Abstract
We discovered stripe patterns of trimerization-ferroelectric domains in hexagonal REMnO3 (RE = Ho, ..., Lu) crystals (grown below ferroelectric transition temperatures (T-c), reaching up to 1435 degrees C), in contrast with the vortex patterns in YMnO3. These stripe patterns roughen with the appearance of numerous loop domains through thermal annealing just below T-c, but the stripe domain patterns turn to vortex-antivortex domain patterns through a freezing process when crystals cross T-c even though the phase transition appears to not be Kosterlitz-Thouless-type. The experimental systematics are compared with the results of our six-state clock model simulation and also the Kibble-Zurek mechanism for trapped topological defects.