Short range order in a steady state of irradiated Cu-Pd alloys:   Comparison with fluctuations at thermal equilibrium
  The equilibrium short-range order (SRO) in Cu-Pd alloys is studied theoretically. The evolution of the Fermi surface-related splitting of the (110) diffuse intensity peak with changing temperature is examined. The results are compared with experimental observations for electron-irradiated samples in a steady state, for which the temperature dependence of the splitting was previously found in the composition range from 20 to 28 at.% Pd. The equilibrium state is studied by analysing available experimental and theoretical results and using a recently proposed alpha-expansion theory of SRO which is able to describe the temperature-dependent splitting. It is found that the electronic-structure calculations in the framework of the Korringa-Kohn-Rostoker coherent potential approximation overestimate the experimental peak splitting. This discrepancy is attributed to the shift of the intensity peaks with respect to the positions of the corresponding reciprocal-space minima of the effective interatomic interaction towards the (110) and equivalent positions. Combined with an assumption about monotonicity of the temperature behaviour of the splitting, such shift implies an increase of the splitting with increasing temperature for all compositions considered in this study. The alpha-expansion calculations seem to confirm this conclusion. 
I. Tsatskis and E.K.H. Salje (University of Cambridge)