Selective impurity segregation at a near-∑5 grain boundary in MgO

Grain boundaries (GBs) together with their associated impurity segregation often affect or alter properties of many polycrystalline materials. However, their atomic-scale structures remain difficult to resolve spatially, especially for those with an orientation misalignment. Here, we apply a bicrystal technique to fabricate the near-∑5 GBs of MgO with a misalignment angle from the exact ∑5 orientation relationship and show an unexpected selective impurity segregation behavior at this GB. We find that the near-∑5 GB comprises an alternating array of five exact ∑5 GB structural units and one deformed ∑17 GB unit, and interestingly that the Ca and Ti impurities are co-segregated to the ∑5 GB structural units, yet are not to the deformed ∑17 GB structural units. The findings are important for the understanding of GBs with a misalignment and impurity segregation and for correlating structures with properties in polycrystalline materials.