Domain wall propagation in meso- and nanoscale ferroelectrics

Abstract

As part of an ongoing programme to evaluate the extent to which external morphology altersdomain wall mobility in ferroelectrics, the electrical switching characteristics of single-crystalBaTiO3 nanorods and thin film plates have been measured and compared. It was found thatferroelectric nanorods were more readily switched than thin plates; increasing the shapeconstraint therefore appears to enhance switchability. This observation is broadlyconsistent with previous work, in which local notches patterned along the length ofnanorods enhanced switching (McMillen et al 2010 Appl. Phys. Lett. 96 042904), whileantinotches had the opposite effect (McQuaid et al 2010 Nano Lett. 10 3566). In this priorwork, local enhancement and denudation of the electric field was expected at the notch andantinotch sites, respectively, and this was thought to be the reason for the differences inswitching behaviour observed. However, for the simple nanorods and plates investigatedhere, no differences in the electric field distributions are expected. To rationalise thefunctional measurements, domain development during switching was imaged directly bypiezoresponse force microscopy. A two-stage process was identified, in which narrowneedle-like reverse domains initially form across the entire interelectrode gap and thensubsequently coarsen through domain wall propagation perpendicular to the appliedelectric field. To be consistent with the electrical switching data, we suggest that the initialformation of needle domains occurs more readily in the nanorods than in the plates.