• Title/Summary/Keyword: Extended X-ray absorption fine structure analysis

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Application of X-ray Absorption Spectroscopy (XAS) in the Field of Stabilization of As and Heavy Metal Contaminated Soil (비소 및 중금속 오염토양 안정화 분야에서의 X선 흡수분광법(XAS) 활용)

  • Lim, Jung Eun;Moon, Deok Hyun;Kim, Kwon-Rae;Ok, Yong Sik
    • Journal of Applied Biological Chemistry
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    • v.58 no.1
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    • pp.65-74
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    • 2015
  • X-ray absorption fine structure (XAFS) analysis using X-ray absorption spectroscopy is being applied as a state-of-the-art method in a wide range of disciplines. This review article summarizes the overall procedure of XAFS analysis from the preparation of soil samples to the analysis of data in X-ray absorption near edge structure (XANES) region and extended Xray absorption fine structure (EXAFS) region. The previous studies on application of XANES and EXAFS techniques in environmental soil science field are discussed and classified them according to metal(loid)s (As, Cd, Cu, Ni, Pb, and Zn). A significant number of previous studies of XAFS application in the environmental soil science field have focused on the identification of Pb chemical species in soil. Moreover, XANES and EXAFS techniques have been widely used to investigate the contamination source via identification of metal species. Similarly, these techniques were applied to identify the mechanisms of metal stabilization in soil after application of various amendments, phytoremediation, etc.

X-ray Absorption Spectra Analysis for the Investigation of the Retardation Mechanism of Iodine Migration by the Silver Ion Added to Bentonite (벤토나이트에 첨가한 은 이온에 의한 아이오딘 이동 저지 메커니즘 규명을 위한 X-선 흡수 스펙트라 분석)

  • Kim, Seung-Soo;Kim, Min-Gue;Baik, Min-Hoon;Choi, Jong-Won
    • Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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    • v.8 no.3
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    • pp.201-205
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    • 2010
  • Most of iodine was captured by the block when NaI solution flowed through a bentonite block sorbed silver to retard the migration of iodine released from high-level radioactive wastes. In order to understand in detail the mechanism for the retardation of the iodine by the silver ion, X-ray Absorption Near Edge Structure (XANES) and Extended X-ray Absorption Fine Structure (EXAFS) spectra of the silver sorbed bentonite before and after the contact with iodide were compared with those of AgO, $Ag_2O$ and AgI as references. This examination suggests that the silver ion sorbed on the bentonite is desorbed, and then it retards the migration of iodine by forming the cluster of AgI precipitate.

Local Structure Refinement of the $BaFe_{1-x}Sn_xO_{3-y}$ System with Fe K-Edge X-Ray Absorption (XANES/EXAFS) Spectroscopy

  • 김민규;곽기섭;로권선;여철현
    • Bulletin of the Korean Chemical Society
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    • v.18 no.7
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    • pp.743-749
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    • 1997
  • Local structure refinement of the BaFe1-xSnxO3-y system (x=0.00-0.50) has been carried out with Fe K-edge x-ray absorpion spectroscopic studies. It is found out that the Fe ions are placed in two different symmetric sites such as tetrahedral and octahedral sites in the compounds by comparison with Fe K-edge x-ray absorption near edge structure (XANES) spectrum of the γ-Fe2O3 compound as a reference. Small absorption peaks of dipole-forbiden transitions appear at a pre-edge region of 7111 eV due to the existence of Fe ions in the tetrahedral and octahedral sites. The peak intensity decreases with the substitution amount of Sn ion. Three different absorption peaks of 1s→4p dipole-allowed transition appear on the energy region between 7123 and 7131 eV. The peaks correspond to 1s→4p main transition of Fe ions in tetrahedral and octahedral sites and 1s→4p transition followed by the shakedown process of ligand to metal charge transfer. The bond distances between Fe ions in the tetrahedral site and nearest neighboring oxygen atom (Fe-4O), and those in octahedral site (Fe-6O) are determined with the extended x-ray absorption fine structure (EXAFS) analysis. Two different interatomic distances increase with the substitution amount of Sn ion and also the bond lengths of Fe-4O are shorter than those of Fe-6O in all compounds.

In Situ X-ray Absorption Spectroscopic Study for α-MoO3 Electrode upon Discharge/Charge Reaction in Lithium Secondary Batteries

  • Kang, Joo-Hee;Paek, Seung-Min;Choy, Jin-Ho
    • Bulletin of the Korean Chemical Society
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    • v.31 no.12
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    • pp.3675-3678
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    • 2010
  • In-situ X-ray absorption spectroscopy (XAS) was used to elucidate the structural variation of $\alpha-MoO_3$ electrode upon discharge/charge reaction in a lithium ion battery. According to the XAS analysis, hexavalent Mo atoms in $\alpha-MoO_3$ framework are reduced as the amount of intercalated lithium ions increases. As lithium de-intercalation proceeds, most of pre-edge peaks are restored again. However, according to the Fourier transforms of the extended X-ray absorption fine structure (EXAFS) spectra, lithium de-intercalation reaction is partially irreversible upon the charge reaction, which is one of the main reasons why the capacity of $\alpha-MoO_3$ electrode decreases upon successive discharge/charge cycles.

