scholarly journals Structural Change Analysis of Cerianite in Weathered Residual Rare Earth Ore by Mechanochemical Reduction Using X-Ray Absorption Fine Structure

Minerals ◽  
2019 ◽  
Vol 9 (5) ◽  
pp. 267 ◽  
Author(s):  
Tatsuya Kato ◽  
Yuki Tsunazawa ◽  
Wenying Liu ◽  
Chiharu Tokoro
Keyword(s):  
Fine Structure ◽  
Rare Earth ◽  
Structural Change ◽  
Oxygen Vacancy ◽  
Structural Changes ◽  
Mechanochemical Reaction ◽  
X Ray ◽  
Absorption Fine ◽  
X Ray Absorption ◽  
Mechanochemical Reactions

Prolonged high-intensity grinding can modify the crystal structure of solid substances and/or induce chemical reaction, which is referred to as mechanochemical reaction. Such reactions can exert positive influences on hydrometallurgical processes, therefore, many researchers have applied mechanochemical reactions for metals dissolution from minerals. The mechanism of mechanochemical reaction has been investigated using solid analyses and simulations. Structural changes caused by mechanochemical reactions are not yet sufficiently clarified because the ground samples are amorphous. The objective of this study was to analyze structural changes of cerianite in weathered residual rare earth ore by mechanochemical reduction. The ore was ground by planetary ball milling for 10, 60 and 720 min. Structural change was analyzed by the X-ray absorption near-edge structure and extended x-ray absorption fine structure analysis at the cerium LIII- and K-edges. These analyses revealed that the structural change of cerianite in this ore induced by mechanochemical reduction involved oxygen vacancy production. The process of the oxygen vacancy formation was closely coupled with the quantum effect of localization–delocalization of the 4f electron of cerium.

scholarly journals Structural Change Analysis of Cerianite in Weathered Residual Rare Earth Ore by Mechanochemical Reduction Using X-ray Absorption Fine Structure

2019 ◽  
Author(s):  
Tatsuya Kato ◽  
Yuki Tsunazawa ◽  
Wenying Liu ◽  
Chiharu Tokoro
Keyword(s):  
Fine Structure ◽  
Rare Earth ◽  
Structural Change ◽  
Oxygen Vacancy ◽  
Structural Changes ◽  
Mechanochemical Reaction ◽  
Edge Structure ◽  
X Ray ◽  
Absorption Fine ◽  
X Ray Absorption

Prolonged high-intensity grinding can modify the crystal structure of solid substances and/or induce chemical reaction, which is referred to as mechanochemical reaction. Such reactions can exert positive influences on hydrometallurgical processes, therefore, many researchers have applied mechanochemical reactions for metals dissolution from minerals. The mechanism of mechanochemical reaction has been investigated using solid analyses and simulations. Structural changes caused by mechanochemical reaction are not yet sufficiently clarified because the ground samples are amorphous. The objective of this study was to analyze structural changes of cerianite in weathered residual rare earth ore by mechanochemical reduction. Structural change was analyzed by x-ray absorption near-edge structure and extended x-ray absorption fine structure analysis at the cerium LIII- and K-edges. These analyses revealed that the structural change of cerianite in this ore induced by mechanochemical reduction involved oxygen vacancy production. The process of the oxygen vacancy formation was closely coupled with the quantum effect of localization–delocalization of the 4f electron of cerium.

Extended X-ray Absorption Fine Structure Studies of GaN Epilayers Doped in situ with Er and Eu During Molecular Beam Epitaxy

2003 ◽  
Vol 798 ◽  
Author(s):  
V. Katchkanov ◽  
J. F. W. Mosselmans ◽  
S. Dalmasso ◽  
K. P. O'Donnell ◽  
R. W. Martin ◽  
...  
Keyword(s):  
Fine Structure ◽  
Rare Earth ◽  
Molecular Beam Epitaxy ◽  
Local Structure ◽  
Molecular Beam ◽  
X Ray ◽  
Absorption Fine ◽  
X Ray Absorption ◽  
The Eu

