Trimerization-polarization domains in ferroelectric hexagonal YMnO3 were
resolved in all three spatial dimensions by piezoresponse force microscopy.
Their topology is dominated by electrostatic effects with a range of 100 unit
cells and reflects the unusual electrostatic origin of the spontaneous
polarization. The response of the domains to locally applied electric fields
explains difficulties in transferring YMnO3 into a single-domain state. Our
results demonstrate that the wealth of non-displacive mechanisms driving
ferroelectricity that emerged from the research on multiferroics are a rich
source of alternative types of domains and domain-switching phenomena