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X-ray absorption spectra near Cu K edges have been obtained for Cu and Cu2O thin films potentiostatically electrodeposited in an acetate bath. The electronic states of Cu ions and the local structures around these ions are studied using X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopy, respectively. The inner strains in micro-size crystals of the electrodeposited Cu thin film are less than those of a commercial Cu foil. The partial electronic states of Cu ions near the Fermi level (EF) and the local structure around these ions show a systematic transformation from a Cu2O single phase (Phase I), to a Cu2O–Cu intermediate phase (Phase II) and a Cu single phase (Phase III) in thin films electrodeposited on titanium substrates for the deposition potential range of –100 to –900 mV. Phase II consists of independent Cu2O-like and Cu-like local structures, but not a Cu2O–Cu complex. Phase II is also characterized by a transition region from the semiconductor Cu2O to the metal Cu for the Cu electronic state having a p-like character near the Fermi level in the oxygen O-2p conduction band. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

X-ray absorption spectra near the absorption edges of Nd, Ba, and Co ions have been taken to study the metal–insulator (M–I) transition occurring at about 360 K (TMI) in NdBaCo2O5.5. In the metallic and insulating phases, the electronic density of states (DOS) just above the Fermi level (EF) consists of the high-density unoccupied bands of Nd–5dσ and Ba–5dσ. The narrow charge-transfer Co–3d7(eg)L band and the broad charge-transfer Co–3d(t2g)nLm bands occupy positions just below and near EF, respectively, where L represent a hole in the O–2p valence band. The negative charge-transfer Nd–4dnL′m and Ba–4dnL′m hybridized bands are also just below EF, where L′ represent a hole in the fully occupied 4d band of the Nd and Ba ions. It is suggested that the metallic conductivity above TMI arises from the itinerant (p–d) hybridized holes having an 3d(eg)-symmetry in the top of the O–2p valence band. The structural deformation localized around the Ba ions but not the Nd and Co ions affects the crystal-field splitting of the Co–3d orbitals in the CoO polyhedra and the hybridization between the outer orbitals of the cations (Nd, Ba, Co ions) and the O–2p orbitals. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The structural deformations around Sr, Bi, and Ta ions, and the electronic density of states near the Fermi level have been studied in paraelectric and ferroelectric phases of the layer pseudo-perovskite compound, SrBi 2 Ta 2 O 9 (SBT), by means of X-ray absorption spectra (XAS) near the absorption edges of Sr, Bi, and Ta ions. The X-ray absorption near edge structure (XANES) shows that localized largely structural deformations appear around Sr and Ta ions, but not around Bi ion in the vicinity of the ferroelectric to paraelectric structural phase transition. In both phases, there are the charge-transfer (4dL, 4d2L2, and 4d 3 L 3 ) bands of Sr, the negative charge-transfer (5d 9 L', 5d 8 L' 2 , and 5d 7 L' 3 ) bands of Bi, and the charge-transfer 5d n L m bands of Ta. The notations L and L' represent a hole in the O-2p valence band, and in the fully occupied 5d band of the Bi ions, respectively. The Sr-4d, Bi-5d, and Ta-5d orbitals are largely hybridized with the 2p orbitals of the nearest-neighbor oxygen ions occupying the (Bi 2 O 2 ) 2+ sheets or the pseudo-perovskite blocks (SrTa 2 O 7 ) 2- . This hybridization is induced by an electronic interaction between the cations (Sr, Bi, and Ta ions) and the anions (O ions). The Fermi level is very close to the unoccupied Sr-5pπ and Ta-5d(e g ) bands, but not the unoccupied Bi-6dπ band. In the ferroelectric phase, the hybridization between the Bi ion and the oxygen ions (02) from the (SrTa 2 O 7 ) 2- blocks considerably reduced and almost disappears. This reduction and disappearance of the hybridization increases the effective charges on 02 in the TaO 6 octahedra, while the (Bi 2 O 2 ) 2+ layers act only as insulators. Thus, the charge-up of 02 contributes a large dielectric permittivity of the pseudo-perovskite (SrTa 2 O 7 ) 2- blocks, in addition to the structural deformation induced near the phase transition at 300 °C. The strong hybridization between the Sr and oxygen ions (O1, 04, and O5) also plays a crucial role to characterize the unusual ferroelectricity in SrBi 2 Ta 2 O 9 family of compounds substituted Sr ions with other ions or vacancies.

