Journal of Applied Crystallography

doi: 10.1107/S0021889810021424pmid: N/A

Pauw, Brian R.; Vigild, Martin E.; Mortensen, Kell; Andreasen, Jens W.; Klop, Enno A.

doi: 10.1107/S0021889810017061pmid: N/A

After consideration of the applicability of classical methods, a novel analysis method for the characterization of fibre void structures is presented, capable of fitting the entire anisotropic two‐dimensional scattering pattern to a model of perfectly aligned, polydisperse ellipsoids. It is tested for validity against the computed scattering pattern for a simulated nanostructure, after which it is used to fit the scattering from the void structure of commercially available heat‐treated poly(p‐phenylene terephtalamide) fibre and its as‐spun precursor fibre. The application shows a reasonable fit and results in size distributions for both the lengths and the widths of the ellipsoidal voids. Improvements to the analysis methods are compared, consisting of the introduction of an orientation distribution for the nano‐ellipsoids, and the addition of large scatterers to account for the effect of fibrillar scattering on the scattering pattern. The fit to the scattering pattern of as‐spun aramid fibre is improved by the introduction of the large scatterers, while the fit to the scattering pattern obtained from the heat‐treated fibre improves when an orientation distribution is taken into account. It is concluded that, as a result of the heat treatment, the average width and length of the scatterers increase.

Shian, S; Sandhage, K.H

doi: 10.1107/S0021889810016730pmid: N/A

The chemical, electrochemical, optical and electro-optical properties of titanium oxyfluoride, TiOF2, have led to interest in this compound for a number of applications. Prior analyses have indicated that TiOF2 possesses a simple cubic structure (space group Pmm) at room temperature. Three-dimensional nanostructured assemblies of polycrystalline TiOF2 have recently been synthesized via chemical conversion of intricate SiO2 structures by metathetic reaction with TiF4(g). Rietveld analysis has been used to evaluate the structure of the TiOF2 product formed by such reaction at 623 K. Unlike prior reports, this TiOF2 product possessed a hexagonal structure (space group Rc) at room temperature. Upon heating through 333-338 K, the hexagonal TiOF2 polymorph converted into cubic (Pmm) TiOF2. Differential scanning calorimetry and X-ray diffraction analyses have been used to evaluate this thermally induced phase transformation.

Hammouda, Boualem

doi: 10.1107/S0021889810015773pmid: N/A

Small‐angle scattering (SAS) curves are characterized by two main features: the Guinier region and the Porod region. Standard linear plots are available to fit SAS data and obtain a radius of gyration and a Porod exponent. A new Guinier–Porod empirical model is introduced to fit SAS data from spherical as well as nonspherical objects such as rods or platelets. It also applies to shapes intermediate between spheres and rods or between rods and platelets. The new model is used to fit SAS data from a Pluronic solution that sequentially forms unimers, then spherical micelles, then cylindrical micelles, then lamellar micelles upon heating. This single model can fit structures associated with all four phases as well as the intermediate structures.

Westrip, S.P

doi: 10.1107/S0021889810022120pmid: N/A

publCIF is an application designed for creating, editing and validating crystallographic information files (CIFs) that are used in journal publication. It validates syntax and dictionary-defined data attributes through internal routines, and also provides a web interface to the checkCIF service of the International Union of Crystallography (IUCr), which provides a full crystallographic analysis of the structural data. The graphical interface allows users to edit the CIF either in its `raw' ASCII form (using a text editor with context-sensitive data validation and input facilities) or as a formatted representation of a structure report (using a word-processing environment), as well as via a number of convenience tools (e.g. spreadsheet representations of looped data). Beyond file and data validation, publCIF provides access to resources to facilitate preparation of a structure report (e.g. databases of author details, experimental data, standard references etc., either distributed with the program or collected during its use), along with tools for reference parsing, spell checking, structure visualization and image management. publCIF was commissioned by the IUCr, both as free software for authors and as a tool for in-house journal production; the tool for authors is described here. Binary distributions for Linux, MacOS and Windows operating systems are available.

