EFFECTS OF POROSITY ON ELECTRIC FATIGUE BEHAVIOR IN PLZT AND PZT FERROELECTRIC CERAMICS

Electric fatigue, namely the decay of the polarization and the consequent elastic strain with increased number of switching cycles under high a.c. field, severely limits the applications of ferroelectric and piezoelectric materials in high-strain electro-mechanical actuators and in thin films used in non-volatile memory devices. Electric fatigue tests have been conducted on lead zirconate titanate (PZT) and lanthanum-doped lead zirconate titanate (PLZT) ferroelectric ceramics. It was found that electric fatigue can be initiated by various factors, the porosity being one of them. Electric fatigue occurred in low-density (93%-97%) PLZT 7/65/35 ceramics after 10(4) switching cycles, while the high-density (>99%) PLZT specimens of the same composition did not fatigue after 10(9) switching cycles. It was also observed that for PZT ceramics, fatigue proceeded much more slowly in the samples with higher density (approximately 98%) than those with lower densities (92% 96%). A tentative explanation for the origin of the fatigue mechanism associated with porosity is proposed.