K-edge Features Research Articles

The effects of pH, neutralizing reagent and co-ions on Mo(VI) removal and speciation in Fe(III)–Mo(VI) coprecipitation process

Coprecipitation of molybdate (Mo(VI)) with ferric iron (Fe(III)) is usually employed for the treatment of Mo-bearing acid mine drainage (AMD) and mineral-processing effluents. However, the speciation of Mo(VI) in the Fe(III)–Mo(VI) coprecipitates and the roles of process parameters in Mo(VI) removal remain unclear. In this work, the effects of pH, neutralization reagents (CaO vs NaOH) and co-ions (Zn2+, Cu2+ and Ni2+) on the removal and speciation of Mo(VI) were investigated. It was found that Mo(VI) removal was significantly enhanced at circum-neutral pH by using CaO as base instead of NaOH or in the presence of Ni2+ ions. X-ray diffraction, Fourier transform infrared, Raman and linear combination fitting of Mo K-edge X-ray absorption near edge structure (XANES) spectra results indicated that amorphous ferric molybdate was the major Mo(VI) phase in the coprecipitates formed at acidic pH regardless of the base used. While at circum-neutral pH, Mo(VI) mainly existed as surface adsorbed form on ferrihydrite in NaOH neutralized coprecipitates, and as calcium molybdate in CaO neutralized coprecipitates. The pre-edge features of Mo K-edge and L3-edge XANES features indicated the formation of polymeric molybdate in the acidic coprecipitates. This work may have implications to Mo(VI) immobilization via coprecipitation with Fe(III) and the fate of Mo(VI) in tailings.

Short Iterative Lanczos Integration in Time-Dependent Equation-of-Motion Coupled-Cluster Theory.

A time-dependent (TD) formulation of equation-of-motion coupled-cluster (EOM-CC) theory can provide excited-state information over an arbitrarily wide energy window with a reduced memory footprint relative to conventional, frequency-domain EOM-CC theory. However, the floating-point costs of the time-integration required by TD-EOM-CC are generally far larger than those of the frequency-domain form of the approach. This work considers the potential of the short iterative Lanczos (SIL) integration scheme [J. Chem. Phys. 1986, 85, 5870-5876] to reduce the floating-point costs of TD-EOM-CC simulations. Low-energy and K-edge absorption features for small molecules are evaluated using TD-EOM-CC with single and double excitations, with the time-integrations carried out via SIL and fourth-order Runge-Kutta (RK4) schemes. Spectra derived from SIL- and RK4-driven simulations are nearly indistinguishable, and with an appropriately chosen subspace dimension, the SIL requires far fewer floating-point operations than are required by RK4. For K-edge spectra, SIL is the more efficient scheme by an average factor of 7.2.

Short-range chemical order and local lattice distortion in a compositionally complex alloy

This work presents an X-ray absorption spectroscopy study on a single-phase state of the Al8Cr17Co17Cu8Fe17Ni33 compositionally complex alloy, focused on the local crystal structure around each alloying element. The comparison of 1st shell bond lengths, obtained by the analysis of extended X-ray absorption fine structure (EXAFS) measured at the K-edges of each alloying element, indicates that Al8Cr17Co17Cu8Fe17Ni33 crystallizes in a distorted arrangement of an fcc lattice. A modest bond length dependence of the alloying elements with increasing atomic number is observed, with minima and maxima at Cr/Co, and Al/Cu, respectively. 1st shell bond lengths spread over ~0.03 Å; consequently, such variations cannot result in lattice distortions greater than ~0.04 Å. EXAFS results clearly indicate short-range order in the alloy: pairing of Al with Ni and Cu is favored, correlating well with a γ’ precipitate composition (Al-Ni-Cu rich) reported in previous work, while Al-Cr bonding is unfavored and no Al-Al pairs are observed. Electronic structure information was obtained through comparison between near-edge regions of alloying elements and corresponding pure metals. Intensity comparison of K-edge features agree with a charge variation of p states in Al8Cr17Co17Cu8Fe17Ni33, where Ni and Cu act as p states electron acceptors, suggesting an orbital hybridization with Al, responsible for a shrinkage in Al metallic radius in the alloy by ∼0.17 Å.

