  Distinct dopant behaviors inside and outside dislocation cores are identified
by atomic-resolution electron microscopy in perovskite BaSnO3 with considerable
consequences on local atomic and electronic structures. Driven by elastic
strain, when A-site designated La dopants segregate near a dislocation core,
the dopant atoms accumulate at the Ba sites in compressively strained regions.
This triggers formation of Ba-vacancies adjacent to the core atomic sites
resulting in reconstruction of the core. Notwithstanding the presence of
extremely large tensile strain fields, when La atoms segregate inside the
dislocation core, they become B-site dopants, replacing Sn atoms and
compensating the positive charge of the core oxygen vacancies. Electron
energy-loss spectroscopy shows that the local electronic structure of these
dislocations changes dramatically due to the segregation of the dopants inside
and around the core ranging from formation of strong La-O hybridized electronic
states near the conduction band minimum to insulator-to-metal transition.
