Abstract
A high-angle annular-dark-field (HAADF) imaging technique was applied to the investigation of domain wall structures in the ferroelectric phase of hexagonal manganites, YMnO3, on an atomic scale. The displacements of the Y3+ ions along the [001] direction can be clearly visualized. The ferroelectric dipole moments are revealed to be caused by the opposite and unequal displacements of Y3+ ions. Two types of domain walls should be identified in the ferroelectric domain structures. One is charged longitudinal domain walls with head-to-head or tail-to-tail configurations and the other is non-charged transverse domain walls with head-to-tail configurations. In addition, the ferroelectric and the structural antiphase domains in YMnO3 change into fragmentary domains because of substitution of Ti4+ for Mn3+, and ferroelectric nanodomains with sizes of 10-20 nm are found in the x = 0.30 compound.