Journal of Applied Crystallography
http://journals.iucr.org/j/issues/2016/05/00/isscontsbdy.html
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 software. For many years, Journal of Applied Crystallography has been the main vehicle for the publication of small-angle scattering articles and powder diffraction techniques. The journal is the primary place where crystallographic computer program information is published.enCopyright (c) 2016 International Union of Crystallography2016-08-23International Union of CrystallographyInternational Union of Crystallographyhttp://journals.iucr.orgurn:issn:1600-5767Journal 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 software. For many years, Journal of Applied Crystallography has been the main vehicle for the publication of small-angle scattering articles and powder diffraction techniques. The journal is the primary place where crystallographic computer program information is published.text/htmlJournal of Applied Crystallography, Volume 49, Part 5, 2016textweekly62002-02-01T00:00+00:005492016-08-23Copyright (c) 2016 International Union of CrystallographyJournal of Applied Crystallography1398urn:issn:1600-5767med@iucr.orgAugust 20162016-08-23Journal of Applied Crystallographyhttp://journals.iucr.org/logos/rss10j.gif
http://journals.iucr.org/j/issues/2016/05/00/isscontsbdy.html
Still imageDesign and performance of a novel neutron powder diffractometer: PEARL at TU Delft
http://scripts.iucr.org/cgi-bin/paper?fs5138
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.Copyright (c) 2016 International Union of Crystallographyurn:issn:1600-5767van Eijck, L.Cussen, L.D.Sykora, G.J.Schooneveld, E.M.Rhodes, N.J.van Well, A.A.Pappas, C.2016-08-04doi:10.1107/S160057671601089XInternational Union of CrystallographyThis manuscript describes the novel neutron powder diffractometer PEARL at Delft University of Technology and shows the first experimental results.ENneutron powder diffractionneutron powder diffractometersThe 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.text/htmlDesign and performance of a novel neutron powder diffractometer: PEARL at TU Delfttext5492016-08-04Copyright (c) 2016 International Union of CrystallographyJournal of Applied Crystallographyresearch papers00Lattice strain and tilt mapping in stressed Ge microstructures using X-ray Laue micro-diffraction and rainbow filtering
http://scripts.iucr.org/cgi-bin/paper?vh5056
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.Copyright (c) 2016 International Union of Crystallographyurn:issn:1600-5767Tardif, S.Gassenq, A.Guilloy, K.Pauc, N.Osvaldo Dias, G.Hartmann, J.-M.Widiez, J.Zabel, T.Marin, E.Sigg, H.Faist, J.Chelnokov, A.Reboud, V.Calvo, V.Micha, J.-S.Robach, O.Rieutord, F.2016-08-04doi:10.1107/S1600576716010347International Union of CrystallographyThe lattice tilts and full strain tensor are measured in Ge micro-devices under uniaxial or biaxial stress using standard and rainbow-filtered Laue micro-diffraction. Maps with sub-micrometre resolution of the strain tensor components are in very good agreement with finite element simulations.ENLaue micro-diffractionrainbow-filtered micro-diffractionstrain mappingGe micro-devicesLaue 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.text/htmlLattice strain and tilt mapping in stressed Ge microstructures using X-ray Laue micro-diffraction and rainbow filteringtext5492016-08-04Copyright (c) 2016 International Union of CrystallographyJournal of Applied Crystallographyresearch papers00Guinier peak analysis for visual and automated inspection of small-angle X-ray scattering data
http://scripts.iucr.org/cgi-bin/paper?vg5047
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.Copyright (c) 2016 Christopher D. Putnamurn:issn:1600-5767Putnam, C.D.2016-08-04doi:10.1107/S1600576716010906International Union of CrystallographyGuinier peak analysis (GPA), derived from the Guinier approximation, transforms the Guinier region of small-angle X-ray scattering data into a characteristic peak that verifies the existence of the Guinier region in the data. Deviation of the Guinier peak position in dimensionless GPA plots can be a useful addition to sample characterization and parameter validation protocols.ENsmall-angle X-ray scatteringsample characterizationGuinier analysisGuinier peak analysiselongation ratioThe 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.text/htmlGuinier peak analysis for visual and automated inspection of small-angle X-ray scattering datatext5492016-08-04Copyright (c) 2016 Christopher D. PutnamJournal of Applied Crystallographyresearch papers00Simultaneous small-angle neutron scattering and Fourier transform infrared spectroscopic measurements on cocrystals of syndiotactic polystyrene with polyethylene glycol dimethyl ethers
