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Many researchers have pointed out that there is a quantum critical point (QCP) in the F-doped SmOFeAs system. In this paper, the electronic structure and local structure of the superconductive FeAs layer in SmO1- xF xFeAs as a function of the F-doping concentration have been investigated using Fe and As K-edge X-ray absorption spectroscopy. Experiments performed on the X-ray absorption near-edge structure showed that in the vicinity of the QCP the intensity of the pre-edge feature at the Fe-edge decreases continuously, while there is a striking rise of the shoulder-peak at the As edge, suggesting the occurrence of charge redistribution near the QCP. Further analysis on the As K-edge extended X-ray absorption fine structure demonstrated that the charge redistribution originates mostly from a shortening of the Fe-As bond at the QCP. An evident relationship between the mysterious QCP and the fundamental Fe-As bond was established, providing new insights on the interplay between QCP, charge dynamics and the local structural Fe-As bond in Fe-based superconductors. [ABSTRACT FROM AUTHOR]

A series of alluaudite Na2Fe3− xMn x(PO4)3 microcompounds, which self-assembled from primary nanorods, were prepared successfully through a solvothermal method. As a promising candidate cathode for sodium-ion batteries, it is necessary to obtain a deeper understanding of the relationship between the structure and physicochemical properties of these materials. The local electronic and geometric environments were systematically investigated, for the first time, by using a combination of soft/hard X-ray absorption, IR, and Mössbauer spectroscopy. The results show that the electrochemical performance is not only associated with morphology, but also with the electronic and crystalline structure. With the introduction of manganese into the lattice, the long-range order maintains the isostructural framework and the lattice parameters expand as expected. However, for short-range order, PO4 tetrahedra and MO6 octahedra (M=Fe and Mn) become more severely distorted as a function of Mn concentration. Meanwhile, larger MnO6 octahedra will compress the space of FeO6 octahedra, which will result in stronger core/electron-electron interactions for Fe, as characterized by hard/soft X-ray absorption spectra. These slight changes in the electronic and local structures lead to different electrochemical performances with changes to the manganese content. Moreover, other physicochemical properties, such as magnetic behavior, are also confirmed to be correlated with these different electron interactions and local geometric environments. [ABSTRACT FROM AUTHOR]

The discovery in 2008 of a new family of high- T superconductor (HTSC), i.e., layered compounds based on iron, has spurred a tremendous interest in the community of condensed matter physics. This discovery has broken cuprate 'monopoly' in the physics of HTSC materials. Until now, thousands of experimental and theoretical methods were devoted to investigate the superconducting properties of this new iron-based HTSCs. Synchrotron radiation-based X-ray absorption spectroscopy (XAS) made great contributions to the local lattice structure, the electronic structure, and even the superconductive mechanism of this iron-based materials. The aim of this review is a short introduction into the progress of research on new iron-based HTSCs probed by the unique technique-XAS, including the electron correlations, local lattice distortions, changes of valence upon doping or pressure, and even the isotope effect for this new iron-based family. [ABSTRACT FROM AUTHOR]

To clarify the contrasting impurity effects of Mn and Zn dopants on the critical temperature of optimally doped Ba0.5K0.5Fe2As2 superconductors, extended X-ray absorption fine-structure spectroscopy was implemented at the Fe and As K-edge. In Mn-doped compounds a gradual deviation of the symmetric FeAs4 tetrahedron and weakening of the Fe-As bond was observed. Conversely, in Zn-doped compounds the perfect FeAs4 tetrahedron is maintained and the Fe-As bond is rigid. The local structural details are consistent with the development of superconductivity in these two systems, suggesting a significant role played by the topology of the FeAs4 tetrahedron and rigidness of the Fe-As bond in Mn/Zn-doped Ba0.5K0.5Fe2As2 superconductors. [ABSTRACT FROM AUTHOR]

Abstract: LiFePO4 composite was synthesized by both solid state and hydrothermal methods. The physical properties of the as-prepared lithium iron phosphates were characterized by X-ray diffraction while electrochemical properties were measured with charge/discharge experiments. X-ray absorption spectroscopy (XAS) was performed to investigate the local structure arrangements of LiFePO4. Both X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectra collected at the Fe K-edge shed light on structural differences between LiFePO4 samples synthesized with the two methods, partially accounting for their different electrochemical properties. [Copyright &y& Elsevier]

