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Li-rich type manganese oxides are one of the most promising cathodes for lithium-ion batteries in recent years; thanks to their high energy density. In these cathodes, partial substitution of manga...

The oxidation/reduction behaviours of lattice oxygen and transition metals in a Li-rich manganese-based layered oxide Li[Li0.25Ni0.20Mn0.55]O1.93 are investigated by using hard X-ray photoelectron spectroscopy (HAX-PES). By making use of its deeper probing depth rather than in-house XPS analyses, we clearly confirm the formation of O- ions as bulk oxygen species in the active material. They are formed on the 1st charging process as a charge compensation mechanism for delithiation and decrease on discharging. In particular, the cation-anion dual charge compensation involving Ni and O ions is suggested during the voltage slope region of the charging process. The Ni ions in the material are considered to increase the capacity delivered by a reversible anion redox reaction with the suppression of O2 gas release. On the other hand, we found structural deterioration in the cycled material. The O- species are still observed but are electrochemically inactive during the 5th charge-discharge cycle. Also, the oxidation state of Ni ions is divalent and inactive, although that of Mn ions changes reversibly. We believe that this is associated with the structural rearrangement occurring after the activation process during the 1st charging, leading to the formation of spinel- or rocksalt-like domains over the sub-surface region of the particles.

Degradation mechanism of surface coating effects at the cathode/electrolyte interface is investigated using thin-film model electrodes combined with operando X-ray absorption spectroscopy (XAS). MgO-coated LiCoO[2] thin-film electrodes prepared via pulsed laser deposition at room temperature and high temperature are used as model systems. The MgO coating improves the durability of the cathode during high-potential cycling. Operando total reflection fluorescence XAS reveals that initial deterioration due to reduction of Co ions at the surface of the uncoated-LiCoO[2] thin film upon electrolyte immersion is inhibited by the MgO coating. Operando depth-resolved XAS reveals that the MgO coating suppresses drastic distortions of local structure at the LiCoO[2] surface as observed in the uncoated-LiCoO[2] during charging process. The electronic and local structure changes at the electrode/electrolyte interface for two types of surface coating morphologies are discussed.

For the further development of lithium-ion batteries, improvement of their cyclic performance is crucial. However, the mechanism underlying the deterioration of the battery cyclic performance is not fully understood. We investigated the effects of the electronic structure at the electrode/electrolyte interface on the cyclic performance of the cathode materials via in situ total-reflection fluorescence X-ray absorption spectroscopy. In a LiCoO2 thin-film electrode that exhibits gradual deterioration upon subsequent Li ion extractions and insertions (cycling), the reduction of Co ions at the electrode/electrolyte interface was observed upon immersion in an organic electrolyte, with subsequent irreversible changes after cycling. In contrast, in a LiFePO4 thin-film electrode, the electronic structure at the electrode/electrolyte interface was stable and reversible upon electrolyte immersion with subsequent cycling. The increased stability of the electronic structure at the LiFePO4/electrolyte interface affect...

The redox reaction of Li1.16Ni0.15Co0.19Mn0.50O2 positive electrode material during the charging and discharging processes was investigated by using spectroscopic methods, i.e. in situ hard X-ray absorption near edge structure (XANES) at transition metal K-edges and ex situ soft XANES at oxygen K- and transition metal L-edges. The spectral changes of constituent elements during the initial charging to 4.5 V vs. Li/Li+ are quite similar to those of conventional layer-structured positive materials, such as LiNi1/3Mn1/3Co1/3O2. Ni2+ and Co3+ ions are fully oxidized to Ni4+ and Co4+, while Mn4+ remains unchanged. Ligand oxygen ions also take part in charge compensation. In the process of charging to 4.8 V via the plateau voltage region, no significant spectral change appears except partial reduction of Ni and Co ions in spite of lithium extraction. By discharging to 2.0 V the spectra of each element return to those of the pristine material.