http://scripts.iucr.org/cgi-bin/paper?jk5009
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.Copyright (c) 2016 Fumitoshi Kaneko et al.urn:issn:1600-5767Kaneko, F.Seto, N.Sato, S.Radulescu, A.Schiavone, M.M.Allgaier, J.Ute, K.2016-08-04doi:10.1107/S160057671601178XInternational Union of CrystallographyA new simultaneous measurement method combining small-angle neutron scattering and Fourier-transform infrared spectroscopy was applied to a study on a syndiotactic polystyrene cocrystal with polyethylene glycol dimethyl ether with a molecular weight of 500. It is suggested that the guest molecules in the crystalline region have an elongated structure along the thickness direction of the crystalline lamellae.ENcocrystalssyndiotactic polystyrenesimultaneous measurementsmall-angle neutron scatteringFourier transform IR spectroscopySyndiotactic 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.text/htmlSimultaneous small-angle neutron scattering and Fourier transform infrared spectroscopic measurements on cocrystals of syndiotactic polystyrene with polyethylene glycol dimethyl etherstext5492016-08-04Copyright (c) 2016 Fumitoshi Kaneko et al.Journal of Applied Crystallographyresearch papers00The new NCPSS BL19U2 beamline at the SSRF for small-angle X-ray scattering from biological macromolecules in solution
http://scripts.iucr.org/cgi-bin/paper?aj5277
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.Copyright (c) 2016 Na Li et al.urn:issn:1600-5767Li, N.Li, X.Wang, Y.Liu, G.Zhou, P.Wu, H.Hong, C.Bian, F.Zhang, R.2016-08-10doi:10.1107/S160057671601195XInternational Union of CrystallographyA new biological small-angle X-ray scattering beamline (BioSAXS, BL19U2) at the Shanghai Synchrotron Radiation Facility (SSRF) is dedicated exclusively to small-angle scattering experiments from biological macromolecules in solution. As part of the important facilities in the National Center for Protein Sciences Shanghai (NCPSS), this BioSAXS beamline is the first in China to serve the rapidly increasing biology communities.ENbiological small-angle X-ray scatteringautomation and high brilliancestructural biologyThe 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.text/htmlThe new NCPSS BL19U2 beamline at the SSRF for small-angle X-ray scattering from biological macromolecules in solutiontext5492016-08-10Copyright (c) 2016 Na Li et al.Journal of Applied Crystallographyresearch papers00Cation distribution and magnetic structure of M-type BaTiMnFe10O19 examined by synchrotron X-ray and neutron studies
http://scripts.iucr.org/cgi-bin/paper?rg5110
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.Copyright (c) 2016 International Union of Crystallographyurn:issn:1600-5767Okube, M.Yoshizaki, J.Toyoda, T.Sasaki, S.2016-08-10doi:10.1107/S1600576716010591International Union of CrystallographyCombinational studies of synchrotron X-rays and neutrons have been performed to determine the site occupancy, valence state and magnetic structure of M-type BaTiMnFe10O19.ENcation distributionresonant scatteringXMCDXANESBa ferritesneutron powder diffractionCombinational 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.text/htmlCation distribution and magnetic structure of M-type BaTiMnFe10O19 examined by synchrotron X-ray and neutron studiestext5492016-08-10Copyright (c) 2016 International Union of CrystallographyJournal of Applied Crystallographyresearch papers00Construction of a quartz spherical analyzer: application to high-resolution analysis of the Ni Kα emission spectrum
http://scripts.iucr.org/cgi-bin/paper?vh5051
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.Copyright (c) 2016 International Union of Crystallographyurn:issn:1600-5767Honnicke, M.G.Bianco, L.M.Ceppi, S.A.Cusatis, C.Huang, X.Cai, Y.Q.Stutz, G.E.2016-08-10doi:10.1107/S1600576716010633International Union of CrystallographyThe construction of an α-quartz spherical analyzer and its application to a high-resolution measurement of the Kα1,2 X-ray emission lines of Ni are presented.ENspherical analyzersX-ray emission spectroscopyinelastic X-ray scatteringX-ray opticsquartz crystalsThe 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.text/htmlConstruction of a quartz spherical analyzer: application to high-resolution analysis of the Ni Kα emission spectrumtext5492016-08-10Copyright (c) 2016 International Union of CrystallographyJournal of Applied Crystallographyresearch papers00A new method of calculating planar density: the position-duplication-number method
http://scripts.iucr.org/cgi-bin/paper?ks5511
