Acta Crystallographica Section A
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Acta Crystallographica Section A: Foundations and Advances covers theoretical and fundamental aspects of the structure of matter. The journal is the prime forum for research in diffraction physics and the theory of crystallographic structure determination by diffraction methods using X-rays, neutrons and electrons. The structures include periodic and aperiodic crystals, and non-periodic disordered materials, and the corresponding Bragg, satellite and diffuse scattering, thermal motion and symmetry aspects. Spatial resolutions range from the subatomic domain in charge-density studies to nanodimensional imperfections such as dislocations and twin walls. The chemistry encompasses metals, alloys, and inorganic, organic and biological materials. Structure prediction and properties such as the theory of phase transformations are also covered.enCopyright (c) 2014 International Union of Crystallography2014-07-18International Union of CrystallographyInternational Union of Crystallographyhttp://journals.iucr.orgurn:issn:2053-2733Acta Crystallographica Section A: Foundations and Advances covers theoretical and fundamental aspects of the structure of matter. The journal is the prime forum for research in diffraction physics and the theory of crystallographic structure determination by diffraction methods using X-rays, neutrons and electrons. The structures include periodic and aperiodic crystals, and non-periodic disordered materials, and the corresponding Bragg, satellite and diffuse scattering, thermal motion and symmetry aspects. Spatial resolutions range from the subatomic domain in charge-density studies to nanodimensional imperfections such as dislocations and twin walls. The chemistry encompasses metals, alloys, and inorganic, organic and biological materials. Structure prediction and properties such as the theory of phase transformations are also covered.text/htmlActa Crystallographica Section A: Foundations and Advances, Volume 70, Part 5, 2014textyearly62002-01-01T00:00+00:005702014-07-18Copyright (c) 2014 International Union of CrystallographyActa Crystallographica Section A: Foundations and Advances417urn:issn:2053-2733med@iucr.orgJuly 20142014-07-18Acta Crystallographica Section Ahttp://journals.iucr.org/logos/rss10a.gif
http://journals.iucr.org/a/issues/2014/05/00/isscontsbdy.html
Still imageOn the subgroup structure of the hyperoctahedral group in six dimensions
http://scripts.iucr.org/cgi-bin/paper?eo5032
The subgroup structure of the hyperoctahedral group in six dimensions is investigated. In particular, the subgroups isomorphic to the icosahedral group are studied. The orthogonal crystallographic representations of the icosahedral group are classified and their intersections and subgroups analysed, using results from graph theory and their spectra.Copyright (c) 2014 Emilio Zappa et al.urn:issn:2053-2733Zappa, E.Dykeman, E.C.Twarock, R.2014-07-10doi:10.1107/S2053273314007712International Union of CrystallographyThe subgroup structure of the hyperoctahedral group in six dimensions is studied, with particular attention to the subgroups isomorphic to the icosahedral group. The orthogonal crystallographic representations of the icosahedral group are classified, and their intersections are studied in some detail, using a combinatorial approach which involves results from graph theory and their spectra.ENsymmetrycrystallographic representationicosahedral grouphyperoctahedral groupspectral graph theoryThe subgroup structure of the hyperoctahedral group in six dimensions is investigated. In particular, the subgroups isomorphic to the icosahedral group are studied. The orthogonal crystallographic representations of the icosahedral group are classified and their intersections and subgroups analysed, using results from graph theory and their spectra.text/htmlOn the subgroup structure of the hyperoctahedral group in six dimensionstext5702014-07-10Copyright (c) 2014 Emilio Zappa et al.Acta Crystallographica Section Aresearch papers00Multiple Bragg reflection by a thick mosaic crystal
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Symmetric Bragg-case reflections from a thick, ideally imperfect, crystal slab are studied mostly by analytical means. The scattering transfer function of a thin mosaic layer is derived and brought into a form that allows for analytical approximations or easy quadrature. The Darwin–Hamilton equations are generalized, lifting the restriction of wavevectors to a two-dimensional scattering plane. A multireflection expansion shows that wavevector diffusion can be studied independently of the real-space coordinate. Combining analytical arguments and Monte Carlo simulations, multiple Bragg reflections are found to result in a minor correction of the reflected intensity, a moderate broadening of the reflected azimuth angle distribution, a considerable modification of the polar angle distribution, and a noticeable shift and distortion of rocking curves.Copyright (c) 2014 International Union of Crystallographyurn:issn:2053-2733Wuttke, J.2014-07-10doi:10.1107/S205327331400802XInternational Union of CrystallographyTo investigate multiple Bragg reflections from a thick and ideally imperfect crystal, the Darwin–Hamilton equations are generalized. Out-of-plane wavevector diffusion causes a noticeable shift and distortion of rocking curves.ENmultiple Bragg reflectionimperfect crystalSymmetric Bragg-case reflections from a thick, ideally imperfect, crystal slab are studied mostly by analytical means. The scattering transfer function of a thin mosaic layer is derived and brought into a form that allows for analytical approximations or easy quadrature. The Darwin–Hamilton equations are generalized, lifting the restriction of wavevectors to a two-dimensional scattering plane. A multireflection expansion shows that wavevector diffusion can be studied independently of the real-space coordinate. Combining analytical arguments and Monte Carlo simulations, multiple Bragg reflections are found to result in a minor correction of the reflected intensity, a moderate broadening of the reflected azimuth angle distribution, a considerable modification of the polar angle distribution, and a noticeable shift and distortion of rocking curves.text/htmlMultiple Bragg reflection by a thick mosaic crystaltext5702014-07-10Copyright (c) 2014 International Union of CrystallographyActa Crystallographica Section Aresearch papers00Octagonal symmetry in low-discrepancy β-manganese
http://scripts.iucr.org/cgi-bin/paper?dm5052
A low-discrepancy cubic variant of β-Mn is presented exhibiting local octagonal symmetry upon projection along any of the three mutually perpendicular 〈100〉 axes. Ideal structural parameters are derived to be x(8c) = (2-\sqrt{2})\big/16 and y(12d) = 1\big/(4 \sqrt{2}) for the P4132 enantiomorph. A comparison of the actual and ideal structure models of β-Mn is made in terms of the newly devised concept of geometrical discrepancy maps. Two-dimensional maps of both the geometrical star discrepancy D* and the minimal interatomic distance dmin are calculated over the combined structural parameter range 0 \leq x(8c) \,\lt\, 1/8 and 1/8 \leq y(12d)\, \lt\, 1/4 of generalized β-Mn type structures, showing that the `octagonal' variant of β-Mn is almost optimal in terms of globally minimizing D* while at the same time globally maximizing dmin. Geometrical discrepancy maps combine predictive and discriminatory powers to appear useful within a wide range of structural chemistry studies.Copyright (c) 2014 International Union of Crystallographyurn:issn:2053-2733Hornfeck, W.Kuhn, P.2014-07-10doi:10.1107/S2053273314009218International Union of CrystallographyA low-discrepancy cubic variant of β-Mn is presented, exhibiting local octagonal symmetry upon projection. A comparison of the actual and ideal structure models of β-Mn is made in terms of the newly devised concept of geometrical discrepancy maps. Geometrical discrepancy maps combine predictive and discriminatory powers to appear useful within a wide range of structural chemistry studies.ENβ-Mnoctagonal symmetrylow-discrepancycubic variantA low-discrepancy cubic variant of β-Mn is presented exhibiting local octagonal symmetry upon projection along any of the three mutually perpendicular 〈100〉 axes. Ideal structural parameters are derived to be x(8c) = (2-\sqrt{2})\big/16 and y(12d) = 1\big/(4 \sqrt{2}) for the P4132 enantiomorph. A comparison of the actual and ideal structure models of β-Mn is made in terms of the newly devised concept of geometrical discrepancy maps. Two-dimensional maps of both the geometrical star discrepancy D* and the minimal interatomic distance dmin are calculated over the combined structural parameter range 0 \leq x(8c) \,\lt\, 1/8 and 1/8 \leq y(12d)\, \lt\, 1/4 of generalized β-Mn type structures, showing that the `octagonal' variant of β-Mn is almost optimal in terms of globally minimizing D* while at the same time globally maximizing dmin. Geometrical discrepancy maps combine predictive and discriminatory powers to appear useful within a wide range of structural chemistry studies.text/htmlOctagonal symmetry in low-discrepancy β-manganesetext5702014-07-10Copyright (c) 2014 International Union of CrystallographyActa Crystallographica Section Aresearch papers00Fast microstructure and phase analyses of nanopowders using combined analysis of transmission electron microscopy scattering patterns
http://scripts.iucr.org/cgi-bin/paper?ib5025
