical properties within solid state functional materials; their study gives insight into the occurrence of such properties and where they may be targeted and tuned in future materials. The synchrotron X-ray diffraction technique has been trialled with respect to the potential it offers for high throughput capability for studying proton transfer processes as a function of an external stimulus or across a number of molecular systems. Chapter 1 contains a review of the literature of the hydrogen bond, including its role in crystal engineering and proton transfer effects. In Chapter 2, the theory behind the analytical techniques used in the study of hydrogen bonded molecular complexes, in which crystallographic methods are fundamental, are described. In Chapter 3 the research project aims and objectives are presented; these objectives are targeted at the use of single crystal synchrotron X-ray diffraction in the study and rationalisation of solid state proton transfer processes. In Chapter 4, the experimental methods implemented in this research project to achieve these research goals are reported. Chapter 5 is the first of the result chapters and applies the synchrotron single crystal X-ray diffraction technique in the study of variable temperature proton disorder in centrosymmetric hydrogen bonded carboxylic acid dimers. Chapter 6 focuses on the design of proton transfer systems implementing a number of crystal engineering strategies in the design of short strong hydrogen bonds (SSHBs) for potential proton migration studies. Chapter 7 applies a combination of diffraction methods (synchrotron and laboratory X-ray diffraction) and refinement strategies in the study of temperature dependent proton migration across SSHBs, allowing the potential of these methods in the study of proton migration to be assessed. Chapter 8 is the final application of the synchrotron technique in studies of proton transfer behaviour investigating static proton transfer behaviour in molecular complexes of the proton sponge 1,8-bis(dimethylamino)naphthalene with organic acids. The urea-acid inclusion materials presented in Chapter 9 additionally allow the investigation of the hydrogen bond as a crystal engineering tool in the design of hydrogen bonded solvent-inclusion networks. In the last chapter, Chapter 10, conclusions from the findings in Chapters 5 to 9 are pulled together and patterns explored. Drawing on these overall findings, some suggestions for future work are also made.

The complex microstructure and properties of dental enamel have been studied for decades using a variety of quantitative and qualitative techniques in order to gain a greater depth of understanding behind the chemical and physical processes that are associated with the formation and destruction of this biological apatite. Dental enamel is composed of highly ordered carbonated hydroxyapatite crystals which, together with its small organic component, are responsible for its mechanical strength, allowing it to serve its functional purpose. Environmental changes at any stage of the biomineralisation process or post eruption can disrupt the orientation and alter the structure and function, which can have detrimental clinical effects. The aim of this study is to understand and characterise the structural and crystallographic properties of disrupted enamel, and compare this to healthy unaffected tissue. Enamel affected by the genetic disorder, Amelogenesis Imperfecta, alongside enamel disrupted by dissolution and caries were studied using Synchrotron X-ray diffraction, 3D X-ray Microtomography, and Scanning Electron Microscopy techniques to relate these features to the clinically observed characteristics; to the chemistry; and to the known genetics of the tooth. Synchrotron radiation was used to map changes in preferred orientation, while the corresponding mineral density distributions were seen by using an in house developed, non-destructive microtomography system. Structural information on dental enamel at the crystallographic and micron length scales can benefit a variety of different disciplines. This project has the potential to inform early diagnosis, develop a tool for an early recognition of progressive or highly variable medical conditions, and design potential treatment regimes. The comparison of affected enamel to that of healthy enamel will provide a unique opportunity to identify the developmental pathways required for normal tooth development and give insights into the basic principles underlying mammalian biomineralisation.

Thesis (Ph.D.); Submitted to The University of California at Berkeley, Berkeley, CA (US); 1 Sep 2003.<br>Published through the Information Bridge: DOE Scientific and Technical Information. "LBNL--55022" Prilliman, Gerald Stephen. USDOE Director. Office of Science. Office of Basic Energy Sciences (US) 09/01/2003. Report is also available in paper and microfiche from NTIS.

