Quasi‐Chemical Theory of Order for the Copper Gold Alloy System

Yang's general quasi‐chemical theory of superstructure is further generalized in terms of the atomic distribution on sublattices of any number and of any geometrical arrangement. The possibility of the formation of different types of long‐distance order due to the different recombinations of sublattices is discussed. By making use of this theory the behavior of the general Cu–Au system at very low temperatures and its phase diagram are shown. The critical temperature, latent heat, curve of long‐distance order and energy vs. temperature for the CuAu tetragonal crystal are obtained. Our results are found to be quite different from those of Shockley's theory. All the experimental findings that are available to the author have been used for comparison with our results; so far no qualitative disagreement can be shown.