Thermodynamics of solid solutions with ordering tendencies

This paper describes a new procedure for the calculation of phase diagrams for quasibinary systems that show ordering phenomena near special stoichiometric compositions. The diagrams are calculated from excess Gibbs energy functions that are modulated in the solid state at the specified stoichiometric compositions by distribution functions of the Gauss type. These 'Gaussian' terms consider the contribution of the composition and temperature depending ordering energy to the excess Gibbs energy of the solid solution. As the solid state is described in this way by a single continuous Gibbs function, the thermodynamic factor for interdiffusion in such quasibinary systems can also be derived as a single continuous function yielding negative values inside the miscibility gaps of the phase diagram.