<p>This thesis is concerned with <i>in-situ</i> time-, temperature- and pressure-resolved synchrotron X-ray powder diffraction investigations of a variety of inorganic compounds with twodimensional layer structures and three-dimensional framework structures. In particular, phase stability, reaction kinetics, thermal expansion and compressibility at non-ambient conditions has been studied for 1) Phosphates with composition <i>M</i><i>IV</i>(HPO₄)₂·<i>n</i>H₂O (<i>M</i><i>IV</i> = Ti, Zr); 2) Pyrophosphates and pyrovanadates with composition<i> M</i><i>IV</i>X₂O₇(<i>M</i><i>IV</i> = Ti, Zr and X = P, V); 3) Molybdates with composition ZrMo₂O₈. The results are compiled in seven published papers and two manuscripts.</p><p>Reaction kinetics for the hydrothermal synthesis of α-Ti(HPO₄)₂·H₂O and intercalation of alkane diamines in α-Zr(HPO₄)₂·H₂O was studied using time-resolved experiments. In the high-temperature transformation of γ-Ti(PO₄)(H₂PO₄)·2H₂O to TiP₂O₇ three intermediate phases, γ'-Ti(PO₄)(H₂PO₄)·(2-x)H₂O, β-Ti(PO₄)(H₂PO₄) and Ti(PO₄)(H₂P₂O₇)_0.5 were found to crystallise at 323, 373 and 748 K, respectively. A new tetragonal three-dimensional phosphate phase called τ-Zr(HPO₄)₂ was prepared, and subsequently its structure was determined and refined using the Rietveld method. In the high-temperature transformation from τ-Zr(HPO₄)₂ to cubic α-ZrP₂O₇two new orthorhombic intermediate phases were found. The first intermediate phase, ρ-Zr(HPO₄)₂, forms at 598 K, and the second phase, β-ZrP₂O₇, at 688 K. Their respective structures were solved using direct methods and refined using the Rietveld method. <i>In-situ</i> high-pressure studies of τ-Zr(HPO₄)₂revealed two new phases, tetragonal ν-Zr(HPO₄)₂and orthorhombic ω-Zr(HPO₄)₂ that crystallise at 1.1 and 8.2 GPa. The structure of ν-Zr(HPO₄)₂ was solved and refined using the Rietveld method.</p><p>The high-pressure properties of the pyrophosphates ZrP₂O₇ and TiP₂O₇, and the pyrovanadate ZrV₂O₇were studied up to 40 GPa. Both pyrophosphates display smooth compression up to the highest pressures, while ZrV₂O₇ has a phase transformation at 1.38 GPa from cubic to pseudo-tetragonal β-ZrV₂O₇ and becomes X-ray amorphous at pressures above 4 GPa.</p><p>In-situ high-pressure studies of trigonal α-ZrMo₂O₈ revealed the existence of two new phases, monoclinic δ-ZrMo₂O₈and triclinic ε-ZrMo₂O₈ that crystallises at 1.1 and 2.5 GPa, respectively. The structure of δ-ZrMo₂O₈was solved by direct methods and refined using the Rietveld method.</p>

Deformation phenomena in shape memory alloys involve stress-, temperature-induced phase transformations and crystallographic variant conversion or reorientation, equivalent to a twinning operation. In near equiatomic NiTi, Ti rich compositions can exist near room temperature as a monoclinic B19' martensitic phase, which when deformed undergoes twinning resulting in strains as large as 8%. Upon heating, the martensite transforms to a cubic B2 austenitic phase, thereby recovering the strain and exhibiting the shape memory effect. Ni rich compositions on the other hand can exist near room temperature in the austenitic phase and undergo a reversible martensitic transformation on application of stress. Associated with this reversible martensitic transformation are macroscopic strains, again as large as 8%, which are also recovered and resulting in superelasticity. This work primarily focuses on neutron diffraction measurements during loading at the Los Alamos Neutron Science Center at Los Alamos National Laboratory. Three phenomena were investigated: First, the phenomena of hysteresis reduction and increase in linearity with increasing plastic deformation in superelastic NiTi. There is usually a hysteresis associated with the forward and reverse transformations in superelastic NiTi which translates to a hysteresis in the stress-strain curve during loading and unloading. This hysteresis is reduced in cold-worked NiTi and the macroscopic stress-strain response is more linear. This work reports on measurements during loading and unloading in plastically deformed (up to 11%) and cycled NiTi. Second, the tension-compression stress-strain asymmetry in martensitic NiTi. This work reports on measurements during tensile and compressive loading of polycrystalline shape-memory martensitic NiTi with no starting texture. Third, a heterogeneous stress-induced phase transformation in superelastic NiTi. Measurements were performed on a NiTi disc specimen loaded laterally in compression and associated with a macroscopically heterogeneous stress state. For the case of superelastic NiTi, the experiments related the macroscopic stress-strain behavior (from an extensometer or an analytical approach) with the texture, phase volume fraction and strain evolution (from neutron diffraction spectra). For the case of shape memory NiTi, the macroscopic connection was made with the texture and strain evolution due to twinning and elastic deformation in martensitic NiTi. In all cases, this work provided for the first time insight into atomic-scale phenomena