In this dissertation, we used a combination of several synchrotron-based x-ray spectroscopic techniques to investigate the effects of strain, ionic defect formation, and heteroengineering in strongly-correlated electronic systems. First, we introduce a method to control and stabilize oxygen vacancies in complex transition-metal oxide thin films. In our approach, we utilized atomic layer-by-layer pulsed laser deposition (ALL laser PLD) from two separate targets to synthesize high-quality single crystalline CaMnO3 films under coherent tensile strain, varying systematically from +0.8% to +4%. An increase of the oxygen vacancy content in the single-crystalline CaMnO3 thin films with applied in-plane strain was experimentally observed using high-resolution soft x-ray absorption spectroscopy (XAS) in conjunction with bulk-sensitive hard x-ray photoelectron spectroscopy (HAXPES). Our experimental results were verified using first-principles theory and atomic core-hole multiplet calculations. Furthermore, our results highlight the importance of protecting the surfaces of CaMnO3 thin-films with thin Pt layers in-situ in order to stabilize the oxygen vacancy content. Next, we discuss the role of oxygen vacancies in driving the metal-insulator transition in LaNiO3 thin films. Here, we also use atomic layer-by-layer pulsed laser deposition (ALL laser PLD) from two separate targets to synthesize high-quality single-crystalline LaNiO3 films with systematically varying thicknesses, ranging from 1 u.c. to 50 u.c. An increase in the oxygen vacancy content was observed with the decreasing LaNiO3 film thickness using XAS. A higher concentration of oxygen vacancies was observed for the ultrathin insulating films (<1.5 u.c.). The experimental results were compared to first-principles theoretical calculations. We found that LaNiO3 exhibits room-temperature metallic behavior for thicknesses down to 1.5 u.c., which is the lowest value reported to date. Finally, we have investigated an atomically-abrupt interface between the paramagnetic LaNiO3 and the antiferromagnetic CaMnO3 thin films. The interface between these two complex oxides exhibits interfacial ferromagnetism, which can be tuned via a thickness-dependent metal-insulator transition in LaNiO3. Here, we used depth-resolved standing-wave photoemission spectroscopy (SW-XPS), scanning transmission electron microscopy (STEM), and XAS to observe a depth-dependent charge reconstruction occurring at the LaNiO3/CaMnO3 interface. Our elemental standing-wave rocking-curve analysis revealed the depth-dependent changes of the Mn and Ni valence states at the interface, yielding increased amounts of Mn3+ and Ni2+ cations at the interface. These results suggest Mn4+-Mn3+ ferromagnetic double exchange and Ni2+-Mn4+ superexchange as possible underlying causes of the emergent interfacial ferromagnetism. / Physics

In the drive towards higher strength alloys, a diverse range of alloying elements is employed to enhance their strength and ductility. Limited solid solubility of these elements in steel leads to segregation during casting which affects the entire down-stream processing and eventually the mechanical properties of the finished product. The work presented in this PhD shows that segregation of alloying elements during casting, particularly aluminium, leads directly to banding in the final product. It has been demonstrated that no significant homogenisation is possible in this alloy within practical time constraints of the industrial thermo-mechanical process. A through-process model was developed to design a thermo-mechanical treatment aimed at reducing the effects of segregation on the formation of banding. A new polynomial function for calculating the local phase transformation temperature (Ae3) between the austenite + ferrite and the fully austenitic phase fields during heating and cooling of steel is presented. Material was produced both with and without banding and used to study the effect upon the mechanical properties. The banded steel variants show a significant reduction in tensile strength for a similar level of ductility compared to non-banded variants. In situ measurement under uniaxial loading using high-energy synchrotron diffraction allowed direct quantification of the impact of the mechanically induced transformation of metastable austenite on the work- hardening behaviour. The results reveal that the mechanically induced transformation of austenite does not begin until the onset of matrix yielding and the experimental evidence demonstrates that the austenite to martensite transformation increases the work-hardening rate of the ferrite phase and delays the onset of Stage-III hardening until the yield point of austenite. The increase in work-hardening rate (and thus work required) supports a driving force approach to transformation induced plasticity. The transformation work required leads to an increase in the macroscopic work-hardening rate after matrix yielding which offsets the decrease in the work-hardening rate in the ferrite and martensite phases up to the UTS. Steels with a high degree of banding do not show this extra contribution due to the more dominant anisotropic effect of martensite bands on the work-hardening of ferrite coupled to increased mechanical austenite stability as a result of increased carbon content. A list of revisions as requested by the examiners is produced on pages 18 and 19 of the thesis for examination. Abstract: In the drive towards higher strength alloys, a diverse range of alloying elements is employed to enhance their strength and ductility. Limited solid solubility of these elements in steel leads to segregation during casting which affects the entire down-stream processing and eventually the mechanical properties of