Dissertations / Theses on the topic 'Neutron diffraction'
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1
Wang, Duan Qiang. "Strain measurement using neutron diffraction." Thesis, Open University, 1996. http://oro.open.ac.uk/57651/.
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This thesis contains a study of improvement and application of strain measurement technique using neutron diffraction. A dedicated neutron strain scanner - ENGIN, funded by Ee. has been developed at ISIS. It has two radial collimators, allowing for the first time, measurements taken simultaneously at two orthogonal directions; uses Pawley refinement permitting both whole pattern and individual peak profile analysis and its positioner allow's specimens weighing 250 kg to be placed with an accuracy of 100 um. Strain measurement using neutron diffraction has been investigated under two extreme circumstances: very shallow (within 1 mm near surface) and very deep in materials (hundred of mm). Near-surface measurement requires both the accurate determination of the effective measurement position associated with precise location of specimen, calculation of centroid and correction for an anomalous near-surface effect. The strain measurements on a shot-peened surface in titanium alloy were carried out using the methodology mentioned above. The result is comparable to that obtained from X-ray diffraction. The latter was exploited by studying the effect of wavelength-dependent attenuation in materials. Experiments and theoretical analysis on aluminium and iron show that the effect is small for a strain scanner using radial collimator and time-of-flight technique. However, the reduction of the diffraction peak intensity, as a function of the amount of material in the beam path, reveals that great care should be taken when measuring texture as a function of depth in materials. The neutron diffraction technique was applied to several sets of engineering strain measurements. Firstly, 3-D residual stresses surrounding a cold expanded hole in a high strength aluminium alloy plate were measured. The result agrees well with that from modified Sachs' method after taking the effect of gauge volume averaging into account. Second, measurements of strain distributions in a Q-joint under zero and 30 kN load have been carried out, which provides a confirmation of the excellence of the joint design as the fastener system has completely shielded the fastener hole from deleterious tensile strains under operational loading. Finally, calibration strain measurement for an energy dispersive neutron transmission spectrometer was performed for the first time and it is found that the transmission spectrometer is feasible for strain and phase transformation measurement.
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Lobban, Colin. "Neutron diffraction studies of ices." Thesis, University College London (University of London), 1998. http://discovery.ucl.ac.uk/10065569/.
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This thesis reports on a series of neutron diffraction measurements on ices in the medium-pressure range of the phase diagram in order to address several outstanding issues. The structure of ice II under its thermodynamic conditions of stability is unknown. Previous studies have used helium gas as the pressurising medium, which is included within the ice structure. Argon gas has been used in this work as the pressure medium, and the detailed structure of ice II is presented and discussed. Similarly, the structure of ice V under its conditions of stability is established for the first time by this work. For ices III and V, the presence of orientational order is controversial with the results obtained from structural studies on recovered samples differing from conclusions drawn from dielectric and spectroscopic measurements. The results obtained in this work indicate partial ordering of the water molecules which, for ice V, appears to be both temperature and pressure dependant. Ice IV is a metastable phase of ice that is difficult to form. A structure has been proposed on the basis of samples recovered to ambient pressure at 110 K . This work has successfully prepared ice IV at high temperature and pressure and a structure refinement confirms, for the first time, that the proposed structure is correct. During studies within the established stability region of ice V, features were observed which could not be identified as any ice or clathrate phase. Further work in this region has successfully formed and retained one such phase. The structure has been solved and the phase identified as a new ice structure. The topology of this phase is unlike that of any known solid water structure, and contains a mixture of seven- and eight-membered rings. General issues concerning hydrogen-bonding, compressibility and expansivity of these phases are discussed.
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Tait, Kimberly. "Inelastic Neutron Scattering and Neutron Diffraction Studies of Gas Hydrates." Diss., The University of Arizona, 2007. http://hdl.handle.net/10150/194926.
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Gas hydrates (clathrates) are elevated-pressure (P) and low-temperature (T) solid phases in which gas molecule guests are physically incorporated into hydrogen-bonded, cage-like ice host frameworks. Natural clathrates have been found worldwide in permafrost and in ocean floor sediments, as well as in the outer solar system (comets, Mars, satellites of the gas giant planets). Diffraction patterns have been collected of gas hydrates at various methane and ethane compositions by preparing samples in an ex situ gas hydrate synthesis apparatus, and CO₂ gas hydrates were prepared in situ to look at the kinetics of formation. Storage of hydrogen in molecular form within a clathrate framework has been one of the suggested methods for storing hydrogen fuel safely, but pure hydrogen clathrates H₂(H₂O)₂ form at high pressures. It has been found that mixed clathrates (a stabilizer molecule in the large cage) and hydrogen gas together can reduce the pressures and temperatures at which these materials form. In situ neutron inelastic scattering experiments on hydrogen adsorbed into a fully deuterated tetrahydrofuran water ice clathrate show that the adsorbed hydrogen has three rotational excitations (transitions between J = 0 and 1 states) at approximately 14 meV in both energy gain and loss. These transitions could be unequivocally assigned the expected slow conversion from ortho- to para-hydrogen resulted in a neutron energy gain signal at 14 meV, at a temperature of 5 K (kT= 0.48 meV). A doublet in neutron energy loss at approximately 28.5 meV are interpreted as J = 1 → 2 transitions. In situ neutron inelastic scattering experiments on hydrogen adsorbed into ethylene oxide, a structure I former, were also carried out at the Los Alamos Neutron Scattering Center (LANSCE). There is convincing evidence (shifted rotational mode of molecular hydrogen) that hydrogen is capable of diffusing in the small cages of ethylene oxide clathrate. Values are also obtained for the librational modes of enclathrated ethylene oxide and several water translation modes. Also reported for the first time are the internal modes (higher frequencies) of ethylene oxide in ethylene oxide clathrate as measured by inelastic neutron scattering.
