Recent studies have demonstrated that a higher dopant concentration in the grain boundary region (which includes boundary core and neighboring layers) of acceptor-doped oxides results in a remarkable decrease of grain boundary electrical resistance. In the present work, the spatial distribution of cations in the proton conducting scandium doped barium zirconate is investigated by transmission electron microscopy with high lateral resolution. Cation profiles with a resolution of 0.5 nm obtained using electron energy-loss spectroscopy indicate segregation of a noticeable part of scandium into the grain boundary core. This direct observation is consistent with the measured grain boundary electrical behavior and is interpreted in terms of the space charge model. (C) 2013 Elsevier B.V. All rights reserved.