Vacancies at the Cu-Nb semicoherent interface

We present the 0 K structures and formation energies for vacancy clusters of up to four vacancies and migration barriers for a single vacancy at a semicoherent Kurdjumov-Sachs Cu-Nb interface using ab initio calculations. Two main results emerge from this study, first that the predicted vacancy structure is compact, differing notoriously with predictions based on available empirical potentials, and second that vacancy clusters containing up to four vacancies have a smaller formation energy than monovacancy in bulk. Additionally, the binding energies show that the vacancy clusters are energetically stable for clusters having up to four vacancies. Nudged elastic band calculations of migration barriers show that the migration of a vacancy from one misfit dislocation intersection to another is highly improbable due to the high barriers. These findings suggest that at nonzero temperatures the interface will be preloaded with vacancy clusters with a relatively large capture radius for interstitials in the interface plane, implying that the semicoherent Cu-Nb interface could be a highly effective sink for point defects that form due to irradiation.