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Morrell, Jonathan T. "Experimental evaluation of polychromatic neutron diffraction." Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/112368.
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Thesis: S.B., Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, 2017.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 57-58).
Neutron diffraction is a technique that allows scientists to measure the arrangement and motions of atoms in a crystalline lattice by observing neutrons scattering at angles that are characteristic of the interatomic distances of the crystal. This is useful for studying the response of crystals to stress, irradiation, or for observing their phases. This thesis implements and analyzes a technique known as polychromatic neutron powder diffraction, which has the potential to be used by an instrument to make many simultaneous neutron diffraction measurements. In this experiment, powder diffraction patterns were measured with a diffractometer in polychromatic mode, using both angle-dispersive and wavelength-dispersive scans of a silicon powder. The intensity and resolution of the Bragg peaks with the instrument in this configuration were compared to Bragg peaks measured by the same instrument in a monochromatic configuration. The intensity of the polychromatic mode was only comparable to the monochromatic mode with looser collimation, which had the consequence of increasing the widths of the measured peaks. This resulted in a polychromatic signal intensity that was greater than the monochromatic signal intensity, and a Bragg peak that was wider than the monochromatic Bragg peak. The effects of the collimators and the sample to detector distances were quantified in experiment and in ray-tracing simulations. While both the monochromatic and the polychromatic configurations had similar counting rates in this experiment, they were both limited by the high background due to the open-beam geometry. A successful implementation of a polychromatic instrument would require substantial filtering and shielding to overcome this effect.
by Jonathan T. Morrell.
S.B.
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Dashjav, Enkhtsetseg, Raphael Hermann, and Frank Tietz. "High-temperature Neutron Diffraction of Li1.2Al0.2Ti1.8P3O12." Diffusion fundamentals 21 (2014) 21, S.1-2, 2014. https://ul.qucosa.de/id/qucosa%3A32431.
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Reynolds, John Melton. "Neutron diffraction and reflection studies of superconductors." Thesis, University of Oxford, 1998. http://ora.ox.ac.uk/objects/uuid:bab01bde-f42e-41ca-830e-655d41499408.
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I have studied two magnetic properties of superconductors using different neutron scattering techniques. Due to their magnetic moment and lack of electrical charge, neutrons can provide an extremely sensitive probe into magnetism on a small scale. Unusual magnetic structures have previously been observed in the non-superconducting PrBa2Cu3O6+δ, in particular showing a coupling between the rare-earth and the Cu-O2 planes. For comparison, I have used elastic neutron scattering to measure the temperature dependent magnetic structure of the high-Tc superconductor NdBa2Cu3O7, and its nonsuperconducting reduced form NdBa2Cu3O6. The magnetic structures of both the Nd and Cu sub-lattices are presented. Measurements are shown for single crystals of both the oxygenated and reduced form, and also for a non-stoichiometric single crystal with Nd substituted on the Ba sites. I present a quantitative analysis of the magnetic moments, with account taken of the instrumental resolution including sample mosaicity and intrinsic peak shapes. No evidence was found for any coupling of the type seen in PrBa2Cu3O6+δ. Many of the underlying properties of superconductors are evidenced in the way magnetic fields are excluded in the different states. I have used polarized neutron reflectometry to measure the magnetic field profile in thin film superconductors. I present measurements for pure niobium and preliminary measurements for YBa2Cu3O7. The samples studied are much thicker than those previously measured, to provide a closer match to the bulk superconductor properties and allow meaningful measurements of the higher field states. For niobium, the applied field dependence is measured for fields covering the Meissner and mixed states, and models are compared for these states and the surface superconductivity state.
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Ibberson, Richard M. "Neutron power diffraction studies of molecular crystals." Thesis, University of Reading, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.357200.
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Criswell, Leah. "Neutron diffraction and quasielastic neutron scattering studies of films of N-alkanes and a branched alkane absorbed on graphite." Diss., Columbia, Mo. : University of Missouri-Columbia, 2007. http://hdl.handle.net/10355/6010.
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Thesis (Ph. D.)--University of Missouri-Columbia, 2007.The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on March 11, 2008) Includes bibliographical references.
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Unruh, Troy Casey. "Development of a neutron diffraction system and neutron imaging system for beamport characterization." Thesis, Manhattan, Kan. : Kansas State University, 2009. http://hdl.handle.net/2097/2324.
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Filippone, Roberto. "Martensite characterization in multiphase steels using neutron diffraction." Thesis, McGill University, 2001. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=32958.
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Previous use of the diffraction technique as a means of characterizing microstructure in multiphase steels has been generally limited to measurements of retained austenite. Other phases, specifically martensite, have not been examined in complex microstructures since there exists peak overlap with ferrite. This research looks at using neutron diffraction as a means to characterize martensite in a multiphase steel microstructure, thus providing a more complete characterization tool.Three low carbon steels, comprised of a dual-phase, ferrite-martensite microstructure, were used in this study. Two diffraction methods were investigated; a direct deconvolution of the martensite peaks from the ferrite peak, and an indirect determination of martensite volume fraction from ferrite peak broadening. Lastly, mechanical properties were investigated in order to determine if a correlation exists with ferrite peak broadening.