Chemical Properties of Mineral Surfaces and Metal Ion Sorption: A Review (광물표면의 화학적 특성과 금속이온 수착의 고찰: A Review)

  • Yoon, Soh-Joung
    • Economic and Environmental Geology
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    • v.45 no.2
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    • pp.205-215
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    • 2012
  • Metal ions, toxic or potentially toxic to biota and human beings, can be immobilized by sorption onto the mineral surfaces in soils and sediments. This article briefly explains theories regarding the chemical properties of mineral surfaces to sorb metal ions and processes of extended X-ray absorption fine structure (EXAFS) analysis for sorption study, and reviews atomic-scale findings on metal sorption on mineral surfaces. The theoretical understanding on the chemistry of mineral surfaces and metal sorption is fundamental to the proper analysis of the atomic-scale spectroscopy to determine the sorption phases. Atomic-scale findings on metal sorption phases discussed here include co-precipitation, ternary complexation, aging effects, and desorption possibilities, as well as outer-sphere complexation, inner-sphere complexation, and surface precipitation.

The Effect of the Oxygen Flow Rate on the Electronic Properties and the Local Structure of Amorphous Tantalum Oxide Thin Films

  • Denny, Yus Rama;Lee, Sunyoung;Lee, Kangil;Kang, Hee Jae;Yang, Dong-Seok;Heo, Sung;Chung, Jae Gwan;Lee, Jae Cheol
    • Proceedings of the Korean Vacuum Society Conference
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    • 2013.02a
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    • pp.398-398
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    • 2013
  • The electronic properties and the local structure of tantalum oxide thin film with variation of oxygen flow rate ranging from 9.5 to 16 sccm (standard cubic centimeters per minute) have been investigated by X-ray photoelectron spectroscopy (XPS), Reflection Electron Energy Loss Spectroscopy (REELS), and X-ray absorption spectroscopy (XAS). The XPS results show that the Ta4f spectrum for all films consist of the strong spin-orbit doublet $Ta4f_{7/2}$ and $Ta4f_{5/2}$ with splitting of 1.9 eV. The oxygen flow rate of the film results in the appearance of new features in the Ta4f at binding energies of 23.2 eV, 24.4 eV, 25.8, and 27.3 eV, these peaks attribute to $Ta^{1+}$, $Ta^{2+}$, $Ta^{4+}$/$Ta^{2+}$, and $Ta^{5+}$, respectively. Thus, the presence of non-stoichiometric state from tantalum oxide ($TaO_x$) thin films could be generated by the oxygen vacancies. The REELS spectra suggest the decrease of band gap for tantalum oxide thin films with increasing the oxygen flow rate. The absorption coefficient ${\mu}$ and its fine structure were extracted from the fluorescence mode of extended X-ray absorption fine structure (EXAFS) spectra. In addition, bond distances (r), coordination numbers (N) and Debye-Waller factors (${\sigma}^2$) each film were determined by a detailed of EXAFS data analysis. EXAFS spectrapresent both the increase of coordination number of the first Ta-O shell and a considerable reduction of the Ta-O bond distance with the increase of oxygen flow rate.

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Distribution of Co Ions in Ferromagnetic Zn (1-x) Co (x)O Films

  • Park, Chang-In;Seo, Su-Yeong;Kim, Jeong-Ran;Han, Sang-Uk
    • Proceedings of the Korean Vacuum Society Conference
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    • 2012.08a
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    • pp.166-166
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    • 2012
  • We examined the distribution of Co ions of ferromagnetic n-type Zn(1-x)Co(x)O semiconducting films with the Co concentrations of 0.03~0.07 using x-ray absorption fine structure (XAFS) measurements at the Co and Zn K edges. Extended XAFS (EXAFS) revealed that Co ions mainly occupied the zinc sites of the films. X-ray absorption near edge structure (XANES) spectra demonstrated that the pre-edge peak of the Co K edge was substantially affected by the second neighboring Co ions at the zinc sites due to hybridizing of the Co 4p conduction electrons with the Co 3d bounded electrons. From XANES and EXAFS analysis using ab initio calculations, we found that Co ions uniformly occupied the zinc sites of the Zn (0.93) Co (0.07)O film, whereas the Co ions of the Zn (0.97) Co (0.03)O and Zn (0.95) Co (0.05)O films were substituted at localized zinc sites. The ferromagnetic properties of the Zn (0.93) Co(0.07)O film could be induced by direct interaction between the magnetic dipoles of the Co ions with a mean distance of 4.3 A or by Co 4p electron mediation.

