Anomalous Diffusion along Metal/Ceramic Interfaces

TL;DR

This paper reveals that diffusion along metal/ceramic interfaces can be surprisingly fast due to low vacancy formation and migration energies, challenging previous assumptions and providing a new model validated by ab initio calculations.

Contribution

It introduces a simple, validated model for metal/ceramic interface diffusion, supported by ab initio calculations and broad applicability.

Findings

Ni diffusion along the interface is much faster than expected.

Activation energy for interface diffusion is comparable to grain boundary diffusion.

Fast diffusion along metal/ceramic interfaces is common but not universal.

Abstract

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.