Les phases alpha'-Fe8N1-x et alpha''-Fe16N2 ont un fort potentiel d’application, en raison de leur anisotropie magnétocristalline uniaxiale et de leur grande aimantation à saturation. Cependant, les valeurs annoncées pour ces propriétés magnétiques restent sujettes à discussion. Les recherches menées au cours de cette thèse de doctorat ont été initiées dans le but de clarifier cette situation. L’élaboration des échantillons a principalement consisté en l’implantation ionique d’azote dans des couches minces de fer alpha épitaxiées sur ZnSe/GaAs (001). Entre autres, les effets de la température de la cible et de la fluence sur la structure cristalline des échantillons ont été analysés par diffractométrie des rayons X. La présence d’une anisotropie magnétique perpendiculaire a été mise en évidence dans les couches minces contenant les phases alpha'-Fe8N1-x ou alpha''-Fe16N2. La constante d’anisotropie a été évaluée par magnétométrie à échantillon vibrant et résonance ferromagnétique. À l’occasion de ces recherches, des domaines en rubans faibles ont été observés par microscopie à force magnétique dans certaines couches minces en Fe-N. Ceux-ci sont particulièrement rectilignes et des dislocations coin se trouvent au sein de leur structure périodique. Des études ont alors été réalisées dans le but de contrôler avec précision la réorientation des domaines en rubans et le déplacement des dislocations magnétiques, à l’aide d’un champ magnétique. / The alpha'-Fe8N1-x and alpha''-Fe16N2 phases have a high potential of application, because of their uniaxial magnetocrystalline anisotropy and their large saturation magnetization. However, the values announced for these magnetic properties remain a subject of discussion. The research conducted during this PhD thesis was initiated in order to clarify this situation. Sample making consisted mainly of nitrogen ion implantation into alpha-Fe thin films, epitaxially grown on ZnSe/GaAs (001). Among others, the effects of target temperature and fluence on the crystal structure of the samples were analyzed by X-ray diffractometry. The presence of a perpendicular magnetic anisotropy was demonstrated in the thin films containing the alpha'-Fe8N1-x and alpha''-Fe16N2 phases. The anisotropy constant was evaluated by vibrating sample magnetometry and ferromagnetic resonance. In this research, weak stripe domains were observed by magnetic force microscopy in some Fe-N thin films. These are particularly straight and edge dislocations are found within their periodic structure. Studies were then carried out to precisely control the reorientation of the stripe domains and the displacement of the magnetic dislocations, using a magnetic field.

No description available.

Disease resistance is critical in soft red winter wheat (Triticum aestivum L.) cultivars. Leaf rust caused by Puccinia triticina Eriks and stripe rust caused by Puccinia striiformis Westend. f.sp. tritici Eriks. are destructive pathogens of wheat. From 2014 to 2015 phenotypic data was collected at diverse locations for resistance to leaf rust (North Carolina, Texas, and Virginia) and stripe rust (Arkansas, North Carolina, Georgia, Texas, and Virginia) in a Pioneer ‘25R47’ /‘Jamestown’ (P47/JT) population composed of 186 F5:9 recombinant inbred lines (RILs). Analysis of the P47/JT population identified two quantitative trait loci (QTL) for leaf rust resistance on chromosome 5B and two QTL for stripe rust resistance on chromosomes 3B and 6A. Phenotypic variation (%) explained by the putative leaf rust resistance QTL of Jamestown on 5B was as high as 22.1%. Variation explained by the putative stripe rust resistance QTL of Jamestown on 3B and 6A was as high as 11.1 and 14.3%, respectively. Jamestown is postulated to contain gene Lr18. Seedlings of 186 F5:9 recombinant inbred lines from the P47/JT population and 200 F2 seedlings from eight other crosses including Jamestown and/or the Lr18 host differential line RL6009 (Thatcher*6/Africa 43) were screened with P. triticina race TNRJJ. Genetic analysis of the populations was conducted to validate the presence of Lr18 in Jamestown. Results of linkage analysis identified SNP maker IWB41960 linked within 5 cM of gene Lr18 in all three populations. From 2016 to 2017 phenotypic data was collected at diverse locations for resistance to leaf rust (Illinois, North Carolina, and Virginia) in a ‘2013412’ (PI 667644) / VA10W-21 (PI 676295) population (412/21) composed of 157 doubled haploid (DH) lines. The 412/21 DH lines were genotyped via genotyping by sequence (GBS). Analysis of the 412/21 population identified one quantitative trait loci (QTL) region associated with adult