Effect of oxygen potential gradient on mass transfer along grain boundary in alumina bicrystal

Mass transfer along a grain boundary (GB) in a Σ31 alumina bicrystal wafer was investigated using the oxygen permeation technique with 18O2 at 1873 K, where oxide ions migrated along the GB from the high oxygen partial pressure [PO2(hi)] surface to the low oxygen partial pressure [PO2(lo)] surface, and aluminum ions moved concurrently in the opposite direction. It was found that the application of an oxygen potential gradient more strongly inhibited the migration of oxide ions along the GB within a shorter distance from the PO2(hi) surface, compared with the case of the polycrystalline alumina. Moreover, in the case of high-angle GBs like Σ31 GB, as the GB gets close to the surface, the GB plane undergoes more pronounced lateral movement in the transverse direction. The GB movement is thought to be due to annihilation of aluminum vacancies stagnating in a nonequilibrium state near the surface.