Fundamental Parameters Line Profile Fitting in Laboratory Diffractometers.

The fundamental parameters approach to line profile fitting uses physically based models to generate the line profile shapes. Fundamental parameters profile fitting (FPPF) has been used to synthesize and fit data from both parallel beam and divergent beam diffractometers. The refined parameters are determined by the diffractometer configuration. In a divergent beam diffractometer these include the angular aperture of the divergence slit, the width and axial length of the receiving slit, the angular apertures of the axial Soller slits, the length and projected width of the x-ray source, the absorption coefficient and axial length of the sample. In a parallel beam system the principal parameters are the angular aperture of the equatorial analyser/Soller slits and the angular apertures of the axial Soller slits. The presence of a monochromator in the beam path is normally accommodated by modifying the wavelength spectrum and/or by changing one or more of the axial divergence parameters. Flat analyzer crystals have been incorporated into FPPF as a Lorentzian shaped angular acceptance function. One of the intrinsic benefits of the fundamental parameters approach is its adaptability any laboratory diffractometer. Good fits can normally be obtained over the whole 20 range without refinement using the known properties of the diffractometer, such as the slit sizes and diffractometer radius, and emission profile

Microscopic co-existence of superconductivity and magnetism in Ba1-xKxFe2As2

It is widely believed that, in contrast to its electron doped counterparts, the hole doped compound Ba1-xKxFe2As2 exhibits a mesoscopic phase separation of magnetism and superconductivity in the underdoped region of the phase diagram. Here, we report a combined high-resolution x-ray powder diffraction and volume sensitive muon spin rotation study of underdoped Ba1-xKxFe2As2 (0 \leq x \leq 0.25) showing that this paradigm is wrong. Instead we find a microscopic coexistence of the two forms of order. A competition of magnetism and superconductivity is evident from a significant reduction of the magnetic moment and a concomitant decrease of the magneto-elastically coupled orthorhombic lattice distortion below the superconducting phase transition.Comment: 4 pages, 4 figure

A waste-derived lithium metasilicate basic catalyst

A mixed product of lithium metasilicate (74%) and minor proportions of calcium carbonate, lithium carbonate and calcium hydroxide was prepared by hydrothermal synthesis from waste green container glass in 4 M lithium hydroxide solution at 125 °C. The reaction product was characterised by powder X-ray diffraction and Fourier transform infrared spectroscopy. The lithium metasilicate product was found to be a successful heterogeneous catalyst for the Knoevenagel synthesis of ethyl trans-α-cyanocinnamate from benzaldehyde and ethyl cyanoacetate

Whole-pattern profile fitting of powder diffraction data collected in parallel-beam flat-plate asymmetric reflection geometry

Abstract: A simple, physically based model that allows the whole-pattern profile fitting of diffraction data collected in parallel-beam flat-plate asymmetric reflection geometry is presented. In this arrangement, there is a fixed angle between the incident beam and the sample, resulting in a fixed-length beam footprint. The use of a wide-angle detector for the simultaneous detection of the data precludes the use of any diffracted beam optics. Therefore, the observed peak widths are a function of the length of the beam footprint on the sample. The model uses up to three refinable parameters, depending on the intensity profile of the beam, to calculate the effect of diffraction angle on the width of all diffracted peaks. The use of this model reduces the total number of parameters required to fit the observed peak widths and shapes, hence leading to increased stability in the profile analysis. Implementations of the model are provided for both fundamental parameters and empirical approaches

Trihexyphenidyl hydro­chloride: a powder diffraction study

In the cation of the title compound [systematic name: 1-(3-cyclo­hexyl-3-hy­droxy-3-phenyl­prop­yl)piperidinium chloride], C20H32NO+·Cl−, the cyclo­hexyl and piperidine rings are in chair conformations. In the crystal structure, cations and anions are linked into chains along the c-axis direction via O—H⋯Cl and N—H⋯Cl hydrogen bonds. Weak inter­molecular C—H⋯Cl inter­actions link further these chains into layers parallel to the bc plane. The salt, obtained from a racemic solution, was found to crystallize in the chiral P21212 space group, indicating that, in the absence of any evident chirality-inducing process, the polycrystalline powders consist of an equivalent mixture of R and S enanti­omers, forming a racemic conglomerate

An In-situ method for the study of strain broadening usingsynchrotronx-ray diffraction

A tensonometer for stretching metal foils has beenconstructed for the study of strain broadening in x-ray diffraction lineprofiles. This device, which is designed for use on the powderdiffractometer in Station 2.3 at Daresbury Laboratory, allows in-situmeasurements to be performed on samples under stress. It can be used fordata collection in either transmission or reflection modes using eithersymmetric or asymmetric diffraction geometries. As a test case,measurements were carried out on a 18mum thick copper foil experiencingstrain levels of up to 5 percent using both symmetric reflection andsymmetric transmission diffraction. All the diffraction profilesdisplayed peak broadening and asymmetry which increased with strain. Themeasured profiles were analysed by the fundamental parameters approachusing the TOPAS peak fitting software. All the observed broadenedprofiles were modelled by convoluting a refineable diffraction profile,representing the dislocation and crystallite size broadening, with afixed instrumental profile pre-determined usinghigh quality LaB6reference powder. The de-convolution process yielded "pure" sampleintegral breadths and asymmetry results which displayed a strongdependence on applied strain and increased almost linearly with appliedstrain. Assuming crystallite size broadening in combination withdislocation broadening arising from fcc a/2111 dislocations,we have extracted the variation of mechanic al property with strain. Theobservation of both peak asymmetry and broadening has been interpreted asa manifestation of a cellular structure with cell walls and cellinteriors possessing high and low dislocation densities

Quantitative X-ray diffraction phase analysis of poorly ordered nontronite clay in nickel laterites

Studies of the extraction of nickel from low-grade laterite ores require a much better quantitative understanding of the poorly ordered mineral phases present, including turbostratically disordered nontronite. Whole pattern refinements with nontronite X-ray diffraction data from a Western Australian nickel deposit (Bulong) using a nontronite lattice model (Pawley phase) with two space groups(P3 and C2/m) and a peaks phase group model were performed to improve the accuracy of quantitative X-ray diffraction of nickel laterite ore samples. Modifications were applied when building the new models to accommodate asymmetric peak shape and anisotropic peak broadening due to the turbostraticdisorder. Spherical harmonics were used as convolution factors to represent anisotropic crystal size and strain and asymmetric peak shape when using the lattice model. A peaks phase group model was also developed to fit the anisotropic peak broadening in the nontronite pattern. The quantitative resultsof the new Pawley phase and peaks phase group models were compared and verified with synthetic mixtures of nontronite, quartz and goethite simulating various West Australian laterite ore compositions. The models developed in this paper demonstrate adequate accuracy for quantification of nontronite in the synthesized reference materials and should be generally applicable toquantitative phase analysis of nontronite in nickel laterite ore samples