It was already showed that spinel present a grain boundary slidingdeformation accommodated by diffusion during creep at hightemperature 1,2. The observed interface reaction controllingdiffusion at low stress (under 60 MPa) can be explained by a spacecharge layer at grain boundary in ionic ceramics. Thenonstoichiometric area due to ionic defect should create anelectrostatic potential between the grain surface and inside graininside. This surface dipole region suppose an excess free energynecessary to form cation and anion vacancies 3, 4. The purpose ofthis presentation is to study the grain boundary region stoichiometryto confirm this theory.
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