EXAFS and cumulant expansion studies of an amorphous Se90P10 alloy produced by mechanical alloying

We investigated the local atomic order of an amorphous Se₉₀P₁₀ alloy produced by Mechanical Alloying through EXAFS measurements on Se K edge at five temperatures followed by a cumulant expansion analysis. We obtained a lot of structural information such as average coordination numbers and interatomic distances, structural and thermal disorder, asymmetry of the pair distribution functions g_ij(r), anharmonicity of the interatomic potential, thermal expansion and Einstein and Debye temperatures for the Se-Se and Se-P pairs. We also reconstructed the g_ij(r) functions for the Se-Se and Se-P pairs at the temperatures investigated.     

Structural, vibrational and optical studies on an amorphous Se90P10 alloy produced by mechanical alloying

We investigated some physicochemical properties of an amorphous Se(90)P(10) alloy produced by mechanical alloying through x-ray diffraction, Raman spectroscopy, optical absorption spectroscopy and EXAFS techniques. The total structure factor obtained from x-ray diffraction and the EXAFS χ(k) oscillations on the Se K edge were used in reverse Monte Carlo simulations to obtain structural information such as average coordination numbers and interatomic distances and the distribution of structural units present in the alloy. In addition, we also determined the vibrational modes and the optical band gap energy of the alloy.     

EXAFS and XRD studies of an amorphous Co57Ti43 alloy produced by mechanical alloying

We have investigated the local atomic order of an amorphous Co₅₇Ti₄₃ alloy produced by mechanical alloying by means of x-ray diffraction and EXAFS analyses on Co and Ti K-edges. Average coordination numbers and average interatomic distances between first neighbors where found from EXAFS and compared with those determined using an additive hard sphere (AHS) model associated with an deconvolution, and also with data from bcc- Co₂Ti compound. EXAFS results obtained indicated a shortening in the Co-Ti and Ti-Ti average interatomic distances when compared to those found by using the AHS-RDF method and an increase in the Co-Co and Ti-Ti average interatomic distances and a shortening in the Co-Ti one when compared to the interatomic distances found in the bcc- Co₂Ti compound. In spite of these differences, average coordination numbers obtained from EXAFS and AHS-RDF are similar to each other and also to those found in bcc- Co₂Ti.     

Thermal and optical studies of an amorphous InSe9 alloy produced by mechanical alloying

In this paper we investigated thermal and optical properties of an amorphous alloy of the In–Se system. The amorphous InSe₉ alloy was produced by mechanical alloying and it was studied using Differential Scanning Calorimetry and microPhotoluminescence spectroscopy techniques, and from them several properties, such as glass transition and crystallization temperatures and energies and the optical gap energy were determined and compared to the values found in other alloys of the In–Se system. This comparison revealed some differences among our alloy produced by mechanical alloying and alloys produced by other techniques, which is a clear indication of the influence of the fabrication technique in their physical properties. The main differences occur in the activation energies associated with the glass transition and crystallization processes and also in the optical gap energy.     

Reverse Monte Carlo simulations and Raman scattering of an amorphous GeSe4 alloy produced by mechanical alloying

The short and intermediate range order of an amorphous GeSe₄ alloy produced by Mechanical Alloying were studied by Reverse Monte Carlo simulations of its X-ray total structure factor and Raman scattering. The simulations were used to compute the , and partial distribution functions and the , and partial structure factors. We calculated the coordination numbers and interatomic distances for the first and second neighbors. The data obtained indicate that the structure of the alloy has important differences when compared to alloys prepared by other techniques. There are a high number of Se-Se pairs in the first shell, and some of the tetrahedral units formed seemed to be connected by Se-Se bridges.     

