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Acta Crystallographica. Section A, Foundations and Advances

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https://www.readbyqxmd.com/read/30378583/prices-of-iucr-journals
#1
A T Ashcroft
No abstract text is available yet for this article.
November 1, 2018: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/30378582/ab-initio-structure-determination-of-nanocrystals-of-organic-pharmaceutical-compounds-by-electron-diffraction-at-room-temperature-using-a-timepix-quantum-area-direct-electron-detector-corrigendum
#2
E van Genderen, M T B Clabbers, P P Das, A Stewart, I Nederlof, K C Barentsen, Q Portillo, N S Pannu, S Nicolopoulos, T Gruene, J P Abrahams
Corrections are made to Table 1 in the article by van Genderen et al. [Acta Cryst. (2016), A72, 236-242].
November 1, 2018: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/30378581/crystal-symmetry-aspects-of-materials-with-magnetic-spin-reorientation
#3
Radosław Przeniosło, Piotr Fabrykiewicz, Izabela Sosnowska
The symmetry of materials which undergo a continuous spin reorientation has been analysed. It is shown that continuous spin reorientation is possible only in materials with triclinic or monoclinic crystal structure symmetry, i.e. other symmetries - orthorhombic, tetragonal, trigonal, hexagonal and cubic - are forbidden.
November 1, 2018: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/30378580/computer-simulations-of-x-ray-spherical-wave-dynamical-diffraction-in-one-and-two-crystals-in-the-laue-case
#4
V G Kohn, I A Smirnova
This article reports computer simulations of X-ray spherical wave dynamical diffraction in one and two single crystals in the Laue case. An X-ray compound refractive lens (CRL) as a secondary radiation source of spherical waves was considered for the first time and in contrast to previous simulations with the assumption of the use of a slit. The main properties of the CRL as a secondary source are discussed and two focusing phenomena are analysed. The first one is the diffraction focusing effect for one single crystal in the reflected beam and in the case of a large source-to-detector distance...
November 1, 2018: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/30378579/intensity-distribution-profile-of-double-bragg-scattering-in-the-small-angle-region-from-highly-oriented-pyrolytic-graphite
#5
Yoshinori Ohmasa, Ayano Chiba
It is observed that radial streak patterns of double Bragg scattering appear in the small-angle X-ray scattering from highly oriented pyrolytic graphite (HOPG). The intensity profile of double Bragg scattering from an HOPG sample is calculated theoretically. Assuming that the c axes of the graphite crystallites in the HOPG sample are distributed around an orientation vector and their distribution function has a Gaussian form, it is found that the intensity profile of double Bragg scattering is expressed by a double Gaussian function of the scattering angle and the azimuthal angle of the streak...
November 1, 2018: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/30378578/an-accurate-theory-of-x-ray-coplanar-multiple-srms-diffractometry
#6
V G Kohn
The article reports an accurate theory of X-ray coplanar multiple diffraction for an experimental setup that consists of a generic synchrotron radiation (SR) source, double-crystal monochromator (M) and slit (S). It is called for brevity the theory of X-ray coplanar multiple SRMS diffractometry. The theory takes into account the properties of synchrotron radiation as well as the features of diffraction of radiation in the monochromator crystals and the slit. It is shown that the angular and energy dependence (AED) of the sample reflectivity registered by a detector has the form of a convolution of the AED in the case of the monochromatic plane wave with the instrumental function which describes the angular and energy spectrum of radiation incident on the sample crystal...
November 1, 2018: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/30378577/a-tenfold-twin-of-the-crb-structure-type
#7
Wolfgang Hornfeck
NiZr crystallized from an amorphous matrix or solidified from an undercooled melt exhibits a tenfold twinned microstructure, which is explained by an ideal twin model utilizing special geometric properties of the CrB structure type. The model is unique in several ways: (i) it contains no adjustable parameters other than a scaling factor accounting for the smallest interatomic distance; (ii) it features an irrational shift in the translational part of the twin operation; and (iii) it has many traits commonly observed for quasicrystals, connected to the occurrence of decagonal long-range orientational order, making NiZr the first experimental example of the recently introduced concept of {\bb Z}-module twinning...
