Showing papers in "Powder Diffraction in 2006"
TL;DR: In this article, it is shown that while the Rietveld error index values indicate a better fit of a model to the data, wrong models with poor quality data may exhibit smaller values error index value than some superb models with very high quality data.
Abstract: !Received 19 December 2005; accepted 27 January 2006 "The deÞnitions for important Rietveld error indices are deÞned and discussed. It is shown that whilesmaller error index values indicate a better Þt of a model to the data, wrong models with poor qualitydata may exhibit smaller values error index values than some superb models with very high qualitydata. © 2006 International Centr e for Diffraction Data. #DOI: 10.1 154/1.2179804 $
978 citations
TL;DR: In this paper, the authors present a methodology for quantification of individual phases that have only partial or unknown structures using the Rietveld method, which is used in the TOPAS program from Bruker AXS.
Abstract: Quantification of mixtures via the Rietveld method is generally restricted to crystalline phases for which structures are well known. Phases that have not been identified or fully characterized may be easily quantified as a group, along with any amorphous material in the sample, by the addition of an internal standard to the mixture. However, quantification of individual phases that have only partial or unknown structures is carried out less routinely. This paper presents methodology for quantification of such phases. It outlines the procedure for calibration of the method and gives detailed examples from both synthetic and mineralogical systems. While the method should, in principle, be generally applicable, its implementation in the TOPAS program from Bruker AXS is demonstrated here.
261 citations
TL;DR: In this paper, a revised structure model of ettringite is presented, in order to provide quantitative X-ray diffraction (QXRD) of this mineral in cement pastes.
Abstract: A revised structure model of ettringite is presented, in order to provide quantitative X-ray diffraction (QXRD) of this mineral in cement pastes. The model is derived from two different existing structure models, both of which are suitable for restricted use but are inferior to the refined ettringite structure presented. In the first published ettringite structure proposed by Moore and Taylor [Acta Crystallogr. B 26, 386–393 (1970)], none of the 128 positions for H are given in the unit cell, which results in reduced scattering power for use of this model for quantification purposes. For the precise quantification of ettringite in samples together with anhydrous phases, the scattering factors of all atoms including the H positions are indispensable. The revised structure model is based on the data of Moore and Taylor, supplemented by the H positions determined by Berliner (Material Science of Concrete Special Volume, The Sydney Diamond Symposium, American Ceramic, Society, 1998, pp. 127–141) on the basis of a neutron diffraction structural investigation of deuterated ettringite at 20 K. Berliner’s (Material Science of Concrete Special Volume, The Sydney Diamond Symposium, American Ceramic Society, 1998, pp. 127–141) thermal parameter should not, however, be used, since a normal application is at room temperature. In order further to improve the structure model of ettringite, Rietveld refinement with the rigid body approach for OH and H2O molecules and SO4 tetrahedra was employed. The refined and improved ettringite structure model was tested for quantitative phase analysis by the determination of actual ettringite contents in mixtures with an internal standard. Synthesized and orientation-free prepared ettringite powders were investigated by X-ray powder diffraction analysis and quantified in four different blends with zircon. The quantification results with the new structure model demonstrate the superior quality of the revised ettringite structure.
151 citations
TL;DR: The crystal structure of La2SiO5 was refined from laboratory X-ray powder diffraction data (CuKα1) using the Rietveld method as discussed by the authors, and the final reliability indices were Rwp=7.14%, RP=5.52%, and RB=3.83%.
Abstract: The crystal structure of La2SiO5 was refined from laboratory X-ray powder diffraction data (CuKα1) using the Rietveld method. The crystal structure is monoclinic (space group P21∕c,Z=4) with lattice dimensions a=0.93320(2) nm, b=0.75088(1) nm, c=0.70332(1) nm, β=108.679(1)°, and V=0.46687(1) nm3. The final reliability indices were Rwp=7.14%, RP=5.52%, and RB=3.83%. There are two La sites in the structural model, La1 and La2. La1 is ninefold coordinated to oxygen, forming a tricapped trigonal prism with a mean La1-O distance of 0.263 nm. The La2O7 coordination polyhedron is a distorted capped octahedron with a mean La2-O distance of 0.251 nm. The La1O9 polyhedra share faces and the La2O7 polyhedra share edges, forming two sets of sheets that alternate parallel to the (100) plane. These sheets are linked through SiO4 tetrahedra and non-silicon-bonded oxygen atoms to form a three-dimensional structure. This compound is isomorphous with the low-temperature (X1) phases of R2SiO5 (R=Y and Gd). The volumes of RO9 polyhedra steadily increase with increasing ionic radius of R, from Y3+ to Gd3+ to La3+, which causes substantial volumetric expansion of the crystals.
