Topological and chemical short-range order in amorphous Ni-Ti alloys

Neutron and x-ray scattering measurements were made on amorphous Ni35Ti65 and Ni40Ti60 alloys prepared by the melt-spinning process. The x-ray interference functions (structure factors) S/sup x/(K) are dominated by the topological short-range order (TSRO) S/sub NN/(K), but exhibited a small prepeak. The neutron structure factors S/sup n/(K) are dominated by the CSRO S/sub CC/(K)/(c1c2), describing the concentration fluctuations in the alloys. Assuming that the size effect term S/sub NC/(K) which describes the correlation between number density and concentration can be approximated by the Percus-Yevick hard sphere model, the TSRO S/sub NN/(K) and CSRO S/sub CC/(K)/(c1c2) were evaluated. From their Fourier transforms it became possible to evaluate the chemical short-range order parameter α which is of the order of -0.1 to -0.15 indicating a preference for unlike nearest neighbors in the amorphous Ni-Ti alloys