Abstract: We used X-ray absorption near edge structure (XANES) spectroscopy to investigate the metal-dependent enzymatic activity of the peptide deformylase from Leptospira interrogans (LiPDF). Ab initio full multiple scattering calculations performed by MXAN are applied to obtain the local structure of the cobalt-containing LiPDF (Co-LiPDF) and zinc-containing LiPDF (Zn-LiPDF) around the metal sites in pH9.0 buffer solution. The result shows the cobalt-wat1 (the bond water molecule) distance of Co-LiPDF is 1.89Å, much shorter than that of Zn-LiPDF, 2.50Å. That is an essential factor for its low catalytic activity. [Copyright &y& Elsevier]

Abstract: The local and geometrical structure around gold (III) e.g., Au3+ ions in aqueous solution with different OH−/Cl− molar ratios, has been investigated by X-ray absorption spectroscopy (XAS). X-ray absorption near-edge structure (XANES) spectra of [AuCl n (OH)4− n ]− solutions have been calculated and the multiple-scattering spectral features have been attributed to Cl d-states, axial water molecules and the replacement of Cl− ligands by OH− ligands. A square–planar geometry for [AuCl n (OH)4− n ]− with two axial water molecules has been identified. Moreover, a spectral correlation between XANES features and the type of planar atoms has been identified. By extended X-ray absorption fine structure spectra (EXAFS), the planar Au bond distances in the solutions have also been determined, e.g., 2.28Å for Au–Cl and 1.98Å for Au–O, respectively. The same EXAFS analysis provides evidence that the peak at about 4.0Å in solutions with the lowest OH−/Cl− molar ratio arises from collinear Cl–Au–Cl multiple-scattering contributions. For the first time, a complete detailed reconstruction of the hydration structure of an Au ion at different pH values has been achieved. [Copyright &y& Elsevier]

A mesoporous LiFe0.99Mo0.01PO4/C composite was synthesized by the sol-gel method using (NH4)2MoO4 as a doping starting material. The formation of conductive carbon, metal doping and mesopores was achieved simultaneously in the prepared material. The characterizations of crystal structures and microstructures were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), extended X-ray-absorption fine-structure (EXAFS) and X-ray-absorption near-structure spectroscopy (XANES), while the surface area was determined using N2 adsorption techniques. Cyclic voltammetry (CV) and charge-discharge cycling performance were used to characterize its electrochemical properties. The sample possessed uniformly distributed mesopores with an average pore size of 4 nm, and the specific surface area was about 69.368 m2/g. The results show that the reversible capacity of mesoporous LiFe0.99Mo0.01PO4/C is about 160 mAh/g at 0.1C, 135 mAh/g at 1C and 90 mAh/g at 5C, respectively. The capacity fading is neglectable. [ABSTRACT FROM AUTHOR]

Abstract: The noble metal ions play an important role in many chemical reactions, but at the present time they represent also potentially new environmental contaminants. There is relatively little information available to adequately assess the potential health hazards, so that to evaluate the potential hazards and identify the necessary actions to reduce the risks associated with exposure to these metals and their compounds it is important to understand the local structure around noble metal ions. In this contribution, the local coordination around platinum (IV) ions e.g., Pt4+ in aqueous solution, has been investigated by using X-ray absorption spectroscopy (XAS). X-ray absorption near-edge spectra (XANES) of both [PtCl6]2− and [PtCl4(OH)2]2− in an aqueous solution have been calculated using FEFF8.2 and both are characterized by an octahedral geometry. From these calculations, we may also assign a characteristic post-edge feature to a contribution of Cl d-states. From the EXAFS analysis we also determined the corresponding Pt bond distances, e.g., 2.33Å for the Pt–Cl distance and 2.03Å for the Pt–O distance in these aqueous solutions. The same analysis provides evidence that the peaks in the Fourier transform at about 4.0Å are due to multiple scattering collinear Cl–Pt–Cl contributions. [Copyright &y& Elsevier]

Abstract: Peptide deformylase (PDF, EC 3.5.1.27) is essential for the normal growth of eubacterium but not for mammalians. Recently, PDF has been studied as a target for new antibiotics. In this paper, X-ray absorption spectroscopy was employed to determine the local structure around the zinc ion of PDF from Leptospira Interrogans in dry powder, because it is very difficult to obtain the crystallized sample of LiPDF. We performed X-ray absorption near edge structure (XANES) calculation and reconstructed successfully the local geometry of the active center, and the results from calculations show that a water molecule (Wat1) has moved towards the zinc ion and lies in the distance range to coordinate with the zinc ion weakly. In addition, the sensitivity of theoretical spectra to the different ligand bodies was evaluated in terms of goodness-of-fit. [Copyright &y& Elsevier]