The application of the Morse potential function in ordered Cu3Au alloy. II. Thermal expansion and the equation of state

For pt. I, see abstr., A7868 of 1973. The application has been extended to the study of anharmonic properties in the partly ordered state of Cu 3 Au alloy below the transition temperature. The quasiharmonic free energy expression for the AB 3 type of superlattice has been obtained from the Bragg-Williams approximation considering the nearest neighbour interaction in the central force model. Utilizing the long range order parameter 'S' and the potential parameters already determined, the nearest neighbour distances have been calculated from the equilibrium condition in the temperature range of 303 to 658K for the ordered alloy. The theoretical pressure-volume (P-V) data up to approximately 300 kbar of pressure at the corresponding temperatures have also been computed. Considerable nonlinearity has been observed in the P-V behaviour.