X-ray Absorption Near-edge Spectroscopy Research Articles

XANES Studies of Zinc Tin Oxide Films Deposited by Atomic Layer Deposition: Revealing Process-Structure Relationships for Amorphous Oxide Semiconductors

Amorphous oxide semiconductors have grown in technological relevance in displays, information technology, energy, and catalysis. Recent research efforts have converged on the need to develop design principles for the electronic structure of these materials. Here, we systematically vary the cation composition and annealing temperatures of zinc tin oxide films using atomic layer deposition (ALD) and study their process-structure relationships with synchrotron X-ray absorption near-edge spectroscopy (XANES). Measurements of the O K-edge, Sn M-edge, and Zn L-edge are analyzed with ab initio and nonlinear statistical modeling to understand the changes in geometric and electronic structure of the films. A key finding from this approach is the ability to measure the changes in the relative contribution of the Zn and Sn s orbitals to the density of states near the conduction band minimum. Furthermore, we identify and delineate critical process-structure design principles when working with amorphous oxide semiconductor (AOS) material systems: (1) use of complementary diffraction and absorption spectroscopy techniques to characterize the as-deposited coordination environment; (2) accounting for gradual and abrupt changes in coordination environment as a function of processing parameters (stoichiometry, annealing, etc.); (3) revealing and exploiting the relevant knowledge and interdependence of coordination environments, orbital hybridizations, the density of states, and band structures. In the future, this multimodal X-ray analysis and modeling framework can be applied to understand the process-structure relationships needed to optimize AOS performance in devices.

Synthesis and Properties of Fe-Ni Nanoparticles

In this work, we report a simple method to prepare the Fe-Ni alloy nanoparticles by reducing NiFe2O4 spinel ferrite nanoparticles at 600 °C in a hydrogen atmosphere. Structural analyses of the Fe-Ni alloy by XRD diffraction showed that the alloy sample is a complete single phase after the deoxidizing time of 12 hours. Field effect scanning electron microscopy (FESEM) images showed microstructure with particle sizes at the nanometer scale. The valence state of the iron ion was determined from X-ray absorption near edge spectroscopy (XANES), showing that the sample had completely Feº. Magnetic curves of Fe-Ni alloy nanoparticles were studied by vibrating sample magnetometer (VSM) at temperatures from 88 K to 900 K from that the technical saturation magnetization Ms and magnetic order temperature TC were determined. The magnetoresistance effect MR of Fe-Ni alloy nanoparticles was also studied which is related to the tunneling of conduction electrons via grain boundaries. The obtained results of the work proved that this synthesis method is a facile, effective, and low-cost route that can be used to prepare Fe-Ni alloy nanoparticles.

Uptake and incorporation of Al, Cr, V, Zn and Mo in hematite: Competition, synergies and influence on structural properties

This study investigated multiple (di-, tri- and tetra-)incorporation of selected minor and trace elements (Al3+, Cr3+, V3–5+, Zn2+, Mo6+ and As5+) into hematite. The purpose was to improve understanding of how hematite may control trace element mobility in the environment, and how physical and chemical properties of hematite are impacted by multi-element incorporation at x/Fe molar ratios of up to 10%. Simultaneous structural incorporation of Al±Cr±V±Zn into hematite was achieved, with both synergistic and antagonistic effects occurring between certain element combinations. Cr+Al had synergistic effects on their co-incorporation, while V negatively affected Al incorporation, and both V and Zn negatively affected Cr incorporation. In contrast, Mo was minimally associated with hematite, and As prevented hematite formation completely. X-ray diffraction indicated contraction and expansion of the hematite unit-cell upon substitution was related to the ionic radius of the substituting element in single-element samples, while V predominantly controlled the direction of deviation in multi-element samples. X-ray absorption near-edge structure spectroscopy indicated V was present as a mixture of V3+-V5+, with a higher average V oxidation state associated with multi-element samples. Results provide new insights into trace element geochemistry within hematite, and highlight the importance of multi-element studies to better understand natural and anthropogenic systems.

