Comparative analysis of XANES and EXAFS for local structural characterization of disordered metal oxides

2021 ◽  
Vol 28 (5) ◽  
Author(s):  
Junying Li ◽  
Yuanyuan Li ◽  
Prahlad K. Routh ◽  
Evgeniy Makagon ◽  
Igor Lubomirsky ◽  
...  
Keyword(s):  
Small Sample Size ◽  
Functional Materials ◽  
Local Environment ◽  
Structural Disorder ◽  
Active Species ◽  
Small Sample ◽  
Edge Structure ◽  
X Ray ◽  
X Ray Absorption ◽  
Xanes Analysis

In functional materials, the local environment around active species that may contain just a few nearest-neighboring atomic shells often changes in response to external conditions. Strong disorder in the local environment poses a challenge to commonly used extended X-ray absorption fine structure (EXAFS) analysis. Furthermore, the dilute concentrations of absorbing atoms, small sample size and the constraints of the experimental setup often limit the utility of EXAFS for structural analysis. X-ray absorption near-edge structure (XANES) has been established as a good alternative method to provide local electronic and geometric information of materials. The pre-edge region in the XANES spectra of metal compounds is a useful but relatively under-utilized resource of information of the chemical composition and structural disorder in nano-materials. This study explores two examples of materials in which the transition metal environment is either relatively symmetric or strongly asymmetric. In the former case, EXAFS results agree with those obtained from the pre-edge XANES analysis, whereas in the latter case they are in a seeming contradiction. The two observations are reconciled by revisiting the limitations of EXAFS in the case of a strong, asymmetric bond length disorder, expected for mixed-valence oxides, and emphasize the utility of the pre-edge XANES analysis for detecting local heterogeneities in structural and compositional motifs.

Time-Dependent X-ray Absorption Spectroscopic (XAS) Study on the Transformation of Zinc Basic Salt into Bis(N-oxopyridine-2-thionato) Zinc (II)

2007 ◽  
Vol 7 (11) ◽  
pp. 3867-3871
Author(s):  
Seung-Min Paek ◽  
Won-Young Jo ◽  
Man Park ◽  
Jin-Ho Choy
Keyword(s):  
Structural Evolution ◽  
Local Environment ◽  
Time Dependent ◽  
Precipitation Reaction ◽  
Reaction Products ◽  
Basic Salt ◽  
Edge Structure ◽  
X Ray ◽  
X Ray Absorption ◽  
Xanes Analysis

Solid transchelation reaction was established for the synthesis of bis(N-oxopyridine-2-thionato) zinc (II), commonly known as zinc pyrithione (ZPT), to control particle size using zinc basic salt (ZBS) and aqueous sodium pyrithione solution. Distinguished from ZPT particles prepared by usual precipitation reaction, the obtained ZPT nanoparticles exhibited very narrow size distribution. X-ray absorption spectroscopy (XAS) at Zn K-edge was systematically examined to elucidate time-dependent local structural evolution during solid transchelation reaction. X-ray absorption near edge structure (XANES) analysis clearly revealed that local environment around zinc atoms transformed into pentahedron as reaction proceeded. Based on quantitative X-ray diffraction and XANES analysis, we made structural models. Theoretical XAS spectrum calculated with FEFF code could reproduce experimental one, suggesting that XAS analysis could be very powerful tool to probe phase transformation. Furthermore, according to extended X-ray absorption fine structure (EXAFS) fitting results, Zn-O distance in reaction products gradually increased from 1.96 to 2.07 Å, suggesting that zinc atoms bounded with oxygen ones in ZBS were transchelated with pyrithione ligands. This study could be a strong evidence for the usefulness of XAS to study time-dependent structural transformation of nanocrystalline materials.

scholarly journals Solving local structure around dopants in metal nanoparticles with ab initio modeling of X-ray absorption near edge structure

2016 ◽  
Vol 18 (29) ◽  
pp. 19621-19630 ◽  
Author(s):  
Janis Timoshenko ◽  
Atal Shivhare ◽  
Robert W. J. Scott ◽  
Deyu Lu ◽  
Anatoly I. Frenkel
Keyword(s):  
Ab Initio ◽  
Metal Nanoparticles ◽  
Local Structure ◽  
Heterogeneous Catalysts ◽  
Edge Structure ◽  
X Ray ◽  
Metal Impurities ◽  
Local Environments ◽  
X Ray Absorption ◽  
Xanes Analysis

XANES analysis guided by ab initio modeling is proposed for refinement of local environments around metal impurities in heterogeneous catalysts.

