The role of quenched‐in vacancies for the decomposition of aluminium alloys

The very early stages of decomposition during room temperature storage, i.e. just a few minutes after quenching, are investigated by positron annihilation lifetime spectroscopy for both an AlMgSi alloy and an AlCuMg alloy. It turns out that by freezing the decomposition kinetics during measurements we can detect vacancy–solute atom pairs. The formation of larger solute clusters with structural vacancies is seen by an increase of the mean positron lifetime in the course of storage at room temperature (RT). Earlier findings concerning aging at RT were unable to discover this effect. The detected changes are interpreted in terms of cluster formation. Thus we show that positron annihilation spectroscopy (PAS) is one of the very few methods to access early stages of decomposition in metallic alloys. Moreover, the lower limit of the concentration of quenched‐in vacancy‐like defects is calculated to be at least 2 × 10^–5 per atom. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

机械合金化Fe100-xCux体系的X射线吸收精细结构研究

利用X射线吸收精细结构(XAFS)方法研究机械合金化制备的Fe_100-xCu_x(x=0,10,20,40,60,70,80,100,x为原子百分比)合金中Fe和Cu原子的局域环境结构.对于Fe_100-xCu_x(x≥40)二元混合物,球磨160h后,Fe原子的近邻配位结构从bcc转变为fcc,但Cu原子的近邻结构保持其fcc不变.与之相反,在Fe₈₀Cu₂₀和Fe₉₀Cu₁₀(x≤20)合金中,Fe原子的近邻配位保持其bcc结构而Cu原子的近邻配位结构从fcc转变为bcc结构.XAFS结果还表明,fcc结构的Fe_100-xCu_x样品中Fe的无序因子σ(0.0099nm)比bcc结构的Fe_100-xCu_x中的σ(0.0081nm)大得多;并且在机械合金化Fe_100-xCu_x(x≥40)样品中Fe原子的σ(0.0099nm)比其Cu原子的σ(0.0089nm)大.这表明机械合金化Fe_100-xCu_x样品中Fe和Cu原子可以有相同的局域结构环境但不是均匀的过饱和固溶体,而是由Fe富集区和Cu富集区组成的合金.我们提出互扩散和诱导相变机理来解释在球磨过程中Fe_100-xCu_x合金产生从bcc到fcc和从fcc到bcc变化的结构相变 关键词： XAFS 100-xCu_x合金')" href="#">Fe_100-xCu_x合金 机械合金化     

New insights into the colour origin of archaeological Egyptian blue and green by XAFS at the Cu K‐edge

New results on the local chemical environment of Cu²⁺ in archaeological Egyptian blue and green and also modern Egyptian green were obtained by x‐ray absorption fine structure (XAFS) analysis. The information is essential for the understanding of the colouring mechanisms in both pigments. In a previous study, a clear physico‐chemical characterisation of Egyptian blue and green was achieved using a complementary analytical approach with ancient and modern synthesized pigments. Electron microscopy (SEM–EDX and TEM), x‐ray diffraction and micro‐Raman and UV–visible spectroscopy were used to gain information about the conditions of the ancient Egyptian fabrication processes and permitted the clear distinction of both pigments. However, the exact colouring mechanisms could not be elucidated by these methods. Different Cu‐bearing amorphous and crystalline phases were found in both pigments. These phases should be at the origin of the blue and turquoise colours. Using XAFS data at the Cu K‐edge, new insights into the origin of the colouring mechanisms of both pigments could be obtained from the precision of the Cu speciation. In Egyptian blue, Cu²⁺ is mainly allocated in a square‐planar site in a crystalline cuprorivaite phase, whereas in Egyptian green, Cu²⁺ is basically situated in a distorted octahedral site in an amorphous phase. Copyright © 2006 John Wiley & Sons, Ltd.     

Suppression of Bragg reflection glitches of a single‐crystal diamond anvil cell by a polycapillary half‐lens in high‐pressure XAFS spectroscopy

In combination with a single‐crystal diamond anvil cell (DAC), a polycapillary half‐lens (PHL) re‐focusing optics has been used to perform high‐pressure extended X‐ray absorption fine‐structure measurements. It is found that a large divergent X‐ray beam induced by the PHL leads the Bragg glitches from single‐crystal diamond to be broadened significantly and the intensity of the glitches to be reduced strongly so that most of the DAC glitches are efficiently suppressed. The remaining glitches can be easily removed by rotating the DAC by a few degrees with respect to the X‐ray beam. Accurate X‐ray absorption fine‐structure (XAFS) spectra of polycrystalline Ge powder with a glitch‐free energy range from ?200 to 800 eV relative to the Ge absorption edge are obtained using this method at high pressures up to 23.7 GPa, demonstrating the capability of PHL optics in eliminating the DAC glitches for high‐pressure XAFS experiments. This approach brings new possibilities to perform XAFS measurements using a DAC up to ultrahigh pressures.     

