scholarly journals First Principles Approach to Extracting Chemical Information from X-Ray Absorption Near-Edge Spectra of Ga-Containing Materials

2021 ◽  
Author(s):  
Kyle Groden ◽  
FERNANDO D. VILA ◽  
Li Li ◽  
Simon Bare ◽  
Susannah Scott ◽  
...  
Keyword(s):  
First Principles ◽  
Chemical Information ◽  
Active Materials ◽  
White Line ◽  
Edge Structure ◽  
Coordination Environment ◽  
X Ray ◽  
Catalytically Active ◽  
Ligand Coordination ◽  
X Ray Absorption

The X-ray absorption near edge structure (XANES) can provide uniquely detailed information on the coordination environments of important Ga-containing materials with unknown structures, including catalytically-active materials. In this study, the Ga K-edge XANES was simulated using first principles-based methods for seven molecular Ga complexes, as well b-Ga2O3, in order to explore the chemical origins of the experimentally observed features. The theoretical spectra were computed using FEFF, CASTEP and StoBE, in order to assess the sensitivity of the results to the computational approach. While the XANES features depend on the Ga coordination environment, they are also sensitive to the electronegativity of the ligands and the symmetry at Ga. The white line position responds to changes in both the core state (due to differential screening) and the valence “p” states (arising from differences in ligand coordination).

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 Structural relaxations around Ti, Cr and Fe impurities in α-Al2O3probed by x-ray absorption near-edge structure combined with first-principles calculations

2005 ◽  
Vol 17 (36) ◽  
pp. 5467-5480 ◽  
Author(s):  
Emilie Gaudry ◽  
Delphine Cabaret ◽  
Philippe Sainctavit ◽  
Christian Brouder ◽  
Francesco Mauri ◽  
...  
Keyword(s):  
First Principles ◽  
First Principles Calculations ◽  
Edge Structure ◽  
X Ray ◽  
X Ray Absorption ◽  
Fe Impurities

scholarly journals An X-ray absorption method for the identification of calcium phosphate species using peak height ratios

2013 ◽  
Vol 10 (11) ◽  
pp. 18723-18756 ◽  
Author(s):  
J. F. Oxmann
Keyword(s):  
Calcium Phosphate ◽  
Peak Height ◽  
Apatite Formation ◽  
Spectral Features ◽  
White Line ◽  
Edge Structure ◽  
X Ray ◽  
Compound Libraries ◽  
Phosphate Species ◽  
X Ray Absorption

Abstract. X-ray absorption near edge structure (XANES) studies on calcium phosphate species (Ca-P) deal with marginal differences among subtle spectral features despite a hitherto missing systematic breakdown of these differences. Related fingerprinting approaches depend therefore on spectral libraries that are not validated against each other, incomplete and scattered among publications. This study compiled a comprehensive spectral library from published reference compound libraries in order to establish more clear-cut criteria for Ca-P determination by distinctive phosphorus K-edge XANES features. A specifically developed normalization method identified diagnostic spectral features within the compiled library, e.g. by uniform calculation of ratios between white-line and secondary peak heights. Post-processing of the spectra (n = 81) verified distinguishability among most but not all phases, which included hydroxylapatite (HAP), poorly crystalline HAP, amorphous HAP, fluorapatite, carbonate fluorapatite (CFAP), carbonate hydroxylapatite, β-tricalcium phosphate, octacalcium phosphate (OCP), brushite, monetite, monocalcium phosphate, amorphous calcium phosphate (ACP), anapaite, herderite, scholzite, messelite, whiteite and P on CaCO3. Particularly, peak height ratios significantly improved analyte specificity, e.g. by supplementary breakdown into OCP and ACP. The spectral analysis also revealed Ca-P standards that were rarely investigated or inappropriately synthesized, and thus provides a basis for standard selection and synthesis. The developed method and resulting breakdown by species were subsequently tested on Ca-P spectra from studies on bone and sediment. The test indicated that bone material likely comprises only poorly crystalline apatite, which implies direct nucleation of apatite in bone. This biological apatite formation is likely opposed to that of sedimentary apatite, which apparently forms by successive crystallization. Application of the method to μXANES spectra of sediment particles indicated authigenic apatite formation by an OCP precursor.

scholarly journals First-principles modeling of X-ray absorption spectra enlightens the processes of scandium sequestration by iron oxides

2020 ◽  
Vol 105 (7) ◽  
pp. 1099-1103 ◽  
Author(s):  
Mathieu Chassé ◽  
Marc Blanchard ◽  
Delphine Cabaret ◽  
Amélie Juhin ◽  
Delphine Vantelon ◽  
...  
Keyword(s):  
Trace Metals ◽  
Iron Oxides ◽  
Absorption Spectra ◽  
First Principles ◽  
Molecular Mechanisms ◽  
Hydration Shell ◽  
Spectral Features ◽  
Edge Structure ◽  
X Ray ◽  
X Ray Absorption