Comparative Experimental and Theoretical Study of the C and O K-Edge X-ray Absorption Spectroscopy in Three Highly Popular, Low Spin Organoiron Complexes: [Fe(CO)5], [(η5-C5H5)Fe(CO)(μ-CO)]2, and [(η5-C5H5)2Fe

The unoccupied electronic structures of three closed-shell, highly popular organoiron complexes ([Fe(CO)5], [(η5-C5H5)Fe(CO)(μ-CO)]2, and [(η5-C5H5)2Fe]; 0, I, and II, respectively) have been investigated both experimentally and theoretically by combining original gas-phase X-ray absorption spectroscopy (XAS) outcomes recorded at the C and O K-edge with results of scalar relativistic time-dependent density functional calculations carried out within the zeroth order regular approximation. Experimental evidence herein discussed complement the Fe L2,3-edges XAS ones we recently recorded, modeled, and assigned for the same complexes (Carlotto et al. Inorg. Chem. 2019, 58, 5844). The first-principle simulation of the C and O K-edge features allowed us to univocally identify the electronic states associated to the ligand-to-metal charge transfer (LMCT) transitions both in I and in II. At variance to that, LMCT transitions with sizable oscillator strengths do not play any role in determining neither the C nor the O K-edge spectral pattern of 0. The higher π-acceptor capability of the CO ligand, regardless of its terminal or bridging coordination, with respect to [(η5-C5H5)]- is herein ultimately confirmed.

In-situ growth of iron mononitride thin films studied using x-ray absorption spectroscopy and nuclear resonant scattering

We studied the structural and magnetic properties of in-situ grown iron mononitride (FeN) thin films. Initial stages of film growth were trapped utilizing synchrotron based soft x-ray absorption near edge spectroscopy (XANES) at the N K-edge and nuclear resonant scattering (NRS). Films were grown using dc-magnetron sputtering, separately at the experimental stations of SXAS beamline (BL01, Indus 2) and NRS beamline (P01, Petra III). It was found that the initial stages of film growth differs from the bulk of it. Ultrathin FeN films, exhibited larger energy separation between the t2g and eg features and an intense eg feature in the N K-edge pattern. This indicates that a structural transition is taking place from the rock-salt (RS)-type FeN to zinc-blende (ZB)-type FeN when the thickness of films increases beyond 5nm. The behavior of such N K-edge features correlates very well with the emergence of a magnetic component appearing in the NRS pattern at 100K in ultrathin FeN films. Combining the in-situ XANES and NRS measurements, it appears that initial FeN layers grow in a RS-type structure having a magnetic ground state. Subsequently, the structure changes to ZB-type which is known to be non-magnetic. Observed results help in resolving the long standing debate about the structure and the magnetic ground state of FeN.

Study of magneto capacitance effect, exchange bias, XMCD and XAS in La0.8Bi0.2Fe0.7Mn0.3O3/LaNiO3/LaAlO3 multiferroic thin film

Magneto capacitance (MC) property of La0.8Bi0.2Fe0.7Mn0.3O3/LaNiO3/LaAlO3 thin film has been studied at an applied magnetic field of 0 T and 5 T. Variation of capacitance versus frequency at different temperatures (80 K, 100 K,180 K and 200 K) with the application of magnetic field depicts the unification of ferroic (ferroelectric and ferromagnetic) properties. This is a significant aspect for a system to be multiferroic, a choice for better device application. Exchange bias effect is observed on meticulous study of hysteresis loop taken at 5 K and 10 K upto ~1 Tesla (while cooling thin film in 5 kOe of applied magnetic field) in the form of systematic shift in loops on positive side of applied magnetic field. Hysteresis loop shifts accordingly on negative side on changing the polarity of field (−5 kOe) in field cooled mode, confirming the intrinsic nature of exchange bias effect in thin film. The NEXAFS technique has been used in finding the electronic structure, charge state and local symmetry of ions present in thin film; therefore the mechanism(s) responsible for its major properties. Magnetic character of thin film is studied using x-ray magnetic circular dichroism (XMCD) measurements. NEXAFS data of Mn L3,2- edge spectra indicates the presence of Mn2+ /Mn3+ valence states with contribution from Mn4+ ions in the system, which corroborates the ferrimagnetic nature revealed by thin film. L3,2- edge of Fe along with reference compound (Fe2O3) reveals that these ions are present in trivalent state (Fe3+) in octahedral symmetry. O K-edge features compliment the magneto-electric (ME) properties of the thin film. Charge transfer multiplet calculations confirm that Mn ions exist in different charge states (Mn2+,3,+4+) whereas Fe ions exhibit single (Fe3+) valent state in thin film.

