Structural study of highly dispersed cerium dioxides

Cerium dioxide samples of different dispersivity, obtained by different methods, have been investigated by X-ray diffraction (XRD) analysis, full-profile analysis of diffraction patterns, calculation of radial distribution function (RDF) of electron density, and extended X-ray absorption fine-structure (EXAFS) spectroscopy. According to the XRD data, the samples studied can be identified in the fluorite structure with conventional unit-cell parameters. However, the local structure of highly dispersed samples, determined by the RDF and EXAFS methods, changes: the coordination spheres for the Ce-O distances are represented by two distances.     

Diagnostics of gold-containing surgical-dressing materials with X-ray and synchrotron radiation

An analysis of biocompatible and antibacterial Au-gauze nanocomposites for medical purposes using X-ray and synchrotron radiation is conducted. The samples are produced by the modification of medical cotton gauze by Au organosol in isopropanol, which is synthesized via the metal-vapor method. The nanocomposites are examined with X-ray photoelectron spectroscopy, as well as with X-ray adsorption diffraction spectroscopy (EXAFS/XANES) and small-angle X-ray scattering using synchrotron radiation.     

EXAFS and diffraction

We discuss advantages and limitations of X-ray absorption fine structure (EXAFS), X-ray diffraction and anomalous X-ray diffraction as structural tools for ordered and (chemically and structurally) disordered solids.     

Pressure effects in Debye-Waller factors and in EXAFS

Anharmonic correlated Einstein model (ACEM) and statistical moment method (SMM) have been developed to derive analytical expressions for pressure dependence of the lattice bond length, effective spring constant, correlated Einstein frequency and temperature, Debye-Waller factors (DWF) or second cumulant, first and third cumulants in Extended X-ray Absorption Fine Structure (EXAFS) at a given temperature. Numerical results for pressure-dependent DWF of Kr and Cu agree well with experiment and other theoretical values. Simulated EXAFS of Cu and its Fourier transform magnitude using our calculated pressure-induced change in the 1st shell are found to be in a reasonable agreement with those using X-ray diffraction (XRD) experimental results.     

Restricting the High-Temperature Growth of Nanocrystalline Tin Oxide

The sensitivity of tin oxide is dependent on various factors, one of which is the grain size. Three methods have been investigated with the aim of stabilising the grain size in the nanometer range, namely; (i) encapsulation within a silica matrix, (ii) coating the crystallites with hexamethyldisilazane and (iii) pinning the grain boundaries with a second metal oxide nanocrystal. The resulting materials have been characterised by X-ray powder diffraction (XRPD), Extended X-ray absorption fine structure (EXAFS) and conductivity measurements.     

Structural and magnetic properties of FeB microfibers

Structural and magnetic properties of FeB microfibers, obtained by electroless deposition on cellulose fibers, were investigated. X-ray diffraction (XRD) showed the presence of an amorphous phase. Extended X-ray absorption fine structure spectroscopy (EXAFS) studies confirmed an amorphous-like structure with the nearest coordination numbers around Fe atom to be 8.7 for Fe and 3.5 for B. The magnetic moment of 2.12 Bohr magnetons/Fe atom is consistent with composition obtained from EXAFS measurements. PACS 61.43.Dq; 61.10.Ht; 75.70.-i; 61.10.Eq; 81.15.Pq     

Investigation of PdZn nanoparticle formation upon the thermal decomposition of acetate precursors by in situ XRD and XAFS

The formation of metal or metal-oxide nanoparticles from four different precursor systems, including palladium(II) acetate, zinc(II) acetate, their 1: 1 mechanical mixture and the palladium-zinc bimetallic acetate complex PdZn(OCOMe)₄(H₂O), upon heating in a He + 5% H₂ atmosphere is studied using the X-ray diffraction and EXAFS (Extended X-ray absorption fine structure) techniques in the in situ mode. X-ray diffraction is primarily used to monitor changes in the phase composition of the samples. At specific moments when qualitative changes in the composition occur, EXAFS spectra at the K-edges of Pd and Zn are also measured. Using a combination of these two techniques, a detailed sequence of the phase transformations in each of the four precursor systems is revealed. It is found that the bimetallic acetate complex and the mixture of two monometallic acetates undergo chemical reduction to form zerovalent palladium under milder conditions than zinc acetate. However, the formation of a PdZn alloy from the mixture of metal acetates proceeds with a significant diffusion barrier.     

实验室EXAFS测量中单色器晶体二级衍射的应用

本文研究了实验室EXAFS测量中,应用单色器晶体二级衍射的有关问题,当测定的能量范围内,X射线连续谱上存在杂质发射线时,将导致测定吸收谱精细结构的畸变,研究了对这种谱线畸变进行修正的方法,并对采用晶面二级衍射测定时,EXAFS谱振幅降低的情况下如何求得正确的结构参数进行了讨论。 关键词：     

XRD AND EXAFS INVESTIGATION OF THE DECOMPOSITION OF Co-Cu SOLID SOLUTION PREPARED BY MELT SPINING

High solid-solubility Co₁₅Cu₈₅ alloys were prepared by melt spining and then submitted to isothermal and anisothermal annealing to obtain granular alloys. The synchrotron radiation X-ray diffraction patterns and extended X-ray absorption fine structure (EXAFS) spectra were measured to investigate the decomposition of supersaturated solid solution upon annealing. Experimental results indicated the precipitation of ultrafine Co-rich particles occurred at about 500℃ and the annealing had a great influence on the middle-range order of Co atoms. While the fitted EXAFS spectra showed that the interfaces of Co precipitates seem to be enriched with vacancy-type defects, leading to distorted interfaces.     

