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Materials Science at Oregon State University

Where structure really matters: dielectric ceramics and ferroelectric nanocrystals

Date: Thursday, Oct 19th
Presenter: Dr. Tedi-Marie Usher-Ditzian, Oak Ridge National Laboratory


The functional properties of many materials are driven by the structural arrangement of their constituent atoms/ions. One of the most notable examples of this is found in piezoelectric and ferroelectric materials, where polar arrangements of the cations and anions enable piezoelectricity (dielectric displacement occurs due to mechanical stress or electric fields create mechanical strain). These materials are used in a multitude of applications, including sensors, actuators, ultrasound, ferroelectric RAM, and as dielectric capacitors for charge storage applications. For such systems, the atomic structure, and how it responds to external stimuli, gives rise to the properties of interest. Consequently, thorough characterization of the structure – accomplished largely through X-ray and neutron diffraction – is key for understanding the origin of the relevant functionalities and how to manipulate them. This seminar will present two areas in particular where structural characterization is yielding new insights. The first is dielectric ceramics based on the BaTiO3–Bi(M3+)O3 system, which can exhibit temperature independent dielectric permittivity over a wide range (0-200C) as the fraction of Bi(M3+)O3 reaches ~0.20. The origin of this unusual behavior has been elucidated by a combination of high resolution X-ray and neutron diffraction and pair distribution function (PDF) analyses, which revealed short-range structural distortions at nm length scales that persist to >200C. The second area is ferroelectric nanoparticles, which are of interest for understanding the fundamental size limit of ferroelectricity and for use in polymer composites and other flexible applications. Preliminary results on the effects of size, shape, and surface ligands on the structure of BaTiO3 nanocrystals will be presented.

Tedi-Marie Usher-Ditzian received her Ph.D. in Materials Science and Engineering from North Carolina State University in 2016 after completing her B.S. and M.S. at the University of Florida’s Department of Materials Science and Engineering. She is currently a postdoctoral research associate in the Neutron Sciences Directorate at Oak Ridge National Laboratory in Oak Ridge, TN. Her main research project employs X-ray and neutron diffraction and total scattering to probe the relationship between the structure of ferroelectric nanoparticles and their size, shape, and surface termination. Her research interests include functional materials, complex oxides, nanomaterials, and using in situ experiments to understand how a material’s structure responds to external stimuli at the atomic level. Usher is a recipient of the Ludo Frevel Crystallography Scholarship and received the Distinguished Dissertation Graduate Award from the NCSU College of Engineering. She hopes to secure a faculty position at a research university for Fall 2018.