Kakinouchi, K; Nakamura, T; Tamada, T; Adachi, H; Sugiyama, S; Maruyama, M; Takahashi, Y; Takano, K; Murakami, S; Inoue, T; Kuroki, R; Mori, Y; Matsumura, H

doi: 10.1107/S0021889810015967pmid: N/A

A method for growing large protein crystals is described. In this method, a cut pipette tip is used to hang large-scale droplets (maximum volume 200 microl) consisting of protein and precipitating agents. A crystal grows at the vapor-liquid interface; thereafter the grown crystal can be retrieved by droplet-droplet contact both for repeated macroseeding and for mounting crystals in a capillary. Crystallization experiments with peroxiredoxin of Aeropyrum pernix K1 (thioredoxin peroxidase, ApTPx) and hen egg white lysozyme demonstrated that this large-scale hanging-drop method could produce a large-volume crystal very effectively. A neutron diffraction experiment confirmed that an ApTPx crystal (6.2 mm3) obtained by this method diffracted to beyond 3.5 A resolution.

Shian, Samuel; Sandhage, Kenneth H.

doi: 10.1107/S0021889810016730pmid: N/A

The chemical, electrochemical, optical and electro‐optical properties of titanium oxyfluoride, TiOF2, have led to interest in this compound for a number of applications. Prior analyses have indicated that TiOF2 possesses a simple cubic structure (space group Pmm) at room temperature. Three‐dimensional nanostructured assemblies of polycrystalline TiOF2 have recently been synthesized via chemical conversion of intricate SiO2 structures by metathetic reaction with TiF4(g). Rietveld analysis has been used to evaluate the structure of the TiOF2 product formed by such reaction at 623 K. Unlike prior reports, this TiOF2 product possessed a hexagonal structure (space group Rc) at room temperature. Upon heating through 333–338 K, the hexagonal TiOF2 polymorph converted into cubic (Pmm) TiOF2. Differential scanning calorimetry and X‐ray diffraction analyses have been used to evaluate this thermally induced phase transformation.

Hammouda, B

doi: 10.1107/S0021889810015773pmid: N/A

Small-angle scattering (SAS) curves are characterized by two main features: the Guinier region and the Porod region. Standard linear plots are available to fit SAS data and obtain a radius of gyration and a Porod exponent. A new Guinier-Porod empirical model is introduced to fit SAS data from spherical as well as nonspherical objects such as rods or platelets. It also applies to shapes intermediate between spheres and rods or between rods and platelets. The new model is used to fit SAS data from a Pluronic solution that sequentially forms unimers, then spherical micelles, then cylindrical micelles, then lamellar micelles upon heating. This single model can fit structures associated with all four phases as well as the intermediate structures.

Tiwari, R.N; Chen, W.-C; Tiwari, J.N; Wang, W.-L; Chang, L

doi: 10.1107/S0021889810018340pmid: N/A

Thin diamond microplates have been grown on dome-like/hemispherical carbon particles on titanium carbide by a microwave plasma chemical vapour deposition (MPCVD) method using a gas mixture of methane and hydrogen. The diamond microplates have a thickness of about 200 nm. A thin (300 nm) film of titanium carbide was formed during carburization of sputtered titanium on an Si(100) substrate in MPCVD. The hemispherical carbon particles were covered with diamond microplates. The diamond microplates are isolated electron-emitting spherules and exhibit a low threshold (50 V microm-1) and high current density (0.92 mA cm-2) in their field emission properties. A possible mechanism for the formation of the diamond microplates and hemispherical carbon particles is presented.

Onoda, M; Takada, K; Sasaki, T

doi: 10.1107/S0021889810012653pmid: N/A

Information about the features of Bragg reflections and/or diffuse streaks was obtained through simulation of a neutron powder diffraction pattern based on the model used in a successful analysis of the superconductor 2H-NaxCoO2.yD2O (x 0.35, y 1.3). Intensity distributions were calculated based on a superstructure expression of a commensurate composite crystal model, where the structures of the CoO2 part (a1 = b1 = 2.82 A) and the guest (a2 = b2 = 3.26 A) with short-range order stacking are described on a cell of A = B = 2a1 = 31/2a2 = 5.64 A, and with alternate stacking based on c = 4.9 A. It is shown that the most conspicuous diffuse reflection band corresponds to the main reflection scattering of the guest sheet, with local maxima at half-integer positions of ' based on the stacking distance 2c, and that the Bragg diffraction components of the host and guest are coherent in terms of the peak height at integer '' based on 4c.