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.Copyright (c) 2016 International Union of Crystallographyurn:issn:1600-5767Fan, Q.2016-08-10doi:10.1107/S1600576716010827International Union of CrystallographyA new position-duplication-number method of calculating planar density is proposed. The new method does not require any auxiliary illustration.ENplanar density calculationposition-duplication-number methodplanar densitiesSiO2The 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.text/htmlA new method of calculating planar density: the position-duplication-number methodtext5492016-08-10Copyright (c) 2016 International Union of CrystallographyJournal of Applied Crystallographyresearch papers00Mechanisms of void shrinkage in aluminium
http://scripts.iucr.org/cgi-bin/paper?ks5509
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.Copyright (c) 2016 International Union of Crystallographyurn:issn:1600-5767Zhang, Z.Liu, T.Smith, A.E.Medhekar, N.V.Nakashima, P.N.H.Bourgeois, L.2016-08-10doi:10.1107/S1600576716010657International Union of CrystallographyThe shrinkage of voids in aluminium 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 also observed that shrinkage is quantized, taking place one atomic layer and one void facet at a time.ENnanovoidstransmission electron microscopy (TEM)vacanciesdiffusionaluminiumVoids 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.text/htmlMechanisms of void shrinkage in aluminiumtext5492016-08-10Copyright (c) 2016 International Union of CrystallographyJournal of Applied Crystallographyresearch papers00Accelerating k-nearest-neighbor searches
http://scripts.iucr.org/cgi-bin/paper?po5069
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.Copyright (c) 2016 International Union of Crystallographyurn:issn:1600-5767Bernstein, H.J.Andrews, L.C.2016-08-10doi:10.1107/S1600576716011353International Union of CrystallographyAn accelerated algorithm is presented for locating k points closest to a probe point, with application to searching for lattices closest to a given experimental cell.ENk-nearest-neighbor searchneartree data structuresearch accelerationcomputational challengesdata miningThe 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.text/htmlAccelerating k-nearest-neighbor searchestext5492016-08-10Copyright (c) 2016 International Union of CrystallographyJournal of Applied Crystallographyresearch papers00Gas-sensitive biological crystals processed in pressurized oxygen and krypton atmospheres: deciphering gas channels in proteins using a novel `soak-and-freeze' methodology
http://scripts.iucr.org/cgi-bin/paper?fs5135
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.Copyright (c) 2016 International Union of Crystallographyurn:issn:1600-5767Lafumat, B.Mueller-Dieckmann, C.Leonard, G.Colloc'h, N.Prangé, T.Giraud, T.Dobias, F.Royant, A.van der Linden, P.Carpentier, P.2016-08-16doi:10.1107/S1600576716010992International Union of CrystallographyA novel cryogenic gas pressure cell has been designed for structural studies of enzymes requiring gaseous substrates. The proof of principle is demonstrated for test crystals. The pressure cell has been designed for the study of O2-sensitive proteins to reveal pores, channels and reactive centres, and thus to decipher O2 traffic in proteins.ENoxygen-sensitive proteinsgas pressure cellsprotein crystallographyoxygen pathwaysnoble gasesMolecular 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.text/htmlGas-sensitive biological crystals processed in pressurized oxygen and krypton atmospheres: deciphering gas channels in proteins using a novel `soak-and-freeze' methodologytext5492016-08-16Copyright (c) 2016 International Union of CrystallographyJournal of Applied Crystallographyresearch papers00The new neutron grating interferometer at the ANTARES beamline: design, principles and applications
http://scripts.iucr.org/cgi-bin/paper?ge5026
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.Copyright (c) 2016 International Union of Crystallographyurn:issn:1600-5767Reimann, T.Mühlbauer, S.Horisberger, M.Betz, B.Böni, P.Schulz, M.2016-08-16doi:10.1107/S1600576716011080International Union of CrystallographyIn this paper the principles, design and applications of the new neutron grating interferometry (nGI) setup at the Heinz Maier-Leibnitz Zentrum are presented. The dark-field contrast modality of the setup allows one to obtain spatially resolved information about the microstructure of a sample. In this way, nGI closes the gap between neutron imaging and small-angle neutron scattering.ENneutron radiographyneutron imagingneutron grating interferometryneutron dark-field imagingsmall-angle neutron scatteringultra-small-angle neutron scatteringNeutron 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.text/htmlThe new neutron grating interferometer at the ANTARES beamline: design, principles and applicationstext5492016-08-16Copyright (c) 2016 International Union of CrystallographyJournal of Applied Crystallographyresearch papers00A rapid two-dimensional data collection system for the study of ferroelectric materials under external applied electric fields
