BiIn-situ Observation Of The Mobility Of A-component 90° Domain And Domain Wall In 4 Ti 3 O 12 -based Ferroelectric Single Crystal

Bismuth titanate(Bi₄Ti₃O₁₂), which belongs to the family of bismuth layer-structured ferroelectrics, has large spontaneous polarization mainly along the a-axis?Ps?a?? and high Curie temperature. However, Bi₄Ti₃O₁₂ films reveal polarization fatigue on metal electrode that hampers its application of nonvolatile memories. Recent studies have found that rare-earth-elements substituted Bi₄Ti₃O₁₂ films(Bi_3.15Nd_0.85Ti₃O₁₂) show a high fatigue endurance, which are one of the best materials to realize the application of ferroelectric memories. The domain structures and mobility of domain walls are the key to understand the electrical properties of ferroelectric materials. In order to reveal fatigue mechanism for Bi₄Ti₃O₁₂ and Nd substituted Bi₄Ti₃O₁₂, it is necessary to investigate and compare their domain structures and domain walls motion. Therefore, the domain structures and domain walls motion of Bi_4-xNd_xTi₃O₁₂?BNdT, x = 0, 0.25, 0.4? single crystals were investigated by using optical microscopy in this paper. The influence of Nd substituted Bi₄Ti₃O₁₂ crystals on Ps?a?-90° domain structures was discussed.Ferroelectric Bi_4-xNd_xTi₃O₁₂?x = 0, 0.25, 0.4? single crystals of 0.1?0.4 mm thick plates were grown by the self-flux method. Ferroelectric hysteresis loops, leakage current, frequency dependence of dielectric constant and loss of Bi₄Ti₃O₁₂-based crystals were measured along the c-axis, respectively. It was found that the Pr value and leakage current of BNdT crystals decrease with increasing Nd content?x?, dielectric constant and loss of crystals are also decreased with the increase of Nd content. In addition, the polarization hysteresis loops of the annealed Bi₄Ti₃O₁₂ crystals were measured along the c-axis, the results show that the Pr value increases after annealing.The Ps?a?-90° domain structures and mobility of its domain walls in Bi₄Ti₃O₁₂-based single crystals were observed by optical microscopy along the c-axis. Optical microscopy observed that the lamellar Ps?a?-90° domains do not have even thickness and 90° domain walls go almost straight along <110> direction in Bi₄Ti₃O₁₂ crystals. The Nd substitution leads to a decrease in domain width, and a finer domain structure is found in BNdT crystals. In addition, it was found that annealing of Bi₄Ti₃O₁₂ crystals at 800 °C in air decreases the number of 90° domain walls, while 90° domain walls of annealed BNdT crystals almost do not change. Lastly, the dynamics behaviors of 90° domain walls were in-situ observed on optical microscope in Bi₄Ti₃O₁₂-based crystals under applied electric field. Not only the movement of 90° domain walls was seen, but also the nucleation and growth of new domains were observed. Compared with Bi₄Ti₃O₁₂ crystals, the mobility of 90° domain walls is weak and nucleation density of new domains is low in BNdT crystals.