Speaker: Dr. Haixue Yan (Queen Mary University of London (QMUL))

Time: 10:00, May 30, 2019

Venue: Room 602, Building 33, Wushan Campus

Abstract: Spark Plasma Sintering (SPS) is a rapid sintering technology to densify ceramics within minutes with additional drive force from mechanical pressure, using high current passing conductive moulds to provide local heating with very high heating rate.  Nano powders can be sintered using SPS to get dense ceramics with nanometer-sized grains. Because of high heating rate, composite materials can be prepared using SPS with minimum diffusion regions between different phases. Moreover, because the mechanical pressures can be applied and recorded during SPS, which not only provides sintering temperature window based on one single sample processing but also opens the possibility to prepare grain oriented textured materials. Properties of ceramics are related to grain size and textured microstructure. SPS has been successfully used to prepare different dense ceramics to research effect of grain size or texture on properties of materials. In this talk, I will discuss the grain size effect in perovskite structured materials, including BaTiO3, Na0.5K0.5NbO3 and BiFeO3 ferroelectrics, and effect of texture in layer structured ferroelectrics prepared using SPS.

Biography: Haixue Yan received his Ph.D. in Materials Science and Technology from Shanghai Institute of Ceramics, Chinese Academy of Sciences in 2001. He is a Senior Lecturer in functional materials at Queen Mary University of London (QMUL). High temperature ferroelectrics, lead-free piezoelectric, energy materials and Spark Plasma Sintering (SPS) are important topics of current fundamental research and industrial applications. His research includes these topics with textured, nano- and metastable structures. He found contradictory evidence on the Tc of ferroelectric CaBa2Nb2O9. Using two independent experiments he measured the Tc of CaBi2Nb2O9. He then obtained ceramics with the highest thermal depoling temperature (800 oC) in polycrystalline ferroelectric ceramics. The material can be operated up to 800 oC without degradation of its properties; this is 200 oC above the operating temperature for currently used ceramics materials. 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 oC). 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 blocks during sintering to improve ferroelectric polarization. Recently his work on ferroelectric characterization provided evidences to answer an open question on phase transitions in lead-free (BiNa)0.5TiO3 and AgNbO3-based materials for high power energy storage and/or actuators.  He has 146 publications (including Adv Mater, Nano Energy, JMCA, JMCC, JPCC and Acta Mater) with H-index=38. He has been serving as an editorial board member of Advance in Applied Ceramics and Materials Research Bulletin.