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Journal of Applied Crystallography



Journal of Applied Crystallography covers a wide range of crystallographic topics from the viewpoints of both techniques and theory. The journal presents articles on the application of crystallographic techniques and on the related apparatus and computer



Published: 2016-09-29

 



Design and performance of a novel neutron powder diffractometer: PEARL at TU Delft

2016-08-04

The performance of the new neutron powder diffraction instrument PEARL that is installed at the research reactor of Delft University of Technology is reported. It is based on the optimization concepts developed by Cussen [Nucl. Instrum. Methods Phys. Res. Sect. A (2007), 583, 394–406], which lead to high performance competing with existing constant-wavelength neutron powder diffractometers, despite the relatively low source brightness of the 2 MW reactor of Delft University of Technology.



Lattice strain and tilt mapping in stressed Ge microstructures using X-ray Laue micro-diffraction and rainbow filtering

2016-08-04

Laue micro-diffraction and simultaneous rainbow-filtered micro-diffraction were used to measure accurately the full strain tensor and the lattice orientation distribution at the sub-micrometre scale in highly strained, suspended Ge micro-devices. A numerical approach to obtain the full strain tensor from the deviatoric strain measurement alone is also demonstrated and used for faster full strain mapping. The measurements were performed in a series of micro-devices under either uniaxial or biaxial stress and an excellent agreement with numerical simulations was found. This shows the superior potential of Laue micro-diffraction for the investigation of highly strained micro-devices.



Guinier peak analysis for visual and automated inspection of small-angle X-ray scattering data

2016-08-04

The Guinier region in small-angle X-ray scattering (SAXS) defines the radius of gyration, Rg, and the forward scattering intensity, I(0). In Guinier peak analysis (GPA), the plot of qI(q) versus q2 transforms the Guinier region into a characteristic peak for visual and automated inspection of data. Deviations of the peak position from the theoretical position in dimensionless GPA plots can suggest parameter errors, problematic low-resolution data, some kinds of intermolecular interactions or elongated scatters. To facilitate automated analysis by GPA, the elongation ratio (ER), which is the ratio of the areas in the pair-distribution function P(r) after and before the P(r) maximum, was characterized; symmetric samples have ER values around 1, and samples with ER values greater than 5 tend to be outliers in GPA analysis. Use of GPA+ER can be a helpful addition to SAXS data analysis pipelines.



Simultaneous small-angle neutron scattering and Fourier transform infrared spectroscopic measurements on cocrystals of syndiotactic polystyrene with polyethylene glycol dimethyl ethers

2016-08-04

Syndiotactic polystyrene (sPS) is a crystalline polymer which has a unique property; it is able to form cocrystals with a wide range of chemical compounds, in which the guest molecules are confined in the vacancies of the host sPS crystalline region. Recently, it has been found that even polyethylene glycol oligomers with a molecular weight of more than several hundreds can be introduced into the sPS crystalline region. It is quite important to know how such a long-chain molecule is stored in the host sPS lattice. To tackle this issue, a new simultaneous measurement method combing small-angle neutron scattering and Fourier transform infrared spectroscopy (SANS/FTIR), which has been recently developed by the authors, was applied to an sPS cocrystal with polyethylene glycol dimethyl ether with a molecular weight of 500 (PEGDME500). The temperature-dependent changes of the SANS profile and FTIR spectrum were followed from room temperature up to 413 K for a one-dimensionally oriented SANS/PEGDME500 cocrystal sample. The intensity of the reflections due to the stacking of crystalline lamellae showed a significant temperature dependence. The two-dimensional pattern in the high Q region of SANS also changed depending on temperature. The combined information obtained by SANS and FTIR suggested that PEGDME500 molecules are distributed in both the crystalline and amorphous regions in the low-temperature region close to room temperature, but they are predominantly included in the amorphous region in the high-temperature region. It was also suggested by the two-dimensional SANS profile that PEGDME500 molecules in the crystalline region have an elongated structure along the thickness direction of the crystalline lamellae.



The new NCPSS BL19U2 beamline at the SSRF for small-angle X-ray scattering from biological macromolecules in solution

2016-08-10

The beamline BL19U2 is located in the Shanghai Synchrotron Radiation Facility (SSRF) and is its first beamline dedicated to biological material small-angle X-ray scattering (BioSAXS). The electrons come from an undulator which can provide high brilliance for the BL19U2 end stations. A double flat silicon crystal (111) monochromator is used in BL19U2, with a tunable monochromatic photon energy ranging from 7 to 15 keV. To meet the rapidly growing demands of crystallographers, biochemists and structural biologists, the BioSAXS beamline allows manual and automatic sample loading/unloading. A Pilatus 1M detector (Dectris) is employed for data collection, characterized by a high dynamic range and a short readout time. The highly automated data processing pipeline SASFLOW was integrated into BL19U2, with help from the BioSAXS group of the European Molecular Biology Laboratory (EMBL, Hamburg), which provides a user-friendly interface for data processing. The BL19U2 beamline was officially opened to users in March 2015. To date, feedback from users has been positive and the number of experimental proposals at BL19U2 is increasing. A description of the new BioSAXS beamline and the setup characteristics is given, together with examples of data obtained.



Cation distribution and magnetic structure of M-type BaTiMnFe10O19 examined by synchrotron X-ray and neutron studies

2016-08-10

Combinational studies of synchrotron X-rays and neutrons have been performed to determine the site occupancy, valence state and magnetic structure of M-type BaTiMnFe10O19. X-ray resonant scattering studies have revealed the site preference, where Ti and Mn ions are distributed evenly over the Fe1, Fe2 and Fe3 sites of five independent Fe sites. X-ray absorption near-edge structure (XANES) and X-ray magnetic circular dichroism (XMCD) results for BaTiMnFe10O19 are similar to those of BaFe12O19 at the Fe K absorption edge. Clear chemical shifts exist at both the Mn and Fe edges, suggestive of a mixed valence of Mn and Fe ions. The Mn K XANES resembles Mn–Zn ferrite, where the observed fourfold peak is explained as the presence of four-coordinated Mn ions, on the basis of the self-consistent calculation of relativistic density functional theory. This can be explained by the presence of spinel substructures within the S block layer. Satellite reflections of 002 ± τ and 004 − τ (τ = 2/3) on 00l were observed at a temperature of 8 K in neutron powder diffraction, due to magnetic scattering on the helicoidal arrangement of ordered spins with a propagation period of c/τ. The magnetic structure observed in the neutron powder diffraction and the XMCD results explain the decreasing uniaxial magnetization from BaFe12O19.