Short-Range Chemical Order and Local Lattice Distortion in a Compositionally Complex Al <sub>8</sub>Cr <sub>17</sub>Co <sub>17</sub>Cu <sub>8</sub>Fe <sub>17</sub>Ni <sub>33</sub> Alloy

This work presents an X-ray absorption spectroscopy study on a single-phase state of the Al8Cr17Co17Cu8Fe17Ni33 compositionally complex alloy, focused on the local crystal structure around each alloying element. The comparison of 1st shell bond lengths, obtained by the analysis of extended X-ray absorption fine structure (EXAFS) measured at the K-edges of each alloying element, indicates that Al8Cr17Co17Cu8Fe17Ni33 crystallizes in a slightly distorted arrangement of an fcc lattice. A modest V-shaped bond length dependence of the alloying elements with increasing atomic number is observed, with minima and maxima at Cr/Co, and Al/Cu, respectively. 1st shell bond lengths spread over ~0.03 A, potentially giving rise to lattice distortions of ~0.04 A. EXAFS results clearly indicate short-range order in the alloy: pairing of Al with Ni and Cu is favored, correlating well with a γ' precipitate composition (Al-Ni-Cu rich) reported in previous work, while Al-Cr bonding is unfavored and no Al-Al pairs are observed. Electronic structure information was obtained through comparison between near-edge regions of alloying elements and corresponding pure metals. Energy shifts and intensity comparison of K-edge features agree with a slight charge variation of p states in Al8Cr17Co17Cu8Fe17Ni33, where Ni and Cu act as p states electron acceptors in the alloy.

Defect States below the Conduction Band Edge of HfO2 Grown on InP by Atomic Layer Deposition

The electronic structure and nature of the defect states below the conduction band edge of an HfO2 gate dielectric grown on InP substrate prepared by atomic layer deposition was examined using X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), and density functional theory (DFT). When the HfO2 dielectric was deposited on an InP substrate with an abrupt interface, the resulting HfO2 develops a tetragonal (t) structure, which minimizes the interfacial lattice mismatch. The O K-edge absorption features and DFT calculations indicated that additional structural distortion occurred by a q = −2 charged O vacancy (VO–2) in the t-HfO2. The electronic structure and the charge-transition levels of t-HfO2 with VO–2 were assigned based on a second derivative analysis of O K-edge features; 12 distinct pre-edge defect states below the Hf 5d conduction band edge were evident when the degeneracies resulting from Jahn–Teller splitting and crystal field splitting were removed. No changes in the ele...

Characterization of Co distribution in ZnO by x-ray magnetic circular dichroism

We analyze the electronic and magnetic properties of the various atomic arrangements of Zn1−xCoxO with x = 10% using K-edge x-ray absorption and magnetic circular dichroism spectra from both measurements and first principle calculations. Significantly, the K-edge spectroscopic features of Co are highly sensitive to the local atomic arrangement, and thus can be used as a powerful tool to investigate structural properties of dilute magnetic semiconductors. We clearly showed that defects such as interstitial Co and O vacancy near to substitutional Co are present in the 10% Co doped ZnO sample. The magnetic ordering of ZnO-based diluted magnetic semiconductors is strongly correlated with the presence of oxygen vacancies. Finally, we elucidated the origin of the X-ray magnetic circular dichroism signals.

Heterogeneous formation of ferric oxide nanoparticles on chlorite surfaces studied by x-ray absorption spectromicroscopy (STXM)

The homogeneous and heterogeneous formation of ferric iron oxides from acidic solution (pH 2.06–2.50) has been studied in the presence of chlorite under constant pH conditions using titration experiments. Significantly shorter induction times for the ferrihydrite formation have been macroscopically observed in the presence of chlorite particles, thus indicating heterogeneous nucleation as a major precipitation mechanism. A combination of Scanning Electron Microscopy (SEM) and Scanning Transmission X-Ray microscopy (STXM) on the O K-edge and Fe L-edge was used to clearly distinguish ferric iron precipitates from chlorite and to obtain the spatial distribution of iron precipitates on the chlorite surface under conditions of homogenous and heterogeneous formation.Oxygen K-edge results show the precipitation of a highly hydrolyzed chlorite surface associated ferric iron phase under heterogeneous conditions. Precipitates with different oxygen K-edge features are observed on the chlorite basal faces compared to the edge surfaces which can be attributed to cluster size effects and differences in the O/OH ratio. The results obtained from iron L-edge XANES corroborate the observations of the oxygen K-edge, indicating a thin surface layer of ferric iron precipitates and preferential precipitation at the chlorite edge surfaces. Under conditions where homogeneous ferrihydrite formation dominates, beside surface coatings separate iron colloids/nanoparticles are observed. Iron L-edge analysis and the pre-edge splitting on the oxygen K-edge indicate a higher long-range order/lower hydration comparable to ferrihydrite reference spectra. The results show that the Fe(III) secondary phase formation as surface coating or nanoparticles and their spatial distribution depends on the degree of supersaturation. These observations may have direct consequences for the retention and mobility of various contaminants in aquifer systems and potential remediation strategies.