http://scripts.iucr.org/cgi-bin/paper?kc5040
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.Copyright (c) 2016 Tikhon Vergentiev et al.urn:issn:1600-5767Vergentev, T.Bronwald, I.Chernyshov, D.Gorfman, S.Ryding, S.H.M.Thompson, P.Cernik, R.J.2016-08-16doi:10.1107/S1600576716011341International Union of CrystallographyThe diffraction response of the PMN–PT relaxor piezoelectric 67% Pb(Mg1/3Nb2/3)O3–33% PbTiO3 has been recorded as a function of externally applied electric field. The DC field was applied using a specially designed sample cell for in situ single-crystal diffraction experiments. The coverage of a significantly large section of reciprocal space allowed precise phase analysis.ENferroelectricitypiezoelectricitydiffuse scatteringin situ two-dimensional X-ray single-crystal diffractionarea detectorssynchrotron X-raysPMN-PTphase transitionsSynchrotron 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.text/htmlA rapid two-dimensional data collection system for the study of ferroelectric materials under external applied electric fieldstext5492016-08-16Copyright (c) 2016 Tikhon Vergentiev et al.Journal of Applied Crystallographyresearch papers00A 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
http://scripts.iucr.org/cgi-bin/paper?to5147
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.Copyright (c) 2016 International Union of Crystallographyurn:issn:1600-5767Toraya, H.2016-08-16doi:10.1107/S1600576716010451International Union of CrystallographyA new method for the quantitative phase analysis of multi-component polycrystalline materials using the X-ray powder diffraction technique is proposed. The method can derive weight fractions from single-measurement integrated intensity datasets for individual phases and their chemical compositions. No standard reference material, reference intensity ratio or crystal structural parameter is required.ENX-ray powder diffractionquantitative phase analysisdirect derivationintensity–composition formulaA 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.text/htmlA 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 phasestext5492016-08-16Copyright (c) 2016 International Union of CrystallographyJournal of Applied Crystallographyresearch papers00Refinement of cryo-EM structures using scattering factors of charged atoms
http://scripts.iucr.org/cgi-bin/paper?ei5007
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.Copyright (c) 2016 International Union of Crystallographyurn:issn:1600-5767Yonekura, K.Maki-Yonekura, S.2016-08-24doi:10.1107/S1600576716011274International Union of CrystallographyThis article reports a suitable refinement of atomic models with charges against cryo-electron microscopy (cryo-EM) maps using a new package, ScatCurve.ENelectron scattering factorselectron three-dimensional crystallographysingle-particle analysisThis 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.text/htmlRefinement of cryo-EM structures using scattering factors of charged atomstext5492016-08-24Copyright (c) 2016 International Union of CrystallographyJournal of Applied Crystallographyresearch papers00Efficient computation of the scattering intensity from systems of nonspherical particles
http://scripts.iucr.org/cgi-bin/paper?po5072
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.Copyright (c) 2016 International Union of Crystallographyurn:issn:1600-5767Persson, R.A.X.Bergenholtz, J.2016-08-24doi:10.1107/S1600576716011481International Union of CrystallographyThe authors present an algorithm to compute the elastic scattering signal from nonspherical particles at arbitrary concentration that scales bilinearly in particle number and angular resolution of the scattering distribution.ENsmall-angle scatteringform factor amplitudenumerical algorithmsMonte CarloThe 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.text/htmlEfficient computation of the scattering intensity from systems of nonspherical particlestext5492016-08-24Copyright (c) 2016 International Union of CrystallographyJournal of Applied Crystallographyresearch papers00An advanced three-dimensional RHEED mapping approach to the diffraction study of Co/MnF2/CaF2/Si(001) epitaxial heterostructures
http://scripts.iucr.org/cgi-bin/paper?nb5179
