Aline Y. Ramos

Incorporation of Ni into natural goethite: An investigation by X-ray absorption spectroscopy

Abstract Goethite (α-FeOOH) is abundant at the Earth’s surface and has the unusual capacity to adsorb and fix ions from migrating solutions. Understanding the mechanisms by which foreign elements are incorporated into natural goethite has implications for environmental and mining problems. X-ray absorption spectroscopy (XAS) was used to obtain structural information on the local environment around Ni in natural Ni-containing goethite (1.8-4.1 mol% Ni) from Vermelho lateritic deposit of Serra dos Carajás (Brazil) and in synthetic analogues. The data were collected at the LNLS XAS beam line at the Ni and Fe K-edges, at room temperature, and at the Ni K-edge at 8 K. Nickel was found in essentially the same environment in all natural and synthetic samples, with negligible thermal disorder. The coordination polyhedron is a tetragonal dipyramid of oxygen atoms showing that Ni preserves its usual local symmetry. This finding is compatible with a model in which substitution of Ni for Fe is accompanied by a proton capture resulting in NiO2(OH)4 octahedra. The polyhedral linkages are similar to that of pure a-FeOOH, consisting of four shared edges at about the same metal-metal distances, as in the pure mineral. The third and longest metal-metal distance is about 6% larger than the expected corner-sharing distance in the α-FeOOH structure, showing that incorporation of Ni locally distorts and opens the structure.

A 2.3 to 25 keV XAS beamline at LNLS

The LNLS XAS beamline has been operating for external users since July 1997. Many facilities and improvements have been progressively added to it, extending the range of applications. Here, a technical description of the main beamline components is given, and results concerning important points, such as available flux at low and high energies, harmonic contamination, energy resolution and stability, are presented. Some key results are given to demonstrate the beamline performance and limitations. It is shown that the beamline can cover a large energy range, starting from the rather low energy of 2.3 keV up to 25 keV.

Size of Cd(S,Se) quantum dots in glasses: Correlation between measurements by high‐resolution transmission electron microscopy, small‐angle x‐ray scattering, and low‐frequency inelastic Raman scattering

The average sizes of Cd(S,Se) quantum dots in glasses have been measured for the same samples by using three methods: high‐resolution transmission electron microscopy, low‐frequency inelastic Raman scattering, and small‐angle x‐ray scattering. Three samples with crystal sizes of 5.5–8, 9–12, and 17 nm have been studied. For each method the interaction mode and the underlying assumptions in measuring the size are discussed. The correlation between the measurements is good and points out a narrow size distribution. The discrepancies observed for the smallest sizes are discussed with respect to the probe and the interactions used by each technique. They may be ascribed to structural effects.

Short-range charge order in R Ni O 3 perovskites ( R = Pr , Nd, Eu, Y) probed by x-ray-absorption spectroscopy

The short-range organization around Ni atoms in orthorhombic

Energy-dispersive X-ray absorption spectroscopy at LNLS: investigation on strongly correlated metal oxides

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Local tetragonal distortion in La0.7Sr0.3MnO3 strained thin films probed by x-ray absorption spectroscopy

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Stability of Jahn Teller distortion in LaMnO3 under pressure: An x-ray absorption study

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Robust perpendicular exchange coupling in an ultrathin CoO/PtFe double layer: Strain and spin orientation

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Zinc incorporation in human dental calculus.

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Emergence of ferromagnetism and Jahn-Teller distortion in LaMn1−xCrxO3 (x < 0.15)

=Pr,Nd,Eu) perovskites has been studied over a wide temperature range by Ni K-edge x-ray absorption spectroscopy. Our results demonstrate that two different Ni sites, with different average Ni-O bond lengths, coexist in those orthorhombic compounds and that important modifications in the Ni nearest neighbors environment take place across the metal-insulator transition. We report evidences for the existence of short-range charge-order in the insulating state, as found in the monoclinic compounds. Moreover, our results suggest that the two different Ni sites coexists even in the metallic state. The coexistence of two different Ni sites, independently on the