Converse Transduction in the Presence of Strong Electrical Field Gradients in Ferroelectrics (ConTraGrad)

这个项目的总体目标是更深入地了解铁电类压电材料在承受高电场和强电场梯度时的行为，包括压电性和挠性电效应。挠性电是指介质中机械应变梯度和电极化之间的机电耦合。近年来，越来越多的科研兴趣转向了铁电材料中的挠性电性。这项调查将在门兴理工大学(TUM)和卡尔斯鲁厄理工学院(KIT)之间进行。TUM组将主要负责进行实验研究，而KIT组将致力于理论研究，即建模和仿真。目标和工作将分两部分安排。第一个目标是利用大信号迟滞行为理论来研究单边交指电极(IDE)结构的驱动器，以了解和优化驱动器极化后的变形，以及在特别考虑可能的压电非线性的情况下研究驱动器的驱动势，主要涉及强电场的产生。第二个目标首先与强的电梯度有关，它涉及到逆曲电效应。对于本文提出的具有单面IDE图案的致动器，这涉及到调查一侧的逆弯电效应与另一侧的致动行为的关系。强电梯度的应用有望导致新类型的行为。鉴于上述目标，我们建议研究：1)压电非线性：材料内的冻结区域变得可移动(即可用)，从而有效地增加了压电系数的大小。2)逆曲电性：具有明显梯度的强非均匀电场导致激活逆曲电效应。3)压电-挠曲电耦合：关于这两种效应之间相互作用的信息目前几乎不存在。从这个项目中获得的知识具有重要的实际意义。例如，它可能实现故障安全执行器，其工作温度超过压电陶瓷的CurieteTemperature。然后，执行器可以作为极端环境中设备的有源部件。

The overall objective of this project is gaining a deeper insight into the behavior of the ferroelectric class of piezoelectric materials when subject to high electric fields and strong electrical gradients covering both, the piezoelectric and flexoelectric effects. Flexoelectricity refers to the electromechanical coupling between the mechanical strain gradient and the electrical polarization in a dielectric. Recently, more and more interest in scientific research has been shifted towards flexoelectricity in ferroelectrics. The investigation will be executed as collaboration between the Technische Universität München (TUM) and the Karlsruhe Institute of Technology (KIT). The TUM group will mainly be responsible for performing the experimental investigations while the KIT group will be working on the theoretical investigation, i.e. modeling and simulation. The objectives and the work will be organized in two parts. The first objective, primarily related to the occurrence of high electric fields, is to study actuators with singlesided interdigitated electrode (IDE)-patterns by means of a theory for large signal hysteresis behavior in view of understanding and optimizing the actuator deformation after poling, as well as investigating the actuation potential with special consideration ofpossible piezoelectric non-linearity. The second objective, related to strong electrical gradients in the first place, concerns the converse flexoelectric effect. For the actuators with single sided IDE-patterns subject of this proposal, this involves investigating the relevance of the converse flexoelectric effect on one side and understanding thecontribution of the converse flexoelectric effect to the actuation behavior on the other. The application of strong electrical gradients is expected to lead to new types of behavior. In view of the above objectives, we propose to study: 1) piezoelectric non-linearity: frozen domains within the material become mobile (i.e. usable), in effectincreasing the magnitude of the piezoelectric coefficients. 2) converse flexoelectricity: strong non-uniform electric fields with pronounced gradients lead to activating the converse flexoelectric effect. 3) piezoelectric-flexoelectric coupling: information on the interplay between the two effects is currently quasi non-existent. The knowledge gained from this project has important practical consequences. For instance, it might enable realization of fail-safe actuators that function in temperatures that exceed the Curietemperature of piezoelectric ceramics. The actuators can then serve as the active components for devices in extreme environments.