Domain Walls and Phase Boundaries in Ferroelectric Oxides

铁电氧化物中的畴壁和相界

• 批准号: 9632989
• 负责人: I-Wei Chen
• 金额: $ 14.51万
• 依托单位: Regents of the University of Michigan - Ann Arbor
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 1996
• 资助国家: 美国
• 起止时间: 1996-09-01 至 1997-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9632989&HistoricalAwards=false
• 关键词: Domain; Walls; Phase; Boundaries; Ferroelectric

9632989 Chen The proposed research will study the dynamics of ferroelectric domain walls and phase boundaries, which, in perovskites, are nearly atomically sharp with a thickness of the order of one to two atomic layer spacings. For such sharp interfaces, the mechanism of interfacial steps (in analogy to dislocation jogs and kinks) along with interactions of interfaces and obstacles (in analogy to dislocation pinning and bow-out) is central to the understanding of interfacial dynamics. These characteristics will be directly probed by measuring the migration energy, formation energy, and activation volume of the interfacial steps in expressly designed experiments under a stress field or an electrical field and will be complemented by additional structural and simulation studies that focus on the atomistics of the step mechanism for domain walls and phase boundaries. Three families of prototypical ferroelectrics with a perovskite structure, BaTiO3, Pb(Zr1-xTix)O3 (PZT) and Pb(Mg1/3Nb2/3)O3 (PMN), along with their various compositional and microstructural modifications, will be investigated. For BaTiO3 and PZT type of ceramics, which have a sharp transition at the Curie temperature, Tc, the interest is primarily on the dynamics of domain walls below Tc. For PMN type of ceramics, which have a broader permittivity peak with the actual transition diffuse and well below the temperature of maximum permittivity (Tmax), the studies will be directed to the dynamics of phase boundaries below Tmax. Relaxation spectroscopy will be used to measure activation energy and activation volumes of mobile interfaces, which can be conveniently performed using polarization relaxation at small field and stress relaxation at large field. To lend further insight into the atomistic mechanisms that affect polarization reversal and interface mobility, synchrotron x- ray absorption spectroscopy (EXAFS) studies and Monte-Carlo lattice simulations will be conducted. These investigations will be carried out for both model ferroelectrics and their modifications to delineate the broader effects of chemistry, defect, and nanostructure that can influence interfacial dynamics by either providing obstacles to interface motion or by altering the mobility of the interface itself. The goal of the research is to provide a unified and detailed understanding, from the viewpoint of interface dynamics, of various interface-controlled ferroelectric, ferroelastic and piezoelectric phenomena that have broad implications to the performance and long-term reliability of ferroelectric ceramics as devices. %%% The goal of the research is to provide a unified and detailed understanding, from the viewpoint of interface dynamics, of various interface-controlled ferroelectric, ferroelastic and piezoelectric phenomena that have broad implications to the performance and long-term reliability of ferroelectric ceramics as devices. Three families of prototypical ferroelectrics with a perovskite structure, barium titantate, lead zirconium titanate, and lead magnesium niobate, long with their various compositional and microstructural modifications, will be investigated. These materials are used in many types of sensors, actuators, and electronic devices. ***

9632989 Chen 拟议的研究将研究铁电畴壁和相界的动力学，在钙钛矿中，铁电畴壁和相界几乎是原子级尖锐的，厚度约为一到两个原子层间距。对于这种尖锐的界面，界面台阶的机制（类似于位错凹凸和扭结）以及界面和障碍物的相互作用（类似于位错钉扎和弓出）是理解界面动力学的核心。 这些特性将通过在应力场或电场下明确设计的实验中测量界面台阶的迁移能、形成能和活化体积来直接探测，并将通过侧重于原子学的额外结构和模拟研究来补充。畴壁和相界的阶梯机制。将研究具有钙钛矿结构的三个典型铁电体家族：BaTiO3、Pb(Zr1-xTix)O3 (PZT) 和 Pb(Mg1/3Nb2/3)O3 (PMN)，以及它们的各种成分和微观结构修饰。对于 BaTiO3 和 PZT 类型的陶瓷，它们在居里温度 Tc 下有急剧的转变，人们的兴趣主要集中在低于 Tc 的磁畴壁动力学上。对于 PMN 类型的陶瓷，其具有更宽的介电常数峰值和实际转变扩散并且远低于最大介电常数 (Tmax) 的温度，研究将针对低于 Tmax 的相界动力学。 弛豫光谱将用于测量移动界面的活化能和活化体积，可以利用小视场的偏振弛豫和大视场的应力弛豫方便地进行测量。 为了进一步了解影响极化反转和界面迁移率的原子机制，将进行同步加速器 X 射线吸收光谱 (EXAFS) 研究和蒙特卡罗晶格模拟。这些研究将针对铁电体模型及其修饰进行，以描述化学、缺陷和纳米结构的更广泛影响，这些影响可以通过为界面运动提供障碍或通过改变界面本身的迁移率来影响界面动力学。该研究的目标是从界面动力学的角度提供对各种界面控制的铁电、铁弹性和压电现象的统一和详细的理解，这些现象对铁电陶瓷器件的性能和长期可靠性具有广泛的影响。 %%% 研究的目标是从界面动力学的角度提供对各种界面控制的铁电、铁弹性和压电现象的统一和详细的理解，这些现象对铁电陶瓷的性能和长期可靠性具有广泛的影响作为设备。将研究具有钙钛矿结构的三个典型铁电体家族：钛酸钡、钛酸铅锆和铌酸铅镁，以及它们的各种成分和微观结构修饰。 这些材料用于多种类型的传感器、执行器和电子设备。 ***