November 1, 2018: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/30378576/atomic-scale-analyses-of-bb-z-module-defects-in-an-nizr-alloy
#8
Abdullah Sirindil, Raphael Kobold, Frédéric Mompiou, Sylvie Lartigue-Korinek, Loic Perriere, Gilles Patriarche, Marianne Quiquandon, Denis Gratias
Some specific structures of intermetallic alloys, like approximants of quasicrystals, have their unit cells and most of their atoms located on a periodic fraction of the nodes of a unique {\bb Z}-module [a set of the irrational projections of the nodes of a (N > 3-dimensional) lattice]. Those hidden internal symmetries generate possible new kinds of defects like coherent twins, translation defects and so-called module dislocations that have already been discussed elsewhere [Quiquandon et al. (2016). Acta Cryst...
November 1, 2018: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/30378575/simulating-the-diffraction-line-profile-from-nanocrystalline-powders-using-a-spherical-harmonics-expansion
#9
K R Beyerlein, P Scardi
An accurate description of the diffraction line profile from nanocrystalline powders can be obtained by a spherical harmonics expansion of the profile function. The procedure outlined in this work is found to be computationally efficient and applicable to the line profile for any crystallite shape and size. Practical examples of the diffraction pattern peak profiles resulting from cubic crystallites between 1 and 100 nm in size are shown.
November 1, 2018: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/30378574/blind-lattice-parameter-determination-of-cubic-and-tetragonal-phases-with-high-accuracy-using-a-single-ebsd-pattern
#10
Ming Han, Chen Chen, Guangming Zhao, Lili Li, Gert Nolze, Baojun Yu, Xiaodong Huang, Ye Zhu
The Bravais lattices and their lattice parameters are blindly determined using electron backscatter diffraction (EBSD) patterns of materials with cubic or tetragonal crystal structures. Since the geometric relationships in a single EBSD pattern are overdetermined, the relative errors of determining the lattice parameters as well as the axial ratios are confined to about 0.7 ± 0.4% and 0.07 ± 0.03%, respectively, for ideal simulated EBSD patterns. The accuracy of the crystal orientation determination reaches about 0...
November 1, 2018: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/30378573/on-the-origin-of-crystallinity-a-lower-bound-for-the-regularity-radius-of-delone-sets
#11
Igor A Baburin, Mikhail Bouniaev, Nikolay Dolbilin, Nikolay Yu Erokhovets, Alexey Garber, Sergey V Krivovichev, Egon Schulte
The mathematical conditions for the origin of long-range order or crystallinity in ideal crystals are one of the very fundamental problems of modern crystallography. It is widely believed that the (global) regularity of crystals is a consequence of `local order', in particular the repetition of local fragments, but the exact mathematical theory of this phenomenon is poorly known. In particular, most mathematical models for quasicrystals, for example Penrose tiling, have repetitive local fragments, but are not (globally) regular...
November 1, 2018: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/30182949/calculation-of-absorption-and-secondary-scattering-of-x-rays-by-spherical-amorphous-materials-in-an-asymmetric-transmission-geometry-corrigendum
#12
J C Bendert, M E Blodgett, K F Kelton
A revised version of Table 2 of Bendert et al. [Acta Cryst. (2013). A69, 131-139] is provided.
September 1, 2018: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/30182948/intensive-x-ray-standing-wave-like-fields-localized-near-a-surface-of-a-crystalline-superlattice
#13
I R Prudnikov
A peculiar kind of intensive X-ray standing wave is analytically shown to exist. Such an X-ray interference field is localized in the vicinity of a surface of a crystalline superlattice and its amplitude decays exponentially in both directions perpendicular to the surface. The appearance of the standing wave is accompanied by a deep dip in a chosen Bragg peak of the superlattice.
September 1, 2018: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/30182947/vertex-collisions-in-3-periodic-nets-of-genus-4
#14
Montauban Moreira de Oliveira, Geovane Matheus Lemes Andrade, Eliel Roger da Silva, Jean Guillaume Eon
Unstable nets, by definition, display vertex collisions in any barycentric representation, among which are approximate models for the associated crystal structures. This means that different vertex lattices happen to superimpose when every vertex of a periodic net is located at the centre of gravity of its first neighbours. Non-crystallographic nets are known to be unstable, but crystallographic nets can also be unstable and general conditions for instability are not known. Moreover, examples of unstable nets are still scarce...