The electronic density of states in BaTiO 3 is studied by means of X-ray absorption near-edge structure in a vicinity of a Ti K edge and Ba L edges. A 4pπ band of the Ti ion and a 5dπ band of the Ba ion having a high-density unoccupied state occupy a level just above the Fermi level (E F ). The pre-edge peaks give that, in addition to an O 2- 2p valence band, the electronic density of states below E F are composed of negative-charge-transfer bands 3d 1 , 3d 1 L and 3d 2 L 2 of Ti ions and 4f 1 , 4f 1 L and 4f 2 L 2 of Ba ions. The 3d 1 , 3d 1 L and 3d 2 L 2 bands of Ti ions gives that a mixture of the different oxidation states Ti 2+ and Ti 3+ is present in addition to Ti 4+ . The 4f 1 , 4f 1 L and 4f 2 L 2 bands are induced by a hybridization between Ba 2+ 4d and O 2- 2p orbitals via an electronic configuration interaction between the 4f and 4d orbitals of the Ba ion. The disappearance of the 4f 1 , 4f 1 L and 4f 2 L 2 bands in the ferroelectric phase suggests that the collective displacement of Ba ions from ideal ionic sites of the cubic perovskite-type structure reduces the hybridization between the Ba and O ions. This gives that the effective charge on the O ions is increased and induces a large dipole moment between the O ions and the Ti ions, which are at an off-center position of TiO 6 octahedra in the ferroelectric phase.

The electronic states of La2− x Sr x CuO4 with 0.00 ≤ x ≤ 0.20 are studied by means of X-ray absorption spectroscopy (XANES, EXAFS) near the K-edge of Cu2+ ion and the L-edges of La3+ ion. It is found that characteristic white lines occurring near L II and L III edges of La3+ ion show a slight energy shift depending on substituted Sr2+ ions, x and temperature. The white lines suggest that unoccupied high-density 5dπ and 5dδ bands of La3+ ion just above a Fermi level transform to a hybridized single band of 5dπδ at 78 K in the superconductors with x = 0.10, 0.16 and 0.20. On the other hand, the XANES spectra near the Cu-K edge including a pre-edge region do not depend on x and temperature in the region of 0.00 ≤ x ≤ 0.20. It is considered that there is no reconstruction of electronic states at the Fermi level in a Mott–Hubbard band gap between an O 2p valence band and a Cu 3d conduction band. The electronic states at the Fermi level are probably consisted of the unoccupied 5dπδ band and an empty charge-tra...

We have studied the influence of metal elements on the passivation of stainless steel (SS) 430 (18Cr) and 444 (18Cr–2Mo) by real time X-ray absorption near edge spectroscopy. We developed an electro-chemical cell that is suitable for in situ electro-chemistry experiments. The behavior of Fe, Cr and Mo elements of SS 430 and 444 was studied in passive region reaction in a borate buffer solution (pH 7.0). We found that the Cr 2 O 3 /Fe 2 O 3 ratio gradually decreased with passivation time due to the oxidation of Cr 2 O 3 to CrO 4 2− , indicating weakening of passivity. In the meanwhile, the amount of Mo at passive films increased with passivation time. The improvement of passivity in the SS 444 is mainly attributed to the substitution of Cr oxide by Mo oxide in the passive film.

The local structure and local conduction paths of Ga–In–Zn–O (GIZO) and Hf–In–Zn–O (HIZO) amorphous thin films were investigated by the extended X-ray absorption fine structure (EXAFS). We found that the local hindrance paths of In–Ga and In–Hf exist in the conduction paths of amorphous GIZO and HIZO semiconductor thin films, respectively.

To investigate the electronic structure of the electrochemically Li-ion deintercalated Li 1 - x CoO 2 system, soft X-ray absorption spectroscopy (XAS) for the oxygen K-edge and the Co L I I , I I I -edge has been carried out intensively with compositional x value variation, compared with Co K-edge X-ray absorption near edge structure (XANES) spectroscopy. To get reasonably good XAS spectra for the electrochemically Li-ion deintercalated Li 1 - x CoO 2 system, we made a binder-free LiCoO 2 film electrode using the electrostatic spray deposition (ESD) technique. The oxygen K-edge XAS for Li 1 - x CoO 2 shows more effective spectral change with respect to Li-ion content than the Co L I I , I I I -edge XAS. The dependence of the absorption peak feature on the Li content is described in terms of the ground state of the Co and O atoms, showing the systematic variation of the hole-state site distribution between Co and oxygen atoms. From the Co L I I , I I I -edge XAS, it is found that the broad peak shift to higher energy with the Li-ion deintercalation is due to rehybridization between Co and O atoms under the local structural distortion of CoO 6 octahedra, which is also confirmed by the formation of two additional absorption peaks below the threshold energy corresponding to the oxygen 2p hole state hybridized with the 3d orbital of Co ion in the distorted CoO 6 octahedral site. In the O K-edge XAS spectra for the deintercalated Li 1 - x CoO 2 film, the shoulder absorption peak in the energy region higher than the threshold energy could be assigned to the higher oxidation state of the oxygen site on Li deintercalation. From the Co L I I , I I I -edge and O K-edge XAS results for the Li-ion deintercalated Li 1 - x CoO 2 film, it is concluded that the charge compensation for the Li-ion deintercalation process could be achieved mainly in the oxygen site and Co metal atomic site simultaneously. O K-edge and Co L I I , I I I -edge XAS results for cycled LiCoO 2 film show that the capacity fading of the LiCoO 2 system is related to the decrease of Co-O bond covalency by the local structural distortion of CoO 6 octahedra remaining in the cycled LiCoO 2 .