Study of solid-state reactions in Sm(Co,Fe, Cu,Zr)z 2:17-type alloys by means of in situ electrical resistivity measurements

In the present work, solid-state reactions in Sm₂(Co, Fe, Cu, Zr)₁₇-type alloys have been investigated by means of in situ electrical resistivity measurements. Changes in the electrical resistivity of a Sm(Co_0.74Fe_0.1Cu_0.12Zr_0.04)_8.5 alloy after solid solution treatment at 1190 °C, quenching to room temperature, and during isothermal ageing at temperatures between 400 and 900 °C, have indicated microstructural/phase changes occurring at temperatures below those commonly used for the development of high coercivity in Sm(Co, Fe, Cu, Zr)_z-type materials. Subsequent crystallographic and magnetic transition measurements have shown a high degree of correlation with respect to the changes observed in the electrical resistivity during isothermal ageing.     

A fast energy‐dispersive multi‐element detector for X‐ray absorption spectroscopy

In this paper results are presented from fluorescence‐yield X‐ray absorption fine‐structure spectroscopy measurements with a new seven‐cell silicon drift detector (SDD) module. The complete module, including an integrated circuit for the detector readout, was developed and realised at DESY utilizing a monolithic seven‐cell SDD. The new detector module is optimized for applications like XAFS which require an energy resolution of ～250–300 eV (FWHM Mn Kα) at high count rates. Measurements during the commissioning phase proved the excellent performance for this type of application.     

miXAFS: a program for X‐ray absorption fine‐structure data analysis

A new program called miXAFS for the analysis of X‐ray absorption fine‐structure (XAFS) data is presented. miXAFS can analyze the XAFS functions simultaneously for all measured X‐ray absorption edges of the constituent elements in a sample under the constraints for the structural parameters over the edges. The program provides a surface plot of the R‐factor as a function of two structural parameters, which is useful to validate the optimized structural parameters. The structural parameters can be obtained from the XAFS data in a few steps using the setting file and batch process. The program, which is coded in MATLAB and freely available, runs on Macintosh and Windows operating systems. It has a graphical user interface and loads experimental data and XAFS functions in a variety of ASCII data formats.     

Origin of tweed in Au–Cu–Al alloys

The premartensitic tweed in Au–Cu–Al alloys, contrary to previous thought that resort to defects, is confirmed to be associated with the coherent embryos of an intermediate phase (I phase) embedded in parent phase. The parent?→?I phase transformation temperature was measured by differential scanning calorimeter and dynamic mechanical analysers, which shifts from 82.3 to 557.6?°C depending on the alloy composition. X-ray diffraction and transmission electron microscopes (TEM) results show that the parent?→?I phase transformation is a charge density wave transition that cannot be suppressed even by melt-spun method, which shows obvious compositional inhomogeneity between I phase and parent. The results imply that the parent?→?I phase transition is a fast displacive transformation coupled with diffusion. Moreover, accompanying the parent?→?I phase transformation, alloys demonstrate diversified microstructure revealed by TEM observation, from tweed to chessboard nanowires or twins. These findings provide the experimental evidence for that parent?→?I phase transformation in Au–Cu–Al alloys is originated from pseudospinodal decomposition as theoretically predicted.     

Effects of Ag or Si on precipitation in the alloy Al-2.5 mass% Cu-1.5 mass% Mg

Calorimetric measurements and electron microscopy observations were performed on Al-2.5?mass% Cu-1.5?mass% Mg alloys containing also 0.4, 1 or 2% Ag or 0.5% Si, in order to improve understanding of the relationships between precipitation processes and age hardening. The analogous behaviour of calorimetric and hardness data confirms that the first hardening stage is initiated in all alloys by GPB zone formation which occurs via a nucleation and growth controlled mechanism. The vacancy-trapping effect of Mg is increased by Ag and Si additions and leads to slower precipitation kinetics. Consequently, refined GPB zones sizes are obtained leading to an increase in hardness with respect to the ternary alloy. During the second hardening stage, the formation of the more stable S′ phase increases the total amount of strengthening precipitates in the ternary alloy. Phases typical for binary Al–Cu alloys form additionally in the Si-containing alloy. In the Ag-bearing alloys, precipitation of the hardening X′ phase occurs the earlier the higher the Ag content; it is followed by S′ precipitation. During heating of the ternary alloy, the S′ phase forms after substantial dissolution of GPB zones and of the S′′ phase identified by high resolution electron microscopy; this contradicts the concept of a continuous precipitation sequence.     