scholarly journals Solution X-Ray Absorption Spectroscopy (XAS) for Analysis of Catalytically Active Species in Reactions with Ethylene by Homogeneous (Imido)vanadium(V) Complexes—Al Cocatalyst Systems

Catalysts ◽  
2019 ◽  
Vol 9 (12) ◽  
pp. 1016 ◽  
Author(s):  
Kotohiro Nomura
Keyword(s):  
Active Species ◽  
Oxidation States ◽  
Donor Ligands ◽  
Ethylene Dimerization ◽  
Edge Structure ◽  
Donor Ligand ◽  
X Ray ◽  
Catalytically Active ◽  
Type V ◽  
X Ray Absorption

Solution V K-edge XANES (X-ray absorption near edge structure) and EXAFS (extended X-ray absorption fine structure) analysis of vanadium(V) complexes containing both imido ligands and anionic ancillary donor ligands (L) of type, V(NR)(L)X2 (R = Ar, Ad (1-adamantyl); Ar = 2,6-Me2C6H3; X = Cl, Me, L = 2-(ArNCH2)C5H4N, OAr, WCA-NHC, and 2-(2’-benzimidazolyl)pyridine; WCA-NHC = anionic NHCs containing weak coordinating B(C6F5)3), which catalyze ethylene dimerization and/or polymerization in the presence of Al cocatalysts, has been explored. Different catalytically actives species with different oxidation states were formed depending upon the Al cocatalyst (MAO, Me2AlCl, AliBu3, etc.) and the anionic ancillary donor ligand employed. The method is useful for obtainment of the direct information of the active species (oxidation state, basic framework around the centered metal) in solution, and for better understanding in catalysis mechanism and organometallic as well as coordination chemistry.

scholarly journals The Role of Structural Representation in the Performance of a Deep Neural Network for X-ray Spectroscopy

Molecules ◽  
2020 ◽  
Vol 25 (11) ◽  
pp. 2715
Author(s):  
Marwah M.M. Madkhali ◽  
Conor D. Rankine ◽  
Thomas J. Penfold
Keyword(s):  
Neural Network ◽  
Deep Neural Network ◽  
Mean Squared Error ◽  
Chemical Space ◽  
Theoretical Calculations ◽  
Local Environment ◽  
Structural Representation ◽  
Edge Structure ◽  
X Ray ◽  
X Ray Absorption

An important consideration when developing a deep neural network (DNN) for the prediction of molecular properties is the representation of the chemical space. Herein we explore the effect of the representation on the performance of our DNN engineered to predict Fe K-edge X-ray absorption near-edge structure (XANES) spectra, and address the question: How important is the choice of representation for the local environment around an arbitrary Fe absorption site? Using two popular representations of chemical space—the Coulomb matrix (CM) and pair-distribution/radial distribution curve (RDC)—we investigate the effect that the choice of representation has on the performance of our DNN. While CM and RDC featurisation are demonstrably robust descriptors, it is possible to obtain a smaller mean squared error (MSE) between the target and estimated XANES spectra when using RDC featurisation, and converge to this state a) faster and b) using fewer data samples. This is advantageous for future extension of our DNN to other X-ray absorption edges, and for reoptimisation of our DNN to reproduce results from higher levels of theory. In the latter case, dataset sizes will be limited more strongly by the resource-intensive nature of the underlying theoretical calculations.

scholarly journals The local environment of metal sites in intracellular granules investigated by using X-ray-absorption spectroscopy

1984 ◽  
Vol 221 (3) ◽  
pp. 855-868 ◽  
Author(s):  
G N Greaves ◽  
K Simkiss ◽  
M Taylor ◽  
N Binsted
Keyword(s):  
Absorption Spectroscopy ◽  
Local Environment ◽  
Nearest Neighbour ◽  
Model Compounds ◽  
Edge Structure ◽  
X Ray ◽  
X Ray Absorption ◽  
Oxygen Bond ◽  
Phosphate Deposits ◽  
Phosphate Groups

We report the use of X-ray-absorption spectroscopy (x.a.s.) to study the local atomic environment of cations in intracellular granules from the hepatopancreas of Helix aspersa. Both the calcium K-edge in these concretions and the manganese K-edge in doped specimens were measured. Electron-microprobe measurements confirm that the introduced Mn2+ is concentrated in irregular growths on the surfaces of the granules. The near-edge structure (x.a.n.e.s.) of calcium is similar to that of manganese, indicating that the oxygen-co-ordination spheres of both cations share a similar symmetry. From the extended structure (e.x.a.f.s.) the metal-oxygen bond lengths of 0.230 nm (2.30A) for Ca-O and 0.218 nm (2.18A) for Mn-O [+/- 0.004 nm (0.04A)] were determined, reference being made to a variety of model compounds. The low density of the granules (2.07 g/cm3), together with the local atomic distribution, suggest an open hydrated structure for these phosphate deposits. Detailed analysis of the distribution of nearest-neighbour oxygen atoms demonstrates that this is asymmetric and considerably broader for Ca2+ than for Mn2+. Compared with the model compounds, the Ca2+ environment in the granules is similar to that observed in Ca2P2O7. I.r. spectra indicate the presence of condensed phosphate groups in the granules, with the strong possibility these are pyrophosphate (P2O7(4-) groups.