plant resistance to leaf rust on chromosome 1B. Phenotypic variation (%) explained by the putative leaf rust resistance QTL of 2013412 on 1B was as high as 40.1%. Kompetitive allele-specific (KASP) markers KASP_S1B_8414614 and KASP_S1B_8566239 were developed as markers for use in marker assisted selection. / Ph. D. / Disease resistance to leaf rust and stripe rust is important when growing soft red winter wheat. Genetic resistance can have a benefit to cost ratio of up to 27:1, considerably better than that of fungicide treatments. From 2013 to 2017 disease data was collected across multiple locations spanning the eastern United States (Arkansas, Georgia, Illinois, North Carolina, Texas, and Virginia). DNA molecular markers were used to identify specific chromosome regions containing genes associated with leaf and stripe rust resistance. DNA markers associated with genes conferring resistance to leaf rust resistance were identified in three chromosome regions, and genes in two regions were associated with stripe rust resistance. These genes and molecular markers associated with them can be used by scientists to further enhance resistance in wheat cultivars. Another study was conducted to determine if Lr18, a gene for leaf rust resistance that has a large effect, is present in the Virginia Tech soft red winter wheat breeding material. This gene (Lr18) is known to have been introduced from an ancestral species highly related to wheat. Wheat seedlings derived from crosses between lines postulated to carry Lr18 with susceptible lines were tested for resistance to a specific strain of leaf rust lacking virulence to Lr18. Genetic analysis of the ratio of resistant versus susceptible seedlings and association between DNA molecular markers and resistant seedlings were conducted to validate the presence of gene Lr18. A molecular marker linked tightly to gene Lr18 was identified in the study. This gene was found to be widely distributed in soft red winter wheat breeding materials and the molecular marker associated with gene Lr18 will be useful for scientists to further improve resistance in wheat cultivars.

Leaf rust and stripe rust of wheat (Triticum aestivum L.) are caused by the fungal pathogens Puccinia triticina, and Puccinia striiformis f.sp. tritici, respectively. In North America, the incorporation of adult-plant resistance (APR) genes into breeding lines has been an important strategy to achieve durable resistance to both diseases. Previously, the spring wheat cultivar AC Domain was reported to express an effective level of adult-plant resistance (APR) to leaf rust under field conditions. Early gene postulation work had suggested AC Domain might carry the APR gene Lr34 due to its phenotypic similarity to other Lr34 carrying lines. However, new gene specific markers have shown that AC Domain is not a carrier of Lr34. The objective of this research was to genetically localize the resistance in AC Domain, which is important because the cultivar has frequently been used as a parent in Canadian breeding programs, primarily for its value as a source of pre-harvest sprouting resistance. A mapping population of 185 doubled haploid (DH) lines derived from the cross ‘RL4452’ by ‘AC Domain’ was used for this study. RL4452 is a known carrier of Lr34. During 2011-2012, the DH population was evaluated in field leaf rust nurseries at Saskatoon, SK and Portage, MB and at a stripe rust nursery at Lethbridge, AB. Field results indicated that rust resistance in the mapping population was variable, with lines ranging from highly resistant, to highly susceptible. DH lines carrying Lr34 showed a high level of resistance to both diseases. Thus, the non-Lr34 carriers were genotyped using select SSR markers, and by an Illumina 9k Infinium iSelect SNP assay for subsequent quantitative trait loci (QTL) analysis. QTL analysis revealed that AC Domain donated a major resistance QTL located on chromosome 2BS, that mapped 46 cM proximal to markers linked to Lr16, and explained a significant portion of the leaf and stripe rust phenotypic variance in all test environments. In addition, this QTL was significantly associated with the expression leaf tip necrosis (LTN), reduction in area under the disease progress curve (AUDPC), and coefficient of infection (CI). In certain environments the interaction between the 2B QTL and Lr34 was additive resulting in a superior level of rust resistance. Indoor rust testing showed AC Domain was susceptible to both diseases at the seedling stage. Taken together these results suggest that the identified resistance in AC Domain is likely due to the presence of an APR gene, on chromosome 2BS.