The full quantitative characterization of nanopowders using transmission electron microscopy scattering patterns is shown. This study demonstrates the feasibility of the application of so-called combined analysis, a global approach for phase identification, structure refinement, characterization of anisotropic crystallite sizes and shapes, texture analysis and texture variations with the probed scale, using electron diffraction patterns of TiO2 and Mn3O4 nanocrystal aggregates and platinum films. Electron diffraction pattern misalignments, positioning, and slight changes from pattern to pattern are directly integrated and refined within this approach. The use of a newly developed full-pattern search–match methodology for phase identification of nanopowders and the incorporation of the two-wave dynamical correction for diffraction patterns are also reported and proved to be efficient.Copyright (c) 2014 International Union of Crystallographyurn:issn:2053-2733Boullay, P.Lutterotti, L.Chateigner, D.Sicard, L.2014-07-17doi:10.1107/S2053273314009930International Union of CrystallographyThe usefulness of combined analysis for fast determination of crystallite sizes and shapes of nanoparticle aggregates using electron diffraction patterns is demonstrated.ENnanocrystalselectron crystallographyRietveld methodThe full quantitative characterization of nanopowders using transmission electron microscopy scattering patterns is shown. This study demonstrates the feasibility of the application of so-called combined analysis, a global approach for phase identification, structure refinement, characterization of anisotropic crystallite sizes and shapes, texture analysis and texture variations with the probed scale, using electron diffraction patterns of TiO2 and Mn3O4 nanocrystal aggregates and platinum films. Electron diffraction pattern misalignments, positioning, and slight changes from pattern to pattern are directly integrated and refined within this approach. The use of a newly developed full-pattern search–match methodology for phase identification of nanopowders and the incorporation of the two-wave dynamical correction for diffraction patterns are also reported and proved to be efficient.text/htmlFast microstructure and phase analyses of nanopowders using combined analysis of transmission electron microscopy scattering patternstext5702014-07-17Copyright (c) 2014 International Union of CrystallographyActa Crystallographica Section Aresearch papers00Strain distributions and diffraction peak profiles from crystals with dislocations
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Diffraction profiles for different models of dislocation arrangements are calculated directly by the Monte Carlo method and compared with the strain distributions for the same arrangements, which corresponds to the Stokes–Wilson approximation. It is shown that the strain distributions and the diffraction profiles are in close agreement as long as long-range order is absent. Analytical calculation of the strain distribution for uncorrelated defects is presented. For straight dislocations, the Stokes–Wilson and the Krivoglaz–Wilkens approximations give the same diffraction profiles, with the Gaussian central part and ∝ q−3 power law at the tails.Copyright (c) 2014 International Union of Crystallographyurn:issn:2053-2733Kaganer, V.M.Sabelfeld, K.K.2014-07-17doi:10.1107/S2053273314011139International Union of CrystallographyDiffraction profiles for different models of dislocation arrangements are calculated directly by the Monte Carlo method and compared with the strain distributions for the same arrangements, which corresponds to the Stokes–Wilson approximation. The strain distributions and the diffraction profiles are in close agreement as long as long-range order is absent.ENdislocationsMonte Carlo methodspowder diffractionstrainpeak profilesDiffraction profiles for different models of dislocation arrangements are calculated directly by the Monte Carlo method and compared with the strain distributions for the same arrangements, which corresponds to the Stokes–Wilson approximation. It is shown that the strain distributions and the diffraction profiles are in close agreement as long as long-range order is absent. Analytical calculation of the strain distribution for uncorrelated defects is presented. For straight dislocations, the Stokes–Wilson and the Krivoglaz–Wilkens approximations give the same diffraction profiles, with the Gaussian central part and ∝ q−3 power law at the tails.text/htmlStrain distributions and diffraction peak profiles from crystals with dislocationstext5702014-07-17Copyright (c) 2014 International Union of CrystallographyActa Crystallographica Section Aresearch papers00Phasing in Crystallography: A Modern Perspective. By Carmelo Giacovazzo. IUCr Texts on Crystallography, No. 20. International Union of Crystallography/Oxford University Press, 2013. Pp. 432. Price GBP 65.00 (hardback). ISBN 978-0-19-968699-5.
http://scripts.iucr.org/cgi-bin/paper?xo0002
Copyright (c) 2014 International Union of Crystallographyurn:issn:2053-2733Blessing, R.H.2014-07-17doi:10.1107/S2053273314010651International Union of CrystallographyENbook reviewtext/htmlPhasing in Crystallography: A Modern Perspective. By Carmelo Giacovazzo. IUCr Texts on Crystallography, No. 20. International Union of Crystallography/Oxford University Press, 2013. Pp. 432. Price GBP 65.00 (hardback). ISBN 978-0-19-968699-5.text5702014-07-17Copyright (c) 2014 International Union of CrystallographyActa Crystallographica Section Abook reviews00