DC-bias Hardening of Piezoceramic Materials

Piezoelectric materials allow the interconversion of mechanical and electrical signals and are therefore employed in a wide range of applications such as sensors, transducers, actuators, power generators, energy harvesters, etc. The best piezoelectrics are ferroelectric perovskites, whereby the electromechanical response in these materials under the application of an external electric field originates from the combined effect of intrinsic (field-induced crystal lattice strain) and extrinsic (irreversible non-180 domain switching) contributions. However, during high-power operations like ultrasound generation, motors, medical applications, and voltage transformation, these materials experience self-heating due to mechanical losses. This leads to serious degradation of electromechanical properties and thermal depolarization. To address this issue, various approaches such as acceptor doping, composite formation, and precipitate formation have been developed and utilized to suppress domain wall motion, which is the main cause of energy losses. Yet, the practicability of these approaches is undermined by poor stability of electromechanical properties, leading to a narrow temperature-vibration velocity operation window. In this project, we aim to develop a new and innovative approach to harden ferroelectric materials, effectively. Ferroelectric materials typically exhibit a nonlinear relationship between the applied electric/mechanical load and electrostrain/polarization. Therefore, we hypothesize that ferroelectric properties can be tailored by superimposing the applied AC voltage with a DC bias voltage. The proposed approach is expected to influence both the domain wall mobility and the lattice response to strain, leading to the realization of low-loss piezoelectric materials with excellent and stable high- power electromechanical properties. The approach will be investigated on lead-free Bi-based piezoelectric ceramics, which have emerged as potential candidates for high-power applications due to their considerable electric-field induced strain and stable properties over a wide vibration velocity range, surpassing the stability of commercial lead-based counterparts. The polycrystalline samples will be prepared by solid-state reaction and then subjected to detailed structural, microstructural, and electric analysis to screen compositions with desired crystal structure and electromechanical properties. These piezoceramics will be used to study the fundamental influence of DC fields on resonance behavior and to examine the effectiveness of the DC hardening approach. This research will provide a facile and new avenue to tune electromechanical properties, thereby opening the door to a broader range of piezoelectric devices and even new applications.