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Effect of BSO addition on Cu-O bond of GdBa2Cu3O7-x films with varying thickness probed by extended x-ray absorption fine structure

  • Jeon, H.K.;Lee, J.K.;Yang, D.S.;Kang, W.N.;Kang, B.
    • Progress in Superconductivity and Cryogenics
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    • v.18 no.4
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    • pp.1-4
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    • 2016
  • We investigated the relation between the Cu-O bond length and the superconducting properties of $BaSnO_3$ (BSO)-added $GdBa_2Cu_3O_{7-x}$ (GdBCO) thin films by using extended x-ray absorption fine structure (EXAFS) spectroscopy. 4 wt.% $BaSnO_3$ (BSO) added $GdBa_2Cu_3O_{7-x}$ (GdBCO) thin films with varying thickness from $0.2{\mu}m$ to $1.0{\mu}m$ were fabricated by using pulsed laser deposition (PLD) method. The transition temperature ($T_c$) and the residual resistance ratio (RRR) of the GdBCO films increased with increasing thickness up to $0.8{\mu}m$, where the crystalline BSO has the highest peak intensity, and then decreased. This uncommon behaviors of $T_c$ and RRR are likely to be created by the addition of BSO, which may change the ordering of GdBCO atomic bonds. Analysis from the Cu K-edge EXAFS spectroscopy showed an interesting thickness dependence of ordering behavior of BSO-added GdBCO films. It is noticeable that the ordering of Cu-O bond and the transition temperature are found to show opposite behaviors in the thickness dependence. Based on these results, the growth of BSO seemingly have evident effect on the alteration of the local structure of GdBCO film.

Local structure and transport properties of $La_{0.7}Ca_{0.3-x}Ba_{x}MnO_3$ manganites

  • A.N.Ulyanov;Yang, Dong-Seok;Yu, Seong-Cho
    • Proceedings of the Korean Magnestics Society Conference
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    • 2003.06a
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    • pp.62-63
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    • 2003
  • Electron-phonon interaction plays a significant role in forming of colossal magnetoresistance effect (CMR). Polaron formation was observed by neutron diffraction and by extended X-ray absorption fine structure (EXAFS) analysis. Local probe as given by the EXAFS is a useful method to study the polaronic charge and its dependence on temperature and ions size. Here we present the EXAFS study of polaronic charge in $La_{0.7}Ca_{0.3-x}Ba_{x}MnO_3$ compositions.

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Lead Stabilization in Soil Amended with Lime Waste: An Extended X-ray Absorption Fine Structure (EXAFS) Investigation

  • Lim, Jung Eun;Lee, Sang Soo;Yang, Jae E.;Ok, Yong Sik
    • Korean Journal of Soil Science and Fertilizer
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    • v.47 no.6
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    • pp.443-450
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    • 2014
  • To determine Pb species in soils following the immobilization process, sequential extraction has been used despite the possibility of overestimating Pb species from unintended reactions during chemical extraction. Meanwhile, the application of extended X-ray absorption fine structure (EXAFS) has been shown to provide a more precise result than chemical extraction. In this study, the immobilization of Pb in contaminated soils treated with liming materials such as oyster shell (OS) or eggshell (ES) was evaluated with thermodynamic modelling and EXAFS analysis. Thermodynamic modelling by visual MINTEQ predicted the precipitation of $Pb(OH)_2$ in OS and ES treated soils. In particular, the values of saturation index (SI) for $Pb(OH)_2$ in OS (SI=0.286) and ES (SI=0.453) treated soils were greater than in the control soil (SI=0.281). Linear combination fitting (LCF) analysis confirmed the presence of $C_{12}H_{10}O_{14}Pb_3$ (lead citrate, 44.7%) by citric acid from plant root, Pb-gibbsite (Pb adsorbed gibbsite, 26.4%), and Pb-kaolinite (Pb adsorbed kaolinite, 20.3%) in the control soil. On the other hand, $Pb(OH)_2$ (16.8%), Pb-gibbsite (39.3%), and Pb-kaolinite (25.6%) were observed in the OS treated soil and $Pb(OH)_2$ (55.2%) and Pb-gibbsite (33.8%) were also confirmed in the ES treated soil. Our results indicate that the treatment with OS and ES immobilizes Pb by adsorption of Pb onto the soil minerals as a result of the increase in soil negative charge and the formation of stable $Pb(OH)_2$ under high pH condition of soils.