应西安交通大学国际电介质研究中心邀请，美国爱荷华州立大学(Iowa State University)谭晓礼(Xiaoli Tan)教授将于5月5日上午11点在教二南304会议室作有关铁电-反铁电材料研究的学术报告，欢迎广大师生参加。

报告题目：The Antiferroelectric<->Ferroelectric Phase Transition: Questioning Common Assumptions

报告时间：5月5日(周四)上午11点

报告地点：教二南304会议室

摘要：Ferroelectric and antiferroelectric materials are of technological importance for transducers, energy storage and electrocaloric devices. Antiferroelectric crystals possess antiparallel-oriented electric dipoles within the unit cell and, as a result, no macroscopic polarization can arise. In contrast, ferroelectric crystals display high remanent polarization due to the presence of long-range aligned dipoles. Due to Coulomb forces, electric dipoles align their moments in the direction of the applied field. The aligning process in antiferroelectric crystals requires cooperative adjustment of the crystal lattice in many unit cells and corresponds to a first order displacive phase transition to a ferroelectric phase. Based on previous investigations, it has always been assumed that applied electric fields favor the ferroelectric phase (hence only lead to the antiferroelectric-to-ferroelectric phase transition) and the induced ferroelectric phase after the transition behaves like a normal ferroelectric ceramic.

In this talk, Prof. Tan will demonstrate with direct experimental evidences that (1) an electric field can induce an antiferroelectric phase out of a ferroelectric phase, and (2) the induced ferroelectric phase after the antiferroelectric-to-ferroelectric phase transition displays an auxetic behavior which is not seen in a normal ferroelectric ceramic. Tan’s group attribute the unexpected ferroelectric-to antiferroelectric phase transition to the volume contraction from the converse piezoelectric effect at the coercive field with a reversed polarity, and the auxetic behavior to a de-tilting process of oxygen octahedra in the crystal lattice. The technological relevance of these discoveries will also be discussed.

报告人介绍：

Xiaoli Tan is an Associate Professor at the Department of Materials Science and Engineering at Iowa State University. He is the Associate Editor of the Journal of the American Ceramic Society and a Senior Member of the Institute of Electrical and Electronics Engineers (IEEE). Xiaoli Tan graduated with a B.E. degree from the Department of Materials Science and Engineering at Xi’an Jiaotong University in 1989. He was a visiting scientist at the Florida International University from 1996 through 1998. He then moved to the University of Illinois at Urbana-Champaign and obtained a Ph.D. degree in Materials Science and Engineering in 2002. He joined the Iowa State University as an Assistant Professor in the same year and was promoted to Associate Professor in 2008. Tan’s research has been focused on the composition-processing-structure-property interrelationship in electroceramics, with the unique in situ TEM technique as the primary characterization tool. His has published more than 80 articles in refereed journals. Since he joined Iowa State University, he has graduated 1 M.S. and 5 Ph.D. students. He won the NSF CAREER Award in 2004 and the ISU Award for Early Achievement in Research in 2008.