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1.
Synthetic orthopyroxenes in the join enstatite-ferrosilite (Mg2Si2O6-Fe2Si2O6)have been studied by XANES with the aim to interpret the variations found in the spectra and evaluate the effects of the Mg-Fe substitution in the orthopyroxene(OPX) structure.The experimental Fe-and Mg-K edge XANES spectra show variations of the peaks intensity as a function of the chemical composition of the samples along the EN-FS join.In the region of the Fe edge,the intensity ratio between peak A and B(IB/IA)varies linearly(R=0.99) with the Mg/Fe substitution. Multiple scattering calculation have been performed both at the Fe and Mg K-edge,to study the geometrical modifications of the M1 and M2 octahedral sites induced by the Mg-Fe substitutions.The spectra,obtained locating Fe(or Mg)in both M1 and M2 and weighing the contributions using the occupancy data for the M1 and M2 sites determined by XRD,allow to discriminate the effects to the total spectrum due to Fe(Mg) located in each sites separately. 相似文献
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The Si L2,3 X-ray absorption near-edge structure(XANES) can be used to probe the local structure around Si and derive electronic information of the unoccupied s- and d-like partial density of states in nano-size SiO2.We present Si L2,3-edge for three different size silicates acquired by total electron yield(TEY) at the photoemission atation of Beijing Synchrotron Radiation Facility (BSRF).The Si L2,3-edge spectra are interpreted based on ab initio full multiple-scattering(MS) calculation.The Si L2,3-edge of nano-size materials has XANES similar to that of α-quartz.The similarities between the Si L2,3-edge shapes attest to a common molecular-orbital picture of their Si-O bonding and the same coordination state.However,a considerable broadening of Si L2,3-edge XANES spectra as decrease of particle size is also an indicative of polyhedral distortions. 相似文献
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ZiyuWu N.L.Saini A.Bianconi 《北京同步辐射装置》2001,(1):42-45
The HgBa2CuO4 δ superconductor has been studied by high resolution Hg L3 x-ray absorption near-edge structure(XANES)spectroscopy.The XANES spectrum has been simulated by full multiple-scattering calculations in order to xplore the origin of different features in the experimental spectrum.The experimental Hg L3-edge spectrum could be ewll reproduced by considering a cluster of 85 atoms,containing 10 shell,within a radius of about 7 A from the central Hg atom.The low energy spectral feature in the XANES spectrum is found to be due to aransition from the Hg p states to the electronic states hybridized with higher shell Ba atoms.This implies that the transition features in the Hg L3-edge XANES are strongly influenced by medium range order effects unlike the case of L3 edge of 3d transition metals where short-range order is enough to describe the main transition feansition featrues. 相似文献
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The pre-edge features in system with “even” symmetry,apart from quadrupolar tranition contribution,are mainly dipolar in character,associated with the existence of unoccupied states made up of mixed cation np with higher-neighboring cation-(n-l)d orbitals,and reflect the density of states due to the medium-range order of the system,while in “ood” symmetry materials these pre-edge features are the result of a transition from the 1s to final denisty of states of p symmetry due to an unsymmetrical mixing of the ligand wave functions with the central cation d orbitals.In the latter case,they contain not only the p but also the d base of orbitals,similar to a tetrahedral configuration.These results are validated for Fe as a photoabsorber by comparing x-ray absorption near-edge spectra of Fe2SiO4(fayalite) and Fe2O3(hematite) to ab initio full multiple scattering calculations at the Fe K edge,but pertain to all systems containing sixfold-coordinated cations. 相似文献
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Variation of electronic structure at the Fermi level in superconducting LaRu2 intermetallic system has been studied by X-ray absorption near edge structure(XANES) spectroscopy.The high resolution Ru K-edge XANES have been measured by fluorescence yield method using multi-element solid state detector assembly allowing to reach a signal to noise ratio of the order of △α/α-10^-4.The results show decrease of the superconducting transition temperature.2001 Elsevier Science B.V.All rights reserved. 相似文献
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利用X射线近边吸收谱对Fe2P,Ni2P及其掺杂物(Fe1-xNix)2P(x=01,025,05)中Fe,Ni,P的K边进行了研究.结合多重散射理论近边计算,讨论了金属原子不同位置格点3f,3g对近边谱特征的贡献,得出当Ni原子取代Fe原子时将优先占据Fe(3f)格点位置;根据第一性原理对能态的计算发现,不考虑磁性时不同格点P的pDOS未占据态电子结构与P-K近边吸收谱实验相符合;与考虑铁磁性Fe2P 的DOS相比较后结果显示Fe2P的磁性主要来源于Fe(3g)格点,铁磁性Ni2P计算的Ni不同格点原子磁矩均接近于0,与它一般显顺磁性结论相一致.