Comparison among the local atomic order of amorphous TM-Ti alloys (TM = Co,Ni, Cu) produced by mechanical alloying studied by EXAFS

We have investigated the local atomic structure of amorphous TM-Ti alloys (TM = Co, Ni, Cu) produced by Mechanical Alloying by means of EXAFS analyses on TM and Ti K-edges. Coordination numbers and interatomic distances for the three alloys where found and compared. EXAFS results obtained indicated a shortening in the unlike pairs TM-Ti as the difference between d electrons of TM and Ti atoms increases, suggesting an increase in the chemical short range order (CSRO) from TM = Co to Cu.Received: 12 October 2003, Published online: 9 April 2004PACS: 61.43.Dq Amorphous semiconductors, metals, and alloys - 61.10.Ht X-ray absorption spectroscopy: EXAFS, NEXAFS, XANES, etc. - 81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation     

Comparative study using MS and XRD of Fe80Al20 alloy produced by mechanical alloying

An X-ray diffraction and 57Fe M ssbauer effect study of mechanically alloyed Fe 80 Al 20 is presented. X-ray measurements indicate that the disordered bcc α-Fe(Al) solid solution was formed after 2 h of milling, while the analysis of M ssbauer spectra suggested that total dissolution of aluminium is achieved after 10 h of milling. These differences can be attributed to: (i) rapid nanocrystallization of aluminium and/or (ii) small particles with small amounts of aluminium cannot be detected by the X-ray diffraction technique.     

Spectroscopic analysis,AIM, NLO and VCD investigations of acetaldehyde thiosemicarbazone using quantum mechanical simulations

The prepared Acetaldehyde thiosemicarbazone (ATSC) have been investigated by both the experimental and theoretical methods; through this work, the essentiality of elucidation of molecular fragments source linear and non-linear optical properties was explored. The stability of the structure and entire calculations have been performed on HF and B3LYP methods with 6-311++G(d,p) level of basis set. The Mulliken charge profile, electronic, optical and hyper polarizability analyses have been carried out in order to evaluate nonlinear optical (NLO) performance of the present compound. The exact optical location of the ATSC was determined by executing UV–Visible calculations on TDSCF method. The existence of the molecular group for the inducement and tuning of NLO properties were thoroughly investigated by performing fundamental vibrational investigation. The optical energy transformation among frontier molecular levels has been described in UV–Visible region. The Gibbs energy coefficient of thermodynamic functions was monitored in different temperature and it was found constant irrespective of temperatures. The appearance of different chemical environment of H and C was monitored from the ¹H and ¹³C NMR spectra. The vibrational optical polarization characteristics with respect to molecular composition in the compound have been studied by VCD spectrum. The bond critical point, Laplacian of electron density, electron kinetic energy density and total electron energy density have calculated and analysed using AIM study.     

Preparation and Mössbauer study of a new Fe-rich amorphous alloy,Fe90Sc10

A new amorphous metal-metal alloy Fe₉₀Sc₁₀ has been prepared by single roller melt quenching. Mössbauer spectra above and below the magnetic ordering temperature of 99K have been analysed in terms of distributions of magnetic hyperfine fields and quadrupole splittings.     

Simultaneous variations of microstructure and magnetic properties of Ni58Fe12Zr20B10 nanostructure/amorphous alloy prepared by mechanical alloying

This study aims to evaluate magnetic and micro-structural properties of amorphous/nanocrystalline mechanically alloyed Ni₅₈Fe₁₂Zr₂₀B₁₀ powders with ball-milling time up to 190 h. Structural, micro-structural and thermal evaluations of the milled powders were carried out by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM) and differential scanning calorimetry (DSC) methods. Magnetic properties were also measured by a vibrating sample magnetometer (VSM) instrument. Results showed that the amorphous phase reached maximum value of 95% and the crystallite size was about 3 nm at the end of the milling. Magnetization saturation (M_s) decreased slightly and coercivity (H_c) reached to the highest value at 72 h of the milling time. At the 190 h of milling, the coercivity and saturation magnetization reached 18 Oe and 20 emu/g, respectively. While, after an appropriate amount of heat treatment, these two variables became approximately 2 Oe and 32 emu/g.     

