An X-ray study of the dissociation of an alloy of copper, iron and nickel

Abstract

A description is given of the unusual X-ray diffraction effects shown by the alloy Cu$_{4}$FeNi$_{3}$ while it is in the process of splitting up from one face-centred cubic structure into two. Before the formation of the tetragonal structures described by Bradley a state is formed in which each line of a powder photograph is accompanied by quite strong side-bands. An explanation of this is given and is shown to be in reasonable agreement with most of the quantitative data from the X-ray photographs. This explanation is that the original cubic lattice is regularly deformed by the segregation of the different atoms. From the positions of the side-bands the directions of the deformations and their average wave-length can be estimated. The intensities, however, do not fit in with the theory; they do not vary exactly in the way predicted. It is shown, however, that the variation is in closer agreement with this sort of modulation of the structure than with any other, but it has not, so far, been found possible to find any factor that will modify the intensities of the side-bands in the way required.