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ISSN: 2053-2733

May 2011 issue

Highlighted illustration

Cover illustration: Polar mode GM6 (left) and antiferrodistortive mode M3-1q (right) present in the monoclinic structure of SrAl2O4, together with a graph of maximal subgroups showing their isotropy subgroups. The amplitude of mode GM6 is much larger, and ab initio calculations confirm its soft character, while distortion M3-1q is a hard mode frozen as an induced secondary distortion [Perez-Mato et al. (2010). Acta Cryst. A66, 558-590]. The mode figures were drawn using FullProf Studio [Rodriguez-Carvajal (1993). Physica B, 192, 55-69].

research papers


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Continuity of octahedral tilting in perovskite compounds necessarily leads to different tilt structures at planar defects such as domain walls.

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An attempt is made to go beyond the distorted-wave Born approximation by using the integral wave equation adjusted with the Green function formalism in application to the grazing-incidence small-angle X-ray (GISAX) scattering from a random rough surface. The self-consistent approximation for the wavefunction is applied to obtain a basic solution of the non-averaged integral wave equation. The analytical expressions for the reflected GISAX specular and diffuse scattering intensities are obtained using the statistical model of a random Gaussian surface in terms of the r.m.s. roughness and two-point cumulant correlation function.

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The variance of electron-density maps (observed, difference and hybrid) is estimated in P1 under the hypothesis that the phases are distributed about the correct values according to von Mises distributions.

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A rapid, easy-to-perform translation calibration procedure has been developed for use with the EMBL/ESRF mini-κ goniometer head and for other inverse-kappa goniometers designed for macromolecular crystallography. Regular calibration ensures the precision of experiments that rely on many degrees of freedom in crystal reorientation.

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Large sets of highly precise and accurate structure factors and anisotropic Debye–Waller factors for the tetragonal chemically ordered and ferromagnetic intermetallic phase FePd were simultaneously obtained using multi-beam convergent-beam electron diffraction (CBED). The CBED pattern sensitivity to structure and Debye–Waller factor changes is assessed and the potential for bonding charge measurements in FePd is discussed.

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An infinite family of non-crystallographic nets is constructed and analysed.

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The effects of faulting on the powder line profile are discussed, in particular considering the case of small crystalline face-centered-cubic domains.

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The peculiar magnetoelectric properties of Ba2CoGe2O7 are explained by making use only of symmetry arguments and symmetry-based phenomenology. This remarkable example shows the general need for a systematic application of magnetic symmetry in the study of multiferroics.

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A reference table of exact direct-space asymmetric units for the 230 crystallographic space groups is presented, based on a new geometric notation for asymmetric unit conditions.

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A new set of statistical formulas estimating the σA parameter are described and their mean features are studied.

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A version of the charge-flipping algorithm is introduced to handle incomplete data. The efficiency of the algorithm is thoroughly tested, and it is shown that many small-molecule structures can be solved by utilizing significantly fewer data than is standard in current crystallographic practice.

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The method of elementary symmetric polynomials with a new origin definition is used to enumerate small one-dimentional crystal structures obtained from a minimum set of diffraction intensities.

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It is shown that a reduction in data quality does not alter the success of structure solution of unknown crystals, with high accuracy of the cation positions. The accuracy of the light-atom positions may be slightly reduced.

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The structures of Mn2O3 and PbMnO2.75 have been solved from powder samples by precession electron diffraction data. The number of reflections measured appears to be the significant parameter for structure solution rather than precession angle, resolution limit and Lorentz-type correction.

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The extra reflection conditions as given in International Tables for Crystallography Volume A may be violated if the atomic thermal vibrations and/or static disorder are anisotropic.

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