such as mismatch accommodation and martensite variant selection. The aforementioned technique of neutron diffraction for mechanical characterization was also extended to engineering components and focused mainly on the determination of residual strains. Two samples were investigated and presented in this work; first, a welded INCONEL 718 NASA space shuttle flow liner was studied at 135 K and second, Ti-6Al-4V turbine blade components were investigated for Siemens Westinghouse Power Corporation. Lastly, also reported in this dissertation is a refinement of the methodology established in the author's masters thesis at UCF that used synchrotron x-ray diffraction during loading to study superelastic NiTi. The Los Alamos Neutron Science Center is a national user facility funded by the United States Department of Energy, Office of Basic Energy Sciences, under Contract No. W-7405-ENG-36. The work reported here was made possible by grants to UCF from NASA (NAG3-2751), NSF CAREER (DMR-0239512), Siemens Westinghouse Power Corporation and the Space Research Initiative.<br>Ph.D.<br>Department of Mechanical, Materials and Aerospace Engineering;<br>Engineering and Computer Science<br>Materials Science and Engineering

Zirconium alloys are widely used in the nuclear industry because of their high strength, good corrosion resistance and low neutron absorption cross-section. However, zirconium has strong affinity for hydrogen, which may lead to hydrogen concentration build-up over time during a corrosion reaction when exposed to water. Hydrogen stays in solution at higher temperature but precipitates as zirconium hydrides at ambient temperatures. The formation of zirconium hydrides is considered to be a major cause of embrittlement, in particular as a key step in the mechanism of delayed hydride cracking. Despite the fact that zirconium hydrides have been studied for several decades, the basic nature and mechanisms of hydride formation, transformation and exact structure are not yet fully understood. In order to find the answer to some of these problems, the precipitation and dissolution of hydrides in commercial grade Zr powder were monitored in real time with high resolution synchrotron and neutron radiations, and the whole pattern crystal structure analysis, using Rietveld and Pawley refinements, were performed. For the first time all commonly reported zirconium hydride phases and complete reversible transformation between two different Zr-hydride phases were recorded with a single setup and their phase transformation type have been analyzed. In addition, the preparation route of controversial γ-zirconium hydride (ZrH), its crystal structure and formation mechanisms are also discussed.<br><p>Paper II in thesis as manuscript with title "The phase transformation between the δ and ε Zr hydrides"</p>

In-situ time-resolved synchrotron X-ray and neutron powder diffraction techniques have been applied to the study of solid state structural transitions within the organic polymorphic molecular systems of lactose, trehalose and theophylline. Diffraction techniques offer an unequalled method of polymorph identification and quantification, and have repeatedly demonstrated throughout this work that they can be utilised to follow and kinetically evaluate structural transitions in real time. The study of lactose crystallisation provides further proof of the transient ( lo::1/3) mixed crystal polymorph as the initial crystallisation product, which is then followed by the typical beta lactose and alpha lactose monohydrate phases. The formation of the (lo:: l,B) mixed crystal form has been mapped and kinetically analysed; the complex multi-step crystallisation behaviour is likely to result from the high degree of polymorphism which is displayed within the lactose system. The dehydration studies of the three systems show that dehydration kinetics can vary as a function of processing conditions and environments. Evidence of a previously undocumeuted theophylline polymorph has been observed which is accessible via the seeded dehydration of theophylline monohydrate with anhydrous theophylline form II. The best production of beta lactose from the 1-biannual dehydration of alpha lactose monohydrate to date is documented and is attained from dehydration within a hydrophobic cocoa butter environment; this transition is mediated via a crystalline phase whose identity is uncertain, yet displays a unique Bragg peak at rv 12.87° 20. Neutron diffraction techniques reveal that the water content and crystalline weight fraction of trehalose dihydrate are decoupled quantities, and the dihydrate lattice can sustain substantial water loss. These observations provide supporting evidence of a transiently stable, partially hydrated state of trehalose. In addition, the applicability of the Dl9 single-crystal diffraction beamline at the Institut Laue-Langevin in the study of hydrated powder samples is reported, demonstrating the versatility of the instrument with the capability of performing dynamic studies with a time-resolution of 15 s.

