Dissertations / Theses: 'X-ray powder diffraction'

1

Hinrichsen, Bernd. "Two-dimensional X-ray powder diffraction." [S.l. : s.n.], 2007. http://nbn-resolving.de/urn:nbn:de:bsz:93-opus-33946.

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2

Rodriguez, Asiloe Jasmina Mora. "High resolution powder diffraction studies of molecular solids." Thesis, Keele University, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.321299.

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Barnett, Stephanie Jayne. "X-ray powder diffraction studies of ettringite and related systems." Thesis, Staffordshire University, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.244708.

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4

Tremayne, Maryjane. "Ab initio structure determination from X-ray powder diffraction data." Thesis, University of St Andrews, 1995. http://hdl.handle.net/10023/6503.

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Many important crystalline solids cannot be prepared in the form of single crystals of sufficient size and quality for single crystal X-ray diffraction studies, and in such cases it is essential that structural information can be extracted from powder diffraction data. In this thesis, a number of crystal structures have been determined directly from X-ray powder diffraction data recorded on a conventional laboratory instrument, and the limitations of this technique explored using both conventional and new more sophisticated methods of structure solution. This work has focussed mainly on the more complex problem of molecular systems. The Patterson method has been applied to the determination of a simple unknown inorganic structure, lithium perchlorate, whereas conventional direct methods have been used in the determination of a number of organic structures, including the previously unknown crystal structure of 1,3,4,6-tetrathiopentalene-2,5-dione and formylurea - the first previously unknown organic structure containing only light atoms to be solved by this technique. The combined maximum entropy and likelihood method has been applied to determinate two crystal structures, lithium triflate and p-toluenesulphonhydrazide. Further developments of this technique are also discussed and illustrated in the structure solution of a previously known system. A Monte Carlo algorithm for ab initio crystal structure determination from powder diffraction data has also been developed, and the success of this method demonstrated by its application to the determination of several known structures, and the previously unknown crystal structure of p-bromophenylacetic acid. The effect of data range on the quality of structure solution obtained from both direct methods and the maximum entropy and likelihood method is also discussed.

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McBride, Lorraine. "Determination of organic crystal structures by X ray powder diffraction." Thesis, University of Strathclyde, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.248694.

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Bell, A. M. T. "Structural studies using synchrotron X-ray powder diffraction and other techniques." Thesis, University of Cambridge, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.596545.

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Chapter 1 gives an introduction to X-ray and neutron powder diffraction and the use of these techniques for crystal structure determination and refinement. The Rietveld structure refinement method is described and examples of different methods of structure determination from powder diffraction data are given. The techniques of EXAFS and Mössbauer spectroscopy, which were used to provide additional structural information, are also introduced. Chapter 2 describes the different radiation sources and experimental techniques used in this work. Chapter 3 describes a structural study of magnetite, Fe₃O₄, below the Verwey phase transition (120 K). The P2/c structure of Fe₃O₄ at 60 K has been refined with lattice parameters of a = 5.9412(3) Å, b = 5.9290(3) Å, c = 16.789(1) Å and β = 90.196(4). A variable temperature study of the Fe₃O₄ lattice parameters between 2-280 K shows this transition is first-order. An EXAFS study between 8-270 K shows that there is no significant change in the average Fe-O distance in Fe₃O₄ around the transition. Chapter 4 describes a structural study on a material related to magnetite, Fe₂OBO₃. Two phase transitions have been found for this material. The first of these is due to magnetic ordering and takes place at 155 K. The second is due to charge ordering and takes place at 315 K, this is a structural (P2₁/c ↔ Pnma) transition. Chapter 5 describes a resonant scattering experiment done on CsI. Resonant scattering parameters have been refined from synchrotron X-ray powder diffraction data collected at room temperature and at 4 K close to the Cs and I K-edges. The refined f parameters are -6.2(2) e/atom (Cs, λ = 0.3453 Å), -9.0(I) e/atom (I, λ = 0.374105 Å) and -6.2(2) e/atom (I, 4 K, λ = 0.37367 Å). Chapter 6 describes the ab initio structure determination of 4-(2'3'4'-trifluorophenyl)-1235 dithiadiazolyl (C₇S₂N₂F₃H₂; P₂/n, a = 11.543(4) Å, b = 20.666(8) Å, c = 7.045(2) Å and β = 100.35(4) using synchrotron X-ray powder diffraction data. A global optimisation method was used to provide a starting model for Rietveld refinement.

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Seaton, Colin Cormack. "Novel methods of structure determination from X-ray powder diffraction data." Thesis, University of Birmingham, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.396462.

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The determination of crystal structures from powder diffraction data is a field that is rapidly expanding due to a range of computational and experimental developments. A major driving force of this expansion is the continuing development of direct space methods of structure solution. This work will show the development of the program POSSUM as a suite of direct space structure determination methods and its subsequent successful application to a number of molecular organic and inorganic materials whose crystal structures were previously unknown. Direct space methods utilise global optimisation algorithms to locate the crystal structure. This work describes the successful application of the differential evolution optimisation algorithm to structure determination from powder diffraction. Differential evolution is shown to be a robust and efficient optimisation technique with the limited number of control parameters associated with the method ensuring that optimisation of the searching is easily achieved. Investigation into improving the computer performance of the method also focused on reduction of the time taken to evaluate agreement between experimental and calculated patterns through the application of the discrete wavelet transform. This effectively reduces the number of points in the powder pattern, yet retains the same level of information as the original data set and is shown to illustrate good discrimination between solutions generated in a direct space structure solution.

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Day, Sarah Joanne. "Studies of cosmic dust analogues using synchrotron X-ray powder diffraction." Thesis, Keele University, 2014. http://eprints.keele.ac.uk/1215/.

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The structural evolution of cosmic dust analogues has been investigated using in situ synchrotron X-ray powder diffraction (SXPD) at the Diamond Light Source. Amorphous Mg/Ca silicates are produced as analogues of cosmic dust using a modified sol-gel method. They are studied under non-ambient temperature and pressure conditions using in situ powder diffraction, complemented by FTIR and Raman spectroscopy. The solid-state mineralisation of amorphous grains is observed by thermal annealing and the results of this allow the environmental conditions leading to the formation of crystalline dust grains in astrophysical environments to be constrained. The solid-gas carbonation of amorphous Ca-rich silicates is studied using in situ SXPD and analysed using full-profile fitting techniques, while the effect of ex situ carbonation on the short range ordering of amorphous grains is investigated using high energy SXPD and Pair Distribution Function (PDF) analysis. The formation of a metastable calcium carbonate phase (vaterite) is observed and the importance of this in relation to astrophysical environments is discussed. In situ Raman and SXPD data of CO2 clathrate hydrates are presented and the importance of the Raman data obtained here with relevance to future remote sensing missions to Solar System bodies is discussed. This work indicates the importance of laboratory work to the field of astrophysics and provides novel experimental approaches to aid our understanding of astrophysical processes.

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9

Leonardi, Alberto. "Molecular Dynamics and X-ray Powder Diffraction Simulations: Investigation of nano-polycrystalline microstructure at the atomic scale coupling local structure configurations and X-ray powder Diffraction techniques." Doctoral thesis, Università degli studi di Trento, 2012. https://hdl.handle.net/11572/368091.

