Search results for "X-RAY ABSORPTION"
showing 10 items of 314 documents
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 metalâ 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…
Local structural investigation of hafnia-zirconia polymorphs in powders and thin films by X-ray absorption spectroscopy
2019
Björn Matthey (Fraunhofer IKTS, Dresden) is acknowledged for providing HfO2 and ZrO2 powders on short notice after DESY’s renowned customs office punished us. Parts of this research were carried out at Petra III at DESY, a member of the Helmholtz Association (HGF). The experiments on single Si:HfO2 thin film samples were performed at the CLAESS beamline at ALBA Synchrotron with the collaboration of ALBA staff. We would like to thank Edmund Welter for assistance (in using beamline P65) and DESY for enabling this research for proposal no. 20160591 and for travel support. T.S. acknowledges the German Research Foundation (DFG) for funding this work in the frame of the project “Inferox” (project…
Short and Medium Range Order in Se1-xTexGlasses
1997
Complementary XAFS measurements (LURE and NSLS) of Se 1 - x Te x glasses have been carried out on both the Se and Te K-edges at low and room temperatures. Using a multi-shell best fit analysis procedure, we have reconstructed the Se and Te local environment: (i) first shell intrachain nearest neighbors (Se-Se 1 , Se-Te 1 , Te-Se 1 ,and Te-Te 1 ); (ii) second shell intrachain (Se-Se 2 and Se-Te 2 ) and interchain next nearest neighbors (Se⇔Se 3 single scattering in the chains Se-Se 1 -Se 3 and Se-Te 1 -Se 3 ). For the first and second coordination shells we suggest that the intrachain chemical order increases with Te content. On the other hand, we propose a model of random distribution of Se…
Quantum chemical modelling of polarons and perovskite solid solutions
2001
Abstract Following our previous study [J. Phys.: Condens. Matter 10 (1998) 6271] of a single Nb impurity and Nb clusters in KTaO 3 , we present results of the calculations for a series of perovskite KNb x Ta 1− x O 3 (KTN) solid solutions ( x =0, 0.125, 0.25, 0.75, 1). The quantum chemical method of the intermediate neglect of the differential overlap (INDO) combined with the large unit cell (LUC) periodic model is used. According to the INDO calculations, Nb impurity becomes off-center in KTaO 3 already at the lowest studied concentrations ( x =0.125), in a good agreement with XAFS measurements. We compare our results with previous ab initio FP-LMTO calculations. Quantum chemical calculati…