This thesis relates about structural studies of crystal oxides with variable oxygen stoichiometry. The synthesis procedure for large single crystal growth is detailed. These materials have a layered atomic structure in which extra-oxygen ions can be intercalated in a topotactic way by different methods, by electrochemistry already at ambient temperature or by thermal treatments under controlled atmosphere composition and pressure. The interstitial oxygen atoms are not statistically distributed within layers but are ordered at long-range, which provokes structural distortions of the crystal lattice. The atomic structure is then modulated by the occupation of interstitial sites and by the displacements of the surrounding atoms. The real structure of the oxygen-rich compounds has been studies by neutron and synchrotron X-ray single crystal diffraction. Reciprocal space plane reconstructions allowed us to measure precisely the positions and intensity of satellite reflections, and applying the maximum entropy method allowed us to visualize the nuclear densities with good precision, both favoring the study of short atomic displacements, and thus yielding better knowledge of the real crystal structure. The phase transition have also been studied with temperature by diffraction and thermogravimetry, showing that the oxygen content varies spontaneously and that the crystal phases of oxygen rich compounds astonishingly remain modulated until high temperature. The oxygen diffusion mechanism in these crystals could involve specific soft-phonon modes implying the rigid tilt of octahedra composing the crystal that amplify the mobility of interstitial oxygen atoms<br>Cette thèse concerne l’étude structurale d’oxydes cristallins à stœchiométrie en oxygène variable. La méthode de synthèse de gros monocristaux est présentée en détail. Ces matériaux présentent une structure atomique en couche entre lesquelles des ions oxygènes peuvent être intercalés de manière topotactique par différentes méthodes, aussi bien par électrochimie à l’ambiante que par traitement thermique sous atmosphère et pression contrôlée. L’insertion d’oxygène entre les couches ne se fait pas aléatoirement mais ces atomes excédentaires restent ordonnés à longue distance et provoquent des distorsions du réseau cristallin par effet stérique. La structure atomique devient modulée par l’occupation des sites interstitiels et par les déplacements des atomes environnants. La structure réelle des composés riches en oxygène a été étudiée par diffraction des neutrons et des rayons-X synchrotron. La reconstruction des plans du réseau réciproque a permis de mesurer précisément la position et l’intensité de chaque réflexion satellite. L’application de la méthode de maximum d’entropie a permis la reconstruction des densités nucléaires avec une haute précision, ce qui favorise la visualisation des déplacements atomiques courts, et donne alors une meilleure connaissance de la structure cristalline réelle. Les transitions de phase en température ont également été étudiées par diffraction et par thermogravimétrie, montrant que la quantité d’oxygène intercalés varie spontanément avec la température, et, contre toute attente, que les phases restent modulées jusqu’à des hautes températures. La diffusion des ions oxygènes dans le réseau hôte aux températures modérées pourrait être amplifiée par l’occurrence de phonons spécifiques impliquant le tilt rigide des octaèdres composant le cristal

The structure and magnetism of selected compounds of the pnictides iron based superconductors with chemical formula LnO{1-x}FeAsFx (Ln = La,Sm and Ce), commonly known as 1111, and of rare earth iron borates RFe3(BO3)4 (R = Tb, Gd, Nd and Y), were studied by means of hard x-ray diffraction. For the 1111 pnictides compounds, Rietveld refinement of powder x-ray diffraction measurements at room temperature reveals, that the ionic substitution of O by F has no effect on the structure of the FeAs layers of tetrahedra, whereas the major changes takes place in the LnO layer. These changes are reflected as a shrinkage of the crystal lattice, specially in the c direction. Additionally, a study of the temperature dependent structure of the Sm and Ce-1111 compounds was performed and an estimation of the the structural transition temperature was obtained. The results of the structural measurements, combined with electrical resistivity and µSR, were used to construct the Sm and Ce-1111 phase diagrams. These phase diagrams are characterized by two regions, consisting of a spin density wave (SDW) state and a superconducting state, which are sharply separated upon doping. Considering the different Ln ion, upon F doping the transition temperatures are more efficiently suppressed in Ce-1111 as compared to Sm-1111. More intriguingly, for the Ce case, a coexistence region between static magnetism and superconductivity without an orthorhombic distortion has been observed. Further analysis of the width of the Bragg peaks reveals strong lattice fluctuations towards phase transitions, which are reflected in magnetic and transport properties. Moreover, a strong damping of the lattice fluctuations is observed at Tc for superconducting Sm-1111 samples, giving experimental evidence of competing orders towards phase transitions in the iron pnictides. Regarding the iron borates, non-resonant x-ray scattering studies have shown several new diffraction features, from the appearance of additional reflections that violate the reflection conditions for the low temperature crystal structure, to the emerging of commensurate superlattice peaks that appear below TN. A detailed analysis of the structure factors and q dependencies of the earlier reflections, demonstrate their magnetic nature. Additional resonant x-ray magnetic scattering experiments on NdFe3(BO3)4 were performed at the Nd L2,3 and Fe K edges. The results show that the magnetization behavior is different for the Nd and for the Fe sublattices. Moreover, we find that the magnetization of the Nd sublattice is induced by the Fe magnetization. The temperature dependent measurements also show a commensurate to incommensurate transition where the magnetic structure changes from a commensurate collinear structure, where both Nd and Fe moments align in the hexagonal basal plane, to an incommensurate spin helix structure that propagates along c. When a magnetic field is applied, the spin helix is destroyed and a collinear structure is formed where the moments align in a direction perpendicular to the applied magnetic field. Moreover, the critical field at which the spin helix is destroyed is the same field at which the magnetic induced electric polarization is maximum, thus, showing that the spin helix is not at the origin of the electric polarization.

