Reinvestigation of first phase nucleation in planar metal-Si reaction couples

It is proposed that the first nucleating phase in planar metal-silicon reaction couples is that congruently melting phase neighboring the central eutectic in the phase diagram, which is closer in composition to the diffusing species. This phase also must have a low interfacial free energy with one of the elements constituting the phase diagram. The low interfacial free energy is indicated either by eutectic formation with, or, by epitaxial growth on one of the elements. It is suggested that a low-energy interface is no barrier to diffusion; therefore, phases that nucleate first in metal-silicon reaction couples are not good as diffusion barriers.