K-edge X-ray Absorption Near-edge Structure Spectra Research Articles

XANES measurements probing the local order and electronic structure of Pb1−xBaxZr0.40Ti0.60O3 ferroelectric materials

In this study, the electronic and local structures of Pb1−xBaxZr0.40Ti0.60O3 ferroelectric ceramic samples were characterized using X-ray absorption near-edge structure (XANES) measurements. The analysis of XANES spectra collected at the Ti K- and L-edges showed that the substitution of Pb by Ba leads to a decrease in the local distortion around the Ti atoms in the TiO6 octahedron. The analysis of O K-edge XANES spectra and density of states ab initio calculations showed that the hybridization between the O 2p and Pb 6sp states is related to the displacement of Ti atoms in the TiO6 octahedra. Based on these results, it is possible to determine that the degree of ferroelectricity in these samples and the manifestation of relaxor behavior are directly related to the weakening of O 2p and Pb 6sp hybridization.

Observation of high-spin mixed oxidation state of cobalt in ceramic Co3TeO6

We report coexistence of high spin Co3+ and Co2+ in ceramic Co3TeO6 using X-ray Absorption Near Edge Structure (XANES), DC magnetization, and first principles ab-initio calculations. The main absorption line of cobalt Co K-edge XANES spectra, along with a linear combination fit, led us to estimate relative concentration of Co2+ and Co3+as 60:40. The pre edge feature of XANES spectrum shows crystal field splitting of ∼1.26 eV between eg and t2g states, suggesting a mixture of high spin states of both Co2+ and Co3+. Temperature dependent high field DC magnetization measurements reveal dominant antiferromagnetic order with two Neel temperatures (TN1 ∼ 29 K and TN2 ∼ 18 K), consistent with single crystal study. A larger effective magnetic moment is observed in comparison to that reported for single crystal (which contains only Co2+), supports our inference that Co3+ exists in high spin state. Furthermore, we show that both Co2+ and Co3+ being in high spin states constitute a favorable ground state through first principles ab-initio calculations, where Rietveld refined synchrotron X-ray diffraction data are used as input.

Mechanism of Enhanced Carbon Cathode Performance by Nitrogen Doping in Lithium–Sulfur Battery: An X-ray Absorption Spectroscopic Study

Lithium–sulfur batteries have drawn much attention in advanced energy storage development due to their high theoretical specific capacity; however, several obstacles hinder their applications, including rapid capacity loss due to dissolution of polysulfide into the electrolyte. Nitrogen-doped mesoporous carbon cathode materials were found to effectively immobilize sulfur species and minimize the sulfur loss. In this work, we use X-ray absorption near-edge structure (XANES) spectroscopy to probe the coordination structures of C, O, and N in a carbon cathode before and after the sulfur loading in order to better understand the effects of nitrogen doping. A significant change in oxygen coordination structure is observed, whereas the carbon and nitrogen chemical environments remain unaltered. In addition, the significant change in S K-edge XANES spectra is also observed after sulfur was loaded on nitrogen-doped carbon cathode material. These observations reveal that strong interaction between the nitrogen-dop...

An alternative method for an interactive determination of the high-order harmonic ratio in monochromatized X-rays

An alternative method for quantifying the high-order harmonic ratio in monochromatized X-rays was developed and compared with the conventional X-ray absorption near-edge structure (XANES) method. The proposed method can calculate the harmonic ratio interactively from data obtained using two ionization chamber detectors without XANES spectra. For a comparison of the result obtained using this method to that obtained using the conventional one, Zr and Mo K-edge XANES spectra were taken by using the 3rd harmonics included in monochromatized X-rays. These spectra were measured in the transmission mode as a function of detuning in the range of 0–30%. The harmonic ratios for the measured XANES spectra were calculated using both methods. Compared to the conventional method, the results of the alternative method showed slight differences that were within experimental errors, except at edge regions. Therefore, the proposed method can give a correct harmonic ratio when using only one data point. Thus, the proposed method greatly simplifies the task of estimating high-order harmonic ratios.

X-ray spectroscopic identification of garnet from the placer deposits of the Taman peninsula

Garnet from recent placer deposits of the Taman peninsula has been investigated by energy-dispersive X-ray fluorescence microanalysis and X-ray absorption near-edge structure (XANES) spectroscopy. Energy-dispersive X-ray fluorescence microanalysis showed that the chemical composition of the garnet under study corresponds to pyrope-almandine-spessartine series. The Fe K-edge X-ray absorption spectra of garnet have been recorded using a Rigaku R-XAS laboratory spectrometer. Iron K-edge XANES spectra for two iron-containing garnet minals (components), almandine and andradite, have been calculated using the full multiple-scattering and finite-difference methods. Based on a comparison of the experimental and theoretical Fe K-XANES spectra, it is concluded that recent magnetite-garnet placer deposits of the Taman peninsula contain garnet in the form of almandine.

