Microstructure and electrical properties of SrTiO3-based ceramics

Relationships between microstructure and electrical properties of SrTiO3-based varistor have been studied. Si-rich amorphous layers(several nm thick) are found at the grain boundaries when reduced enough under much lower oxygen partial pressure(Po2) than that of firing step after sintering. Then, the sample shows a large V-I nonlinear coefficient(α). On the other hand, the sample without reducing treatment has grain boundaries of facet structure, and then, shows a small α. Behavior of oxygen diffusion during re-oxidation is changed by the reducing treatment; from volume diffusion controlled to grain-boundary diffusion controlled.