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.

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.

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 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.

Stoichiometric Study of Iron Sulfide Prepared by Mechanochemical Reaction

2007 ◽  
Vol 561-565 ◽  
pp. 2099-2102 ◽  
Author(s):  
Chung Kwei Lin ◽  
Chin Yi Chen ◽  
Pee Yew Lee ◽  
Chih Chieh Chan
Keyword(s):  
Ball Milling ◽  
Nearest Neighbor ◽  
Iron Sulfide ◽  
Structural Evolution ◽  
High Energy ◽  
Mechanochemical Reaction ◽  
Iron Sulfides ◽  
Edge Structure ◽  
X Ray ◽  
X Ray Absorption

In the present study, pure elemental powders of Fe and S were mixed to give the desired compositions of Fe50S50. A SPEX 8000D high-energy ball mill was used to synthesize iron sulfide powders under an Ar-filled atmosphere. The prepared powders were examined by conventional X-ray diffractometry and synchrotron X-ray absorption spectroscopy. The experimental results revealed that mechanochemical reactions occurred during the ball milling process for all the compositions. The Fe50S50 phase was obtained after ball milling for 20 h. Extended X-ray absorption fine structure (EXAFS) results revealed that the nearest neighbor bond lengths of the radial distribution function (RDF) for iron decreased when iron sulfides formed. X-ray absorption near edge structure (XANES) of S K-edges distinguished better the structural evolution of these iron sulfides.

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.

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 Structural Evolution of MoO3 Thin Films Deposited on Copper Substrates upon Annealing: An X-ray Absorption Spectroscopy Study

2019 ◽  
Vol 4 (2) ◽  
pp. 41 ◽  
Author(s):  
Macis ◽  
Rezvani ◽  
Davoli ◽  
Cibin ◽  
Spataro ◽  
...  
Keyword(s):  
Thin Films ◽  
Absorption Spectroscopy ◽  
Structural Changes ◽  
Structural Evolution ◽  
Ex Situ ◽  
Edge Structure ◽  
X Ray ◽  
High Gradients ◽  
Different Temperatures ◽  
X Ray Absorption

Structural changes of MoO3 thin films deposited on thick copper substrates upon annealing at different temperatures were investigated via ex situ X-Ray Absorption Spectroscopy (XAS). From the analysis of the X-ray Absorption Near-Edge Structure (XANES) pre-edge and Extended X-ray Absorption Fine Structure (EXAFS), we show the dynamics of the structural order and of the valence state. As-deposited films were mainly disordered, and ordering phenomena did not occur for annealing temperatures up to 300 °C. At ~350 °C, a dominant α-MoO3 crystalline phase started to emerge, and XAS spectra ruled out the formation of a molybdenum dioxide phase. A further increase of the annealing temperature to ~500 °C resulted in a complex phase transformation with a concurrent reduction of Mo6+ ions to Mo4+. These original results suggest the possibility of using MoO3 as a hard, protective, transparent, and conductive material in different technologies, such as accelerating copper-based devices, to reduce damage at high gradients.

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