Speciation of Phosphorus and Cadmium in a Contaminated Soil Amended with Bone Char: Sequential Fractionations and XANES Spectroscopy

The phosphorus (P) and cadmium (Cd) speciation was analyzed in a contaminated soil having a Cd concentration of 1,028 mg kg−1 in order to assess the value of bone char (BC) as a Cd immobilizing agent. The soil was incubated with BC and triple superphosphate (TSP, as control) in the dark at 60 to 70 % water holding capacity for time periods between 1 and 145 days. Samples from the various incubation periods were sequentially extracted and investigated by X-ray absorption near edge structure (XANES) spectroscopy. The sequential P extraction revealed that BC increased the H2SO4 extractable P fraction, mainly consisting of Ca- and Mg-phosphates, by 14 %, whereas TSP increased the water extractable P fraction by 7 % of total P at day 1. Subsequently, the proportions of these two P fractions decreased during incubation. The increase in these two P fractions is explained by the solubility of the main components of BC (hydroxylapatite (HAP)) and TSP (Ca(H2PO4)2). Furthermore, this finding was confirmed for BC by the P K-edge XANES spectra using partial least square regression that provided independent evidence for increased proportion of HAP after BC application. As a result of BC dissolution, the soil pH increased resulting in Cd immobilization as indicated by significantly reduced concentrations of mobile Cd in the sequential extraction up to 23 mg Cd kg−1. This observed immobilization was explained by the Cd L 3 -edge XANES spectra revealing an immediate increase in the proportion of insoluble Cd3(PO4)2. By contrast, none of the speciation methods indicated a Cd immobilizing capability of TSP. Thus, by using this multi-methodological approach, we could show that besides its potential as renewable and clean P fertilizer, BC is a superior immobilization agent for Cd compared to TSP.

Time-resolved XAS (Bonn-SUT-SLRI) beamline at SLRI

An energy-dispersive X-ray absorption spectroscopy beamline has been constructed at the Synchrotron Light Research Institute, Thailand. The beamline was designed to utilize the synchrotron radiation with photon energies between 2400 and 8000 eV. The horizontal focusing of the bent crystal in the energy-dispersive monochromator offers a small polychromatic focal spot of 1 mm at the sample position. By employing an energy-dispersive scheme, the whole X-ray absorption near-edge structure (XANES) can be obtained simultaneously using a position-sensitive detector with a fastest readout speed of 25 ms. The short data collection time opens a new opportunity for time-resolved X-ray absorption spectroscopy (XAS) experiments such as studies of changes of the electronic structures or the local coordination environments of an atom during a change in thermodynamic conditions. For this purpose, an in situ cell was designed and fabricated for the beamline. Thermal oxidation of TiO(2) was chosen as an in situ experiment example. The structural change of TiO(2) as a function of temperatures was monitored from the change in the measured XAS spectra. The obtained Ti K-edge XANES spectra clearly show the formation of an anatase phase when the temperature was raised to 673 K.

Electronic structure of chromium-containing amorphous hydrogenated carbon thin films studied by X-ray absorption spectroscopy

C K-, Cr L3.2-, and K-edge X-ray absorption near-edge structure (XANES) analysis, high-resolution transmission electron microscopy examination, and optical absorptance have been examined to obtain a correlation between the optical absorptance and electronic structure of chromium-containing amorphous hydrogenated carbon thin films (a-C:H/Cr) deposited using a dc magnetron sputter deposition technique. It was found that the C 2pCr 3d hybridization gradually increases as the Cr nanoparticle (NP) size decreases, accompanied by a C 2p interband transition. The amount of CH bonding and the change in crystalline structure are the main factors affecting the optical absorptance of the thin films. The size of the Cr NP affects the absorption wavelength range of the films. The optical absorptance and C K-edge XANES spectra indicate that a decrease in the size of Cr NP raises the conduction-band-minimum and may also increase the bandgap.

