Optical methods in X-ray analysis. I. The study of imperfect structures

The correspondence between the diffraction of X-rays by crystals and of light by gratings can be used to test hypotheses put forward to explain the X-ray diffraction patterns of imperfect structures. Two-dimensional gratings of holes in cardboard are made and their diffraction patterns observed in a specially constructed large spectrometer (the Bragg X-ray microscope). Illustrations are given of the application of the method to (a) the transition from the cubic to the hexagonal close-packed structure, and (b) the ordering process in the ahoy AuCu 8. From the latter investigation it would appear that the X-ray diffraction effects observed can be accounted for entirely by changes in the degree of short-range order. Some rules are given for guidance in the interpretation of the X-ray diffraction patterns of imperfect structures.