Piezoelectric Hardening Mechanisms under External Stress

Modern electro-mechanical conversion technologies are frequently based on piezoelectric materials, which enable efficient and miniaturized actuators/motors, devices for generating ultrasound, or sensors. Such elements are used in the automotive industry, robotics, medical diagnostics, acoustics, energy conversion, and consumer electronics as haptic devices. These applications are required to operate under increasingly severe conditions, which imposes a large challenge for piezoelectric materials. In fact, the materials limits currently also represent the limits for the applicability of these devices, for example in terms of temperature range or mechanical stress. In the case of applications that utilize the piezoelectric resonance vibration, these limits are poorly investigated and expose the lack of understanding of the fundamental underlying physical mechanisms that take place within the material during high-frequency drive. The goal of this project is to investigate the influence of mechanical stress on resonating piezoelectric materials, both on the macroscopic and the microscopic levels. During operation, such stresses are imposed on the piezoelectric element either through mounting into the electro-mechanical device, or intentionally by mechanical pre-loading. The project will investigate how the microscopic piezoelectric hardening mechanisms (i.e., interaction of domain walls with defects) are influenced by externally- applied mechanical stress. During the first stage, a measurement procedure for resonance measurements under stress will be developed, which will provide new insights to study the local processes, relate them to the macroscopic functional properties, and additionally help to advance the theoretical formalisms. In the second stage, different piezoceramic materials will be investigated and compared, in order to identify the efficiency of individual hardening mechanisms. The project will enhance the basic knowledge of materials behavior under extreme conditions and enable us to better understand their limitations. On the one hand, this will help to critically evaluate the different piezoelectric hardening mechanisms and facilitate the development of new material compositions with improved properties. On the other hand, this improvement will also enable further miniaturization and identification of new piezoelectric applications in environments, which seem inconceivable today.