An X-ray absorption spectroscopic study on mixed conductive La0.6Sr0.4Co0.8Fe0.2O3−δ cathodes. I. Electrical conductivity and electronic structure

The electrical conduction mechanism of mixed conductive perovskite oxides, La(0.6)Sr(0.4)Co(0.8)Fe(0.2)O(3-δ), for cathode materials of solid oxide fuel cells has been investigated from electronic structural changes during oxygen vacancy formation. La(0.6)Sr(0.4)Co(0.8)Fe(0.2)O(3-δ) was annealed under various oxygen partial pressures p(O(2))s at 1073 K and quenched. Iodometric titration indicated that the oxygen nonstoichiometry of La(0.6)Sr(0.4)Co(0.8)Fe(0.2)O(3-δ) depended on the annealing p(O(2)), with more oxygen vacancies introduced at lower than at higher p(O(2))s. X-Ray absorption spectroscopic measurements were performed at the O K-, Co L-, Fe L-, Co K-, and Fe K-edges. The valence states of the Co and Fe ions were investigated by the X-ray absorption near edge structure (XANES) at the Co and Fe L(III)-edges. While the Fe average valence was almost constant, the valence of the Co ions decreased with oxygen vacancy introduction. The O K-edge XANES spectra indicated that electrons were injected into the Co 3d/O 2p hybridization state with oxygen vacancy introduction. Both absorption edges at the Co and Fe K-edge XANES shifted towards lower energies with oxygen vacancy introduction. The shift at the Co K-edge resulted from the decrease in the Co average valence and that at the Fe K-edge appeared to be caused by changes in the coordination environment around the Fe ions. The total conductivity of La(0.6)Sr(0.4)Co(0.8)Fe(0.2)O(3-δ) decreased with decreasing p(O(2)), due to a decreasing hole concentration.

Phosphorus Speciation in Sequentially Extracted Agro‐Industrial By‐Products: Evidence from X‐ray Absorption Near Edge Structure Spectroscopy

The phosphorus (P) in agro-industrial by-products--a potential source of freshwater eutrophication but also a valuable fertilizer--needs to be speciated to evaluate its fate in the environment. We investigated to what extent X-ray absorption near edge structure (XANES) spectroscopy at the P K- and L2.3-edges reflected differences in sequentially extracted filter cakes from sugarcane (Saccharum officinarum L.) (FIC) and niger seed (Guizotia abyssinica Cass.; NIC) processing industry in Ethiopia. The P fractionation removed more labile (54%) and H2SO4-P (28%) from FIC than from NIC (18% labile, 12% H2SO4-P). For the FIC residues after each extraction step, linear combination (LC) fitting of P K-edge spectra provided evidence for the enrichment of Ca-P after the NaOH-extraction and its almost complete removal after the H2SO4-treatment. The LC-fitting was unsuccessful for the NIC samples, likely because of the predominance of organic P compounds. The different proportions of Ca-P compounds between FIC (large) and NIC (small) were more distinctive in L2-than in the K-edge XANES spectra. In conclusion, the added value of complementary P K- and L2.3-edge XANES was clearly demonstrated, and the P fractionation and speciation results together justify using FIC and NIC as soil amendments in the tropics.

XANES Investigation of Pristine and Fluorinated Single-Walled Carbon Nanotubes Before and After Annealing

X-ray absorption near-edge structure (XANES) spectroscopy has been used for comparative investigation of the electronic structure of pristine and fluorinated single-walled carbon nanotubes (SWCNTs) before and after annealing. The SWCNTs were produced by catalytic chemical vapor deposition method and fluorinated using a gaseous mixture of BrF3 and Br2 at room temperature. The samples were annealed at 250°C for 0.5 hour directly in the vacuum chamber of the X-ray spectrometer. C K-edge XANES spectra showed increase in the π* resonance intensity after the treatment of as-produced and fluorinated SWCNTs that was attributed to the detachment of adsorbed molecules and defunctionalization of nanotubes with the heating. Furthermore, analysis of the spectra revealed the annealing of the SWCNT samples produces topological defects in the nanotube walls.

The determination of zinc, copper and iron oxidation state in invasive ductal carcinoma of breast tissue and normal surrounding tissue using XANES

X-ray absorption near-edge structure (XANES) spectroscopy was used to examine the oxidation state of Zn, Fe and Cu in 22 normal and 23 tumour regions spread over 30 formalin-fixed, paraffin-embedded tissue samples of human primary invasive breast cancer. A micro-mapping analysis of the metal distribution in the tissue was performed prior to the XANES analysis to identify and localise the metals in the tumour and normal tissue regions. The aim of this study was to identify the oxidation state of Zn, Fe and Cu in normal and tumour tissues of the breast, in order to correlate the oxidation state of these elements with the carcinogenesis process. The position of the Zn K-edge in normal and tumour tissues suggests that Zn exists in a bounded form. The shape of the Cu K-edge XANES spectra and the first derivative spectra of normal and tumour tissues shows that a significant portion of the total copper is present as Cu (I). Nevertheless, the position of the edges in the normal and tumour tissue spectra does not exclude the presence of Cu (II). The shape and position of both normal and tumour regions of the tissue suggest that they contain mixtures of Fe (II) and Fe (III) ions with a significant fraction being Fe (III). However, normal tissue regions were found to have a higher fraction of Fe (II) compared to the tumour tissues. In order to estimate the best target for therapy, more information is required about the relative abundance of Zn, Fe and Cu binding proteins, their oxidation state and their localisation at the subcellular level. Copyright © 2010 John Wiley & Sons, Ltd.