the finished product. The work presented in this PhD shows that segregation of alloying elements during casting, particularly aluminium, leads directly to banding in the final product. It has been demonstrated that no significant homogenisation is possible in this alloy within practical time constraints of the industrial thermo-mechanical process. A through-process model was developed to design a thermo-mechanical treatment aimed at reducing the effects of segregation on the formation of banding. A new polynomial function for calculating the local phase transformation temperature (Ae3) between the austenite + ferrite and the fully austenitic phase fields during heating and cooling of steel is presented. Material was produced both with and without banding and used to study the effect upon the mechanical properties. The banded steel variants show a significant reduction in tensile strength for a similar level of ductility compared to non-banded variants. In situ measurement under uniaxial loading using high-energy synchrotron diffraction allowed direct quantification of the impact of the mechanically induced transformation of metastable austenite on the work- hardening behaviour. The results reveal that the mechanically induced transformation of austenite does not begin until the onset of matrix yielding and the experimental evidence demonstrates that the austenite to martensite transformation increases the work-hardening rate of the ferrite phase and delays the onset of Stage-III hardening until the yield point of austenite. The increase in work-hardening rate (and thus work required) supports a driving force approach to transformation induced plasticity. The transformation work required leads to an increase in the macroscopic work-hardening rate after matrix yielding which offsets the decrease in the work-hardening rate in the ferrite and martensite phases up to the UTS. Steels with a high degree of banding do not show this extra contribution due to the more dominant anisotropic effect of martensite bands on the work-hardening of ferrite coupled to increased mechanical austenite stability as a result of increased carbon content.

During loss-of-coolant accidents (LOCA) and reactivity-initiated accidents (RIA), nuclear fuel rods experience high heating rates that change the microstructure and properties of zirconium cladding materials, which are in forms of stress-relieved, like cold-worked (CW) or recrystallised (RX) microstructure. The present study aimed to determine how different fast heating rates and starting microstructures affect the kinetics of phase transformation, the transformation textures and eventually the mechanical response in the dual-phase region. The LOCA/RIA cycles from heating at 8 to 100C/s to alpha+beta or above beta transus temperature were achieved via resistive heating in an electro-thermal-mechanical tester. Synchrotron X-ray diffraction (SXRD) and electrical resistivity measurements showed that the approach curves of CW Zircaloy-4 shift to higher temperature at faster constant heating rates and change to a new approach curve when changing rates. 2-second holding at two-phase temperature produces identical phase fractions as equilibrium. These observations are consistent with the diffusional character of the phase trans- formation. Heated at 100oCs1, RX samples transform with 2D beta-growth while CW ones show simultaneous beta-nucleation and growth. The difference arises because the fast heating rate helps preserve low-angle grain boundaries (GB) in the CW microstructure up to phase transformation temperature, increasing beta nucleation sites and prevent beta-growth. This gives rise to different textures of RX and CW materials before transformation, producing different textures, which are weak in both cases. However, this difference is enhanced during grain growth and transformation on cooling. Thus, the RX material shows strong final alpha texture with 0002 maxima aligned in TD and tilted 20deg from ND towards TD while the CW reveals an essentially random one. In both RX and CW materials, variant selection does not occur during transformation on heating. During beta-grain growth, although there is variability in beta-textures measured by SXRD and EBSD beta reconstruction, it is clear that variant selection occurs, leading to strengthening of the beta texture. During transformation on cooling, variant selection occurs early in nucleation of the alpha phase from the shared 110 beta GB in the RX condition. The flow stresses of CW Zircaloy-4 in the two-phase regime at a given temperature depend on the heating rates, despite having the same phase fractions. Heated at a slower rate, the material shows an upper yield stress followed by softening behaviour while that heated faster has a smaller yield stress followed by a high work-hardening rate and then stable flowing stresses. The evolution of diffraction elastic strains and intensity suggest the upper yield stress and softening are due to stress-induced transformation of the harder alpha grains into large and isolated softer beta grains. In contrast, the sample heated faster develops an almost continuous film of beta grains along the GB of unrecrystallised alpha-grains which results in early beta-yielding and coherent deformation of the two phases, leading to constant flow stresses. The findings will improve the accuracy of inputs from phase fractions, microstructure and texture of zirconium claddings when modelling LOCA/RIA. A crystal plasticity model should consider the effects of heating rates and cold-work, which are often ignored. The link between deformation, fast heating rates and microstructure evolution might be relevant to other processes like additive layer manufacturing and even forging in the two-phase region.

