Mechanisms of Enhancement in Lead-Free Piezoceramic Composites

• Main Author: Ayrikyan, Azatuhi
• Format: Others
• Language: en
• Published: 2019
• Online Access: https://tuprints.ulb.tu-darmstadt.de/9061/1/AyrikyanDissertationSep2019v7.pdf; Ayrikyan, Azatuhi <http://tuprints.ulb.tu-darmstadt.de/view/person/Ayrikyan=3AAzatuhi=3A=3A.html> : Mechanisms of Enhancement in Lead-Free Piezoceramic Composites. Technische Universität, Darmstadt [Ph.D. Thesis], (2019)

The aim of this work is to investigate lead-free ferroelectric ceramic/ceramic composites, with the ultimate goal of elucidating the mechanisms of their enhanced electromechanical response. Previous work has shown that a composite comprised of a highly disordered nonpolar ferroelectric matrix material and an ordered polar seed material results in an increased electromechanical response under specific circumstances. The mechanisms used to explain this enhancement have been based on the electrical and mechanical interactions between the seed and matrix during application of an electric field. However, the interactions between the seed and matrix during processing also play a significant role in the enhancement observed in lead-free ferroelectric composite systems. The fabrication of ceramic/ceramic composites requires high-temperature sintering of the seed and matrix for formation of densified pellets. Fundamental laws of kinetics dictate that diffusion between the two constituents should occur at the high temperatures required for ceramics processing. In addition, a difference in the sintering trajectories will result in a nonzero stress state during sintering, which is well established to effect the microstructure. The structure-property relationships in composites can provide new insight into these mechanisms, but there have been significant challenges in investigating structure at the microscale. To that end, model systems of 2-2 composites were prepared and utilized to investigate these phenomena. In light of the influences of diffusion and internal stress on electromechanical behavior, the electromechanical response of several 0-3 and 2-2 composite systems are investigated. The influence of co-sintering interactions on the electromechanical behavior of electroceramics plays an important role in the improvement of lead-free material systems for the replacement of current commercially dominant lead-based systems.