Construction of a quartz spherical analyzer: application to high-resolution analysis of the Ni Kα emission spectrum

2016-08-10

The construction and characterization of a focusing X-ray spherical analyzer based on α-quartz 4{\bar 4}04 are presented. The performance of the analyzer was demonstrated by applying it to a high-resolution X-ray spectroscopy study of the Kα1,2 emission spectrum of Ni. An analytical representation based on physical grounds was assumed to model the shape of the X-ray emission lines. Satellite structures assigned to 3d spectator hole transitions were resolved and determined as well as their relative contribution to the emission spectrum. The present results on 1s−13d−1 shake probabilities support a recently proposed calculation framework based on a multi-configuration atomic model.



A new method of calculating planar density: the position-duplication-number method

2016-08-10

The traditional method of calculating planar density requires an auxiliary sectional view showing the arrangement of atoms on the plane, this being very difficult for those planes with higher indices. In the present paper, a new position-duplication-number method is developed to calculate the planar density of all Bravais lattices and all crystal structure types using the formula ρ(hkl)(m/q) = N(hkl)(m/q)d′(hkl)/Vcell. The new method is illustrated for calculating planar densities of the (110) and (579) planes of the β-cristobalite SiO2 structure, with additional examples in hexagonal close-packed, face-centred cubic and body-centred cubic systems. These examples show the advantages of the new method: it does not require any auxiliary sectional view, and it is suitable for all crystal structures and all plane indices.



Mechanisms of void shrinkage in aluminium

2016-08-10

Voids can significantly affect the performance of materials and a key question is how voids form and evolve. Voids also provide a rare opportunity to study the fundamental interplay between surface crystallography and atomic diffusion at the nanoscale. In the present work, the shrinkage of voids in aluminium from 20 to 1 nm in diameter through in situ annealing is imaged in a transmission electron microscope. It is found that voids first shrink anisotropically from a non-equilibrium to an equilibrium shape and then shrink while maintaining their equilibrium shape until they collapse. It is revealed that this process maximizes the reduction in total surface energy per vacancy emitted. It is also observed that shrinkage is quantized, taking place one atomic layer and one void facet at a time. By taking the quantization and electron irradiation into account, the measured void shrinkage rates can be modelled satisfactorily for voids down to 5 nm using bulk diffusion kinetics. Continuous electron irradiation accelerates the shrinkage kinetics significantly; however, it does not affect the energetics, which control void shape.



Accelerating k-nearest-neighbor searches

2016-08-10

The search for which k points are closest to a given probe point in a space of N known points, the `k-nearest-neighbor' or `KNN' problem, is a computationally challenging problem of importance in many disciplines, such as the design of numerical databases, analysis of multi-dimensional experimental data sets, multi-particle simulations and data mining. A standard approach is to preprocess the data into a tree and make use of the triangle inequality to prune the search time to the order of the logarithm of N for a single nearest point in a well balanced tree. All known approaches suffer from the `curse of dimensionality', which causes the search to explore many more branches of the tree than one might wish as the dimensionality of the problem increases, driving search times closer to the order of N. Looking for k nearest points can sometimes be done in approximately the time needed to search for one nearest point, but more often it requires k searches because the results are distributed widely. The result is very long search times, especially when the search radius is large and k is large, and individual distance calculations are very expensive, because the same probe-to-data-point distance calculations need to be executed repeatedly as the top of the tree is re-explored. Combining two acceleration techniques was found to improve the search time dramatically: (i) organizing the search into nested searches in non-overlapping annuli of increasing radii, using an estimation of the Hausdorff dimension applicable to this data instance from the results of earlier annuli to help set the radius of the next annulus; and (ii) caching all distance calculations involving the probe point to reduce the cost of repeated use of the same distances. The result of this acceleration in a search of the combined macromolecular and small-molecule data in a combined six-dimensional database of nearly 900 000 entries has been an improvement in the overall time of the searches by one to two orders of magnitude.



Gas-sensitive biological crystals processed in pressurized oxygen and krypton atmospheres: deciphering gas channels in proteins using a novel `soak-and-freeze' methodology

2016-08-16

Molecular oxygen (O2) is a key player in many fundamental biological processes. However, the combination of the labile nature and poor affinity of O2 often makes this substrate difficult to introduce into crystals at sufficient concentrations to enable protein/O2 interactions to be deciphered in sufficient detail. To overcome this problem, a gas pressure cell has been developed specifically for the `soak-and-freeze' preparation of crystals of O2-dependent biological molecules. The `soak-and-freeze' method uses high pressure to introduce oxygen molecules or krypton atoms (O2 mimics) into crystals which, still under high pressure, are then cryocooled for X-ray data collection. Here, a proof of principle of the gas pressure cell and the methodology developed is demonstrated with crystals of enzymes (lysozyme, thermolysin and urate oxidase) that are known to absorb and bind molecular oxygen and/or krypton. The successful results of these experiments lead to the suggestion that the soak-and-freeze method could be extended to studies involving a wide range of gases of biological, medical and/or environmental interest, including carbon monoxide, ethylene, methane and many others.



The new neutron grating interferometer at the ANTARES beamline: design, principles and applications

2016-08-16

Neutron grating interferometry is an advanced method in neutron imaging that allows the simultaneous recording of the transmission, the differential phase and the dark-field image. The latter in particular has recently been the subject of much interest because of its unique contrast mechanism which marks ultra-small-angle neutron scattering within the sample. Hence, in neutron grating interferometry, an imaging contrast is generated by scattering of neutrons off micrometre-sized inhomogeneities. Although the scatterer cannot be resolved, it leads to a measurable local decoherence of the beam. Here, a report is given on the design considerations, principles and applications of a new neutron grating interferometer which has recently been implemented at the ANTARES beamline at the Heinz Maier-Leibnitz Zentrum. Its highly flexible design allows users to perform experiments such as directional and quantitative dark-field imaging which provide spatially resolved information on the anisotropy and shape of the microstructure of the sample. A comprehensive overview of the neutron grating interferometer principle is given, followed by theoretical considerations to optimize the setup performance for different applications. Furthermore, an extensive characterization of the setup is presented and its abilities are demonstrated using selected case studies: (i) dark-field imaging for material differentiation, (ii) directional dark-field imaging to mark and quantify micrometre anisotropies within the sample, and (iii) quantitative dark-field imaging, providing additional size information on the sample's microstructure by probing its autocorrelation function.