NiTi-based shape memory alloys (SMAs) offer a good combination of high-strength, ductility, corrosion resistance, and biocompatibility that has served them well and attracted the attention of many researchers and industries. The alloys unique thermo-mechanical ability to recover their initial shape after relatively large deformations by heating or upon unloading due to a characteristic reversible phase transformation makes them useful as damping devices, solid state actuators, couplings, etc. However, there is a need to increase the temperature of the characteristic phase transformation above 150 °C, especially in the aerospace industry where high temperatures are often seen. Prior researchers have shown that adding ternary elements (Pt, Pd, Au, Hf and Zr) to NiTi can increase transformation temperatures but most of these additions are extremely expensive, creating a need to produce cost-effective high temperature shape memory alloys (HTSMAs). Thus, the main objective of this research is to examine the relatively unstudied NiTiZr system for the ability to produce a cost effective and formable HTSMA. Transformation temperatures, precipitation paths, processability, and high-temperature oxidation are examined, specifically using high energy X-ray Diffraction (XRD) measurements, in NiTi-20 at.% Zr. This is followed by an in situ XRD study of the phase growth kinetics of the favorable H-phase nano precipitates, formed in NiTiHf and NiTiZr HTSMAs, based on prior thermo-mechanical processing in a commercial NiTi-15 at.% Hf HTSMA to examine the final processing methods and aging characteristics. Through this research, knowledge of the precipitation paths in NiTiZr and NiTiHf HTSMAs is extended and methods for characterization of phases and strains using high energy XRD are elucidated for future work in the field.

La compréhension des aspects fondamentaux de la diffusion de l'oxygène dans les oxydes solides à des températures modérées, jusqu'à température ambiante, est un enjeu majeur pour le développement d'une variété de dispositifs technologiques dans un avenir proche. Cela concerne, par exemple, le développement de la prochaine génération des électrolytes et membranes solides d'oxygène pour les piles à combustible de type SOFC. Autrement, les réactions d'intercalation de l'oxygène réalisées à basse température présentent un outil puissant pour contrôler le dopage en oxygène ainsi que des propriétés physiques. Dans ce contexte, les oxydes ayant une structure type brownmillérite (A2BB'O5) ou type K2NiF4, ont attiré beaucoup d'attention, car ils montrent une mobilité de l'oxygène déjà à température ambiante.Dans cette thèse, nous avons étudié les mécanismes d'intercalation d'oxygène dans SrFeO2.5+x, ainsi que Pr2NiO4+x par des méthodes de diffraction in situ, réalisées sur des monocristaux dans une cellule électrochimique spécifiquement conçue, explorant principalement le rayonnement synchrotron. Ceci a permis d’explorer en 3D tout le réseau réciproque, et d'obtenir des informations précieuses sur la diffusion diffuse, sur les faibles intensités des raies de surstructure, ainsi que des informations sur la fraction volumique des différents domaines de maclage au cours de la réaction, impossibles à accéder par diffraction de poudre.Les deux systèmes montrent des changements structuraux complexes, accompagnés par une mise en ordre de l'oxygène à longue portée. Au cours de l'intercalation d'oxygène nous avons mis en évidence deux phases intermédiaires, SrFeO2.75 et SrFeO2.875, possédant des lacunes en oxygène ordonnées à longue échelle. En raison du maclage, avec jusqu'à douze possibles individus, nous avons suivi directement la formation et l'évolution des domaines de maclage ainsi que leur micro-structure apparentée. Nous avons ainsi observé un mécanisme de réaction topotactique pour SrFeO2.5 vers SrFeO2.75, tandis que l'oxydation de SrFeO2.75 conduit à des importants réarrangements de l’oxygène, associés à un changement de nombre de domaines de maclage. La réduction électrochimique de la phase orthorhombique Pr2NiO4.25 donne Pr2NiO4.0 comme produit final, ayant la même symétrie, tandis que la phase tétragonale Pr2NiO~4.12 apparaît comme phase intermédiaire. Utilisant un monocristal avec un diamètre de 50 microns, la réaction se déroule dans des conditions d'équilibre dans moins que 24 heures, ce qui implique un coefficient de diffusion de l’oxygène anormalement élevé, supérieur à 10-^11cm2*s-1 à température ambiante. Nous avons également étudié le diagramme de phase de Pr2NiO4.25 sur monocristal jusqu’à 1100°C en chauffant sous air. Une série complexe de transition de