LiCoO 2 thin-film cathode was deposited on Pt-coated alumina substrate by the electrostatic spray deposition method. The average film weight of LiCoO 2 increased linearly with the deposition time. Electrochemical characterization was carried out by cyclic voltammetry and charge/discharge tests. These tests revealed that single phase HT-LiCoO 2 films could be obtained by the ESD method at temperature as low as 600°C and the LiCoO 2 film deposited by the ESD method showed very stable cycling characteristics. The crystallinity of the LiCoO 2 layers increased with increasing annealing temperature. XANES results showed that the LiCoO 2 film deposited by the ESD method does not show any changes of the local geometry and electronic structure around Co atoms after electrochemical cycling.

Extended X-ray absorption fine structure was studied at the Pb L 3 -edge for lead oxyiodine glasses with (PbO) x .(PbI 2 ) 1-x formula chosen at x =0.2, 0.4, 0.5, 0.6, 0.8 and 1.0. Using a fitting technique, we observed structural modifications in the first Pb-O shell, estimating the changes in inter-atomic distance (ΔR = 0.02-0.04 A in x < 0.8) and in structural disorder (Debye-Waller factor, Δσ 2 = 5.6 ± 1.6 × 10 -3 at x = 0.5) with respect to PbO glass reference (x = 1.0). To interpret our data, we describe the specific local site configuration and the relevant glass formation tendency. In PbO or PbO-rich glasses, Pb ions have four neighboring oxygen atoms forming the PbO 4 tetrahedral unit. As PbI 2 content increases, PbO 4 units are gradually modified to different neighboring environments, such as the octahedron PbO 2 I 4 unit, which is the most realistic site configuration at compositions between PbO and PbI 2 .

The electronic states in Zn1−xCuxCr2Se4 have been studied by X-ray near edge absorption spectra (XANES) of K-edges of Zn2+, Cu1+, Cr3+ and Se2− ions. Ferromagnetism of the spinel compounds with x>0.10 are interpreted by a double exchange interaction between localized spins of Cr3+ ions and conductive Cr4+ spin polarons. The spin polaron is a triplet 3d orbital of 3dxy, 3dyz, and 3dzx, hybridized with spinless charge carriers (holes), which are induced in a top region of O 2p valence band by a substitution of Zn2+ with Cu1+ ions.

Microstructural change during the mechanical alloying of Co 20 Cu 80 has been studied by X-ray di!ractometry (XRD) and extended X-ray absorption "ne structure (EXAFS) techniques. EXAFS analysis shows clearly the formation of supersaturated Co 20 Cu 80 solid solution with FCC crystal structure during mechanical alloying, which is in good agreement with XRD analysis. Magnetic properties also have been studied by SQUID magnetometer from 4 to 290 K. The supersaturated Co 20 Cu 80 solid solution shows wide distribution in Co cluster size due to the continuous blocking of Co cluster as a function of temperature. ( 1999 Elsevier Science B.V. All rights reserved.

Inverse problem solving computation was performed for solving PDF (pair distribution function) from simulated data EXAFS based on data FEFF. For a realistic comparison with experimental data, we chose a model of the first sub‐shell Mn‐0 pair showing the Jahn Teller distortion in crystalline LaMnO3. To restore the Fourier filtering signal distortion, involved in the first sub‐shell information isolated from higher shell contents, relevant distortion matching function was computed initially from the proximity model, and iteratively from the prior‐guess during consecutive regularization computation. Adaptive computation of EXAFS background correction is an issue of algorithm development, but our preliminary test was performed under the simulated background correction perfectly excluding the higher shell interference. In our numerical result, efficient convergence of iterative solution indicates a self‐consistent tendency that a true PDF solution is convinced as a counterpart of genuine chi‐data, provided tha...