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.Copyright (c) 2016 International Union of Crystallographyurn:issn:1600-5767Suturin, S.M.Korovin, A.M.Fedorov, V.V.Valkovsky, G.A.Tabuchi, M.Sokolov, N.S.2016-08-24doi:10.1107/S1600576716011407International Union of CrystallographyAn advanced three-dimensional mapping approach to reflection high-energy electron diffraction (RHEED) is discussed in detail and applied to study epitaxially grown magnetically ordered Co/MnF2/CaF2/Si(001) heterostructures.ENreflection high-energy electron diffractionX-ray diffractionthree-dimensional mappingepitaxial growthfluorides on siliconAn 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.text/htmlAn advanced three-dimensional RHEED mapping approach to the diffraction study of Co/MnF2/CaF2/Si(001) epitaxial heterostructurestext5492016-08-24Copyright (c) 2016 International Union of CrystallographyJournal of Applied Crystallographyresearch papers00Crystal structure of Re-substituted lanthanum tungstate La5.4W1−yReyO12–δ (0 ≤ y ≤ 0.2) studied by neutron diffraction
http://scripts.iucr.org/cgi-bin/paper?pd5082
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.Copyright (c) 2016 International Union of Crystallographyurn:issn:1600-5767Fantin, A.Scherb, T.Seeger, J.Schumacher, G.Gerhards, U.Ivanova, M.E.Meulenberg, W.A.Dittmeyer, R.Banhart, J.2016-08-24doi:10.1107/S1600576716011523International Union of CrystallographyThis work describes in detail the structure of nonsubstituted and Re-substituted lanthanum tungstates studied through neutron diffraction as a function of temperature between 1.5 and 1200 K. Thermogravimetry and electron probe micro-analysis techniques were employed in combination with neutron diffraction to locate Re atoms in the LaWO crystal structure.ENRe-substituted lanthanum tungstatesLa5.6WO12−δanharmonic vibrationsanisotropic displacement parametersmixed protonic electronic conductorsneutron diffractionA 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.text/htmlCrystal structure of Re-substituted lanthanum tungstate La5.4W1−yReyO12–δ (0 ≤ y ≤ 0.2) studied by neutron diffractiontext5492016-08-24Copyright (c) 2016 International Union of CrystallographyJournal of Applied Crystallographyresearch papers00Realization of two-dimensional anomalous small-angle scattering of Al alloys at the K absorption edge of Al
http://scripts.iucr.org/cgi-bin/paper?ks5520
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.Copyright (c) 2016 International Union of Crystallographyurn:issn:1600-5767Okuda, H.Sakohata, R.Kitajima, Y.Tamenori, Y.2016-08-04doi:10.1107/S1600576716010669International Union of CrystallographyAnomalous small-angle scattering measurements at the K absorption edge of Al for alumina powder and Al–Zn alloy foil have been demonstrated using a CCD detector. The change in the scattering intensity agreed with the expected contrast.ENanomalous small-angle scatteringsoft (tender) X-raysAl absorption edgeTwo-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.text/htmlRealization of two-dimensional anomalous small-angle scattering of Al alloys at the K absorption edge of Altext5492016-08-04Copyright (c) 2016 International Union of CrystallographyJournal of Applied Crystallographyshort communications00Asymmetric band flipping for time-of-flight neutron diffraction data
http://scripts.iucr.org/cgi-bin/paper?aj5281
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.Copyright (c) 2016 International Union of Crystallographyurn:issn:1600-5767Whitfield, P.S.Coelho, A.A.2016-08-24doi:10.1107/S1600576716011961International Union of CrystallographyThe band-flipping algorithm for structure solution with neutron data has been modified to account for the possible differing size of positive and negative neutron scattering lengths in a sample. Together with the band modification of low-density elimination it has been implemented in TOPAS and tested with both powder and Laue single-crystal time-of-flight neutron diffraction data.ENtime of flightcharge flippingstructure solutionneutron diffractionCharge 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.text/htmlAsymmetric band flipping for time-of-flight neutron diffraction datatext5492016-08-24Copyright (c) 2016 International Union of CrystallographyJournal of Applied Crystallographyshort communications00SPICA: stereographic projection for interactive crystallographic analysis
http://scripts.iucr.org/cgi-bin/paper?po5070
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.Copyright (c) 2016 International Union of Crystallographyurn:issn:1600-5767Li, X.-Z.2016-08-16doi:10.1107/S1600576716011109International Union of CrystallographySPICA provides fully interactive operations for stereographic analysis and beyond. It also includes various modules for essential crystallographic calculations.ENstereographic projectionorientation relationshipsKikuchi mapsselected-area electron diffractioncomputer programsIn 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.text/htmlSPICA: stereographic projection for interactive crystallographic analysistext5492016-08-16Copyright (c) 2016 International Union of CrystallographyJournal of Applied Crystallographycomputer programs00