Polarization switching and fatigue anisotropy in relaxor-lead titanate ferroelectric single crystals.

摘要

In this study, fatigue anisotropy was discovered in rhombohedral Pb(Zn 1/3Nb2/3)O3-PbTiO3 (PZN-PT) single crystals. When the electric field is applied along [001]C or [110]C orientations, single crystals do not fatigue, while normal fatigue occurs along [111]C orientations. Further studies focused on the study of the origin of fatigue anisotropy in PZN-PT and other ferroelectric systems. Experiments consistently showed that if a ferroelectric to ferroelectric phase transition occurs (i.e., rhombohedral → tetragonal) through composition, temperature, and field strength, fatigue reappears in otherwise "fatigue-free" orientations. These results indicated that the fatigue rates depend on both the ferroelectric phase and crystallographic orientation. Fatigue anisotropy was investigated also in several other ferroelectric systems including both relaxor based and normal ferroelectrics. Normal ferroelectric BaTiO3 and its solid solutions with BaZrO3 did not exhibit fatigue anisotropy in the rhombohedral phase in [001]C orientations. From these studies it seems a combination of engineered domain states (orientation) and relaxor nature is required for fatigue free orientations.; Given the relaxor ferroelectric nature of PZN-PT single crystals, the field and frequency dependence of switching and relaxation of sub-coercive field dc field excited polarization were studied as a function of fatigue history. A power law fit gives less field and frequency dependence for [001] C. The behavior remains constant throughout cycling. However, strong field and frequency dependence was noted in [111]C as a function of fatigue. Polarization relaxation data was analyzed by a stretched exponential function. Fitting parameters indicate a broader time constant distribution for relaxation along [001]C, meaning more diverse contribution to the switching process. These parameters also remained constant with cycling along [001]C. On the other hand, a narrower time constant distribution with a higher stretched exponent was determined along [111]C direction. With fatigue evolution, changes occur along [111]C. These observations are consistent with the progressive loss of the slower elements from the switched polarization signal, demonstrated in conventional P-E loops.; Finally, optical microscopy was performed in PZN-4.5PT single crystals along [001]C and [111]C orientations as a function of fatigue (cycling) history. With fatigue evolution, domains became more fractal (discontinuous) along [111]C, whereas the presence of finer domains with a wide size range was noted along [001]C. (Abstract shortened by UMI.)