Predicting XAFS scattering path cumulants and XAFS spectra for metals (Cu,Ni, Fe,Ti, Au) using molecular dynamics simulations

The ability of molecular dynamics (MD) simulations to support the analysis of X‐ray absorption fine‐structure (XAFS) data for metals is evaluated. The low‐order cumulants (ΔR, σ², C₃) for XAFS scattering paths are calculated for the metals Cu, Ni, Fe, Ti and Au at 300 K using 28 interatomic potentials of the embedded‐atom method type. The MD cumulant predictions were evaluated within a cumulant expansion XAFS fitting model, using global (path‐independent) scaling factors. Direct simulations of the corresponding XAFS spectra, χ(R), are also performed using MD configurational data in combination with the FEFFab initio code. The cumulant scaling parameters compensate for differences between the real and effective scattering path distributions, and for any errors that might exist in the MD predictions and in the experimental data. The fitted value of ΔR is susceptible to experimental errors and inadvertent lattice thermal expansion in the simulation crystallites. The unadjusted predictions of σ² vary in accuracy, but do not show a consistent bias for any metal except Au, for which all potentials overestimate σ². The unadjusted C₃ predictions produced by different potentials display only order‐of‐magnitude consistency. The accuracy of direct simulations of χ(R) for a given metal varies among the different potentials. For each of the metals Cu, Ni, Fe and Ti, one or more of the tested potentials was found to provide a reasonable simulation of χ(R). However, none of the potentials tested for Au was sufficiently accurate for this purpose.     

XAFS和XRD研究高能球磨对Fe70Cu30合金结构的影响

利用XRD和XAFS方法研究机械合金化Fe₇₀Cu₃₀二元金属合金随球磨时间的结构变化.XRD结果表明，球磨2 h后，部分金属Fe与Cu生成Fe-Cu合金；球磨20h后，金属Fe与Cu已完全合金化生成Fe-Cu合金，并只在2θ=44°处出现一个宽化的弱衍射峰，认为是在球磨20h后的Fe₇₀Cu₃₀合金中共存着fcc和bcc结构的Fe-Cu合金相.XAFS结果进一步表明，在球磨的初始阶段(2h)，fcc结构的Cu颗粒的晶 关键词： XAFS XRD 70Cu₃₀合金')" href="#">Fe₇₀Cu₃₀合金 机械合金化     

纳米超微晶Fe73.5Cu1Mo3Si13.5B9合金显微结构和磁性的研究

对纳米晶Fe_73.5Cu₁Mo₃Si_13.5B₉合金的原始制备态和各退火态样品进行了室温Mossbauer谱研究,结果表明晶化态的合金存在α-Fe(Si)微晶相和晶界的非晶相。晶相和非晶相内场和面积随退火温度的变化是退火时Cu,Mo,B等成分的扩散和在各相中的再分配引起的。最佳磁性能对应非晶相中的铁量占合金铁总量的30％左右,超微晶合金的双相无规各向异性模型表明,一定量的非晶相对保持纳米晶优异的软 关键词：     

Synthesis of homogeneous pentenary chalcopyrite alloys with a classical two-step growth process

Homogeneous single-phase Cu(In_0.75Ga_0.25)(Se_1−yS_y)₂ chalcopyrite alloys were prepared by a novel two-step growth process. CuIn_0.75Ga_0.25 precursors were deposited by DC magnetron sputtering and the subsequent reaction processes in a reactive H₂Se/Ar/H₂S atmosphere was optimized to prevent the formation and separation of stable ternary phases. X-ray diffraction (XRD) analysis of these films revealed characteristic chalcopyrite peaks with a high degree of symmetry, indicative of homogeneous rather than compositionally graded material. The lattice parameters of the single-phase Cu(In_0.75Ga_0.25)(Se_1−yS_y)₂ pentenary alloys decreased linearly with an increase in the S/(S+Se) ratio in accordance with Vegard's law. X-ray photoelectron spectroscopy (XPS) depth profiling confirmed the in-depth compositional uniformity of the pentenary alloys, prepared under optimized selenization/sulfurization conditions.     

