Doctor of Philosophy(PhD) / This project focuses on the examination of the structures of lanthanide containing double perovskites of the type Ba2LnB'O6-d (Ln = lanthanide or Y3+ and B' = Nb5+, Ta5+, Sb5+ and/or Sn4+) using synchrotron X-ray and neutron powder diffraction. The first part of this project examined the relative stability of R3 rhombohedral and I4/m tetragonal structures as the intermediate phase adopted by the series Ba2LnB'O6 (Ln = lanthanide (III) or Y3+ and B' = Nb5+, Ta5+ or Sb5+). It was found that I4/m tetragonal symmetry was favoured when B' was a transition metal with a small number of d electrons, such as Nb5+ or Ta5+. This is due to the presence of p-bonding in these compounds. In the Ba2LnNbO6 and Ba2LnTaO6 series R3 rhombohedral symmetry was, however, favoured over I4/m tetragonal symmetry when Ln = La3+ or Pr3+ due to the larger ionic radius of these cations. The incompatibility of the d0 and d10 B'-site cations in this family of compounds was indicated by significant regions of phase segregation in the two series Ba2Eu1-xPrxNb1-xSbxO6 and Ba2NdNb1-xSbxO6. In the second part of this project the compounds in the series Ba2LnSnxB'1-xO6-d (Ln = Pr, Nd or Tb and B' = Nb5+ or Sb5+) were examined to understand the relative stability of oxygen vacancies in these materials compared to the oxidation of the lanthanide cations and to determine if any oxygen vacancy ordering occurred. It was found, using a combination of structural characterisation, X ray Absorption Near Edge Structure and Ultra-Violet, Visible and Near Infrared spectroscopies, that with Ln = Pr or Tb increased Sn4+ doping results in a change in the oxidation state of the Ln3+ cations to Ln4+. This leads to those series containing little or no oxygen vacancies. A loss of B site cation ordering was found to accompany this oxidation state change and phase segregation was found to occur in the Ba2PrSnxSb1-xO6-d series most likely due to the Pr3+ and Pr4+ cations segregating into different phases. The Nd3+ cations in the series Ba2NdSnxSb1-xO6-d, however, can not oxidise to the tetravalent state so the number of oxygen vacancies rises with increasing x. It was found that oxygen vacancies concentrate onto the axial site of the compounds with x = 0.6 and 0.8 at ambient temperature. In Ba2Sn0.6Sb0.4O5.7 the oxygen vacancies were found to change to concentrating on the equatorial site at higher temperatures and it is suggested that this oxygen vacancy ordering plays a role in the adoption of I2/m monoclinic symmetry.

Les éléments de diffraction sont largement utilises aujourd'hui dans un nombre grandissant d'applications grâce à la progression des technologies de micro-structuration dans le sillage de la microélectronique. Pour un design optimal de ces éléments, des méthodes de modélisation précises sont nécessaires. Plusieurs méthodes ont été développées et sont utilisées avec succès pour des réseaux de diffraction unidimensionnel de différents types. Cependant, les méthodes existantes pour les réseaux deux dimensionnel ne couvrent pas tous types de structures possibles. En particulier, le calcul de l'efficacité de diffraction sur les réseaux métalliques à deux dimensionnel avec parois verticales représente encore une grosse difficulté pour les méthodes existantes. Le présent travail a l'objectif le développement d'une méthode exacte de calcul de l'efficacité de diffraction de tels réseaux qui puisse servir de référence. La méthode modale développée ici - dénommée -true-mode" en anglais - exprime le champ électromagnétique sur la base des vrais modes électromagnétiques satisfaisant les conditions limites de la structure 2D à la différence d'une méthode modale où les modes sont ceux d'une structure approchée obtenue, par exemple, par développement de Fourier. L'identification et la représentation de ces vrais modes 'a deux dimensions restait 'a faire et ce n'est pas le moindre des résultats du présent travail que d'y avoir conduit. Les expressions pour la construction du champ sont données avec des exemples de résultats concrets. Sont aussi fournies les équations pour le calcul des intégrales de recouvrement et des éléments de la matrice de diffusion.

