Structural study of an amorphousNiZr2alloy by anomalous wide-angle x-ray scattering and reverse Monte Carlo simulations

Abstract

The local atomic structure of an amorphous NiZr2 alloy was investigated using the anomalous wide-angle x-ray scattering (AWAXS), differential anomalous scattering (DAS) and reverse Monte Carlo (RMC) simulations techniques. The AWAXS measurements were performed at eight different incident photon energies, including some close to the Ni and Zr K edges. From the measurements eight total structure factor S(K, E) were derived. Using the AWAXS data four differential structure factors DSFi(K, Em, En) were derived, two about the Ni and Zr edges. The partial structure factors SNi-Ni(K), SNi-Zr(K) and SZr-Zr(K) were estimated by using two different methods. First, the S(K, E) and DSFi(K, Em, En) factors were combined and used in a matrix inversion process. Second, three S(K, E) factors were used as input data in the RMC technique. The coordination numbers and interatomic distances for the first neighbors extracted from the partial structure factors obtained by these two methods show a good agreement. By using the three-dimensional structure derived from the RMC simulations, the bond-angle distributions were calculated and they suggest the presence of distorted triangular-faced polyhedral units in the amorphous NiZr2 structure. We have used the Warren chemical short-range order parameter to evaluate the chemical short-range order for the amorphous NiZr2 alloy and for the NiZr2 compound. The calculated values show that the chemical short-range order found in these two materials is similar to that found in a solid solution.

Micro-focussed XAFS spectroscopy to study Ni-bearing precipitates in the metal of corroded Zircaloy-2

“…The contribution from NiNi pair is practically negligible from EXAFS perspective. Similar behavior was earlier observed in an x-ray scattering study performed on an amorphous Zr 2 Ni alloy, in particular for the Ni-Ni pairs which have the smallest weighting factor [36]. Comparing the unirradiated and irradiated SPP, it is evident that a transformation towards a state of greater structural disorder has taken place upon irradiation, as manifested most notably by a reduction in the EXAFS amplitudes.…”

Nanocrystalline FexNi1−x (x≤0.65) alloys formed by chemical synthesis

“…The effects of temperature on the atomic structure of the as-prepared Fe 0.22 Ni 0.78 and Fe 0.50 Ni 0.50 samples are better observed by comparing the reduced radial distribution functions (G(r)) or the radial distribution functions (RDF(r)) obtained for these samples before and after heat treatment. These functions are obtained by Fourier transform of the TSF functions [19][20][21]. We have used the G(r) functions obtained for the as-prepared and thermally treated Fe 0.50 Ni 0.50 samples to evaluate the variations in their densities.…”

“…The heating rate was 10 • C/min, when not specified. The XRD patterns were converted to absolute scale following the normalization procedure described in [19][20][21]. The anomalous dispersion terms f and f for the Fe and Ni atoms [22] were taken into account.…”

Modeling the atomic structure of an amorphous Co25Nb75 alloy produced by mechanical alloying using an additive hard sphere model and RMC simulations

“…The algorithm of the standard RMC method are described elsewhere [16,17,20] and several applications are reported in the literature [5,[21][22][23][24][25][26][27][28][29][30]. To perform the simulations, we have considered the RMC program available on the Internet [18] and a cubic cell with 5000 atoms (1250 Co and 3750 Nb).…”