phases a été mise en évidence, la vraie symétrie de Pr2NiO4.25 s’avérée en fait monoclinique.Outre l'exploration des diagrammes de phases complexes de SrFeO2.5+x et Pr2NiO4+d, nous avons pu étudier les changements détaillés concernant la micro-structure à l'aide de diffraction sur monocristaux in situ, impossible à accéder par des méthodes de diffraction de poudre classique. Les changements de la micro-structure des domaines va bien au-delà des composés étudiés ici et porte une grande importance pour extrapoler sur la performance, la stabilité et la durée de vie par exemple des matériaux utilisés pour le stockage de l’énergie<br>Understanding fundamental aspects of oxygen diffusion in solid oxides at moderate temperatures, down to ambient, is an important issue for the development of a variety of technological devices in the near future. This concerns e.g. the progress and invention of next generation solid oxygen ion electrolytes and oxygen electrodes for solid oxide fuel cells (SOFC) as well as membrane based air separators, oxygen sensors and catalytic converters to transform e.g. NOx or CO from exhaust emissions into N2 and CO2. On the other hand oxygen intercalation reactions carried out at low temperatures present a powerful tool to control hole doping, i.e. the oxygen stoichiometry, in electronically correlated transition metal oxides. In this aspect oxides with Brownmillerite (A2BB’O5) and K2NiF4-type frameworks, have attracted much attention, as they surprisingly show oxygen mobility down to ambient temperature. In this thesis we investigated oxygen intercalation mechanisms in SrFeO2.5+x as well as Pr2NiO4+x by in situ diffraction methods, carried out on single crystals in especially designed electrochemical cell, mainly exploring synchrotron radiation. Following up oxygen intercalation reactions on single crystals is challenging, as it allows to scan the whole reciprocal lattice, enabling to obtain valuable information as diffuse scattering, weak superstructure reflections, as well as information of the volume fraction of different domains during the reaction, to highlight a few examples, difficult or impossible to access by powder diffraction. Both title systems are able to take up an important amount of oxygen on regular and interstitial lattice sites, inducing structural changes accompanied by long range oxygen ordering. For SrFeO2.5+x the uptake of oxygen carried out by electrochemical oxidation yields SrFeO3 as the final reaction product. The as grown SrFeO2.5 single crystals we found to show a complex defect structure, related to the stacking disorder of the octahedral and tetrahedral layers. During the oxygen intercalation we evidenced the formation of two reaction intermediates, SrFeO2.75 and SrFeO2.875, showing complex and instantly formed long range oxygen vacancies. Due to the specific twinning with up to totally twelve possible twin individuals, we directly follow up the formation and changes of the specific domain and related micro-structure. We thus observed a topotactic reaction mechanism from SrFeO2.5 to SrFeO2.75, while further oxidation lead to important rearrangements in the dimensionality of the oxygen defects in SrFeO2.75, implying the formation of an additional twin domain in course of the reaction. The electrochemical reduction of orthorhombic Pr2NiO4.25 yields stoichiometric Pr2NiO4.0 as the final reaction product with the same symmetry, while tetragonal Pr2NiO~4.12 appears as a non-stoichiometric intermediate phase. Using a single crystal with 50µm diameter, the reaction proceeded under equilibrium conditions in slightly less than 24h, implying an unusually high oxygen ion diffusion coefficient of &gt; 10^-11cm2*s-1 at already ambient temperature. From the changes of the associated twin domain structure during the reduction reaction, the formation of macro twin domains was evidenced. Heating up Pr2NiO4.25 single crystals in air revealed a complex series of phase transition, evidencing the true symmetry of the starting phase to be in fact monoclinic. Beside exploring the complex phase diagrams of SrFeO2.5+x and Pr2NiO4+d we were able to investigate detailed changes in the micro-structure using in situ single crystal diffraction techniques, impossible to access by classical powder diffraction methods. The importance of changes in the domain structure goes far beyond the investigated title compounds and has utmost importance of the performance, stability and lifetime of e.g. battery materials