关键词:
X射线近边吸收谱
电子结构
多重散射理论
态密度 相似文献
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Improvement of dielectric (Ba,Sr)TiO3 thin tunability and loss tangent of films with K doping
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Ba0.6Sr0.4 TiO3 thin films doped with K were deposited on Pt/Ti/SiO2 /Si substrates by the chemical solution deposition method. The structure, surface morphology and the dielectric and tunable properties of Ba0.6Sr0.4 TiO 3 thin films have been studied in detail. The K content in Ba0.6Sr0.4TiO3 thin films has a strong influence on the material’s properties including surface morphology and the dielectric and tunable properties. It was found that the Curie temperature of K-doped Ba0.6Sr0.4 TiO3 films shifts to a higher value compared with that of undoped Ba0.6Sr0.4TiO3 thin films, which leads to a dielectric enhancement of K-doped Ba0.6Sr0.4 TiO3 films at room temperature. At the optimized content of 0.02 mol, the dielectric loss tangent is reduced significantly from 0.057 to 0.020. Meanwhile, the tunability is enhanced obviously from 26% to 48% at the measured frequency of 1 MHz and the maximum value of the figure of merit is 23.8. This suggests that such films have potential applications for tunable devices. 相似文献
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A series of (La_{1-x}Tb_x)_{2/3}Sr_{1/3}MnO_3 polycrystalline samples has been studied by means of x-ray diffraction, magnetostriction, and thermal expansion measurements. It has been found that this series undergoes a phase transition from a rhombohedral to an orthorhombic form at the doping level x≈0.20 at room temperature accompanied by an anisotropic magnetostriction up to -50×10^{-6} under a magnetic field of 1T. The linear and volume magnetostrictions vary with chemical composition, even change sign. At T=80K, the magnetostrictions for the samples of x=0.20 and 0.40 exhibit different behaviours. The sample of x=0.20 has positive volume and linear magnetostrictions and a negative anisotropic magnetostriction, while the sample of x=0.40 has an opposite behaviour. The magnitude of volume magnetostriction for both the samples is essential (~10^{-4}) at T=80K under a magnetic field of 4T. We conclude that these anomalous effects are due to the charge delocalization and the structural phase transition between orthorhombic and rhombohedral forms induced by the applied magnetic field. 相似文献
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采用固相反应法, 制备了钙钛矿结构氧化物LaFe1-xCrxO3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LaFe1-xCrxO3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. 相似文献
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MinhuaJiang YuliaTian JianhuaJiang WanxiaHuang JiyangWang Xiao 《北京同步辐射装置》2001,(2):131-137,
Pure and neodymium-doped gadolinium calcium oxoborate crystals of high quality were grown by the Czochralski method.The orientation of crystal was precisely determined,and the samples for measurements were prepared.Through synchrotron x-ray topography and high-resolution x-ray diffractometry,the twin structure was discovered.Some properties such as the figure of merit value,and dielectric,piezoelectric,and elastic constants were meausured along with a discussion of the anisotropy of the laser properties. 相似文献
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利用X射线近边吸收谱对Fe2P,Ni2P及其掺杂物(Fe1-xNix)2P(x=0.1,0.25,0.5)中Fe,Ni,P的K边进行了研究.结合多重散射理论近边计算,讨论了金属原子不同位置格点3f,3g对近边谱特征的贡献,得出当Ni原子取代Fe原子时将优先占据Fe(3f)格点位置;根据第一性原理对能态的计算发现,不考虑磁性时不同格点P的pDOS未占据态电子结构与P-K近边吸收谱实验相符合;与考虑铁磁性Fe2P的DOS相比较后结果显示Fe2P的磁性主要来源于Fe(3g)格点,铁磁性Ni2P计算的Ni不同格点原子磁矩均接近于0,与它一般显顺磁性结论相一致. 相似文献
15.
Structures and luminescence properties of Yb3+ in the double perovskites Ba2YB'O6 (B'=Ta5+, Nb5+) phosphors
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The Yb3+ doped Ba2YB'O6 (B'=Ta5+, Nb5+) were prepared by high temperature solid-state reaction method, their structures were determined by x-ray diffraction and refined by Rietveld method. The diffuse reflection absorption, excitation and emission spectra of Yb3+:Ba2YB'O6 (B'=,Ta5+, Nb5+) were measured at room temperature. Under the excitation of ultraviolet light, these phosphors exhibit broad charge transfer band emissions of TaO6 or NbO6 centre with large Stokes shift. The Yb3+ doped into these hosts are situated at Y3+ sites of cubic symmetry (Oh). The experimental energy levels of Yb3+ in Ba2YTaO6 and Ba2YNbO6 were determined by photoluminescence and diffuse reflection absorption spectra. Their wavefunctions and theoretical energy levels were obtained by diagonalising the Hamiltonian matrix. The experimental energy levels were fitted by Levenberg--Marquardt iteration algorithm to determine crystal field parameters. Then, the magnetic-pole transition line strengths of Yb3+:Ba2YB'O6(B'=Ta5+, Nb5+) from (2F5/2)Γ8- to the low-energy states were calculated. 相似文献