Microstructural properties and local atomic structures of cobalt oxide nanoparticles synthesised by mechanical ball-milling process

In this study, facile preparation of pure and nano-sized cobalt oxides particles was achieved using low-cost mechanical ball-milling synthesis route. Microstructural and morphological properties of synthesised products were characterised by X-ray diffraction (XRD) and transmission electron microscopy (TEM) techniques. XRD results indicated that the fabricated samples composed of cubic pure phase CoO and Co₃O₄ nanocrystalline particles with an average crystallite size of 37.2 and 31.8 nm, respectively. TEM images showed that the resulting samples consisted of agglomerates of particles with average diameter of about 37.6 nm for CoO and 31.9 nm for Co₃O₄. Phase purity of the prepared samples was further investigated due to their promising technological applications. Local atomic structure properties of the prepared nanoparticles were probed using synchrotron radiation-based X-ray absorption spectroscopy (XAS) including X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS). EXAFS data analysis further confirmed the formation of single-phase CoO and Co₃O₄ nanoparticles. In addition, structural properties of cobalt oxide nanoparticles were investigated by performing density functional theory calculations at B3LYP/TZVP level and Born–Oppenheimer molecular dynamics. Theoretical calculations for both prepared samples were found to be consistent with the experimental results derived from EXAFS analysis. Obtained results herein reveals that highly crystalline and pure phase CoO and Co₃O₄ nanoparticles can be synthesised using simple, inexpensive and eco-friendly ball-milling method for renewable energy applications involving fuel cells and water splitting devices.     

Local surrounding of Mn in LaMn1−xCoxO3 compounds by means of EXAFS on Mn–K

A systematic study of LaMn_1?xCo_xO₃ perovskite series by means of X-ray absorption spectroscopy in the extended X-ray absorption fine structure (EXAFS) range of the K-absorption edge of Mn is reported. The Mn–K edge absorption measurements in the EXAFS region were performed to study the local surrounding of Mn ions. Polycrystalline powder samples of LaMn_1?xCo_xO₃ (x=0, 0.02; 0.2; 0.4; 0.5; 0.6; 0.8) prepared by solid-state reaction were used. The EXAFS spectra were analyzed with the FEFF8 computer program. The Mn–O distances of Mn to the nearest oxygen surroundings were evaluated for the samples in the series and compared with the Co–O distances obtained by EXAFS in V. Procházka et al., JMMM 310 (2007) 197 and with results of X-ray powder diffraction in C. Autret, J. Phys. Condens. Matter 17 (2005) 1601.     

Local order and structural transitions in the molecule-based layer ferrimagnet (n-C4H9)4N FeFe(C2O4)3

Local structural order and temperature-dependent structural variation have been studied in the molecular-based layer ferrimagnet (n-C₄H₉)₄N Fe^IIFe^III(C₂O₄)₃ by EXAFS and high resolution X-ray powder diffraction. The EXAFS spectra measured at the Fe K-edge are successfully modelled by successive O, C, O and metal shells, showing that even when there is extensive structural disorder due to stacking faults, the local structural order in this class of ferrimagnets is fully retained. In this salt, which shows remarkable negative magnetisation at low temperature (Néel class Q), the EXAFS Debye-Waller factor has a discontinuity at 40 K, corresponding to one found in the magnetisation. At the same temperature there is also a change in the expansion of the lattice as evidenced by the high resolution X-ray powder diffraction.     

The characterization of EuO nanocrystals using synchrotron light

We have studied the physical structure, optical property, electronic band structure and atomic structure of europium oxide (EuO) nanocrystals. The physical structures of nanocrystals are confirmed by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The optical property and electronic band structure are studied by X-ray absorption near-edge structure (XANES) measurement. We have also investigated the L₃-edge energy of europium(II) ion by extended X-ray absorption fine structure (EXAFS) measurement, which clarified the atomic structure of europium oxide nanocrystals.     

LaFe1－xCrxO3系列氧化物的EXAFS研究

采用固相反应法, 制备了钙钛矿结构氧化物LaFe_1－xCr_xO₃较宽范围内(x=0.0—0.7)的系列单相样品, 并测量了各样品的X射线衍射谱(XRD)和扩展X射线吸收精细结构(EXAFS)谱. 通过对XRD的分析样品均为钙钛矿结构正交相, 同时晶格常数随着掺杂量x的增加而减小. 通过对EXAFS的分析和研究得到在LaFe_1－xCr_xO₃氧化物中Fe-O键长和Fe-La键长随掺杂浓度x的变化, 发现Fe-La键长发生比较大的变化, 说明La在体系掺杂中对结构的稳定起到重要作用.     

