issue contents

Journal logoSTRUCTURAL SCIENCE
CRYSTAL ENGINEERING
MATERIALS
ISSN: 2052-5206

December 2006 issue

Highlighted illustration

Cover illustration: Room-temperature structure of the cation-deficient perovskite, Nd0.7Ti0.9Al0.1O3 [Zhang et al. (2006). Acta Cryst. B62, 60-67>]. The superlattice peaks associated with out-of-phase octahedral tilting (shown) have intensities consistent with tilting around the x and y axes (sum of a- and c-), but tilting around the y axis (contribution b-) evidently does not occur. The tilt system in Glazer's notation is thus a-b0c-, and the space group and structure are found from the tree displayed. Two views of the structure are shown - the (TiAl)O6 are shown as octahedra, the Ti/Al atom being visible within them, and the darker and lighter spheres outside these octahedra represent fully and partly occupied layers of Nd, respectively. The octahedral tilting, around both x and y axes, is clearly seen.

research papers


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The order–disorder phase transition in monoclinic β-sulfur has been characterized using high-resolution neutron powder diffraction. The transition is critical and continuous, with a transition temperature, Tc = 198.4 (3) K, and a critical exponent, β = 0.28 (3), which is indicative of three-dimensional ordering.

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The structure of strontium barium niobate crystals is studied in the whole range of the tetragonal tungsten bronze phase using X-ray diffraction measurements. Unit-cell parameters, density, site-occupancy factors and interionic distances show pronounced composition dependencies which are explained by model calculations.

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The crystal structure of Ni4Ti3 precipitates was refined by means of quantitative electron diffraction in combination with density functional theory. Application of the multi-slice least-squares (MLSL) method made the refinement possible.

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The fully ordered crystal structure of Zr2NiD4.5 has been determined by combined synchrotron-radiation powder diffraction, electron diffraction and powder neutron diffraction.

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The neutron diffraction study on the ordered Cr2N superstructure has been carried out. The occupancies of the N atoms in four crystallographic sites were determined, and the deviations of the metal atoms from their ideal positions are also specified. The ideal and measured crystal structures of Cr2N are compared.

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The compression mechanism of FeF3 has been studied by time-of-flight neutron powder diffraction. No structural phase transitions were observed, but a small octahedral strain was found to develop during compression which reflects an elongation of the FeF6 octahedra along the c axis.

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Bibliometric studies based on data from the Inorganic Crystal Structure Database were performed with a focus on growth rates and distribution of publications, productivity of authors and multiple authorship.

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The crystal structure, stacking faults and twinning of the low-temperature form of barium metagermanate are described using X-ray powder diffraction and electron microscopy.

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A general algorithm to analyze voids in crystal structures was developed and implemented into the computer package TOPOS. This approach was used to predict the positions of Li+ and Na+ cations and to analyze their possible migration paths in the solid superionic materials Li3M2P3O12 (M = Sc, Fe; LIPHOS) and Na1 + xZr2SixP3 − xO12 (NASICON)

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Ab initio crystal structure determination of a new high-pressure high-temperature phase of GaAsO4 from powder data. This new hexagonal phase contains fragments of the rutile-like structure and represents the preceding high-pressure step before the stabilization of the rutile structure.

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The crystal structures of several possible low-temperature polymorphs of CaSiO3 perovskites, and their evolution with pressure, are determined from first-principles calculations.

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The five-dimensional incommensurately modulated structure of a natural fresnoite crystal has been solved and refined from X-ray single-crystal diffraction data at 110 K in terms of superspace representation.

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A vectorial interpretation of the bond-valence concept is proposed to adequately describe coordination geometry in metal complexes which involve multidentate ligands. Representation of the latter by a single such vector often leads to the direct applicability of the valence-shell electron-pair repulsion model.

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The structure of the co-crystal hexamethylenetetramine resorcinol is incommensurately modulated at room temperature. The structure is noteworthy for the simultaneous presence of disorder and occupational modulation.

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The radical p-benzosemiquinone was detected in the solid state by X-ray structure analysis and EPR spectroscopy. A low-barrier O—H⋯O hydrogen bond stabilizes the radical. The two polymorphs of p-benzosemiquinone were observed and their structures solved.

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The hydrophobic recognition of N-4-nitrobenzoyl-D- or N-4-nitrobenzoyl-L-amino acids at the surface of strychnine self-assemblies causes the resulting surface to have more hydrophilic properties, which are more appropriate for interactions in the hydrophilic environments from which the strychnine salts were investigated.

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The pressure-frozen structure of 1,2,3-trichloropropane, C3H5Cl3, has been determined by single-crystal X-ray diffraction at 0.28 and 0.35 GPa, and the intermolecular electrostatic, halogen⋯halogen and halogen⋯H crystal cohesion forces have been related to the crystal morphology and compressibility.

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The crystal structures of three new high-pressure phases of 1,2-diaminoethane have been determined, and transformation between the four known phases of 1,2-diaminoethane has been rationalized by revealing the competing patterns of NH⋯N hydrogen bonding.

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Pressure-frozen CH2Br2 at 0.61 GPa forms C2/c crystals, while CH2I2 crystallizes at 0.16 GPa in the polar space group Fmm2. Transformations between C2/c and Fmm2 structures of CH2I2 at varied temperature and intermolecular electrostatic halogen⋯halogen and H⋯halogen crystal cohesion forces have been analysed.

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The crystal structure of salicylaldoxime has been determined at room temperature at pressures from 0.75 to 5.28 GPa. Salicylaldoxime forms a pseudo-macrocycle which contains a cavity which decreases in size with pressure. Above 5.28 GPa the structure transforms to a new polymorph, the structure of which has been determined at 5.93 GPa. The changes in intermolecular interactions during the phase transition are interpreted with the aid of PIXEL calculations.

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The crystal structures of five β-enaminones, forming strong intramolecular N—H⋯O resonance-assisted hydrogen bonds, have been determined at 150 K. These structures were compared with those of other similar compounds in order to discover which steric and electronic factors are important in the formation of very strong hydrogen bonds.

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The crystal structures of the β1 polymorphs of mono-unsaturated triacylglycerols and of the isomorphous β-VI cocoa butter have been solved from high-resolution powder diffraction data. This complicated but successful structure solution has led to a new model for the published β2 (β-V) structure.

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An improved crystal structure model has been established for the β2 polymorph of mono-unsaturated triacylglycerols and the isomorphous β-V structure of cocoa butter. For the first time two asymmetric β2 polymorphs are reported and the fat-bloom mechanism of chocolate is explained.
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