Structural study of an amorphous NiZr 2 alloy by anomalous wide-angle x-ray scattering and reverse Monte Carlo simulations

The local atomic structure of an amorphous NiZr 2 alloy was investigated using the anomalous wide-angle x-ray scattering (AWAXS), differential anomalous scattering, 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 factors S(K,E) were derived. Using the AWAXS data four differential structure factors DSF i (K,E m ,E n ) were derived, two about the Ni and Zr edges. The partial structure factors S N i - N i (K), S N i - Z r (K), and S Z r - Z r (K) were estimated by using two different methods. First, the S(K,E) and DSF i (K,E m ,E n ) 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 NiZr 2 structure. We have used the Warren chemical short-range order parameter to evaluate the chemical short-range order for the amorphous NiZr 2 alloy and for the NiZr 2 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.