ABSTRACTThe local structure around Er and Eu atoms introduced into GaN epilayers was studied by means of Extended X-ray Absorption Fine Structure above the appropriate rare-earth X-ray absorption edge. The samples were doped in situ during growth by Molecular Beam Epitaxy. The formation of ErN clusters was found in samples with high average Er concentrations of 32±6% and 12.4±0.8%, estimated by Wavelength Dispersive X-ray analysis. When the average Er concentration is decreased to 6.0±0.2%, 1.6±0.2% and 0.17±0.02%, Er is found in localised clusters of ErGaN phase with high local Er content. Similar behaviour is observed for Eu-doped samples. For an average Eu concentration of 30.5±0.5% clusters of pure EuN occur. Decreasing the Eu concentration to 10.4±0.5% leads to EuGaN clusters with high local Eu content. However, for a sample with an Eu concentration of 14.2±0.5% clustering of Eu was not observed.

Fluorescence Extended X-Ray Absorption Fine Structure Study on Local Structures of Rare-Earth-Doped InGaGdN

2016 ◽  
Vol 1133 ◽  
pp. 429-433
Author(s):  
Siti Nooraya Mohd Tawil ◽  
Shuichi Emura ◽  
Daivasigamani Krishnamurthy ◽  
Hajime Asahi
Keyword(s):  
Fine Structure ◽  
Rare Earth ◽  
Nearest Neighbor ◽  
Structure Study ◽  
Edge Structure ◽  
X Ray ◽  
Local Structures ◽  
Absorption Fine ◽  
X Ray Absorption

Local structures around gadolinium atoms in rare-earth (RE)-doped InGaGdN thin films were studied by means of fluorescence extended X-ray absorption fine structure (EXAFS) measured at the Gd LIII-edges. The samples were doped with Gd in-situ during growth by plasma-assisted molecular beam epitaxy (PAMBE). Gd LIII-edge EXAFS signal from the GaGdN, GdN and Gd foil were also measured as reference. The X-ray absorption near edge structure (XANES) spectra around Gd LIII absorption edge of InGaGdN samples observed at room temperature indicated the enhancement of intensities with the increase of Gd composition. Further EXAFS analysis inferred that the Gd atoms in InGaN were surrounded by similar atomic shells as in the case of GaGdN with the evidence indicating majority of Gd atoms substituted into Ga sites of InGaGdN. A slight elongation of bond length for the 2nd nearest-neighbor (Gd–Ga) of sample with higher Gd concentration was also observed.

Structural determinations of liquid semiconductors using extended X-ray absorption fine structure

1977 ◽  
Vol 55 (11) ◽  
pp. 1968-1974 ◽  
Author(s):  
E. D. Crozier ◽  
F. W. Lytle ◽  
D. E. Sayers ◽  
E. A. Stern
Keyword(s):  
Fine Structure ◽  
Disordered Systems ◽  
Structural Changes ◽  
Structural Information ◽  
Structural Rearrangement ◽  
Nearest Neighbour ◽  
X Ray ◽  
Absorption Fine ◽  
Amorphous States ◽  
X Ray Absorption

The extended fine structure in the X-ray absorption coefficient is dominated by the interference of the photoelectron scattered by atoms in the immediate neighbourhood of the atom which absorbs the X-ray photon and thus can provide structural information about ordered or disordered systems. In this paper it is demonstrated that Extended X-Ray Absorption Fine Structure (EXAFS) measurements can be made on liquid systems at high temperatures. The technique is illustrated with results for As2Se3 in the liquid and amorphous states for temperatures between 100 and 773 K. A Fourier analysis of the EXAFS data reveals that a major structural rearrangement does not occur in the nearest neighbour shell when As2Se3 is melted. However, small structural changes do occur at the melting point which, within the limitations of the present data, suggest a slight increase in the nearest neighbour As–Se distance, a decrease in the number of nearest neighbours, and a decrease in the nearest neighbour disorder term σ12.

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