The results indicate that the martensite phase has a prominent strain broadening effect in diffraction. The nature of this strain effect was hypothesized and a model was developed to confirm the findings. Finally, tensile testing showed that the mechanical properties were dependent on peak broadening and martensite volume fraction.
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Clarke, Stuart James. "Neutron diffraction studies of silicate and borate glasses." Thesis, University of Reading, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.493994.
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Two systems of glasses have been studied: soda-lime-silica and alkali borate glasses. Vitreous boron oxide was included as a standard for comparison with alkali borates. Silica and irradiated vitreous silica were included for low Q diffraction studies as comparison with previous results.
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Dong, Bo. "Neutron diffraction studies of lithium-based battery materials." Thesis, University of Sheffield, 2018. http://etheses.whiterose.ac.uk/19190/.
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Donnelly, Mary-Ellen. "Neutron diffraction of hydrogen inclusion compounds under pressure." Thesis, University of Edinburgh, 2017. http://hdl.handle.net/1842/31471.
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When ice is compressed alongside a gas, crystalline 'host - guest' inclusion compounds known as gas clathrate hydrates form. These compounds are of interest not only for their environmental and possible technological impact as gas storage and separation materials, but also for their ability to probe networks not readily adopted by the pure `host' water molecules, and to study the interactions between water and gas molecules. Despite the pressure dependent crystal structures being fully determined for a large variety of `guest' gas species there is still relatively little known about the crystal structures in small guest gas systems such as H2 hydrate. The majority of structural studies have been done with x-ray diffraction and report a number of conflicting structures or hydrogen contents for the four known stable phases (sII, C0, C1 and C2). As this is a very hydrogen rich system the most ideal method to study the structure is neutron diffraction, which is able to fully determine the location of the hydrogen atoms within the structure and would allow a direct measurement of any hydrogen ordering within the host structure and the H2 content. In this work the phase diagram of the deuterated analogue of the H2-H2O system is explored at low pressures (below 0.3 GPa) with neutron diffraction. In the pressure/temperature region where the sII phase is known to be stable, two metastable phases were observed between the formation of sII from ice Ih and that this transition sequence occurred in line with Ostwald's Rule of Stages. One of these metastable phases was the C0 phase known to be stable in the H2-H2O system above 0.5 GPa, and the other is a new structure not previously observed in this system and is dubbed in this work as C-1 . Prior to this work the C0 phase has been reported with various structures that were determined with x-ray diffraction, and here the crystal structure and H2 content at low pressure are determined with neutron diffraction. The C0 phase was found to form a similar host structure to those of the previous studies with spiral guest sites but is best described with highly mobile H2 guests and a higher symmetry space group which make it the same structure as the spiral hydrate structure (s-Sp) recently observed in the CO2 hydrate system. In addition to this structure being determined at pressure a sample of C0 was also recovered to ambient pressure at low temperature and its structure/H2 content is presented as it was warmed to decomposition. The crystal structure of the C-1 phase was determined to be similar to ice Ih and a sample was recovered to ambient pressure to study its decomposition behaviour. Evidence for a similar structure in the helium hydrate system at low pressure is also reported here. This work was then extended to higher pressures with the recent developments of a hydrogen-compatible gas loader and large-volume diamond anvil cells. Several test experiments on gas-loaded Paris-Edinburgh presses are described on systems that are similar to hydrogen-water like urea-hydrogen and neon-water. And a further preliminary high pressure study on the deuterated analogue of the H2- H2O system in a diamond anvil cell between 3.6 and 28 GPa shows decomposition behaviour as pressure was increased.
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Bianchini, Matteo. "In situ diffraction studies of electrode materials for Li-ion and Na-ion batteries." Thesis, Amiens, 2015. http://www.theses.fr/2015AMIE0022/document.
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Ce travail vise à étudier les matériaux d'électrodes pour batteries Li-ion et Na-ion lors qu’ils fonctionnent à l'intérieur des batteries. Afin de comprendre l'évolution structurelle des matériaux alors que les ions Li+ ou Na+ sont insérés/extraits de leur cadre, on utilise principalement la diffraction, exploitant neutrons, rayons X et le rayonnement synchrotron (SR). Nous avons adopté une approche combinée des mesures ex situ, in situ et operando. Au début, nous avons conçu une cellule électrochimique pour mesures in situ de diffraction de neutrons sur poudre (NPD), avec un alliage en (Ti,Zr) "transparent aux neutrons"; cette cellule s'est ajoutée à l’ensemble de nos outils pour effectuer des études de type operando. Nous avons démontré leur faisabilité en utilisant LiFePO4, montrant de bonnes performances électrochimiques et des données NPD de haute qualité pour affinements structurales Rietveld. Ensuite, nous avons réalisé des études des spinelles Li1+xMn2-xO4 (x=0,0.05,0.10) et LiNi0.4Mn1.6O4: pendant le cyclage, nous avons rapporté des évolutions structurelles, des diagrammes de phases et paramètres subtils tels que le comportement du Li, ou les facteurs de température. L’utilisation complémentaire du SR a clarifié la nature de la phase ordonnée Li0.5Mn2O4. Nos études combinées ont concernées d’autres matériaux d'électrodes prometteurs: LiVPO4O et Na3V2(PO4)2F3. Les 2 révèle des comportements complexes pendant la (de)intercalation du Li+/Na+. Les données de haute qualité ont permis des analyses quantitatives, dévoilant la structure d'un grand nombre des phases ordonnées et menant à la compréhension du comportement des cations dans ces matériauxThis work aims at studying electrode materials for Li-ion and Na-ion batteries as they function inside batteries. Diffraction is the mainly used technique, exploiting neutrons, X-Rays and synchrotron radiation (SR), to obtain insights on the structural evolution of such materials as Li+ or Na+ are inserted/extracted from their framework. We adopted a combined approach of ex situ, in situ and operando measurements to extract a maximum of information from our studies. At first, we designed an electrochemical cell for in situ neutron powder diffraction (NPD) measurements, featuring a “neutron-transparent” (Ti,Zr) alloy; this cell, joined to others previously developed in our group, gave us a complete set of tools to perform our studies. We demonstrated the feasibility of operando NPD using LiFePO4, showing good electrochemical performances and high-quality NPD patterns for Rietveld structural refinements. Then we carried out detailed studies of spinels Li1+xMn2-xO4 (x = 0, 0.05, 0.10) and LiNi0.4Mn1.6O4: we reported phase diagrams, structural evolutions and subtle parameters as lithium's behavior inside the spinel framework, or thermal displacement parameters, directly upon cycling. Complementary use of SR shed light on other features, as the nature of the ordered phase Li0.5Mn2O4. Our combined studies concerned other promising electrode materials: LiVPO4O and Na3V2(PO¬4)2F3. Both revealed complex behaviors upon Li+/Na+
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Ye, Hong. "X-ray diffraction, neutron diffraction and circular dichroism studies of nucleic acids and proteins." Thesis, Keele University, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.245601.