La diffraction des rayons X a été développée depuis près d'un siècle pour la détermination de structures cristallographiques. Mais la détermination des structures les plus complexes (protéines, structures incommensurables...) nécessite l'utilisation de la diffraction anomale, i.e. la mesure des intensités de diffraction à plusieurs longueurs d'onde au voisinage du seuil d'absorption d'un élément du cristal. Cette technique permet d'obtenir une information sur la phase du facteur de structure, ainsi que sur les positions des atomes anomaux. Dans cette thèse, nous présentons la Diffraction Anomale Dispersive (DAD), qui permet de mesurer simultanément les intensités diffractées à plusieurs longueurs d'onde, pour de nombreuses réflexions. Nous présentons deux modes de collecte, continu (DDAFS-Dispersive Diffraction Anomalous fine Structure), et discret (SMAD-Simultaneous Multiwavelength Anomalous Diffraction). Nous avons développé une procédure et un programme (DAD) pour l'analyse quantitative des images de diffraction dispersive. Ce programme permet également l'analyse d'images de diffraction monochromatique présentant des réflexions satellites proches des pics principaux. Nous présentons les deux premières expériences quantitatives de diffraction dispersive sur des cristaux biologiques. Nos résultats montrent que la détermination de structure par la méthode SMAD est possible. Des améliorations aux protocoles de collecte et d'analyse sont encore nécessaires pour ces cristaux. Une partie importante de cette thèse a été consacrée à l'étude de (TaSe4)2I : ce cristal quasi-1D présente une transition de Peierls, la condensation des atomes de tantale étant recherchée depuis 15 ans. Notre étude a d'abord caractérisé la structure en domaines de ce matériau, et la diffraction anomale a mis en évidence de manière spécifique la tétramérisation des atomes de tantale, accompagnant la modulation acoustique déjà connue.

La détermination de la structure cristalline d'un échantillon nécessite la prise en compte de son caractère anisotrope et du même coup l'analyse quantitative de texture devient de plus en plus importante. Ce type d'analyse a recours à la mesure de figures de pôles par diffraction de RX ou de neutrons, et à l'affinement des ODF. Couplée à d'autres types d'analyses (microstructure, contraintes résiduelles ...) utilisant les mêmes diagrammes de diffraction, l'analyse du profil global incluant l'analyse texturale a pris le nom d'analyse combinée.<br />Ce travail détaille les mesures d'analyse combinée, pour des expériences de diffraction X et de neutrons. Nous appliquons l'analyse combinée par diffraction X à la détermination des vitesses de propagation d'ondes élastiques générées par excitation photoacoustique picoseconde, dans des films d'or texturés. L'évolution technologique a permis le développement de détecteurs 2D, réduisant considérablement les temps de mesures neutroniques. Nous développons l'analyse combinée et la calibration associée sur le détecteur CAPS de l'instrument D19, qui réduit les temps d'acquisition et permet de développer l'analyse quantitative de texture magnétique, pour mettre en évidence la réorientation des moments magnétiques sous champ modéré (~0,3 T).<br />Ce mémoire est finalement consacré à l'étude de l'analyse MQTA, qui caractérise les matériaux magnétiques en termes de distribution macroscopique de l'orientation des moments, et étudie comment le signal magnétique résultant est lié aux cristallites et aux microstructures de l'échantillon. Nous détaillons ici l'aspect théorique de l'analyse MQTA, et illustrons son application sur un échantillon de fer « doux ».

