CRACK-GROWTH IN FERROELECTRIC CERAMICS DRIVEN BY CYCLIC POLARIZATION SWITCHING

Ferroelectric ceramics are susceptible to stable crack growth under cyclic electric field of high magnitude. The stresses originate from mismatch strains induced by the electric field around inhomogeneities, such as processing flaws, terminated electrodes and the cracks themselves. The phenomenon is studied using a lead lanthanum zirconate-titanate ceramic. A flaw is indented on the surface of a ceramic sample. Subject to a cyclic electric field of magnitude exceeding the coercive field, cracks eminate from the flaw, in the direction perpendicular to the voltage drop. Tests relevant to the phenomenon are also performed. Polarization and strain as functions of applied electric field are measured at various temperatures and applied stresses. Discharge is demonstrated through an air gap between two ceramic plates subjected to a voltage drop. Models are presented that explain the cyclic nature of the crack growth.