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ISSN: 2053-2733

March 2019 issue

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Cover illustration: Tensor tomography methods reconstruct the orientation of a sample's local anisotropic micro/nanostructure without the need for sections. The new iterative reconstruction tensor tomography (IRTT) algorithm [Gao et al. (2019). Acta Cryst. A75, 223-238] is a simple, fast and robust algorithm, thanks to its use of a rank-2 tensor (ellipsoid) model, shown at the top, combined with a linearized iterative reconstruction scheme. Here it is showcased based on SAXS data from different samples, such as a carbon fibers tied in a knot (bottom left), collagen fibers in a human bone trabecula and myelinated axons in a mouse brain (bottom right).

editorial


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A collection of articles from presentations at the Aperiodic 2018 conference is introduced.

advances

research papers


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In situ single-crystal X-ray diffraction data were used to unravel the structural dynamics and enthalpy and entropy of adsorption of CO2 into Y zeolite. A principal-component-analysis- (PCA) based approach is applied in an innovative way to single-crystal X-ray diffraction data analysis, allowing one to selectively detect the information from the subset of active atoms. The potential of and limitations of PCA in single-crystal diffraction are discussed.

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A fast and robust reconstruction algorithm for small-angle scattering tensor tomography, named iterative reconstruction tensor tomography, is presented. It employs a second-rank tensor model and an iterative error backpropagation to simplify and accelerate tensor tomography reconstruction.

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Reconstruction of an object from the averaged coherent diffracted intensity of finite crystals of that object with arbitrary lattice occupancies is possible. An algorithm capable of reconstructing both the so-called averaged shape transform and the object density at the same time is demonstrated.

aperiodic 2018


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Quantitative parameters of modulated crystal structures are determined from density functional theory calculations applied to superstructures obtained using the superspace formalism. The example of mullite is used to demonstrate that with this approach versatile aspects ranging from ordering phenomena to phase diagrams can be understood on a new level.

foundations

aperiodic 2018


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Ted Janssen's contributions to the field of aperiodic crystals are reviewed.

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The nucleation and growth dynamics of a decagonal quasicrystal and its approximant `X' phase are considered. Various similarities and differences are elucidated.

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The Fe2Al5 structure is remarkable among intermetallic phases for its channels of weakly ordered Al atoms. This article traces the origins of these channels to the cooperative effects of soft atomic motions dictated by chemical pressure quadrupoles and preferred electron concentrations.

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Analysis of a dodecagonal quasicrystal based on 8100 vertices from atomically resolved scanning tunnelling microscopy has been carried out. A detailed frequency and orientational analysis is presented for the triangle–square–rhomb tiling of a BaTiO3-derived quasicrystal.

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The physical significance of clusters in Al13TM4 compounds is invesitgated through ab initio methods based on density functional theory.

research papers


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All homogeneous sphere packings were derived that refer to the trivariant lattice complexes of monoclinic space groups of types P2/c and P21/c.

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Combining multi-slice ptychography with multi-modality scanning probe microscopy reconstructs two planes of nanostructures separated by 500 nm with sub-20 nm lateral resolution, assisted by simultaneously measured fluorescence maps for decoupling low-spatial-frequency features.

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An inhomogeneity of material in W/Si multilayer structures was studied with grazing-incidence small-angle X-ray scattering. The experimental study revealed lateral density fluctuations in the Si spacer layers.

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The structure factor with lattice phason flips for a decagonal quasicrystal is derived. Bias in the calculated diffraction data is most likely to be a consequence of multiple scattering.

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Absorption and secondary scattering corrections for a cylindrical sample geometry are developed for the case when the incident beam is smaller than the sample and, in general, off-center from the cylinder.

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Consideration of the maximum space-filling principle and the short-range (local) and long-range (translational) order using Voronoi–Dirichlet polyhedra reveals the most probable number of neighboring atoms and the concept of antiliquid.

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A group-theoretical analysis of 1:3 A-site-ordered perovskite structures is reported.

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The transferable aspherical pseudoatom data bank, UBDB2018, is extended with over 130 new atom types present in small and biological molecules of importance in biology and chemistry. UBDB2018 can be used to enhance the physical meaning of molecular electrostatic potentials which can be utilized in, amongst other fields, drug discovery studies.

addenda and errata


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A correction and additions concerning the limiting point groups are made to the article by Grimmer [Acta Cryst. (2017), A73, 333–345].

book reviews


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