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Abstract
Increasing demand for environmentally friendly materials in electronic and automotive industries has promotedextensive studies on searching lead-freealternatives of PZT-based piezoelectrics that contain more than 60 wt% Pb. For systematic investigation of new lead-free piezoceramics with large electric field-induced strains (EFISs),the Korean governmentalso launched a team project on July 2008, in which four Korean national research institutes based on authors’ group and seven universities have participated. In the integrated project, four groups have played each role in 1) exploitation of new compositions with domain engineering, 2) preparation of nanosized lead-free ceramic powders, 3) development of multilayer ceamic actuators using lead-free ceramics, and 4) development of microelectrmechanical system (MEMS) devices using lead-free thin films.This talk will give a brief introduction to the team project.
As one of various research topics, we studied the dielectric, ferroelectric, EFIS properties of BNKT modified with A- or B-site dopants or other ABO3 compounds. As a result, we found that many modifiedBi1/2Na1/2TiO3- Bi1/2Na1/2TiO3 solid solution (BNKT) ceramics exhibited a large strain when there was a ferroelectric-relaxor (FE-R) crossover as the modifier content increased, which was very similar to previous works on BNT-BT-KNN [1] or BNT-BKT-Bi(Zn1/2Ti1/2)O3[2]. In the case of A- or B-site impurities, the FE-R crossover was observed when the tolerance factor (t) of the perovskite structure was decreased by doping, whereas the FE state of unmodified BNKT remained stable when the dopant increased the t. Despite the fact that BNKT-based ceramics have shown large normalized strains in the range of Smax/Emax= 500 – 700pm/V at RT near the FE-R transition region, there were severalproblems in applications such as large strain-field hysteresis,high electric-field to trigger large strain, and strain stability in a limited temperature range. In order to resolve such problems, we attempted to prepare ceramic-ceramic composites by embedding FE particles in a relaxor matrix. The normalized strain Smax/Emaxwas remarkably enhanced by lowering the triggering field even though the maximum strain was almost unchanged. The ceramic-ceramic composite is believed to enlighten a new road to large strain lead-free alternatives of Pb-based actuator materials.
[1] S. T. Zhang, A. B.Kounga, E.Aulbach, H. Ehrenberg, and J. Rödel, Appl. Phys. Lett. 91, 112906 (2007).
[2] R. Dittmer, W. Jo, J. Daniels, S Schaab, and J. Rödel, J. Am. Ceram. Soc., 94 [12] 4283–4290 (2011).
CV
Jae-Shin Lee，韩国蔚山大学材料学院教授。1982 年毕业于韩国首尔国立大学陶瓷工程系，1986 年获韩国科学技术高等研究院（KAIST）博士学位，2000年起任蔚山大学正教授，并担任系主任（1999 至2000年）。Jae-Shin Lee 教授是活跃在压电材料领域的韩国著名教授，是铁电压电材料与器件方面的国际知名专家，Lee教授领导的课题组是韩国最早开展无铅压电陶瓷研究的小组之一，近年来尤其在以钛酸铋钠和铌酸钾钠基为代表的驱动器用无铅压电陶瓷材料的结构设计和性能调控方面做出了有影响的工作，受到国际同行的关注。Lee 教授已经发表102 篇学术期刊论文（其中70 篇SCI 收录）和近300 篇会议论文，并拥有65 项发明专利。
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