X-Ray Study of Order in the Alloy CuAu3

Abstract

Measurements of the integrated intensity of the superstructure reflections 100 and 110 from powders and a single crystal of CuAu₃ give a long‐range order parameter S=0.87±0.04 for a temperature below T_c not well defined. At the composition CuAu₃, T_c=199°C. With decreasing Au content, T_c increases. Compositions richer in Au than CuAu₃ could not be ordered. No annealing treatment was found which would sharpen the superstructure reflections. The breadths correspond to antiphase domains about 50 A in size. Measurements of the diffuse intensity from a single crystal of CuAu₃ quenched from 285°C, or held at temperatures of 250°C and 320°C, gave short‐range order coefficients qualitatively similar to those for Cu₃Au. Compared with Cu₃Au, CuAu₃ shows a weaker first neighbor and a stronger second neighbor ordering.