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Rovira, Esteva Muriel. "Short-range order in disordered phases using neutron diffraction." Doctoral thesis, Universitat Politècnica de Catalunya, 2014. http://hdl.handle.net/10803/283110.
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Neutron diffraction is a powerful technique that allows to probe the structure of disordered phases across a variety of length scales. However, due to the inherent complexity of these disordered hases, the analysis of the information contained in the experimental data is not obvious.
In this work, a few alternative methods are presented that allow to make the most of the neutron diffraction measurements as well as the molecular configurations obtained from molecular dynamics simulations or data modelling. They mainly consist in a Bayesian approach to fit the molecular structures measured with neutron diffraction, and a multidimensional analysis of the molecular structure probability distribution functions obtained from simulations or data modelling techniques, instead of the standard averaging over many variables.
These methodologies are then applied to the structural investigation of several disordered systems in order to answer a series of open questions: the origin of the liquid-liquid transition in trans-1,2-dichloroethene (C2Cl2H2), the extreme fragility of 1,1,2,2-tetrachloro-1,2-difluoroethane's orientational glass (F-112, C2Cl4F2), the local density paradox in carbon tetrachloride (CCl4), and the roles of steric and electrostatic interactions in the short range order of the liquids of quasitetrahedral molecules, particularly trichlorobromomethane (CBrCl3) and dibromodichloromethane (CBr2Cl2).
Additionally, a concise summary of the theoretical framework for neutron diffraction of disordered systems, as well as the practicalities of the experimental setup and the necessary data treatment, are also included to provide interested researchers with a self-contained overview on the topic.La difracció de neutrons és una tècnica molt potent que permet sondar l'estructura de fases desordenades en un ventall d'escales de longitud. Tanmateix, degut a la complexitat inherent d'aquestes fases desordenades, l'anàlisi de la informació que es desprèn de les dades experimentals no és evident. En aquest treball es presenten diversos mètodes alternatius que permeten treure el màxim profit de les mesures de difracció de neutrons, així com de les configuracions moleculars obtingudes en simulacions de dinàmica molecular o del modelatge de les dades. Aquests mètodes consisteixen principalment en un enfocament bayesià en l'ajust de les estructures moleculars mesurades amb difracció de neutrons, i en una anàlisi multidimensional de les funcions de distribució de probabilitat de l'estructura molecular obtingudes en simulacions o tècniques de modelatge de dades, en comptes del mitjanat de diverses variables estàndard. Aquestes metodologies s'apliquen a la investigació de diversos sistemes desordenats per tal de resoldre una sèrie de qüestions obertes: l'origen de la transició líquid-líquid en el trans-1,2-dicloroetà (C2Cl2H2), l'extrema fragilitat del vidre orientacional del 1,1,2,2-tetracloro-1,2-difluoroetà (F-112, C2Cl4F2), la paradoxa de la densitat local en el tetraclorur de carboni (CCl4), i els rols de les interaccions estèrica i electrostàtica en l'ordre de curt abast de líquids de molècules quasitetraèdriques, en particular el triclorobromometà (CBrCl3) i el dibromodiclorometà (CBr2Cl2). Addicionalment, també s'hi inclou un breu repàs del marc teòric de la difracció de neutrons en sistemes desordenats, així com dels aspectes pràctics de l'equip experimental i del tractament de dades necessari, per tal que els investigadors interessats disposin d'una visió general completa sobre tema.
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Cheyne, Simon M. "Total neutron diffraction studies of disordered cyanide crystal structures." Thesis, University of Reading, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.402196.
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Hall, Christopher David. "Neutron diffraction and molecular dynamics studies of fluid halocarbons." Thesis, University of Liverpool, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.316495.
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Bourke, Mark A. M. "Residual stress measurement in engineering components by neutron diffraction." Thesis, Imperial College London, 1990. http://hdl.handle.net/10044/1/47782.
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Williams, Anthony James. "Synthesis and neutron diffraction studies of manganese oxide perovskites." Thesis, University of Cambridge, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.615786.