This thesis is concerned with in-situ 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 MIV(HPO4)2·nH2O (MIV = Ti, Zr); 2) Pyrophosphates and pyrovanadates with composition MIVX2O7 (MIV = Ti, Zr and X = P, V); 3) Molybdates with composition ZrMo2O8. The results are compiled in seven published papers and two manuscripts. 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-ZrP2O7 two 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. In-situ high-pressure studies of τ-Zr(HPO4)2 revealed two new phases, tetragonal ν-Zr(HPO4)2 and 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. The high-pressure properties of the pyrophosphates ZrP2O7 and TiP2O7, and the pyrovanadate ZrV2O7 were 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. In-situ high-pressure studies of trigonal α-ZrMo2O8 revealed the existence of two new phases, monoclinic δ-ZrMo2O8 and triclinic ε-ZrMo2O8 that crystallises at 1.1 and 2.5 GPa, respectively. The structure of δ-ZrMo2O8 was solved by direct methods and refined using the Rietveld method.

X-ray lasers are creating unprecedented research opportunities in physics,chemistry and biology. The peak brightness of these lasers exceeds presentsynchrotrons by 1010, the coherence degeneracy parameters exceedsynchrotrons by 109, and the time resolution is 105 times better. In theduration of a single flash, the beam focused to a micron-sized spot has the samepower density as all the sunlight hitting the Earth, focused to a millimetresquare. Ultrafast coherent X-ray diffractive imaging (CXDI) with X-ray lasers exploitsthese unique properties of X-ray lasers to obtain high-resolution structures fornon-crystalline biological (and other) objects. In such an experiment, thesample is quickly vaporised, but not before sufficient scattered light can berecorded. The continuous diffraction pattern can then be phased and thestructure of a more or less undamaged sample recovered% (speed of light vs. speed of a shock wave).This thesis presents results from the first ultrafast X-ray diffractive imagingexperiments with linear accelerator-driven free-electron lasers and fromoptically-driven table-top X-ray lasers. It also explores the possibility ofinvestigating phase transitions in crystals by X-ray lasers. An important problem with ultrafast CXDI of small samples such as single proteinmolecules is that the signal from a single measurement will be small, requiringsignal enhancement by averaging over multiple equivalent samples. We present anumerical investigation of the problems, including the case where samplemolecules are not exactly identical, and propose tentative solutions. A new software package (Hawk) has been developed for data processing and imagereconstruction. Hawk is the first publicly available software package in thisarea, and it is released as an open source software with the aspiration offostering the development of this field.

The primary objective of the presented research is to develop a class of integrated compact silicon diffractive sensors (CSDS) based on in-plane diffraction gratings. This class of sensors uses a silicon-on-insulator (SOI) substrate to limit costs, exploit established fabrication processes, enable integration of supporting electronics, and use the well-understood telecommunications wavelength of 1.55µm. Sensing is achieved by combining constant-diffraction-efficiency and highly-angularly-selective in-plane resonance-domain diffraction gratings. Detection is based on the diffraction efficiency of the highly angularly selective grating. In this research, the design processes for the constant-diffraction-efficiency and the highly angularly selective gratings are detailed. Grating designs are optimized with rigorous coupled-wave analysis (RCWA) and simulated with finite-difference time-domain (FDTD) analysis. Fabrication results are presented for the CSDS gratings. An inductively coupled plasma (ICP) Bosch etch process enables grating fabrication to within one percent of designed values with nearly vertical sidewalls. Experimental results are presented for individual CSDS gratings, the prototype sensor, and a prototype linear sensor array. The results agree well with simulation. The linear sensor array prototype demonstrates the intrinsic splitting mechanism and forms the basis of a 2-D sensor array. Finally, a toluene sensor was functionally demonstrated. The proof-of-concept device includes a polymer immobilization layer and microfluidic delivery of toluene. Toluene concentrations as low as 100ppm are measured, corresponding to a refractive index change of 3x10⁻⁴ RIU.

