Electron Diffraction Study of Order in the CuAu_3 Alloys

Single crystal CuAu_3 alloy films were studied by electron diffraction and it was concluded that these alloys in general have a two-dimensional anti-phase domain structure of the Cu_3Pd type in the equilibrium ordered state, but the periodicity of the second type of domain boundary is indefinite. The mean saturation sizes of both types of domains increase with decreasing gold content, but the rate of increase of the second type domains seems to be greater than the first type, so that with decreasing gold content the structure tends to approximate to a one-dimensional structure with the first type domains. High temperature experiments to observe the short range order scattering above the transition temperature indicated the presence of an anti-phase relationship of the same two-dimensional character as in the ordered state. This fact means the existence of long range correlations (>34A) and necessitates some revision of the conventional concept of short range order in alloys