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Guthrie, Malcolm. "Developments in single-crystal neutron diffraction at high pressure." Thesis, University of Edinburgh, 2002. http://hdl.handle.net/1842/13969.
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An in-depth analysis of neutron powder-diffraction data from a sample of ice VII is presented. This study involved an attempt to extract information about the detailed nature of atomic disorder present in the water molecule, information only accessible via neutron techniques. The resulting difficulties lead to an exploration of the fundamental limits of powder-diffraction. This investigation highlighted a need to extend the maximum accessible pressure for single-crystal techniques that, for structural neutron-diffraction, is currently limited to 25kbars. The majority of the work constituting this thesis was devoted to increasing this limit. In order to realise this advance, two different techniques were developed in parallel. The first of these centred on the use of the Paris-Edinburgh (PE) cell to compress single-crystal samples. The new instrumentation, experimental methodologies and software developed by the author included modifications to both the cell and diffractometer and are presented here. These successfully facilitated a significant increase in accessible pressure up-to at least 70kbars. This new capability was used in a comparative powder and single-crystal study of the structure of potassium di-hydrogen phosphate (KDP). The results of this study challenged the previously published structure. They also facilitated a detailed comparison of the relative capabilities of powder and single-crystal measurements confirming the significant advantages of the latter in the measurement of low d-spacing intensities. The second technique to be developed by the author used a new large-volume diamond-anvil cell (DAC). This device provides optical access to the sample and thus the possibility of the in-situ growth of high-pressure phases. This property combined with large apertures for the diffracted beam gives the DAC a significant advantage over the PE cell. The techniques developed to perform neutron diffraction with the cell are presented as are the techniques of crystal growth. It was found that the DAC was currently limited in maximum pressure by the size of available anvils. However, this was sufficient to enable a investigation of D2-D2O clathrate, a compound only formed under high pressure. The results of this first neutron study are discussed in comparison with the previous published structure determined by x-ray diffraction, which was unable to resolve the hydrogen atoms.
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Hamacher, Klaus A. "Neutron diffraction studies of organic and magnetic layered structures /." free to MU campus, to others for purchase, 1998. http://wwwlib.umi.com/cr/mo/fullcit?p9901240.
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McKnight, Thomas Kevin. "An Improved Flexible Neutron Detector For Powder Diffraction Experiments." BYU ScholarsArchive, 2005. https://scholarsarchive.byu.edu/etd/463.
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Large amounts of money are being applied to the construction of the next generation of spallation sources for neutron scattering. Neutron powder diffraction instruments will be an important element of these facilities and the incorporation of detectors into these instruments with a high neutron capture efficiency is desirable. A new detector design named the Flexible Embedded Fiber Detector (FEFD) has been developed and tested for this thesis. This detector is based on wavelength shifting fibers embedded in a zinc-sulfide lithium-fluoride based scintillator. The virtue of this design is that the detecting surface can be curved around the Debye-Scherrer rings. This virtue is lacking in other detector designs, making them more complex and poorer in performance than our FEFD detectors. Monte Carlo calculations were performed to determine the neutron capture efficiencies of our FEFD detectors, which proved to be much higher than those of the proposed powder diffractometer design for the Spallation Neutron Source and about equal with the efficiency for the ISIS powder diffractometer design. Four FEFD detector prototypes were then fabricated and tested at the Intense Pulsed Neutron Source at Argonne National Laboratory. We find that our measured and calculated relative efficiencies are in good agreement.
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Pang, Judy Wai Lan. "A neutron diffraction study of intergranular strains and plastic deformation." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape9/PQDD_0006/NQ41267.pdf.
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Fowkes, Amelia Jane. "High resolution powder neutron diffraction in solid state inorganic chemistry." Thesis, University of Oxford, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.299525.
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Parrot, Ingrid Michele. "X-ray and neutron diffraction studies of fibrous biological molecules." Thesis, Keele University, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.423428.
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Wilson, Claire. "Structure-reactivity relationships through X-ray and neutron diffraction studies." Thesis, Durham University, 1995. http://etheses.dur.ac.uk/5314/.
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This thesis is primarily concerned with the investigation of a structure-reactivity relationship in a series of pentacyclic Isodrin derivatives. These compounds undergo a two-hydrogen atom dyotropic rearrangement at vastly differing rates when apparently small structural changes are made. Two pairs of these isomers (with the formulas C(_16)H(_8)Cl(_10) and C(_16)H(_9)Cl(_9) ) have been investigated using both X-ray and neutron single crystal diffraction studies, at ambient and low temperatures. The experimental details of these studies are given for five experiments and the results of the least-squares refinements made using the data from these experiments are reported herein. In addition to conventional crystallographic studies, an experimental charge density study of one of these compounds, C(_16)H(_9)Cl(_9), has been made at 123K. The electron density was modelled using a multipole model which allows explicitly for the aspherical nature of the electron density. The results of this study, including a topological analysis of the charge density are reported in this thesis. The structures of six organometallic, four molybdenum bis(imido) and two half-sandwich niobium imido complexes, are also reported herein. Their structures were determined from single crystal diffraction data. These compounds show the expected structures predicted using the pseudo-isolobal relationship to the Group 4 bent metallocenes of which they may be considered analogues.
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Hayama, Shusaku. "Neutron and X ray diffraction studies of metal amine solutions." Thesis, University College London (University of London), 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.249712.