Le travail présenté dans cette thèse porte sur l'inspection de surfaces métalliques industrielles. Nous proposons de généraliser des méthodes de l'imagerie hyperspectrale à des données multimodales comme des images optiques multi-canales, et des images thermographiques multi-temporelles. Dans la première application, les cubes de données sont construits à partir d'images multi-composantes pour détecter des défauts de surface. Les meilleures performances sont obtenues avec les éclairages multi-longueurs d'ondes dans le visible et le proche IR, et la détection du défaut en utilisant l'angle spectral, avec le spectre moyen comme référence. La deuxième application concerne l'utilisation de l'imagerie thermique pour l'inspection de pièces métalliques nucléaires afin de détecter des défauts de surface et sub-surface. Une approche 1D est proposée, basée sur l'utilisation du kurtosis pour sélectionner la composante principale parmi les premières obtenues après réduction des données avec l’ACP. La méthode proposée donne de bonnes performances avec des données non-bruitées et homogènes, cependant la SVD avec les algorithmes de détection d'anomalies est très robuste aux perturbations. Finalement, une approche, basée sur les techniques d'analyse de franges et la lumière structurée est présentée, dans le but d'inspecter des surfaces métalliques à forme libre. Après avoir déterminé les paramètres décrivant les modèles de franges sinusoïdaux, l'approche proposée consiste à projeter une liste de motifs déphasés et à calculer l'image de phase des motifs enregistrés. La localisation des défauts est basée sur la détection et l'analyse des franges dans les images de phase. / The work presented in this thesis deals with the quality control and inspection of industrial metallic surfaces. The purpose is the generalization and application of hyperspectral imagery methods for multimodal data such as multi-channel optical images and multi-temporal thermographic images. In the first application, data cubes are built from multi-component images to detect surface defects within flat metallic parts. The best performances are obtained with multi-wavelength illuminations in the visible and near infrared ranges, and detection using spectral angle mapper with mean spectrum as a reference. The second application turns on the use of thermography imaging for the inspection of nuclear metal components to detect surface and subsurface defects. A 1D approach is proposed based on using the kurtosis to select 1 principal component (PC) from the first PCs obtained after reducing the original data cube with the principal component analysis (PCA) algorithm. The proposed PCA-1PC method gives good performances with non-noisy and homogeneous data, and SVD with anomaly detection algorithms gives the most consistent results and is quite robust to perturbations such as inhomogeneous background. Finally, an approach based on fringe analysis and structured light techniques in case of deflectometric recordings is presented for the inspection of free-form metal surfaces. After determining the parameters describing the sinusoidal stripe patterns, the proposed approach consists in projecting a list of phase-shifted patterns and calculating the corresponding phase-images. Defect location is based on detecting and analyzing the stripes within the phase-images.

