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Diffraction Profiles (diffraction + profile)
Kinds of Diffraction Profiles Selected AbstractsMicrostrain and grain-size analysis from diffraction peak width and graphical derivation of high-pressure thermomechanicsJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 6 2008Yusheng Zhao An analytical method is presented for deriving the thermomechanical properties of polycrystalline materials under high-pressure (P) and high-temperature (T) conditions. This method deals with non-uniform stress among heterogeneous crystal grains and surface strain in nanocrystalline materials by examining peak-width variation under different P,T conditions. Because the method deals directly with lattice d spacing and local deformation caused by stress, it can be applied to process any diffraction profile, independent of detection mode. In addition, a correction routine is developed using diffraction elastic ratios to deal with severe surface strain and/or strain anisotropy effects related to nano-scale grain sizes, so that significant data scatter can be reduced in a physically meaningful way. Graphical illustration of the resultant microstrain analysis can identify micro/local yields at the grain-to-grain interactions resulting from high stress concentration, and macro/bulk yield of the plastic deformation over the entire sample. This simple and straightforward approach is capable of revealing the corresponding micro and/or macro yield stresses, grain crushing or growth, work hardening or softening, and thermal relaxation under high- P,T conditions, as well as the intrinsic residual strain and/or surface strain in the polycrystalline bulk. In addition, this approach allows the instrumental contribution to be illustrated and subtracted in a straightforward manner, thus avoiding the potential complexities and errors resulting from instrument correction. Applications of the method are demonstrated by studies of ,-SiC (6H, moissanite) and of micro- and nanocrystalline nickel by synchrotron X-ray and time-of-flight neutron diffraction. [source] An in situ method for the study of strain broadening using synchrotron X-ray diffractionJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 4 2007C. C. Tang A tensonometer for stretching metal foils has been constructed for the study of strain broadening in X-ray diffraction line profiles. This device, which is designed for use on powder diffractometers and was tested on Station 2.3 at Daresbury Laboratory, allows in situ measurements to be performed on samples under stress. It can be used for data collection in either transmission or reflection modes using either symmetric or asymmetric diffraction geometries. As a test case, measurements were carried out on an 18,µm-thick copper foil experiencing strain levels of up to 5% using both symmetric reflection and symmetric transmission diffraction. All the diffraction profiles displayed peak broadening and asymmetry which increased with strain. The measured profiles were analysed by the fundamental-parameters approach using the TOPAS peak-fitting software. All the observed broadened profiles were modelled by convoluting a refineable diffraction profile, representing the dislocation and crystallite size broadening, with a fixed instrumental profile predetermined using high-quality LaB6 reference powder. The deconvolution process yielded `pure' sample integral breadths and asymmetry results which displayed a strong dependence on applied strain and increased almost linearly with applied strain. Assuming crystallite size broadening in combination with dislocation broadening arising from f.c.c. a/2,110,{111} dislocations, the variation of mechanical property with strain has been extracted. The observation of both peak asymmetry and broadening has been interpreted as a manifestation of a cellular structure with cell walls and cell interiors possessing high and low dislocation densities. [source] Neutron Powder Diffraction Study of a Phase Transition in La0.68(Ti0.95Al0.05)O3JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 12 2006Roushown Ali Crystal structures and structural changes of the compound La0.68(Ti0.95Al0.05)O3 have been studied using neutron powder diffraction data and the Rietveld method in the temperature range from 25° to 592°C. The Rietveld profile-fitting analyses of the neutron data and the synchrotron diffraction profile revealed that the crystal symmetry of the low-temperature phase of La0.68(Ti0.95Al0.05)O3 is orthorhombic Cmmm (2ap× 2ap× 2ap; p: pseudo-cubic perovskite). The unit-cell and structural parameters were successfully refined with the orthorhombic Cmmm for the intensity data measured at 25°, 182°, and 286°C, and with the tetragonal P4/mmm (ap×ap× 2ap) for intensity data obtained at 388° and 592°C. The P4/mmm -to- Cmmm phase transition was found to be induced by