Structural studies of a new series of ester derivatives in cyclopropanol chemistry

L. Torre-Fernandez, S. Garcia-Granda, M.G. Suero
2008 Acta Crystallographica Section A Foundations of Crystallography  
A large number of simple and complex perovskite oxides have been performed due to the interesting features of superconductor, insulator-metallic transition, ion conduction characteristics, dielectric properties. We synthesized perovskite-type boride CeRh3Bx and ScRh3Bx (x = 0~1) and measured various physical and chemical properties. On the basis of the powder X-ray diffraction, although the lattice constant changes almost linearly with B content, it could be found no drastic transitions of the
more » ... rystal structures, i.e., CeRh3Bx and ScRh3Bx exists in a wide range of boron concentration with the space group Pm-3m. On the other hand, the observed electron diffraction patterns of CeRh3B0.5 and ScRh3B0.5 show the appearance of 1/2 1/2 1/2-type superlattice reflections and fine satellite reflections around all reflections in which anomalous drop of hardness was observed in both system. The new ordered structures producing the superlattice reflections belong to a tetragonal system, space group I4/ mmm. The observed high-resolution images taken with diffraction patterns showing the satellite reflections along the [011] direction show a domain structure, and a lattice modulation and some edge dislocations have been observed at boundaries between the domains. Conclusively, ordering of B atoms and followed by the appearance of the long-ranged modulated structure could lead to the anomalous behavior of hardness in CeRh3Bx and ScRh3Bx alloys. The present paper is aimed at refining the concept of macroscopic self-organization of plastic flow variation, which is based on the assumption that the localization behavior of plastic deformation is related to the conventional parameters of the processes of form changing of material in a stress-strain state. The investigations were performed for FCC single crystals of gamma-Fe alloys. The choice of material is motivated by its capability to deform by different mechanisms (glide or twinning); moreover, the shape of the deformation curve obtained for the test specimens is determined by extension axis orientation. The investigation of plastic deformation macrolocalization was performed by the method of double-exposure speckle photography. It is found that active localized plasticity nuclei would emerge and evolve on the macro-scale level over the entire flow process. It should be noted that this phenomenon has not been earlier observed for materials deforming by twinning. These nuclei can be regarded as meso-scale defects responsible for plastic flow development on the macro-scale level. Their salient feature is that the spatial distributions of elongation, shear and rotation increments within a nucleus are interrelated. Each active localization nucleus corresponds with a set of shears or deformation twins over the glide plane of the acting glide or twinning system, which have maximal Schmidt factor values. A new two-component plastic flow model is proposed, which is appropriate for addressing the distinctive features of plastic flow localization in solids which cannot be explicitly interpreted in the framework of conventional approaches.
doi:10.1107/s0108767308085346 fatcat:flri3y7k75czvpcdrcr6qz26ci