In-situ time-resolved X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD) are applied to investigate the phase transition mechanism between LiFePO4 and FePO4. Phase formation kinetics is discussed by using the phase fractions of LiFePO4 and FePO4 directly obtained from the XRD measurement and the amount of the passed current synchronized by the XRD measurement with Kolmogorov-Johnson-Mehl-Avrami (KJMA) analysis. For both of the lithium extraction and insertion process, the KJMA analysis from the XRD and amount of the passed current data indicate that the phase formation of LiFePO4 and FePO4 proceeds via one-dimensional phase boundary movement. For the lithium extraction process, the two phase coexistence of LiFePO4 and FePO4 is observed under the potential step conditions, and the KJMA plot based on the passed current data is relatively in good agreement with the one based on the XRD data. On the other hand, for the lithium insertion process, considerable peak boarding which implies intermediate state formation during the phase transition occurs, and the LiFePO4 phase formation is delayed compared with the amount of the passed current, especially in the case of small particle size. These results indicate that the phase transition behavior during lithium insertion is different from that of the typical two phase reaction.

The polarized total-reflection X-ray absorption fine structure (TR-XAFS) method was applied in situ to the liquid−liquid interface. The TR-XAFS spectrum at the Zn K-edge for 5,10,15,20-tetrakis(4-carboxypheny)porphyrinato zinc(II) (ZnTPPC4−) adsorbed at the heptane−water interface exhibited a spectral difference depending on the linear polarization of the incident X-ray. The 1s−4pz transition response for a square planar zinc(II) complex was observed in the pre-edge region (9662 eV) only with a vertically polarized X-ray. The appearance of the transition response indicates that the axial coordination sites of the zinc center tend to be partially dehydrated at the heptane−water interface. The polarization dependence of the TR-XAFS spectrum demonstrated that the porphyrin macrocycle orients almost in the interfacial plane similar to ZnTPPC at the air−water interface. Polarized TR-XAFS measurement was also carried out in the presence of a cationic surfactant, hexyltrimethylammonium bromide (C6TAB), in the aq...

The transformation of inorganic iodine (I − and IO 3 − ) incubated in soils with varying amounts of organic matter (Andosols from the surface layer of an upland field and forest, as well as Acrisols from surface and subsurface layers of an upland field) was investigated by using the iodine K-edge X-ray absorption near-edge structure (XANES). After 60 d of reaction, both I − and IO 3 − were transformed into organoiodine in surface soils containing sufficient amounts of organic matter, whereas IO 3 − remained unchanged in the subsurface soil of Acrisols with low organic matter contents. Transformation of IO 3 − into organoiodine was not retarded when the microbial activity in soil was reduced by γ-ray irradiation, suggesting that microbial activity was not essential for the transformation of inorganic iodine into organoiodine. Soil organic matter has the ability to transform inorganic iodine into organoiodine.

Alloying elements added to steel for improving surface properties such as corrosion resistance are often enriched to the surface of the alloys during annealing at high temperatures. Their behavior depends on difference in their chemical characters and the condition of annealing. In this study, nondestructive depth-resolved analysis of amount distribution and chemical state of alloying element by using X-ray fluorescence analysis (XRF) technique in combination with X-ray absorption spectroscopy (XAS) in order to characterize the enrichment and oxidation of manganese on the surface layers of an Fe-Mn alloy annealed under low oxygen partial pressure. The experiments were carried out using a two-dimensional detector with geometrical arrangement of grazing exit in detection of fluorescence X-ray emitted from sample surface. The results showed that manganese was enriched to surface layers of the Fe-Mn alloys during annealing at high temperatures and formed as manganese oxide. The preferential oxidation of manganese by annealing under low oxygen partial pressure is considered the driving force for their enrichment on the alloy surface.

Alloying elements are added to steel for improving surface properties such as corrosion resistance. The alloying elements exhibit different chemical characters, and they are often enriched to the surface of the alloys during annealing at high temperatures. In this study, depth-resolved X-ray absorption spectroscopy (XAS) measurements were carried out using a two-dimensional detector with geometrical arrangement of grazing exit in detection of fluorescence X-ray emitted from sample surface, in order to characterize the enrichment and oxidation of manganese on the surface layers of an Fe-Mn alloy annealed under low oxygen partial pressure. This technique facilitates non-destructive measurement for characterizing the compositional distribution of manganese in the depth direction. The results showed that manganese was enriched to surface layers of the Fe-Mn alloys during annealing at high temperatures and formed as manganese oxide. The preferential oxidation of manganese by annealing under low oxygen partial pressure is considered the driving force for their enrichment on the alloy surface.