September 1, 2018: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/30182946/experimental-and-theoretical-investigations-of-an-x-ray-lll-interferometer-with-a-wedge-shaped-mirror-plate
#15
Tigran H Eyramjyan, Tamara S Mnatsakanyan, Minas K Balyan
An X-ray LLL interferometer with a wedge-shaped mirror plate is experimentally and theoretically investigated. Experimentally obtained interference patterns show that the Moiré fringes are superposed on Pendellösung fringes and the period of the Pendellösung fringes is not changed after passing the analyzer plate. An eikonal theory of interference-fringe formation in an LLL interferometer with a wedge-shaped mirror plate is developed, and provides predictions that coincide with experimentally obtained results...
September 1, 2018: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/30182945/the-real-part-of-the-dispersion-surface-in-x-ray-dynamical-diffraction-in-the-laue-case-for-perfect-crystals
#16
Takashi Saka
The real part of the dispersion surface in X-ray dynamical diffraction in the Laue case for perfect crystals is analysed using a Riemann surface. In the conventional two-beam approximation, each branch or wing of the dispersion surface is specified by one sheet of the Riemann surface. The characteristic features of the dispersion surface are analytically revealed using four parameters, which are the real and imaginary parts of two quantities that specify the degree of departure from the exact Bragg condition and the reflection strength...
September 1, 2018: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/30182944/energy-flow-of-bloch-waves-in-x-ray-dynamical-diffraction-in-the-laue-case-for-perfect-crystals
#17
Takashi Saka
The direction of energy flow for Bloch waves during X-ray dynamical diffraction in perfect crystals is investigated. The energy flow is spread uniformly within the Borrmann fan in the conventional Laue case where the imaginary part of the crystal structure factor is much smaller than the real part. However, when the imaginary part is large, as in the case of X-rays with energies close to the absorption edge for single atoms in crystals, the energy flow direction is found to be restricted, and the results are discussed in relation to the Bragg case...
September 1, 2018: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/30182943/x-ray-reflectivity-of-chemically-vapor-deposited-diamond-single-crystals-in-the-laue-geometry
#18
S Stoupin, J P C Ruff, T Krawczyk, K D Finkelstein
The absolute X-ray reflectivity of chemically vapor-deposited (CVD) single-crystal diamond plates was measured in the Laue geometry in the double-crystal non-dispersive setting with an asymmetric Si beam-conditioner crystal. The measurements were supplemented by rocking-curve topography. The measured reflectivity curves are examined in the framework of the Darwin-Hamilton approach using a set of two independent parameters: the characteristic thickness of mosaic blocks and their average angular misorientation...
September 1, 2018: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/30182942/application-of-differential-resonant-high-energy-x-ray-diffraction-to-three-dimensional-structure-studies-of-nanosized-materials-a-case-study-of-pt-pd-nanoalloy-catalysts
#19
Valeri Petkov, Sarvjit Shastri, Jong Woo Kim, Shiyao Shan, Jin Luo, Jinfang Wu, Chuan Jian Zhong
Atoms in many of the increasingly complex nanosized materials of interest to science and technology do not necessarily occupy the vertices of Bravais lattices. The atomic scale structure of such materials is difficult to determine by traditional X-ray diffraction and so their functional properties remain difficult to optimize by rational design. Here, the three-dimensional structure of Ptx Pd100-x nanoalloy particles is determined, where x = 0, 14, 36, 47, 64 and 100, by a non-traditional technique involving differential resonant high-energy X-ray diffraction experiments conducted at the K edge of Pt and Pd...
September 1, 2018: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/30182941/specular-reflection-intensity-modulated-by-grazing-incidence-diffraction-in-a-wide-angular-range
#20
K V Nikolaev, I A Makhotkin, S N Yakunin, R W E van de Kruijs, M A Chuev, F Bijkerk
Grazing-incidence X-ray diffraction (GID) is a well known technique for the characterization of crystal surfaces. A theoretical study has been performed of the sensitivity of GID to the structure of a crystal surface and distorted nanometre-thin surface layers. To simulate GID from crystals that have a complex subsurface structure, a matrix formalism of the dynamical diffraction theory has been applied. It has been found that the azimuthal rocking curves of a crystal that has a distorted subsurface, measured over a wide angular range, show asymmetric thickness oscillations with two distinguishable sets of frequencies: one corresponding to the diffraction in the single-crystal subsurface layer and the second corresponding to the diffraction in the single-crystal substrate...
September 1, 2018: Acta Crystallographica. Section A, Foundations and Advances
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