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Atomistic simulations based on Molecular Dynamics (MD) were used to model the lattice distortions in metallic nano-polycrystalline microstructures, with the purpose of supporting the analysis of the X-ray powder diffraction patterns with a better, atomic level understanding of the studied system. Complex microstructures were generated with a new modified Voronoi tessellation method which provides a direct relation between generation parameters and statistical properties of the resulting model. MD was used to equilibrate the system: the corresponding strain field was described both in the core and in surface regions of the different crystalline domains. New methods were developed to calculate the strain tensor at the atomic scale. Line Profile Analysis (LPA) was employed to retrieve the microstructure information (size and strain effects) from the powder diffraction patterns: a general algorithm with an atomic level resolution was developed to consider the size effects of crystalline domains of any arbitrary shape. The study provided a new point of view on the role of the grain boundary regions in nano-polycrystalline aggregates, exploring the interference effects between different domains and between grain boundary and crystalline regions. Usual concepts of solid mechanics were brought in the atomistic models to describe the strain effects on the powder diffraction pattern. To this purpose the new concept of Directional - Pair Distribution Function (D-PDF) was developed. D-PDFs calculated from equilibrated atomistic simulations provide a representation of the strain field which is directly comparable with the results of traditional LPA (e.g. Williamson-Hall plot and Warren-Averbach method). The D-PDF opens a new chapter in powder diffraction as new insights and a more sound interpretation of the results are made possible with this new approach to diffraction LPA.

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Leonardi, Alberto. "Molecular Dynamics and X-ray Powder Diffraction Simulations: Investigation of nano-polycrystalline microstructure at the atomic scale coupling local structure configurations and X-ray powder Diffraction techniques." Doctoral thesis, University of Trento, 2012. http://eprints-phd.biblio.unitn.it/843/1/PhDThesis_ALeonardi.pdf.

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Atomistic simulations based on Molecular Dynamics (MD) were used to model the lattice distortions in metallic nano-polycrystalline microstructures, with the purpose of supporting the analysis of the X-ray powder diffraction patterns with a better, atomic level understanding of the studied system. Complex microstructures were generated with a new modified Voronoi tessellation method which provides a direct relation between generation parameters and statistical properties of the resulting model. MD was used to equilibrate the system: the corresponding strain field was described both in the core and in surface regions of the different crystalline domains. New methods were developed to calculate the strain tensor at the atomic scale. Line Profile Analysis (LPA) was employed to retrieve the microstructure information (size and strain effects) from the powder diffraction patterns: a general algorithm with an atomic level resolution was developed to consider the size effects of crystalline domains of any arbitrary shape. The study provided a new point of view on the role of the grain boundary regions in nano-polycrystalline aggregates, exploring the interference effects between different domains and between grain boundary and crystalline regions. Usual concepts of solid mechanics were brought in the atomistic models to describe the strain effects on the powder diffraction pattern. To this purpose the new concept of Directional - Pair Distribution Function (D-PDF) was developed. D-PDFs calculated from equilibrated atomistic simulations provide a representation of the strain field which is directly comparable with the results of traditional LPA (e.g. Williamson-Hall plot and Warren-Averbach method). The D-PDF opens a new chapter in powder diffraction as new insights and a more sound interpretation of the results are made possible with this new approach to diffraction LPA.

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11

Wilkinson, Angus P. "Some applications of synchrotron X-ray powder diffraction to solid-state chemistry." Thesis, University of Oxford, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.302908.

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12

Wang, Te-Kang. "A powder X-ray diffraction study of two aluminum-lithium based alloys." Thesis, Monterey, California. Naval Postgraduate School, 1991. http://hdl.handle.net/10945/43736.

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Approved for public release; distribution is unlimited.
The microstructures of solution treated, quenched and aged A1-2.5 wt. %Li and A1-2.0 wt.%Li-2.76 wt.%Mg-1.03 wt.%Cu alloys were studied by powder X- ray diffraction. The as-quenched alloys showed extensive X-ray line broadening due to particle size effects and the intensity measurements indicated a significant amount ordering in the as-quenched state. These results were interpreted using a 'spinodal ordering' model which suggests that A1-Li-based alloys order during quenching and then spinodally decompose into regions of order and disorder so that the final microstructure comprises small ordered regions (size 40 nm) in a disordered matrix Studies on the aged A1-2.5 wt.%Li alloy indicated that after initial short-time aging, particle growth follows Ostwald ripening kinetics in agreement with previous work. Studies on the aged quaternary alloy indicated that T1 and S phases grow in this system so that precipitates are not a dominant strengthening mechanism in this alloy.

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13

Chan, Fung Choy. "Powder X-ray diffraction studies of structural and kinetic aspects of polymorphism." Thesis, King's College London (University of London), 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.327050.

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14

Sitepu, Husinsyah. "Characterisation of preferred orientation in crystalline materials by x-ray powder diffraction." Thesis, Curtin University, 1991. http://hdl.handle.net/20.500.11937/1897.

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Texture, i.e. preferred orientation, can cause large systematic errors in quantitative analysis of crystalline materials using x-ray powder diffraction (XRPD) data. Various mathematical forms have been proposed for the application of preferred orientation corrections. The most promising of these appears to be the single-parameter March (1932) model proposed by Dollase (1986).Li and O'Connor (1989) applied the March model to determine the level of preferred orientation in various gibbsites using two procedures. The first involved the Rietveld (1969) least squares pattern-fitting method. Each pattern was Rietveld-analysed in two ways, initially assuming random orientation of the crystallites and subsequently with the March model. The second procedure for preferred orientation analysis, described here as the line ratio method, determines preferred orientation factors according to the intensity ratios of carefully selected line pairs.In the thesis the procedures proposed by Li and O'Connor for texture analysis have been evaluated with XRPD data sets for molybdite, calcite and kaolinite. The results indicate that while the March formula improves agreement between the' calculated and measured patterns in Rietveld analysis, other forms of systematic error in the intensity data appear to limit the effectiveness of the March formula in general. It has been found also that the line ratio method improves agreement between the data sets, but less effectively than the Rietveld method. It is proposed that extinction is likely to be the most influential source of systematic error competing with texture.

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15

Sitepu, Husinsyah. "Characterisation of preferred orientation in crystalline materials by x-ray powder diffraction." Curtin University of Technology, School of Physical Sciences, 1991. http://espace.library.curtin.edu.au:80/R/?func=dbin-jump-full&object_id=10554.

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Texture, i.e. preferred orientation, can cause large systematic errors in quantitative analysis of crystalline materials using x-ray powder diffraction (XRPD) data. Various mathematical forms have been proposed for the application of preferred orientation corrections. The most promising of these appears to be the single-parameter March (1932) model proposed by Dollase (1986).Li and O'Connor (1989) applied the March model to determine the level of preferred orientation in various gibbsites using two procedures. The first involved the Rietveld (1969) least squares pattern-fitting method. Each pattern was Rietveld-analysed in two ways, initially assuming random orientation of the crystallites and subsequently with the March model. The second procedure for preferred orientation analysis, described here as the line ratio method, determines preferred orientation factors according to the intensity ratios of carefully selected line pairs.In the thesis the procedures proposed by Li and O'Connor for texture analysis have been evaluated with XRPD data sets for molybdite, calcite and kaolinite. The results indicate that while the March formula improves agreement between the' calculated and measured patterns in Rietveld analysis, other forms of systematic error in the intensity data appear to limit the effectiveness of the March formula in general. It has been found also that the line ratio method improves agreement between the data sets, but less effectively than the Rietveld method. It is proposed that extinction is likely to be the most influential source of systematic error competing with texture.

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16

Atkins, Alison J. "Solid state studies of ternary oxides and sulphides." Thesis, University of Nottingham, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.320791.

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17

McDowell, John Christopher. "Preparation characterisation and stability of selected high critical temperature ceramic superconductors." Thesis, University of Ulster, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.260854.

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Mohamed, Zakiah. "Relationships Among Structure, Magnetism and State of Charge in Positive Electrode Materials for Metal-Ion Batteries." Thesis, The University of Sydney, 2015. http://hdl.handle.net/2123/14438.

