The simulation of EXAFS spectra of thin films via ab initio methods is discussed. The procedure for producing the spectra is presented as well as an application to a two-dimensional material (WSe 2 ) ...where the effectiveness of this method in reproducing the spectrum and the linear dichroic response is shown. A series of further examples in which the method has been employed for the structural determination of materials are given.
Gd-YBa2Cu3O7-δ (Gd-YBCO) thin films with 10 mol% and 20 mol% excess-Gd concentration with respect to Y were investigated at the Gd L3 and Y K core absorption edges by EXAFS spectroscopy with the aim ...of determining the local structure of the Gd dopant. To this purpose, EXAFS data were collected also on GdBa2Cu3O7-δ (GdBCO) and pristine YBCO films and on Gd2O3 and Y2O3 model compounds for comparison with the YBCO films with Gd excess. The EXAFS analysis was based on Y and Gd oxides as well as on a cluster obtained by Density Functional Theory (DFT) where Gd atoms were inserted substitutional to Y atoms. The EXAFS data clearly reveal the incorporation of Gd in the lattice as substitute of Y and no evidence of segregated Gd oxide was found within the film matrix.
•Gd-YBa2Cu3O7-δ thin films with excess-Gd concentration were investigated by EXAFS.•For comparison EXAFS was measured on GdBa2Cu3O7-δ, YBa2Cu3O7-δ, Gd2O3 and Y2O3.•A DFT model with Gd atoms substitutional to Y in the YBCO lattice was calculated.•The model’s FFT modulus was compared with the FFT of the Gd-doped thin films.
Palladium is one of the best anodic catalysts for Alkaline Direct Alcohol Fuel Cell (DAFC) applications. However, its adoption in Fuel Cells (FCs) is still limited because of the deactivation of the ...catalyst, which hinders the long-term performance stability of the devices. In this article, we report the results of a Fixed Energy X-Ray Absorption Voltammetry (FEXRAV) investigation of a carbon-supported palladium electrocatalyst operating in a complete alkaline direct ethanol fuel cell (DEFC). Our results show palladium dissolution unambiguously, especially at cell polarizations corresponding to high anodic stresses. We have also investigated the behaviour of Pd electrocatalyst in a direct alkaline formate fuel cell (DFFC). Data show that when using formate as a fuel, the electrode Pd loss is negligible compared to the case of DEFC.
LISA is the acronym of Linea Italiana per la Spettroscopia di Assorbimento di raggi X (Italian beamline for X-ray Absorption Spectroscopy) and is the upgrade of the former GILDA beamline installed on ...the BM08 bending magnet port of European Synchrotron Radiation Facility (ESRF). Within this contribution a full description of the project is provided.
We report a comparative study of Ln2M2O7 (Ln = Gd, Tb, Dy; M = Ti, Zr) synthesized by combination of the sol-gel and coprecipitation methods followed by calcination at elevated temperatures. The ...long-range average crystal as well as short-range local structure in the samples were analyzed using X-ray diffraction, X-ray absorption spectroscopy (XAFS) and Raman spectroscopy. It has been found that Ln-Ti precursors crystallize directly to pyrochlore phase, whereas crystallization of Ln-Zr precursors to pyrochlore phase goes through intermediate fluorite phase. We have shown that X-ray absorption data make possible to detect the crystallization and phase transition features in Ln2M2O7 such as splitting of Ln-O coordination shells and changes of the symmetry in local environment.
Display omitted
•Crystallization and phase transitions in Ln2M2O7 (Ln = Gd,Tb,Dy; M = Ti,Zr) were studied.•K-Ti pre-edge region of XANES spectra is very sensitive to Ln2Ti2O7 crystallization.•The shape of the LnL3-XANES spectra is sensitive to pyrochlore phase formation.•Formation of a pyrochlore structure causes the splitting of Ln-O shell in EXAFS-FT.
Developing new rare-earth ion-doped optical fibres for power amplifiers and lasers requires continuous improvements in fibre spectroscopic properties. To overcome some limitations inherent to silica ...glass, it is proposed to embed rare-earth ions in dielectric nanoparticles. In this article we focus on the modifications of the Er3+ ion spectroscopy in Mg-silicate nanoparticles doped into optical fibre preforms. Through EXAFS and fluorescence measurements, we demonstrate that different local environments are experienced by Er3+ ions, attributed to the depolymerization of the phosphate network. These results gain insight into the tailoring of luminescence properties.
•Structural study carried out directly on fibre preforms by using synchrotron sub-mm X-ray beams•Determined evolution of the Er3+ photoluminescence with the content of Mg in silica fibre preforms•Proposal of an unconventional method of analysis of EXAFS data for Er ions based on the Bond Valence Method•Links between the local structure and composition
The control on the distribution of magnetic ions into a semiconducting host is crucial for the functionality of magnetically doped semiconductors. Through a structural analysis at the nanoscale, we ...give experimental evidence that the aggregation of Fe ions in (Ga,Fe)N and consequently the magnetic response of the material are affected by the growth rate and doping with shallow impurities.
In this study, the first coupled FEXRAV and chemical speciation modelling study of the Pd deactivation is presented. Due to the high brilliance of synchrotron light, FEXRAV can investigate deeply ...buried surfaces. More specifically, we directly analyzed the evolution of the Pd/C catalytic layer during a voltammetric cycle, through a specifically designed electrochemical cell. Still, we observed a complex interfacial chemistry of Pd, which impairs a straightforward interpretation of FEXRAV data. Exploiting thermodynamic chemical speciation modelling we were able to overcome this issue. The study leads to three main results: 1) the confirmation of the relationship between the change of the Pd/Pd(II) ratio and the change of the Fluorescence intensity 2) the investigation of the deactivation mechanism 3) the identification of the relevant species leading to the electrodissolution of Pd under operative conditions. This study opens new perspectives for the application of the chemical speciation modelling to the study of the deactivation mechanism of Pd in Pd/C catalytic layers under operative conditions in different electrolytes.
PDF
