Speaker: Dr. Kyle Webber, FAU

Speaker:  Dr. Kyle Webber, Department of Materials Science and Engineering

FAU, Germany

Title: Stress-Modulated Electromechanical Properties of Lead-Free Ferroelectrics

Abstract:

Ferroelectrics are a critical enabling technology used in numerous applications in, e.g., automotive, aerospace, military, and medical fields, due to an electromechanical coupling. Currently, however, the majority of these applications depend on material systems containing lead, posing serious environmental and health concerns. This has led to a concerted effort over the past ~20 years to develop lead-free alternatives, paralleling previous efforts to remove lead from gasoline, paint, and solder. A number of promising lead-free alternatives have been developed, demonstrating comparable and even enhanced electromechanical properties under certain conditions to current lead-containing materials. One of these candidates, (Na1/2Bi1/2)TiO3-based solid solutions, have shown considerable promise for actuation systems due to a large electromechanical response, in addition to being of interest for use in high energy density solid state capacitors as well as electrolyte materials in intermediate temperature solid oxide fuel cells. Importantly, these applications can result in significant mechanical fields being applied to the ferroelectric element, which can influence both the electromechanical response and the crystal structure through various stress-modulated hysteretic processes. 

During this presentation, the stress-modulated electromechanical behavior will be introduced, with a particular focus on the field-induced long-range ferroelectric order observed in NBT-based relaxor ferroelectrics. Analogous to the electric-field-induced ferroelectric long-range order in relaxor ferroelectrics, which is understood to be the origin of the large strain response in NBT-base materials, we have discovered a stress-induced transition to long-range ferroelectric order. Macroscopic mechanical constitutive properties as well as temperature- and stress-dependent dielectric and piezoelectric measurements are presented together with in situ and ex situ structural investigations, providing insight into the disorder-order transition and structural phase transformations. Finally, recent work applying these finding to tuning of the electromechanical properties of aerosol deposited films will be discussed, where internal residual stresses are leveraged to enhance the functional properties and operating temperature range. 

Bio:

Kyle G. Webber is a Professor of Functional Ceramics in the Department of Materials Science and Engineering, Friedrich-Alexander-Universität Erlangen-Nürnberg, Germany, where he is interim Head of the Glass and Ceramics Institute, Dean of Studies for the Engineering Department, and Director of the International Research and Training Center “Energy Conversion Systems: From Materials to Devices”, a joint project together with the Nagoya Institute of Technology, Japan. He received a B.Sc. in Marine Systems Engineering from Maine Maritime Academy in 2003, where he obtained a 3rd Assistant Engineer US Coast Guard license, and a M.Sc. and Ph.D. in Mechanical Engineering from the Georgia Institute of Technology in 2005 and 2008. His primary research focus is temperature-dependent electromechanical properties of functional ceramics, field-induced phase transformations, mechanics of ceramics, and ceramic/ceramic composites. He is an Emmy Noether Research Fellow of the German Research Foundation and was awarded the IEEE UFFC Ferroelectrics Young Investigator Award in 2017.