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Xu, Xuelian. "X-ray and neutron diffraction studies of organic molecular crystals." Thesis, University of Strathclyde, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.416190.
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Van, Duijn Joost. "Powder neutron diffraction studies of some magnetic boron-containing compounds." Thesis, University of Cambridge, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.620967.
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Pope, Lisa Helen. "X-ray and neutron fibre diffraction studies of deoxyribonucleic acid." Thesis, Keele University, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.388355.
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Binns, Jack. "Development of high-pressure single-crystal neutron diffraction on KOALA." Thesis, University of Edinburgh, 2016. http://hdl.handle.net/1842/20416.
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This thesis project has focused on the development of high-pressure single-crystal diffraction experiments on the neutron Laue diffractometer KOALA at the OPAL reactor at ANSTO, Australia. Over the course of this project several candidate systems have been studied under conditions of high-pressure using X-ray diffraction with a view to their use in developmental experiments on KOALA. The results of two high-pressure KOALA experiments are presented as well as the notable results from X-ray diffraction on the candidate systems. The first experiment on hexamethylenetetramine provided valuable insights into how reduced crystallite size and reciprocal-space access affects data collected on KOALA. In addition, data treatment techniques were developed to deal with the unique and challenging high-pressure Laue data, including corrections for attenuation due to the cell body. The ability to collect data through the body of cell prompted a further experiment on the complex, low-symmetry structure of the amino acid l-arginine dihydrate. Despite the smaller crystal size and dominant parasitic scattering from the diamond-anvil cell, the data collected allow a full anisotropic refinement of hexamethylenetetramine with bond lengths and angles that agree with literature data within experimental error. This technique is highly suited to low-symmetry crystals, as shown by the successful refinement of data from a l-arginine dihydrate crystal. In such cases the transmission of diffracted beams results in higher completeness values than are possible with X-rays. The hydrogen-bonded ferroelectric rubidium hydrogensulfate was the subject of ambient-pressure experiments on KOALA investigating the nature of the ferroelectric transition. Further high-pressure X-ray diffraction studies were carried out to resolve the structures of phases at high-pressure and to investigate the ferroelectric transition under pressure. The potassium cobalt citrate metal-organic framework UTSA-16 has shown a wide variety of pressure-mediated framework-solvent interactions including negative linear compressibility, the ordering of potassium ions, and coordination changes which were investigated by high-pressure single-crystal and powder X-ray diffraction. These behaviors are rationalised by examination of the structural changes occurring in the framework under pressure. Two members of the widely studied alkylammonium tetrachlorometallate family, tetramethylammonium tetrachloroferrate(III) and tetramethylammonium tetrachlorogallate(III), display numerous phase transitions with temperature. The structures of these phases have been determined for the first time, and the contrast between the two materials explored with first-principles calculations.
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Alianelli, Lucia. "Characterization and modelling of imperfect crystals for thermal neutron diffraction." Université Joseph Fourier (Grenoble), 2002. http://www.theses.fr/2002GRE10170.
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Al-Hayalee, Yaseen Ahmed. "Neutron high angle fibre diffraction of biological and synthetic polymers." Thesis, Keele University, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.357084.
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Bachra, Bilber. "Studies of the structure of oxide glasses by neutron diffraction." Thesis, University of Reading, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.359050.
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Garawi, M. S. "Thermal neutron scattering by some molecular liquids." Thesis, University of Kent, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.378356.
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England, Roger D. "Measurement Of Residual Stresses in Diesel Components using X-ray, Synchrotron, and Neutron Diffraction." University of Cincinnati / OhioLINK, 2000. http://rave.ohiolink.edu/etdc/view?acc_num=ucin966625751.
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Lee, Jang Seob. "Solid-state NMR, X-ray diffraction and neutron diffraction studies on organic guest/zeolite ZSM-5 complexes." Thesis, University of British Columbia, 2007. http://hdl.handle.net/2429/31380.
Full textAbstract:
Zeolites are microcrystalline aluminosilicate materials that have intricate channel systems, into which molecules can be adsorbed. Important as industrial materials, they are used in gas separations, sorption and catalysis where the property of 'molecular sieving' is exhibited toward guest species. Thus, understanding the interactions between guest species and the host zeolite frameworks is central to predicting the syntheses and applications of zeolites, and this requires detailed structural information about the guest/zeolite complexes. For most zeolites, structure determination by single crystal XRD is precluded due to the microcrystalline nature of the materials. As an exception, ZSM-5, which was used exclusively for this thesis, is available in large crystals (> 100 μm). In the quest for a universal method to probe the structures of various types of guest/zeolite complexes, we have developed an alternative approach using solid-state NMR, which is not limited by crystal size, unlike single crystal XRD. The main focus of this thesis is exploring the potential of the NMR method by using it to determine various guest/zeolite complexes followed by verification by diffraction techniques where possible. The NMR method uses the dipolar coupling interactions between nuclei on the organic guest molecules and the silicon nuclei in the zeolite framework, which contain information regarding relative proximities of the protons in the guest to the silicon atoms in the rigid framework. The complexes tested were: o-xylene/ZSM-5, p-dicyanobenzene/ZSM-5, p -dinitrobenzene/ZSM-5 and benzene/ p -xylene/ZSM-5 (the mixture of the two organics as guest molecules in the structure determination of the complex for the first time). Precise structures for all the complexes listed have been determined successfully by the NMR method. Other relevant NMR studies, including connectivity, dynamics and spin diffusion, are also presented to support a better understanding of the interactions between the organic guests and the zeolite frameworks. Verification of the first three complex structures determined by NMR has been done successfully by diffraction methods. For o-xylene/ZSM-5, attempts to apply single crystal XRD were unsuccessful due to the very low diffusivity of the organic. Instead, powder neutron diffraction was used.Science, Faculty of
Chemistry, Department of
Graduate
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Boysen, Hans, Ines Kaiser-Bischoff, and Martin Lerch. "Anion diffusion processes in O- and N-mayenite investigated by neutron powder diffraction: Anion diffusion processes in O- and N-mayenite investigated by neutron powder diffraction." Diffusion fundamentals 8 (2008) 2, S. 1-7, 2008. https://ul.qucosa.de/id/qucosa%3A14148.