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Polyanionic framework materials containing 3d transition metals such as iron, cobalt and manganese are attractive candidates as electrodes in lithium and sodium ion batteries due to their thermal stability, long cycle life and environmental friendliness. LiFePO4 is already used in some commercial lithium ion batteries as a positive electrode material where these are key attributes, but it still has lower energy density and higher costs compared to the more commonly used LiCoO2. This thesis describes a combined physical properties and magnetic structures some of these materials, aimed at improving our understanding of their solid-state chemistry, and ultimately their performance as battery materials by relating those physical and magnetic properties to the state of charge of the battery. A variety of polyanionic materials including phosphates, pyrophosphates and silicates were prepared using solid-state synthesis. All compounds were intensively characterized using specific heat capacity and magnetic measurements, X-ray, neutron and synchrotron X-ray diffraction techniques. Low-temperature neutron diffraction was used to solved and refined the magnetic structures. During the lithium extraction process, the magnetic properties can vary significantly because it involve redox reaction of transition metals. Measuring the magnetic properties of working electrode materials can therefore potentially provide information about local structural changes including the introduction of defects, decomposition and phase segregation. The magnetic properties of chemically delithiated samples were also studied so that they could be used as reference materials. In the first part of the thesis, the phosphates family AM1-xM′xPO4 (A = Li, Na; M = Mn, Fe; M′ = Zn, Mn, Fe) are intensively studied. These phosphates are modified in two ways: by doping with magnetic and non-magnetic transition metals. It was found that all compounds exhibit antiferromagnetic ordering at low temperatures, but the nature and ordering temperatures depend on doping. In the course of this work, the magnetic structures of two types of sodium phosphate were determined for the first time,triphylite and maricite NaFePO4. The triphylite type showed similar crystal and magnetic properties as LiFePO4, while the maricite type demonstrated a transition from commensurate (T < 12 K) to incommensurate (12 < T < 13 K) magnetic phases. A spin-flop transition in the commensurate phase was also observed. These results are discussed in the context of spin frustration on the Fe2+ sites. The second type of cathode material studied was the pyrophosphate A2M1-xM′xP2O7 (A = Li, Na; M = Fe; M′ = Co, Mn). Varying the compositions of these materials led to significant changes in crystallographic and electronic structure with remarkable effects on the magnetic properties and structures.The magnetic structures of Li2(Fe1-xCox)P2O7 and Na2(Fe1-xMnx)P2O7 solid solutions were explored in the course of this work. The crystal and magnetic structures of the silicates γ-Li2MnSiO4 and β-Li2CoSiO4 were investigated and their magnetic structures solved for the first time, including for chemically delithiated versions of Li2CoSiO4. Magnetic property measurements confirmed that Co had oxidised from Co2+ to Co3+, confirming that delithiation was successful while also serving to demonstrate the sensitivity of magnetic measurements to lithium content. In addition, the structural evolution of Li2CoSiO4 was tracked by in situ S-XRD and revealed no phase transformation during cycling. In summary, the outcome of this study is an extension of the state of knowledge of the low-temperature magnetic properties and structures of polyanion-based transition metal oxides, and a demonstration of the sensitivity of those properties and structures to electrochemical state. Further refinement of this approach could lead to a new tool for developing improved positive electrode materials for rechargeable batteries. The work also yielded crucial missing information concerning the electronic ground state of these materials, required for future high-level computational studies aimed at predicting properties including ionic conductivity.

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Aziz, Fauziah Haji. "Indexing and structural studies of materials by high-resolution X-ray powder diffraction." Thesis, University of Surrey, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.232903.

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20

Docherty, Andrea. "Crystal structure solution and refinement of pharmaceutical molecules using x-ray powder diffraction." Thesis, University of Strathclyde, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.399726.

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Intisar, Amir. "A portable CCD array detector for in-situ analysis of powder samples using combined X-ray diffraction/X-ray fluorescence techniques." Thesis, Brunel University, 2010. http://bura.brunel.ac.uk/handle/2438/4401.

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This work describes the design, development and testing of a portable charge-coupled device detector system to be used for the simultaneous collection of X-ray diffraction and X-ray fluorescence data from powdered samples. The detector was designed for both terrestrial and extra-terrestrial applications that require in-situ analysis of samples, where access to a laboratory instrument is restricted. The detector system incorporates 4 e2v technologies CCD30-11 devices, employing multi-phase pinned technology for low noise operation. Geometrical calculations and thermal studies concerning the design of the detector are presented, with particular emphasis on motivations for the chosen geometry. Initial characterisation and calibration of the detector was performed in a laboratory environment using a purpose built test facility. The test facility included a high brightness X-ray micro-source from Bede Scientific Instruments, coupled with an XOS polycapillary collimating optic, which was used to deliver a focused beam of low divergent X-rays to the sample. The design of the test facility is discussed and the spectra and flux produced by the X-ray micro-source are investigated. The operational performance of the detector is highlighted and the use of the instrument in different applications is described, namely the planetary sciences and pharmaceuticals sector. Finally, based on the knowledge gained from initial testing of the instrument, improvements to the detector design are outlined, which greatly enhance the combined X-ray diffraction/X-ray fluorescence performance of the instrument.

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Edwards, Clare M. "Applications of high-pressure spectroscopic and powder x-ray diffraction techniques to inorganic materials." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape10/PQDD_0005/NQ44419.pdf.

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Edwards, Clare M. "Application of high-pressure spectroscopic and powder X-ray diffraction techniques to inorganic materials." Thesis, McGill University, 1998. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=37544.

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The vibrational spectra (IR, Raman) of (eta6-C 6H5CO2CH3)Cr(CO)3, (eta 6-C6H5CO2CH3)Cr(CO) 2(CS), [Pt(NH3)4][PtCl4] (MGS), [Pt(ND 3)4] [PtCl4] (MGS-D), [Pt(NH 3)4][PtBr4] (MGS-Br), ReH7(dppe) (dppe = 1,2-bis(diphenylphosphino)ethane) and CpCo(C64H4) (Cp = cyclopentadiene) have been studied under pressures up to ∼45 kbar. The magnitude and direction of the pressure-induced shift of the Raman-active nu(CO) and nu(CS) vibrational modes of (eta6-C6H 5CO2CH3)Cr(CO)3 and (eta6 -C6H5CO2CH3)Cr(CO) 2(CS) indicate an increase in the amount of pi-backbonding to the CO and CS ligands, under pressure, the increase being greater to the CO ligand than to the CS ligand. Wavenumber vs. pressure plots revealed a phase transition in both the tricarbonyl and thiocarbonyl complexes between 10--15 kbar. For CpCo(C64H4), discontinuities in the wavenumber vs. pressure plots at 10 kbar indicate a phase transition at this pressure, most likely involving rotation of the Cp ring. Insertion of the Co atom into the cage does not occur under compression; a shift to higher wavenumbers was observed for all the Raman and IR vibrational modes of CpCo(C64H4) and the parent fulleride, C 64H4. Phenyl ring rotation is thought to occur in ReH 7(dppe) under compression. Three pressure regions, from ambient pressure to ∼16 kbar, between 16 and 29 kbar and above 29 kbar, were identified from the wavenumber vs. pressure plots. A broad, weak feature in the ER spectrum appears from 5 kbar, increasing in intensity with increasing pressure. This peak has been assigned to the nu(HH) mode of a coordinated dihydrogen ligand, Re(eta2-H2). Ring rotation may assist the pressure-induced dihydride-dihydrogen interconversion. The pressure-tuning IR study of MGS and its derivatives probed the intermolecular interactions, in particular the interactions of the NH3 groups and investigated the hypothesis that hydrogen bonding of the type N- H&cdots;Cl exists in MGS. Splitting of the IR bands at ambient pressure, and

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Taylor, Ryan. "Structural insights into pharmaceutical solids from synchrotron and laboratory x-ray powder diffraction data." Thesis, University of Strathclyde, 2012. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=25783.

