Barrier formation of single junctions with oxidation in SrCoO₃-doped ZnO varistors sintered in a reducing atmosphere

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Nonlinear electrical properties of individual grain boundaries in SrCoO₃-doped ZnO varistor ceramics are investigated using a nano-prober system. In particular, the effect of post-annealing is clarified for them after sintering in a reducing atmosphere. The nonlinear characteristics are enhanced by annealing in air at above 600°C. The resulting characteristics are attributed to an increase of p-type carrier concentration in SrCoO₃ phase at grain boundaries. By annealing at a higher temperature (e.g., 800°C), the grain boundaries possess nonlinear characteristics similar to conventional Bi-doped ZnO varistors, as well as bulk-bodies.