非均匀电蠕变导致裂纹尖端铁电畴反转及发射机理研究

Domain switching and its dynamic behavior around crack tips are crucial to understand the fracture behavior in ferroelectrics. Current experimental research of domain dynamics focus on using the scanning tips to apply the loads for ferroelectric thin films and then observe the resulted change in domain structure during the same scanning，whilst inhomogeneous creep induced the evolution of domain structure around crack tips is inadequately investigated in bulk ferroelectrics in the literature. This project is about the in-situ AFM/PFM study of electrical creep induced domain dynamic behaviors, such as domain nucleation, growth, and coalescence, in an orientated barium titanate single crystalline/polycrystalline ferroelectric with and without a crack. In the meanwhile, the resulted time-dependent strains and polarization can be correlated with the evolution of domain features for each specimen under various constant levels of electric field and with a variation in crystal orientation, grain boundary and the crack inclusion. These results allow for establishing a phenomenological model consisting of a macroscopic power-law creep relationship between the remnant polarization rate and electric field, and an orientation-dependent relationship governing the saturation of polarization. The model is then used to explore the inhomogeneous creep induced domain switching/emission and propogation near the crack tip in the single crystal/polycrystalline specimen with a crack angled to the applied electric field. In particular, the feature of the domain switching emitted from the crack tip and the prorogation process will be studied in great details, as well as the interactions between the crystal orientation, the angle of the crack, domain structure, grains, grain boundaries and loadings. Finally, the simulation is performed for each individual test using the phase field models such that it agrees with the experimental observations. The study is aimed to improve the reliability in ferroelectric devices and their capability of fine controls.

电畴动力学对理解铁电体断裂行为至关重要，但目前实验研究集中在扫描极加载下薄膜的电畴运动行为，明显缺乏非均匀电蠕变对裂纹尖端电畴结构演变的研究。本项目在不同取向钛酸钡单晶/多晶中引入裂纹，设计构建基于AFM/PFM显微镜的电致蠕变实验系统，原位观测裂纹尖端非均匀蠕变引起的电畴成核、长大、聚合及畴壁运动等行为，研究晶体取向、晶界和裂纹对电畴结构、电位移和应变的影响规律，建立控制电致蠕变的唯象模型，并对裂纹尖端电畴的发射机理及其传播过程中电畴与晶界/两相材料界面的干涉问题进行分析，阐明晶体取向和电场集中效应对非均匀蠕变特性的影响规律，揭示非均匀蠕变效应引起的裂纹尖端电畴反转/发射机理，并建立相应问题的相场理论模型，研究结果可为提高铁电器件的可靠性和精确控制奠定理论基础。

电畴动力学对理解铁电体断裂行为至关重要，但目前实验研究集中在扫描极加载下薄膜的电畴运动行为，明显缺乏非均匀电蠕变对裂纹尖端电畴结构演变的研究。本项目在不同取向钛酸钡单晶/多晶中引入裂纹，设计构建基于AFM/PFM 显微镜的电致蠕变实验系统，原位观测裂纹尖端非均匀蠕变引起的电畴成核、长大、聚合及畴壁运动等行为，研究晶体取向、晶界和裂纹对电畴结构、电位移和应变的影响规律，建立控制电致蠕变的唯象模型，并对裂纹尖端电畴的发射机理及其传播过程中电畴与晶界/两相材料界面的干涉问题进行分析，阐明晶体取向和电场集中效应对非均匀蠕变特性的影响规律，揭示非均匀蠕变效应引起的裂纹尖端电畴反转/发射机理，并建立相应问题的相场理论模型，研究结果可为提高铁电器件的可靠性和精确控制奠定理论基础。