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

该项目的总体目标是更深入地了解铁电类压电材料在高电场和强电场梯度下的行为，包括压电和挠曲电效应。挠曲电性是指电介质中机械应变梯度与电极化之间的机电耦合。近年来，铁电体的挠曲电性已成为科学研究的热点。该调查将由慕尼黑工业大学（TUM）和卡尔斯鲁厄理工学院（KIT）合作执行。TUM小组将主要负责进行实验研究，而KIT小组将致力于理论研究，即建模和仿真。目标和工作将分为两部分。第一个目标，主要涉及到高电场的发生，是研究致动器与单面叉指电极（IDE）-图案的大信号滞后行为的理论的手段，在了解和优化致动器的变形后极化，以及调查的驱动潜力，特别考虑到可能的压电非线性。第二个目标，首先与强电梯度有关，涉及匡威挠曲电效应。对于本提案主题的具有单侧IDE图案的致动器，这涉及研究一侧上的匡威挠曲电效应的相关性，以及理解另一侧上的匡威挠曲电效应与致动行为的相关性。强电梯度的应用有望导致新类型的行为。基于上述目的，我们提出研究：1）压电非线性：材料内部的冻结畴变得移动的（即可用），从而有效地增加压电系数的大小。 2)匡威挠曲电：具有明显梯度的强非均匀电场导致激活匡威挠曲电效应。 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，它可以实现在超过压电陶瓷的居里温度的温度下起作用的故障安全致动器。然后，致动器可以作为极端环境中设备的主动组件。

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.