Atomic-scale analysis of impurity segregated Al2O3 grain boundaries and its physical properties evolution

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Small concentrations of dopants that diffuse and segregate to the grain boundaries can significantly change the properties of polycrystalline Al2O3. The purpose of this research is to reveal the mechanisms of dopants segregation and diffusion in grain boundaries. Firstly, pristine and Y-doped Al2O3 grain boundaries were fabricated by the bicrystal method. By using atomic resolution STEM and EDS mapping, the grain boundary structural transformation and segregation of both Y and Ca were clearly revealed. The preferential segregation of Y and Ca to the same sites was observed, mainly due to the ionic size mismatch between dopants and the host Al. On the other hand, atomistic Ti diffusion behaviors in Al2O3 grain boundaries were investigated, by controlling the diffusion length and precisely preparing the TEM sample. The diffusion coefficients along two mutual vertical directions of the grain boundary were directly determined and the atomic structures of the structural transition areas were characterized. These results further deepen our understanding of dopants segregation and diffusion behaviors and provide important guidance towards the design of Al2O3 ceramics with better performance.