The thesis is dealing with the investigation of charge and orbital order and their behaviour under external pressure. Therefore, a new pressure cell has been developed which allows the observation of superlattice reflections corresponding to the order phenomena under pressure using scattering of high-energy synchrotron radiation. The maximum pressure that can be reached is 1.25 GPa. Until today there has been no possibility to conduct such studies of charge and orbital order superlattice reflections under pressure using x-ray scattering. The intensities of the reflections of the single crystalline samples are quite weak compared to fundamental peaks. Therefore the measurements are strongly affected by the absorption of the radiation in the pressure cell itself. Further difficulties result from the facts that low temperatures are needed and the sample has to be oriented in reciprocal space after being mounted into the cell. Therefore, the design of a compact clamp-type piston pressure cell was chosen here. The cell is made from a copper-beryllium alloy with the wall thickness reduced in the height of the sample volume. This allows the usage inside a closed-cycle cryostat mounted on a three-axis-diffractometer. Absorption effects are minimized due to the combination of reduced wall thickness and the usage of high energy synchrotron radiation (E = 100 keV at the beamline BW5 at HASYLAB/DESY). The new experimental technique was established and used for a study of two representatives of the transition metal oxide compounds, i.e. doped cuprates and manganites, which belong to the class of strongly correlated electron systems. The 1/8-doped cuprate La_{2-x}Ba_{x}CuO_{4} reveals an ordered state at low temperatures. Inside the CuO_{2} planes a combined order of charge stripes and antiferromagnetic spin stripes is observed. The ordering results from the interaction between charge, spin and lattice degrees of freedom. Here the lattice degrees of freedom play a major role. Particularly, a structural transition from an orthorhombic to a tetragonal symmetry is prerequisite for the observation of the ordered state. The cell constructed in this work allows a more exact analysis of the coupling between the crystal lattice and the formation of the charge and spin ordered phase. The manganite system Pr_{0.7}(Ca_{0.9}Sr_{0.1})_{0.3}MnO_{3} shows a strong magnetoresistive effect, called colossal magnetoresistance (CMR). In this system, several ordered phases can be found, which exhibit charge, spin and - since the orbital degree of freedom is also present in the manganites - additionally orbital ordering phenomena. In particular, an antiferromagnetically spin ordered insulating phase, which is connected to a charge- and orbital ordered state competes with a ferromagnetic metallic phase. This competition leads to a phase separation, which determines the properties of the sample. Both phases are strongly coupled to the lattice degrees of freedom, so that application of external pressure drastically affects the interplay between the different phases and allows a detailed study of the relation between the charge and orbital ordered phase and the crystal structure. / Die vorliegende Arbeit befaßt sich mit dem Studium der Ordnungszustände von Ladungen und Orbitalen und deren Beeinflußung durch externen Druck. Als experimentelle Neuentwicklung wurde dafür eine Druckzelle entworfen, mit deren Hilfe die Beobachtung der jeweiligen Ordnungsphänomene unter Druck mittels der Streuung hochenergetischer Synchtrotronstrahlung möglich ist. Die Zelle erlaubt die Messung der orbitalen und Ladungsüberstrukturreflexe, welche aus den geordneten Zuständen resultieren, in einem Druckbereich bis 1.25 GPa. Die experimentelle Herausforderung ergibt sich hierbei aus der Tatsache, dass die Überstrukturreflexe im Vergleich zu den fundamentalen Reflexen der einkristallinen Proben sehr schwach sind und zusätzlich durch die Absorption im Mantelmaterial der Druckzelle stark beeinträchtigt werden. Darüber hinaus soll die Zelle bei tiefen Temperaturen einsetzbar und die Probe auch innerhalb der Zelle im reziproken Raum orientierbar sein. Bei dem hier realisierten Ansatz wurde für das Design daher der Typ einer kompakten Klemmdruckzelle aus einer Kupfer-Beryllium-Legierung gewählt, deren Zellwände im Bereich des Probenvolumens reduziert wurden. Dadurch ist der Einsatz der Zelle im Inneren eines Closed-Cycle-Kryostaten auf einem Einkristall-Diffraktometer möglich. Aufgrund der geringen Wandstärke der Zelle und der Nutzung von hochenergetischer Röntgenstrahlung (E = 100 keV am Messplatz BW5 des HASYLAB/DESY) werden Absorptionseffekte minimiert. Die neue Messmethode wurde im Rahmen der Arbeit etabliert und zur Untersuchung zweier wichtiger