This thesis is concerned with the study of two families of materials which contain magnetically frustrated triangular lattices. Each material is concerned with a different use; the first, analogues of YMnO₃, is from a family of materials called multiferroics, the second, A₂MCu₃F₁₂ (where A = Rb¹⁺, Cs¹⁺, M = Zr⁴⁺, Sn⁴⁺, Ti⁴⁺, Hf⁴⁺), are materials which are of interest due to their potentially unusual magnetic properties deriving from a highly frustrated Cu²⁺-based kagome lattice. YFeO₃, YbFeO₃ and InFeO₃ have been synthesised as their hexagonal polymorphs. YFeO₃ and YbFeO₃ have been studied in depth by neutron powder diffraction, A.C. impedance spectroscopy, Mössbauer spectroscopy and magnetometry. It was found that YFeO₃ and YbFeO₃ are structurally similar to hexagonal YMnO₃ but there is evidence for a subtle phase separation in each case. Low temperature magnetic properties are also reported, and subtle correlations between the structural, electrical and magnetic properties of these materials have been found. InFeO₃ was found to adopt a higher symmetry and is structurally similar to the high temperature phase of YMnO₃. TbInO₃ and DyInO₃ have also been synthesised and studied at various temperatures. The phase behaviour of TbInO₃ was analysed in detail using neutron powder diffraction and internal structural changes versus temperature were mapped out – there is also evidence for a subtle isosymmetric phase transition. Neither DyInO₃ nor TbInO₃ show long-range magnetic order between 2 and 300 K, or any signs of ferroelectricity at room temperature. The new compounds Cs₂TiCu₃F₁₂ and Rb₂TiCu₃F₁₂ have both been synthesised and shown to be novel kagome lattice based materials. The former shows a transition from rhombohedral to monoclinic symmetry in the powder form and from rhombohedral to a larger rhombohedral unit cell in the single crystal – a particle size based transition pathway is suggested. For Rb₂TiCu₃F₁₂ a complex triclinic unit cell is found, which distorts with lowering temperature. Both materials show magnetic transitions with lowering temperature. The solid solution Cs₂₋ₓRbₓSnCu₃F₁₂ (x = 0, 0.5, 1.0, 1.5, 2.0) was synthesised and investigated crystallographically, demonstrating a range of behaviours. Rb₂SnCu₃F₁₂ displays a rare re-entrant structural phase transition. In contrast, Cs₀.₅Rb₁.₅SnCu₃F₁₂ shows only the first transition found in the Rb⁺ end member. CsRbSnCu₃F₁₂ adopts a lower symmetry at both room temperature and below. Cs₁.₅Rb₀.₅SnCu₃F₁₂ and Cs₂SnCu₃F₁₂ show a rhombohedral - monoclinic transition, which is similar to that found in Cs₂TiCu₃F₁₂.

