Evolution Of Short-range Order Research Articles

Short-range order evolution in S-rich Ge–S glasses by X-ray photoelectron spectroscopy

The structure of binary Ge x S 100 − x chalcogenide glasses (10 < x < 30) is determined by high-resolution X-ray photoelectron spectroscopy (XPS). On the basis of compositional dependence of fitting parameters for Ge and S core level XPS spectra, the ratio between edge- and corner-shared tetrahedra is determined. It is shown that short-range order of these glasses includes fragments of high-temperature crystalline form of GeS 2. When subjected to X-irradiation, the structure of investigated glasses appears to become more homogeneous than that of the as-prepared samples.

Thermal evolution of short-range order in Cu–Hf-based amorphous alloys

A Perturbed Angular Correlation study on melt-spun Cu60Hf20Ti20 and Cu60Hf40 is presented. The influence of Ti addition on thermal stability and crystallization mechanism is followed by differential scanning calorimetry. The evolution of quadrupole parameters with measurement temperature is analyzed in both alloys in order to get insight into the crystallization process. Although an intricate crystallization mechanism is observed for the Ti containing alloy, the final stage is similar, irrespective of minority atom.

Structural and thermal properties of Cu–Hf–Ti ternary metallic glasses

Cu–Hf–Ti ternary metallic alloys were prepared by melt spinning. The thermal stability of the alloys with various Ti contents was studied by differential scanning calorimetry. The evolution of short range order with annealing treatment was also investigated by means of perturbed angular correlation. The results for the initial as-spun alloys indicate that the short range order can be described by a dense packing of atoms. The variation of electric field gradient with alloy composition is comparable to that previously observed in binary and multi-component Zr- and Hf-based amorphous alloys.

The Evolution of Short-Range Order in Ti-Hf-Ni Alloys with Hydrogenation

ABSTRACTThe evolution of the short-range order in a Ti-Hf-Ni 3/2 approximant phase, has been studied as a function of hydrogenation by means of extended X-ray absorption fine structure (EXAFS). The local structure of the non-hydrogenated alloy has been derived from that of 1/1 Ti-Zr-Ni. After hydrogenation, drastic changes are observed in the local structure of Ti-Hf-Ni. Preliminary results of the EXAFS analysis are also presented for an amorphous Ti-Hf-Ni alloy.

Equilibrium kinetics of short-range order formation in the ternary Au 40Ag 40Pd 20 alloy

The kinetics of short range order (SRO) were investigated in the ternary Au 40Ag 40Pd 20 alloy under equilibrium conditions using residual electrical resistivity measurements. The changes in electrical resistivity were measured during isothermal annealing experiments after producing small deviations from the SRO-equilibrium. The analysis of these measurements gives evidence of three kinetic processes involved in the evolution of SRO. The results obtained from the determined kinetic parameters were found to be in good agreement with the Yu–Lucke theory of kinetics of SRO-formation in multi-component alloys.

Mössbauer study of ball-milled Fe-Ge alloys

In this work the mechanical alloying of ${\mathrm{Fe}}_{100\ensuremath{-}x}{\mathrm{Ge}}_{x}$ was studied as a function of alloying composition $(9&lt;~x&lt;~40)$ processing time and annealing treatment. The alloys were prepared using a high-energy vibratory ball mill. For $9&lt;~x&lt;~27.5$ a single phase $A2$ solid solution was formed while for $x&gt;~30$ besides the solid solution an increasing amount of disordered ${B8}_{1}$ (NiAs type) ${\mathrm{Fe}}_{3}{\mathrm{Ge}}_{2}$ was found. Thermally induced $A\stackrel{\ensuremath{\rightarrow}}{2}{D0}_{3}$ transition was investigated for $9&lt;~x&lt;~27.5.$ The detailed annealing temperature dependence of short- and long-range ordering into the ${D0}_{3}$ structure was studied for the case of ${\mathrm{Fe}}_{75}{\mathrm{Ge}}_{25}$ by means of M\"ossbauer-effect spectroscopy and x-ray diffraction. The solid solution orders gradually and homogenously into the ${D0}_{3}$ structure. To follow and quantify the evolution of short-range order a special fitting routine for M\"ossbauer spectra was used that takes into account local and nonlocal contributions to the hyperfine interactions experienced by a ${}^{57}\mathrm{Fe}$ probe, and that assumes nonlinearity dependences on the number of neighbors of a given class. By this means the short-range ${D0}_{3}$ order parameter S was determined for as milled steady states as well as annealed states for $9&lt;~x&lt;~27.5.$ In the case of ${\mathrm{Fe}}_{75}{\mathrm{Ge}}_{25}$ the evolution of mechanical alloying with time was investigated. It was found that alloying proceeds in two stages. In the first one, iron rich (with $A2$ structure) and disordered Ge-rich regions coexist along with an almost equiatomic $A2$ Fe-Ge solid solution, which was interpreted as an interphase physically located between the former two. The three phases collapse into just one bcc solid solution with $S\ensuremath{\approx}0.3$ for a critical time ${t}_{c},$ which was identified as the chemical mixing time reported by other authors. The second stage of mechanical alloying produces the complete homogenization of the solid solution. Plausible basic mechanisms of mechanical alloying of Fe-Ge mixtures are discussed on the basis of the results presented here.

