Polarization relaxation kinetics and 180° domain wall dynamics in ferroelectric thin films

The time-dependent relaxation of remanant polarization in epitaxial lead zirconate titanate [Pb(Zr0.2Ti0.8)O3,PZT] ferroelectric thin films, containing a uniform two-dimensional grid of 90° domains (c axis in the plane of the film), is examined using voltage-modulated scanning force microscopy. 90°domain walls preferentially nucleate 180° reverse domains during relaxation, which grow and coalesce as a function of relaxation time. Relaxation is seen to saturate at different levels depending on the write voltage. Late (saturation) stages of relaxation are accompanied by pinning and faceting of the domain walls (drastically reducing the wall mobility), which is direct evidence of the role of defect sites and crystallographic features on polarization relaxation. The kinetics of relaxation is modeled through the nucleation and growth Johnson-Mehl-Avrami-Kolmogorov theory with a decreasing driving force