A rapid two-dimensional data collection system for the study of ferroelectric materials under external applied electric fields

2016-08-16

Synchrotron X-rays on the Swiss Norwegian Beamline and BM28 (XMaS) at the ESRF have been used to record the diffraction response of the PMN–PT relaxor piezoelectric 67% Pb(Mg1/3Nb2/3)O3–33% PbTiO3 as a function of externally applied electric field. A DC field in the range 0–18 kV cm−1 was applied along the [001] pseudo-cubic direction using a specially designed sample cell for in situ single-crystal diffraction experiments. The cell allowed data to be collected on a Pilatus 2M area detector in a large volume of reciprocal space using transmission geometry. The data showed good agreement with a twinned single-phase monoclinic structure model. The results from the area detector were compared with previous Bragg peak mapping using variable electric fields and a single detector where the structural model was ambiguous. The coverage of a significantly larger section of reciprocal space facilitated by the area detector allowed precise phase analysis.



A new method for quantitative phase analysis using X-ray powder diffraction: direct derivation of weight fractions from observed integrated intensities and chemical compositions of individual phases

2016-08-16

A new method for the quantitative phase analysis of multi-component polycrystalline materials using the X-ray powder diffraction technique is proposed. A formula for calculating weight fractions of individual crystalline phases has been derived from the intensity formula for powder diffraction in Bragg–Brentano geometry. The integrated intensity of a diffraction line is proportional to the volume fraction of a relevant crystalline phase in an irradiated sample, and the volume fraction, when it is multiplied with the chemical formula weight, can be related to the weight fraction. The structure-factor-related quantity in the intensity formula, when it is summed in an adequate 2θ range, can be replaced with the sum of squared numbers of electrons belonging to composing atoms in the chemical formula. Unit-cell volumes and the number of chemical formula units are all cancelled out in the formula. Therefore, the formula requires only single-measurement integrated intensity datasets for the individual phases and their chemical compositions. No standard reference material, reference intensity ratio or crystal structure parameter is required. A new procedure for partitioning the intensities of unresolved overlapped diffraction lines has also been proposed. It is an iterative procedure which starts from derived weight fractions, converts the weight fractions to volume fractions by utilizing additional information on material densities, and then partitions the intensities in proportion to the volume fractions. Use of the Pawley pattern decomposition method provides more accurate intensity datasets than the individual profile fitting technique, and it expands the applicability of the present method to more complex powder diffraction patterns. Test results using weighed mixture samples showed that the accuracy, evaluated by the root-mean-square error, is comparable to that obtained by Rietveld quantitative phase analysis.



Refinement of cryo-EM structures using scattering factors of charged atoms

2016-08-24

This paper reports a suitable treatment of electron scattering factors of charged atoms for refinement of atomic models against cryo-electron microscopy (cryo-EM) maps. The ScatCurve package developed here supports various curve models for parameterization of scattering factors and the parameter tables can be implemented in major refinement programs in structural biology. Partial charge values of charged amino acids in crystal structures were changed in small steps for refinement of the atomic models against electron diffraction data from three-dimensional crystals. By exploring a range of partial charges, the authors found the electrostatic setting that produces atomic models with improved statistics and better reflects experimental data. Structure refinement for single-particle analysis also benefits from the more accurate analysis and the programs could find wide use for model refinement against cryo-EM maps.



Efficient computation of the scattering intensity from systems of nonspherical particles

2016-08-24

The analysis of the angle dependence of the elastic scattering of radiation from a sample is an efficient and non-invasive technique that is used in fundamental science, in medicine and in technical quality control in industry. Precise information on the shape, size, polydispersity and interactions of a colloidal sample is readily obtained provided an underlying scattering model, i.e. form and structure factors, can be computed for the sample. Here, a numerical method that can efficiently compute the form factor amplitude (and thus the scattering intensity) of nonspherical scatterers through an importance sampling algorithm of the Fourier integral of the scattering density is presented. Using the precomputed form factor amplitudes, the calculation of the scattering intensity at any particle concentration then scales linearly with the particle number and linearly with the number of q points for its evaluation. This is illustrated by an example calculation of the scattering by concentrated suspensions of ellipsoidal Janus particles and the numerical accuracy for the computed form factor amplitudes is compared with analytical benchmarks.



An advanced three-dimensional RHEED mapping approach to the diffraction study of Co/MnF2/CaF2/Si(001) epitaxial heterostructures

2016-08-24

An advanced three-dimensional mapping approach utilizing reflection high-energy electron diffraction (RHEED) is introduced. The application of the method is demonstrated in detail by resolving the crystal structure and epitaxial relations of individual components within epitaxially grown magnetically ordered Co/MnF2/CaF2/Si(001) heterostructures. The electron diffraction results are cross-checked using synchrotron X-ray diffraction measurements. A number of advantages of the three-dimensional mapping technique as compared to conventional electron diffraction are demonstrated. Not least amongst these is the possibility to build arbitrary planar cross sections and projections through reciprocal space, including the plan-view projection onto the plane parallel to the sample surface, which is otherwise impossible to obtain.



Crystal structure of Re-substituted lanthanum tungstate La5.4W1−yReyO12–δ (0 ≤ y ≤ 0.2) studied by neutron diffraction

2016-08-24

A precise determination of sample composition and water uptake of La6−xWO12−δ (0.4 ≤ x ≤ 0.8) and Re-substituted La5.4W1−yReyO12−δ (0 ≤ y ≤ 0.2) lanthanum tungstate is carried out. Sample compositions and water uptake were determined by electron probe micro-analysis and thermogravimetry, respectively. A single-phase region of Re-substituted lanthanum tungstates is reported. The crystal structure of two selected specimens produced by the citrate-complexation route based on the Pechini method, namely La5.4WO12−δ and La5.4W0.8Re0.2O12−δ, was investigated by neutron diffraction in the temperature range 1.5 ≤ T ≤ 1200 K. The structural model for lanthanum tungstates is validated, according to which the Wyckoff site shared by La and W (Fm{\overline 3}m space group, 24d site) is split with half-site occupancies (Fm{\overline 3}m space group, 48h site). Replacement of W by up to 20 mol% Re does not change the lattice structure, and Re atoms substitute for W statistically in both 4a and 48h Wyckoff sites of the Fm{\overline 3}m space group, as shown by combining the average neutron scattering length procedure, thermogravimetry and electron probe micro-analysis. Using the Willis and Pryor approach to anisotropic displacement parameters it is shown that the remaining static disorder in the unit cell found in La5.4WO12−δ and La5.4W0.8Re0.2O12−δ structures is comparable, when the Fm{\overline 3}m space group with split 48h site is employed. Through the estimation of the Debye temperature for both compounds, extracted from the analysis of thermal expansion coefficients and from the Willis and Pryor approach, anion anharmonic vibrations like those in yttria-stabilized zirconia are proven to exist in LaWO for the first time.



