An X-ray diffuse scattering study of short-range order in CuAu

Abstract

The diffuse X-ray scattering has been measured from a CuAu single crystal held at 700 and 800 K and from a crystal quenched from 1070 K and held at room temperature and 126 K. The short-range order and size effect parameters were calculated by use of the appropriate Fourier transforms. The order parameters obtained indicate that with increasing temperature the short-range order both decreases in magnitude and damps out faster with increasing co-ordination shell number. A calculation of the diffuse intensity using the Clapp-Moss pair correlation theory reveals that the interatomic potential ratios V 2 V 1 and V 3 V 1 are not sufficient to reproduce the experimental results but inclusion of V 4 V 1 and V 5 V 1 greatly improves the simulation. The values of V i V 1 used fit the form of a long-range oscillatory potential. Computer simulation of the atomic arrangement shows the existence of small ordered regions in a random matrix above T c but for the quenched state a microdomain structure is predicted.