SWITCHING AND DIELECTRIC NONLINEARITY OF FERROELECTRIC CERAMICS

The switching of the polarization in tetragonal ferroelectric ceramics can be achieved by the generation of one new 90 degrees domain wall at the boundary of every grain and a transit of it through the grain driven by the electric field. This transient domain wall is perpendicular to the regular 90 degrees domain walls. In any domain of the grain then the polarization is rotated by 90 degrees and the average polarization of the grain is rotated by 180 degrees due to the specific domain configurations. The observed relationship E-c similar to P-0(3) between the spontaneous polarization P-0 and the coercive field E-c is confirmed by the model. The dielectric nonlinearity of ferroelectric ceramics can also be explained by the new 90 degrees domain walls which have a very high mobility. Possibly the high permittivity of fine grained Barium Titanate can be attributed to these domain walls too.