Domain Walls and Phase Boundaries in Ferroelectric Oxides

小行星9632989 拟议的研究将研究铁电畴壁和相边界的动力学，在钙钛矿中，它们几乎是原子级尖锐的，厚度为一到两个原子层间距。对于这种尖锐的界面，界面台阶（类似于位错颠簸和扭结）沿着与界面和障碍物（类似于位错钉扎和弓出）的相互作用的机制是理解界面动力学的核心。 这些特性将直接探测通过测量的迁移能，形成能，和活化体积的界面步骤在明确设计的实验下的应力场或电场，并将补充额外的结构和模拟研究，重点是原子的域壁和相边界的步骤机制。三个家庭的原型铁电体与钙钛矿结构，钛酸钡，铅（锆1-xTix）O3（PZT）和铅（镁1/3铌2/3）O3（PMN），沿着与他们的各种组成和微观结构的修改，将进行研究。对于BaTiO 3和PZT类型的陶瓷，其在居里温度Tc处具有急剧转变，主要关注低于Tc的畴壁的动力学。对于PMN类型的陶瓷，其具有更宽的介电常数峰值，实际过渡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的相边界的动力学。 弛豫光谱将用于测量移动的界面的激活能和激活体积，这可以方便地使用极化弛豫在小场和应力弛豫在大场进行。 为了进一步深入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。这些调查 将进行两个模型铁电体和它们的修改，以描绘更广泛的影响化学，缺陷，和纳米结构，可以影响界面的动态，通过提供障碍，界面运动或通过改变界面本身的流动性。研究的目标是从界面动力学的角度，对各种界面控制的铁电、铁弹和压电现象提供统一和详细的理解，这些现象对铁电陶瓷作为器件的性能和长期可靠性具有广泛的影响。 本研究的目的是从界面动力学的角度，对各种界面控制的铁电、铁弹和压电现象提供一个统一而详细的理解，这些现象对铁电陶瓷作为器件的性能和长期可靠性具有广泛的影响。三个家庭的原型铁电体与钙钛矿结构，钛酸钡，锆钛酸铅，和铅镁钛酸盐，长期与他们的各种组成和微观结构的修改，将进行研究。 这些材料用于许多类型的传感器、致动器和电子设备。 ***

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. ***