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Structural insights into a wide range of pharmaceutically relevant solids, including pharmaceutical salts, co-crystals and amorphous solids have been gained through the use of X-ray powder diffraction techniques. By combining global optimisation methods with high-quality powder diffraction data collected in the laboratory or at a synchrotron radiation source, the crystal structures of pharmaceutically relevant materials were solved successfully and reproducibly. The crystal structures which were solved are moderately complex, and at the midpoint of the complexity that can be routinely tackled by the DASH structure solution package. The crystal structures of six salts of the β2-adrenoceptor agonist, salbutamol were solved directly from powder diffraction data collected in the laboratory. For five of these salts, no single crystals could be grown, however, for one salt, a single crystal was obtained, and comparison of the single crystal structure with the structure solved from powder diffraction data confirms the excellent accuracy of structures from powder diffraction data. Co-crystals of the anti-epileptic drug, carbamazepine were examined on beamline I11 at Diamond Light Source in Oxfordshire. The beamline was in the optimisation phase when the co-crystals were examined, and were the first fully organic structures to be examined on the beamline. The accuracy of the structures solved from powder data was confirmed by comparison with published single crystal structures. Additional carbamazepine co-crystal structures were solved from laboratory powder diffraction data in order to assess the increase in accuracy associated with high resolution powder diffraction collected at a synchrotron radiation source. Total scattering pair distribution function (TS-PDF) analysis was carried out on nanocrystalline powders of carbamazepine and the NSAID indomethacin, and it was found that melt-quenched “amorphous” carbamazepine is in actual fact a nanocrystalline version of form II, which is the clinically used polymorph.

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Guo, Peng. "Structure Determination and Prediction of Zeolites : A Combined Study by Electron Diffraction, Powder X-Ray Diffraction and Database Mining." Doctoral thesis, Stockholms universitet, Institutionen för material- och miljökemi (MMK), 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-127750.

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Zeolites are crystalline microporous aluminosilicates with well-defined cavities or channels of molecular dimensions. They are widely used for applications such as gas adsorption, gas storage, ion exchange and catalysis. The size of the pore opening allows zeolites to be categorized into small, medium, large and extra-large pore zeolites. A typical zeolite is the small pore silicoaluminophosphate SAPO-34, which is an important catalyst in the MTO (methanol-to-olefin) process. The properties of zeolite catalysts are determined mainly by their structures, and it is therefore important to know the structures of these materials in order to understand their properties and explore new applications. Single crystal X-ray diffraction has been the main technique used to determine the structures of unknown crystalline materials such as zeolites. This technique, however, can be used only if crystals larger than several micrometres are available. Powder X-ray diffraction (PXRD) is an alternative technique to determine the structures if only small crystals are available. However, peak overlap, poor crystallinity and the presence of impurities hinder the solution of structures from PXRD data. Electron crystallography can overcome these problems. We have developed a new method, which we have called “rotation electron diffraction” (RED), for the automated collection and processing of three-dimensional electron diffraction data. This thesis describes how the RED method has been applied to determine the structures of several zeolites and zeolite-related materials. These include two interlayer expanded silicates (COE-3 and COE-4), a new layered zeolitic fluoroaluminophosphate (EMM-9), a new borosilicate (EMM-26), and an aluminosilicate (ZSM-25). We have developed a new approach based on strong reflections, and used it to determine the structure of ZSM-25, and to predict the structures of a series of complex zeolites in the RHO family. We propose a new structural principle that describes a series of structurally related zeolites known as “embedded isoreticular zeolite structures”, which have expanding unit cells. The thesis also summarizes several common structural features of zeolites in the Database of Zeolite Structures.

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Manuscript. Paper 3: Manuscript.

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Strusevich, Dmitry. "Development of in-situ synchrotron X-ray powder diffraction techniques for studies of catalytic systems." Thesis, Birkbeck (University of London), 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.497909.

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Smith, Elaine D. L. "Combined molecular modelling and powder X-ray diffraction for crystal structure solution of organic materials." Thesis, Heriot-Watt University, 2004. http://hdl.handle.net/10399/249.

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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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Hernandez, Antonio. "Ultrafast Soft Mode Dynamics in Ferroelectrics studied with Femtosecond X-Ray Diffraction." Doctoral thesis, Humboldt-Universität zu Berlin, 2020. http://dx.doi.org/10.18452/21041.

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Ferroelektrische Materialien sind ein Schlüsselbereich der aktuellen Forschung und weisen zahlreiche wichtige technologische Anwendungen auf. Diese Klasse kristalliner Feststoffe zeichnet sich üblicherweise durch eine Vielzahl von para- und ferroelektrischen Phasen auf. Letztere sind dadurch charakterisiert, dass sie auch in Abwesenheit eines äußeren Feldes eine spontane elektrische Polarisation aufweisen. Diese Eigenschaft hat ihren Ursprung in der besonderen elektronischen Struktur ferroelektrischer Materialien, die sich aus einer großen Vielfalt von Gittergeometrien und mikroskopischen Ladungsdichteverteilungen ergibt. Auf atomarer Ebene sind die komplexen Eigenschaften der Ferroelektrika bis jetzt jedoch nur teilweise verstanden. Insbesondere die Verbindung zwischen mikroskopischen elektronischen Ladungsverteilungen und der daraus resultierenden makroskopischen elektrischen Polarisation wirft eine entscheidende, momentan noch offene Frage auf. Die Ladungsdynamik und ihr Zusammenspiel mit Gitteranregungen, insbesondere Softmoden, sind auf atomaren Längen- und Zeitskalen ungelöst. In dieser Arbeit wird das Potenzial der Femtosekunden-Röntgenpulverbeugung aufgezeigt, diese Frage zu adressieren. Diese Methode ermöglicht im Rahmen dieser Arbeit die Bestimmung transienter elektronischer Ladungsdichtekarten für das prototypische ferroelektrische Ammoniumsulfat direkt unterhalb seiner Curie-Temperatur nach einer optischen Anregung. Die Analyse der experimentellen Daten deckte eine bislang unbekannte niederfrequente Gitteroszillation mit einer Periode von 3 ps und nukleare Verschiebungen im Sub-Picometer-Bereich auf, die Ladungsverschiebungen auf einer 100-pm-Längenskala induzieren. Dies sind klare Merkmale, die auf die Anregung einer Softmode hinweisen. Schließlich wird zum ersten Mal die Dynamik der makroskopischen Polarisationsänderung abgeleitet, die eine oszillatorische Umkehr der Polarität aufweist und für ultraschnelle Schaltanwendungen geeignet ist.
Ferroelectrics are an area of current research, with important technological applications such as ferroelectric random access memories, infrared cameras or medical ultrasound equipment. This class of crystalline solids do not commonly only exhibit a ferroelectric phase, but rather go through an abundant variety of para- and ferroelectric phases that depend on the temperature. The ferroelectric phases present a spontaneous electric polarization even in the absence of an external field, in contrast to paraelectric phases and also exhibit a hysteresis loop in analogy to ferromagnets. This macroscopic feature has its origin in their peculiar electronic structure, which results from a rich diversity of lattice geometries and complex microscopic charge distributions. At the atomic level, however, the intricate characteristics of ferroelectrics are only partially understood. The link between microscopic charge distributions and macroscopic electric polarization poses a crucial question to be solved. The interplay of charge dynamics and lattice excitations are still unresolved on atomic length and time scales. In this thesis, femtosecond X-Ray powder diffraction is used to find solutions for these unanswered questions. This method allows for the experimental determination of time-resolved charge density maps from where the structural, charge and polarization dynamics are can be derived. These maps are determined for the photoexcited ferroelectric ammonium sulphate just below its Curie temperature. Data analysis has revealed a newly discovered low frequency lattice oscillation with a 3ps period and sub-picometer nuclear displacements that is related to periodic charge relocations on a 100pm length scale, which is a feature indicative of soft mode behavior. Finally, the dynamics of the variation of polarization are derived for the first time, showing an oscillatory reversal of polarity that holds potential for ultrafast switching applications.

