Acta Crystallographica Section A
https://journals.iucr.org/a/issues/2024/05/00/index.html
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) 2024 International Union of Crystallography2024-08-27International 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 80, Part 5, 2024textweekly62002-01-01T00:00+00:005802024-08-27Copyright (c) 2024 International Union of CrystallographyActa Crystallographica Section A: Foundations and Advances358urn:issn:2053-2733med@iucr.orgAugust 20242024-08-27Acta Crystallographica Section Ahttp://journals.iucr.org/logos/rss10a.gif
https://journals.iucr.org/a/issues/2024/05/00/index.html
Still imageInstrumental broadening and the radial pair distribution function with 2D detectors
https://journals.iucr.org/paper?ib5123
The atomic pair distribution function (PDF) is a real-space representation of the structure of a material. Experimental PDFs are obtained using a Fourier transform from total scattering data which may or may not have Bragg diffraction peaks. The determination of Bragg peak resolution in scattering data from the fundamental physical parameters of the diffractometer used is well established, but after the Fourier transform from reciprocal to direct space, these contributions are harder to identify. Starting from an existing definition of the resolution function of large-area detectors for X-ray diffraction, this approach is expanded into direct space. The effect of instrumental parameters on PDF peak resolution is developed mathematically, then studied with modelling and comparison with experimental PDFs of LaB6 from measurements made in different-sized capillaries.Copyright (c) 2024 International Union of Crystallographyurn:issn:2053-2733Chernyshov, D.Marshall, K.P.North, E.T.Fuller, C.A.Wragg, D.S.2024-07-15doi:10.1107/S2053273324006569International Union of CrystallographyThe instrumental resolution function for pair distribution functions (PDFs) with 2D detectors is expressed and used to simulate the impact of various parameters on experimental PDF data sets.ENpowder diffractioninstrumental resolutionpair distribution functions2D detectorThe atomic pair distribution function (PDF) is a real-space representation of the structure of a material. Experimental PDFs are obtained using a Fourier transform from total scattering data which may or may not have Bragg diffraction peaks. The determination of Bragg peak resolution in scattering data from the fundamental physical parameters of the diffractometer used is well established, but after the Fourier transform from reciprocal to direct space, these contributions are harder to identify. Starting from an existing definition of the resolution function of large-area detectors for X-ray diffraction, this approach is expanded into direct space. The effect of instrumental parameters on PDF peak resolution is developed mathematically, then studied with modelling and comparison with experimental PDFs of LaB6 from measurements made in different-sized capillaries.text/htmlInstrumental broadening and the radial pair distribution function with 2D detectorstext5802024-07-15Copyright (c) 2024 International Union of CrystallographyActa Crystallographica Section Aresearch papers358366On uniform edge-n-colorings of tilings
https://journals.iucr.org/paper?uv5027
An edge-n-coloring of a uniform tiling {\cal T} is uniform if for any two vertices of {\cal T} there is a symmetry of {\cal T} that preserves the colors of the edges and maps one vertex onto the other. This paper gives a method based on group theory and color symmetry theory to arrive at uniform edge-n-colorings of uniform tilings. The method is applied to give a complete enumeration of uniform edge-n-colorings of the uniform tilings of the Euclidean plane, for which the results point to a total of 114 colorings, n = 1, 2, 3, 4, 5. Examples of uniform edge-n-colorings of tilings in the hyperbolic plane and two-dimensional sphere are also presented.Copyright (c) 2024 International Union of Crystallographyurn:issn:2053-2733Abila, A.K.De Las Peñas, M.L.A.Tomenes, M.2024-07-29doi:10.1107/S2053273324005643International Union of CrystallographyA method is presented for arriving at uniform edge-n-colorings of uniform tilings using concepts in group theory and color symmetry theory.ENuniform edge-n-coloringsuniform tilingsedge orbitscolor symmetryAn edge-n-coloring of a uniform tiling {\cal T} is uniform if for any two vertices of {\cal T} there is a symmetry of {\cal T} that preserves the colors of the edges and maps one vertex onto the other. This paper gives a method based on group theory and color symmetry theory to arrive at uniform edge-n-colorings of uniform tilings. The method is applied to give a complete enumeration of uniform edge-n-colorings of the uniform tilings of the Euclidean plane, for which the results point to a total of 114 colorings, n = 1, 2, 3, 4, 5. Examples of uniform edge-n-colorings of tilings in the hyperbolic plane and two-dimensional sphere are also presented.text/htmlOn uniform edge-n-colorings of tilingstext5802024-07-29Copyright (c) 2024 International Union of CrystallographyActa Crystallographica Section Aresearch papers367378Indexing neutron transmission spectra of a rotating crystal