Phase-targeted X-ray diffraction

2016-09-01

A powder X-ray diffraction (XRD) method to enhance the signal of a specific crystalline phase within a mixture is presented for the first time. Specificity to the targeted phase relies on finding coincidences in the ratios of crystal d spacings and the ratios of elemental characteristic X-ray energies. Such coincidences can be exploited so that the two crystal planes diffract through the same scattering angle at two different X-ray energies. An energy-resolving detector placed at the appropriate scattering angle will detect a significantly enhanced signal at these energies if the target mineral or phase is present in the sample. When implemented using high scattering angles, for example 2θ > 150°, the method is tolerant to sample morphology and distance on the scale of ∼2 mm. The principle of the method is demonstrated experimentally using Pd Lα1 and Pd Lβ1 emission lines to enhance the diffraction signal of quartz. Both a pure quartz powder pellet and an unprepared mudstone rock specimen are used to test and develop the phase-targeted method. The technique is further demonstrated in the sensitive detection of retained austenite in steel samples using a combination of In Lβ1 and Ti Kβ emission lines. For both these examples it is also shown how the use of an attenuating foil, with an absorption edge close to and above the higher-energy characteristic X-ray line, can serve to isolate to some degree the coincidence signals from other fluorescence and diffraction peaks in the detected spectrum. The phase-targeted XRD technique is suitable for implementation using low-cost off-the-shelf components in a handheld or in-line instrument format.



New insight on cubic–tetragonal–monoclinic phase transitions in ZrO2: ab initio study and symmetry analysis

2016-09-01

A group-theory analysis of temperature-induced phase transitions in ZrO2 has been performed in the framework of the group–subgroup relationship tree (Bärnighausen tree) with the computer tools of the Bilbao Crystallographic Server. The transition paths including symmetry-allowed intermediate phases have been established. The active irreducible representations corresponding to soft phonon modes and spontaneous deformation strains responsible for the phase transitions have been determined. The phonon mode frequencies at the symmetry points of the Brillouin zones of cubic, tetragonal and monoclinic phases have been calculated using the ab initio density functional theory method. As a result, the soft modes and their symmetries have been revealed, which are in a complete agreement with the group-theoretical predictions.



Rapid measurement scheme for texture in cubic metallic materials using time-of-flight neutron diffraction at iMATERIA

2016-09-01

A rapid texture measurement system has been developed on the time-of-flight neutron diffractometer iMATERIA (beamline BL20, MLF/J-PARC, Japan). Quantitative Rietveld texture analysis with a neutron beam exposure of several minutes without sample rotation was investigated using a duplex stainless steel, and the minimum number of diffraction spectra required for the analysis was determined experimentally. The rapid measurement scheme employs 132 spectra, and by this scheme the quantitative determination of volume fractions of texture components in ferrite and austenite cubic phases in a duplex stainless steel can be made in a short time. This quantitative and rapid measurement scheme is based on the salient features of iMATERIA as a powder diffractometer, i.e. a fairly high resolution in d spacing and numerous detectors covering a wide range of scattering angle.



Crystallographic insights into Ni–Co–Mn–In metamagnetic shape memory alloys

2016-09-01

In the present work, the morphological and crystallographic features of the 6M modulated martensite in the Ni45Co5Mn37In13 alloy were investigated by electron backscatter diffraction and high-resolution transmission electron microscopy (HRTEM) at room temperature. The 6M modulated martensite is in plate form and organized in colonies within which the plates stretch roughly in the same direction. Each colony has four types of orientation variants that are related to three kinds of twin relations, i.e. \{ 1 \bar 2\bar 3\} _{\rm M} type I, \langle \bar 3\bar 3{{1}} \rangle _{\rm M} type II and {{\{ 103\} }}_{\rm M} compound twins. The twinning shears of type I and type II twins are the same and equal to 0.2681, being about one order of magnitude higher than that of the compound twin (0.0330). Variant interfaces are microscopically defined by their corresponding twinning plane K1. The HRTEM investigations show that the interfaces of the type I twin are straight and coherent at atomic scale, whereas those of the type II and compound twins are `stepped'. The step height of the compound twin interfaces is much larger than that of the type II twin interfaces. In view of variant organization, there is only one oriented type I interface and one compound twin interface, but there are two oriented type II interfaces which have an angular deviation of ±5.32° with respect to the type I twin interface. The results of the present work provide comprehensive information on morphological and crystallographic features of Ni–Co–Mn–In metamagnetic shape memory alloys.



High-performance powder diffraction pattern simulation for large-scale atomistic models via full-precision pair distribution function computation

2016-09-09

A new full-precision algorithm to solve the Debye scattering equation has been developed for high-performance computing of powder diffraction line profiles from large-scale atomistic models of nanomaterials. The Debye function was evaluated using a pair distribution function computed with high accuracy, exploiting the series expansion of the error between calculated and equispace-sampled pair distances of atoms. The intensity uncertainty (standard deviation) of the computed diffraction profile was estimated as a function of the algorithm-intrinsic approximations and coordinate precision of the atomic positions, confirming the high accuracy of the simulated pattern. Based on the propagation of uncertainty, the new algorithm provides a more accurate powder diffraction profile than a brute-force calculation. Indeed, the precision of floating-point numbers employed in brute-force computations is worse than the estimated accuracy provided by the new algorithm. A software application, ROSE-X, has been implemented for parallel computing on CPU/GPU multi-core processors and distributed clusters. The computing performance is directly proportional to the total processor speed of the devices. An average speed of ∼30 × 109 computed pair distances per second was measured, allowing simulation of the powder diffraction pattern of an ∼23 million atom microstructure in a couple of hours. Moreover, the pair distribution function was recorded and reused to evaluate powder diffraction profiles of the same system with different properties (i.e. Q rather than 2θ range, step and wavelength), avoiding additional pair distance computations. This approach was used to investigate a large collection of monoatomic and polyatomic microstructures, isolating the contribution from atoms belonging to different moieties (e.g. different species or crystalline domains).



Quantitative characterization of the microstructure of heat-treated Zr-Excel by neutron line profile analysis

2016-09-09

Neutron diffraction line profile analysis (DLPA) and transmission electron microscopy were used to characterize the components of the bimodal microstructure of Zr-Excel (Zr–3.5Sn–0.8Mo–0.8Nb), a nuclear structural material. The dual microstructure, consisting of equiaxed primary grains and martensitic domains both having hexagonal close-packed (h.c.p.) α crystal structure, forms when the as-received Zr-Excel alloy is heat treated at a high temperature and subsequently quenched, i.e. is solution treated. Because both microstructure components have the same crystal structure the reflections from the two components overlap significantly. The article presents how the multi-phase analysis capability of modern DLPA methods can be used to model the measured neutron diffraction patterns as the sum of two sub-patterns corresponding to the components of such a bimodal microstructure, which can be found in many hexagonal alloys relevant for industrial applications. The results show that the large equiaxed primary h.c.p. α grains have a highly correlated low-density dislocation structure and large sub-grains (∼300 nm), while the large martensitic domains have a randomly arranged very high density dislocation structure and sub-grains the size of ∼30 nm. The significantly different defect structures of the primary and martensitic phases manifest as large differences in the hardness and ductility of the individual components. As a result of this duality of the mechanical properties, solution-treated Zr-Excel materials can be considered as analogous to metal matrix composites where a softer ductile matrix contains a harder brittle reinforcing phase.



