Observation of chemical short-range order in an amorphous Ni40Ti60alloy

Abstract

X-ray and neutron scattering measurements were made on an amorphous Ni₄₀Ti₆₀ alloy. The X-ray scattering pattern S^x(q), although dominated by the topological short-range order (TSRO) S_NN(q), showed a small pre-peak which indicated chemical short-range order (CSRO) in the alloy. Since the average scattering amplitude (b) of this alloy for neutrons is small, the neutron scattering pattern Sⁿ(q) is dominated by the term S_CC(q) describing the concentration fluctuation in the alloys. Indeed, the X-ray pre-peak becomes the main peak in the neutron scattering Sⁿ(q). From the diffraction data, the chemical short-range order parameter was calculated, indicating a preference for unlike neighbours in the amorphous Ni₄₀Ti₆₀ alloy. On heating the sample to 400K and 500K, irreversible variations of Sⁿ(0) and, correspondingly, of the extent of composition fluctuations, were observed.