"Mechanics of Smart Materials Origins of Property Coefficients from in situ X-ray and Neutron Scattering"

Jacob L. Jones, PhD - University of Florida

ABSTRACT
Dielectric and piezoelectric materials are used in a broad range of applications including impact and displacement sensors, actuators, capacitors, micro-electromechanical systems, diesel fuel injectors, vibrational energy harvesting, sonar, and ultrasound. In these applications, the dielectric and piezoelectric coefficients define the performance and limits of device operation. However, the true origin of the coefficients is not understood because of the numerous and complex microstructural and crystallographic contributions to these properties (e.g., ionic and dipolar polarizability, ferroelastic domain wall motion, interphase boundary motion, the intrinsic piezoelectric effect, etc.) This talk will demonstrate our use of in situ X-ray and neutron scattering methods to discern these mechanisms, thereby revealing the underlying mechanics of smart materials and the contribution of these various mechanis ms to the property coefficients. In all cases, direct measurements of the contribution from the lattice (e.g., piezoelectric) and the motion of intragranular interfaces (e.g., domain walls, interphase boundaries) are quantitatively related to the property coefficients using micromechanics-based formulations. It is first observed that the electric-field-induced lattice strain in donor-modified or 'soft' lead zirconate titanate (PZT) is dominated by domain wall motion contributions, suppressing piezoelectric distortions of the lattice. In contrast, the response of acceptor-modified or 'hard' PZT and tetragonal BaTiO3 under similar conditions is not as strongly dominated by domain walls. The lead-free composition Ba(Zr0.2Ti0.8)O3-x(Ba0.7Ca0.3)TiO3 is shown to exhibit significantly enhanced domain wall motion contributions at compositions approaching the morphotropic phase boundary (i.e., x=0.5), correlating and contributing to the very high piezoelectric coefficient of 620 pC/ N . The high-temperature piezoelectric ceramic PbTiO3-xBiScO3 also exhibits significant domain wall motion, contributing to equally large piezoelectric coefficients. These results introduce a new paradigm in the understanding and design of electromechanical materials. The authors gratefully acknowledge support from the NSF through DMR-0746902 and the Department of the Army through contract number W911NF-09-1-0435.

BIOGRAPHY
Dr. Jones is an Associate Professor in the Department of Materials Science and Engineering at the University of Florida with research interests in ferroelectric and piezoelectric ceramics, mechanics of materials, and crystallography and has published over 75 papers on these topics since 2004. Dr. Jones' research has been supported by the National Science Foundation, the Army Research Office, Sandia National Laboratories, Oak Ridge National Laboratory, and various industrial sponsors. He has received numerous research awards including the National Science Foundation CAREER award (2007), a Presidential Early Career Award for Scientists and Engineers (2009) awarded at a White House ceremony in January 2010, the IEEE Ferroelectrics Young Investigator Award (2011), a National Nuclear Security Administration (NNSA) 2009 Defense Program Award of Excellence, and the 2010 Edward C. Henry "Best Paper" award fro m the Electronics Division of the American Ceramic Society. From UF, he has been recognized through the prestigious Pramod Khargonekar Award (2012), the HHMI Science for Life Distinguished Mentor (DM) Award (2012), a 2010 Provost's Excellence Award for Assistant Professors, and three MSE Faculty Excellence Awards (2010, 2011, 2012).

If you are interested in scheduling a time to meet the speaker, please contact Cecelia Jones.