| Relaxor ferroelectrics PMN-PT single crystals exhibit extra-high dielectric and piezoelectric properties compared with conventional piezoelectric ceramics. They are becoming widely used in high performance electromechanical devices. However, PMN-PT single crystals are elastically softer than PMN-PT polycrystalline ceramics. Mechanical loads and electric fields interact to produce fractures at relatively low stresses, and cracks grow under both AC and DC electric fields. To prevent the failure of the electromechanical devices, we need to have a better understanding of the mechanisms of fracture in this material when it is subjected to mechanical and electrical loadings.;Photoelasticity is an efficient and effective method to measure the internal stress distributions of materials that result from both internal residual stress and external loading. I report the exploration of the use of this classic technique to study internal stresses inside PMN-PT single crystals through bending and Hertzian contact experiments. Effects under electric field loading were also investigated using birefringence techniques. |
