Structural studies in single and poly crystals of Yb_(1-x)Tb_(x)MnO₃ manganites

Rare-earth manganites, RMnO3, have been object of intense theoretical and experimental research; mainly focused on the exotic properties observed in these materials. Ferroelectricity, ferromagnetism, superconductivity and multiferroicity are some of the properties observed in RMnO3, been the multiferroicity the most important phenomena of the parent manganites YbMnO3 and TbMnO3 [1]. The focus of the present work is to find correlations between structural characteristics and the physical properties of some type of ferroic materials. Polycrystalline perovskites of Yb1-xTbxMnO3 (x=0, 0.25, 0.50, 0.75 and 1) were synthesized using solid-state method. Single crystals of the same compounds are to be produced by LHPG (Laser Heated Pedestal Growth) [2]. In the present work structural studies at room temperature will be reported. Samples with x=0 and 1 crystallizes in the P63cm and Pnma space groups, respectively. In the case of mixed compounds attention was paid to the study of the phase coexistence as well as to the site occupancy shared between rare-earth Tb and Yb [3]. Magnetic studies using powder samples were not conclusive due to the high anisotropy observed in these materials. Single crystals are under production in order to allow magnetic directional studies and consequently to search for results that can be correlated to the crystal structure. Improvement has to be made in the rare-earth site occupancy model to better associate magnetic results with atomic positions and individual magnetic moments.

IYCr2014: Special Events Organized in Brazil - ABCr

IYCr2014 activities of the Brazilian Crystallographic Association started last year, with its members actively participating in the First Latin American Congress of Crystallography (Oct.29-Nov.2, 2013) in Córdoba, Argentina. This meeting was a milestone to integrate the Latin American Crystallographic community, originating the Founding Act of the Latin American Crystallographic Association. After this event, groups from different parts of Brazil started planning activities for the celebration of IYCr2014. Some of the main events are: The EMBL sponsored the Structural and Biophysical Methods for Macromolecules in Solution course (Jan.19-26), that took place at the Univ. of Sao Paulo, within the Global Exchange Lecture Course Program. At IFSC-USP, a Macromolecular Crystallography School "from data processing to structure refinement and beyond" will be held on April 8-16, organized by CCCP4 and local researchers. At the annual meeting of the Braz. Chem. Soc. the symposium Past, Present and Future of Protein Crystallography in Brazil (26-29 May) is being organized. A Latin American Summit Meeting on Biological Crystallography and Complementary Methods will take place at the Brazilian Synchrotron Laboratory (22-24 Sept), with the presence of Nobel Prize laureate Ada Yonath. In the state of Minas Gerais, a Symposium on Evolution of Crystallography and a two month exhibition entitled Symmetry and diffraction: from the art to crystal structure in our daily lives will take place in October. Other exhibitions are also being planned with panels from the "100 Years of Crystallography" Grenoble team. An International Symposium on Crystallography will take place in Fortaleza/CE (UFC, 12-15 Oct.). Workshops and Lecture Courses on Appl. Crystallography (UFES, Vitoria- 23-25 May) and Rietveld methods (USP-SP, 1-5 Sep.) are also being announced. Two Open Lab activities are being planned with commercial sponsorship: Bruker-Axs (in Goiás-Oct.), Rigaku and Panalytical (SP, Aug. 20-21).

X-ray powder diffraction use in forensic analysis in Brazilian context

The forensic analysis of evidences must be able to extract maximum of information from small quantities of samples, while preserving as much material as possible for future tests. In this case, the accuracy and speed are vital in order to obtain relevant and trustful results. Among the many types of materials that are subject of a criminal investigation, a great quantity of them can be analyzed by using the X-ray powder diffraction (XPD) technique [1] [2] [3]: inorganic, organic and metals. It's required that the material should be solid and crystalline or partially crystalline. The huge advantages lie in the fact that it is a nondestructive technique and the unique characterization is possible because each compound has its own specific pattern, like a `fingerprint'. It was not found any publication about the use of the XPD by the Brazilian laboratories that is dedicated to forensic analysis. The aim of this work is to show the versatility of the technique and the great cost-beneficial that this technique can offer. Many Brazilian laboratories situated in universities possess the equipment and can eventually help the investigations along with the police. This partnership can provide advances in technology and can encourage the fundamental and applied science students to contribute with the Forensic Science in Brazil, increasing the quality and variety of the national scientific research.