Shape memory alloys (SMAs) are a new generation material which exhibits unique nonlinear deformations due to a phase transformation which allows it to return to its original shape after removal of stress or a change in temperature. It shows a shape memory effect (martensitic condition) and pseudoelasticity (austenitic condition) properties depends on various heat treatment conditions. The reason for these properties depends on phase transformation through temperature changes or applied stress. Many technological applications of austenite SMAs involve cyclical mechanical loading and unloading in order to take advantage of pseudoelasticity, but are limited due to poor fatigue life. In this thesis, I investigated two important mechanical feature to fatigue behavior in pseudoelastic NiTi SMA wires using high energy synchrotron radiation X-ray diffraction (SR-XRD). The first of these involved simple bending and the second of these involved relaxation during compression loading. Differential scanning calorimetry (DSC) was performed to identify the phase transformation temperatures. Scanning electron microscopy (SEM) images were collected for the initial condition of the NiTi SMA wires and during simple bending, SEM revealed that micro-cracks in compression regions of the wire propagate with increasing bend angle, while tensile regions tend to not exhibit crack propagation. SR-XRD patterns were analyzed to study the phase transformation and investigate micromechanical properties. By observing the various diffraction peaks such as the austenite (200) and the martensite (100), (110), and (101) planes, intensities and residual strain values exhibit strong anisotropy depending upon whether the sample is in compression or tension during simple bending. This research provides insight into two specific mechanical features in pseudoelastic NiTi SMA wires.

La distribution in vivo des médicaments est étudiée par des techniques quantitatives faiblement ou non résolues spatialement. Avec l'apparition des thérapies personnalisées, des études plus approfondies sont nécessaires pour connaître précisément le comportement des molécules vectorisées sous la forme de nanoparticules (NPs). Dans le cadre du programme européen Ternanomed, ce projet de recherche a pour objectif d’évaluer la capacité de deux techniques d’imagerie appliquées à l’étude de la distribution de nanomédicaments à base de squalène et de Cis platine (Cis-Pt). Ces deux techniques ont été sélectionnées pour leur apport d’informations complémentaires à l’échelle des organes et des tissus : i) l’imagerie par résonnance magnétique (IRM) pour suivre in vivo la biodistribution de NPs modèles à base de Cis-Pt et BiSqualène (BiSQ), marquées par des agents de contraste type oxyde de fer (USPIO), ii) l’imagerie de microfluorescence X, couplée au rayonnement synchrotron (SR-μXRF), qui ne nécessite pas de marquage préalable des nanomédicaments, pour le suivi tissulaire du Cis-Pt.Concernant l’approche par IRM, nous avons encapsulé avec succès nos USPIO synthétisées au sein des NPs de Cis-Pt BiSQ (210nm, polydispersité 0,1), tout en leur conférant un pouvoir contrastant à 7 tesla (r2=404 ms.mol-1 et r1=3 ms.mol-1). Ces NPs nouvellement préparées sont également traçables chez notre modèle murin Nudes. Les résultats de biodistribution montrent une arrivée rapide du contraste dans les organes épurateurs : le foie et la rate (5 minutes après l’injection). Au final, l’analyse par IRM a permis d’obtenir les données de biodistribution en temps réel des NPs à base de Cis Pt BiSQ, grâce au suivi du contraste apporté par les USPIO encapsulés. Concernant l’imagerie par SR-μXRF, nous avons démontré que cette technique est suffisamment sensible pour détecter et cartographier le Cis-Pt, vectorisé par nos NPs modèles. La distribution du Cis Pt a été quantifiée localement à partir d’une référence interne de concentration connue, le Zinc, à partir de notre méthode validée par le dosage globale du Platine par spectrométrie d’absorption atomique. Lorsque notre référence tissulaire n’est pas distribuée de façon homogène, une méthode semi-quantitative a été mise au point pour comparer la distribution à 2h, 8h et 24h, tel qu’au niveau des coupes de tumeurs PANC-1.Au final, ces travaux ont permis de démontrer, que la SR-μXRF et l’IRM sont des approches de choix pour l’étude pharmacocinétique et pharmacodynamique de nanomédicaments tels que les NPs à base de Cis-Pt. La technique de microfluorescence X contribue au caractère original et pionnier de ce travail de recherche, apportant des nouveaux résultats de détection et quantification important dans le domaine des nanomédecines. / Nowadays, the in vivo distribution of drugs is studied by non-spatial or partially spatial quantitative techniques. With the development of personalized therapies, many studies are required to know the in vivo behaviour of these innovative treatments, which target drugs, such as nanoparticles (NPs). Into