Abstract Scandium is often associated with iron oxides in the environment. Despite the use of scandium as a geochemical tracer and the existence of world-class supergene deposits, uncertainties on speciation obscure the processes governing its sequestration and concentration. Here, we use first-principles approaches to interpret experimental K-edge X-ray absorption near-edge structure spectra of scandium either incorporated in or adsorbed on goethite and hematite, at concentrations relevant for the environment. This modeling helps to interpret the characteristic spectral features, providing key information to determine scandium speciation when associated with iron oxides. We show that scandium is substituted into iron oxides at low concentrations without modifying the crystal structure. When scandium is adsorbed onto iron oxide surfaces, the process occurs through outer-sphere complexation with a reduction in the coordination number of the hydration shell. Considering available X-ray absorption spectra from laterites, the present results confirm that scandium adsorption onto iron oxides is the dominant mechanism of sequestration in these geochemical conditions. This speciation explains efficient scandium recovery through mild metal-lurgical treatments of supergene lateritic ores. The specificities of scandium sorption mechanisms are related to the preservation of adsorbed scandium in million-years old laterites. These results demonstrate the emerging ability to precisely model fine X-ray absorption spectral features of trace metals associated with mineral phases relevant to the environment. It opens new perspectives to accurately determine trace metals speciation from high-resolution spatially resolved X-ray absorption near-edge structure spectroscopy in order to constrain the molecular mechanisms controlling their dynamics.

scholarly journals Correction: X-ray absorption near edge structure simulation of LiNi0.5Co0.2Mn0.3O2via first-principles calculation

RSC Advances ◽  
2020 ◽  
Vol 10 (7) ◽  
pp. 3882-3882
Author(s):  
Toshiharu Ohnuma ◽  
Takeshi Kobayashi
Keyword(s):  
First Principles ◽  
First Principles Calculation ◽  
Edge Structure ◽  
X Ray ◽  
Structure Simulation ◽  
X Ray Absorption

Correction for ‘X-ray absorption near edge structure simulation of LiNi0.5Co0.2Mn0.3O2via first-principles calculation’ by Toshiharu Ohnuma et al., RSC Adv., 2019, 9, 35655–35661.

scholarly journals X-ray absorption near edge structure simulation of LiNi0.5Co0.2Mn0.3O2via first-principles calculation

RSC Advances ◽  
2019 ◽  
Vol 9 (61) ◽  
pp. 35655-35661 ◽  
Author(s):  
Toshiharu Ohnuma ◽  
Takeshi Kobayashi
Keyword(s):  
First Principles ◽  
First Principles Calculation ◽  
Edge Structure ◽  
X Ray ◽  
Structure Simulation ◽  
X Ray Absorption

Simulation of Ni K-edge X-ray absorption near edge structure (XANES) spectra in LiNi0.5Co0.2Mn0.3O2 (NCM523) was performed.

X-ray absorption near edge structure and first-principles spectral investigations of cationic disorder in MgAl2O4 induced by swift heavy ions

2018 ◽  
Vol 20 (7) ◽  
pp. 4962-4969 ◽  
Author(s):  
S. Yoshioka ◽  
K. Tsuruta ◽  
T. Yamamoto ◽  
K. Yasuda ◽  
S. Matsumura ◽  
...  
Keyword(s):  
First Principles ◽  
Heavy Ions ◽  
Edge Structure ◽  
X Ray ◽  
Swift Heavy Ions ◽  
X Ray Absorption ◽  
Cationic Disorder

Cationic disorder in MgAl2O4 induced by swift heavy ions was quantitatively determined using experimental and theoretical XANES spectra.

Tb L3-edge X-ray Absorption Near-edge Structure Spectroscopic Analysis of Terbium-doped Phosphor Compoundsfor Plasma Display Panel Applications

2002 ◽  
Vol 17 (1) ◽  
pp. 31-35 ◽  
Author(s):  
Yong Gyu Choi ◽  
Kee-Sun Sohn ◽  
Kyong Hon Kim ◽  
Hee Dong Park
Keyword(s):  
Spectroscopic Analysis ◽  
Green Emission ◽  
Concentration Quenching ◽  
Plasma Display Panel ◽  
White Line ◽  
Edge Structure ◽  
X Ray ◽  
Line Absorption ◽  
Plasma Display ◽  
X Ray Absorption

We have analyzed Tb L3-edge x-ray absorption near-edge structure spectra of Tb-doped phosphor compounds for plasma display panel applications. Intensity and lifetime of the green emission from the Tb3+:5D4→7F5 transition were measured with respect to nominal terbium concentration in the host compounds, i.e., YBO3, YPO4,and Y4Al2O9, all of which were made through the solid-state reaction. Typical concentration quenching was evident on the fluorescence intensity and the fluorescing level lifetime in our samples. From the analyses of white line absorption peaks at TbL3-edge, it was verified that terbium is essentially trivalent in all the samples, even invery highly concentrated ones. Thus, this implies that the concentration quenching was not caused by presence of mixed-valent states of terbium. Instead, it is believed that anonradiative energy transfer route among Tb3+ ions might be responsible for thebehavior.

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