Copper(II) complexes spread on an aqueous solution surface were studied by a polarized total-reflection X-ray absorption fine structure (TR-XAFS) technique. The polarized TR-XAFS spectra at the Cu-K edge for copper(II) porphyrins and copper(II) chlorophyllin in a monolayer were measured in situ at the air-water interface. The polarization dependences of X-ray absorption near-edge structure (XANES) involving a 1s→4pz transition allowed us to estimate the molecular orientation and the local coordination structure around the copper(II) atom in the polarization plane selectively. The extended X-ray absorption fine structure (EXAFS) region of the polarized TR-XAFS spectra for the metal complexes present at the air-water interface was successfully analyzed for the first time. The relative coordination number for the copper center evaluated from the EXAFS analysis indicated larger values in the vertical polarization than in the horizontal one, in agreement with the standing-up molecular orientation at the air-water interface estimated from the XANES region., Analytical sciences, 25(4), pp.475-480; 2009

The uranium L III -edge XANES spectra for natural rocks at the concentration range of 0.96–124 mg kg −1 were measured using a log spiral bent crystal Laue analyzer (BCLA) combined with a multi-element Ge detector. It was found that the quality of the XANES spectra using the BCLA was greatly improved due to a reduction of interfering fluorescence from major components such as Rb and Sr. The ratio of signal to background intensities in the U L III -edge XANES spectra increased by a factor of 2.9–17 with the use of the BCLA, which greatly enhanced the detection limit for the speciation of the oxidation states of U or the U(IV)/U(VI) ratio of natural samples. In addition, it was demonstrated that the fluorescence XANES method coupled with the BCLA enable determination of the speciation of U for various natural samples such as acidic igneous rocks, ferromanganese nodules, sediments, and some sedimentary rocks such as shale and limestone.

Local atomic structures of Re and radiogenic Os in molybdenite from the Onganja mine, Namibia, were examined using X-ray absorption fine structure (XAFS). Rhenium L III -edge X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) show that the oxidation state of Re, the interatomic distances between Re and the neighboring atoms, and the coordination number of Re to S are very similar to those of Mo in molybdenite. The results confirm that Re is present as Re(IV) in the Mo site in molybdenite. Measurement of L III -edge XANES and EXAFS of a minor concentration (8.55 ppm) of radiogenic Os was accomplished in fluorescence mode by removing the interfering X-rays from Re and other elements using a crystal analyzer system. The data indicate that the oxidation state of radiogenic Os is Os(III) and Os(IV) and clearly different from Os(II) in natural sulfide minerals, such as OsS 2 (erlichmanite). XANES data also suggest that radiogenic Os does not form a secondary Os phase, such as OsS 2 or Os metal, in molybdenite. EXAFS of radiogenic Os was successfully simulated assuming that Os is present in the Mo site in molybdenite. The data are consistent with the XANES data; Os does not form Os phases in molybdenite. The EXAFS simulation showed that the interatomic distance between Os and S is 2.27 A, which is 0.12 A smaller than the distances of Re–S and Mo–S (2.39 A) in molybdenite. Similar valences and ionic sizes of Re and Mo in molybdenite support the fact that large amounts of Re can be incorporated into the Mo site as has been observed in previous studies, whereas the different properties of Os compared to Mo and Re suggested here support much lower abundance of common Os in molybdenite. This makes molybdenite an ideal mineral for the Re–Os geochronometer as shown in many studies. However, the shorter distance between radiogenic Os and S compared to those of Re–S and Mo–S in molybdenite suggests that the radiogenic Os has a smaller ionic size than Re(IV) and Mo(IV). Furthermore, Os may be partly present as Os(III). Smaller and lower charge Os can diffuse faster than larger and higher charge Re in molybdenite at a given set of conditions. Hence, our study provides an atomic-level explanation for the high mobility of Os compared to Re, which has been suggested by earlier workers using laser ablation ICP-MS.

