On the nucleation of an intermediate phase at an interface in the presence of a concentration gradient

The nucleation of an intermediate phase at the planar boundary of two other phases in a diffusion couple is considered. An extension of classical nucleation theory is presented which yields the shape of the critical intermediate phase nucleus and the critical work of formation. With the use of a simple example it is demonstrated that the work of formation decreases, and hence the nucleation rate increases, with increasing interdiffusion time.