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Hou, Weimin. "A novel method for the determination of single crystal elastic constants using powder X-ray diffraction." Thesis, University of Ottawa (Canada), 2002. http://hdl.handle.net/10393/6338.

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The elastic properties of a material have long been a subject of interest in materials science and physics. Especially, a complete determination of the single crystal compliance and stiffness tensor is of great importance, as the single crystal elastic tensor provides a complete description of the elastic properties of a material. There are numerous materials that are only available in polycrystalline form. Many of these polycrystalline materials are of great interest, such as the polycrystalline materials synthesized under high pressure conditions, for which the elastic properties under high pressure conditions are particularly important. However, traditional methods to measure the elastic constants apply only to single crystals. Recently, Singh and co-workers have developed a method, using energy dispersive X-ray diffraction to measure the single crystal elastic constants of a material at elevated pressures, which, for the first time, enabled the single crystal elastic tensors of numerous polycrystalline samples to be determined. Inspired by the energy dispersive X-ray diffraction method, we have undertaken to develop a novel method, using angle dispersive X-ray diffraction techniques combined with a two-dimensional X-ray recording area detector, to measure the single crystal elastic constants of powder samples. We have obtained important results that will enable the single crystal elastic constants of concerned material to be determined from Debye rings recorded on the X-ray recording image plate. In comparison to the energy dispersive X-ray diffraction method, the angle dispersive X-ray diffraction method offers advantages, as we will demonstrate.

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Soleilhavoup, Anne. "Structural studies on functional materials using solid-state NMR, powder X-ray diffraction and DFT calculations." Thesis, Durham University, 2009. http://etheses.dur.ac.uk/8/.

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Analytical and theoretical techniques were used in this work for structural studies of framework materials. One and two dimensional 31P and 17O solid state NMR experiments highlight subtle thermally induced structural changes in (MoO2)2P2O7 pyrophosphate, tungsten trioxide WO3 and negative thermal expansion ZrW2O8. DFT methods using CASTEP software to calculate 31P and 17O NMR parameters are performed on these structures and discussed in comparison to experimental results, published structures and thermal mechanisms.

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Stoner, Troy A. "Preparation of Extinction Free Gamma Ti-51at.%Al Alloy Powder and Characterization by X-ray Diffraction." Thesis, Monterey, California. Naval Postgraduate School, 1992. http://hdl.handle.net/10945/27221.

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The lattice parameters, structure factors, and Debye-Waller temperature factor of a homogenized, binary Ti-51at.%Al intermetallic alloy were determined using powder X-ray diffraction (XRD). Previous studies have been hampered by extinction at low Bragg angles, therefore improved powdering methods were implemented. The powder was produced by pulverizing lathe turnings taken from the sample ingot using a ceramic mortar and pestle. then the powder was passed through a U.S. Standard 400 sieve mesh (38 microns). After further grinding a new acoustical sieving procedure was performed where powder particles were passed through a 2000 line per inch sieve mesh (5-7 microns). Next the powder was annealed to relieve induced stress produced during grinding. An X-ray diffraction study was conducted for Bragg angles 10-140 deg. The L1 structured TiAl lattice parameters of a =4.002 and c=4.081 were determined using XRD peak positions. the resulting c/a ratio equalled 1.02. The measured integrated intensities of the fundamental reflections were used to determine a Debye-Waller temperature factor of B=0.65 using the Wilson method. these values were determined to be accurate based on comparison to previous research and theoretical approximations. The effects of extinction at low angles were not completely avoided with the refined powder particle size however, they were significantly reduced

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Dall'Olio, Laura <1991&gt. "Survey of methodologies of pharmaceutical interest for quantification of crystal form via X-Ray Powder Diffraction." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2021. http://amsdottorato.unibo.it/9769/1/Dall%27Olio_Laura_Tesi.pdf.

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The interest on polymorphism of arises from their different properties. A strategy to improve the properties of compound, is the formation of cocrystal. In this PhD project, cocrystal statistical analysis and experimental screening of allantoin and some coformers were performed. No cocrystal was obtained, experimental results disagree with the statistical analysis. Quantitative method of crystalline forms via X-Ray Powder Diffraction are extremely interesting for pharmaceutical companies. In the thesis real cases with different approaches of quantitative analysis are reported. I presented the quantification of paracetamol form II impurity in Tachifludec containing paracetamol form I using univariate method in which the main issue is the identification of a specific peak. The presence of several peaks in the formulation was overcome by applying the standard addition method spiking the formulation with form II. Univariate and multivariate method NAS were compared, and the best results were obtained with the application of the multivariate method. These approaches were also evaluated in the case of mixture amorphous-crystalline. Furthermore, it was studied the potential use of stable amorphous surrogate instead to the unstable real amorphous. Even in these cases, multivariate method achieved the best results. The novel quantification method Direct derivation (DD) based on intensity–composition equation was applied to determine crystallinity of mixture amorphous-crystalline. The quantification method was evaluated in three scenarios: method a) with unit cell parameters, method b) structural information is unknown, and method c) only the mixtures’ patterns are available. Method a and b achieved more accurate results because of better description of the crystalline phase. Method b was evaluated in sample covered by containment system as the Kapton® film to evaluate the analysis of highly potent compounds. The DD method has been revealed the best method to estimate the crystallinity degree of formulation containing highly potent compound deposited on catheter balloon.

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Tsuboi, Chiaki. "X-ray crystal structure analyses of magnetically oriented microcrystalline suspensions." Kyoto University, 2016. http://hdl.handle.net/2433/216190.

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Kyoto University (京都大学)
0048
新制・課程博士
博士(農学)
甲第19936号
農博第2186号
新制||農||1044(附属図書館)
学位論文||H28||N5009(農学部図書室)
33022
京都大学大学院農学研究科森林科学専攻
(主査)教授木村恒久, 教授西尾嘉之, 教授髙野俊幸
学位規則第4条第1項該当

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35

Vella-Zarb, Liana. "The complementary use of theoretical structure prediction and X-ray powder diffraction data in crystal structure determination." Thesis, University of Birmingham, 2009. http://etheses.bham.ac.uk//id/eprint/504/.

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The successful prediction of the crystal structure and symmetry of a material can give valuable insight into many of its properties, as well as the feasibility of thermodynamically stable poly-morphs to exist. It is not uncommon, however, for numerous theoretical structures to be found within a narrow energy range, making absolute characterisation of the crystal structure impossi-ble. The aim of this project was to investigate a number of structures from this scenario, high-lighting the key differences between three potential methods for the automated comparison of predicted and experimental crystal structures. This work was carried out by comparing the simulated powder diffraction patterns of theoretical predicted crystal structures of small organic materials with their experimental powder diffraction patterns, so that the experimentally identified structure could be automatically singled out from the many calculated. The use of traditional agreement factors (eg. Rwp) was compared with more sophisticated approaches namely PolySNAP, which uses principal-component analysis, and Compare.x, an algorithm based on weighted cross-correlation. Five structures were analysed, two of which had not been previously characterised. As the structure prediction calculations are carried out at 0K, and experimental data were collected over a range of temperatures (10K-293K), the effect of the resulting variations in lattice parameters on the automated processes is discussed. In all cases, Rwp has proven to be a poor and unreliable discriminator in the comparison of pre-dicted and experimental structures. The more contemporary methods based on PolySNAP and Compare.x both gave encouraging results when used to study the three known structures imida-zole, chlorothalonil and 5-azauracil, and they have consequently been used in the successful so-lution of the two previously unknown structures adenine and guanine. A difference in sensitivity in the matching of data collected at different temperatures between the latter approaches was noted. It was found that although there is considerable overlap between the two methods, they are not absolutely interchangeable, and this distinction may be exploited in future work where more case-specific comparisons are carried out. Automated comparison techniques cannot yet replace visual comparison completely, but they reduce it drastically. Ultimately, comparisons made computationally serve as a complement to human judgement, but they may not yet elimi-nate it.