Iron oxidation state in serpentines and magnesian chlorites of subduction-related rocks

Abstract. The ferric iron content in hydrothermally altered ultrabasic rocks and their major minerals, serpentines and Mg-chlorites, is important for establishing the oxidation state budget from oceanic ridges to subduction zones, in carbonaceous chondrites, and for modeling phase equilibria. A compilation of literature Mössbauer spectroscopic data on serpentines and magnesian chlorites from high-pressure ophiolites yields much lower ferric-to-total-iron ratios (Fe3+ / Fetotal) than those obtained on similar samples by X-ray absorption near-edge spectroscopy (XANES), leading to contradictory estimates of the ferric iron budget of subduction zones. New Mössbauer analysis of antigorite and Mg-chlorite samples from suites of high-pressure ophiolitic terrains of various Phanerozoic ages confirms the low and homogeneous values previously obtained by this technique, while lizardite inherited from oceanic hydrothermal alteration is ferric iron rich. We argue that XANES values may be biased by photo-oxidation when samples have a high Mg content, which is the case for serpentines and chlorites from subduction zones. Photo-oxidation is less important in Fe-poor phyllosilicates of the mica and talc families and does not affect the Fe-rich serpentines (greenalite, cronstedtite) of meteorites or Fe-rich terrestrial phyllosilicates. Mössbauer Fe3+ / Fetotal ratios of serpentine confirm the occurrence of a major redox change at the lizardite–antigorite transition near 300–400 ∘C rather than at the dehydration of antigorite at 500–650 ∘C in serpentinites from high-pressure ophiolites.

Synthesis and Structure Stabilization of Disordered Rock Salt Mn/V-Based Oxyfluorides as Cathode Materials for Li-Ion Batteries

The demand for high-performance lithium-ion batteries and thus efficient cathode materials is steadily increasing. In addition to a high energy density and long lifetime, these should also be cost-effective and environmentally benign. Manganese-based materials have particular potential because manganese is available in sufficient quantities and can be supplied at a comparatively low cost. Hence, in this study, manganese-based disordered rock salt oxyfluorides Li2Mn1–xVxO2F (0 ≤ x ≤ 0.5) are synthesized as cathode materials for lithium-ion batteries using high-energy mechanochemical ball-milling. The effect of partial vanadium substitution on the sample properties is analyzed, focusing on the electrochemical properties. Furthermore, a heat treatment process for stabilization of the samples is followed, where the morphology and structure of the samples are studied by powder X-ray diffraction and electron microscopy (SEM/TEM). The oxidation states of the transition metals in the synthesized compositions are further investigated using X-ray absorption near-edge structure spectroscopy. The data analysis reveals that the heat treatment resulted in increased symmetry and reduced defects of ball-milled compounds, but it may also affect the local fluorination degree in the structure. However, the results show that this treatment process has a beneficial effect on capacity retention of the formulated electrodes (∼81% after 100 cycles), a faster response to the change of cycling rate, and less increase in charge-transfer resistance of the samples during cycling. Such a structural improvement attributed to mitigation of the surface/bulk defects is an additional input to the series of cathode candidates of low temperature stability.

Transition-Metal Catalysts for Methane Dehydroaromatization (Mo, Re, Fe): Activity, Stability, Active Sites, and Carbon Deposits

