ABSTRACTThe multiferroic material YbMnO3 has been reported to exhibit both
ferroelectric and antiferromagnetic orders in the ground state. Of these two
orders, the ferroelectric order is associated with the
P63/mmc-to-P63cm structural transition, which occurs
around 1270 K. The interesting feature of the ferroelectric state is that a
cloverleaf domain structure with a pseudo-six-fold symmetry is observed in
transmission electron microscopy images with the beam incidence parallel to the
hexagonal axis. To understand the origin of the formation of the cloverleaf
domain structure, we have examined the crystallographic features of the
ferroelectric state in YbMnO3 by transmission electron microscopy. In
this study, particularly, we adopted the experimental condition that electron
beam incidences are perpendicular to the hexagonal axis. It was, as a result,
found that there existed various ferroelectric domain structures including the
cloverleaf domain structure under the present condition. The notable feature of
domain structures found in this study is that each domain structure basically
consists of six domains, whose domain boundaries are terminated at one point.
Because this feature makes us reminiscent of a discommensurate structure in an
incommensurate state, we took high-resolution electron micrographs of areas
including domain boundaries. Their analysis indicated that a domain boundary
could be identified as a discommensuration with a phase slip of π/3.
It is thus understood that the cloverleaf domain structure should be one of
domain morphologies for a discommensurate structure, which is related to the
break of the translational symmetry.
