清华大学材料科学与工程研究院《材料科学论坛》

学术报告

报告题目：Rate-Dependent Stress-Modulated Long-Range Ferroelectric Order in Lead-free Ferroelectrics

报告人：Prof. Kyle G. Webber（ Friedrich-Alexander-Universit?t Erlangen-Nürnberg, Germany.）

报告时间：8月31日（周五）上午10:00

报告地点：清华大学逸夫技术科学楼A205报告厅

联系人：王轲 62786252

报告摘要：
Among the possible lead-free alternatives to lead-based ferroelectrics, materials based on (Na1/2Bi1/2)TiO3 have displayed the largest unipolar strain response, making them particularly attractive for actuation applications. The origin of this exceptional electromechanical behavior is understood to be due to an electric-field-dependent transition from the relaxor state (RE) to long-range ferroelectric order (FE), which results in a closed strain-electric field hysteresis loop and subsequent large unipolar strain. Importantly, the RE-FE transition can also be induced with an external mechanical field. The time-dependent electromechanical behavior of lead-free ferroelectrics is presently unclear, although reports have shown a strong dependence on frequency.
In this presentation, the recent experimental investigations of the time- and rate-dependent electromechanical response of polycrystalline (Na1/2Bi1/2)TiO3-xBaTiO3 during electrical and mechanical loading will be discussed. In particular, during electrical loading, a two-step creep-like behavior was observed at intermediate electric field levels, consistent with a “self-catalyzed” behavior that depends on both the magnitude of electric loading and holding time. These findings will be discussed together with previous observations in lead-based relaxors. Analogous to the electrical case, a significant rate-dependence has also been recently observed during mechanical loading (Fig. 1b), where testing was performed over 5 orders of magnitude and revealed a substantial change in the critical RE-FE stress as well as remanent strain. These results are important for actuator applications, as many actuator applications apply large electrical and mechanical fields during operation. In addition, current multilayer composite structures can have large internal residual stresses, thereby affecting the electromechanical response.

报告人简介：
Kyle G. Webber is a Professor in the Materials Science and Engineering Department of the Friedrich-Alexander-Universit?t Erlangen-Nürnberg, Germany. He received a B.Sc. in Marine Systems Engineering from Maine Maritime Academy in 2003 and a M.Sc. and Ph.D. in Mechanical Engineering from the Georgia Institute of Technology in 2005 and 2008. His primary research focus is temperature-dependent mechanical properties of functional ceramics, phase transformations, and fracture of single crystal and polycrystalline ferroelectrics. He received the Emmy Noether Research Fellowship from the Deutsche Forschungsgemeinschaft in 2013 and the IEEE UFFC Ferroelectrics Young Investigator Award in 2017. He has coauthored more than 80 refereed publications.