The most studied catalysts for methane dehydroaromatization (MDA)─Mo/ZSM-5─are not commercialized yet due to the rapid deactivation and insufficient activity. Catalytic systems based on Fe and Re are potential alternatives to Mo-containing zeolites. Here, we compare the catalytic performance of these catalysts as a function of metal type and its loading in ZSM-5 zeolite. The results show that the catalytic activity decreases in the order of Re/ZSM-5 > Mo/ZSM-5 > Fe/ZSM-5, while the catalyst stability decreases in the opposite order: Fe/ZSM-5 > Mo/ZSM-5 > Re/ZSM-5. The active metal species in the working catalysts were determined by operando X-ray absorption near-edge structure spectroscopy combined with mass spectrometry. We found that Re0 and Fe2+ species are the most likely active species for the catalytic dehydroaromatization of CH4 to aromatics in respective catalysts. Combining the pulse reaction technique with operando thermogravimetry analysis–mass spectrometry experiments, we demonstrate that the length of the induction period strongly correlates to the activity of the catalyst. The longer induction period of the Fe/ZSM-5 catalyst indicates the slow growth of hydrocarbon pool intermediates inside the zeolite pores and thus explains its poor catalytic performance. Finally, both the formation of hydrocarbon pool species and the activity of Fe/ZSM-5 can be improved by increasing the Fe loading, reaction pressure, and space velocity.

Rhombohedral and Turbostratic Boron Nitride Polytypes Investigated by X-ray Absorption Spectroscopy

The electronic structure of rhombohedral sp2-hybridized boron nitride (r-BN) is characterized by X-ray absorption near-edge structure spectroscopy. Measurements are performed at the boron and nitrogen K-edges (1s) and interpreted with first-principles density functional theory calculations, including final state effects by applying a core hole. We show that it is possible to distinguish between different 2D planar polytypes such as rhombohedral, twinned rhombohedral, hexagonal, and turbostratic BN by the difference in chemical shifts. In particular, the chemical shift at the B 1s-edge is shown to be significant for the turbostratic polytype. This implies that the band gap can be tuned by a superposition of different polytypes and stacking of lattice planes.

A combination of soft X-ray and laser light sources offer 3D high content information on the native state of the cellular environment

Beamline B24 is a life sciences correlative cryo-imaging beamline at Diamond Light Source. B24 uses a combination of conventional and super-resolution visible-light fluorescence microscopy and soft X-ray tomography (cryoSXT) to provide 3D imaging of the cellular landscape at a resolution up to 25 nm in cryo-preserved biological samples up to 12 μm thick. B24 offers user-friendly, semi-automated 3D correlative cryo-imaging through an integrated platform of methods that encompass (a) sample preparation and evaluation, (b) data collection and processing and (c) data analysis and correlation. CryoSXT fills the current resolution gap between fluorescence and electron microscopy while cryo-structured illumination microscopy provides the additional dimension of chemical localization within the same cellular ultrastructure captured by cryoSXT. Beamline instruments can be accessed biannually by academics and industry globally through peer-reviewed standard and rapid access proposal processes. The B24 user base is primarily academic research groups studying cell function and cytopathology in biological systems ranging from viruses and algae to mammalian cells and proto-tissue complexes. Future work will consolidate development efforts and experiences gained thus far to enable high-throughput data collection. Special emphasis is placed on the delivery of other integrated advanced imaging methods such as X-ray absorption near-edge spectroscopy and phase contrast.

Engineering adjacent N, P and S active sites on hierarchical porous carbon nanoshells for superior oxygen reduction reaction and rechargeable Zn-air batteries

Heteroatom-doped carbon materials have been regarded as sustainable alternatives to the noble-metal catalysts for oxygen reduction reaction (ORR), while the catalytic performances still remain unsatisfactory. Herein, we develop a metal-free adjacent N, P and S-codoped hierarchical porous carbon nanoshells (NPS-HPCNs) through a novel layer-by-layer template coating method. The NPS-HPCNs is rationally fabricated by crosslinking of polyethyenemine (PEI) and phytic acid (PA) on nano-SiO2 template surface and subsequently coating of viscous sulfur-bearing petroleum pitch, followed by pyrolysis and alkaline etching. Soft X-ray absorption near-edge spectroscopy (XANES) analysis and density functional theory (DFT) calculations prove the engineering of adjacent N, P and S atoms to generate synergistic and reinforced active sites for oxygen electrocatalysis. The NPS-HPCNs manifests excellent ORR activity with a half-wave potential (E1/2) of 0.86 V, as well as promoted durability and methanol tolerance in alkaline medium. Remarkably, the NPS-HPCNs-based Zn-air battery delivers an open-circuit voltage of 1.479 V, a considerable peak power density of 206 mW cm−2 and robust cycling stability (over 200 h), even exceeding the commercial Pt/C catalyst. This study offers fundamental insights into the construction and synergistic mechanism of adjacent heteroatoms on carbon substrate, providing advanced metal-free electrocatalysts for Zn-air batteries and other energy conversion and storage devices.