33 citations
TL;DR: In this article, Rietveld refinement using neutron, laboratory X-ray, and synchrotron powder diffraction data of NIST SRM clinker 8488 was performed.
Abstract: Rietveld refinement using neutron, laboratory X-ray, and synchrotron powder diffraction data of NIST SRM clinker 8488 was performed. Quantitative phase analysis (QPA) results were compared between data, and with other studies. QPA results for the main phases in the clinker were found to be in agreement between the different data used here, and in and other studies, although the QPA of the tricalcium silicate polymorphs was shown to be inconsistent. The QPA results for the tricalcium aluminate phase varied between data types, and the neutron data were unable to distinguish this phase.
30 citations
TL;DR: In this paper, a detailed Rietveld analysis of powder X-ray diffraction data showed that La 1− x Ca x MnO 3 undergoes a structural phase transformation from R -3 c to Pnma at X = 0.05-0.075.
Abstract: Single-phase samples of La 1− x Ca x MnO 3 compounds have been synthesized by solid-state reaction. Detailed Rietveld analysis of powder X-ray diffraction data showed that La 1− x Ca x MnO 3 undergoes a structural phase transformation from R -3 c to Pnma at X =0.05–0.075. There is a linear variation of lattice parameters as a function of calcium concentration. The slope of this linear variation changes at X =0.6. A correlation between observed Mn-O bond lengths, corresponding to different compositions, and possible magnetic phases is discussed.
25 citations
TL;DR: The structural models of three synthetic Al-substituted goethite specimens have been refined from the neutron data, including crystallographic determinations of the Al levels and H positions as mentioned in this paper.
Abstract: The structural models of three synthetic Al-substituted goethite specimens have been refined from the neutron data, including crystallographic determinations of the Al levels and H positions. The d-I data were calculated for the final models. A relationship between the c unit cell parameter and Al content has been extended to the entire goethite-diaspore solid-solution system, which makes the regression equation procedure simpler and more accurate. A second prospective H site could not be confirmed because of the quality of existing neutron data. However, it is hoped that a further neutron powder diffraction study of a synthetic, fully deuterated goethite material may allow the existence of the site to be demonstrated.
18 citations
TL;DR: The general structure and analysis system (GSAS) software suite is commonly used for Rietveld analysis and includes the ability to compute magnetic scattering as discussed by the authors, and different approaches are presented to provide a tutorial on how magnetic scattering data may be modeled using differing treatment of symmetry.
Abstract: Neutron diffraction provides a direct probe for the ordering of spins from unpaired electrons in materials with magnetic properties. The ordering of the spins can be modeled in many cases by adding spin directions to standard crystallographic models. This requires, however, that crystallographic space groups be extended by addition of a “color” attribute to symmetry operations, which determines if the operation maintains or flips the direction of a magnetic spin. Rietveld analysis provides a mechanism for fitting magnetic structure models to powder diffraction data. The general structure and analysis system (GSAS) software suite is commonly used for Rietveld analysis and includes the ability to compute magnetic scattering. Different approaches are commonly used within GSAS to create models that include magnetism. Three equivalent but different approaches are presented to provide a tutorial on how magnetic scattering data may be modeled using differing treatment of symmetry. Also discussed is how magnetic models may be visualized. The commands used to run the GSAS programs are summarized within, but are shown in great detail in supplementary web pages.
17 citations
TL;DR: This work discusses an integrated approach for the implementation of analytical XMT to support basic research into the structure-property relationships of a variety of materials and gives examples of image analysis of resolved and unresolved pore spaces of sandstones.
