1、Optimising Pb-free Actuators through Pseudosymmetry
Ian M. Reaney(Functional Materials and Devices Laboratory，Materials Science and Engineering，University of Sheffield)
2、Bismuth Ferrite-Based Lead-Free Relaxor Ceramics and Multilayers with High Energy Density
Dawei Wang(Department of Materials Science and Engineering, University of Sheffield, Sheffield S1 3JD, UK)
Although most commercial multilayer actuators are fabricated from normal ferroelectric materials such as lead zirconate titanate (PZT), electrostrictive actuators based on relaxor-ferroelectrics such as Pb(Mg1/3Nb2/3)O3 have been commercialised. Lead based electrostrictive actuators offer high strains but at the expense of higher operating voltages and are only used in a comparatively small numbers for niche applications.
The search for a lead-free, piezoelectric replacement for PZT has stalled because of the limited number of solid solutions which exhibit a suitable morphotropic phase boundary. However, PbO-free relaxor-ferroelectric solid solutions offer the possibility of fabricating multilayer actuators using a dominant electrostrictive rather than piezoelectric response.
This contribution reviews recent work on PbO-free, high-strain, electrostrictive multilayer actuators at the University of Sheffield. Crystallochemical concepts of how to optimise PbO-free solid solutions for electrostrain are discussed and its crystallographic origin presented.
Ian is the Director of Research and Innovation at the Department of Materials Science and Engineering. He was awarded a Personal Chair at University of Sheffield in 2007 and is now the Dyson Chair in Ceramics. He joined the Faculty of Engineering in 1994, initially as a PDRA, then as a Lecturer from 1995. He obtained his PhD from the University of Manchester in 1989 and worked as post-doctoral researcher at the University of Essex before joining the Laboratoire de Ceramique, Ecole Polytechnique Federale de Lausanne in Switzerland in 1991.
Ian has been awarded over ?20M in career income for engineering research, over ?1.5M of which has been industrially related; he has been Principal or Co-Investigator on 30 EPSRC awards. His scientific achievements have arisen from the successful delivery of a wide portfolio of large projects, with a research group of over 15 researchers for the last 15 years. During this time he has supervised to completion over 50 PhD & MSc students. His publications, over 300 scientific papers, receive ~1400 citations per year; many of these have announced major breakthroughs in scientific understanding with 30 papers having over 100 citations. His career H-index = 59 (H5 = 43, Googlescholar). His research leadership in a wide range of functional ceramic disciplines has been recognized by >70 Invited/Plenary talks at International Conferences on topics such as MW ceramics, bioceramics, relaxor-ferroectrics and piezoelectrics. Recently, he gave an invited lecture recent to a multidisciplinary audience on ‘Failure, The Greatest Teacher’ at Electronic Materials and their Applications in 2015. He is the European site director of the Centre for Dielectrics and Piezoelectrics whose members include: Murata, Apple and Samsung.
Lead-free ceramics with high recoverable energy density (Wrec) and energy storage efficiency (η) are attractive for advanced pulsed power capacitors to enable greater miniaturization and integration. Bismuth ferrite (BF)-based, lead-free relaxor ceramics and multilayers were fabricated and the role of composition on the structure-property relations investigated, with a focus on energy storage characteristics. Due to the enhanced electric field (E) breakdown strength (BDS) and large maximum polarization (Pmax), high Wrec (1.8~2.5 J/cm3) was achieved across a range of compositions. Multilayers of optimum compositions possessed high Wrec of 10.5 J/cm3 and η ~ 87%, were stable up to 125 °C, and were therefore considered promising candidates for lead-free energy storage applications.
Dr. Dawei Wang is a Research Associate in the Department of Materials Science and Engineering at the University of Sheffield (UK) since 2014. He received his PhD degree from Beijing Institute of Technology (China) in 2012. He was also a Joint PhD student (2010-2011) and a visiting scholar (2016.4-6) at the Materials Research Institute of Pennsylvania State University (USA). His research focuses on the synthesis and characterization of innovative energy storage/conversion/harvesting materials, and translation of new materials to porotype devices/components for electronic systems. He has published 80+ refereed papers (Energy & Environmental Science, Journal of Materials Chemistry A, etc.), with a total citation of 1700+ and an H-index of 27 (google scholar). Also, he holds 5 issued patents and has given 10+ invited talks on international conference (EMA 2019, CICC-11, etc.). He is the invited reviewers for 30+ international journals and also the topic editor of Frontiers in Materials, guest editor of Journal of Advanced Dielectrics.