  Simultaneous imaging of the piezoresponse phase, amplitude and bare surface
topography of displacive ferroelectric thin films by scanning probe microscopy
directly shows the nature of domain wall pinning and its relation to
morphological disorder. Strong and stable pinning of walls occurs at grain
boundaries while weak and unstable pinning occurs within the grains. The
results show that polarization reversal consists of both nucleation of domains
and spreading of domain walls, the latter being the dominant process in
multi-grain regions. A characteristic single-grain switching in faceted grains
is observed as the motion of a single domain wall parallel to one of the
facets.