MOMAC: a SAXS/WAXS laboratory instrument dedicated to nanomaterials

2016-09-09

This article presents the technical characteristics of a newly built small- and wide-angle X-ray scattering (SAXS/WAXS) apparatus dedicated to structural characterization of a wide range of nanomaterials in the powder or dispersion form. The instrument is based on a high-flux rotating anode generator with a molybdenum target, enabling the assessment of highly absorbing samples containing heavy elements. The SAXS part is composed of a collimation system including a multilayer optic and scatterless slits, a motorized sample holder, a vacuum chamber, and a two-dimensional image-plate detector. All the control command is done through a TANGO interface. Normalization and data correction yield scattering patterns at the absolute scale automatically with a q range from 0.03 to 3.2 Å−1. The WAXS part features a multilayer collimating optic and a two-dimensional image-plate detector with variable sample-to-detector distances. The accessible q range is 0.4–9 Å−1, ensuring a large overlap in q range between the two instruments. A few examples of applications are also presented, namely coupled SAXS/WAXS structure and symmetry determination of gold nanocrystals in solution and characterization of imogolite nanotubes and iron-filled carbon nanotube samples.



Thermal expansion anisotropy as source for microstrain broadening of polycrystalline cementite, Fe3C

2016-09-09

Cementite (Fe3C) powder consisting of polycrystalline particles was investigated by synchrotron X-ray diffraction and neutron diffraction at temperatures between 10 and 973 K. The data reveal a pronouncedly anisotropic thermal expansion of the orthorhombic unit cell as well as microstrain broadening varying considerably with temperature. Using a theory for predicting thermal-microstress-induced microstrain already applied in previous work to ambient-temperature sealed-tube X-ray powder diffraction data from the same material [Leineweber (2012). J. Appl. Cryst. 45, 944–949], the temperature-dependent extent of the measured microstrain broadening could be quantitatively related to the measured temperature-dependent anisotropy of the thermal expansion. Thereby, the fact that the extent of the measured microstrain broadening is somewhat smaller than the predicted amount can be explained by the presence of the free surfaces of the powder particles reducing the level of microstress-induced microstrain.



Insitu observation of the motion of ferroelectric domain walls in Bi4Ti3O12 single crystals

2016-09-09

Five types of ferroelectric domain walls (DWs) are present in Bi4Ti3O12 single crystals (Ye et al., 2015). Here their motion was investigated in situ using transmission electron microscopy and optical microscopy. The motion of P(a)-90° DWs, P(a)-180° DWs and P(c)-180° DWs was observed through electron beam poling in a transmission electron microscope. The growth of new Ps(a)-180° nanodomains was frequently seen and they tended to nucleate at preexisting Ps(a)-90° DWs. Irregularly curved P(c)-180° DWs exhibit the highest mobility, while migration over a short range occurs occasionally for faceted Ps(a)-90° DWs. In addition, the motion of Ps(a)-90° DWs and the growth/annihilation of new needle-like Ps(a)-90° domains in a 20 µm-thick crystal were observed under an external electric field on an optical microscope. Most of the new needle-like Ps(a)-90° domains nucleate at preexisting Ps(a)-90° DWs and the former are much smaller than the latter. This is very similar to the situation for Ps(a)-180° domain switching induced by electron beam poling in a transmission electron microscope. Our observations suggest the energy hierarchy for different domains of Ps(c)-180° ≤ Ps(a)-180° ≤ Ps(a)-90° ≤ new needle-like Ps(a)-90° in ferroelectric Bi4Ti3O12.



Theoretical considerations in the construction of hard X-ray resonators at inclined incidence with ultra-high efficiency and resolution

2016-09-16

Detailed considerations of how to construct inclined-incidence hard X-ray resonators are presented. Owing to the symmetry of the crystals used, the Bragg back reflection usually employed in normal-incidence two- and multi-plate resonators to reflect the X-ray beam is often accompanied by unavoidable multiple-beam diffraction, and thus the reflectivity and cavity finesse are quite low. In contrast, crystal-based Fabry–Perot (FP) resonators at inclined incidence utilize multiple-beam diffraction to excite the back reflection inside the resonator to generate FP resonance with high efficiency, while avoiding the incident beam suffering from crystal absorption. The useful characteristics of inclined-incidence resonators are derived from numerical calculations based on the inclined-incidence diffraction geometry and the dynamical theory. Experimental results with Laue inclined incidence are in accordance with the simulation. The sub-millielectronvolt energy resolution and ultra-high efficiency of the transmission spectrum of the proposed resonators are also described.



Magnetic scattering in the simultaneous measurement of small-angle neutron scattering and Bragg edge transmission from steel

2016-09-16

Pulsed neutron sources enable the simultaneous measurement of small-angle neutron scattering (SANS) and Bragg edge transmission. This simultaneous measurement is useful for microstructural characterization in steel. Since most steels are ferromagnetic, magnetic scattering contributions should be considered in both SANS and Bragg edge transmission analyses. An expression for the magnetic scattering contribution to Bragg edge transmission analysis has been derived. The analysis using this expression was applied to Cu steel. The ferrite crystallite size estimated from this Bragg edge transmission analysis with the magnetic scattering contribution was larger than that estimated using conventional expressions. This result indicates that magnetic scattering has to be taken into account for quantitative Bragg edge transmission analysis. In the SANS analysis, the ratio of magnetic to nuclear scattering contributions revealed that the precipitates consist of body-centered cubic Cu0.7Fe0.3 and pure Cu, which probably has 9R structure including elastic strain and vacancies. These results show that effective use of the magnetic scattering contribution allows detailed analyses of steel microstructure.



A radially accessible tubular in situ X-ray cell for spatially resolved operando scattering and spectroscopic studies of electrochemical energy storage devices

2016-09-16

A tubular operando electrochemical cell has been developed to allow spatially resolved X-ray scattering and spectroscopic measurements of individual cell components, or regions thereof, during device operation. These measurements are enabled by the tubular cell geometry, wherein the X-ray-transparent tube walls allow radial access for the incident and scattered/transmitted X-ray beam; by probing different depths within the electrode stack, the transformation of different components or regions can be resolved. The cell is compatible with a variety of synchrotron-based scattering, absorption and imaging methodologies. The reliability of the electrochemical cell and the quality of the resulting X-ray scattering and spectroscopic data are demonstrated for two types of energy storage: the evolution of the distribution of the state of charge of an Li-ion battery electrode during cycling is documented using X-ray powder diffraction, and the redistribution of ions between two porous carbon electrodes in an electrochemical double-layer capacitor is documented using X-ray absorption near-edge spectroscopy.