ChromAIX: Fast photon-counting ASIC for Spectral Computed Tomography

X-ray attenuation properties of matter (i.e. human body in medical Computed Tomography) are energy and material dependent. This dependency is largely neglected in conventional CT techniques, which require the introduction of correction algorithms in order to prevent image artefacts. The exploitation of the inherent energy information contained in the X-ray spectrum allows distinguishing the two main physical causes of energy-dependent attenuation (photo-electric effect and Compton effect). Currently a number of methods exist that allow assessing the energy-dependent attenuation in conventional systems. These methods consist of using two distinct spectra (kVp switching or dual source) or of discriminating low and high energy photons by means of stacking two detectors. Further improvements can be achieved by transitioning to direct-conversion technologies and counting-mode detection, which inherently exhibits a better signal-to-noise ratio. Further including energy discrimination enables new applications, which are not feasible with dual-energy techniques, e.g. the possibility to discriminate K-edge features (contrast agents, e.g. gadolinium) from other contributions to the X-ray attenuation of a human body. The capability of providing energy-resolved information with two or more independent measurements is referred to as Spectral CT. A new proprietary photon-counting ASIC (ChromAIX) has been developed to provide high count-rate capabilities while offering energy discrimination. ChromAIX consists of a pixel array with an isotropic pitch of 300 μm. Each pixel contains independent discriminators that enable the possibility to discretize the incoming photons into a number of energy levels. Extensive electrical characterization has been carried out to assess the performance in terms of count-rate performance and noise. Observed rates exceed 10 Mcps/pixel (Poissonian, mean incoming rates >27 Mcps). The energy resolution is better than 4.1 keV FWHM and has been shown to be consistent with the simulations. First measurement with X-rays have also been carried out on samples directly flip-chip bonded to CdTe and CZT crystals. The pulse shape and spectrum obtained from a 241Am source is consistent with the simulations.

Molecular Basis of the Bohr Effect in Arthropod Hemocyanin

Flash photolysis and K-edge x-ray absorption spectroscopy (XAS) were used to investigate the functional and structural effects of pH on the oxygen affinity of three homologous arthropod hemocyanins (Hcs). Flash photolysis measurements showed that the well-characterized pH dependence of oxygen affinity (Bohr effect) is attributable to changes in the oxygen binding rate constant, k(on), rather than changes in k(off). In parallel, coordination geometry of copper in Hc was evaluated as a function of pH by XAS. It was found that the geometry of copper in the oxygenated protein is unchanged at all pH values investigated, while significant changes were observed for the deoxygenated protein as a function of pH. The interpretation of these changes was based on previously described correlations between spectral lineshape and coordination geometry obtained for model compounds of known structure (Blackburn, N. J., Strange, R. W., Reedijk, J., Volbeda, A., Farooq, A., Karlin, K. D., and Zubieta, J. (1989) Inorg. Chem., 28, 1349-1357). A pH-dependent change in the geometry of cuprous copper in the active site of deoxyHc, from pseudotetrahedral toward trigonal was assigned from the observed intensity dependence of the 1s --> 4p(z) transition in x-ray absorption near edge structure (XANES) spectra. The structural alteration correlated well with increase in oxygen affinity at alkaline pH determined in flash photolysis experiments. These results suggest that the oxygen binding rate in deoxyHc depends on the coordination geometry of Cu(I) and suggest a structural origin for the Bohr effect in arthropod Hcs.

X-ray Raman scattering study of MgSiO3 glass at high pressure: implication for triclustered MgSiO3 melt in Earth's mantle.