Short-range order in bulk Zr- and Hf-based amorphous alloys

The local order in mechanically alloyed Hf 65Al 7.5Cu 17.5Ni 10 and Zr 65Al 7.5Cu 17.5Ni 10 amorphous alloys was studied by means of perturbed angular correlation measurements. The amorphous state of the starting material was confirmed by X-ray diffraction. Differential scanning calorimetry analysis showed the existence of an extended supercooled liquid region. Two exothermic effects, indicating a two-step crystallization process, were also observed. Perturbed angular correlation measurements indicated similar short-range order in the supercooled liquid state and in the starting amorphous state. The evolution of short-range order with annealing temperature was also studied ,being the intermediate and final phases characterized by this hyperfine technique.

Mechanical milling of the intermetallic compound AlFe

The intermetallic compound AlFe in its ordered $B2$ phase has been ground under Ar in a ball-milling device. The system evolution under mechanical work has been examined as a function of time of milling by x-ray diffraction, transmission M\"ossbauer spectroscopy, and differential scanning calorimetry. Short and long range disorder was observed. The evolution of the long range order parameter with milling time is analyzed up to the completion of the solid state reaction when a steady state value is reached. The short range order evolution is consistent with a nonstatistical order distribution throughout the sample but mainly distributed in two regions with different degrees of order each. Kinetic analysis of the reordering and recrystallization has been performed under continuous heating and isothermal calorimetric regimes. Modeling of these processes is presented as well as the estimated values of both the enthalpy and the activation energy of the reordering process. Results are compared with preceding information on related systems.

Short Range Order Evolution during the Nitrification of IVb Metals

Short Range Order Evolution during the Nitrification of IVb Metals

Short Range Order Evolution during the Nitrification of IVb Metals

Short Range Order Evolution during the Nitrification of IVb Metals

Short range order evolution in the preparation of SnO2 based materials

The evolution of Eu3+ doped SnO2 xerogels to the cassiterite structure observed during sintering was studied by means of Eu3+ spectroscopy, XRD and EXAFS at the Sn K-edge. Eu3+ ions adsorbed at the surface of colloidal particles present a broad distribution of sites, typical of oxide glasses. With sintering at 300°C, this distribution is still broadened. Crystallization is clearly observed by the three techniques with increasing sintering temperature. It is found that the addition of Eu3+ limits the crystallite growth.

Thermal evolution of the local order in amorphous Hf62Ni38.

This paper reports on time-differential perturbed angular correlation measurements on amorphous ${\mathrm{Hf}}_{62}$${\mathrm{Ni}}_{38}$ alloys prepared by melt spinning. The main objective was to analyze the evolution of short-range order around Hf atoms during crystallization, i.e., the identification of stable or metastable phases formed by thermal activation. The results indicate that the crystallization is a two-step process as it was previously observed by other techniques. After the first one a disordered phase precipitates in a still amorphous matrix. The further crystallization process is not a simple one, involving the growing and dissolution of different phases before the final equilibrium compounds are reached.

Kinetics of B2 and D03 Ordering: Theory

AbstractMonte-Carlo simulations (MCS) and the path probability method (PPM) were used to study disorder→order transformations in bcc alloys having the AB3 stoichiometry. Both methods used an explicit vacancy mechanism of ordering and an activated-state rate theory for the vacancy jumps. We studied the evolution of short-range order (SRO) as well as B2 and D03 long-range order (LRO) in alloys that began as random solid solutions. The growth rates of SRO and LRO were significantly higher for the PPM than for the MCS. We attribute this difference to improper handling of correlated vacancy motions in the PPM. The PPM also suffered from an artificial incubation time for the initiation of LRO. Both the MCS and the PPM showed that SRO has a tendency to develop in two stages. In the first stage there is a quick relaxation of the SRO by itself. In the second stage, which occurs with a longer time constant, the SRO and LRO grow simultaneously. Parametric plots of one order parameter against another, here termed “kinetic paths”, are discussed. A variety of different kinetic paths through the B2 and D03 order parameters can be predicted theoretically, depending on the choice of interatomic potentials. This range of calculated kinetic paths is broad enough to encompass our experimental results of SRO and LRO evolution in Fe3Al.