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梯度作用下的行为，包括压电和挠性电效应。挠性电是指介质中机械应变梯度与电极化之间的机电耦合。近年来，人们对铁电体挠性电的研究越来越感兴趣。该调查将由德国理工大学Universität m<e:1> (TUM)和卡尔斯鲁厄理工学院（KIT）合作进行。TUM小组将主要负责进行实验研究，KIT小组将进行理论研究，即建模和仿真。目标和工作将分为两部分。第一个目标，主要与高电场的发生有关，是通过大信号滞后行为理论来研究具有单侧交叉电极（IDE）模式的执行器，以便理解和优化执行器在极化后的变形，并研究特别考虑可能的压电非线性的驱动电位。第二个目标，首先与强电梯度有关，涉及反向挠曲电效应。对于本提案主题的单面ide模式执行器，这涉及调查一侧反挠性电效应的相关性，并了解反挠性电效应对另一侧驱动行为的贡献。强电梯度的应用有望导致新的行为类型。鉴于上述目标，我们建议研究：1)压电非线性：材料内的冻结域变得可移动（即可用），实际上增加了压电系数的大小。2)逆挠曲电：具有明显梯度的强非均匀电场会激活逆挠曲电效应。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居里温度的温度下工作的故障安全执行器。然后，执行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.