Microbially influenced tungsten mobilization and formation of secondary minerals in wolframite tailings

Wolframite [(Fe,Mn)WO4] tailings represent a hazardous waste that can pose a threat to the environment, humans, animals and plants. The present study aims to conduct a high-resolution depth profile characterization of wolframite tailings from Wolfram Camp, North Queensland, Australia, to understand the biogeochemical influences on W mobilization. Several indigenous Fe- and S-oxidizing bacteria (e.g., Streptococcus pneumoniae and Thiomonas delicata) in wolframite tailings were found highly associated with W, As, and rare earth elements. Biooxidation of metal sulfides, i.e., pyrite, molybdenite and bismuthinite, produced sulfuric acid, which accelerated the weathering of wolframite, mobilizing tungstate (WO42-). Using synchrotron-based X-ray fluorescence microscopy (XFM) and W L-edge X-ray absorption near-edge spectroscopy (µ-XANES) analysis, wolframite was initially transformed into Na- and Bi- tungstate as well as tungstic acid (partial weathering) followed by the formation of Ga- and Zn- tungstate after extensive weathering, i.e., the wolframite had disappeared. While W (VI) was the major W species in wolframite tailings, minor W(0) and W(II), and trace W(IV) were also detected. The major contaminant in the Wolfram Camp tailings was As. Though wolframite tailings are hazardous waste, the toxicity of W was unclear. Tungsten waste still has industrial value; apart from using them as substitution material for cement and glass production, there is interest in reprocessing W waste for valuable metal recovery. If the environmental benefits are taken into consideration, i.e., preventing the release of toxic metals into surrounding waterways, reprocessing may be economic.

Atomic-scale characterisation of sodium aluminosilicate hydrates (N-A-S-H) and Mg-substituted N(-M)-A-S-H using XANES

The chemical structures of aluminosilicate hydrates presented in alkali-activated geopolymer materials underpin their performances. Mg-substituted sodium aluminosilicate hydrates (N(-M)-A-S-H) are likely to be present in alkali-activated geopolymer materials prepared using MgO-containing precursors, however, their atomic-level structures remain unclear. The lack of such knowledge made it challenging to identify and distinguish N(-M)-A-S-H from complex alkali-activated geopolymer systems (i.e., alkali-activated slag, alkali-activated Mg-rich minerals), and therefore brought challenges in understanding and predicting their durability. This study characterised for the first time the atomic structures of the synthetic N(-M)-A-S-H gels, prepared through ion-exchange or co-synthesis, using X-ray absorption near-edge spectroscopy (XANES) at Si, Al and Mg K-edge. The results suggest that the substitution of Mg in the extra-framework locations of the alkali aluminosilicate hydrates (N-A-S-H) leads to negligible changes in the coordination environments of the aluminosilicate framework. However, the Mg coordination environment is distinguishably different from other Mg-containing phases in the systems, e.g., hydrotalcite. The Mg K-edge XANES of N(-M)-A-S-H shows a 0.8–1.2 eV shift compared with hydrotalcite. The results presented in this study can be used as the fingerprint to probe the presence of N(-M)-A-S-H in alkali-activated geopolymer materials containing Mg element.

Operando Laboratory-Based Multi-Edge X-Ray Absorption Near-Edge Spectroscopy of Solid Catalysts.

