Abstract
e ideal 180° ferroelectric walls that are a unit cell wide 0.5 nm, real walls in ferroelectrics
have been reported to be many nanometers wide 1–10 nm. Using scanning nonlinear dielectric
microscopy of lithium niobate LiNbO3 and lithium tantalate LiTaO3 ferroelectrics, we show that
the wall width at surfaces can vary considerably and even reach 100 nm in places where polar
defects adjoin a wall. The consequence of such variable wall widths is investigated on the specific
property of threshold field required for wall motion. Using microscopic phase-field modeling, we
show that the threshold field for moving an antiparallel ferroelectric domain wall dramatically drops
by two to three orders of magnitude if the wall was diffuse by only 1–2 nm, which agrees with
experimental wall widths and threshold fields for these materials. Modeling also shows that wall
broadening due to its intersection with a surface will influence the threshold field for wall motion
only for very thin films 1–10 nm where the surface broadening influences the bulk wall width.
Such pre-existing and slightly diffuse domain walls with low threshold fields for wall motion may
offer a general mechanism to explain significantly lower experimental coercive fields for domain
reversal in ferroelectrics as compared to the thermodynamic predictions.