Abstract: For research facilities with access to synchrotron X-ray sources, X-ray absorption microtomography (XMT) has evolved from an experimental imaging method to a specialized, if not yet routine, microscopy for imaging the three-dimensional (3D) distribution of linear attenuation coefficients and, in some cases, elemental concentration with micron spatial resolution. Recent advances in source and detector design have produced conventional X-ray source instruments with comparable spatial resolution but with lower throughput and without element specific imaging. Both classes of instrument produce 3D images for analysis. We discuss an integrated approach for the implementation of analytical XMT to support basic research into the structure-property relationships of a variety of materials. The essential components include instrumentation for collecting quantitative 3D images, a 3D image processing environment to address questions as to the quantity, composition, geometry, and relationships among the features in one or more images, and visualization to provide insight and communicate results. We give examples of image analysis of resolved and unresolved pore spaces of sandstones.
16 citations
TL;DR: In this article, the structural properties of La1-xBaxCoO3 (LBCO) have been investigated by means of X-ray powder diffraction and Rietveld analysis.
Abstract: Detailed structural properties of La1-xBaxCoO3 (LBCO) have been investigated by means of X-ray powder diffraction and Rietveld analysis. A structural phase transformation from R (3) over barc to Pm (3) over barm at x=0.30-0.35 has been detected based on a comparison between the refinements of R (3) over barc and Pm (3) over barm. The Co-O bond length of the CoO6 octahedron expanded rapidly with increasing Ba content when x = 0.35, where the Co-O-Co bond angle reaches, 180 degrees. The Co-O bond length expansion resumed with increasing Ba content beyond x=0.35. (C) 2006 International Centre for Diffraction Data.
15 citations
TL;DR: In this paper, a general expression for the peak profile produced by a system of simple-shape crystalline domains (sphere, cube, tetrahedron, octahedron) whose size is dispersed according to a gamma distribution is proposed.
Abstract: A general expression is proposed for the peak profile produced by a system of simple-shape crystalline domains (sphere, cube, tetrahedron, octahedron) whose size is dispersed according to a gamma distribution. The analytical expression obtained is particularly suited to “on the fly” pattern simulation or profile fitting for nanocrystalline materials. An advantage of using the proposed profile expression is that it always corresponds to a physically meaningful, though a priori fixed, size distribution, whereas the traditionally employed Voigtian profiles can produce unphysical negative size distributions for certain combinations of profile parameters. The peak profile depends on the distribution mean and variance instead of the more common empirical parameters of peak width and shape.
TL;DR: In this article, a simple approach to determine experimental X-ray elastic constants (XECs) of thin films by coupling the sin2ψ method and the substrate curvature technique was introduced.
Abstract: This work introduces a new simple approach to determine experimental X-ray elastic constants (XECs) of thin films by coupling the sin2ψ method and the substrate curvature technique. The approach is demonstrated on polycrystalline Cu thin films with the thickness 200, 800, and 2400 nm deposited on Si(100) substrates. Applying synchrotron radiation, the elastic strains in the films are determined using sin2ψ method while the macroscopic stresses are assessed by measuring the substrate curvature. The stresses are calculated using the Stoney formula from the radius of substrate curvature determined by the rocking curve measurement of substrate 400 reflection at different sample positions. Results show that the magnitude of the macroscopic stress in the films is proportional to the magnitude of the slope in the sin2ψ plots. On the basis of this observation, XECs of the films were calculated showing no dependence on the film thickness. The characterization of the samples was performed at the synchrotron source Hasylab.
TL;DR: In this paper, the structure of two new orthophosphates, Ca0.50SbFe(PO4)3 and CaSb 0.50Fe1.50(PO 4)3, obtained by conventional solid state reaction techniques at 900 °C, were determined at room temperature from X-ray powder diffraction using Rietveld analysis.
Abstract: Crystallographic structures of two new orthophosphates Ca0.50SbFe(PO4)3 and CaSb0.50Fe1.50(PO4)3 obtained by conventional solid state reaction techniques at 900 °C, were determined at room temperature from X-ray powder diffraction using Rietveld analysis. The two compounds belong to the Nasicon structural family. The space group is R3 for Ca0.50SbFe(PO4)3 and R3c for CaSb0.50Fe1.50(PO4)3. Hexagonal cell parameters for Ca0.50SbFe(PO4)3 and CaSb0.50Fe1.50(PO4)3 are: a=8.257(1) A, c=22.276(2) A, and a=8.514(1) A, c=21.871(2) A, respectively. Ca2+ and vacancies in {[Ca0.50]3a[◻0.50]3b}M1SbFe(PO4)3 are ordered within the two positions, 3a and 3b, of M1 sites. Structure refinements show also a quasi-ordered distribution of Sb5+ and Fe3+ ions within the Nasicon framework. Thus, in {[Ca0.50]3a[◻0.50]3b}M1SbFe(PO4)3, each Ca(3a)O6 octahedron shares two faces with two Fe3+O6 octahedra and each vacancy (◻(3b)O6) site is located between two Sb5+O6 octahedra. In [Ca]M1Sb0.50Fe1.50(PO4)3 compound (R3c space group), all M1 sites are occupied by Ca2+ and the Sb5+ and Fe3+ ions are randomly distributed within the Nasicon framework.