In situ time-of-flight neutron imaging of NiO–YSZ anode support reduction under influence of stress

2016-09-16

This article reports on in situ macroscopic scale imaging of NiO–YSZ (YSZ is yttria-stabilized zirconia) reduction under applied stress – a phase transition taking place in solid oxide electrochemical cells in a reducing atmosphere of a hydrogen/nitrogen mixture and at operation temperatures of up to 1073 K. This process is critical for the performance and lifetime of the cells. Energy-resolved neutron imaging was applied to observe the phase transition directly with time and spatial resolution. Two different approaches are presented for using this imaging technique for the investigation of chemical and physical processes requiring controlled atmosphere and elevated temperature. The first type of measurement is based on alternating stages of short-term partial chemical reaction and longer neutron image acquisition, and the second type is a real in situ neutron imaging experiment. Results of applying energy-resolved neutron imaging with both approaches to the NiO–YSZ reduction investigation indicate enhancement of the reduction rate due to applied stress, which is consistent with the results of the authors' previous research.



Morphology of Fe nanolayers with Pt overlayers on low-temperature annealing

2016-09-23

Agglomeration or dewetting is technologically important in the microelectronics industry as it is one of the methods of producing arrays of nanosized metal clusters. This report investigates the grain morphology evolution due to low-temperature annealing (473 K) in Fe layers with Pt overlayers. X-ray diffuse scattering and grazing-incidence small-angle X-ray scattering (GISAXS) have been used to access different correlation lengths and correlate them with grain sizes from transmission electron microscopy. Overall, the GISAXS data indicate that the nanoparticles or nanoclusters in the samples appear as bimodal distributions. It is shown that, for an Fe layer with vertical grain sizes of 5 and 11 nm, irrespective of cluster size, there is no signature of agglomeration between the Fe and Pt layers even with very long annealing times (3000 min). The vertical grain sizes are mediated by the film thickness. Furthermore, an alternating variation with grain sizes of 4 and 7 nm is achieved by Al doping, but without a restriction on the Fe layer thickness. Even in this case, the agglomeration process is seen to remain unaffected by annealing for the same time durations, but only for the larger sized nanoclusters. The smaller ones are seen to grow in size, with increased correlation lengths for the maximum annealing time owing to higher surface energy.



Self-organized in-plane ordering of nanostructures at epitaxial ferroelectric–ferromagnetic interfaces

2016-09-23

The formation of self-assembled structures is of great interest in the field of ferroelectric (FE)–ferromagnetic (FM) oxide interfaces with novel functionalities driven by the combination of strain relaxation and diffusion/segregation processes occurring during epitaxial growth of Mn-based heterostructures. In epitaxial bilayers and multilayers of La0.67Sr0.33MnO3 (LSMO)/BaTiO3 (BTO) on (001) SrTiO3, using the grazing-incidence small-angle X-ray scattering technique, self-assembled in-plane structural ordering with a repeated sequence of the bilayers has been found. This ordering has important magnetic consequences, as the materials show characteristics of a superparamagnetic type of behavior even with an increased number of bilayers. Transmission electron microscopy images reveal strain due to lattice mismatch between BTO and LSMO. This strain is greatly enhanced with the number of BTO and LSMO repetitions in a multilayer as an interdiffused columnar structure is formed. Electron energy loss spectra indicate a variation in oxygen environment from one monolayer to another within one LSMO layer. Reflectivity measurements with polarized neutrons prove that the LSMO layers are grown with sufficient periodicity but have a strongly reduced magnetic moment. This reduction is plausibly associated with interfacial strain and varying oxygen deficiencies within the layers or symmetry breaking effects which can turn the LSMO layer almost antiferromagnetic.



Formation of swift heavy ion tracks on a rutile TiO2 (001) surface

2016-09-23

Nanostructuring of surfaces and two-dimensional materials using swift heavy ions offers some unique possibilities owing to the deposition of a large amount of energy localized within a nanoscale volume surrounding the ion trajectory. To fully exploit this feature, the morphology of nanostructures formed after ion impact has to be known in detail. In the present work the response of a rutile TiO2 (001) surface to grazing-incidence swift heavy ion irradiation is investigated. Surface ion tracks with the well known intermittent inner structure were successfully produced using 23 MeV I ions. Samples irradiated with different ion fluences were investigated using atomic force microscopy and grazing-incidence small-angle X-ray scattering. With these two complementary approaches, a detailed description of the swift heavy ion impact sites, i.e. the ion tracks on the surface, can be obtained even for the case of multiple ion track overlap. In addition to the structural investigation of surface ion tracks, the change in stoichiometry of the rutile TiO2 (001) surface during swift heavy ion irradiation was monitored using in situ time-of-flight elastic recoil detection analysis, and a preferential loss of oxygen was found.



Pore shape and sorption behaviour in mesoporous ordered silica films

2016-09-23

Mesoporous silica films templated by pluronic P123 were prepared using spin and dip coating. The ordered cylindrical structure within the films deforms due to shrinkage during calcination. Grazing-incidence small-angle X-ray scattering (GISAXS) measurements reveal that both the unit cell and the cross section of the pores decrease in size, mainly normal to the surface of the substrate, leading to elliptical cross sections of the pores with axis ratios of about 1:2. Water take-up by the pores upon changing the relative humidity can be monitored quantitatively by the shift in the critical angle of X-ray reflection as seen by the Yoneda peak.



X-ray multi-beam resonant diffraction analysis of crystal symmetry for layered perovskite YBaCuFeO5

2016-09-23

The open question of crystal symmetry for YBaCuFeO5, still under debate, is resolved by using diffraction anomalous fine structure and resonant multi-beam X-ray diffraction at the Fe and Cu K edges. The different asymmetric intensity distributions observed at 7, 7.1305 and 8.9945 keV give direct evidence that the space group of YBaCuFeO5 should be P4/mmm with the distance between Cu and apical O atoms longer than that between Fe and O atoms. This approach provides a direct way to resolve detailed structural symmetry which is indeterminate in conventional Bragg diffraction.