the European funded program Ternanomed, the aim of this multidisciplinary research project was to evaluate two complementary imaging methods to study the distribution of squalene and Cis platinum (Cis Pt) NPs. The 2 imaging methods were selected to provide complementary data at the scale of organs and tissues: i) Magnetic resonance imaging (MRI) to monitor the in vivo biodistribution of NPs models based on Cis-Pt and BiSqualene (BiSQ), labelled with "UltraSmall Iron Oxide Particle" (USPIO) contrast agents, ii) X-ray microfluorescence imaging, coupled with synchrotron radiation (SR-μXRF) without any labelling of these nanomedicines, by following the Cis-Pt drug distribution into tissues.Regarding the MRI approach, we first successfully prepared Cis-Pt BiSQ NPs loading with USPIO (210nm, polydispersity 0,1). These NPs were given a contrast at 7 Tesla (r2 = 404 ms.mol-1 and r1 = 3 ms.mol-1). These newly prepared and characterized NPs were also trackable into our Nude murine model. The results show a rapid arrival of contrast in the liver and spleen scavengers (5 minutes after injection). Ultimately, MRI analysis yielded real-time biodistribution data for Cis-Pt BiSQ-based NPs by monitoring the contrast provided by encapsulated USPIO. Regarding the SR-μXRF imaging analysis, we demonstrated that this technique is very sensitive to detect and map the Cis-Pt distribution, the drug vectorized by our squalene NPs models. Additionally, a local quantitative analysis is feasible when a microelement present in the tissue is used as a reference, in our study the Zinc element. The distribution of Cis-Pt was quantified in the hepatic, renal and fat tissues, after 2h and 24h, with our method validated by the global Platinum microanalyse using atomic absorption spectrometry. When the tissue reference appears not homogenously distributed, a semi-quantitative analysis method is possible to compare the distribution such as into PANC-1 tumour sections.Finally, these two complementary approaches illustrate the use of SR-μXRF and lay the optimized bases of MRI to study the pharmacokinetics and pharmacodynamics of two new types of Cis-Pt/squalene NPs. The SR-μXRF technique, newly used in pharmaceutical field, had an effective contribution to these original and pioneering research studies with an original way of in vivo assessment of the distribution of drug embedded into nanomedicine system. The issue of detecting correct and measurable distribution of the drugs is extremely important, timely and relevant to improve current knowledge in the state of the art. This research study brings new data which can produce significant impact to the overall area of nanomedicine.

No description available.

The durability of Thermal Barrier Coatings (TBCs) used on the turbine blades of aircraft and power generation engines has been known to be affected by sand particle ingression comprised of Calcium-Magnesium-Alumina-Silicate (CMAS). Previous studies have shown that these effects present themselves through variations in the thermomechanical and thermochemical properties of the coating. This study investigated the impact of CMAS ingression on the Yttria Stabilized Zirconia Topcoat (YSZ) and Thermally Grown Oxide (TGO) strain in sprayed Thermal Barrier Coating (TBC) samples of varying porosity with and without CMAS ingression. In-Situ Synchrotron X-ray Diffraction measurements were taken on the sample under thermal loading conditions from which the YSZ and TGO peaks were identified and biaxial strain calculations were determined at high temperature. Quantitative strain results are presented for the YSZ and TGO during a thermal cycle. In-plane strain results for YSZ near the TGO interface for a complete thermal cycle are presented, for a 6% porous superdense sample with CMAS infiltration. The outcomes from this study can be used to understand the role of CMAS on the strain tolerance of the TBC coating. It is well known that under engine operational conditions the development of the TGO layer, with large critical stresses, has been linked to failure of the coating. The growth of the TGO manifests as undulations in a series of peaks and troughs. Understanding the mechanics of the oxide layer at these locations provides significant information with respect to the failure mechanisms of the TBC coating. This study investigated the stress at the peak and trough of a TGO undulation for a cycled Dense Vertically Cracked (DVC) plasma sprayed TBC sample through photo-luminescence (PL) spectroscopy. High resolution nanoscale stress maps were taken nondestructively in the undulation of the TGO. Preliminary results from first line mapping of TGO peak and trough scan, at a resolution of 200 nm, have shown a non-uniform TGO stress variation. The results obtained from this study can be used to understand the stress variation in the peak and trough of a DVC sample's TGO undulation and how it contributes to the life of the TBC coating.