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Beyerlein, Kenneth Roy. "Simulation and modeling of the powder diffraction pattern from nanoparticles: studying the influence of surface strain." Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/41211.

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Accurate statistical characterization of nanomaterials is crucial for their use in emerging technologies. This work investigates how different structural characteristics of metal nanoparticles influence the line profiles of the corresponding powder diffraction pattern. The effects of crystallite size, shape, lattice dynamics, and surface strain are all systematically studied in terms of their impact on the line profiles. The studied patterns are simulated from atomistic models of nanoparticles via the Debye function. This approach allows for the existing theories of diffraction to be tested, and extended, in an effort to improve the characterization of small crystallites. It also begins to allow for the incorporation of atomistic simulations into the field of diffraction. Molecular dynamics simulations are shown to be effective in generating realistic structural models and dynamics of an atomic system, and are then used to study the observed features in the powder diffraction pattern. Furthermore, the characterization of a sample of shape controlled Pt nanoparticles is carried out through the use of a developed Debye function analysis routine in an effort to determine the predominant particle shape. The results of this modeling are shown to be in good agreement with complementary characterization methods, like transmission electron microscopy and cyclic voltammetry.

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Krogh, Andersen Anne. "Studies of Inorganic Layer and Framework Structures Using Time-, Temperature- and Pressure-Resolved Powder Diffraction Techniques." Doctoral thesis, Stockholm University, Department of Physical, Inorganic and Structural Chemistry, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-23.

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This thesis is concerned with in-situ time-, temperature- and pressure-resolved synchrotron X-ray powder diffraction investigations of a variety of inorganic compounds with twodimensional layer structures and three-dimensional framework structures. In particular, phase stability, reaction kinetics, thermal expansion and compressibility at non-ambient conditions has been studied for 1) Phosphates with composition MIV(HPO₄)₂·nH₂O (MIV = Ti, Zr); 2) Pyrophosphates and pyrovanadates with composition MIVX₂O₇(MIV = Ti, Zr and X = P, V); 3) Molybdates with composition ZrMo₂O₈. The results are compiled in seven published papers and two manuscripts.

Reaction kinetics for the hydrothermal synthesis of α-Ti(HPO₄)₂·H₂O and intercalation of alkane diamines in α-Zr(HPO₄)₂·H₂O was studied using time-resolved experiments. In the high-temperature transformation of γ-Ti(PO₄)(H₂PO₄)·2H₂O to TiP₂O₇ three intermediate phases, γ'-Ti(PO₄)(H₂PO₄)·(2-x)H₂O, β-Ti(PO₄)(H₂PO₄) and Ti(PO₄)(H₂P₂O₇)_0.5 were found to crystallise at 323, 373 and 748 K, respectively. A new tetragonal three-dimensional phosphate phase called τ-Zr(HPO₄)₂ was prepared, and subsequently its structure was determined and refined using the Rietveld method. In the high-temperature transformation from τ-Zr(HPO₄)₂ to cubic α-ZrP₂O₇two new orthorhombic intermediate phases were found. The first intermediate phase, ρ-Zr(HPO₄)₂, forms at 598 K, and the second phase, β-ZrP₂O₇, at 688 K. Their respective structures were solved using direct methods and refined using the Rietveld method. In-situ high-pressure studies of τ-Zr(HPO₄)₂revealed two new phases, tetragonal ν-Zr(HPO₄)₂and orthorhombic ω-Zr(HPO₄)₂ that crystallise at 1.1 and 8.2 GPa. The structure of ν-Zr(HPO₄)₂ was solved and refined using the Rietveld method.

The high-pressure properties of the pyrophosphates ZrP₂O₇ and TiP₂O₇, and the pyrovanadate ZrV₂O₇were studied up to 40 GPa. Both pyrophosphates display smooth compression up to the highest pressures, while ZrV₂O₇ has a phase transformation at 1.38 GPa from cubic to pseudo-tetragonal β-ZrV₂O₇ and becomes X-ray amorphous at pressures above 4 GPa.

In-situ high-pressure studies of trigonal α-ZrMo₂O₈ revealed the existence of two new phases, monoclinic δ-ZrMo₂O₈and triclinic ε-ZrMo₂O₈ that crystallises at 1.1 and 2.5 GPa, respectively. The structure of δ-ZrMo₂O₈was solved by direct methods and refined using the Rietveld method.

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Chen, Hong. "Open-framework Structures Built by Inorganic Clusters : Synthesis and Characterization." Doctoral thesis, Stockholms universitet, Institutionen för material- och miljökemi (MMK), 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-106853.

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Novel open-framework germanates and vanadoborates, which are constructed from typical types of clusters, have been synthesized based on different strategies. The crystal structures are solved by using single crystal X-ray diffraction (SXRD) technique or by combined techniques. Additionally, the structures of two open-framework materials, PKU-3 and PKU-16, are determined from nano-sized crystals by rotation electron diffraction (RED) combined with powder X-ray diffraction (PXRD). This thesis serves as an introduction to synthesis of open-framework germanates and vanadoborates based on different design strategies. Two germanates are obtained; SU-74 is achieved by employing a novel structure directing agent (SDA), SUT-8 is achieved by assembling the novel structure building units (SBUs) of Co@Ge14 with the introduction of cobalt ions in the synthesis. Four strategies are successfully used in construction of open-framework vanadoborates: using metal-oxo polyhedra as the linkages in SUT-6; applying the scale chemistry approach in SUT-7; employing metal-organic complexes as the linkages in SUT-12, SUT-13, SUT-14; and introducing covalent bond organic linkages into SUT-10 and SUT-11. Single crystal X-ray diffraction is used to conduct the structure determination in combination with other techniques. Furthermore, the structures of two open-framework materials, an aluminoborate PKU-3 and a germanosilicate PKU-16, are solved from nano-sized crystals using RED data. The structures are further confirmed by Rietveld refinement against PXRD data. The advantages of the RED techniques are demonstrated in two aspects. In PKU-3, the presence of seriously preferred orientation and light elements in the structure makes it difficult for structure determination by PXRD, but it is easier by RED. In PKU-16, the RED technique is used to determine its structure from the as-synthesized multi-phasic sample containing nano-sized crystals. After the structure of PKU-16 has been solved, the synthesis of this interesting phase can be optimized and pure PKU-16 can be obtained. Keywords: Open-framework, germanates, vanadoborates, aluminoborates, germanosilicates, crystal structure, hydrothermal synthesis, single crystal X-ray diffraction, rotation electron diffraction, powder X-ray diffraction

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Runcevski, Tomce [Verfasser], and Robert E. [Akademischer Betreuer] Dinnebier. "Application of in situ X-ray powder diffraction in solid state processes visualization / Tomce Runcevski. Betreuer: Robert E. Dinnebier." Stuttgart : Universitätsbibliothek der Universität Stuttgart, 2015. http://d-nb.info/1067843868/34.