Übergangsmetalloxidverbindungen (dotierte Kuprate, Manganate), die zur Klasse der stark korrelierten Elektronensysteme gehören, eingesetzt. Das 1/8-dotierte Kupratsystem La_{2-x}Ba_{x}CuO_{4}, weist bei tiefen Temperaturen einen statisch geordneten Zustand auf. Innerhalb der CuO_{2}-Schichten des Kristalls ergibt sich eine Ordnung, bei der sich Streifen lokalisierter Löcher und antiferromagnetische Bereiche abwechseln. Ursache dieses Zustands ist das Wechselspiel von Ladungen, Spins und strukturellen Freiheitsgraden. Dabei spielen letztere eine herausgehobene Rolle. So ist insbesondere ein struktureller Übergang von einer orthorhombischen zu einer tetragonalen Phase Voraussetzung für die Beobachtung der Ordnung. Die in dieser Arbeit aufgebaute Druckzelle erlaubt eine genauere Analyse des Zusammenhangs zwischen Struktur des Kristalls und der Ausbildung der ladungs- und spingeordneten Phase. Das Manganatsystem Pr_{0.7}(Ca_{0.9}Sr_{0.1})_{0.3}MnO_{3}, zeichnet sich durch einen sehr starken magnetoresistiven Effekt aus, der auch als kolossaler Magnetowiderstand (CMR) bezeichnet wird. Auch hier kann bei tiefen Temperaturen eine geordnete Phase beobachtet werden. Allerdings spielt in diesem System zusätzlich der orbitale Freiheitsgrad der Elektronen eine entscheidende Rolle, so dass sich eine kombinierte Ladungs- und Orbitalordnung ergibt. Diese Phase, die isolierend und zusätzlich antiferromagnetisch geordnet ist, steht im direkten Wettbewerb zu einer ferromagnetischen Phase. Aus dieser Konkurrenz ergibt sich eine Tendenz zur Phasenseparation, deren Effekte die Eigenschaften des Kristalls dominieren. Da beide Phasen stark an die strukturellen Freiheitsgrade gekoppelt sind, läßt sich das Gleichgewicht zwischen ihnen durch externen Druck beeinflussen und die Abhängigkeit der ladungs- und orbitalgeordneten Phase von den strukturellen Eigenschaften des Kristalls im Detail untersuchen.

The aim of this work is to explore the joining of inspiration, such as different garments and materials, in relation to commonly used methods in the fashion industry when it comes to joining of different trends and references such as clashing and collaging. The work proposes a new method and framework for join- ing inspiration which generates different results depending on what kind of inspiration that is put in to it. A garment can roughly be broken down to a silhouette and shape, materials and details. The material put in to the method and framework is based on information from trend seminars for SS16, because that is how many of today’s trend-oriented fashion brands get there inspiration. Trendy garment silhouettes are mixed through processes of computational morphing in Adobe Flash by a generation of spin in the mixing process were shape hints are used in a new manner. The new generated silhouettes are further developed and materialized through procedures of interpretation and figuration. Different trendy materials are melded in a direct and concrete way through mixed media techniques such as laminating, fusing and vacuum-techniques. The final steps of the method is a garment shape and material synthesis with starting point in the generated shape with the final material. The projects intention is to let the physical experimentation, interpretation and figuration play a central role in the research process for new types of methods, garments, materials and expressive pos- sibilities.

Studies were conducted on three field trials of wheat cv. Kopara to investigate the lack of compensation by later determined components of yield because of early disease constraints. The investigation was based on the hypothesis that early disease reduces root development and thus causes the plants to be water constrained at later growth stages when soil water deficits usually occur. The reduced root development and soil water deficits may reduce the ability of the plant to compensate for reductions in early determined components. The hypothesis was tested by the application of irrigation to alleviate water stress. In a disease free crop, the possible phytotonic effects of the fungicides benomyl and triadimefon on wheat were investigated. These fungicides had no phytotonic effects on shoot, root growth, or yield under the prevailing conditions. The effect of disease on root development was analysed by root length measurements. Disease present in the crop at any stage of growth affected root development. Root development in the upper zones of the soil profile was reduced more by disease compared to those zones below 35 cm. A full disease epidemic reduced root development more than an early or late disease epidemic. The early and late disease epidemics had similar effects on root length. Alleviation of early disease constraints enabled