New insights into BaTi1–xSnxO3 (0 ≤ x ≤ 0.20) phase diagram from neutron diffraction data

2016-09-29

Neutron powder diffraction (NPD) was employed to further investigate the BaTi1−xSnxO3 (BTS) system previously studied by X-ray diffraction. The room-temperature phase compositions and crystal structures of BTS samples with x = 0, 0.025, 0.05, 0.07, 0.10, 0.12, 0.15 and 0.20 were refined by the Rietveld method using NPD data. It is well known that barium titanate powder (x = 0) crystallizes in the tetragonal P4mm space group. The crystal structures of the samples with 0.025 ≤ x ≤ 0.07 were refined as mixtures of P4mm and Amm2 phases; those with x = 0.1 and 0.12 show the coexistence of rhombohedral R3m and cubic phases, while the samples with x = 0.15 and 0.20 crystallize in a single cubic Pm{\overline 3}m phase. Temperature-dependent NPD was used to characterize the BaTi0.95Sn0.05O3 sample at 273, 333 and 373 K, and it was found to form single-phase Amm2, P4mm and Pm{\overline 3}m structures at these respective temperatures. The NPD results are in agreement with data obtained by differential scanning calorimetry and dielectric permittivity measurements, which show a paraelectric–ferroelectric transition (associated with structural transition) from Pm{\overline 3}m to P4mm at about 353 K followed by a P4mm to Amm2 phase transition at about 303 K.



A critical examination of the decoupling approximation for small-angle scattering from hard ellipsoids of revolution

2016-09-29

The decoupling approximation, proposed by Kotlarchyk & Chen [J. Chem. Phys. (1983), 79, 2461–2469], is a first-order correction to the experimentally determined apparent structure factor that is necessary because of concentration effects in polydisperse and/or nonspherical systems. While the approximation is considered accurate for spheres with low polydispersity (<10%), the corresponding limitations for nonspherical particles are unknown. The validity of this approximation is studied for monodisperse dispersions of hard ellipsoids of revolution with aspect ratios ranging from 0.333 to 3 and a guide for its accuracy is provided.



Averaging the intensity of many-layered structures for accurate stacking-fault analysis using Rietveld refinement

2016-09-29

Many technologically important synthetic and natural materials display stacking faults which lead to complex peak broadenings, asymmetries and shifts in their powder diffraction patterns. The patterns can be described using an enlarged unit cell (called a supercell) containing an explicit description of the layers. Since the supercell can contain hundreds of thousands of atoms with hundreds of thousands of hkl reflections, a Rietveld approach has been too computationally demanding for all but the simplest systems. This article describes the implementation of the speed-ups necessary to allow Rietveld refinement in the computer program TOPAS Version 6 (Bruker AXS, Karlsruhe, Germany). Techniques implemented include: a peaks buffer that allows hundreds of thousands of hkl-dependent peak shapes to be automatically approximated by a few hundred peaks; an averaging process for hundreds of large supercells with minimum impact on computational time; a smoothing technique that allows for the use of small supercells which approximate supercells ten to 20 times larger; and efficient algorithms for stacking sequence generation. The result is Rietveld refinement of supercells operating at speeds several thousand times faster than traditional Rietveld refinements. This allows quantitative and simultaneous analysis of structure and microstructure in complex stacking-faulted samples.



MAGNDATA: towards a database of magnetic structures. I. The commensurate case

2016-09-29

A free web page under the name MAGNDATA, which provides detailed quantitative information on more than 400 published magnetic structures, has been developed and is available at the Bilbao Crystallographic Server (http://www.cryst.ehu.es). It includes both commensurate and incommensurate structures. This first article is devoted to explaining the information available on commensurate magnetic structures. Each magnetic structure is described using magnetic symmetry, i.e. a magnetic space group (or Shubnikov group). This ensures a robust and unambiguous description of both atomic positions and magnetic moments within a common unique formalism. A non-standard setting of the magnetic space group is often used in order to keep the origin and unit-cell orientation of the paramagnetic phase, but a description in any desired setting is possible. Domain-related equivalent structures can also be downloaded. For each structure its magnetic point group is given, and the resulting constraints on any macroscopic tensor property of interest can be consulted. Any entry can be retrieved as a magCIF file, a file format under development by the International Union of Crystallography. An online visualization tool using Jmol is available, and the latest versions of VESTA and Jmol support the magCIF format, such that these programs can be used locally for visualization and analysis of any of the entries in the collection. The fact that magnetic structures are often reported without identifying their symmetry and/or with ambiguous information has in many cases forced a reinterpretation and transformation of the published data. Most of the structures in the collection possess a maximal magnetic symmetry within the constraints imposed by the magnetic propagation vector(s). When a lower symmetry is realized, it usually corresponds to an epikernel (isotropy subgroup) of one irreducible representation of the space group of the parent phase. Various examples of the structures present in this collection are discussed.



Complex precipitation phenomena in strip cast steels with high sulfur and copper contents

2016-09-29

A series of three steel alloys with increasing Cu and S concentrations has been prepared by simulated direct strip casting. It was found that the rapid solidification that occurs during direct strip casting results in the formation of a high number density of fine MnS precipitates, while Cu was retained in solid solution above equilibrium concentration. Upon ageing the MnS particles were found to coarsen and increase in volume fraction, indicating that some S was retained in solid solution in the as-cast condition. Ageing also resulted in the precipitation of Cu-rich precipitates. A new method to determine precipitate composition from small-angle neutron scattering is presented. This methodology, in conjunction with atom-probe tomography, has been used to show that the composition of the Cu-rich precipitates depends on the alloy's bulk Cu content.



Orientations – perfectly colored

2016-09-29

The inverse pole figure (IPF) coloring for a suitable evaluation of crystal orientation data is discussed. The major goal is a high correlation between encoding color and crystal orientation. Revised color distributions of the fundamental sectors are introduced which have the advantages of (1) being applicable for all point groups, (2) not causing color discontinuities within grains, (3) featuring carefully balanced regions for red, cyan, blue, magenta, green and yellow, and (4) an enlarged gray center in opposition to a tiny white center. A new set of IPF color keys is proposed which is the result of a thorough analysis of the colorization problem. The discussion considers several topics: (a) the majority of presently applied IPF color keys generate color discontinuities for specifically oriented grains; (b) if a unique correlation between crystal direction and color is requested, discontinuity-preventing keys are possible for all point groups, except for {\overline 4}, {\overline 3} and {\overline 1}; (c) for a specific symmetry group several IPF color keys are available, visualizing different features of a microstructure; and (d) for higher symmetries a simultaneous IPF mapping of two or three standard reference directions is insufficient for an unequivocal orientation assignment. All color keys are available in MTEX, a freely available MATLAB toolbox.



