Domain switching and microcracking in ferroelectric single crystals and polycrystalline ceramics

This study investigated the domain switching and the microcracking driven by contact forces, static electric fields and cyclic electric fields in a PZT ceramic and PMN-PT single crystals. Field-driven polarization switching was studied in a soft PZT ceramic by an in-situ transmission electron microscopy (TEM) technique. Responses of nanometer-sized domains to the first cycle of a bipolar field were recorded for the first time. Domain switching in PMN-PT single crystals was investigated by optical microscopy. The bipolar fields were found to drive the lamellar domains into complex mosaic patterns of domain zones with elastic distortion and electric charge at the zone boundaries.; Contact force-driven 90° domain switching was studied by pressing a Vickers diamond indentor against the surface of a PMN-PT crystal. The stress-induced domain switching was confined to butterfly-shaped zones that extended preferentially along the <101> directions. Based on a critical shear stress criterion, a stress analysis was made to determine the conditions for the 90° domain switching.; The field-driven in-situ TEM technique was applied to the study of domain boundary cracking in a 0.65PMN–0.35PT crystal. Fracture of the 90° domain wall was directly observed under both static and cyclic electric fields. The amplitude of the cyclic field required to cause the crack growth was much less than that of the static field. The mechanical energy produced due to the incompatible piezoelectric strain between neighboring domains was shown to be the driving force for the fracture.; In polycrystalline piezoelectric ceramics, electric field-induced cracking occurred by intergranular fracture. The macroscopic path of the crack growth depended strongly upon the applied field and the poling direction. Analysis showed that cracks extended along the place of maximum normal strain. Mechanisms for the intergranular fracture were investigated by the in-situ TEM technique. During electrical cycling, transient dielectric breakdown and local melting in the amorphous grain boundary layers were the likely precursors to fracture. Assisted by the incompatible stresses, cavitation took place. The increase of the density and the linkage of these cavities weakened the grain boundary, leading to crack growth along the boundary.