Atomic-resolution observation of Hf-doped alumina grain boundaries

Aberration-corrected high-angle annular dark-field imaging was used to provide atomic-resolution imaging of the Hf distribution within grain boundaries in polycrystalline alumina. In general, the projected image gave the appearance of multiple layers of segregating Hf ions. However, by combining image simulation with the results of through-focus imaging, it was demonstrated that the observations resulted from atomic layer faceting of the grain surface, and that the Hf segregation in each grain was in fact confined to the outermost cation layer.