Realization of two-dimensional anomalous small-angle scattering of Al alloys at the K absorption edge of Al

2016-08-04

Two-dimensional anomalous small-angle X-ray scattering (ASAXS) measurements at the K absorption edge of Al have been successfully performed. Contrast change below the absorption edge was detected with the use of a CCD detector. The change of ASAXS intensities near the edge for alumina nanopowder and that for Guinier–Preston zones in an Al–Zn alloy were explained by the anomalous dispersion of Al. The present results showed that two-dimensional SAXS measurements with a dynamic range extended to show Porod's law have been achieved for photon energies of about 1.5 keV with the use of a CCD detector optically coupled with a P43 phosphor plate.



Asymmetric band flipping for time-of-flight neutron diffraction data

2016-08-24

Charge flipping with powder diffraction data is known to produce a result more reliably with high-resolution data, i.e. visible reflections at small d spacings. Such data are readily accessible with the neutron time-of-flight technique but the assumption that negative scattering density is nonphysical is no longer valid where elements with negative scattering lengths are present. The concept of band flipping was introduced in the literature, where a negative threshold is used in addition to a positive threshold during the flipping. However, it was not tested with experimental data at the time. Band flipping has been implemented in TOPAS together with the band modification of low-density elimination and tested with experimental powder and Laue single-crystal neutron data.



Origin of quasi-mosaic effect for symmetric skew planes in a silicon or germanium plate

2016-09-23

Bent silicon and germanium crystals are used for several modern physics applications, above all for focusing of hard X-rays and for steering of charged particle beams by means of channeling and related coherent phenomena. In particular, anisotropic deformations are effectively exploited for these applications. A typical anisotropic deformation that is used is the quasi-mosaic (QM) curvature. It involves the bending of crystallographic planes that would be otherwise flat in the case of an isotropic medium. Here, the curvature the {110} planes was obtained through the quasi-mosaic effect in the symmetric configuration for the first time. This achievement is important because the {110} family of planes is highly efficient for both the applications mentioned above. Until now, the curvature of {110} planes in the QM configuration has not been used because it vanishes if the direction of the planes is aligned with the applied moment that bends the crystal plate. Indeed, to obtain the curvature of this particular family of crystallographic planes, the 〈110〉 direction has not to be aligned with respect to the imparted moment that bends the plate, i.e. the {110} planes have to be skew planes. Experimental verification of the quasi-mosaic curvature for the {110} planes was provided through hard X-ray diffraction at beamline ID15A of the European Synchrotron Radiation Facility in Grenoble, France, showing good agreement with the theoretical expectation.



Evaluation of intragranular strain and average dislocation density in single grains of a polycrystal using K-map scanning

2016-09-29

Quick scanning X-ray microscopy combined with three-dimensional reciprocal space mapping was applied to characterize intragranular orientation and strain in a single grain of uniaxially deformed Al polycrystal. The strain component perpendicular to the direction of the applied tensile load was found to be very heterogeneous with high compressive and tensile values in the grain interior and near two grain boundaries, respectively. The distribution of the magnitude of diffraction vectors indicates that dislocations are the origin of the strain. The work opens new possibilities for analysing dislocation structures and intragranular residual stress/strain in single grains of polycrystalline materials.



SPICA: stereographic projection for interactive crystallographic analysis

2016-08-16

In numerous research fields, especially the applications of electron and X-ray diffraction, stereographic projection represents a powerful tool for researchers. SPICA is a new computer program for stereographic projection in interactive crystallographic analysis, which inherits features from the previous JECP/SP and includes more functions for extensive crystallographic analysis. SPICA provides fully interactive options for users to plot stereograms of crystal directions and crystal planes, traces, and Kikuchi maps for an arbitrary crystal structure; it can be used to explore the orientation relationships between two crystalline phases with a composite stereogram; it is also used to predict the tilt angles of transmission electron microscopy double-tilt and rotation holders in electron diffraction experiments. In addition, various modules are provided for essential crystallographic calculations.



US-SOMO HPLC-SAXS module: dealing with capillary fouling and extraction of pure component patterns from poorly resolved SEC-SAXS data

2016-09-01

Size-exclusion chromatography coupled with SAXS (small-angle X-ray scattering), often performed using a flow-through capillary, should allow direct collection of monodisperse sample data. However, capillary fouling issues and non-baseline-resolved peaks can hamper its efficacy. The UltraScan solution modeler (US-SOMO) HPLC-SAXS (high-performance liquid chromatography coupled with SAXS) module provides a comprehensive framework to analyze such data, starting with a simple linear baseline correction and symmetrical Gaussian decomposition tools [Brookes, Pérez, Cardinali, Profumo, Vachette & Rocco (2013). J. Appl. Cryst. 46, 1823–1833]. In addition to several new features, substantial improvements to both routines have now been implemented, comprising the evaluation of outcomes by advanced statistical tools. The novel integral baseline-correction procedure is based on the more sound assumption that the effect of capillary fouling on scattering increases monotonically with the intensity scattered by the material within the X-ray beam. Overlapping peaks, often skewed because of sample interaction with the column matrix, can now be accurately decomposed using non-symmetrical modified Gaussian functions. As an example, the case of a polydisperse solution of aldolase is analyzed: from heavily convoluted peaks, individual SAXS profiles of tetramers, octamers and dodecamers are extracted and reliably modeled.



PyNX.Ptycho: a computing library for X-ray coherent diffraction imaging of nanostructures

2016-09-16

X-ray imaging techniques have undergone a remarkable development during the past decade, taking advantage of coherent X-ray sources. Among these techniques, ptychography allows reconstruction of the specimen and the illumination probe from a series of diffraction patterns without any prior knowledge about the sample. However, the reconstruction of the ptychographic data remains challenging and the reconstruction software is often not publicly available. Presented here is an open-source library for the reconstruction of two-dimensional ptychographic data, written in Python. This library implements existing algorithms, with examples of data reconstruction on both simulated and experimental (Bragg ptychography on heterogeneous strained InAs/GaAs nanowires) data sets. It can be used for educational (simulation) purposes or experimental data analysis, and also features an OpenCL version of the ptychography algorithm for high-performance computing.



ISOSUBGROUP: an internet tool for generating isotropy subgroups of crystallographic space groups

2016-09-29

ISOSUBGROUP, the newest member of the ISOTROPY Software Suite (http://iso.byu.edu), generates isotropy subgroups of crystallographic space groups based on superpositions of multiple irreducible representations, along with a wealth of information about each one. Like the original ISOTROPY program, its scope is general rather than being restricted to common types of order parameters of a user-specified parent structure. But like the newer ISODISTORT program, its user-friendly interface has menu-driven selections. This combination of features has been oft requested but unavailable until now. Program output includes information about the subgroup symmetry, ferroic species, phase-transition continuity, active k vectors, domains and secondary order parameters.