Temperature dependence of the diffuse-scattering fine structure in equiatomic CuAu

The temperature dependence of the diffuse-scattering fine structure from di sordered equiatomic CuAu is studied using in situ x-ray scattering. In cont rast to Cu3Au the diffuse peak splitting in CuAu is found to be relatively insensitive to temperature. Consequently, no evidence for a divergence of t he antiphase length-scale at the transition temperature is found. At all te mperatures studied the peak splitting is smaller than the value correspondi ng to the CuAuII modulated phase. An extended Ginzburg-Landau approach is u sed to analyze the temperature dependence of the diffuse peak profiles in t he ordering and modulation directions. The estimated mean-field instability point is considerably lower than is the case for Cu,Au. [S0163-1829(99)021 18-9].