Laboratory-based X-ray absorption spectroscopy (XAS) and especially X-ray absorption near-edge structure (XANES) offers new opportunities in catalyst characterization and presents not only an alternative, but also a complementary approach to precious beamtime at synchrotron facilities. We successfully designed a laboratory-based setup for performing operando, quasi-simultaneous XANES analysis at multiple K-edges, more specifically, operando XANES of mono-, bi-, and trimetallic CO2 hydrogenation catalysts containing Ni, Fe, and Cu. Detailed operando XANES studies of the multielement solid catalysts revealed metal-dependent differences in the reducibility and re-oxidation behavior and their influence on the catalytic performance in CO2 hydrogenation. The applicability of operando laboratory-based XANES at multiple K-edges paves the way for advanced multielement catalyst characterization complementing detailed studies at synchrotron facilities.

Comprehensive Analysis of Two H13-Type Starting Materials Used for Laser Cladding and Aerosol Particles Formed in This Process.

Laser cladding with H13 steel powders was performed and the related material transformations were studied for the particles emitted during this process. Fractions of various sizes of the aerosol particles formed during the laser cladding were collected on a cascade impactor, while the electromobility and the aerodynamic size of the particles were measured using a scanning mobility particle spectrometer and an aerodynamic particle sizer, respectively. The aerosol particles deposited onto the impactor plates were analyzed using scanning electron microscopy–energy-dispersive X-ray spectroscopy, as well as total-reflection X-ray fluorescence and X-ray absorption near-edge structure spectroscopy. Both the concentration and mean oxidation state of the major components were correlated with the aerosol particle size. The ultrafine aerosol particles (with a diameter less than about 100 nm) were predominantly oxidized and formed as the result of an evaporation–oxidation–condensation process sequence. The larger particles (>200 nm in geometric diameter) were primarily the residues of the original metal powder and exhibited a composition change as compared to the as-received metal powder. Correlations between the changes in the concentration ratio of the components were detected and explained.

Toxicity of ceria nanoparticles to the regeneration of freshwater planarian Dugesia japonica: The role of biotransformation

Cerium oxide nanoparticles (n-CeO2) have wide applications ranging from industrial to consumer products, which would inevitably lead to their release into the environment. Despite the toxicity of n-CeO2 on aquatic organisms has been largely reported, research on developing organisms is still lacking. In this study, we investigate the toxic effects of n-CeO2 on the stem cells, tissue- and neuro-regeneration, using freshwater planarian Dugesia japonica as a model. Effects of bulk sized (μ-) CeO2 and ionic Ce (Ce3+) were compared with that of n-CeO2 to explore the origin of the toxic effects of n-CeO2. No overt toxicity was observed in μ-CeO2 treatment. n-CeO2 not only impaired the homeostasis of normal planarians, but also inhibited the regeneration processes of regenerated planarians, demonstrated by the inhibited blastema growth, disturbed antioxidant defense system at molecular levels, elevated DNA-damage and decreased stem cell proliferation. Regenerating organisms are more susceptible to n-CeO2 than the normal ones. Ce3+ exhibited significantly higher toxicity than n-CeO2, even though the total Ce uptake is 0.2 % less in Ce3+ than in n-CeO2 treated in planarian. X-ray absorption near edge spectroscopy (XANES) analysis revealed that 12.8 % of n-CeO2 (5.95 mg/kg Ce per planarian) was transformed to Ce3+ after interaction with planarian, suggesting that biotransformation at the nano-bio interface might play an important role in the observed toxicity. Since the biotransformation of n-CeO2 is a slow process, it may cause long-term chronic toxicity to planarians due to the slow while sustained release of toxic Ce3+ ions.