XAFS spectra from X-ray fluorescence Kβ line using conventional energy-discriminating detector

X-ray fluorescence spectra of copper (Cu) metal, copper monoxide (CuO), and potassium chromate (K₂CrO₄) were recorded as a function of incident X-ray energy near the Cu K-edge and chromium (Cr) K-edge, respectively, using a conventional silicon drift detector. The spectra contained components due to elastic, inelastic, and multiple scattering, in addition to the Kα and Kβ lines. Cu and Cr K-edge X-ray absorption fine structure (XAFS) spectra of Cu, CuO, and K₂CrO₄ were obtained by an intensity analysis of the Kα and Kβ lines. The intensity of the Kβ line for the different incident photon energies was obtained by numerically removing the additional scattering components using the MUSCAT program. These spectra exhibited a jump near the K absorption edges, which reproduced the spectral features obtained in transmission mode for both Cu, CuO, and K₂CrO₄. A chemical shift was also clearly identified in the X-ray absorption near edges structure using the X-ray fluorescence Kβ line. In addition, the Cr K-edge extended XAFS spectrum of K₂CrO₄ was clearly observed using the Cr Kβ fluorescent line. The XAFS measurements on the Kα and Kβ lines are possible, and they carry equally valuable information.     

Growth mechanism of thermally processed Cu(In,Ga)S2 precursors for printed Cu(In,Ga)(S,Se)2 solar cells

We investigate a process used for the selenisation of particle‐based precursors to prepare low‐cost Cu(In,Ga)(S,Se)₂ (CIGS) solar cells. It is suitable for high throughput with a short optimum selenisation duration of 3–5 min and employs a rapid thermal annealing system with elemental selenium vapour. Homogeneous crack‐free Cu(In,Ga)S₂ precursor films of up to 1 µm are obtained via doctor blading. The high selenium vapour pressure in the selenisation reaction chamber results in the formation of a compact Cu(In,Ga)(S,Se)₂ layer on top of a carbon‐rich underlayer. In order to investigate the phase development in the film, the selenisation process was interrupted at different stages and the samples were monitored via XRD and surface‐sensitive Raman measurements. We find the formation of a polycrystalline Cu(In,Ga)Se₂ phase already after 1 s at the target temperature of 550 °C. Furthermore, the effect of initial precursor thickness on solar cell parameters is discussed. Complete solar cells are prepared by conventional methods, leading to conversion efficiencies well above 8%. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Characteristics of a tapered undulator for the X‐ray absorption fine‐structure technique at PLS‐II

An in‐vacuum undulator (IVU) with a tapered configuration was installed in the 8C nanoprobe/XAFS beamlime (BL8C) of the Pohang Light Source in Korea for hard X‐ray nanoprobe and X‐ray absorption fine‐structure (XAFS) experiments. It has been operated in planar mode for the nanoprobe experiments, while gap‐scan and tapered modes have been used alternatively for XAFS experiments. To examine the features of the BL8C IVU for XAFS experiments, spectral distributions were obtained theoretically and experimentally as functions of the gap and gap taper. Beam profiles at a cross section of the X‐ray beam were acquired using a slit to visualize the intensity distributions which depend on the gap, degree of tapering and harmonic energies. To demonstrate the effect of tapering around the lower limit of the third‐harmonic energy, V K‐edge XAFS spectra were obtained in each mode. Owing to the large X‐ray intensity variation around this energy, XAFS spectra of the planar and gap‐scan modes show considerable spectral distortions in comparison with the tapered mode. This indicates that the tapered mode, owing to the smooth X‐ray intensity profile at the expense of the highest and most stable intensity, can be an alternative for XAFS experiments where the gap‐scan mode gives a considerable intensity variation; it is also suitable for quick‐XAFS scanning.     

