X-Ray Measurement of Order in Single Crystals of Cu3Au

X-ray diffraction methods have been used to measure long- and short-range order parameters for single crystals of the alloy Cu3Au held at elevated temperatures. It is shown that short-range order parameters may be obtained by a three-dimensional Fourier analysis of the ``scattering power'' for the diffuse background scattering of x-rays, expressed as a function of reciprocal lattice coordinates. Appropriate experimental and computational procedures are outlined. Intensity measurements have been made with a special arrangement of a bent-crystal monochromator and a Geiger-counter spectrometer. Short-range parameters are given for the first ten shells of atoms surrounding a given atom for three temperatures above the critical temperature of Cu3Au. These results, and those for the long-range order parameter agree well with theoretical predictions.