tilting of the (TiAl)O6 octahedron. The tilt angle decreased with increasing temperature, reaching 0° at the Cmmm,P4/mmm transition temperature. [source] Structural anisotropy of InGaAs/GaAs(001) quantum dot chains structuresPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 8 2007V. P. Kladko Abstract We have studied the structural properties of ordered InGaAs/GaAs(001) quantum dot chains multilayer by high-resolution X-ray diffraction. Two systems of lateral satellites, one of which being inclined with respect to the sample surface normal, i.e. the growth direction [001], were observed. The measured inclination of 30.0° ± 2.5° does not affect the diffraction profile from planar superlattice (SL), i.e. SL peaks are not inclined with respect to the GaAs substrate peak. We identify the splitting of coherent SL satellites for all orders as well as for two perpendicular directions. This splitting most likely indicates that two discrete periods exist in SL structure. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Redetermination of the crystal structure of ,-copper phthalocyanine grown on KClACTA CRYSTALLOGRAPHICA SECTION B, Issue 3 2003Akitaka Hoshino The crystal structure of a polymorph of copper phthalocyanine (CuPc) grown on a KCl substrate is redetermined by transmission electron diffraction. It has a triclinic unit cell containing one molecule; the crystal does not have a herringbone-type molecular arrangement, which is a common packing mode of planar phthalocyanines. The molecular packing is determined by the diffraction intensity with the aid of the calculation of molecular packing energy. One of the striking features of this polymorph is its stacking mode within a molecular column: the molecular stacking direction projected on a molecular plane is different by an angle of about 45° from that of the ,-modifications of platinum phthalocyanine (PtPc) and metal-free phthalocyanine (H2Pc). A powder X-ray diffraction profile calculated for the polymorph agrees well with that of so-called ,-CuPc and Rietveld analysis for ,-CuPc indicates that the CuPc crystals grown on KCl are actually ,-CuPc; hence, ,-CuPc is not isostructural with either ,-PtPc or ,-H2Pc. On the basis of the present results and the reported crystal structures of the planar phthalocyanines that form molecular columns, the polymorphs of the phthalocyanines can be classified into four types distinguished by the molecular stacking mode within the column: ,(×)-, ,(+)-, ,(×)- and ,(+)-types. [source] Determination of lattice parameters and thermal expansion of CuGe2P3 + 0.2 Ge3P4 at elevated temperaturesCRYSTAL RESEARCH AND TECHNOLOGY, Issue 9 2006G. Bhikshamaiah Abstract CuGe2P3 is a p-type semiconductor with zincblende structure. Ge3P4 is soluble up to 35 mole% in CuGe2P3. Lattice parameters of CuGe2P3 + 0.2 Ge3P4 have been determined at elevated temperatures from room temperature to 873 K using the x-ray diffraction profiles (111), (200), (220), (311), (222), (400), (331), (420), (422) and (511) obtained from high temperature diffractometer. It is found that the lattice parameter increases linearly from 0.53856 nm at RT to 0.54025 nm at 873 K. The data on lattice parameter is used and coefficient of lattice thermal expansion of CuGe2P3 +0.2 Ge3P4 was determined at different temperatures. It is found that the coefficient of thermal expansion of CuGe2P3 +0.2 Ge3P4 is 5.48 x 10 -6 K -1 and is independent of temperature. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] An in situ method for the study of strain broadening using synchrotron X-ray diffractionJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 4 2007C. C. Tang A tensonometer for stretching metal foils has been constructed for the study of strain broadening in X-ray diffraction line profiles. This device, which is designed for use on powder diffractometers and was tested on Station 2.3 at Daresbury Laboratory, allows in situ measurements to be performed on samples under stress. It can be used for data collection in either transmission or reflection modes using either symmetric or asymmetric diffraction geometries. As a test case, measurements were carried out on an 18,µm-thick copper foil experiencing strain levels of up to 5% using both symmetric reflection and symmetric transmission diffraction. All the diffraction profiles displayed peak broadening and asymmetry which increased with strain. The measured profiles were analysed by the fundamental-parameters approach using the TOPAS peak-fitting software. All the observed broadened profiles were modelled by convoluting a refineable diffraction profile, representing the dislocation and crystallite size broadening, with a fixed instrumental profile predetermined using high-quality LaB6 reference powder. The deconvolution process yielded `pure' sample integral breadths and asymmetry results which displayed a strong dependence on