Papers by Keyword: EXAFS

Abstract: We have succeeded in synthesizing electron-doped cuprates T’-Pr_2-xCe_xCuO₄ (PCCO) with x = 0 and 0.10 nanocrystals prepared by the chemically dissolved method. Reduction annealing of the PCCO samples at 700°C under a flowing argon gas atmosphere has been performed for the removal of excess oxygen in the apical sites. The XRD data showed that the reduction annealing process decreases c-axis length indicating successful removal of the excess oxygen. The bond distortion of PCCO including coordination number and bond distance between the absorber atoms with the nearest neighboring atoms (Cu-O) was investigated by extended x-ray absorption fine structure (EXAFS) using Cu K-edge. The implication of our results is discussed on the basis of tremendous influence of oxygen vacancies on the magnetism of the nanosized T’-cuprates at the normal state.

Abstract: Local structures around gadolinium atoms in rare-earth (RE)-doped InGaGdN thin films were studied by means of fluorescence extended X-ray absorption fine structure (EXAFS) measured at the Gd L_III-edges. The samples were doped with Gd in-situ during growth by plasma-assisted molecular beam epitaxy (PAMBE). Gd L_III-edge EXAFS signal from the GaGdN, GdN and Gd foil were also measured as reference. The X-ray absorption near edge structure (XANES) spectra around Gd L_III absorption edge of InGaGdN samples observed at room temperature indicated the enhancement of intensities with the increase of Gd composition. Further EXAFS analysis inferred that the Gd atoms in InGaN were surrounded by similar atomic shells as in the case of GaGdN with the evidence indicating majority of Gd atoms substituted into Ga sites of InGaGdN. A slight elongation of bond length for the 2nd nearest-neighbor (Gd–Ga) of sample with higher Gd concentration was also observed.

Abstract: We examined structural properties of nitrogen doped (ZnO:N) thin films prepared by reactive RF magnetron sputtering technique in conjunction with gas timing method. The deposited films were polycrystalline ZnO in wurtzite structure. Morphology of the ZnO:N films could be modified by adjusting gas timing conditions. The x-ray photoelectron spectroscopy (XPS) and extended x-ray absorption fine structure (EXAFS) analysis showed that incorporation of nitrogen may cause structural distortion in the ZnO:N crystal.

Abstract: In order to characterize the local structure of Pb_1-xCa_xTiO₃ (PCT) samples, Ti K-edge XANES measurements were performed and showed that Ca incorporation to PbTiO₃ structure leads to a decreasing of local distortion of Ti atoms in relation to oxygen atoms at the TiO₆ octahedra. Moreover, according to EXAFS measurements, the local structure around Ti atoms exhibits tetragonal symmetry with P4mm space group for samples with x 0.475, whereas orthorhombic symmetry with Pbnm space group was observed for x equals to 0.50 and 0.55.

Abstract: The composites of polycrystalline (La_1.85Sr_0.15CuO₄)_1-x(La_0.5Sr_0.5MnO₃)_x were prepared by solid state reaction method. By means of X-ray absorption spectroscopy, it is found that electrons can transit at grain boundaries from La_1.85Sr_0.15CuO₄ to La_0.5Sr_0.5MnO₃. Additional holes are formed in La_1.85Sr_0.15CuO₄ when the electron transitions happen. The experimental results of both X-ray absorption near edge structure and extended X-ray absorption fine structure excluded the possibility of that the electron transitions are induced by local lattice structure. According to the X-ray absorption experimental results of O K-edge of the La_1.85Sr_0.15CuO₄ and La_0.5Sr_0.5MnO₃ materials, a possible mechanism of the electron transitions and a phenomenological model of the band structure around Fermi level are proposed to explain the transition behavior.

Abstract: In this work, new information on surface morphology, phase and local structure of titanium nitride (TiN) nanocrystal thin films grown with different nitrogen gas concentration by direct current (DC) magnetron sputtering is provided. Surface morphology of the thin films was studied by field emission scanning electron microscope (FE-SEM). Phase and local structure of the TiN nanocrystals were determined by X-ray diffraction spectroscopy (XRD) and X-ray absorption fine structure (XAFS). The TiN nanocrystals were prepared on silicon substrates. N₂/Ar gases were used as reactive gases for sputtering Ti target. The amount of these two reactive gases was varied at different ratios (N₂/Ar), i.e. 100:0, 75:25, 50:50 and 25:75 respectively. Our results suggested that sputtering Ti target with high N2/Ar gas ra_{Subscript text}tio (higher than 75%) provides good TiN layer while sputtering with low N₂/Ar gas ratio (lower than 25%) gives Ti layer instead of TiN. In addition, sputtering with 50% N₂/Ar gas ratio gives a multiphase system between TiN and Ti. Local structure parameters of these nanocrystal thin films are reported.

Abstract: For the first time the rearrangement of cerium local environment in Ce2Fe17-xMnx(x = 0; 1; 2) intermetallics vs. Mn concentration and temperature was investigated by thespectroscopy of extended X-ray absorption fine structure (EXAFS) above K-Ce absorptionedge. At the same time under similar conditions by the spectroscopy of X-ray absorption near-edge structure (XANES) above L3-Ce absorption edge the valence state of Ce was studied. Thecorrelation is found between changes in local electronic and crystalline structure observed inCe2Fe17-xMnx and the types of magnetic states in these compounds.

Abstract: Abstract. The valence state of Ce and Eu was investigated by X-ray absorption near-edge structure (XANES) spectroscopy above L3-Ce and L3-Eu absorption edges in series of RCo₂P₂ (R = La, Ce, Pr, Eu) magnetic intermetallics. At the same time under similar conditions the rearrangement of Co and Pr local environment vs. temperature was studied by extended X-ray absorption ¯ne structure (EXAFS) spectroscopy above K-Co and L3-Pr absorption edges.

Abstract: We have obtained relatively unambiguous evidence that validates a simple, predictive model describing the uptake of noble metal coordination complexes from aqueous solutions onto oxide surfaces. The results confirm that the metal-oxide interaction is essentially electrostatic in nature. The evidence has been obtained by applying extended x-ray absorption fine structure (EXAFS) analysis to noble metal adsorption systems in which the effect of surface-localized pH has been isolated and quantified. The model has applications ranging from catalysts preparation to heavy metal pollution abatement and precious metal recovery.

Abstract: We performed first-principles calculations to examine the interaction among rare-earth (RE), alkaline-earth (AE) elements and oxygen vacancy (V_O) in BaTiO₃, in order to clarify the combined effects of V_O trapping by two different elements. It was found that there is a synergistic effect of V_O trapping by RE at Ba site and AE at Ti site, so that the co-doping is effective to improve insulating reliability of BaTiO₃. We also verified that the local atomic structures around dopants obtained by calculations well agree with that obtained experimentally by extended X-ray absorption fine structure (EXAFS) analyses. The present work is the first one to clarify the structural environment around dopants including V_O by both theoretical and experimental approaches.