Analysis of the Ni K-edge X-ray absorption near edge structure in Ni((C2H5O)2PS2)2

The Ni((C2H5O)2PS2)2 complex has been investigated using the X-ray absorption near edge structure (XANES) analysis. Nickel K-edge XANES spectra of the complex have been measured and theoretical calculations of the spectra have been carried out using the finite difference method; the calculation of molecular potential has been carried out both in the full potential and in the muffin-tin approximation. The analysis of results obtained has shown that a good agreement between theoretical and experimental spectra in the low-energy region is achieved only in the case of full potential calculations (beyond the muffin-tin approximation for the potential shape).

Determination of the host phase of rare earth elements in natural carbonate using X-ray absorption near-edge structure

The Y K-edge X-ray absorption near-edge structure (XANES) spectra of various materials were measured to investigate whether rare earth elements (REEs) are incorporated in carbonate phase or in other minor phases such as Fe-Mn oxides and phosphate within limestone. As reported in our previous work, a white line peak specific to synthetic Y-doped calcite is observed in the Y K-edge XANES spectrum. Natural limestone and dolomite samples show XANES spectra similar to that of the Y-doped calcite. The similarity of XANES spectra between natural and synthetic carbonates strongly indicates that Y is incorporated into the carbonate phase of natural samples, and that local coordination structures of Y in natural and synthetic carbonates are the same. Previous work reported a difference of local coordination structure between light and heavy REEs. Furthermore, we reported that local coordination structures of Y and Ho are similar. The results of this study therefore demonstrate that the Y K-edge XANES spectrum can be used as a fingerprint to trace heavy REEs including Y in natural carbonate. The information that REEs are not distributed to other minor phases is an important basis for the use of limestone to estimate REE pattern of ancient seawater coupled with the REE partition coefficient data between seawater and carbonate.

X-ray Absorption at the Pr L1-edge in PrNiO3

X-ray absorption near edge structure (XANES) measurements at the Pr L1-edge of PrNiO3 exhibit a change across the metal insulator transition. This structural change is consistent with the observation of a lattice distortion, inferred from the Ni K-edge XANES spectra. Theoretical calculations of the XANES show that the observed features of the spectra are consistent with the orthorhombic structure in the metallic phase and a monoclinic structure in the insulating phase. The presence of such distortion provides a unified view of the structural change concurrent with the metal-insulator transition in the whole family RNiO3 (R being a rare earth atom).

Quantitative XANES Spectroscopy Study on the Prototype Hole- and Electron-Doped High-Tc Superconductor Systems, (La,Sr)2CuO4 and (Nd,Ce)2CuO4

Here we demonstrate that the Cu L-edge XANES (X-ray absorption near-edge structure) spectroscopy can be employed for quantitative analysis of the level of carrier-doping in the prototype hole- and electron-doped high-T c superconductor systems, (La 1-x sr x ) 2 CuO 4+δ and (Nd 1-x Ce x ) 2 CuO 4+δ . The progress in hole-doping in the (La 1-x Sr x ) 2 CuO 4+δ system is seen as development of the shoulder peak (due to nominally trivalent copper) on the high-energy side of the main peak (due to nominally divalent copper) in the Cu L 3 -edge region, whereas the progress in electron-doping in the (Nd 1-x Ce x ) 2 CuO 4+δ system results in an additional absorption peak at about 934 eV (due to nominally monovalent copper), together with a decrease in the intensity of the main peak (due to nominally divalent copper). On the basis of these features, Cu-valence values are quantitatively obtained in excellent agreement with those calculated for the same samples from the precise oxygen contents, 4+δ, determined by means of wet-chemical analysis. The valence of Ce in (Nd 1-x Ce x ) 2 CuO 4+δ is revealed to be somewhat lower than +4 (ca. +3.8) on the basis of Ce M 5 -edge XANES data. In the O K-edge XANES spectra, the increase in the CuO 2 -plane hole concentration with increasing x in (La 1-x Sr x ) 2 CuO 4+δ is seen as an enhancement in the intensity of the pre-edge feature at ∼528.9 eV, whereas for (Nd 1-x Ce x ) 2 CuO 4+δ , no signs are observed that could be directly assigned to the change in electron-doping level.