applied strain and increased almost linearly with applied strain. Assuming crystallite size broadening in combination with dislocation broadening arising from f.c.c. a/2,110,{111} dislocations, the variation of mechanical property with strain has been extracted. The observation of both peak asymmetry and broadening has been interpreted as a manifestation of a cellular structure with cell walls and cell interiors possessing high and low dislocation densities. [source] Time-of-flight neutron powder diffraction with a thick-walled sample cellJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 3 2007M. P. Pitt The time-of-flight diffraction techniques that are normally practiced at pulsed neutron sources afford opportunities that are not readily available at continuous fixed-wavelength sources. The present work concerns the increasing trend in materials science to study samples in complex non-ambient environments, such as high gas pressure. Taking the example of a sample cell in which a material is studied under fluid pressure, the optimization of the cell design for best data collection rate is considered. The design of primary- and scattered-beam masks for eliminating background scattering from the sample cell and the correction of the data for cell and sample attenuation are addressed. The outputs of this work include a simple expression for the optimum wall thickness of a thick-walled sample cell, a procedure for accurately determining the required mask aperture width for any scattering angle, more compact expressions for some of the results of the work of Paalman & Pings [J. Appl. Phys. (1962), 33, 2635,2639] on absorption corrections, and guidance as to the correction of diffraction profiles for cell and background effects. Examples are given, drawn from studies of materials under hydrogen gas pressures up to 1800,bar in cells constructed from Ti2.1Zr and Inconel. [source] Visrock: a program for digital topography and X-ray microdiffraction imagingJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 3 2007Tilo Baumbach Visrock is a program for interactive analysis of sequences of digital X-ray images. Visrock was developed in the context of the rocking-curve imaging method of full-field X-ray microdiffraction imaging. Its functionality is based on parallel profile analysis of millions of local diffraction profiles. Options for subsequent visualization of the spatial distribution of extracted parameters include automatic contrast enhancement, noise reduction and multi-peak analysis. In addition to microdiffraction imaging, further useful applications of the program lie particularly in computed tomography, sequential radiography and analyser-based imaging. [source] Performance of a new furnace for high-resolution synchrotron powder diffraction up to 1900,K: application to determine electron density distribution of the cubic CaTiO3 perovskite at 1674,KJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 5 2004Masatomo Yashima Accurate crystal structure analysis at high temperatures is an important challenge in science and technology. A new electric furnace for the measurement of high-resolution (,d/d = 0.03%) synchrotron radiation powder diffraction profiles from materials at high temperatures (up to 1900,K in air) has been designed and fabricated. This furnace consists of a ceramic refractory with MoSi2 heaters, an aluminium body cooled by flowing water, and a sample stage with a spinner and a controller for sample-height adjustment. In situ synchrotron powder diffraction measurement for a calcium titanate perovskite specimen at 1674,K has been performed using the furnace at beamline 3A of the Photon Factory. The electron density distribution of the cubic perovskite at 1674,K was successfully obtained using a combination of Rietveld refinement, the maximum-entropy method (MEM) and MEM-based pattern-fitting techniques. The Ti atoms exhibit covalent bonding with the O atoms in the cubic CaTiO3 perovskite at this temperature, while the Ca atoms are ionic. These results indicate that the new furnace yields high-quality data for accurate crystal structure analysis. [source] Quantitative microstructural and texture characterization by X-ray diffraction of polycrystalline ferroelectric thin filmsJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 1 2004Jesús Ricote Texture becomes an important issue in ferroelectric materials as it greatly influences the physical properties of polycrystalline films. The use of advanced methods of analysis of the X-ray diffraction profiles, namely quantitative texture analysis or the recently developed combined approach, allows access to quantitative information on the different components of the global texture and to more accurate values of structural and microstructural parameters of both the ferroelectric film and the substrate, not available by more conventional methods of