Mechanism of Aging in Polycrystalline BaTiO₃

Microscopic observation of the domain structure in polycrystalline BaTiO 3 is carried out. After the specimen is cooled down to room temperature through the Curie point the domain structure changes gradually from an initial irregular one to a final one consisting of fine stripes of 90°-domains. Such a change is named “90°-splitting.” The aging of dielectric constant may be due to an increase in clamping effect by the 90°-splitting. This “90°-splitting model” may explain also the agings in dielectric loss and hysteresis loop. The dielectric constant decreases linearly with logarithm of aging time. It was shown theoretically that the displacement of a 90°-wall towards the mechanically most stable position is proportional to the logarithm of time in the case of whisker crystal. The “logarithmic time dependence” of dielectric constant in polycrystalline specimen may be explained as due to the 90°-splitting which progresses at a rate proportional to logarithm of time.