Short-Range Order Coexisting with Long-Range Order in Cu3Au

Abstract

Diffuse x‐ray scattering from a single crystal of Cu₃Au was observed at T/T_c≅0.995 where the long‐range order parameter S equals 0.85. By annealing at low temperatures, nearly perfect order was obtained. A difference curve yields the diffuse scattering attributable to short‐range order coexisting with the long‐range order state of S=0.85. Analysis of the diffuse intensity in absolute units gives values of the first three short‐range order coefficients. The first coefficient is found to be close to the perfect order value: α₁=0.33. Within experimental error the observed coefficients fit both the Cowley theory and a random long‐range order model equally well.