Synthesis, characterization, and microwave absorption properties of Fe-40 wt%Ni alloy prepared by mechanical alloying and annealing

Fe-40 wt%Ni alloys with granular shape and flake shape were prepared by a mechanical alloying (MA) and annealing method. The phase composition and morphology of the FeNi alloys, electromagnetic parameters, and microwave absorbing properties of the silicone rubber composite absorbers filled with the as-prepared FeNi alloy particles were characterized using X-ray diffraction (XRD), scanning electron microscope (SEM) and vector network analyzer. The XRD results indicate that the crystalline structures of the Fe-40 wt%Ni alloys prepared by both one-step and two-step MA processes are face-centered cubic (fcc) Ni (Fe) solid solutions, and the structures can be retained after annealing at 600 °C for 2 h. SEM images show that the FeNi alloy powders for one-step process have a granular shape; however the particles turned into flake form when they were sequentially milled with absolute ethyl alcohol. With the increase in thickness of composite absorber, the reflection loss (RL) decreases, and the peak for minimum reflection loss shifts towards the lower frequency range. Compared to the absorbers filled with the granular FeNi alloy, the absorbers filled with flaky FeNi alloys possess higher complex permittivities and permeabilities and have a lower RL and peak frequency under the same thickness. Microwave absorbing materials with a low reflection loss peak in the range of 1-4 GHz are obtained, and their microwave absorbing properties can be adjustable by changing their thicknesses.     

Structural analysis of Cu(In,Ga)Se2 films fabricated by using sputtering and post-selenization

We made Cu(In,Ga)Se₂ (CIGS) films by using sputtering and post-selenization. First, we deposited stacked metallic films by using the sputtering method and then carried out post-selenization for the precursor stacked metals with different amounts of Se powder, 0.160 g, 0.321 g, 0.642 g, and 0.964 g. We found that with a small amount of Se, separated CuInSe₂ and CuGaSe₂ layers were formed, which was confirmed by X-ray diffraction (XRD), Raman spectroscopy, and energy-dispersive X-ray analysis. For larger Se amounts, the CIGS phase was observed in the results of XRD and Raman spectroscopy. These results indicate that the amount or the partial pressure of Se plays an important role in the reaction kinetics for stacked precursor metals to form the CIGS phase.     

Changes of thermal, mechanical and magnetic properties of an amorphous Fe80Cr5B15 alloy during magnetic and structural phase transitions

Thermal, mechanical and thermomagnetic properties associated with the magnetic and structural transition of an amorphous Fe₈₀Cr₅B₁₅ alloy are described. The investigation was carried out in a simultaneous dilatometric and thermomagnetic experiment. An anomaly of the thermal expansion coefficient at the Curie point and a change in mechanical properties just before the onset of crystallization are observed. The results are compared with the thermal behavior obtained by differential scanning calorimetry.     

X-ray diffraction,microstructure, Mössbauer and magnetization studies of nanostructured Fe50Ni50 alloy prepared by mechanical alloying

Nanocrystalline Fe₅₀Ni₅₀ alloy samples were prepared by the mechanical alloying process using planetary high-energy ball mill. The alloy formation and different physical properties were investigated as a function of milling time, t, (in the 0–50 h range) by means of the X-ray diffraction (XRD) technique, scanning electron microscopy (SEM), energy dispersive X-ray (EDAX), Mössbauer spectroscopy and the vibrating sample magnetometer (VSM). The complete formation of γ-FeNi is observed after 24 h milling. When milling time increases from 0 to 50 h, the lattice parameter increases towards the Fe₅₀Ni₅₀ bulk value, the grain size decreases from 67 to 13 nm, while the strain increases from 0.09% to 0.41%. Grain morphologies at different formation stages were observed by SEM. Saturation magnetization and coercive fields derived from the hysteresis curves are discussed as a function of milling time.     

Structural and optical properties of Cu2ZnSn(S,Se)4 films obtained by magnetron sputtering of a Cu2ZnSn alloy target

Results of the study of structural and optical properties of Cu₂ZnSn(S,Se)₄ thin films obtained by sulfitation (selenization) of Cu₂ZnSn films which were sputtered by target direct current magnetron sputtering using a stoichiometric Cu₂ZnSn (99.99%) target are presented. It has been found that Cu₂ZnSn(S,Se)₄ thin films are polycrystalline with a grain size of ~60 nm. The optical bandgap of Cu₂ZnSnS₄ (E ^op _g = 1.65 eV) and Cu₂ZnSnSe₄ (R ^op _g = 1.2 eV) thin films have been determined.