TL;DR: In this paper, an analysis of the microstructure of nanocrystalline magnesium oxide produced by thermal decomposition of magnesium oxalate, in the temperature range 500 °C-1200 °C, is described.
Abstract: An analysis of the microstructure of nanocrystalline magnesium oxide produced by thermal decomposition of magnesium oxalate, in the temperature range 500 °C–1200 °C, is described. The study is based on diffraction line broadening analysis carried out with the integral breadth (Langford) and Fourier methods, combined with the pattern decomposition technique. Additionally, the whole pattern matching method is also applied. No marked line broadening anisotropy is observed in the patterns. It is shown that the nanopowders are characterized by minimal strain and that crystallites have an average spherical shape. Volume-weighted and area-weighted apparent sizes are in the ranges 98–480 A and 72–282 A, respectively, within the temperature range considered. The results obtained from line broadening analysis are compared to those observed with scanning electron microscopy and surface area measurements. A satisfactory agreement is found between sizes derived from the different techniques.
TL;DR: In this article, the structure of two K2SnX(PO4)3(X=Fe,Yb) phosphates, obtained by conventional solid state reaction techniques at 950 °C, were determined at room temperature by X-ray powder diffraction using Rietveld analysis.
Abstract: Structures of two K2SnX(PO4)3(X=Fe,Yb) phosphates, obtained by conventional solid state reaction techniques at 950 °C, were determined at room temperature by X-ray powder diffraction using Rietveld analysis. The two materials exhibit the langbeinite-type structure (P213 space group, Z=4). Cubic unit cell parameter values are: a=9.9217(4) A and a=10.1583(4) A for K2SnFe(PO4)3 and K2SnYb(PO4)3, respectively. Structural refinements show that the two crystallographically independent octahedral sites (of symmetry 3) have a mixed Sn∕X (X=Fe,Yb) population although ordering is stronger in the Yb phase than in the Fe phase.
Abstract: A state-of-art semiconductor technology-based position sensitive area detector, namely D/teX-25, has recently been developed for high-speed and high-sensitivity X-ray diffraction (XRD) analysis of materials. X-ray powder diffraction intensities obtained by a D/teX-25 detector were found to over 50 times higher than those by a conventional scintillation counter. A D/teX-25 detector mounted on a conventional 2 kW XRD system has been used to collect ultrafast XRD data with scanning speeds up to 160°2θ per minute. Ultrahigh-speed XRD is particularly useful for time-resolved dynamical and in-situ studies. A D/teX-25 detector was successfully used on a Rigaku XRD differential scanning calorimetry (DSC) system for simultaneous measurements of XRD and DSC data under controlled temperature and humidity conditions. This has made possible the study of complex and rapid phase transformations of pharmaceutical terfenadine. The D/teX-25 area detector has also been used for recording two-dimensional XRD patterns showing the particle-size effects on α-quartz powder intensities and to obtain digital X-ray topographic images of a complex dislocation network in a Si wafer.
TL;DR: An experimental X-ray powder diffraction pattern was produced and analyzed for alpha-polymorphic tegafur, also called Ftorafur (an antineoplastic agent).
Abstract: An experimental X-ray powder diffraction pattern was produced and analyzed for alpha-polymorphic tegafur, also called Ftorafur (an antineoplastic agent). The indexed data matched the powder patterns in the ICDD PDF-4/Organics database calculated from the reported single-crystal X-ray diffraction data in the Cambridge Structural Database. Alpha tegafur has a triclinic crystal system, with reduced cell parameters of a=16.720(6) A, b=9.021(5) A, c=5.995(3) A, α=93.66(4)°, β=93.15(8)°, γ=100.14(4)°. There are four formula units contained in one unit cell. The cell volume and space group were determined to be 886.27 A3 and P-1, respectively.
