Vol. 3 No. 1 (2022): Suplemento de la Revista Mexicana de Física. Synchrotron light in Mexico and the world
Proceedings of the 1st National Congress of the Mexican Society of Synchrotron Light and the 1st International Congress on Synchrotron Light Techniques
Guest Editors:
Dr. Matías Moreno Yntriago. Instituto de Física, Universidad Nacional Autónoma de México
Dr. Abel Moreno Cárcamo. Instituto de Química, Universidad Nacional Autónoma de México
Dr. Luis Fuentes Cobas. Centro de Investigación en Materiales Avanzados, S.C., Chihuahua
06 I National Congress of the Mexican Society of Synchrotron Light
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Electron density contour maps via Rietveld-MEM analysis using HR-XRD for the polycrystalline ferroelectric BCZT
Abstract:⬇️ Scroll down to see the full summaryThe maximum entropy method in combination with the Rietveld refinement method applied to the analysis (Rietveld-MEM analysis) of high-resolution x-ray diffraction (HR-XRD) is an important tool to elucidate the electron density distribution and chemical bonding nature of materials. In this work, we present the comparison of electron density distribution obtained from the Rietveld-MEM analysis for polycrystalline perovskite BaTiO3 (reference sample) and Ba0.9Ca0.2Ti0.9Zr0.1O3 (BCZT). To perform this task, HR-XRD patterns using synchrotron radiation were acquired. Tetragonal phase with P4mm (No.99) space group and pseudo-Voigt function were considered to model the HR-XRD peaks by the Rietveld method using the profile fitting Fullprof suite program. VESTA software was used to visualize 3D, 2D electron density distribution maps and line profiled to monitor the chemical bonding nature between Ba-O and Ti-O interactions and to visualize the off-center displacement of Ti cations by the incorporation of Zr and Ca cations. The interaction between Ti contours with O contours in the electron density distribution and the minimum electron density values revealed the enhancement of covalent nature and predominant ionic nature between barium and oxygen ions in the BCZT. To monitor the ferroelectric hysteresis behavior, polarization versus electric field curves complement the characterization of these samples.
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Chemical speciation of lead adsorbed onto volcanic ashes by ICP-OES and XANES
Abstract:⬇️ Scroll down to see the full summaryThis study focuses on the assessment of the VA materials from the Cameroon volcanic line (CVL) for their use as natural adsorbents to remove Pb(II) pollutant from aqueous solutions. The chemical speciation of lead adsorbed onto volcanic ashes based by means of inductively coupled plasma optical emission spectroscopy (ICP-OES) and X-ray absorption near edge spectroscopy (XANES) study is reported. The ashes from CVL are used to remove lead in aqueous solutions. The maximum value of the adsorption capacity of lead in volcanic ashes was 7.60 mg g-1 at pH 5. Regarding the adsorption process, the contribution of the mixture lead components after adsorption and a strong interaction of adsorbed lead with the surface of volcanic ashes were proven. The chemical elements present in the volcanic ash and their concentrations are determined by ICP-OES. Chemical speciation was carried out measuring Pb saturated volcanic ash sample at the L3 edge (13035 eV) at the XAFS beam line in Elettra Sincrotrone Trieste. The XANES measurements showed that the lead removal occurred mainly by microprecipitation of lead acetate and carbonate associated with a possible ion-exchange forming lead monoxide.
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Aspectos dinámicos en el diseño del anillo de almacenamiento del sincrotrón mAspectos dinámicos en el diseño del anillo de almacenamiento del sincrotrón mexicanoexicano
Abstract:⬇️ Scroll down to see the full summarySe investigan varios diseños de redes magnéticas para la fuente de luz sincrotrón mexicana, los cuales hacen uso de algunos recursos de diseño de las actualización recientes de fuentes de luz sincrotrón, tales como celdas acromáticas múltiples, dipolos con gradiente longitudinal, dipolos invertidos y esquemas híbridos. Mediante el uso de bloques fijos de imanes (tipo LEGO), también, se investiga la posibilidad de reducir aún más la emitancia de algunos diseños.
