ATOMISTIC LANDAU THEORY OF ORDERING AND MODULATED PHASES IN CU-AU ALLOYS

We present a Landau theory derived from an alloy Hamiltonian based on a quantum mechanical description of cohesion in metallic systems. This Landau theory, obtained by making a mean-field approximation, provide s an excellent description of the ordering transitions in CuAu, Cu3Au, and CuAu3, including the sequence of transitions from the disordered to the modulated CuAu II phase to the low-temperature CuAu I phase.