No description available.

Thesis (M.S.)--University of Florida, 2003. / Title from title page of source document. Includes vita. Includes bibliographical references.

A new three-angle energy-dispersive (ED) diffractometer has been successfully commissioned on station 16.4 SRS, Daresbury, England. The diffractometer facilitates the simultaneous collection of three spectra at three Bragg scattering angles. This enables the sampling of a far greater range of reciprocal space as compared to conventional single-angle diffractometers. Additionally the arrangement allows changes in sample density to be monitored. A protocol has been developed to align the diffractometer such that the origins of the diffracting volume are coincident on the diffractometer axis. Spectra obtained from the diffractometer were improved by the construction and placement of shielding. Experimental determination of components of the resolution function show that the resolution is close to the instrumental limit. The flux distribution of station 16.4 was determined experimentally. A novel whole pattern method has been developed for the quantitative analysis of synchrotron ED diffraction data. The method, which accounts for the differential absorption across the ED spectrum, was developed using spectra collected from a set of test binary phase mixtures and pure phases. Parameters relating to the proposed models were determined using linear and non-linear least-squares methods. Although the final model is the most physically complete it does not take account of certain non-diffraction derived events which appear as counts within the test spectra. A novel application of synchrotron ED diffraction, energy-dispersive diffraction tomography (EDD-T), is described. The method facilitates the non-destructive examination of the interior of crystalline and semi-crystalline objects. The resolution and limitations of this technique have been demonstrated using test objects. The method has been used to map the phase distributions of a variety of materials in a range of different samples. Quantitative EDD-T was used to determine the invasion of calcite into simulated oil-reservoir rocks.

No description available.

No description available.

This project proposes a reactor-based instrument, which retains most of the above advantages of spallation source engineering instruments, while maintaining the advantages inherent to steady-state instruments. The main idea is to allow the entire white beam from the reactor onto the sample---no monochromation. Diffraction is then allowed at a fixed angle, and information from two sample directions can be obtained simultaneously. Since a white beam is incident onto the sample, the diffraction condition is satisfied for multiple sample planes in the fixed angle of diffraction. Multiple analyzer/detector pairs are placed downstream from the sample and tuned to scatter only one of the diffracted wavelength bands. Monte Carlo methods were used to create models of both a standard two-axis engineering diffractometer, found on current reactor sources, and the proposed white beam instrument. There models were validated by experiments performed on a standard two-axis instrument, which was also modified to operate in a white beam configuration, in which the position of the sample and monochromator were interchanged. Both the models and the experiments of the white beam instrument showed proof of concept for this design and identified areas of concern that required special attention. Upon a comparison on the results from the standard two-axis instrument to the results from the white beam instrument (both simulation and experimental), it was found that the standard diffractometer showed a better performance in all aspects. However, this project proposes numerous areas where the white beam design can be improved upon in order to enhance its performance as an engineering instrument. The most important of these is the design of an appropriate analyzer/detector system, as the results overwhelmingly show this to be the area of greatest concern. Ideas for a few such designs are also given. / Thesis (Master, Physics, Engineering Physics and Astronomy) -- Queen's University, 2009-04-23 17:46:59.419

The structural chemistry and magnetic properties of a number of manganese containing hexagonal perovskites have been studied by X-ray diffraction, neutron diffraction and magnetometry. Trends in the magnetic properties are investigated as a function of the hexagonal stacking sequence and manganese oxidation state. The synthesis of the series of BaMnO_3-x hexagonal perovskites is discussed. By varying both the partial pressure of oxygen and the firing temperature, stacking sequences with a range of hexagonal to cubic layer ratios can be synthesised. Factors which increase the structural tolerance factor are found to increase the proportion of hexagonal layers in the stacking sequence. The crystallographic properties of the BaMnO_3-x compounds are discussed, and the oxide vacancies are found to be exclusively located in the face-sharing hexagonal (h) layers, particularly those which are adjacent to two apex-sharing cubic (c) layers. The preferential localisation of oxide vacancies in chc sites can be used to rationalise the observed stacking sequences, as well as the limiting stoichiometries of BaMnO_3-x structures. The magnetic behaviour of the BaMnO_3-x phases is investigated, both individually and as a function of the stacking sequence. A strong direct exchange interaction between face-sharing cations couples all magnetic moments antiferromagnetically above ambient temperature. A slightly weaker interaction (utilising the 180° superexchange pathways between apex-sharing MnOe octahedra) results in three-dimensional antiferromagnetic order at a temperature in the range 230 ≤ T (K) ≤ 280. The strength of this interaction is found to be dependent on the length of the face-sharing chains. A third interaction occurs at T ~ 45K, believed to represent a canting transition. Low temperature neutron diffraction data reveal that the magnetic moments order in a simple antiferromagnetic manner. The magnitude of the ordered moment shows a dependence on the length of the face sharing chains, where phases with shorter chains have a larger ordered moment. Long-range magnetic order is disrupted by charge disorder in the mixed Mn(III)/Mn(IV) system 4H-BaMnO_{2.6 5(1)}. The hexagonal BaMn_1-zTi_z O_{3- x} and BaMn_1-zZr_z0_3-x systems were also studied. Synthesis under argon atmospheres allows a range of new phases to be accessed. These include a novel manganese-zirconium phase, 6H-BaMn_0.8Zr_0.2O_2.81(1), and BaMn_o.55Ti<sub>0.45,/sub>O_3-x, which adopts the rare 15R' stacking sequence. The BaMn_1-z Ti_zO_3-x system confirms that although the tolerance factor controls the proportion of cubic layers, it does not control the arrangement of these layers. This is controlled by the size of the B cations and the proportion of oxide vacancies. Partial cation order occurs in 6H-BaMn_o.8Zr_0.2O_2.81(1), which can be rationalised on the basis of the size difference between manganese and zirconium ions. Topotactic reductions using binary hydrides are carried out in order to decouple the manganese oxidation state from the adopted stacking sequence. Using hydride reductions, 4H-Ba_o.5Sr_o.5MnO_3-x can be topotactically reduced to 4H-Ba_o.5Sr_o.5MnO_2.o2(1). This increases the strength of the 180° superexchange interaction, and antiferromagnetic order is achieved above ambient temperature. Using the same techniques, 4H-BaMnO_3-x can be reduced to 4H-BaMnO_2.47(1) or 4H-BaMnO_2.o6(1). These phases undergo a distortion to an orthorhombic unit cell.

Thesis (MSc.(Metallurgy)--University of Pretoria, 2008. / Includes bibliographical references.

Thesis (M. Sc.)--Carleton University, 2002. / Includes bibliographical references (p. 116-117). Also available in electronic format on the Internet.

This graduation thesis deals with Bruker AXS D8 Advance adjustment. Target of this thesis is design and realization of equipment which is going to be applicable on existing D8 advance machine and works with Göbel mirror adjustment. Mentioned adjustment is basic part of service operations necessary for D8. Introduction deals with theory of diffraction and basics of X-ray. Following part is presenting design of model which can be applicable and useful for solving of our problem. This design is completed with function device. This device realization is created by driving mechanism, control unit and mechanical adapter which is flexible and compatible with existing D8 Advance machine. All parts of designed device are fully described and complemented for full technical documentation, which is part of attachments.