https://journals.iucr.org/paper?lu5036
Neutron time-of-flight transmission spectra of mosaic crystals contain Bragg dips, i.e., minima at wavelengths corresponding to diffraction reflections. The positions of the dips are used for investigating crystal lattices. By rotating the sample around a fixed axis and recording a spectrum at each rotation step, the intensity of the transmitted beam is obtained as a function of the rotation angle and wavelength. The questions addressed in this article concern the determination of lattice parameters and orientations of centrosymmetric crystals from such data. It is shown that if the axis of sample rotation is inclined to the beam direction, the reflection positions unambiguously determine reciprocal-lattice vectors, which is not the case when the axis is perpendicular to the beam. Having a set of such vectors, one can compute the crystal orientation or lattice parameters using existing indexing software. The considerations are applicable to arbitrary Laue symmetry. The work contributes to the automation of the analysis of diffraction data obtained in the neutron imaging mode.Copyright (c) 2024 International Union of Crystallographyurn:issn:2053-2733Morawiec, A.2024-08-08doi:10.1107/S2053273324007253International Union of CrystallographyNeutron transmission spectra of a rotating crystal carry information about its lattice. The relationship between Bragg-dip positions in the spectra and the crystal lattice is investigated theoretically, and schemes for unambiguous determination of crystal orientation and lattice parameters are presented.ENneutron diffractionneutron transmission spectraBragg dipsindexingorientation determinationNeutron time-of-flight transmission spectra of mosaic crystals contain Bragg dips, i.e., minima at wavelengths corresponding to diffraction reflections. The positions of the dips are used for investigating crystal lattices. By rotating the sample around a fixed axis and recording a spectrum at each rotation step, the intensity of the transmitted beam is obtained as a function of the rotation angle and wavelength. The questions addressed in this article concern the determination of lattice parameters and orientations of centrosymmetric crystals from such data. It is shown that if the axis of sample rotation is inclined to the beam direction, the reflection positions unambiguously determine reciprocal-lattice vectors, which is not the case when the axis is perpendicular to the beam. Having a set of such vectors, one can compute the crystal orientation or lattice parameters using existing indexing software. The considerations are applicable to arbitrary Laue symmetry. The work contributes to the automation of the analysis of diffraction data obtained in the neutron imaging mode.text/htmlIndexing neutron transmission spectra of a rotating crystaltext5802024-08-08Copyright (c) 2024 International Union of CrystallographyActa Crystallographica Section Aresearch papers379386Superstructure reflections in tilted perovskites
https://journals.iucr.org/paper?tw5009
The superstructure spots that appear in diffraction patterns of tilted perovskites are well documented and easily calculated using crystallographic software. Here, by considering a distortion mode as a perturbation of the prototype perovskite structure, it is shown how the structure-factor equation yields Boolean conditions for the presence of superstructure reflections. This approach may have some advantages for the analysis of electron diffraction patterns of perovskites.Copyright (c) 2024 International Union of Crystallographyurn:issn:2053-2733Beanland, R.Sjökvist, R.2024-07-26doi:10.1107/S2053273324007113International Union of CrystallographyBoolean conditions are derived from the structure-factor equation, relating distortions of a prototype perovskite structure to the emergence of superstructure reflections.ENperovskiteselectron diffractionstructure factorsoctahedral tiltingThe superstructure spots that appear in diffraction patterns of tilted perovskites are well documented and easily calculated using crystallographic software. Here, by considering a distortion mode as a perturbation of the prototype perovskite structure, it is shown how the structure-factor equation yields Boolean conditions for the presence of superstructure reflections. This approach may have some advantages for the analysis of electron diffraction patterns of perovskites.text/htmlSuperstructure reflections in tilted perovskitestext5802024-07-26Copyright (c) 2024 International Union of CrystallographyActa Crystallographica Section Ashort communications387390Dieter Schwarzenbach (1936–2024)
https://journals.iucr.org/paper?es5057
Copyright (c) 2024 International Union of Crystallographyurn:issn:2053-2733Chapuis, G.2024-08-12doi:10.1107/S2053273324007642International Union of CrystallographyObituary for Dieter Schwarzenbach.ENobituaryelectron densitycharge densityfullerenesstatistical descriptorsInternational Union of Crystallographytext/htmlDieter Schwarzenbach (1936–2024)text5802024-08-12Copyright (c) 2024 International Union of CrystallographyActa Crystallographica Section Aobituaries391393