Sn Kα1-detecting Sn K-edge XANES spectrum was successfully measured for Pt–Sn/SiO2 catalyst (2.5 wt.% Pt, Sn/Pt atomic ratio 1.0) in the energy resolution 5.0 eV using Rowland-type fluorescence spectrometer equipped with Ge(13,13,13) bent crystal. The steeper, more clearly resolved XANES spectrum thus obtained could be compared quantitatively to theoretical XANES spectra generated by ab initio calculations for thirteen plausible Pt–Sn site models (alloy, adsorbed Sn, and mixture models). This spectral simulation suggested that fluorescence-detecting XANES is a simple method to judge the plausible site structure without detailed spectral analyses. The comparison supported an adsorbed Sn site model structure on highly dispersed Pt[–Sn] nanoparticles on SiO2.

The total-reflection X-ray absorption fine structure (XAFS) method previously employed for the adsorption of dodecyltrimethylammonium bromide (DTAB) at the air/water interface was applied to that in the presence of NaBr. The surface concentration of the bromide ions Gamma(X)(B) of DTAB and NaBr was evaluated by using the Br K-edge absorption jump values of the total-reflection XAFS spectra and was compared to the corresponding value Gamma(H)(B) estimated from the dependence of surface tension on the bulk concentrations of DTAB m(1) and NaBr m(2). The Gamma(X)(B) values trace almost perfectly the Gamma(X)(B) versus m(1) curve up to a concentration near the critical micelle concentration (cmc) and deviate gradually above the concentration. This behavior is basically similar to that of the single DTAB system and ensures that the XAFS method is also applicable to the DTAB system, even in the presence of NaBr. In addition, this method was extended to the single nonionic amphiphile with covalently bonded bromine, and the surface concentrations of 6-bromo-1-hexanol (BrC6OH), Gamma(X)(1) and Gamma(H)(B), were evaluated and compared with each other. It was found that the Gamma(X)(1) value almost perfectly traces the Gamma(H)(1) versus m(1) curve, even at high surface concentrations. The excellent coincidence confirmed that the total-reflection XAFS method can be applied to the nonionic amphiphile system as well as a cationic surfactant with or without an added salt system. Finally, the difference between the Gamma(X)(B) and Gamma(H)(B) values observed in the DTAB with and without an added salt system is briefly described.

The purpose of this study was to accurately determine the valency of Yb at high pressure and room temperature and to clarify the relation between the valence state and the crystal structure of Yb metal. LIII-edge X-ray absorption near-edge structure (XANES) spectra were measured to determine the valence state of Yb metal in the pressure range from 0 to 34.6 GPa at room temperature, using a diamond anvil cell (DAC) and synchrotron radiation at SPring-8. In the fcc phase, Yb metal exhibits mixed valence (the mean valence v >2.1 ). At the fcc-to-bcc phase transition, a 0.1 jump is found in v . In the bcc phase, v (P) is an increasing function of pressure with downward curvature, reaching only 2.55 at 26 GPa. The v is only 2.65 in the hcp phase at 34.6 GPa. A tendency for saturation in v (P) to values smaller than 3.0 is found.

Spontaneous dispersion and clustering processes of Pd were measured by means of the energy-dispersive EXAFS method. The spontaneous dispersion of bulky metal Pd into highly dispersed PdO was directly observed on the H-type zeolite in the atmosphere of O2. In contrast to H-type zeolites, simple oxidation of the agglomerated Pd was observed on Na-ZSM-5. The structural change of Pd was followed in the atmosphere of hydrogen. The clustering processes of metal Pd depended on the kind of zeolite, and these were categorized into three groups. The first group, i.e., Na-ZSM-5 and H-beta, showed monotonic agglomeration of metal Pd by increasing the reduction temperature. The second group consisted of H-ZSM-5 and H-mordenite where the formation of Pd6 clusters was found. On these zeolites, the generation of Pd6 clusters was reversibly observed upon the repetition of reduction and oxidation treatments. The third group consisted of H-Y and USY zeolites where the formation of Pd13 clusters was observed. From these findings, it was concluded that the crystal structure and acid sites of zeolites had profound influences on the dynamic behavior and the genesis of Pd clusters with various structures.

