Study on crack propagation in ferroelectric single crystal under electric loading

The crack propagation in ferroelectric single crystals subjected to electric fields was studied experimentally and theoretically. An in situ observation of crack propagation and domain switching near the crack tip in a poled PMN-PT62/38 single crystal was carried out using polarized optical microscopy. It was found that a pure negative electric field leads to a larger domain switching zone near the crack tip than a positive one does. A negative electric field below the coercive field can cause crack propagation, while no crack growth was observed for a positive electric field far larger than the coercive field. A fracture model based on energy analysis was developed which indicates that the energy variation due to the domain switching provides the thermodynamic driving force for the crack propagation under pure electric loading. The critical electrical loading for the crack growth determined by this model agrees well with experiments.