Synthesis of Ti-containing MCM-48 by using TiF 4 as titanium source

TiF 4 and Ti(OEt) 4 were used as titanium source to prepare Ti-containing MCM-48 by hydrothermal method, respectively. The products were characterized by X-ray diffraction (XRD), N 2 adsorption–desorption, UV–visible absorption spectra and X-ray absorption near edge structure (XANES). The analysis results indicated that the types of titanium sources have great effects on the formation of Ti-MCM-48. Using TiF 4 as precursor, Ti-containing silica with cubic mesoporous structure can be synthesized simply and quickly. The UV–visible absorption spectra and Ti K-edge XANES spectra confirmed that the isolated tetrahedrally-coordinated titanium oxide moieties were highly dispersed in the framework of MCM-48 by using TiF 4 as titanium source.

A comparative study of the electronic structures of oxygen- and chlorine-treated nitrogenated carbon nanotubes by x-ray absorption and scanning photoelectron microscopy

The electronic structures and bonding properties of oxygen- and chlorine-treated nitrogenated carbon nanotubes (N-CNTs) were studied using x-ray absorption near-edge structure (XANES) and scanning photoelectron microscopy. Features in the C K-edge XANES spectra are shifted by ∼0.3eV toward higher energies and by ∼1.1eV toward lower energies relatively to those of the more symmetrical pyridinelike and graphitelike structured N-CNTs upon chlorination and oxidation, respectively. Increases in N K-edge XANES intensities for both chlorination and oxidation reveal substitution of C–C bonds by C–N bonds consistent with the observed valence-band photoemission spectra of the decrease of the C 2s bond and the increase of the N 2s bond.

Determination of Phosphorus Speciation in Dairy Manure using XRD and XANES Spectroscopy

Intensive manure application is an important source of diffuse phosphorus (P) pollution. Phosphorus availability from animal manure is influenced by its chemical speciation. The major objective of this study was to investigate the P speciation in raw and anaerobically digested dairy manure with an emphasis on the calcium (Ca) and magnesium (Mg) phosphate phases. Influent and effluent from an on-farm digester in Wisconsin were sampled and sieved, and the 25 to 53 microm size fraction was dried for X-ray powder diffraction (XRD) and P K-edge X-ray absorption near edge structure (XANES) analyses. Struvite (MgNH4PO4.6H2O) was identified in both the raw (influent) and anaerobically digested (effluent) manure using XRD. Qualitative analysis of P K-edge XANES spectra indicated that the Ca orthophosphate phases, except dicalcium phosphate anhydrous (DCPA) or monetite (CaHPO4), were not abundant in dairy manure. Linear combination fitting (LCF) of the P standard compounds showed that 57.0 and 43.0% of P was associated with DCPA and struvite, respectively, in the raw manure. In the anaerobically digested sample, 78.2% of P was present as struvite and 21.8% of P was associated with hydroxylapatite (HAp). The P speciation shifted toward Mg orthophosphates and least soluble Ca orthophosphates following anaerobic digestion. Similarity between the aqueous orthophosphate (aq-PO4), newberyite (MgHPO4.3H2O), and struvite spectra can cause inaccurate P speciation determination when dairy manure is analyzed solely using P K-edge XANES spectroscopy; however, XANES can be used in conjunction with XRD to quantify the distribution of inorganic P species in animal manure.

Investigation of inorganic compounds on the surface of cathode materials using Li and O K-edge XANES

Inorganic compounds on the surfaces of the cathode materials LiNi 0.80Co 0.15Al 0.05O 2 and LiCoO 2 were studied using Li and O K-edge X-ray absorption near edge structure (XANES) measurements. Rietveld analysis revealed that the LiNi 0.80Co 0.15Al 0.05O 2 sample contained 2% Li 2CO 3, while the LiCoO 2 sample was single-phase. The Li and O K-edge XANES spectra indicated that the surface of LiCoO 2 was almost free of residual Li 2CO 3. In contrast, the presence of both residual Li 2CO 3 and an additional cubic phase were observed, respectively, on and near the surface of LiNi 0.80Co 0.15Al 0.05O 2. These results demonstrate that the XANES technique, using a combination of the total electron yield and fluorescence methods, is an effective tool for probing the surfaces of cathode materials.