scholarly journals Random Forest Machine Learning Models for Interpretable X-Ray Absorption Near-Edge Structure Spectrum-Property Relationships

2020 ◽  
Author(s):  
Steven Torrisi ◽  
Matthew Carbone ◽  
Brian Rohr ◽  
Joseph H. Montoya ◽  
Yang Ha ◽  
...  
Keyword(s):  
Machine Learning ◽  
Functional Materials ◽  
Learning Models ◽  
Linear Quadratic ◽  
White Line ◽  
Edge Structure ◽  
Line Energy ◽  
X Ray ◽  
X Ray Absorption ◽  
Machine Learning Models

X-ray absorption spectroscopy (XAS) produces a wealth of information about the local structure of materials, but interpretation of spectra often relies on easily accessible trends and prior assumptions about the structure. Recently, researchers have demonstrated that machine learning models can automate this process to predict the coordinating environments of absorbing atoms from their XAS spectra. However, machine learning models are often difficult to interpret, making it challenging to determine when they are valid and whether they are consistent with physical theories. In this work, we present three main advances to the data-driven analysis of XAS spectra: we demonstrate the efficacy of random forests in solving two new property determination tasks (predicting Bader charge and mean nearest neighbor distance), we show that multiscale featurization can elucidate the regions and trends in spectra that encode various local properties, and we address the effect of normalization on model interpretability. The multiscale featurization transforms the spectrum into a vector of polynomial-fit features, and is contrasted with the commonly-used "pointwise" featurization that directly uses the entire spectrum as input. We find that across thousands of transition metal oxide spectra, the relative importance of features describing the curvature of the spectrum can be localized to individual energy ranges, and we can separate the importance of constant, linear, quadratic, and cubic trends, as well as the white line energy. This work has the potential to assist rigorous theoretical interpretations, expedite experimental data collection, and automate analysis of XAS spectra, thus accelerating discovery of new functional materials.

Extraction of local coordination structure in a low-concentration uranyl system by XANES

2016 ◽  
Vol 23 (3) ◽  
pp. 758-768 ◽  
Author(s):  
Linjuan Zhang ◽  
Jing Zhou ◽  
Jianyong Zhang ◽  
Jing Su ◽  
Shuo Zhang ◽  
...  
Keyword(s):  
Structural Information ◽  
Chemical Properties ◽  
Edge Structure ◽  
X Ray ◽  
Low Concentration ◽  
Simplified Approach ◽  
Bond Lengths ◽  
Uranyl Carbonate ◽  
X Ray Absorption ◽  
Xanes Analysis

Obtaining structural information of uranyl species at an atomic/molecular scale is a critical step to control and predict their physical and chemical properties. To obtain such information, experimental and theoreticalL3-edge X-ray absorption near-edge structure (XANES) spectra of uranium were studied systematically for uranyl complexes. It was demonstrated that the bond lengths (R) in the uranyl species and relative energy positions (ΔE) of the XANES were determined as follows: ΔE1= 168.3/R(U—Oax)2− 38.5 (for the axial plane) and ΔE2= 428.4/R(U—Oeq)2− 37.1 (for the equatorial plane). These formulae could be used to directly extract the distances between the uranium absorber and oxygen ligand atoms in the axial and equatorial planes of uranyl ions based on the UL3-edge XANES experimental data. In addition, the relative weights were estimated for each configuration derived from the water molecule and nitrate ligand based on the obtained average equatorial coordination bond lengths in a series of uranyl nitrate complexes with progressively varied nitrate concentrations. Results obtained from XANES analysis were identical to that from extended X-ray absorption fine-structure (EXAFS) analysis. XANES analysis is applicable to ubiquitous uranyl–ligand complexes, such as the uranyl–carbonate complex. Most importantly, the XANES research method could be extended to low-concentration uranyl systems, as indicated by the results of the uranyl–amidoximate complex (∼40 p.p.m. uranium). Quantitative XANES analysis, a reliable and straightforward method, provides a simplified approach applied to the structural chemistry of actinides.