Structural investigations on an amorphous Se90Te10 alloy produced by mechanical alloying using EXAFS, cumulant expansion and RMC simulations

We investigated an amorphous Se(90)Te(10) alloy produced by mechanical alloying using two different approaches. First, we used extended x-ray absorption fine structure (EXAFS) spectroscopy and the cumulant expansion method using the Einstein model for the temperature dependence of the cumulants to obtain the cumulants C(*)(1), C(*)(2), and C(*)(3). From these, we found information about the structure of the alloy as well as the thermal and structural disorder, anharmonicity of the effective interatomic pair potentials, thermal expansion of the Se-Se and Se-Te bonds and asymmetry of the partial distribution functions g(Se-Se)(r) and g(Se-Te)(r). The cumulants C(*)(1), C(*)(2), and C(*)(3) also allowed us to reconstruct the g(EXAFS)(ij)(r,T) functions from EXAFS. Then, we made reverse Monte Carlo (RMC) simulations using the total structure factor S(K) obtained from synchrotron x-ray diffraction and the EXAFS oscillations χ(k) on the Se K edge as input data to obtain the g(RMC)(ij)(r) functions. Both methods furnished very similar g(ij)(r) functions, and the structural data obtained from them were also very similar. The results obtained from both methods showed the presence of Se-Te pairs indicating that there is alloying at the atomic level. In addition, we could not find any evidence of the presence of Te clusters in the alloy.     

Structural disorder in the paraelectric phase of the Fe<Subscript>3</Subscript>B<Subscript>7</Subscript>O<Subscript>13</Subscript>Br boracite

A structural model of the cubic paraelectric phase of a Fe₃B₇O₁₃Br crystal belonging to the boracite family has been developed using the data obtained by single-crystal X-ray diffraction with due regard for the results of extended X-ray absorption fine structure (EXAFS) spectroscopy. It has been shown that the best agreement between the data obtained by these two methods is achieved within a model assuming a disorder in the arrangement of both the Fe and Br atoms and a high degree of correlation of their displacements. It has been found that, during the phase transition from the rhombohedral ferroelectric phase to the cubic paraelectric phase, no significant transformation of the structure is observed on a local level. In this case, a change in the macroscopic symmetry occurs predominantly as a result of the variation in the set of possible spatial orientations of stable structural fragments, which is characteristic of order-disorder phase transitions.     

XANES and EXAFS in Cu-Ti and Ni-Zr glasses

X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) measurements have been done at the K-edge of Cu in Cu-Ti glasses and on the K-edges of Ni and Zr in Ni-Zr glasses using a synchrotron radiation source. The results are discussed in terms of the shape shift and intensity of the absorption edge as well as the principal absorption maximum. The values of bondlength calculated by the one-electron multiple scattering XANES theory as well as the graphical analysis EXAFS technique show good agreement.     

Radial-distribution function by EXAFS: Asymmetry in metallic glasses

Summary The authors discuss the information on the radial-distribution function (RDF) obtainable from EXAFS as compared with X-ray diffraction. The cases of Gaussian and non-Gaussian RDFs are illustrated showing how the Fourier transform (FT) of the experimental spectrum is connected with the RDF parameters in the two cases. The evidence of an asymmetric RDF in a metal glass, Fe₈₀B₂₀, is presented and discussed in detail. Paper presented at the Workshop on ?EXAFS Data Analysis in Disordered Systems?, held in Parma, October 5–7, 1981.     

遗传算法在EXAFS谱图解析中的应用

扩展Ｘ射线吸收精细结构（ＥＸＡＦＳ）谱是研究物质原子近邻结构和表面结构的有力工具。ＥＸＡＦＳ谱的解析通常采用标准样品比较法或最小二乘曲线拟合方法。但前者对标样的要求很高，而后者则参数初值难以确定，且结果有时不唯一。本文提出一种ＥＸＡＦＳ曲线拟合的新方法一遗传算法，并对单配位层Ｃｕ样品的ＥＸＡＦＳ谱图进行了解析，取得满意的结果。     

Optimization of Paris–Edinburgh press cell assemblies for in situ monochromatic X-ray diffraction and X-ray absorption

We describe some important improvements allowed by the development of new cell assemblies coupled to opposed conical sintered diamond anvils in the Paris–Edinburgh press. We provide X-ray absorption and diffraction experiments carried out at pressures up to 16.5 GPa. The maximum temperature reached was 1800 K for P<10 GPa and 1300 K for higher pressures. The sintered diamond anvils are X-ray transparent and give access to a much larger X-ray window than the tungsten carbide anvils, even at the highest pressure. Therefore, X-ray measurements are performed using in situ cross-calibration simultaneously. We also describe a new heating setup used to reach high temperatures, despite the low conductivity of the sintered diamond core by deviating the electrical current using copper strips. These improvements are illustrated by recent data collected using angle dispersive in situ X-ray diffraction on liquid Fe-18%wt S and using EXAFS at the barium K-edge on Ba₈Si₄₆ silicon clathrates and at the iodine K-edge on iodine-intercalated nanotubes.