The elastic diffuse neutron scattering was measured for a Ni-8.4 at.% Au single crystal above the miscibility gap at 1083 K. The Ni-58 isotope was used to reduce the incoherent scattering. In contrast to previous x-ray investigations, short-range order scattering reflects local atomic arrangements characteristic of decomposition. This can be uniequivocally concluded from the diffuse scattering within the first Brillouin zone. For larger scattering vectors, the diffuse scattering is dominated by the displacement scattering due to the large difference in atomic sizes. The magnitudes of the extracted Warren-Cowley short-range order parameters show a smooth decrease with increasing distance. Crystals modeled on the basis of these parameters reveal basic arrangements of small Au clusters consisting of a tetrahedron and an attached fifth Au atom. The effective pair interaction parameters obtained from an inverse Monte Carlo analysis give no hint for a metastable state with ${L1\mathrm{}}_2$ structure.

• Received 21 June 2001

DOI:https://doi.org/10.1103/PhysRevB.65.024110