Correlating Computation and Structural Analysis for LiFePO4 through Operando Characterization of Lithium-Ion Pouch-Cell Batteries

X-ray absorption spectroscopy (XAS) is a powerful technique for exploring the electronic and structural characteristics of battery materials. Historically, XAS measurements require synchrotron-based photon sources to achieve necessary sensitivity and energy control, but with breakthroughs in X-ray optics, laboratory-based XAS systems are now available on the commercial market. The Chemistry Division at the Naval Research Laboratory recently acquired an easyXAFS™ system, a laboratory-scale spectrometer that is capable of collecting XANES (X-ray Absorption Near-Edge Spectroscopy) and EXAFS (Extended X-ray Absorption Fine Structure) measurements in the 5–18 keV energy window. This energy range covers K-edge absorptions for the first-row transition metals that are of primary interest for electrochemical energy storage. In order to demonstrate the utility of such a laboratory-based XAS, we perform operando measurements on pouch-cell batteries containing the common lithium-ion battery cathode, LiFePO4 (LFP; lithium iron phosphate), tracking Fe oxidation state and bonding environment as a function of state-of-charge. X-ray absorption spectra collected with the easyXAFS™ compare favorably to those from prior investigations of LFP cells analyzed at synchrotron sources [1]. In parallel with XAS measurements, we perform DFT (Density Functional Theory) computation of the LFP structure. Calculations of LFP show that hole-polaron formation during charging alters the local environment around the Fe ion, decreasing the Fe–O bond length. Bond contraction increases with the addition of the Hubbard "U", which also increases the valence difference (formally 2+/3+). We further refine the computational model for the LFP system by tuning the DFT input parameter “U” to correlate with experimental XAS data.[1] C. T. Love, A. Korovina, C. J. Partridge, K. E. Swider-Lyons, M. E. Twigg, and D. E. Ramaker, J. Electrochem. Soc. 160 (2013) A3153.

Use of pristine CNTs to measure H2S in the solution containing bovine serum albumin and gamma-globulin by confocal laser scanning microscopy

It is reported that the pristine carbon nanotube (pCNT) can be used to measure H2S in water solutions and in the solution containing hemoglobin using confocal laser scanning microscopy at a special wavelength. Under the motivation of further understanding the specificity of measuring H2S in blood, in this paper, we report the measurement of H2S in the solution containing bovine serum albumin (BSA) and bovine gamma-globulin (γ-Globulin), which are two major proteins in blood, using Raman spectroscopy, sulfur K-edge X-ray absorption near-edge spectroscopy, and confocal laser scanning microscopy. The results show that although these two proteins can bind to the sidewall of the pCNTs, the binding does not affect the H2S measurement by confocal laser scanning microscopy. The results thus suggest that CNTs be readily used in H2S measurement under the presence of proteins.

Temperature Dependence of Yb Valence in an Au–Al–Yb Intermediate-Valence Quasicrystal Investigated by Yb <i>L</i><sub>3</sub>-Edge X-ray Absorption Near-Edge Structure Spectroscopy

In this paper, we investigate the temperature dependence of Yb valence in an Au–Al–Yb intermediate-valence quasicrystal by Yb L3-edge synchrotron X-ray absorption near-edge structure spectroscopy. The Yb valence of 2.61+ at room temperature decreases monotonically as the temperature decreases, indicating that the Yb ionic radius increases as the temperature decreases and is consistent with the anomalous suppression of the thermal shrinkage of this quasicrystal by cooling, as previously reported. The Yb valence changes by −0.053 on cooling from 298 to 2 K, and its change is more gradual on the high-temperature side than on the low-temperature side with the boundary around 200 K. Additionally, the effect of the changes in the Yb valence on the volume is quantitatively examined. The ratio of the volume changes due to the change in Yb valence per Yb atom, ΔVYb, to the amount of change in Yb valence, Δν, which is expressed as ΔVYb/Δν, was evaluated. The value of ΔVYb/Δν was estimated to be −2.8 Å3/unit Yb valence/Yb atom, whose value was close to that evaluated for YbInCu4.

