X-Ray Diffraction Study of Short-Range Order and Fermi Surface Effects in Cu–Au Alloys

Abstract

Measurement with improved resolution of X-ray diffuse scattering from short-range ordered Cu-39, 53 and 59 at.%Au alloys has been carried out by photographic method using tiny single crystals. In the pattern taken with both crystal and film kept stationary, diffuse scattering maxima appear as satellite crosses accompanied by streaks at the 110, 210 and other equivalent positions. The separation between the diffuse satellites shows a composition dependence, decreasing with increasing gold content. Fermi-surface-imaging idea suggests that this decrease is attributed to a change in the ⟨110⟩ diameter of the Fermi starface of the alloys. Fourier transformation of the intensities of one of the diffuse maxima gives an interatomic correlation function, which suggests the existence of an antiphase relation between the local L1₀ ordered regions separated by 28 Å.