Through numerical simulation of inverse problem computation, our new method of EXAFS analysis was tested for a simple structure of copper metal. For a simulation test, we constructed a structural model with all possible paths of single and multiple scattering within 6 A. Typically, the first‐shell PDF (pair distribution function) is computed according to an algebraic equation describing the temperature dependence of specific anharmonic distribution. Through the MEPP (matched EXAFS PDF projection) method — combing iterative regularization and matched correction of Fourier filtering distortion, it is shown that the original function of anharmonic PDF is iteratively solved from the initial proximity model, even approximated in terms of non‐realistic sub‐shell mixture of anharmonic distribution feature. To remove the problem of extraneous pattern at intermediate PDF solution, we also tested a proper pattern fit on the anharmonic curve formula, resulting in significantly suitable convergence to the true PDF solution. Our simulation results indicate that the projection to true PDF solution is only reachable when the perfect background correction is selected. Our precision EXAFS analysis performance requires manipulating the apparent correlation between the first and second shells using a typical numerical process of first‐shell matching Fourier filtering.

An EXAFS expression was introduced for analysis of positive or negative thermal expansion. The EXAFS parameters were directly related to the interatomic potential. Also, it was shown that the sign of anharmonic potential parameter k3 depends on the sign of thermal expansion coefficient. Simulation works showed that the positive or negative thermal expansion can be sensitively measured by EXAFS study.

Using the FEFF kernel A(k,r), we describe the inverse computation from χ(k)-data to g(r)-solution in terms of a singularity regularization method based on complete Bayesian statistics process. In this work, we topologically decompose the system-matched invariant projection operators into two distinct types, (A+AA+A) and (AA+AA+), and achieved Synthesized Topological Inversion Computation (STIC), by employing a 12-operator-closed-loop emulator of the symplectic transformation. This leads to a numerically self-consistent solution as the optimal near-singular regularization parameters are sought, dramatically suppressing instability problems connected with finite precision arithmetic in ill-posed systems. By statistically correlating a pair of measured data, it was feasible to compute an optimal EXAFS phase retrieval solution expressed in terms of the complex-valued χ(k), and this approach was successfully used to determine the optimal g(r) for a complex multi-component system.

We propose the chemical matched EXAFS regularization method through the numerical analysis of Mn Kedge EXAFS data for La1−xCaxMnO3 specimens. A relatively narrow k-space window (kmax − kmin = 6 A−1) has been used to compute the Mn–O pair distribution function in the specific r-space range of 1.8–2.2 A. Results show that the resolution in r-space is greatly improved in the pair distribution functions of the Mn–O bond. EXAFS data of specimens with double shell pair distributions were hardly analyzed by the conventional method because they are not resolved in the Fourier transform. A preliminary test of the EXAFS regularization method shows that this is very effective method to study the double shell distribution due to the Jahn Teller effect. The test was performed on La1−xCaxMnO3 at x = 0.2 and 0.3.

To investigate the electronic structure of the electrochemically Li-ion deintercalated Li1-xCoO2 system, soft X-ray absorption spectroscopy (XAS) for the oxygen K-edge and the Co LII,III-edge has been carried out intensively with compositional x value variation, compared with Co K-edge X-ray absorption near edge structure (XANES) spectroscopy. To get reasonably good XAS spectra for the electrochemically Li-ion deintercalated Li1-xCoO2 system, we made a binder-free LiCoO2 film electrode using the electrostatic spray deposition (ESD) technique. The oxygen K-edge XAS for Li1-xCoO2 shows more effective spectral change with respect to Li-ion content than the Co LII,III-edge XAS. The dependence of the absorption peak feature on the Li content is described in terms of the ground state of the Co and O atoms, showing the systematic variation of the hole-state site distribution between Co and oxygen atoms. From the Co LII,III-edge XAS, it is found that the broad peak shift to higher energy with the Li-ion deinterca...

The reaction characteristics and the local structural changes of Li 2 . 6 Co 0 . 4 N anode material for lithium secondary batteries were investigated by electrochemical methods and extended X-ray absorption fine structure (EXAFS) analysis. The main reaction during the initial discharge corresponded to Li insertion into Li vacant sites in synthetic Li 2 . 6 Co 0 . 4 N. The variation of Fourier transform magnitude for focused multiple scattering in EXAFS spectrum disclosed the change of local structure around cobalt ions during Li insertion/extraction. Local fine structure around Co ions lost linear symmetry of its own with excess Li extraction during the initial charge. However, the linear symmetric bond was recovered by Li reinsertion during the subsequent discharge, and local structural change during the first cycle can be considered as a reversible process.