Search results for "X-ray absorption fine structure"
showing 10 items of 220 documents
EDA: EXAFS data-analysis software package
2021
The EXAFS data-analysis software package EDA consists of a suite of programs running under a Windows operating system environment that is designed to perform all steps of conventional EXAFS data analysis such as extraction of the XANES/EXAFS parts of the X-ray absorption coefficient, Fourier filtering and EXAFS fitting using the Gaussian and cumulant models. The package also includes two advanced approaches which allow the reconstruction of the radial distribution function (RDF) from EXAFS based on the regularization-like method and the calculation of configuration-averaged EXAFS using a set of atomic configurations obtained from molecular-dynamics or Monte Carlo simulations.---- / / / ----…
Cationic vacancies and anomalous spectral-weight transfer in Ti1−xTaxO2thin films studied via polarization-dependent near-edge x-ray absorption fine …
2013
We report the electronic structures of Ta-doped anatase TiO 2 thin films grown by pulsed laser deposition (PLD) with varying magnetization using a combination of first-principles calculations and near-edge x-ray absorption fine structure (NEXAFS) spectroscopy. The roles of Ta doping and Ti vacancies are clarified, and the observed room-temperature ferromagnetism is attributed to the localized magnetic moments at Ti vacancy sites ferromagnetically ordered by electron charge carriers. O K -edge spectra exhibit significant polarization dependence which is discussed and supported by first-principles calculations in relation to both the crystal symmetry and the formation of defects. In particula…
Electronic and crystallographic structure, hard x-ray photoemission, and mechanical and transport properties of the half-metallic Heusler compound Co…
2011
This work reports on the electronic and crystalline structure and the mechanical, magnetic, and transport properties of the polycrystalline Heusler compound Co${}_{2}$MnGe. The crystalline structure was examined in detail by extended x-ray absorption fine-structure spectroscopy and anomalous x-ray diffraction. The compound exhibits a well-ordered $L{2}_{1}$ structure as is typical for Heusler compounds with 2:1:1 stoichiometry. The low-temperature magnetic moment agrees well with the Slater-Pauling rule and indicates a half-metallic ferromagnetic state of the compound, as is predicted by ab initiocalculations. Transport measurements and hard x-ray photoelectron spectroscopy were performed t…
Structure and oxide ion conductivity: local order, defect interactions and grain boundary effects in acceptor-doped ceria
2014
The long-range and short-range structure of nanocrystalline and microcrystalline acceptor-doped ceria is investigated by a combined approach using EXAFS, XANES, Raman, and XRD, and correlated with the oxide-ion conductivity in the bulk and in grain boundaries. Compared to Yb3+ and Er3+, the positive influence of Sm3+ is attributed to the ability to repel oxygen vacancies, and to keep a localized disorder around the dopant. The long-range structural analysis shows lattice contraction for Yb- and Er-doping and lattice expansion for Sm-doping. The short-range analysis around the dopants and cerium highlights that a more complex structural rearrangement has to be assumed to explain the compleme…
Indium Doping in Barium Cerate: the Relation between Local Symmetry and the Formation and Mobility of Protonic Defects
2007
The solid solution series Ba(In,Ce)O3-ä has been investigated with respect to structure, formation, and mobility of protonic defects. Compared to the limited solubility of Y2O3 in BaCeO3 and BaZrO3, the complete solubility of In2O3 is suggested to reflect a relation between absolute hardness of the dopant and the ease of insertion into the hosting lattices. Extended X-ray absorption fine structure (EXAFS) was used to probe the local environment of In3+ in barium cerate: in the surroundings of the dopant, the orthorhombic structure is strongly modified, resulting in an increase of local symmetry. The InO6 octahedra are very regular, and there is no indication for any defect clustering. This …
Structural and CO [sub] 2 capture properties of ethylenediamine-modified HKUST-1 metal-organic framework
2020
The high structural and compositional flexibility of metal–organic frameworks (MOFs) shows their great potential for CO2 capture and utilization in accordance with the environmental guidelines of low-carbon technology developments. HKUST-1 as one of the most intensively studied representatives of MOFs for such purposes excels because of its simplicity of production and high ability to tune its intrinsic properties by various functionalization processes. In the present work, ethylenediamine functionalization was performed for the first time in order to thoroughly investigate the amine sorption sites’ impact on the CO2 capture performance of HKUST-1. The placement of ethylenediamine moieties …
Local structure of copper nitride revealed by EXAFS spectroscopy and a reverse Monte Carlo/evolutionary algorithm approach
2016
Physica scripta 91(5), 054003 (2016). doi:10.1088/0031-8949/91/5/054003
Molecular dynamics and reverse Monte Carlo modeling of scheelite-type AWO4(A = Ca, Sr, Ba) WL3-edge EXAFS spectra
2016
Classical molecular dynamics (MD) and reverse Monte Carlo methods coupled with ab initio multiple-scattering extended x-ray absorption fine structure (EXAFS) calculations were used for modeling of scheelite-type AWO4 (A = Ca, Sr, Ba) W L 3-edge EXAFS spectra. The two theoretical approaches are complementary and allowed us to perform analysis of full EXAFS spectra. Both methods reproduce well the structure and dynamics of tungstates in the outer coordination shells, however the classical MD simulations underestimate the W–O bond MSRD due to a neglect of quantum zero-point-motion. The thermal vibration amplitudes, correlation effects and anisotropy of the tungstate structure were also estimat…
Effect of Pressure and Temperature on the Local Structure and Lattice Dynamics of Copper(II) Oxide
2016
Abstract Microcrystalline and nanocrystalline (6 nm) CuO were studied in situ by the Cu K-edge X-ray absorption spectroscopy as a function of pressure (0-20 GPa) and temperature (10-300 K). Pressure dependence of X-ray absorption near edge structure (XANES) was interpreted within the full-multiple-scattering formalism based on the relaxed atomic structure determined by ab initio linear combination of atomic orbital (LCAO) calculations. Temperature dependence of the mean-square relative displacement (MSRD) for the four shortest Cu–O distances was obtained from the analysis of extended X-ray absorption fine structure (EXAFS) and described by the correlated Einstein model with the characterist…
Optical, X-ray absorption and photoelectron spectroscopy investigation of the Co site configuration in Zn1−xCoxO films prepared by pulsed laser depos…
2007
Abstract In this paper, we investigate the Co site configuration in Zn1−xCoxO thin films by means of different spectroscopic techniques. Thin films were prepared by pulsed laser deposition with Co proportion from 1% to 30%. The Co 2p doublet observed in the X-ray photoelectron spectra exhibits the spin–orbit splitting and shake-up satellites typical of Co+2 ionization states. X-ray absorption spectra at the Co K-edge, taken in fluorescence mode, unambiguously show that Co atoms are in tetrahedral configuration substituting for Zn over the whole composition range. Optical absorption spectra provide further evidence of the tetrahedral coordination of Co cations, both through the internal tran…