greater development of roots to offset any earlier reductions. Soil water deficits increased root development in the lower zones of the nil disease plants. The presence of adequate soil water from irrigation reduced the requirement for further root growth in all treatments. In the 1981-1982 field trial a full disease epidemic reduced yield by 14% whereas an early disease epidemic reduced yield by 7%. The reduction in yield was attributed to a lower grain number. With irrigation the yield reduction in the full disease plants was 12% whereas in the early disease plants the reduction was only 2.4%. This indicated that plants affected by the early disease epidemic were water constrained. In this study, the results suggested that, for conditions prevailing in Canterbury, the supply of water at later growth stages increased grain weight in plants which were subject to early disease epidemics. This suggests that reduced root development caused by early disease and soil water deficits may prevent compensation by grain weight. Water use was similar in all disease treatments. After irrigation the irrigated plants of all treatments used more water. Disease affected water use in relation to yield production however, and was better expressed by water use efficiency. Water use efficiency was reduced in the full disease plants. A stepwise regression analysis suggested that water use efficiency was affected directly by disease at later growth stages, and indirectly via an effect on total green leaf area at early growth stages. This study partially proves the hypothesis that reductions in root development caused by an early disease epidemic may constrain the plants at later growth stages when water deficits usually occur. It was shown that the reduction in root development caused by disease could be counteracted by irrigation. In this respect, water served as a tool to study the effect of disease constraints on the yield of wheat. A knowledge of cereal crop physiology, root growth and function is used to explain and discuss the observations made in this research programme. The results are discussed in relation to the way in which disease affects yield through its effect on root development. The possible reasons for the continued effects of disease even after the control of disease at later growth stages are discussed. The economic use of fungicides and water in diseased crops are also outlined. Suggestions for future studies on disease-yield loss relationships are provided. The repetition of these experiments in different sites and climatic regions could provide information which may be incorporated in disease-yield loss simulation models. This could then be used to predict root development and water requirements of diseased plants, and provide a basis for economic use of fungicides and water, and for better disease management programmes.

The thesis is dealing with the investigation of charge and orbital order and their behaviour under external pressure. Therefore, a new pressure cell has been developed which allows the observation of superlattice reflections corresponding to the order phenomena under pressure using scattering of high-energy synchrotron radiation. The maximum pressure that can be reached is 1.25 GPa. Until today there has been no possibility to conduct such studies of charge and orbital order superlattice reflections under pressure using x-ray scattering. The intensities of the reflections of the single crystalline samples are quite weak compared to fundamental peaks. Therefore the measurements are strongly affected by the absorption of the radiation in the pressure cell itself. Further difficulties result from the facts that low temperatures are needed and the sample has to be oriented in reciprocal space after being mounted into the cell. Therefore, the design of a compact clamp-type piston pressure cell was chosen here. The cell is made from a copper-beryllium alloy with the wall thickness reduced in the height of the sample volume. This allows the usage inside a closed-cycle cryostat mounted on a three-axis-diffractometer. Absorption effects are minimized due to the combination of reduced wall thickness and the usage of high energy synchrotron radiation (E = 100 keV at the beamline BW5 at HASYLAB/DESY). The new experimental technique was established and used for a study of two representatives of the transition metal oxide compounds, i.e. doped cuprates and manganites, which belong to the class of strongly correlated electron systems. The 1/8-doped cuprate La_{2-x}Ba_{x}CuO_{4} reveals an ordered state at low temperatures. Inside the CuO_{2} planes a combined order of charge stripes and antiferromagnetic spin stripes is observed. The ordering results from the interaction between