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Abstract

The segregation of hydrogen and silicon atoms in two high-angle symmetric tilt grain boundaries in transition metal Iridium are investigated using density functional theory simulations. Two distinct grain boundaries, Sig5(210)[001] and Sig11(113)[110], were chosen to study the segregation. Both the GBs show a contrasting behavior with respect to trapping sites of the impurity atoms: while the relatively loosely packed Sig5 GB has multiple low energy trapping sites, the close-packed Sig11 GB has very few. Even the behavior of the impurities is markedly different from each other, with Si showing a much stronger preference to segregate to the GBs than H.

In addition, a detailed analysis was done for one case where we studied the migration of H atom through the Sig5 GB and found that the open structure of the GB provides an easy migration path into the GB plane and a high energy barrier for reverse migration, effectively trapping the atom in the GB plane.