Concurrent Measurement of Volume, Grain‐Boundary, and Surface Diffusion Coefficients in the System NiO‐Al 2 O 3

Surface, grain‐boundary, and volume inter diffusion coefficients for the NiO‐Al 2 O 3 system were measured concurrently by using a diffusion couple consisting of an A1 2 O 3 bicrystal and an NiO single crystal. The A1 2 O 3 bicrystals having various tilt angles were fabricated by firing 2 single crystals to be joined in an H 2 atmosphere at 1800°C for 30 h. Diffusion profiles over the surface, along the grain boundary, and in the bulk of the bicrystal were determined with an electron probe microanalyzer. Mathematical analysis of the diffusion profiles gives D s = 7.41×10 ‐2 exp (‐35,200/ RT ), D gb = 2.14×10 ‐1 exp (‐63,100/ RT ) (tilt angle =30°), and D v = 1.26×10 4 exp (‐104,000/ RT ). The grain‐boundary diffusion coefficient increases with the mismatch at the boundary.