charge, spin and lattice degrees of freedom. Here the lattice degrees of freedom play a major role. Particularly, a structural transition from an orthorhombic to a tetragonal symmetry is prerequisite for the observation of the ordered state. The cell constructed in this work allows a more exact analysis of the coupling between the crystal lattice and the formation of the charge and spin ordered phase. The manganite system Pr_{0.7}(Ca_{0.9}Sr_{0.1})_{0.3}MnO_{3} shows a strong magnetoresistive effect, called colossal magnetoresistance (CMR). In this system, several ordered phases can be found, which exhibit charge, spin and - since the orbital degree of freedom is also present in the manganites - additionally orbital ordering phenomena. In particular, an antiferromagnetically spin ordered insulating phase, which is connected to a charge- and orbital ordered state competes with a ferromagnetic metallic phase. This competition leads to a phase separation, which determines the properties of the sample. Both phases are strongly coupled to the lattice degrees of freedom, so that application of external pressure drastically affects the interplay between the different phases and allows a detailed study of the relation between the charge and orbital ordered phase and the crystal structure. / Die vorliegende Arbeit befaßt sich mit dem Studium der Ordnungszustände von Ladungen und Orbitalen und deren Beeinflußung durch externen Druck. Als experimentelle Neuentwicklung wurde dafür eine Druckzelle entworfen, mit deren Hilfe die Beobachtung der jeweiligen Ordnungsphänomene unter Druck mittels der Streuung hochenergetischer Synchtrotronstrahlung möglich ist. Die Zelle erlaubt die Messung der orbitalen und Ladungsüberstrukturreflexe, welche aus den geordneten Zuständen resultieren, in einem Druckbereich bis 1.25 GPa. Die experimentelle Herausforderung ergibt sich hierbei aus der Tatsache, dass die Überstrukturreflexe im Vergleich zu den fundamentalen Reflexen der einkristallinen Proben sehr schwach sind und zusätzlich durch die Absorption im Mantelmaterial der Druckzelle stark beeinträchtigt werden. Darüber hinaus soll die Zelle bei tiefen Temperaturen einsetzbar und die Probe auch innerhalb der Zelle im reziproken Raum orientierbar sein. Bei dem hier realisierten Ansatz wurde für das Design daher der Typ einer kompakten Klemmdruckzelle aus einer Kupfer-Beryllium-Legierung gewählt, deren Zellwände im Bereich des Probenvolumens reduziert wurden. Dadurch ist der Einsatz der Zelle im Inneren eines Closed-Cycle-Kryostaten auf einem Einkristall-Diffraktometer möglich. Aufgrund der geringen Wandstärke der Zelle und der Nutzung von hochenergetischer Röntgenstrahlung (E = 100 keV am Messplatz BW5 des HASYLAB/DESY) werden Absorptionseffekte minimiert. Die neue Messmethode wurde im Rahmen der Arbeit etabliert und zur Untersuchung zweier wichtiger Übergangsmetalloxidverbindungen (dotierte Kuprate, Manganate), die zur Klasse der stark korrelierten Elektronensysteme gehören, eingesetzt. Das 1/8-dotierte Kupratsystem La_{2-x}Ba_{x}CuO_{4}, weist bei tiefen Temperaturen einen statisch geordneten Zustand auf. Innerhalb der CuO_{2}-Schichten des Kristalls ergibt sich eine Ordnung, bei der sich Streifen lokalisierter Löcher und antiferromagnetische Bereiche abwechseln. Ursache dieses Zustands ist das Wechselspiel von Ladungen, Spins und strukturellen Freiheitsgraden. Dabei spielen letztere eine herausgehobene Rolle. So ist insbesondere ein struktureller Übergang von einer orthorhombischen zu einer tetragonalen Phase Voraussetzung für die Beobachtung der Ordnung. Die in dieser Arbeit aufgebaute Druckzelle erlaubt eine genauere Analyse des Zusammenhangs zwischen Struktur des Kristalls und der Ausbildung der ladungs- und spingeordneten Phase. Das Manganatsystem Pr_{0.7}(Ca_{0.9}Sr_{0.1})_{0.3}MnO_{3}, zeichnet sich durch einen sehr starken magnetoresistiven Effekt aus, der auch als kolossaler Magnetowiderstand (CMR) bezeichnet wird. Auch hier kann bei tiefen Temperaturen eine geordnete Phase beobachtet werden. Allerdings spielt in diesem System zusätzlich der orbitale Freiheitsgrad der Elektronen eine entscheidende Rolle, so dass sich eine kombinierte Ladungs- und Orbitalordnung ergibt. Diese Phase, die isolierend und zusätzlich antiferromagnetisch geordnet ist, steht im direkten Wettbewerb zu einer ferromagnetischen Phase. Aus dieser Konkurrenz ergibt sich eine Tendenz zur Phasenseparation, deren Effekte die Eigenschaften des Kristalls dominieren. Da beide Phasen stark an die strukturellen Freiheitsgrade gekoppelt sind, läßt sich das Gleichgewicht zwischen ihnen durch externen Druck beeinflussen und die Abhängigkeit der ladungs- und orbitalgeordneten Phase von den strukturellen Eigenschaften des Kristalls im Detail untersuchen.