Full textAbstract:
The crystal structure of mayenite (ideal composition: Ca12Al14O33) consists of a (disordered) calcium-aluminate framework comprising 32 of the 33 oxygen anions. It contains large open cages, 1/6 of them being filled randomly by the remaining
“free” oxygen which is available for diffusion and very high ionic conductivities. This extraframework oxygen could be substituted by nitrogen, opening up possibilities for a pure nitrogen ionic conductor. From high temperature neutron powder diffraction experiments, data analysis employing difference Fourier methods and anharmonic Debye-Waller factors and comparing pure O-mayenite with partly exchanged N/O-mayenite it is concluded that oxygen diffusion proceeds via jump-like processes, intimately coupled to relaxations of Ca and involving exchange of the “free” oxygen with framework oxygen, while nitrogen diffusion appears to proceed via an interstitial process.
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Davies, Edward. "Neutron diffraction studies of amorphous ice and amorphous ice co-deposits." Thesis, University of Kent, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.305366.
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Dutta, Monojit. "Residual stress measurement in engineering materials and structures using neutron diffraction." Thesis, Open University, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.301945.
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Coates, Leighton. "Quasi laue neutron and atomic resolution x-ray diffraction of endothiapepsin." Thesis, University of Southampton, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.249945.
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Jupe, Andrew Charles. "Development of X-ray and neutron diffraction methods for cement research." Thesis, Birkbeck (University of London), 2000. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.392173.
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Payne, Stephen John. "Critical scattering and time resolved neutron diffraction studies of phase transitions." Thesis, Keele University, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.245355.
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Shotton, Mark William. "DNA structure investigated using complementary x-ray and neutron fibre diffraction." Thesis, Keele University, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.245356.
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Bianchi, Laurent. "The structure of molecular liquids : neutron diffraction and molecular dynamics simulations." Thesis, University of Dundee, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.312329.
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McNally, Graham Michael. "High pressure synthesis and neutron diffraction studies of new magnetic manganites." Thesis, University of Edinburgh, 2018. http://hdl.handle.net/1842/31185.
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With the discovery of appreciable room temperature magnetoresistance (MR) in high Curie temperature (Tc) ferrimagnetic double perovskites such as Sr2FeMoO6, research surrounding other materials of this type has expanded. Most ferrimagnetic double perovskites of the formula A2BB'O6 have non-magnetic A-site cations, such as Sr2+, Ca2+ or Ba2+. Replacing non-magnetic cations with magnetic variants offers further possibilities to tune magnetic effects. This thesis focuses on the substitution of non-magnetic A-site cations with relatively small magnetic Mn2+ cations. This substitution is made possible through the use of high-pressure/temperature (P/T) synthesis, and the characterisation of structural and magnetic properties of new phases discovered through these syntheses. The first of these new phases to be reported herein is Mn2FeReO6, which can be described as the Mn analogue of the well-known ferrimagnetic double perovskite Ca2FeReO6. These materials are well ordered with Fe3+/Re5+ on B-sites and crystallise in a P21/n structure. Mn2FeReO6 shows a high Tc of 520 K due to ferrimagnetic Fe/Re magnetic order above RT, and a large saturated magnetisation of 5.0 μB, which peaks at 75 K. Interestingly, the A-site Mn2+ (3d5) magnetic order has the effect of causing a spin reorientation of the Fe/Re sublattice observed by neutron powder diffraction (NPD) at temperatures below ~75 K. This causes the MR to exhibit the expected negative intergrain tunnelling behaviour above the transition and colossal positive behaviour below. Also reported are a series of perovskite related structures with formulae CaxMn2- xFeReO6 (x = 0.5, 1.0, 1.5). Of particular note among these is CaMnFeReO6, which exhibits 1:1 A-site ordering of Ca/Mn and adopts the P42/n space group. This material belongs to a family of newly discovered 'double double' perovskites, in which Ca/Mn order in columns pointing along the c-axis and Mn has alternating tetrahedral and square planar coordination environments. MR in this material remains negative down to 20 K, potentially due to the presence of Ca disrupting magnetic interactions between Mn2+ cations and suppressing the spin transition. Alternating coordination environments in the double double perovskite structure type were exploited in the synthesis of Ca(Mn0.5Cu0.5)FeReO6. This material also crystallises in the P42/n structure and is well ordered on B-sites, as evidenced by X-ray powder diffraction. Neutron diffraction yields, in addition to columnar order, a slight preference for Cu to occupy the square planar sites and for Mn to occupy tetrahedral sites. This doping of square planar sites with Cu has the effect of enhancing magnetic properties compared to CaMnFeReO6, increasing the saturated magnetisation, raising the ferrimagnetic ordering temperature of the B-sites from 500 to 560 K, and also having a profound effect on the observed MR effects, as a switch in the sign of the MR is observed in this material through a magnetic transition. Finally, B-site substitution has been experimented with in the synthesis of CaMnMnReO6. This also possesses the combined A and B-site orders observed in CaMnFeReO6 and an unusual magnetic structure, with perpendicular A and B-site magnetism due to frustration, deviating greatly from the magnetic structures of materials with B-site Fe/Re. In summary, this thesis compiles the synthesis and analysis of a series of new double perovskites, double double perovskites and a new 'triple double' five-fold cation ordered structure with a general formula of AA'0.5A''0.5BB'O6. These materials show that new types of structural ordering can be used to increase the number of degrees of freedom available for tuning the interplay between many different magnetic cations in different coordination environments.