Combining synchrotron radiation techniques for the analysis of gold coins from the Roman Empire

Four gold coins minted in the V century have been studied with non-destructive synchrotron radiation techniques, namely X-Ray Fluorescence (XRF) and X-ray Absorption Near Edge Spectroscopy (XANES). XRF data analyzed coupling standard and statistical methods were used to distinguish the composition of the alloy constituting the coins from that of successive deposits processes. Our analysis presents a quantification of the trace elements present in the metallic alloy providing interesting details for historical insight. Furthermore, on the basis of the XRF maps, some regions of interest were selected for XANES at the K-edge of Fe. Our analysis of the Fe spectra points out two main phases which can be related to Fe oxides naturally present in soil. From the relative abundance of these oxides, information on the site where the coins were found can be obtained, providing additional information on their fate across the centuries.

Oxidation behaviour of thorium-uranium mixed oxides in controlled oxidation experiments

Oxidation experiments in Ar/H2O/H2 gas mixtures were performed using a coulometric titration technique to investigate the oxidation behaviour of single-phase thorium–uranium mixed oxides under a controlled oxygen potential relevant to defective fuel operating conditions. The oxidation behaviour of the mixed-oxide (Th,U)O2 solid solutions with 8, 30, 60 and 100 wt% UO2 was investigated through oxygen-to-metal (O/M) ratio measurements combined with X-ray photoelectron spectroscopy (XPS), X-ray absorption near edge spectroscopy (XANES), extended X-ray absorption fine structure (EXAFS) analysis, and neutron diffraction analysis (NDA). The local structure around U examined by EXAFS did not show any evidence of local clustering. The U L3 EXAFS results of (Th,U)O2 show that the local structures do not appear to depend on the UO2 content. This is an indication that Th and U are randomly distributed in the mixed oxides, which is in good agreement with the long-range structural properties determined by XRD and NDA. The XPS results combined with XANES results of the U L3 edge confirmed the oxidation of U4+ for all compositions. An examination of the U L3 EXAFS spectra from the oxidized samples shows a split in the first coordination shell peak, which indicates the presence of different U–O bond-lengths in the oxidized materials. The long-range structure of the oxidized materials was characterized with NDA. Rietveld refinement revealed that the oxidized (Th,U)O2 materials with high UO2 content were biphasic. The quantitative phase analysis demonstrated the co-existence of two closely cubic structures: a stoichiometric (Th,U)O2 phase and a UO2.06 phase. These observations suggest that the oxidation of uranium in the (Th,U)O2 mixed oxides occurred in the bulk of the samples as well as at the surface as revealed by XPS analysis.

XANES characterizations of amorphous mixed metal oxides derived from Zn/Al layered double hydroxides through thermal treatment

The amorphous phase obtained by thermal treatment of Zn/Al-layered double hydroxide (Zn/Al-LDH) was characterized by X-ray absorption near-edge Spectroscopy (XANES) and Ultraviolet–Visible Diffuse Reflection (UV–vis DR). The highly crystalline Zn/Al-LDH was synthesized through homogeneous precipitation with urea as precursor, and then calcined up to 900 ​°C. X-ray Diffraction (XRD) and Thermogravimetry-Differential Thermal Analysis (TG-DTA) results showed that the crystalline Zn/Al-LDH was changed to amorphous phase through dehydroxylation by 300 ​°C. The amorphous phase decomposed to wurtzite-ZnO and spinel (Zn/Al2O4) above 600 ​°C. The amorphous phase was characterized with Zn L-edge, O K-edge and Al K-edge spectra. Those spectra determined the formation of amorphous Zinc/Aluminium mixed metal oxide (ZAO) with characteristic electron. The ZAO showed absorption of UV light which is higher energy band gap than pure zinc oxide. The analysis indicated changes in coordination due to the formation of a metal oxide phase by dehydration of the hydroxide layer of Zn/Al-LDH, and the formation of ZAO. This research is believed to be the first to apply Zn L-edge, along with O K-edge XANES spectra to analyses and clarify the thermal behavior of Zn/Al-LDH and is demonstrated to be a powerful tool for probing the structure of a variety of mixed metal oxides and catalysts based on Zn based LDH materials.