Resonant Perturbation of Phonons in Cu(Au) Alloys Studied by Neutron Scattering

Abstract

The atomic vibrations in single crystals of Cu(Au) alloys containing 1, 3, and 9 at.% Au have been studied by means of neutron inelastic scattering. Measurements have been carried out for the [00ζ]T and [ζζ0]T1 branches of all three alloys and also for the [00ζ]L branch of the 9% alloy. In general, the impurity-induced widths, Γ, and the shifts, Δ, from the corresponding frequencies for pure copper exhibit definite resonance behavior. The detailed behavior of Δ and Γ as functions of frequency is, however, generally not in good agreement with calculations based on a mass-defect theory valid only for low impurity concentration. From the observed behavior of Δ and Γ for different branches and impurity concentrations, we conclude that, although the large mass change is undoubtedly the most important factor, force-constant changes and concentration effects also play important roles in determining the details of the resonance behavior in Cu(Au) alloys.