TL;DR: In this article, a comprehensive database based on the Powder Diffraction File (PDF) was used to identify complex formulations with crystalline and non-crystalline ingredients, and phase identification and digital pattern simulations were used to correctly identify complex formularies.
Abstract: Developments in X-ray analysis hardware and software have combined to dramatically improve the throughput, speed, and accuracy of formulation analyses. We will focus on a complimentary development, the growth and application of a comprehensive database based on the Powder Diffraction File™ (PDF®). The PDF is an edited and standardized combination of several crystallographic databases with ∼497 000 published entries. The comprehensive nature of this database, combined with phase identification and digital pattern simulations, was used to identify complex formulations with crystalline and noncrystalline ingredients. We will show how these parallel developments enhance the ability to correctly identify complex formularies.
TL;DR: In this paper, the structural details of a typical defective F-type composition were investigated and the structure was unequivocally found to be that of a C-type cubic lattice and selected bond distances were also reported.
Abstract: Neutron diffraction studies were carried out to ascertain the structural details of the composition Ce 0.5 Nd 0.5 O 1.750 . The structure was unequivocally found to be that of C-type cubic. The refinement on an F-type cubic lattice was found to be unacceptable because of high R values. Selected bond distances are also being reported. In addition, the neutron diffraction studies on a typical defective F-type composition Ce 0.75 Nd 0.25 O 1.875 were also carried out.
TL;DR: In this article, an energy-dispersive X-ray detector with an ultrathin window, designated low-Z particle EPM, has been developed for quantitative determination of concentrations of low Z elements, such as C, N, and O, as well as higher Z elements that can be analyzed by conventional EPM.
Abstract: An electron probe X-ray microanalysis (EPMA) technique using an energy-dispersive X-ray detector with an ultrathin window, designated low-Z particle EPM, has been developed. The low-Z particle EPMA allows the quantitative determination of concentrations of low-Z elements, such as C, N, and O, as well as higher-Z elements that can be analyzed by conventional energy-dispersive EPMA. The quantitative determination of low-Z elements (using full Monte Carlo simulations, from the electron impact to the X-ray detection) in individual environmental particles has improved the applicability of single-particle analysis, especially in atmospheric environmental aerosol research; many environmentally important atmospheric particles, e.g. sulfates, nitrates, ammonium, and carbonaceous particles, contain low-Z elements. The low-Z particle EPMA was applied to characterize loess soil particle samples of which the chemical compositions are well defined by the use of various bulk analytical methods. Chemical compositions of the loess samples obtained from the low-Z particle EPMA turn out to be close to those from bulk analyses. In addition, it is demonstrated that the technique can also be used to assess the heterogeneity of individual particles.
TL;DR: In this article, a novel method for preparing thin films was investigated for quantifying gallium and iron in plutonium solutions using WDXRF, which can eliminate the potential for radioactive liquid to leak into the spectrometer, decrease specimen preparation time, and minimize waste.
Abstract: A novel method for preparing thin films was investigated for quantifying gallium and iron in plutonium solutions using WDXRF. This technique was developed to eliminate the potential for radioactive liquid to leak into the spectrometer, decrease specimen preparation time, and minimize waste. Samples were cast in µL quantities onto Kapton, and a surfactant was added to disperse the solution uniformly across the Kapton. After drying the specimens, they were sealed in a cell for analysis. Results to date indicate the method can provide a relative precision of ~0.5% for gallium and ~2% for iron, which is more than sufficient for routine sample analyses.
TL;DR: In this paper, the authors discuss the basics in capillary design and explore the question of how well a single-bounce monocapillary can best match synchrotron sources to particular microbeam experiments.
Abstract: Ellip tically-shaped hollow glass capillaries are the custom ary optic for micro X-ray beam experiments at the Cornell High Energy Synchrotron Source (CHESS) We have been able to manufacture optics that have produced x-ray spot sizes from 5 to 50 μm, gains in intensity of 10 to 500, divergences from 2 to 9 milliradians, and working distances between the tip of the capillary to the focus ranging from 20 to 150 mm We discuss the basics in capillary design and explore the question of how well a single-bounce monocapillary can best match synchrotron sources to particular microbeam experiments, such as confocal X-ray fluorescence, microbeam powder X-ray diffraction, microbeam protein crystallography, and microbeam small angle X-ray scattering
TL;DR: In this article, the authors used micro-beam X-radiation (micro-Laue) to characterizepolycrystalline materials in spatial location as well as with increasing stress.