Silicate melts at the top of the transition zone and the core-mantle boundary have significant influences on the dynamics and properties of Earth's interior. MgSiO3-rich silicate melts were among the primary components of the magma ocean and thus played essential roles in the chemical differentiation of the early Earth. Diverse macroscopic properties of silicate melts in Earth's interior, such as density, viscosity, and crystal-melt partitioning, depend on their electronic and short-range local structures at high pressures and temperatures. Despite essential roles of silicate melts in many geophysical and geodynamic problems, little is known about their nature under the conditions of Earth's interior, including the densification mechanisms and the atomistic origins of the macroscopic properties at high pressures. Here, we have probed local electronic structures of MgSiO3 glass (as a precursor to Mg-silicate melts), using high-pressure x-ray Raman spectroscopy up to 39 GPa, in which high-pressure oxygen K-edge features suggest the formation of tricluster oxygens (oxygen coordinated with three Si frameworks; 3O) between 12 and 20 GPa. Our results indicate that the densification in MgSiO3 melt is thus likely to be accompanied with the formation of triculster, in addition to a reduction in nonbridging oxygens. The pressure-induced increase in the fraction of oxygen triclusters >20 GPa would result in enhanced density, viscosity, and crystal-melt partitioning, and reduced element diffusivity in the MgSiO3 melt toward deeper part of the Earth's lower mantle.

Interaction of SO2 with Oxygen on Ni(100) Studied by XPS and NEXAFS

at 80 K followed by annealing briefly at 160 K. Itclearly shows three features at 2478.0 eV, 2480.0 eV, and2482.4 eV. The intensities of two features at 2478.0 eV and2480.0 eV show strong angular dependency on the angle ofthe incident photon beam. The 2480.0 eV feature disappearscompletely when the photon beam is perpendicular to thesurface. This observation indicates that the upper statemolecular orbital related to this transition is orientatedperpendicular to the surface. That the feature at 2482.4 eVdoes not show clear angular dependency implies that theupper state molecular orbital related to this transition istotally symmetric. Based on these interpretations, we assignthree K-edge features of SO

A New Structural Motif for Biological Iron: Iron K-Edge XAS Reveals a [Fe4-μ-(OR)5(OR)9-10] Cluster in the Ascidian Perophora annectens

The Phlebobranch ascidian Perophora annectens surprisingly exhibited a biological Fe/V ratio of approximately 15:1 on multichannel X-ray fluorescence analysis of two independent collections of organisms. Iron K-edge X-ray absorption spectroscopy (XAS) indicated a single form of iron. The XAS K-edge of the first collection of blood cells was shifted approximately +1 eV relative to that of the second, indicating redox activity with average iron oxidation states of 2.67+ and 2.60+. The first-derivative iron XAS K-edge features at 7120.5, 7124, and 7128 eV resembled the XAS of magnetite but not of ferritin or of dissolved Fe(II) or Fe(III). Pseudo-Voigt fits to blood-cell iron K-edge XAS spectra yielded 12.4 integrated units of preedge intensity, indicating a noncentrosymmetric environment. The non-phase-corrected extended X-ray absorption fine structure (EXAFS) Fourier transform spectrum showed a first-shell O/N peak at 1.55 angstroms and an intense Fe-Fe feature at 2.65 angstroms. Fits to the EXAFS required a split first shell with two O at 1.93 angstroms and three O at 2.07 angstroms, consistent with terminal and bridging alkoxide ligands, respectively. More distant shells included three C at 2.87 angstroms, two Fe at 3.08 angstroms, three O at 3.29 angstroms, and one Fe at 3.8 angstroms. Structural models consistent with these findings include a [Fe4(OR)13](2-/3-) broken-edged Fe4O5 cuboid or a [Fe4(OR)14](3-/4-) "Jacob's ladder" with three edge-fused Fe2(OR)2 rhombs. Either of these models represents an entirely new structural motif for biological iron. Vanadium domination of blood-cell metals cannot be a defining trait of Phlebobranch tunicates so long as P. annectens is included among them.

Thermal Stability of Flame-Synthesized Anatase TiO2 Nanoparticles

The thermal stability of anatase TiO2 nanoparticles, produced by flame synthesis, is investigated in the current study. Phase-pure anatase particles of ∼4 nm in size can be reproducibly synthesized by using a tubular burner and rotating sampler. Transmission electron microscopy (TEM), glancing incidence X-ray diffraction (XRD), and near-edge X-ray absorption fine structure (NEXAFS) were utilized to characterize the particles before and after annealing to various temperatures. TEM investigations reveal a primary particle size of ∼4 nm with standard deviations around 1 nm. XRD and selected area electron diffraction (SAED) indicate that TiO2 nanoparticles are phase-pure anatase. Our results indicate that the particles remain kinetically trapped upon annealing up to 773 K in air for 2 h. At 973 K, increases in average size, rutile content, and particle shape are observed, consistent with recent reports in the literature. NEXAFS measurements indicate that the O K-edge features of the nanoparticles show similar...

