Current-voltage characteristics of Σ1 boundaries with and without cobalt ions in niobium-doped SrTiO₃ bicrystals

Current-voltage (I-V) characteristics across Σ1 boundaries of Nb-doped SrTiO₃ bicrystals were investigated with a special interest in the effect of an impurity ion, cobalt. The Σ1 boundary with cobalt ions was fabricated by hot-joining technique after evaporating metallic cobalt onto the (001) plane used for a contact plane. High-resolution transmission electron microscopy (HREM) study associated with X-ray energy dispersive spectroscopy (EDS) revealed that cobalt solved and distributed around the Σ1 boundary which was perfectly joined without any second films. It was found that the Σ1 boundary with cobalt ions exhibited a nonlinear I-V relationship while the Σ1 boundary without cobalt ions showed a linear I-V relationship. This result indicates that the presence of cobalt itself at the boundary can form a potential barrier irrespective of grain boundary coherency.