Contribution of triple junctions to the diffusion anomaly in nanocrystalline materials

Diffusion in nanocrystalline materials is often greatly enhanced even beyond what is expected from a high density of equilibrated grain boundaries. We propose that this ‘anomalous diffusion’ may in many cases be due to short-circuit diffusion along triple junctions. Quantitative analysis shows that triple junction diffusion can reasonably explain anomalies of several orders of magnitude. Therefore, previous suggestions of non-equilibrium grain boundary structures in nanocrystalline materials may not be required to rationalize the anomaly in every case.