A SHIFT-LATTICE INTERPRETATION OF STRUCTURES IN THE AU4MN REGION OF THE AU-MN SYSTEM

The structures of a number of ordered phases in the Au-Mn system deriv ed from the face-centred cubic structure of Au4Mn have been described in a systematic manner by use of shift-lattice distributions of the ma nganese atoms throughout the matrix of the alloys. The simplest struct ures are describable in terms of one-dimensional shift lattices, but m any are best treated as two- or three-dimensional shift lattices. This approach has allowed structural correlations to be presented that hav e not been described previously and the variation in stoichiometry of these phases to be accounted for without recourse to defect population s. The diffraction patterns of such structures are also discussed, esp ecially incommensurate patterns from materials with 'infinitely large' crystallographic unit cells.