Abstract: Determination of the strains in a polycrystalline materialusing 4-D XRD reveals sub-grain and grain-to-grain behavior as a functionof stress. Here 4-D XRD involves an experimental procedure usingpolychromatic micro-beam X-radiation (micro-Laue) to characterizepolycrystalline materials in spatial location as well as with increasingstress. The in-situ tensile loading experiment measured strain in a modelaluminum-sapphire metal matrix composite using the Advanced Light Source,Beam-line 7.3.3. Micro-Laue resolves individual grains in thepolycrystalline matrix. Results obtained from a list of grains sorted bycrystallographic orientation depict the strain states within and amongindividual grains. Locating the grain positions in the planeperpendicular to the incident beam is trivial. However, determining theexact location of grains within a 3-D space is challenging. Determiningthe depth of the grains within the matrix (along the beam direction)involved a triangulation method tracing individual rays that producespots on the CCD back to the point of origin. Triangulation wasexperimentally implemented by simulating a 3-D detector capturingmultiple diffraction images while increasing the camera to sampledistance. Hence by observing the intersection of rays from multiple spotsbelonging to the corresponding grain, depth is calculated. Depthresolution is a function of the number of images collected, grain to beamsize ratio, and the pixel resolution of the CCD. The 4DXRD methodprovides grain morphologies, strainmore » behavior of each grain, andinteractions of the matrix grains with each other and the centrallylocated single crystal fiber.« less
TL;DR: Improved X-ray powder diffraction data for synthetic PdSn are reported in this article, where the powder data were collected with a laboratory Xray source (CuKα) for Rietveld refinement.
Abstract: Improved X-ray powder diffraction data for synthetic PdSn are reported. Powder diffraction data were collected with a laboratory X-ray source (CuKα) for Rietveld refinement. Refined crystallographic data for PdSn (orthorhombic, Pnma) are a=6.1388(4), b=3.89226(3), c=6.3377(4) A, V=151.43(2) A3, Z=4, and Dx=9.87 g∕cm3.
TL;DR: In this paper, X-ray diffraction characterization of materials used in traditional silver halide and digital semiconductor photo graphic systems is described. Butts et al. measured the extent of polymer intercalation and disorder of the clay platelets by observing any change in the clay basal plane d-spacing as a function of composition.
Abstract: X-ray diffraction characterization of materials used in traditional silver halide and digital semiconductor photo graphic systems is described. Silver halide grains precipitated as multicomponent AgBr1-xIx phases were found to be comprised of a core with three shells. The composition of the core and shells was determined using lattice constant measurements. Nanocomposites for photographic antistatic applications were generated by mixing an aqueous dispersion of a 2:1 layered clay with a polyester ionomer. The extent of polymer intercalation and disorder of the clay platelets was monitored by observing any change in the clay (001) basal plane d-spacing as a function of composition. Silicon wafers used as substrates for digital photographic sensors were evaluated for the effect of depositing an epitaxial silicon layer on the wafer. A reciprocal space map constructed from high-resolution triple axis diffraction scans revealed that there was no detectable strain and the bulk silicon was comprised of a very smooth surface and few bulk-crystal defects. A gallium arsenide wafer with an epitaxial aluminum gallium arsenide film, utilized for light-emitting diodes, was also analyzed using a triple-axis diffractometer. The reciprocal space map revealed that the gallium arsenide substrate has a tilt boundary, and there is a compositional grading with a large population of dislocations.
TL;DR: The Interactive Data Language has been used to produce a software program capable of advanced three-dimensional visualizations of pole figure and θ-2θ data, and the data can also be used to calculate quantitative properties such as strain level and to minimize the peak-height texture effects in individual ιθ scans.
Abstract: The Interactive Data Language has been used to produce a software program capable of advanced three-dimensional visualizations of pole figure and θ-2θ data. The data can also be used to calculate quantitative properties such as strain level and to minimize the peak-height texture effects in individual θ-2θ scans. The collection of the large data sets necessary for the analyses is facilitated by use of a position sensitive detector or area detector.
TL;DR: In this paper, the impact of strong absorption for thermal neutrons on data analysis and compare absorption corrections in the GSAS and MAUD Rietveld codes for texture and structural parameter refinement.
