Dynamical effects in the integrated X-ray scattering intensity from imperfect crystals in Bragg diffraction geometry. I. Semi-dynamical model
The analytical expressions for the coherent and diffuse components of the integrated reflection coefficient are considered in the case of asymmetric Bragg diffraction geometry for a single crystal of arbitrary thickness, which contains randomly distributed Coulomb-type defects. The possibility to choose the combinations of diffraction conditions optimal for characterizing defects of several types by accounting for dynamical effects in the integrated coherent and diffuse scattering intensities, i.e. primary extinction and anomalous absorption, has been analysed based on the statistical dynamical theory of X-ray diffraction ...
Source: Acta Crystallographica Section A - December 5, 2019 Category: Chemistry Authors: Molodkin, V.B. Olikhovskii, S.I. Dmitriev, S.V. Nizkova, A.I. Lizunov, V.V. Tags: dynamical X-ray diffraction theory diffuse scattering Bragg diffraction geometry Coulomb-type defects Borrmann effect extinction research papers Source Type: research
Converting three-space matrices to equivalent six-space matrices for Delone scalars in S6
The transformations from the primitive cells of the centered Bravais lattices to the corresponding centered cells have conventionally been listed as three-by-three matrices that transform three-space lattice vectors. Using those three-by-three matrices when working in the six-dimensional space of lattices represented as Selling scalars as used in Delone (Delaunay) reduction, one could transform to the three-space representation, apply the three-by-three matrices and then back-transform to the six-space representation, but it is much simpler to have the equivalent six-by-six matrices and apply them directly. The general for...
Source: Acta Crystallographica Section A - November 25, 2019 Category: Chemistry Authors: Andrews, L.C. Bernstein, H.J. Sauter, N.K. Tags: Delaunay Delone centering transformations centered lattices reduced cells lattice centering Niggli Selling matrix transformations research papers Source Type: research
Normally supportive sublattices of crystallographic space groups
The tabulation of normal subgroups of 3D crystallographic space groups that are themselves 3D crystallographic space groups (csg's) is an ambitious goal, but would have a variety of applications. For convenience, such subgroups are referred to as `csg-normal' while normal subgroups of the crystallographic point group (cpg) of a crystallographic space group are referred to as `cpg-normal'. The point group of a csg-normal subgroup must be a cpg-normal subgroup. The present work takes a significant step towards that goal by tabulating the translational subgroups (a.k.a. sublattices) that are capable of supporting csg-normal s...
Source: Acta Crystallographica Section A - November 24, 2019 Category: Chemistry Authors: Clemens, M.A. Campbell, B.J. Humphries, S.P. Tags: space-group symmetry normal subgroups crystallographic sublattices research papers Source Type: research
Elastic propagation of fast electron vortices through amorphous materials
This work studies the elastic scattering behavior of electron vortices when propagating through amorphous samples. A formulation of the multislice approach in cylindrical coordinates is used to theoretically investigate the redistribution of intensity between different angular momentum components due to scattering. To corroborate and elaborate on our theoretical results, extensive numerical simulations are performed on three model systems (Si3N4, Fe0.8B0.2, Pt) for a wide variety of experimental parameters to quantify the purity of the vortices, the net angular momentum transfer, and the variability of the results with res...
Source: Acta Crystallographica Section A - November 3, 2019 Category: Chemistry Authors: L ö ffler, S. Sack, S. Schachinger, T. Tags: electron vortex beams amorphous materials elastic scattering research papers Source Type: research
Verification of the de Wolff hypothesis concerning the symmetry of β -MnO2
The symmetry lowering from tetragonal to orthorhombic is demonstrated using high-resolution diffraction and also justified by using the magnetic superspace groups formalism for the rutile-type compound β -MnO2. The (lower) orthorhombic symmetry is observed at temperatures both below and above the N é el temperature. The magnetic ordering of β -MnO2 is of spin density type and not screw-type helical. The results support the de Wolff [Acta Cryst. (1959), 12, 341 – 345] hypothesis about the orthorhombic symmetry of β -MnO2. (Source: Acta Crystallographica Section A)
Source: Acta Crystallographica Section A - November 3, 2019 Category: Chemistry Authors: Fabrykiewicz, P. Przenioslo, R. Sosnowska, I. Fauth, F. Oleszak, D. Tags: β -MnO2 MnF2 magnetic ordering magnetic space groups symmetry neutron diffraction X-ray diffraction modulated magnetic structures pyrolusite superspace groups research papers Source Type: research