Hydrogen atom position in the hydrated iodide anion complex is determined from X-ray Absorption Near Edge Structure (XANES) of an aqueous iodide solution at both the K- and L-edges. The spectra are compared with the theoretical ones calculated by using the FEFF method for several model geometries having hydrogen atoms at different positions. Satisfactory agreements are obtained from models with an almost linear alignment of iodine–hydrogen–oxygen atoms, indicating the capability of the XANES analysis when it is combined with the multiple scattering calculations as a method to detect the positions of hydrogen atoms in the first coordination sphere.

The reaction distribution in the composite electrodes used in lithium-ion batteries greatly affects battery performances, including rate capability and safety. In this study, the generation of the reaction distribution and its relaxation in cross sections of LiCoO2 and LiFePO4 composite electrodes were analyzed using microbeam X-ray absorption spectroscopy. The reaction distribution immediately after delithiation could be observed clearly with different oxidation states of the transition metal (i.e., different concentrations of lithium ions). The distribution in the Li1–xCoO2 electrodes disappeared, whereas that in the Li1–xFePO4 electrodes remained unchanged even after 15 h of relaxation. After comparing the potential profile of both types of electrodes, it is suggested that the potential difference between the more delithiated area and the less delithiated area in the composite electrode is the primary driving force for the relaxation.

LiNi0.5Mn1.5O4 (LNMO) is a promising positive electrode material for lithium ion batteries because it shows a high potential of 4.7 V vs. Li/Li(+). Its charge-discharge reaction includes two consecutive phase transitions between LiNi0.5Mn1.5O4 (Li1) ↔ Li0.5Ni0.5Mn1.5O4 (Li0.5) and Li0.5 ↔ Ni0.5Mn1.5O4 (Li0) and the complex transition kinetics that governs the rate capability of LNMO can hardly be analyzed by simple electrochemical techniques. Herein, we apply temperature-controlled operando X-ray absorption spectroscopy to directly capture the reacting phases from -20 °C to 40 °C under potential step (chronoamperometric) conditions and evaluate the phase transition kinetics using the apparent first-order rate constants at various temperatures. The constant for the Li1 ↔ Li0.5 transition (process 1) is larger than that for the Li0.5 ↔ Li0 transition (process 2) at all the measured temperatures, and the corresponding activation energies are 29 and 46 kJ mol(-1) for processes 1 and 2, respectively. The results obtained are discussed to elucidate the limiting factor in this system as well as in other electrode systems.

The dynamical oxidation processes of Pt-skin layers on Pt(3)Co were investigated in situ and in real-time by time-resolved X-ray absorption spectroscopy combined with electrochemical measurements. Growth limit behaviors and the suppression of higher-order formation of surface oxides were observed, and these might explain the highly durable nature of Pt-skin layers.

Iodine K-edge XAFS of triiodide ions in various solvents were measured at SPring-8 BL01B1 and analyzed. Though the anion takes a linear and symmetric form, the second peak expected from enhanced multiple scatterings can be hardly observed because of its large vibrations. The bond distances and the Debye-Waller factors for the I-I couple vary when protic solvents were used and they were similar when aprotic solvents were used. It was indicated that the larger the Mayers' acceptor number of the solvent is, the larger the Debye-Waller factor is. It was also found that among the aprotic solvents, the larger the Gutmann's donor number is, the smaller the Debye-Waller factor is.

The influence of stress on the phase change behaviour of Ge2Sb2Te5 encapsulated by ZnS-SiO2 and TiN is investigated using temperature dependent Extended X-ray Asbsorption Fines Structure and Ellipsometry to determine the crystallisation temperature. The encapsulation material surrounding the Ge2Sb2Te5 has an increasingly dominant effect on the material's ability to change phase and can cause a profound increase in its crystallization temperature. We have experimentally shown that the increased crystallization temperature originates from compressive stress exerted from the encapsulation material. By minimizing the stress we have maintained the bulk crystallization temperature in Ge2Sb2Te5 films just 2 nm thick.

