In-situ Investigation Of Domain Switching In PLZT Ferroelectric Ceramics During An Electric Fatigue Process And The Study Of Electric Fatigue Mechanism In Ceramics

The electric fatigue and failure have significantly impeded the commercial applications of ferroelectric ceramics in micro-actuator and micro-performer devices. It is, therefore, of academical and practical importance to investigate and to clarify the electrical fatigue mechanism of ferroelectrics by using on-line or in-situ technologies. This work was initiated to establish an in-situ XRD measuring system through which the variations of XRD peak intensities on the surfaces of PLZT ferroelectrics with fatigue numbers during an electric process can be in-situ observed. The cross-sectional morphologies of the samples were studied by SEM before and after the fatigue tests. The effects of electric field characteristics and temperature on fatigue behaviors of the PLZT samples were systematically investigated by performing a series of experimental measurements.It was found that the dropping rate in remnant polarization, Pr(N), of the samples would be accelerated when a high intensity or low frequency or square-wave of electric field was applied or at a lower temperature. The in-situ XRD results obtained during an electric fatigue process revealed that the numbers of a domain kept increasing, while those of c domain decreasing with the increase of the fatigue number (N) after the end of each fatigue cycle. The ability of 90° domain-switching of a→c in the ferroelectrics under an applied electrical field was adversely affected, accordingly, an approximate evaluation equation for the 90° domain switching of c→a was provided based on the in-situ XRD measurements. It was proposed that the reduction in Pr(N) during the electric fatigue process was probably caused by the increase of a domain andanti-ferroelectric c* domain (both leading to the increase in non-switching of c domain) in combining with the experimental observation that the Pr(N) values lowered with the rise of N. The equation which can be used to calculate the differences in non-switchable domain due to the increase of N was also given. Variations of domain-switching with changes of N are discussed according to the in-situ XRD measurements. It was demonstrated that the values of domain strain decreased while the rate in reduction of the domain strain lowered with larger N. Combined the XRD with SEM results, the non-fracture mechanism of the sample when pure electric fatigue was applied can be described as: at an earlier stage of electric fatigue, the high repeated incompatible strain led the major fracture mode for the fatigued sample to be of inter-granular. The ability of domain switching in a-->c of the sample along with the direction of an applied electric field kept dropping, hence, reduced the domain strain. As it further decreased to some extent, the induction of the new micro-crack or the elongation of original micro-cracks in PLZT became less favorable.