Anomalous Diffusion along Metal/Ceramic Interfaces

Hole formation in a polycrystalline Ni film on an $\alpha$-Al$_2$O$_3$ substrate coupled with a continuum diffusion analysis demonstrates that Ni diffusion along the Ni/$\alpha$-Al$_2$O$_3$ interface is surprisingly fast. Ab initio calculations demonstrate that both Ni vacancy formation and migration energies at the coherent Ni/$\alpha$-Al$_2$O$_3$ interface are much smaller than in bulk Ni, suggesting that the activation energy for diffusion along coherent Ni/$\alpha$-Al$_2$O$_3$ interfaces is comparable to that along (incoherent/high angle) grain boundaries. Based on these results, we develop a simple model for diffusion along metal/ceramic interfaces, apply to a wide range of metal/ceramic systems and validate it with several ab initio calculations. These results suggest that fast metal diffusion along metal/ceramic interfaces should be common, but is not universal.