Grain boundary structure and electrical properties in Nb-doped SrTiO₃ bicrystals

Grain boundary structure and electrical properties were examined for Nb-doped SrTiO₃ bicrystals. Bicrystals with Σ1, cobalt-segregated Σ1, and small angle boundaries were prepared by hot joining technique. High-resolution transmission electron microscopy (HRTEM) study revealed that two single crystals were perfectly joined without any secondary phases in all kinds of bicrystals. Σ1 boundary exhibited linear I-V characteristic while non-linear I-V behavior appeared in cobalt-segregated Σ1 boundary in spite of the similar coherent boundary. On the other hand, it was found that non-linearity became remarkable by reduction of cooling-rate after joining even in a small angle boundary, whose dislocation structure is stable against annealing treatment. This result suggests that negative-charged point defects must play an important role on the formation of potential barriers.