     

Research on Zr50Al15−xNi10Cu25Yx amorphous alloys prepared by mechanical alloying with commercial pure element powders

Amorphous Zr₅₀Al_15−xNi₁₀Cu₂₅Y_x alloy powders were fabricated by mechanical alloying at low vacuum with commercial pure element powders. The effects on glass forming ability of Al partial substituted by Y in Zr₅₀Al₁₅Ni₁₀Cu₂₅ and thermal stability of Si₃N₄ powders addition were investigated. The as-milled powders were characterized by X-ray diffraction, scanning electron microscopy and differential scanning calorimeter. The results show that partial substitution of Al can improve the glass forming ability of Zr₅₀Al₁₅Ni₁₀Cu₂₅ alloy. Minor Si₃N₄ additions raise the crystallization activation energy of the amorphous phase and thus improve its thermal stability.     

The behaviour of carbon species produced by CO disproportionation on Ru(1, 1, 10) and Ru(001) surfaces

The behaviour of adsorbed CO on Ru(001) flat and Ru(l,1,10) stepped surfaces in the CO pressure range between 10^?6 and 10¹ Pa has been investigated by TDS, AES, LEED and UPS. The disproportionation of CO proceeds rapidly on the stepped surface and its apparent activation energy was obtained to be 20 kJ mol^?1 at nearly zero coverage. The carbon species produced by CO disproportionation show non-uniform reactivity with ¹⁸O₂ and provide four CO desorption peaks in TPR spectra, which are assigned to α-C¹⁸O,ß-C¹⁸O and those derived from carbidic and graphitic carbons. At smaller carbon coverage, only α-CO and β-CO were observed, but with increasing coverage the amount of ß-CO reaches a maximum and carbidic carbon is newly formed. Further increase of carbon deposition gives graphitic carbon. The conversion from carbidic to graphitic carbon and the dissolution into the bulk took place upon heating to 1000 K. It is remarkable that very active carbon species are converted to molecular CO through the reaction with O₂ even at low temperature such as 200 K. It was also confirmed that active carbon species are formed on Ru surface during COH₂ reaction.     

Effect of carbon content on structure and magnetic properties for (Fe,Ni)1−xCx by mechanical alloying

FCC (Fe₅₅Ni₄₅)_1−xC_x   supersaturated solid solution was prepared in a wide concentration range (0?x?0.9)$(0?x?0.9)$ by mechanical alloying of nanocrystalline Fe₅₅Ni₄₅ with graphite. The lattice constant of Fe₅₅Ni₄₅ increases linearly with increasing carbon content up to x=0.25$x=0.25$. At the same time, it is found that the magnetic moment per metal atom (Fe, Ni) decreases linearly with increasing carbon content for 0?x?0.25$0?x?0.25$ with a slope of 1.2 μ_B/at. For high carbon content, x?0.5$x?0.5$, it is observed that the decrease of lattice constant and increase of moment per metal atom (Fe, Ni) with increasing C content, indicates that the dissolution of carbon is hindered by the high-volume fraction of graphite in the initial powder mixture. The complete amorphization of x=0.5$x=0.5$ does not occur after the extended ball milling. The alloying effect of carbon on the magnetization is compared with other metalloid B, P, and Si in Fe- and Ni-based binary system.     

EPR, X-ray, and magnetization studies of metastable alloys Ti2Fe, Al40Cu10Mn25Ge25 and Al65Cu20Fe15 as prepared by mechanical alloying

Mechanical alloying (MA) technique has been used to synthesize metastable alloys with nominal compositions Ti₂Fe (MA for 1, 5, and 26 h), Al₆₅Cu₂₀Fe₁₅ (MA for 26 and 34 h) and Al₄₀Cu₁₀Mn₂₅Ge₂₅ (MA for 42 h). These have been studied by EPR, X-ray diffraction, differential thermal analysis (Ti₂Fe only), and magnetization (Ti₂Fe only) techniques. X-ray diffraction provided information on transformation to metastable phases, while the EPR spectra gave insight into inequivalent paramagnetic transition metal sites in the alloys and the temperature variation of magnetic ordering of the samples. Magnetization data on Ti₂Fe system has been interpreted in terms of phase separations within the amorphous phase. It is concluded that MA process significantly influences the magnetic properties of the samples, wherein the duration of MA process plays an important role. The EPR and magnetization data indicate that the disorder of paramagnetic ions within the samples increases with increasing temperature.