This thesis describes the creation of a metrology system based upon an actively controlled diffraction grating interferometer, which measures relative linear distances. The dynamics of this sensor are estimated based on experimental testing, and a suitable controller is designed to maintain the position of the sensor in the most sensitive operating region. This controller is implemented on a field programmable gate array (FPGA) processor, which allows for flexible programming and real-time control. The sample under test is mounted atop a three axis linear stage system, which allows the diffraction grating interferometer to scan across the surface of the device, creating maps of the static and dynamic measurements. The controller is shown to maintain the sensitivity of the sensor during this operation. This insures all data are taken on the same scale, creating more accurate results. The controller increases the signal to noise ratio as compared to the system without the controller. The specifications of the entire metrology system are detailed including the sensor and controller bandwidth, the vertical and horizontal resolution, and the signal to noise ratio. A case study utilizing a capacitive micromachined ultrasonic transducer (cMUT) is presented. The sensor generates static and dynamic displacement maps of the surface of this MEMS device. The controller improves these measurements by maintaining a position of high sensitivity during operation. Finally, the preliminary results of a miniaturized version of this system are presented including the implementation of two fully independent parallel sensors. This allows for array implementation of these sensors, which is crucial for the batch fabrication photolithography techniques used to create many MEMS devices. Recommendations on the future work needed to complete the array implementation are given in conjunction with methods for increasing the resolution and robustness of the macroscale system described in this thesis.

Nitrochemicals are widely used as explosives, biocides and drugs. In addition, 3-nitro-tyrosine and other nitrated protein residues are important markers for many cardiovascular, neurodegenerative, and malignant conditions. Because of the wide presence of the nitrocompounds as toxins, potential nitrogen/carbon sources, and metabolic intermediates, different organisms have evolved to produce enzymes that can biodegrade nitrocompounds. The structural studies of the enzymes, which catalyze the removal of nitro group from nitrochemicals, are of considerable interest for both applied and fundamental reasons. The insights into the reaction mechanism of these enzymes can be used for designing efficient biocatalysts for bioremediation and for developing antibiotics for disease resistant microbes. Nitroalkane oxidase (NAO) produced by

Predicting performance metrics for the next-generation of multi-mode and multi-antenna wireless communication systems demands site-specific knowledge of the wireless channel's underlying radio wave propagation mechanisms. This thesis describes the first measurement system capable of characterizing individual propagation mechanisms in situ. The measurement system merges a high-resolution spatio-temporal wireless channel sounder with a new field reconstruction technique to provide complete knowledge of the wireless channel's impulse response throughout a 2-dimensional region. This wealth of data may be combined with space-time filtering techniques to isolate and characterize individual propagation mechanisms. The utility of the spatio-temporal measurement system is demonstrated through a measurement-based investigation of diffraction around building corners. These measurements are combined with space-time filtering techniques and a new linear wedge diffraction model to extract the first semi-mpirical diffraction coefficient. Specific contributions of this thesis are: * The first ultra-wideband single-input multiple-output (SIMO) channel sounder based upon the sliding correlator architecture. * A quasi 2-dimensional field reconstruction technique based upon a conjoint cylindrical wave expansion of coherent perimeter measurements. * A wireless channel ``filming' technique that records the time-domain evolution of the wireless channel throughout a 2-dimensional region. * High-resolution measurements of the space-time wireless channel near a right-angled brick building corner. * The application of space-time filtering techniques to isolate the edge diffraction problem from the overall wireless channel. * An approximate uniform geometrical theory of diffraction (UTD)-style linear model describing diffraction by an impedance wedge. * The first-ever semi-empirical diffraction coefficient extracted from in situ measurement data. This thesis paves the way for several new avenues of research. The comprehensive measurement data provided by channel "filming" will enable researchers to develop and implement powerful space-time filtering techniques that facilitate measurement-based investigations of radio wave propagation. The measurement procedure described in this thesis may be adapted to extract realistic reflection and rough-surface scattering coefficients. Finally, exhaustive measurements of individual propagation mechanisms will enable the first semi-empirical propagation model that integrates empirical descriptions of propagation mechanisms into a UTD-style mechanistic framework.