主讲人：晏海学 博士（Reader）（伦敦大学玛丽女王学院）

题目：Phase transitions in Bi_0.5Na_0.5TiO₃based ferroelectrics

时间：2023年06月09日（周五）上午10:00

地点：理工楼1226报告厅

联系人：贾成龙

报告摘要：

Due to the worldwide concerns of environmental protection and sustainable development, lead-free ferroelectric materials are greatly desired for piezoelectric sensor applications and high power energy storage in dielectric capacitors. However, their lower piezoelectric constant and energy density compared to the conventional lead-containing materials significantly limits their applications. Bi_0.5Na_0.5TiO₃(BNT)-based ceramics are good lead-free candidates for piezoelectric and dielectric application and their properties are related to their phase transitions. Normally, there are polar rhombohedral R3c and the weakly polar tetragonal P4bm phases in BNT systems. Electrical poling produces an increase of the rhombohedral phase fraction together with a rise of the rhombohedral and tetragonal distortion. This confirms the occurrence of a phase transition from the weakly polar to the polar phase during electrical poling. Four peaks found in the current−electric field (I−E) loops are related to electric field induced transitions. By studying the temperature dependence of the current peaks in the I−E loops, the thermal depoling temperature of BNT-based ceramics can be characterised. The thermal depoling temperature sets the upper limit high temperature for piezoelectric application, but for high power energy storage it is necessary to shift the depoling temperature below working temperature of dielectric capacitors. Introducing ZnO in BNT system is useful for increase the depoling temperature for piezoelectric application. Sr doping in BNT system is beneficial for high power energy storage applications due to decreasing the depoling temperature.

个人简介：

Dr. Haixue Yan is a Reader in Materials Science and Engineering at Queen Mary University of London. He is a Fellow of the IOM3 and a world leading expert on high temperature piezoelectric, lead-free ferroelectrics, SPS and ferroelectric phase transitions. He has >200 peer reviewed papers and 9 patents (Google scholar H-index=52), including 25 papers on lead-free ferroelectrics and SPS with more than 100 citations each.