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Naica’s “Cueva de los Cristales”: Synchrotron radiation characterization of the wall-crystal interface
Abstract:⬇️ Scroll down to see the full summaryNaica’s ”Cueva de los Cristales” was discovered in 2000. It has been considered particularly interesting for its beauty and the challenges it poses to crystallography. This article focuses on the study of the wall-selenite interface by various techniques, particularly X-ray diffraction (XRD), scanning electron microscopy (SEM), with emphasis on micro-X-ray fluorescence (micro-XRF) and micro-X-ray absorption near edge structure (micro-XANES). The main phases calcite, quartz, goethite and montmorillonite were identified by XRD, as well as the association of crystalline and amorphous minor and trace phases of Zn, Mn, Cu, As and Pb. The latter were identified in micro-XRF maps and micro-XANES spectra. The results for the morphology and the chemical description of the crystal-wall interface may contribute to propose a nucleation and growth mechanism for Naica megacrystals.
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System of methods and programs for the characterization of axial textures by synchrotron light and electrons
Abstract:⬇️ Scroll down to see the full summaryCrystallographic algorithms and computer programs play significant roles in materials’ characterization. A software package for the quantitative characterization of crystallographic texture, under axial symmetry conditions, is presented. The proposed methodology is intended for use with both electrons and high-energy synchrotron X-rays. Three different programs are introduced. Anaelu and Grazing are based on the Rietveld modelling approach. Dianne follows the Bunge’s symmetrized spherical harmonics method. A SrTiO3 model sample is proposed as a hypothetical study case.
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Transport and concentration of uranium isotopes in the Laguna del Cuervo, Chihuahua, Mexico
Abstract:⬇️ Scroll down to see the full summaryIn Chihuahua, an important source of environmental radioactivity is found in the Sierra Peña Blanca, in the center of the state. The site comprises about 70% of uranium reserves in Mexico. The uranium of Peña Blanca was explored and partially exploited in the '80s. Due to the closure of operations, the extracted and unprocessed ore (hundreds of tons) was confined to rocky stacks, exposed to weathering. Subject to leaching, this uranium is transported from the mountains to Laguna del Cuervo. The mineral exposed in the repository and the uranium transport by surface water and recent sediments must be studied, to assess the effects on the environment, with radiometric and materials science techniques in conventional laboratories and synchrotron light. This work presents the study of sediment and pore water samples at various points along the lagoon, and the values of the activity ratio of the 234U/238U isotopes and the sediment-water distribution coefficient of these isotopes, obtained by applying uranium liquid scintillation alpha spectrometry, gamma-ray spectrometry, scanning electron microscopy and X-ray diffraction methods.
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Monte Carlo simulation of vacancies produced in lead-free piezo-ceramics by X-ray radiation damage
Abstract:⬇️ Scroll down to see the full summaryThis work presents the results of a simulation by the Monte Carlo method, performed through the GEANT4 code, of the irradiation and energy deposition by high flux X-rays on the piezoelectric ceramic Bismuth-Sodium Titanate doped with Barium. X-rays energies were around the Ti-K absorption edge emulating a transmission experiment, and the irradiation with 5300 eV X-rays for a fluorescence experiment. The method consists of introducing the data that describes a characteristic R3c structure of the polarized ceramic, reported in the literature. The absorption coefficients for the energies of interest, as well as the energy deposited in the form of radiation doses, are calculated. Intensity changes for specific energy lines in the micro-fluorescence spectra, which suggest the presence of vacancies in the crystal structure, are verified via simulation. The vacancy density produced by a typical photon flux of a fourth-generation synchrotron beam is calculated through the threshold displacement energy for vacancy production. Consequently, the simulation is carried out for a structure with appropriate Bi and O vacancies, and the ability to detect the radiation damage is verified by comparison with micro-XRF and XAFS experimental results. The simulation predicts a maximum dose of 1.21-1.27x105 Gy irradiating 107 photons for the given energy and a maximum vacancy density of 1.10x108 / micron3 for oxygen atoms and 6.90x107 /micron3 for bismuth atoms.
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Ion beams and synchrotron light in perspective
Abstract:⬇️ Scroll down to see the full summaryThis work is devoted to reflecting on the very different features and dynamics of ion beam and synchrotron facilities and user communities. Whereas both suites of techniques are highly interdisciplinary and offer good science opportunities to similar fields of science, traditionally the two communities have lived in separate worlds, with scarce knowledge of one another and very limited collaboration.
