Model of Intermediate Phase

Without loss of generality, let us choose the model of the new phase as a Hne (strictly stoichiometric) intermediate phase with composition C = Ci = 0.5, and exclude the elastic contributions to the Gibbs energy. The parent phase in the vicinity of the phase transition points will be described by the ideal solution law and will be also denoted as the a-phase. In fact, the model of regular solution would be more reasonable since the existence of intermediate phases usually correlates with negative mixing energy. Yet, for simpHcity, below we restrict ourselves to the 

To guarantee the decrease of the driving force with increasing temperature, we have used a, which leads to metastabihty at low temperatures and corresponds to the case of common tangent at certain temperature T  

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