Orientador: Antonio Jose Ramirez Londono<br>Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica<br>Made available in DSpace on 2018-08-26T15:15:59Z (GMT). No. of bitstreams: 1 Faria_GuilhermeAbreu_M.pdf: 7344692 bytes, checksum: e531c95d64110532e988972471c0e25d (MD5) Previous issue date: 2014<br>Resumo: O objetivo deste trabalho foi desenvolver a metodologia de medição e análise de dados para a instalação experimental XTMS. Esta instalação foi projetada para possibilitar a medição simultânea de difração de raios X e informações térmicas e mecânicas de materiais enquanto estes são submetidas a condições termomecânicas controladas. Esta é uma área de grande interesse para cientistas de materiais uma vez que uma vasta gama de propriedades termomecânicas têm suas origens em propriedades microscópicas que são acessíveis através de dados de difração. Durante o trabalho, foram estudadas estratégias de medição, desenhos de amostras, métodos de processamento e análise de dados, assim como foi feita a caracterização da instalação como equipamento de medida de dados de difração. Como parte do trabalho, a instalação foi aplicada no estudo de casos científicos de interesse, que envolvem tanto diferentes metodologias de ensaios quanto dados de difração que exigem diferentes metodologias de análise. Os estudos consistiram em um ensaio de deformação em uma liga com memória de forma, ensaios de decomposição isotérmica em um aço inoxidável Superduplex UNS-S32750, e um ensaio de dilatometria acompanhado por difração do aço supermartensítico SuperCr13<br>Abstract: The aim of this work was to develop measurement and data analysis methodologies for the XTMS experimental installation. This facility was engineered to simultaneously collect X-ray diffraction and thermo-mechanical information of materials as they are subjected to controlled thermo-mechanical conditions. This is an area of great interest for material scientists given the wide range of thermo-mechanical properties correlated with microscopic properties which are accessible through X-ray diffraction. Developments performed during this work include the development and/or study of measurement strategies, sample designs, and data processing and analysis, as well as the characterization of the XTMS installation as an X-ray diffraction station. As part of the work, the installation was used to study several cases of scientific interest, involving different testing and data analysis methodologies. The studies performed were the deformation of a shape memory alloy, the isothermal ferrite decomposition on a Superduplex stainless steel UNS-S32750, and phase transformations on a SuperCr13 supermartensitic steel through dilatometry coupled with time resolved X-ray diffraction<br>Mestrado<br>Materiais e Processos de Fabricação<br>Mestre em Engenharia Mecânica

This thesis is largely a study of the ADOR process (assembly-disassembly-organisation-reassembly) when applied to zeolite UTL. The final chapter of this thesis deals with the adsorption of the medical gases NO and CO onto the metal organic framework NiNaSIP. Chapter 4 is devoted to the disassembly and organisation steps of the ADOR process. Calcined UTL was hydrolysed using 0.1 – 12 M HCl solutions from 75 – 95 °C run over 10 mins to 72 hrs. A three step mechanism is proposed, which is comprised of an initial rapid hydrolysis that removes the majority of the interlayer constituents of UTL, causing the silica-rich layers to largely collapse. This is followed by a slow, temperature and molarity dependent, deintercalation process that sees the remainder of the interlayer material removed resulting in the full collapse of the layers to form IPC-1P. The third step is a temperature and molarity dependent rebuilding process, whereby the interlayer region is slowly rebuilt, eventually forming a precursor which upon calcination becomes IPC-2 (OKO). Chapter 5 uses the pair distribution function (PDF) technique to structurally confirm the intermediate of the ADORable zeolite UTL. The intermediate, IPC-1P, is a disordered layered compound formed by the hydrolysis of UTL in 0.1 M HCl. Its structure is unsolvable by traditional X-ray diffraction techniques. The PDF technique was first benchmarked against high-quality synchrotron Rietveld refinements of IPC-2 (OKO) and IPC-4 (PCR) – two end products of IPC-1P condensation that share very similar structural features. An IPC-1P starting model derived from density functional theory was used for the PDF refinement, which yielded a final fit of Rw = 18% and a geometrically reasonable structure. This confirms that the layers do stay intact throughout the ADOR process, and shows that PDF is a viable technique for layered zeolite structure determination. Chapter 6 examines the reassembly stage by following the in-situ calcination of a variety of hydrolysed intermediates into their three-dimensional counterparts. Beamline I11 at Diamond Light Source provided high-quality PXRD patterns as a function of temperature, which were refined against using sequential Pawley refinements to track the unit cell changes. 