The O self-diffusivity in mullite ceramics was measured via gas/solid exchange experiments in an atmosphere that was enriched in 18O. The resultant 18O isotope depth distributions were measured by secondary ion mass spectrometry depth profiling. The investigations showed that grain boundary diffusion coefficients were about 5 orders of magnitude higher than lattice diffusivities. While the pre-exponential factors differ by about 2 orders of magnitude, the activation enthalpies in the volume (433kJ/mol) and in the grain boundaries (363kJ/mol) were surprisingly close to each other.

Measurement of Oxygen Grain Boundary Diffusion in Mullite Ceramics by SIMS Depth Profiling. P.Fielitz, G.Borchardt, M.Schmücker, H.Schneider, P.Willich: Applied Surface Science, 2003, 203-204, 639-43