The Observation On Domain Switching Of BDT And NBT-KBT Ferroelectric Thin Film At Applied Force And Electric Fields

At present, the lead zirconate-titanate (PZT) series are still the mainly materials for non-volatile random access memories, sensors, and actuators. Because the PZT series have good ferroelectric performance, such as biggerValues of remnant polarization and lower heat treatment temperature and so on. But PZT thin films have one fatal weakness that the lead in which is toxicity. Consequently, developing new type of free-lead ferroelectric materials to replace the PZT series is much of a necessity. The bismuth titanium (Bi₄Ti₃O₁₂, BIT) and series have a lower crystallize temperature, better free-fatigue and higherValue of remnant polarization and are the potential materials to replace the PZT. And bismuth sodium titanate (Na_0.5Bi_0.5TiO₃, NBT) series are considered as one type of the major lead-free ferroelectric materials due to the strong ferroelectricity and high Curie temperature. However, the NBT series are have some disadvantage such as large coercive field and high leakage current and lower piezoelectric properties. The NBT was usually modified by other materials such as K_0.5Bi_0.5TiO₃, BaTiO₃ and make the capability improved. Domain switching is the source power for ferroelectric material to generate the P-E hysteresis loops and butterfly curves.There are many reasons to induce the domain switching such as applied stress, polarization electric field and annealing temperature and so on. Scanning force microscopy (SFM) has emerged as a powerful technique for noninvasive domain imaging and polarization dynamics study in ferroelectric thin films.In this paper, nanoscale domain switching in Bi_4-xDy_xTi₃O₁₂ (BDT) and (1-x)Na_0.5Bi_0.5TiO₃-xK_0.5Bi_0.5TiO₃ (NBT-KBT) ferroelectric thin films , which is NBT modified K_0.5Bi_0.5TiO₃ solid solution, have been studied by SFM at different loading forces and polarizing voltages. The results can be summarized as follows:(1) Nanoscale domain switching in BDT ferroelectric thin films have been studied by SFM at different loading forces and polarizing voltages exerted by SFM tip. The mechanisms of those domains switching process have been discussed and interpreted. The domain switching induced by loading force is corresponding to the scanning mode of the tip. When the scanning mode is forward-and-backward, 90°domains switching occur from±90°-domains to 0°-domains with the increase of loading force. When the scanning mode is unidirectional by SFM lift-mode, 90°domains switching occur from 0°-domains to 90°-domains with the increase of loading force. When polarizing voltage is applied, 180°domain switching occurred and the reversed domains may be parallel or anti-parallel to the polarizing field. When both loading force and polarizing voltage are applied, 90°domain and 180°domain switching are observed. The 90°domain switching may be induced by loading force and 180°domain switching may induced by polarizing voltage.(2) Nanoscale domain switching in NBT-KBT thin films have been studied by SFM at different loading forces and polarizing voltages. The mechanisms of those domains switching process are discussed.