analysis. The results obtained allow important conclusions to be drawn regarding the mechanisms that lead to the development of preferred orientations in thin films and, also, the correlation between them and the ferroelectric behaviour. For example, it is observed that the inducement of a strong ,111, texture component does not mean the complete disappearance of the so-called `natural' ,100,, ,001, components, and that the ratio between the contributions to the global texture of these two components can be changed by the presence of tensile or compressive stress during crystallization of the films. The relative contributions of these texture components are also related to the final properties of the ferroelectric films. [source] Automated profile analysis for single-crystal diffraction dataJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 2 2003R. J. Angel An integration method for step-scanned single-crystal intensity data based upon fitting of the individual diffraction profiles by a pseudo-Voigt function is presented. Algorithms for both the recovery of weak intensities from data sets and the rejection of aberrant peak profiles are discussed. The ideas presented in this paper have been implemented in a software package for Microsoft Windows, WinIntegrStp, which is available at http://www.crystal.vt.edu/. [source] Measurement of the speed of X-raysJOURNAL OF SYNCHROTRON RADIATION, Issue 2 2002E. Zolotoyabko X-ray pulses from the Advanced Photon Source at Argonne National Laboratory were used to measure the speed of X-rays in the energy range between 21 and 60,keV. An LiNbO3 -based 0.58,GHz surface acoustic wave device served as a temporal analyzer in the stroboscopic time-resolved diffraction measurements. By synchronizing the surface acoustic wave excitation and periodic X-ray illumination of the LiNbO3 crystal, the temporal modifications in the LiNbO3 diffraction profiles could be followed and the time points of X-ray arrivals at the analyzer position for different analyzer to storage ring distances determined. The speed of the X-rays was determined as the ratio of measured spacings and corresponding delay time intervals. Within the experimental error bars, the obtained X-ray velocities converged to the tabulated constant for the speed of light in a vacuum. [source] A general approach for determining the diffraction contrast factor of straight-line dislocationsACTA CRYSTALLOGRAPHICA SECTION A, Issue 2 2009Jorge Martinez-Garcia Dislocations alter perfect crystalline order and produce anisotropic broadening of the X-ray diffraction profiles, which is described by the dislocation contrast factor. Owing to the lack of suitable mathematical tools to deal with dislocations in crystals of any symmetry, contrast factors are so far only known for a few slip systems in high-symmetry phases and little detail is given in the literature on the calculation procedure. In the present paper a general approach is presented for the calculation of contrast factors for any dislocation configuration and any lattice symmetry. The new procedure is illustrated with practical examples of hexagonal metals and some low-symmetry mineral phases. [source] Powder crystallography on macromoleculesACTA CRYSTALLOGRAPHICA SECTION A, Issue 1 2008I. Margiolaki Following the seminal work of Von Dreele, powder X-ray diffraction studies on proteins are being established as a valuable complementary technique to single-crystal measurements. A wide range of small proteins have been found to give synchrotron powder diffraction profiles where the peak widths are essentially limited only by the instrumental resolution. The rich information contained in these profiles, combined with developments in data analysis, has stimulated research and development to apply the powder technique to microcrystalline protein samples. In the present work, progress in using powder diffraction for macromolecular crystallography is reported. [source] On the possibility of using polycrystalline material in the development of structure-based generic assaysACTA CRYSTALLOGRAPHICA SECTION D, Issue 4 2009Marc Allaire The discovery of ligands that bind specifically to a targeted protein benefits from the development of generic assays for high-throughput screening of a library of chemicals. Protein powder diffraction (PPD) has been proposed as a potential method for use as a structure-based assay for high-throughput screening applications. Building on this effort, powder samples of bound/unbound states of soluble hen-egg white lysozyme precipitated with sodium chloride were compared. The correlation coefficients calculated between the raw diffraction profiles were consistent with the known binding properties of the ligands and suggested that the PPD approach can be used even prior to a full description using stereochemically restrained Rietveld refinement. [source] | |||||||||||||