Ferroelectric ceramics: Switching and hysteresis curve

The average polarization of a crystallite in a ferroelectric ceramic is switched by 180/spl deg/ by an electric field which exceeds the critical strength E/sub 2crit/. At this field strength a new 90/spl deg/ domain wall is generated at the grain boundary and is driven by the field through the whole grain. This polarization reversal of the grain does not change the gross shape of the grain, i.e. exchange of elastic energy is negligible in the switching process. Switching thus is mainly an electric process with no or only small irreversible deformation. The electric hysteresis curve P(E) is developed with a process parameter /spl delta/ such that P(/spl delta/) and E(/spl delta/) are separate hysteresis curves. The final hysteresis curve results from the elimination of /spl delta/.