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

• Applicants: Professor Dr.-Ing. Marc Kamlah; Professor Dr.-Ing. Norbert Schwesinger
• Subject Area: Microsystems ; Electronic Semiconductors, Components and Circuits, Integrated Systems, Sensor Technology, Theoretical Electrical Engineering ; Synthesis and Properties of Functional Materials
• Term: from 2018 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 391065131

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.

• DFG Programme: Research Grants