0.1, 1.75, 2.5 and 12 M hydrolysed lamellar precursor phases were calcined. The largest unit cell changes were observed for 0.1 M, and the smallest for 12 M. This shows that increasing the molarity must prebuild most of the interlayer connections, such that upon calcination, only minimal condensation occurs to fully connect the layers. Chapter 7 probes the uptake of the medical gases CO and NO into the metal organic framework NiNaSIP. An in-situ single-crystal XRD study was undertaken using an environmental gas cell at beamline 11.3.1 at the Advanced Light Source. NiNaSIP was first dehydrated to reveal an open nickel site, which acted as the main site of adsorption for the inputted gases. NO was observed in a bent geometry at an occupancy of 40 % and a Ni – N bond length of 2.166(16) Å. The oxygen was modelled to be disordered over two sites. CO was not fully observed, as only the carbon was able to be modelled with an occupancy of 31.2 % and a Ni – C bond length of 2.27(3) Å.

The structure and magnetism of selected compounds of the pnictides iron based superconductors with chemical formula LnO{1-x}FeAsFx (Ln = La,Sm and Ce), commonly known as 1111, and of rare earth iron borates RFe3(BO3)4 (R = Tb, Gd, Nd and Y), were studied by means of hard x-ray diffraction. For the 1111 pnictides compounds, Rietveld refinement of powder x-ray diffraction measurements at room temperature reveals, that the ionic substitution of O by F has no effect on the structure of the FeAs layers of tetrahedra, whereas the major changes takes place in the LnO layer. These changes are reflected as a shrinkage of the crystal lattice, specially in the c direction. Additionally, a study of the temperature dependent structure of the Sm and Ce-1111 compounds was performed and an estimation of the the structural transition temperature was obtained. The results of the structural measurements, combined with electrical resistivity and µSR, were used to construct the Sm and Ce-1111 phase diagrams. These phase diagrams are characterized by two regions, consisting of a spin density wave (SDW) state and a superconducting state, which are sharply separated upon doping. Considering the different Ln ion, upon F doping the transition temperatures are more efficiently suppressed in Ce-1111 as compared to Sm-1111. More intriguingly, for the Ce case, a coexistence region between static magnetism and superconductivity without an orthorhombic distortion has been observed. Further analysis of the width of the Bragg peaks reveals strong lattice fluctuations towards phase transitions, which are reflected in magnetic and transport properties. Moreover, a strong damping of the lattice fluctuations is observed at Tc for superconducting Sm-1111 samples, giving experimental evidence of competing orders towards phase transitions in the iron pnictides. Regarding the iron borates, non-resonant x-ray scattering studies have shown several new diffraction features, from the appearance of additional reflections that violate the reflection conditions for the low temperature crystal structure, to the emerging of commensurate superlattice peaks that appear below TN. A detailed analysis of the structure factors and q dependencies of the earlier reflections, demonstrate their magnetic nature. Additional resonant x-ray magnetic scattering experiments on NdFe3(BO3)4 were performed at the Nd L2,3 and Fe K edges. The results show that the magnetization behavior is different for the Nd and for the Fe sublattices. Moreover, we find that the magnetization of the Nd sublattice is induced by the Fe magnetization. The temperature dependent measurements also show a commensurate to incommensurate transition where the magnetic structure changes from a commensurate collinear structure, where both Nd and Fe moments align in the hexagonal basal plane, to an incommensurate spin helix structure that propagates along c. When a magnetic field is applied, the spin helix is destroyed and a collinear structure is formed where the moments align in a direction perpendicular to the applied magnetic field. Moreover, the critical field at which the spin helix is destroyed is the same field at which the magnetic induced electric polarization is maximum, thus, showing that the spin helix is not at the origin of the electric polarization.