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40

OLIVEIRA, TEREZINHA FERREIRA DE. "ANALYSIS OF THE UNCERTAINTIES OF THE QUANTITATIVE PHASE ANALYSIS BY X-RAY POWDER DIFFRACTION BASED ON THE RIETVELD METHOD." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2005. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=6377@1.

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COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR
UNIVERSIDADE FEDERAL DA BAHIA
A análise de sistemas de medição consiste do exame da adequação do sistema quanto ao operador, ao instrumento e a outras fontes de variação, bem como da comparação da variância do erro de medição com a variância natural do processo. Nesse aspecto, esta pesquisa teve por objetivo a análise das incertezas da quantificação de fase pelo método de Rietveld em análise de pó. Os efeitos de vários fatores na quantificação de fase foram avaliados utilizando técnicas estatísticas de planejamento experimental e de análise multivariada, com a utilização de materiais de alto nível de rastreabilidade na realização dos experimentos, no Laboratório de difração de raios X do Departamento de Ciências de Materiais e Metalurgia da PUC-Rio. Através da determinação do construto de variação do processo, constatou-se que a quantificação das fases analisadas sofre influência das condições de medição de forma diferenciada de material para material, impossibilitando a obtenção de uma fórmula geral para cálculo dos erros de quantificação, embora os erros possam ser determinados por uma análise de repetitividade e reprodutibilidade apropriadamente conduzida.
The analysis of measurement systems is done by the examination of the adequacy of the system according to the operator, the instrument and other sources of variability, as well as by the comparison of the measurement error variance with the natural process variance. This research consisted in the evaluation of the uncertainties of phase quantification in powder analysis by the Rietveld method. The evaluation of the effects of several factors on the phase quantification was performed using statistical techniques of design of experiments and of multivariate analysis, with the use of materials of high level of traceability for the conduction of the experiments, in the Laboratory of X-ray Diffraction of the Pontifícia Universidade Católica do Rio de Janeiro. Through the determination of the variational structure of the process it was verified that the analyzed phases suffer influence of the measurement conditions in a differentiated way, which prevents the obtention of a general formula for calculation of the quantification error, although the errors can be determined by a repeatability and reproducibility analysis properly conducted.

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Bhange, D. S. "Structural studies of silicalite and metallosilicate molecular sieves of MFI type using non-ambient powder x-ray diffraction technique." Thesis(Ph.D.), CSIR-National Chemical Laboratory, Pune, 2008. http://dspace.ncl.res.in:8080/xmlui/handle/20.500.12252/2648.

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42

Rajiv, Paneerselvam [Verfasser], and Manfred [Akademischer Betreuer] Joswig. "Automated parametric Rietveld refinement and its application to two dimensional X-ray powder diffraction experiments / Rajiv Paneerselvam. Betreuer: Manfred Joswig." Stuttgart : Universitätsbibliothek der Universität Stuttgart, 2011. http://d-nb.info/1016874731/34.

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43

Barnes, Paris W. "Exploring structural changes and distortions in quaternary perovskites and defect pyrochlores using powder diffraction techniques." Columbus, Ohio : Ohio State University, 2003. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1064346592.

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Thesis (Ph. D.)--Ohio State University, 2003.
Title from first page of PDF file. Document formatted into pages; contains xxvi, 255 p.; also includes graphics. Includes abstract and vita. Advisor: Patrick M. Woodward, Dept. of Chemistry. Includes bibliographical references (p. 221-228).

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Coduri, M. "LOCAL DISORDER IN DOPED CERIA: A CRYSTALLOGRAPHIC STUDY." Doctoral thesis, Università degli Studi di Milano, 2013. http://hdl.handle.net/2434/215536.

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In recent years, doped ceria compounds have attracted increasing attention as electrolytes for application in Solid Oxide Fuel Cell devices, thanks to their high performance at intermediate temperature. In cerium oxide, ionic conductivity is driven by the presence of oxygen vacancies, introduced for charge balance after doping with a lower valent cation. With increasing doping concentration the oxygen diffusion is impeded, probably because of the formation of aggregates that trap oxygen vacancies. Their nature is though still under debate. Owing to the close interplay between transport properties and local structure, an accurate description of the defects on the atomic scale is of the utmost importance for understanding the mechanisms at work in doped ceria. In this study we propose to unveil the complex disorder in doped ceria with a combined powder diffraction study. On the one hand, X-ray and Neutron powder diffraction are joint to couple their potentialities; on the other hand, two different crystallographic approaches are exploited. The conventional crystallographic methods allow to study the long range structure modifications that occur with doping. The Pair Distribution Function is instead employed to study the local structure, in terms of deviations from the long range atomic ordering. The goal of the thesis is to provide a crystallographic description of the atomic rearrangements induced by doping, looking for a relationship between the local structure and the transport properties.

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45

Santarelli, Xenja. "Development of capabilities for "in situ" analysis of nanoparticles at the MCX powder diffraction beamline." Doctoral thesis, Università degli studi di Trieste, 2011. http://hdl.handle.net/10077/4479.

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2009/2010
Riassunto Presso la linea di diffrazione MCX (Material Characterization by X-ray diffraction) del Sincrotrone di Trieste e' stata messa a punto una stazione sperimentale che consente di eseguire analisi "in situ" di nanostrutture. Il sistema e' indipendente dal diffrattometro e consente di ottenere in tempi ridotti (grazie all’uso di un Imaging Plate come detector) pattern di diffrazione da polveri o film sottili. La stazione sperimentale e’ dotata di un forno che puo’ riscaldare i campioni fino a 1000ºC. Inoltre e' stato implementato un sistema che consente il flusso di gas attraverso i campioni (contenuti in capillari di vetro o quarzo). L'interfacciamento e' stato realizzato attraverso il software Labview. La struttura e’ stata collocata su un tavolo mobile per agevolarne lo spostamento nell'hutch solo quando necessario. Nel 2009 e' stata accolta l’utenza che ha portato a termine le prime misure. Sono previste le necessarie modifiche che daranno la possibilita' di usare la stazione anche per misure SAXS e di reazioni catalitiche. Abstract An Experimental Station has been set up at the MCX (Material Characterization by X-ray diffraction) beamline at the Italian National Synchrotron Radiation facility ELETTRA (Trieste, Italy). The main goal of the system is the possibility to perform “in situ” analysis of nanostructures. This new capability is independent of the diffractometer (an Imaging Plate has been chosen as a detector) and allows to reduce the required times to obtain diffraction patterns from powder samples and thin films. The Experimental Station is equipped with a furnace that heats the samples till 1000ºC, while the implementation of a gas line allows to flow gases through the samples (placed in glass or quartz capillaries). A Labview program has been developed to control the system. The system is located on a wheeled table, so it can be easily moved inside and outside the hutch only when necessary. In 2009, the first users performed their experiments by using this experimental station. Some developments are planned to allow both Small Angle X-ray Scattering (SAXS) experiments and to follow sample behaviour during catalytic reactions.
XXIII Ciclo
1975

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46

Swann, Nichola Jean. "Time-resolved studies of the crystallisation and dehydration of lactose and other hydrates using synchrotron X-ray and neutron powder diffraction techniques." Thesis, Keele University, 2015. http://eprints.keele.ac.uk/4216/.

