Further evidence of tetragonality in bainitic ferrite

There is growing evidence that bainitic ferrite which retains a substantial amount of carbon in solid solution does not have cubic symmetry. We provide additional data on a different nanostructured bainitic steel to support this evidence, based on synchrotron X-ray diffraction experiments. The data are consistent only with a displacive transformation mechanism for bainite. </jats:p

Textural record of an intra-oceanic subduction: the Careón ophiolite (NW Spain)

Texture analyses were done in mylonitic amphibolites from the Careón ophiolite (Órdenes Complex, NW Iberia). Experiments were carried out using time-of-flight (TOF) neutron diffraction and electron back scattered diffraction (EBSD) techniques to determine crystallographic preferred orientation of the principal phases. While both techniques appear to be complimentary, neutron diffraction plus Rietveld data refinement showed better resolution of low-symmetry phases. Results are discussed within the geological context (Gómez Barreiro et al., 2007a) supporting a continuous deformative evolution from the closure of the Rheic Ocean to the Variscan accretion

Fabric Development in a Middle Devonian Intraoceanic Subduction Regime: The Careón Ophiolite (Northwest Spain)

A Middle Devonian suprasubduction zone ophiolite, the Careo´n Unit (northwest Spain), displays amphibolite-facies ductile deformation fabrics related to the onset of the Rheic Ocean closure. Two different fabrics, an early high-T foliation and a subsequent lower-T foliation, each of which characterized by distinct deformation mechanisms, have been identified in two distinct crustal-scale shear zones of the same ophiolitic thrust sheet. Combined quantitative texture analysis by electron backscattered diffraction and time-of-flight neutron diffraction, were carried out on the shear zones and correlated with micro- and macrostructural data. The results indicate that the regional lineation and shear zone kinematics (east-west, top-to-the-east) represent fabrics developed essentially during the intraoceanic subduction of the Rheic Ocean, and their orientation may be considered a reference vector for convergence models in this part of the Variscan belt

ReX.Cell: a user-friendly program for powder diffraction indexing

ReX.Cellis a novel software package dedicated to the automation of crystal cell indexing starting from powder diffraction data. The program aims to help both novice and experienced powder diffractionists overcome the practical difficulties encountered during powder data indexing, by offering a user-friendly highly interactive interface to classical indexing engines. The software provides a wizard-style approach, accompanying the user through all the typical steps of the indexing procedure: preliminary data processing, background subtraction, data smoothing, peak finding and finally autoindexing. Each step can be carried out automatically or fine-tuned through custom options; in either mode, algorithms and filters are applied in real time to the diffraction data, giving an immediate visual feedback. The program is written in the Java programming language and runs on several different operating systems; source code is provided to allow developers to add support for additional indexing programs and/or powder diffraction data formats.</jats:p

Determination of the crystal structure of nifedipine form C by synchrotron powder diffraction

The crystal structure of the metastable form C polymorph of nifedipine [C17H18N2O6, 3,5-dimethyl 2,6-dimethyl-4-(2-nitrophenyl)-1,4-dihydropyridine-3,5-dicarboxylate] was determined by means of direct-space techniques applied to high-resolution synchrotron powder diffraction data. The polymorph crystallizes in the space group P\bar 1 and exhibits a molecular packing significantly different from that of the stable modification, with molecules aligned in an orthogonal configuration inside the unit cell. The molecular conformation, on the other hand, remains substantially unmodified between the two polymorphs. Additionally, in situ thermal characterization of nifedipine crystallization behaviour was performed, confirming the nucleation of another metastable polymorph (form B) prior to the complete crystallization of the stable modification. A complete structural characterization of form B was not possible owing to its very limited stability interval.</jats:p

ReX: a computer program for structural analysis using powder diffraction data

Multi-platform software has been developed for the analysis of powder diffraction data, with particular focus on structure solution. The program provides a Rietveld optimization engine, with the possibility of refining parameters describing both the sample and the instrument model. Geometric constraints such as rigid fragments and torsion angles can be defined for the atomic structure, to reduce the number of degrees of freedom of the model. An innovative hierarchical description of the asymmetric unit has been adopted, which allows, in principle, the definition of arbitrarily complex geometric relationships. Additionally, global optimization algorithms may be used in place of the standard nonlinear least squares, when particularly challenging problems are being faced