Indium K‐edge EXAFS measurements were carried out to study local structures around In atoms in InxGa1−xN multi‐quantum‐well (MQW) structures of 10 periods with In0.2Ga0.8N (2.5 nm) and In0.05Ga0.95N (7.5 nm). We found the following: (1) Debye‐Waller factors for In‐In and In‐Ga atomic pairs in MQW are smaller than those in single QW (SQW) InxGa1−xN. (2) The differences in the interatomic distances of In‐In and In‐Ga between the horizontal and vertical direction are small. These results indicate that the strain in the InxGa1−xN layer is reduced in MQW in comparison to SQW. (3) In atoms are randomly distributed in both the horizontal and vertical directions of the sample.

The polarized total-reflection X-ray absorption fine structure method was applied to characterize zinc porphyrins at the air-water interface. The X-ray absorption near edge structure exhibited a significant difference depending on the polarization of the X-ray. A shoulder peak of the Zn K-edge corresponding to the 1s-4p(z) transition for a square planar metal complex without axial coordination(s) was observed at 9662 eV, which indicates that the axial coordination sites of zinc porphyrin molecules examined are not fully hydrated at the air-water interface. The molecular orientation of zinc porphyrins was determined by analyzing the polarization dependence of the transition peak intensity. The meso-substituted porphyrin derivative 5,10,15,20-tetraphenylporphyrinatozinc(II) (ZnTPP) orients rather parallel to the solution surface. In contrast to ZnTPP, the zinc(II) protoporphyrin IX (ZnPP) with hydrophilic carboxyl groups at one side of the molecule stands up with respect to the solution surface, and the average tilting angle of the porphyrin plane to the surface was evaluated to be between 57 degrees and 43 degrees. In addition, the axial coordination of ZnPP is modified depending on the surface concentration, in which the axial hydration to the zinc center is effectively inhibited in the compressed surface layer.

Reliable speciation of tungsten (W) in natural ferromanganese oxides was realized by wavelength-dispersive XAFS using a Laue-type analyzer. The quality of W L3-XANES spectrum was greatly enhanced b...

Depth-resolved X-ray absorption spectroscopy (DR-XAS) measurements were performed for the direct observation of the chemical state and local structure at the LiCoO2 electrode–solid electrolyte model interface, which can contribute towards the enhancement of the power density in all solid-state lithium batteries. The charge transfer resistance, measured by AC impedance spectroscopy, of the LiCoO2 electrode–solid electrolyte interface decreased with the introduction of a NbO2 interlayer at the interface, while the resistance increased with ZrO2 and MoO2 interlayers. Using DR-XAS with a depth resolution of about 7 nm, the changes in electronic structure and local structure of the LiCoO2 electrode were clarified. The extended X-ray absorption fine structure of DR-XAS revealed that the introduction of the NbO2 layer is effective for restricting the large Co–O bond change at the interface during delithiation. This interlayer relieved the stress at the interface due to the volume change of LiCoO2 during delithiation and then decreased the activation energy for the charge transfer process.

Soil core samples were taken on April 13, 2011 at three sites in Fukushima prefecture: Hiwada in Koriyama-city (Site 1; N 37°28′32′′, E 140°23′17′′; two cores were obtained in Site 1), Yabuki in Nishi-Shirakawa-county (Site 2; N 37°11′59′′, E 140°20′37′′), and Iizaka in Fukushimacity (Site 3; N 37°48′50′′, E 140°26′34′′). The distances of the three sites from the Fukushima Daiichi Nuclear Power Station are 55 km (Site 1) and 65 km (Sites 2 and 3). We selected the three sites to investigate different types of soils. The soil types of the samples for Sites 1–3 were gray lowland soil, andosol, and brown forest soil, respectively. The soil at Site 1 was taken from a field, whereas the soil at Sites 2 and 3 was used to grow fruit trees. A stainless steel pipe with a diameter of 4.7 cm and length of 30 cm was inserted into the soil at each site to recover the soil core sample, which was divided into 8 fractions Vertical profiles of Iodine-131 and Cesium-137 in soils in Fukushima Prefecture related to the Fukushima Daiichi Nuclear Power Station Accident