THE ARRANGEMENTS OF CR ATOMS IN FCC AU-CR ALLOYS

The intensity of X-ray diffuse scattering was measured at room temperature for FCC Au-Cr alloys whose compositions are 20.2, 12.6 and 8.4 at.% Cr. Diffuse maxima due to atomic short-range order (ASRO) were observed at 1 1/2O and its equivalent positions for the three specimens, while their intensities decrease with decreasing Cr content. From computer-simulated arrangements of Cr atoms in a FCC lattice, based on the observed ASRO parameters, the Cr atoms were found to have a preference for lining up along the (100) direction for the Au-20.2 at.% Cr alloy. On the other hand, the Cr atoms tend to have random positions for the Au-8.4 at.% Cr alloy and have an intermediate arrangement for the Au-12.6 at.% Cr alloy. The relationship between the ASRO state and the magnetic property in FCC Au-Cr alloys is discussed.