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In-situ time-resolved synchrotron X-ray and neutron powder diffraction techniques have been applied to the study of solid state structural transitions within the organic polymorphic molecular systems of lactose, trehalose and theophylline. Diffraction techniques offer an unequalled method of polymorph identification and quantification, and have repeatedly demonstrated throughout this work that they can be utilised to follow and kinetically evaluate structural transitions in real time. The study of lactose crystallisation provides further proof of the transient ( lo::1/3) mixed crystal polymorph as the initial crystallisation product, which is then followed by the typical beta lactose and alpha lactose monohydrate phases. The formation of the (lo:: l,B) mixed crystal form has been mapped and kinetically analysed; the complex multi-step crystallisation behaviour is likely to result from the high degree of polymorphism which is displayed within the lactose system. The dehydration studies of the three systems show that dehydration kinetics can vary as a function of processing conditions and environments. Evidence of a previously undocumeuted theophylline polymorph has been observed which is accessible via the seeded dehydration of theophylline monohydrate with anhydrous theophylline form II. The best production of beta lactose from the 1-biannual dehydration of alpha lactose monohydrate to date is documented and is attained from dehydration within a hydrophobic cocoa butter environment; this transition is mediated via a crystalline phase whose identity is uncertain, yet displays a unique Bragg peak at rv 12.87° 20. Neutron diffraction techniques reveal that the water content and crystalline weight fraction of trehalose dihydrate are decoupled quantities, and the dihydrate lattice can sustain substantial water loss. These observations provide supporting evidence of a transiently stable, partially hydrated state of trehalose. In addition, the applicability of the Dl9 single-crystal diffraction beamline at the Institut Laue-Langevin in the study of hydrated powder samples is reported, demonstrating the versatility of the instrument with the capability of performing dynamic studies with a time-resolution of 15 s.

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Konar, Sumit. "Structure and Phase Stability of CaC2 Polymorphs, Li2C2 and Lithium Intercalated Graphite : A Revisit with High Pressure Experiments and Metal Hydride–Graphite Reactions." Doctoral thesis, Stockholms universitet, Institutionen för material- och miljökemi (MMK), 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-120109.

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Alkali (A) and alkaline earth (AE) metals can form carbides and intercalated graphites with carbon. The carbides mostly represent acetylides which are salt-like compounds composed of C22− dumbbell anions and metal cations. Both the acetylide carbides and intercalated graphites are technologically important. Superconductivity has been observed in several intercalated graphites such as KC8 and CaC6. Li intercalated graphites are a major ingredient in Li ion batteries. CaC2 is an important commodity for producing acetylene and the fertilizer CaCN2. In spite of the extensive research on A–C and AE–C compounds, phase diagrams are largely unknown. The thermodynamic and kinetic properties of both carbides and intercalalated graphites are discussed controversially. Recent computational studies indicated that well-known carbides, like CaC2 and BaC2, are thermodynamically unstable. Additionally, computational studies predicted that acetylide carbides will generally form novel polymeric carbides (polycarbides) at high pressures. This thesis is intended to check the validity of theoretical predictions and to shed light on the complicated phase diagrams of the Li–C and the Ca–C systems. The Li–C and the Ca–C systems were investigated using well-controllable metal hydride–graphite reactions. Concerning the Li–C system, relative stabilities of the metastable lithium graphite intercalation compounds (Li-GICs) of stages I, IIa, IIb, III, IV and Id were studied close to the competing formation of the thermodynamically stable Li2C2. The stage IIa showed distinguished thermal stability. The phase Id showed thermodynamic stability and hence, was included in the Li–C phase diagram. In the Ca–C system, results from CaH2–graphite reactions indicate compositional variations between polymorphs I, II and III. The formation of CaC2 I was favored only at 1100 ◦C or higher temperature and with excess calcium, which speculates phase I as carbon deficient CaC2−δ . To explore the potential existence of polycarbides, the acetylide carbides Li2C2 and CaC2 were investigated under various pressure and temperature conditions, employing diamond anvil cells for in situ studies and multi anvil techniques for large volume synthesis. The products were characterized by a combination of diffraction and spectroscopy techniques. For both Li2C2 and CaC2, a pressure induced structural transformation was observed at relatively low pressures (10–15 GPa), which was followed by an irreversible amorphization at higher pressures (25–30 GPa). For Li2C2 the structure of the high pressure phase prior to amorphization could be elucidated. The ground state with an antifluorite Immm structure (coordination number (CN) for C22− dumbbells = 8) transforms to a phase with an anticotunnite Pnma structure (CN for C22− dumbbells = 9). Polycarbides, as predicted from theory, could not be obtained.

At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 2: Manuscript.

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48

Germann, Luzia S. [Verfasser], and Robert E. [Akademischer Betreuer] Dinnebier. "Investigation of solid state reactions of molecular functional materials by in situ X-ray powder diffraction / Luzia S. Germann ; Betreuer: Robert E. Dinnebier." Stuttgart : Universitätsbibliothek der Universität Stuttgart, 2018. http://d-nb.info/1194373089/34.

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49

Husband, Rachel Jane. "Structural studies of mid-Z lanthanide elements at high pressure." Thesis, University of Edinburgh, 2015. http://hdl.handle.net/1842/28703.

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The majority of the metallic elements adopt simple, high-symmetry structures at ambient pressure. These consist of a highly-ordered arrangement of atoms, which can be described by a crystal lattice that is periodic in three dimensions. It may be expected that close-packed structures, such as face-centred cubic (fcc) and hexagonal close-packed (hcp), would be favoured at high pressures due to the increase in density. However, many of these elements transform to lowsymmetry, complex structures on compression. In particular, a number have been observed to adopt incommensurately-modulated structures at high pressure. In these structures, atoms are displaced from their average positions by a modulation wave, the wavelength of which is an irrational multiple of the lattice periodicity. Diamond-anvil cells (DACs) can be used to compress materials to over a million times atmospheric pressure. In these devices, a small sample is compressed between the tips of two diamond anvils. The atomic arrangement of materials at extreme pressures can then be probed using the intense x-ray beams provided by synchrotron sources. In this work, the high-pressure crystal structures of the lanthanide elements europium (Eu) and samarium (Sm) have been investigated using angle-dispersive x-ray powder dffraction techniques. The high-pressure structural behaviour of Eu has been found to be remarkably different from that of the other lanthanide elements. Two new high-pressure phases of Eu are reported, both of which have an incommensurately-modulated crystal structure.

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50

ARDIT, Matteo. "Lattice relaxation in solid solutions: long-range vs. short-range structure around Cr3+ and Co2+ in oxides and silicates." Doctoral thesis, Università degli studi di Ferrara, 2012. http://hdl.handle.net/11392/2389265.

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This dissertation reports the results derived from the 3-year doctoral thesis project aimed at exploring some oxide and silicate structures as promising ceramic pigments with enhanced colorimetric properties with respect to the traditional colorants. Solid solutions of perovskite, alumoniobite, and melilite compounds were obtained by doping octahedral and tetrahedral coordination sites with transition metal ions (e.g. Cr3+, Co2+, and Zn2) through a solid-state synthesis performed by means of an industrial-like process. The analytical techniques adopted to investigate the synthesized compounds allowed the determination of the "averaged" crystal structure, or the so termed long-range properties, and the short-range properties (i.e. the local structure around the substituting ions) through X-ray powder diffraction and electron absorption spectroscopy (EAS), respectively. As stated by Geiger (2001) "an understanding of the microscopic, mesoscopic and macroscopic properties and of the behaviour of solid solutions under different conditions is a challenge for all disciplines concerned with the solid state". As a matter of fact, the precise determination of a structure around impurities results fundamental to provide detailed information on their incorporation and on physical properties. For instance, in the case of the solid solutions here reported, the lattice incorporation of transition metal ions as impurities is the cause of their gradual coloration. Most of the times, such a coloration is more intense as greater is the impurity amount. The final goal of this work, was attained by calculating the structural relaxation coefficient for each studied solid solution by combining the mean with the local bond distances achieved by XRPD and EAS, respectively.

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