Search results for "X-ray absorption fine structure"

Interpretation of the Co K-edge EXAFS in LaCoO3 using molecular dynamics simulations

2011

Abstract Temperature dependent (180–400 K) Co K-edge EXAFS spectra from perovskite-type rhombohedral ( R 3 ¯ c ) LaCoO 3 have been successfully interpreted using a combination of classical NVT molecular dynamics (MD) and ab initio multiple-scattering (MS) theory. The method allowed us to account entirely for thermal disorder and to interpret reliably the contribution from the coordination shells beyond the first one into the total EXAFS spectrum taking into account many-body effects. The best agreement between experimental and configuration-averaged EXAFS spectra was obtained for pure ionic La 3+ and partially ionic Co 1.35+ and O 1.45− charges indicating the mixed ionic-covalent character …

Transient and near‐edge absorption in YVO 4 crystals

2007

The process of near-edge absorption annealing in air was studied up to 1500C in YVO4. In this annealing process, two stages with activation energies of 0.16 eV and 0.38 eV were obtained. (Should combine to make this one paragraph)In addition to the annealing study, the transient absorption induced by pulsed electron beam excitation (270 keV, 8 ns) was completed on a set of YVO4 samples with different near-edge absorption levels in the spectral region 3.2-3.5 eV. The spectral range from ∼1.25 eV up to 3.0 eV is covered by strong transient absorption. Transient absorption spectra show at least three broad overlapping bands (∼1.3 eV, ∼2.0 eV and ∼3.0 eV). The 3 eV peak position is close to the…

The fate of silver ions in the photochemical synthesis of gold nanorods: an Extended X-ray Absorption Fine Structure analysis

2009

Water-soluble gold nanorods (Au NRs) were synthesized using a silver-ion mediated photochemical route under UV irradiation. Extended X-ray Absorption Fine Structure (EXAFS) measurements on the Ag K-edge were performed on samples obtained at different Ag/Au ratios and at increasing irradiation times in order to investigate the fate of silver ions during the growth of Au NRs. EXAFS measurements allowed to probe the chemical state and the local environment of silver in the final product. Experimental data suggest that Ag atoms are placed on top of the Au particles as metallic Ag(0), while no significant contribution to the EXAFS spectra comes from AgBr or other Ag(+) based species. The reporte…

High pressure EXAFS on GaTe single crystal including polarization

1999

Toward tailorable surfaces: a combined theoretical and experimental study of lanthanum niobate layered perovskites.

2014

A comprehensive theoretical investigation of the MLaNb2O7 (M = H, Li, Na, K, Rb, and Cs) series of ion-exchangeable layered perovskite is presented. These perovskites are in particular interesting in view of their potential applications as inorganic supports for the design of new hybrid inorganic-organic proton conductors. In particular, their structural and electronic properties have been investigated by periodic calculations in the framework of Density Functional Theory, using different exchange-correlation functionals. A general very good agreement with the available experimental (XRD, NPD, and EXAFS) data has been found. The structure of the protonated HLaNb2O7 form has also been furthe…

Extended X-Ray Absorption Fine Structure Spectroscopy of Perovskite-Type Compounds

2000

Application of the extended x-ray absorption fine structure (EXAFS) spectroscopy to a study of the local atomic structure in perovskitetype materials is discussed on the example of several compounds (m-WO3, NaxWO3, ReO3 and FeF3). The sensitivity of the EXAFS to the out-of-center and rotational distortions is discussed in details.

Determination of Geometry Arrangement of Copper Ions in HKUST-1 by XAFS During a Prolonged Exposure to Air

2017

We present an experimental investigation focused on the local structural changes taking place around Cu2+ions in metal− organic framework (MOF) HKUST-1 for different times of exposure to air by XAFS (X-ray absorption fine structure). The analysis involves both XANES (X-ray absorption near edge structure) and EXAFS (extended X-ray absorption fine structure) regions around the Cu K-edge. Starting from the paddle-wheel structures proposed in literature, a more detailed description of the geometrical environment of Cu2+ions has been found. In particular, the paddle-wheel structure of a fresh sample, which means a pristine HKUST-1 material with a single water molecule weakly adsorbed on each C…

Slow relaxation of the magnetization in Oximato-bridged heterobimetallic Copper(II)-Manganese(III) chains

2011

The use of the oximato-containing copper(II) complexes, [Cu(Hdeg)2] (H2deg = diethylglyoxime), [Cu(Hmeg)2] (H2meg = methylethylglyoxime) and [Cu(Hdmg)2] (H2dmg = dimethylglyoxime), as ligands toward manganese(II) acetate in methanol afforded the heterobimetallic compounds of formula [MnCu(deg)2(CH3COO)(H2O)2] (1), [MnCu(meg)2(CH3COO)(H2O)2] (2) and [MnCu(dmg)2(CH3COO)(H2O)2] (3) where the starting manganese(II) ion was oxidized to manganese(III) by air. In the lack of single crystals suitable for X-ray diffraction analysis, X-ray absorption techniques (EXAFS and XANES) at 40 K were used for the structural characterization of 1-3. The analysis of the X-ray absorption data reveals that 1-3 ar…

Equilibrium, Structural and Biological Activity Studies on [Organotin(IV)]n+ Complexes

2008

Organotin(IV) compounds are characterized by the presence of at least one covalent C–Sn bond. The compounds contain tetravalent {Sn} centers and are classified as mono-, di-, tri-, and tetraorganotin(IV), depending on the number of alkyl (R) or aryl (Ar) moieties bound. The anions are usually Cl, F, O2, OH,–COO, or –S. It seems that the nature of the anionic group has only secondary importance in biological activity. The rapid rise in the industrial (catalyst in PVC and foam production), agricultural (fungicides and acaricides), and biological applications (wood, stone, and glass preservatives) of organotin(IV) compounds during the last few decades has led to their accumulation in the envir…

Tuning up the Tc in Mn(II)Cu(II) bimetallic planes and design of molecular-based magnets

1998

Abstract A family of related compounds of general formula (PPh4)2Mn2[Cu((L)]3nH2O, where PPh4+ is the tetraphenylphosphonium cation and L stands for ortho-phenylenebis(oxamate) (opba, 1), ortho-phenylene (N′-methyloxamidate) (oxamate) (Meopba, 2) and ortho-phenylenebis (N′-methyloxamidate) (Me2opba, 3), have been synthesized. The X-ray absorption near-edge structure (XANES) and extended X-ray Within absorption fine structure (EXAFS) spectra at both Mn and Cu K-edges for all three compounds, as well as their powder X-ray patterns, are consistent with a layered structure built up of parallel Mn11Cu11 two-dimensional honeycomb networks separated by PPh4+ cations. Within the antonic metallic la…