scholarly journals INCORPORATION OF Mo6+ IN FERRIHYDRITE, GOETHITE, AND HEMATITE

2021 ◽  
Author(s):  
Marcel G. Görn ◽  
Ralph M. Bolanz ◽  
Stephen Parry ◽  
Jörg Göttlicher ◽  
Ralph Steininger ◽  
...  
Keyword(s):  
Inductively Coupled Plasma ◽  
Structural Disorder ◽  
Unit Cell ◽  
Emission Spectrometry ◽  
Charge Balance ◽  
Unit Cell Parameters ◽  
Edge Structure ◽  
X Ray ◽  
Cell Parameters ◽  
X Ray Absorption

AbstractAmong all iron oxides, hematite (α-Fe2O3), goethite (α-FeOOH), and ferrihydrite (FeOOH⋅nH2O) are the most common mineral species. While immobilization of Mo6+ by surface adsorption on ferric oxides has been studied extensively, the mechanisms of incorporation in their structure have been researched little. The objective of this study was to investigate the relation between Mo content and its structural incorporation in hematite, goethite, and six-line ferrihydrite by a combination of X-ray absorption spectroscopy (XAS), powder X-ray diffraction (pXRD), and inductively-coupled plasma optical emission spectrometry (ICP-OES). Synthesized in the presence of Mo, the hematite, goethite, and six-line ferrihydrite phases incorporated up to 8.52, 0.03, and 17.49 wt. % Mo, respectively. For hematite and goethite, pXRD analyses did not indicate the presence of separate Mo phases. Refined unit-cell parameters correlated with increasing Mo concentration in hematite and goethite. The unit-cell parameters indicated an increase in structural disorder within both phases and, therefore, supported the structural incorporation of Mo in hematite and goethite. Analysis of pXRD measurements of Mo-bearing six-line ferrihydrites revealed small amounts of coprecipitated akaganéite. X-ray absorption near edge structure (XANES) measurements at the Mo L3-edge indicated a strong distortion of the MoO6 octahedra in all three phases. Fitting of extended X-ray absorption fine structure (EXAFS) spectra of the Mo K-edge supported the presence of such distorted octahedra in a coordination environment similar to the Fe position in the investigated specimen. Incorporation of Mo6+ at the Fe3+-position for both hematite and goethite resulted in the formation of one Fe vacancy in close proximity to the newly incorporated Mo6+ and, therefore, charge balance within the hematite and goethite structures.

scholarly journals Oxidation State analysis of LiFeSixP1-xO4/C (x = 0.06) with X-ray Absorption Near Edge Structure (XANES) in Fe K-edge and Si K-edge

2021 ◽  
Vol 5 (1) ◽  
pp. 37
Author(s):  
Sahara Hamas Intifadhah ◽  
Vera Laviara Maghfirohtuzzoimah ◽  
Pelangi Az-zahra ◽  
Wantana Klysubun ◽  
Fahmi Astuti ◽  
...  
Keyword(s):  
Oxidation State ◽  
Carbon Coating ◽  
Standard Sample ◽  
Lithium Ion ◽  
Solid State Method ◽  
Edge Structure ◽  
X Ray ◽  
State Method ◽  
X Ray Absorption ◽  
Xanes Analysis

The development of LiFePO<sub>4</sub> as a cathode materials on lithium-ion battery was increased with the use of additional techniques such as atomic doping and coating. The material used in this report was LiFeSi<sub>0.06</sub>P<sub>0.94</sub>O<sub>4</sub>/C (LFP Si-6%), synthesized with doping silicon 6% and 11wt% carbon coating by a solid state method. X-ray Absorption Spectroscopy (XAS) characterization was used to investigate the effect on electronic and atomic structure of LFP Si-6%, especially in X-ray Absorption Near Edge Strucuture (XANES) region. XANES data measured on Fe K-edge and Si K-edge. Fe foil, FeO, Fe<sub>2</sub>O<sub>3</sub>, FePO<sub>4</sub>, Si powder, SiO, SiO<sub>2</sub> were used as a standard sample for comparison with the result of LFP Si-6%. XANES analysis showed that the energy absorption of Fe K-edge and Si K-edge in LFP Si-6% was 7124.94 eV and 1846.16 eV, respectively. The oxidation state of Fe was Fe<sup>2.576+</sup> between Fe<sup>2+</sup> and Fe<sup>3+</sup>, while Si was close to the estimation of Si<sup>4+</sup>. In addition, the linear combination fitting (LCF) in XANES Fe K-edge was performed to show the ratio of Fe<sup>2+</sup>/Fe<sup>3+</sup> (FeO/Fe<sub>2</sub>O<sub>3</sub>).

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