X-Ray-Absorption Fine-Structure Spectroscopy Study of the Interactions between Contaminant Tetrahedral Anions and Self-Assembled Monolayers on Mesoporous Supports

Self-assembled monolayers on mesoporous supports (SAMMSs) have been found to be superior sorbent materials for sequestering environmentally problematic species. Coupling the rich coordination chemistry of transition metal complexes with the SAMMS concept has afforded anion-specific sorbent materials with unprecedented anion binding capabilities. X-ray-absorption fine-structure (XAFS) spectroscopy is used to investigate the chemical interaction between an interfacially bound copper ethylenediamine complex (Cu(EDA)) and arsenate and chromate anions within these nanoporous hybrid materials. The Cu K-edge XAFS data indicate a structural change of Cu(EDA)3 caused by the anion bonding, consistent with a lock-and-key mechanism. The As and Cr K-edge features of the normalized absorption data signify As(V) and Cr(VI) in the SAMMS samples. The Cr K-edge data show a distorted CrO4 tetrahedron with two short and two long oxygen distances, whereas the AsO4 tetrahedron is symmetric. The average local structure about Cu...

A NEXAFS investigation of the formation and decomposition of CuO and Cu2O thin films on Cu(100)

We report the use of near-edge X-ray absorption fine structure (NEXAFS) to unambiguously characterize the oxidation state of copper in copper oxides. The method is based on the analysis of the oxygen K-edge and copper L-edge features of Cu2O and CuO powder materials. To further demonstrate its utility, NEXAFS was also used to follow spectroscopically the oxidation of a Cu(100) single crystal surface by NO2, and the thermal decomposition of the resulting oxides. In agreement with previous studies [J.A. Rodriguez, J. Hrbek, J. Vac. Sci. Technol. 12 (1994) 2140], our NEXAFS results indicate that NO2 dissociates on the metal surface, generating NO and atomic oxygen which subsequently reacts with the Cu(100) surface to produce Cu2O (300K) or a mixture of Cu2O and CuO (250K). Upon heating, the thermodynamically unstable CuO transforms into Cu2O.

Manifestation of T′ and 1-2-3 features in [Nd 2/3(Ce 1− xTh x) 1/3] 2(Ba 2/3Nd 1/3) 2Cu 3O 9− δ compounds: a XANES study

The Cu K- and Ce L 3-edge regions have been measured in the hole doped hybrid structured [Nd 2/3(Ce 1− x Th x ) 1/3] 2(Ba 2/3Nd 1/3) 2Cu 3O 9− δ (2-2-3), 0≤ x≤1.0, compounds which are superconducting for x≤0.30. From the energy positions of the Cu K-edge features, it is clearly noted that 2-2-3 compounds incorporate the K-edge features seen in the oxygen deficient 1-2-3 and the T′-type 2-1-4 superconductors. On progressive Th substitution in 2-2-3, Ce continues to show mixed valence (3 +, 4 + predominant), Cu remains mainly in 2+ state and no significant change is seen in the weak feature at Cu 1+ position. However, noticeable changes in the split white line features at the Cu K-edge are observed. It is inferred from the analysis of the spectral features that a re-distribution of oxygen on the Cu(1) octahedral (defect) site in 2-2-3 occurs with increasing x, affecting adversely the carrier density. This plausibly causes a steep fall in T c with Th substitution.

A NEXAFS determination of the electronic structure of carbons for lithium-ion cells

We have applied the near-edge X-ray absorption fine structure (NEXAFS) technique to investigate the electronic and structural properties of specialty carbonaceous materials and anode electrodes made from the synthesized carbons. The carbon K-edge features of the carbonaceous materials were characterized by two relatively sharp resonances at 286 and 293 eV and a broad peak centered at 305 eV. A peak at 288 eV is related to the C–H* interaction and the relative intensity of this peak is higher for those samples prepared with pyrene as the carbon precursor. Oxygen and Li K-edges were also determined. The electrochemical performance of the carbon anodes is compared and related to the electronic and structural features of the NEXAFS spectra.