Abstract: We discuss the impact of strong absorption for thermal neutrons on data analysis and compare absorption corrections in the GSAS and MAUD Rietveld codes for texture and structural parameter refinement. Diffraction data were collected on the neutron powder diffractometer HIPPO at LANSCE from dysprosium and erbium, which are moderate to strong absorbers for thermal neutrons with absorption cross-sections of 159 barns for Er and 994 barns for Dy at�e O = 1.8 A. Both elements have hexagonal close-packed (hcp) crystal structures, and the samples were various thicknesses of rolled foils. The orientation distribution functions (ODF) were fit to the same neutron time-of-flight data sets using two very different full pattern Rietveld analysis procedures. Spherical harmonics functions were fit to the textured data using GSAS. These data were also analyzed by the modified direct method E-WIMV using MAUD. The resulting pole figures from the ODFs determined by both Rietveld analysis packages are qualitatively similar, and the textures were confirmed by X-ray diffraction. Additionally, data from orthorhombic dysprosium and erbium fluoride powders show that atomic positions are not sensitive to absorption. We address inconsistencies and methodologies in data analysis when strong absorption is present.
TL;DR: A quantitative energy dispersive X-ray fluorescence (EDXRF) spectrometry method was developed for determining the concentration of palladium applied to tobacco cut filler and demonstrated minimum variation between replicates and distinct variation between levels of concentration.
Abstract: A quantitative energy dispersive X-ray fluorescence (EDXRF) spectrometry method was developed for determining the concentration of palladium (Pd) applied to tobacco cut filler. Control and standards were created in-house with different levels of Pd concentration. After application of the Pd in a salt solution, the tobacco had an average oven volatiles (OV) value of 27.6%. Three aliquots were analyzed at each concentration level by EDXRF and inductively coupled plasma - atomic emission spectrometry (ICP-AES). Results were plotted against target values to perform a linear regression. EDXRF and ICP-AES coefficient of determination (R 2 ) values were both lower than the accepted minimum value of 0.990. Also, measured concentrations varied significantly between replicates. To improve the calibration technique, two options were evaluated: (a) Improve sample homogeneity by lyophilizing and finely grinding the tobacco, and (b) Improve the linear fit of the EDXRF calibration curve by plotting against ICPAES results. EDXRF and ICP-AES analyses were performed on lyophilized samples with an average OV value of 3.3%. Results demonstrated minimum variation between replicates and distinct variation between levels of concentration. Results were plotted against target values, and both EDXRF and ICP-AES R 2 values improved. For evaluation of option (b), EDXRF results were plotted against ICP-AES results to create the calibration curve with an R 2 value of 0.994. Compton scatter was implemented in the method to account for the difference in the moisture content of the lyophilized standards and the unknown samples with high OV values.
TL;DR: In this paper, the authors developed an alkali reaction procedure as a precursor to borate fusion for the preparation of test specimens from the metal powder for X-ray fluorescence spectrometry (XRF).
Abstract: provided an opportunity to develop an alkali reaction procedure as a precursor to borate fusion for the preparation of test specimens from the metal powder for X-ray fluorescence spectrometry (XRF). Suggested for this purpose by Blanchette (Adv. X-Ray Anal., 45, 415, 2002), the alkali reaction uses LiOH·H2O to convert Si to Li2SiO3. Lithium silicate is fused with lithium borate flux without damage to platinum ware. Once specimens are fused and cast as beads, calibration standards are prepared to closely match the compositions of the specimens allowing a linear calibration for each analyte. The XRF method yields results that are directly traceable to the mole through NIST SRM spectrometric solutions. The method was validated in two ways. First, the reaction was used on older SRMs for Si metal: SRM 57 and SRM 57a. Second, XRF results for candidate SRM 57b were compared to results obtained using prompt gamma-ray activation analysis (PGAA) and inductively coupled plasma optical emission spectrometry (ICPOES). Bias tests show the XRF results are accurate for the elements Al, S, Ca, Ti, Cr, Mn, Ni, Cu, and Zr. Levels of S, Ca, Cr, and Cu in candidate SRM 57b are near the limits of quantification of the borate fusion method. Iron results may be subject to a low bias. Phosphorus is not quantitatively retained during the alkali reaction and borate fusion. These elements, plus B which cannot be determined after borate fusion, are listed in manufacturing specifications for Si metal.