题目：Phase Transitions in Lead-Free 0.94(Bi0.5Na0.5TiO3)–0.06(BaTiO3) Based Ferroelectrics

报告人：Dr. Haixue Yan

时 间：2017年8月3日（星期四）上午10:00

地 点：齐云楼620会议室

摘要：Lead-free 0.94(Bi0.5Na0.5TiO3)–0.06(BaTiO3) (BNTBT) is a potential piezoelectric candidate to replace lead-based PZT ceramics. The thermal depoling temperature sets the upper limit for the high temperature application of piezoelectric materials. Recently, an interface model was proposed to explain the good resistance to thermal depoling of BNTBT-ZnO composite. However, we found that the presence of ZnO was not limited to the interface, but contributed intrinsically to the BNTBT lattice. This played a critical role in the structural changes of BNTBT, confirmed by a unit volume change supported by XRD, which was further proved by Raman, EDS, and dielectric characterization at different temperatures. The previous interface model is not correct because BNTBT shows thermally stable piezoelectric properties, even though there is no interface between BNTBT and ZnO. The thermal depoling behavior of BNTBT-based materials is directly related to the transition temperature from the rhombohedral phase to the tetragonal phase in our phase transition model, which is consistent with four current peaks in their ferroelectric loops close to the depoling temperature.

简介：Dr. Haixue Yan is a Senior Lecturer in functional materials at Queen Mary University of London (QMUL). Thermoelectric materials, high temperature piezoelectric, lead-free ferroelectrics, multiferroics and SPS are hot topics of current fundamental research and industrial application. The research in his group includes these topics with textured,1-3 nano-4-7 and metastable structures.8,9 He found contradictory evidence on the Tc of ferroelectric CaBa2Nb2O9. Using two independent experiments1 he measured the Tc of CaBi2Nb2O9. He then obtained ceramics with the highest thermal depoling temperature (800 °C) in polycrystalline BLSFs ceramics. His work on the texturing of ferroelectric ceramics has solved a thirty year problem in this field. In 2009 he reported for the first time ferroelectricity and piezoelectricity in layer-structured A2B2O7 compounds with super-high Curie points (>1,450 °C).3 This work has opened up this field, with the prospect of producing a step change in the operating temperature of piezoelectric sensors. His work on nanotechnology demonstrated that nano particles can work as building blocks4 during SPS to improve ferroelectric polarization, and multiferroic BiFeO3 bulk ceramics are ferroelectric active in 40 nm sized grains.7 Recently his work on ferroelectric characterization provided evidences to answer an open question on four current peaks in I-E loops of lead-free (BiNa)0.5TiO3 materials (field induced transitions).10 His research has been funded by EC, TSB, Royal Society, Royal Academy of Engineering, EPSRC and industry. He has 4 patents and 117 papers in peer-reviewed SCI journals (H-index of 27).