Demands for designing prime reliant, energy-efficient, and high performance thermal barrier coatings (TBCs) in gas turbines have led to a growing interest toward comprehensive microstructural characterization. Over the last decade, Synchrotron X-ray Diffraction (XRD) has established itself as a high-resolution strain measurement method for the thermally grown oxide (TGO) layer of thermal barrier coatings (TBCs). In this work, we present in-situ X-ray strain measurements of the TGO layer on cycled TBC specimens under thermo-mechanical loading using powerful high energy X-rays (~80.7- 86 keV) at Sector I-ID of the Advanced Photon Source at the Argonne National Laboratory. The evolution of TGO stresses was examined over one complete thermal cycle on TBC samples at various stages of the life fraction under various mechanical loads. Synchrotron X-Ray Diffraction under thermo-mechanical loading has shown the existence of strain qualitatively within the diffraction patterns. Quantitative results obtained through Pseudo-Voigt peak fitting over selected peaks show the evolution of strain over a thermal cycle. In initial experiments, it was shown that mechanical loading at 32 MPa resulted in a tensile strain (£22 = 0.00053±0.00039 for 7 minutes) along the [024] atomic plane of a-AbO3 that was brief before going into strain relief in the compressive region but higher in magnitude than the 64 MPa (£22 = 0.00039±0.00024 for 14 minutes). Follow-on experiments indicate the presence of tensile strains within the bond coat region of the TBC system. After initial assessment of the effect of mechanical loading, our findings indicate that the effect of mechanical load during the cycle, often neglected in TBC studies, is of significance to the strain evolution within each cycle. This determination of critical conditions for strain evolution ( e.g. the first cycle) will serve to improve overall accuracy in life prediction of these coatings and contribute to developing methods of improving fatigue behavior.

Nous avons étudié in situ et en temps réel la structure de grains du silicium multi-cristallin issue de la solidification dirigée en utilisant l’imagerie X synchrotron. La radiographie X permet de suivre l’évolution de l’interface solide/liquide et de caractériser sa dynamique et sa morphologie. La topographie X nous donne des informations sur la structure de grains formée, les contraintes et les défauts issus de la solidification. Nous avons montré l’importance la préparation de l’état initial de la solidification en particulier pour les expériences de reprise sur germe. L’analyse de la morphologie de l’interface solide/liquide nous a permis de caractériser la surfusion cinétique du front de solidification, de comprendre l’évolution des sillons de joints de grains et d’analyser les mécanismes de compétition de grains ainsi que de révéler l’impact des impuretés sur la structure de grains formée à l’issue de la solidification. Le phénomène de maclage a aussi été observé dans nos expériences et nous avons démontré que les macles dans le silicium multi-cristallin peuvent être des macles de croissance. Deux types de macles ont été identifiés et le phénomène de compétition de grains en présence de macles étudié. / We studied in situ and real-time the grain structure of multi-crystalline silicon from directional solidification using synchrotron X-ray imaging techniques. X-ray Radiography gives information on the evolution, dynamics and morphology of the solid/liquid interface. X- ray Topography gives more information on the grain structure, strains and defects that occur during solidification step. We showed the importance of the preparation of the initial stage of solidification in particular in the experiments where solidification is initiated from seed. The analysis of the solid/liquid interface morphology allowed us to characterize the kinetic undercooling of the solidification front, to understand the evolution of the grains boundary grooves and to analyze the mechanisms of grain competition and also to reveal the impurities impact on the grain structure formed at the end of the solidification. We also observed twinning phenomenon in our experiments and we demonstrated that twins in multi-crystalline silicon can be growth twins. Two kinds of silicon twins have been identified and the grain competition phenomenon with twins studied.