EAPSI: Determining Grain Size Effects on Ferroelectric Switching Speed by Time-Resolved Neutron Diffraction Measurements

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Ferroelectric materials possess an inherent polarization that can be reoriented (or ?switched?) with an applied electric field. Understanding how defects, grain size, and other material parameters affect this switching process is important to be able to improve device performance in applications such as capacitors in consumer electronics, inertial sensors such as those in automotive collision detection systems, or precise positioners used for camera focusing. This EAPSI project seeks to identify the effects that grain size has on ferroelectric switching speed by collecting time-resolved neutron diffraction data on barium titanate ceramics with a broad distribution of grain sizes during electric-field-induced polarization. This work will be conducted in collaboration with Dr. John Daniels, an Associate Professor at the University of New South Wales who helped pioneer this time-resolved diffraction technique, at the Australian Nuclear Science and Technology Organization.The effect of grain size on the magnitude of dielectric permittivity of ferroelectrics is well known, but the effects on switching speeds are not yet completely understood. Current hypotheses claim that new domains form at grain boundaries due to local electric field enhancements caused by a difference in permittivity between the grain boundary and the lattice. This theory will be explored via time-resolved, stroboscopic neutron diffraction experiments performed on barium titanate samples with a broad range of grain size distributions while undergoing electric-field-induced polarization. Strain contributions from intrinsic (piezoelectric) and extrinsic (non-180° domain switching) components are easily separable and the ability to collect structural information on time scales of interest to ferroelectrics (1 s) with this technique. These combined pieces of information will allow for accurate detection of piezoelectric strain rate and the associated ferroelectric polarization speeds. This work will be conducted in collaboration with Dr. John Daniels, an Associate Professor at the University of New South Wales who helped pioneer this time-resolved diffraction technique, at the Australian Nuclear Science and Technology Organization.This award under the East Asia and Pacific Summer Institutes program supports summer research by a U.S. graduate student and is jointly funded by NSF and the Australia Academy of Science.