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Noor, Faizani M. "Advanced techniques for extracting structural information from neutron diffraction of glasses." Thesis, University of Warwick, 2016. http://wrap.warwick.ac.uk/82169/.
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The structures of lithium and lead tellurite glasses (Li2O-TeO2 and PbO-TeO2) are studied using the combinations of neutron diffraction, isotope substitution neutron diffraction, and synchrotron X-ray diffraction. Additional complementary methods such as density measurement, thermal analysis and Raman spectroscopy show that the tellurite networks in lithium and lead tellurite glasses exhibit similar behaviour as a function of composition. From the diffraction data, real-space interatomic information on the glasses was extracted. The local environments of Te remain largely unchanged in both glasses if the second content is less than 15 mol%, as reported earlier for K2O-TeO2. For Li2O or PbO contents greater than 15 mol%, however, the average Te-O coordination number changes with composition and differently for the two oxides. A TeO2 Model, which has been successfully applied to K2O-TeO2 glasses, is extended to Li+ and Pb2+. By comparing the total correlation functions of the glasses to relevant crystal phases, the short-range parameters of the crystals can be used to optimise the model for Li+ and Pb2+ and explain the value of the average coordination number of Te. The environments of Li+ and Pb2+ were extracted using isotope substitution neutron diffraction (Li) and complementary neutron–X-ray diffraction (Pb). In the glasses studied (10, 15, 20, 25 and 30 mol% Li2O and 10, 12.5, 15, 17.5 and 20 mol% PbO), both Li+ and Pb2+ behave as modifiers with the average nLiO = 4 – 5 and nPbO = 8 with the distances rLiO and rPbO comparable to crystal phases of similar composition. The structures of lithium and potassium borogermanate glasses are studied using the combinations of neutron diffraction, isotope substitution neutron diffraction, and 11B MAS NMR. From the complementary methods such as density measurement, and Raman spectroscopy, changes are seen to occur in both borate and germanate networks. From 11B NMR, the average B-O coordination number, nBO, in lithium borogermanate glasses is different from nBO in potassium borogermanate glasses of the same stoichiometry and resembles the behaviour of Li+ and K+ in in borosilicate glasses, as described by the Zhong’s lithium borosilicate model and Dell and Bray’s sodium borosilicate model. From neutron diffraction data (null isotope neutron diffraction for lithium borogermanate), the average Ge-O coordination number nGeO is extracted and, like nBO, nGeO in lithium borogermanate is different from potassium borogermanate. In the former, nGeO increases as a function of Li2O, whilst in the latter, nGeO shows a maximum at about 20% K2O. For Li+, the average Li-O coordination number nLiO can be obtained using the difference technique (using diffraction data from samples made with natural and null-scattering lithium isotopes). For the limited samples examined, nLiO was found to have a value of 4 to 5 with two distinct Li-O distances which can be assigned to Li-OB and Li-OGe distances.
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Badyal, Yaspal Singh. "The structure of binary molten salt mixtures : a neutron diffraction study." Thesis, University of Leicester, 1994. http://hdl.handle.net/2381/34931.
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Structural modification in a series of polyvalent metal chloride - alkali chloride binary molten salt mixtures has been investigated using the pulsed neutron diffraction technique. Structure factors have been measured for NiCl2- KCl, NiCl2-LiCl and ZnCl2-LiCl samples spanning the entire composition range. The key finding was that the degree of structural modification is dependent on the relative size and polarising power of the two cation species. The mixtures of NiCl2, and ZnCl2, with LiCl largely appear to be admixtures of the two pure salt structures, whereas adding KCl to NiCl2 results in a better ordered, more regularly tetrahedral local structure around the metal cation and enhancement of the first sharp diffraction peak (FSDP). A simple model involving charge ordering of discrete tetrahedral units by alkali counter-ions is proposed as an explanation for the enhanced intermediate range order. In order to identify some of the partial structure factor contributions to the enhanced FSDP, the scattering was measured for three isotopically-enriched NiCl2+2KCl samples. A complementary isotopic substitution experiment was performed on three ZnCl2+2KCl samples. The results generally confirm the findings of the composition study, with a strong similarity between the two molten salt systems also being evident. In addition, RMC modelling supports the proposed model for intermediate range order in the mixtures. Structure factors were also measured for AlCl3-LiCl and AlCl3-NaCl samples covering the entire composition range. Several features consistent with strong charge ordering of discrete tetrahedral units by alkali counter-ions were identified. In addition, RMC modelling of the data for pure AICl3 strongly challenges the 'established' view of the structure and an alternative 'sparse network liquid' model is proposed which emphasises the similarity to ZnCl2.
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Castellan, John-Paul Adrian Gaulin B. D. "X-ray and neutron diffraction studies of strongly correlated electron systems." *McMaster only, 2007.
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