High‐accuracy X‐ray absorption spectra from mM solutions of nickel (II) complexes with multiple solutions using transmission XAS

A new approach is introduced for determining X‐ray absorption spectroscopy (XAS) spectra on absolute and relative scales using multiple solutions with different concentrations by the characterization and correction of experimental systematics. This hybrid technique is a development of standard X‐ray absorption fine structure (XAFS) along the lines of the high‐accuracy X‐ray extended range technique (XERT) but with applicability to solutions, dilute systems and cold cell environments. This methodology has been applied to determining absolute XAS of bis(N‐n‐propyl‐salicylaldiminato) nickel(II) and bis(N‐i‐propyl‐salicylaldiminato) nickel(II) complexes with square planar and tetrahedral structures in 15 mM and 1.5 mM dilute solutions. It is demonstrated that transmission XAS from dilute systems can provide excellent X‐ray absorption near‐edge structure (XANES) and XAFS spectra, and that transmission measurements can provide accurate measurement of subtle differences including coordination geometries. For the first time, (transmission) XAS of the isomers have been determined from low‐concentration solutions on an absolute scale with a 1–5% accuracy, and with relative precision of 0.1% to 0.2% in the active XANES and XAFS regions after inclusion of systematic corrections.     

Augmentation of the step‐by‐step Energy‐Scanning EXAFS beamline BL‐09 to continuous‐scan EXAFS mode at INDUS‐2 SRS

An innovative scheme to carry out continuous‐scan X‐ray absorption spectroscopy (XAS) measurements similar to quick‐EXAFS mode at the Energy‐Scanning EXAFS beamline BL‐09 at INDUS‐2 synchrotron source (Indore, India), which is generally operated in step‐by‐step scanning mode, is presented. The continuous XAS mode has been implemented by adopting a continuous‐scan scheme of the double‐crystal monochromator and on‐the‐fly measurement of incident and transmitted intensities. This enabled a high signal‐to‐noise ratio to be maintained and the acquisition time was reduced to a few seconds from tens of minutes or hours. The quality of the spectra (signal‐to‐noise level, resolution and energy calibration) was checked by measuring and analysing XAS spectra of standard metal foils. To demonstrate the energy range covered in a single scan, a continuous‐mode XAS spectrum of copper nickel alloy covering both Cu and Ni K‐edges was recorded. The implementation of continuous‐scan XAS mode at BL‐09 would expand the use of this beamline in in situ time‐resolved XAS studies of various important systems of current technological importance. The feasibility of employing this mode of measurement for time‐resolved probing of reaction kinetics has been demonstrated by in situ XAS measurement on the growth of Ag nanoparticles from a solution phase.     

Development of dispersive XAFS system for analysis of time‐resolved spatial distribution of electrode reaction

Apparatus for a technique based on the dispersive optics of X‐ray absorption fine structure (XAFS) has been developed at beamline BL‐5 of the Synchrotron Radiation Center of Ritsumeikan University. The vertical axis of the cross section of the synchrotron light is used to disperse the X‐ray energy using a cylindrical polychromator and the horizontal axis is used for the spatially resolved analysis with a pixel array detector. The vertically dispersive XAFS (VDXAFS) instrument was designed to analyze the dynamic changeover of the inhomogeneous electrode reaction of secondary batteries. The line‐shaped X‐ray beam is transmitted through the electrode sample, and then the dispersed transmitted X‐rays are detected by a two‐dimensional detector. An array of XAFS spectra in the linear footprint of the transmitted X‐ray on the sample is obtained with the time resolution of the repetition frequency of the detector. Sequential measurements of the space‐resolved XAFS data are possible with the VDXAFS instrument. The time and spatial resolutions of the VDXAFS instrument depend on the flux density of the available X‐ray beam and the size of the light source, and they were estimated as 1 s and 100 µm, respectively. The electrode reaction of the LiFePO₄ lithium ion battery was analyzed during the constant current charging process and during the charging process after potential jumping.     

三元Co-Cu-Pb偏晶合金的快速凝固组织形成规律研究

在自由落体条件下实现了三元Co-Cu-Pb合金的液相分离与快速凝固. 实验发现,随液滴直径减小,Co₅₁Cu₄₇Pb₂合金液滴发生由枝晶→两层壳核→枝晶组织的转变,Co₄₇Cu₄₄Pb₉合金液滴的组织形态由壳核组织演化为均匀组织. 两种合金的快速凝固组织均由α(Co),(Cu)和(Pb)固溶体三相组成,α(Co)和(Cu)相主要以枝晶方式生长,(Pb)相分布在(Cu)枝晶间. 关键词： 液相分离 偏晶合金 快速凝固 自由落体