Domain structures in dielectric polarization vortex of BaTiO3 nanoclusters: A shell model molecular dynamics study

The domain structures in the dielectric polarization vortex of BaO-terminated cubic BaTiO3 nanoclusters were calculated by classical molecular dynamics simulations using a shell model at low temperatures. The cluster with the toroidal moment g parallel to the [111] direction is known to be the ground structure at low temperatures. In this paper, we examined possible structures of clusters with the toroidal moment parallel to the [111], [110], and [001] directions with varying the size. We found that for larger clusters with n > 6, where n is the number of unit cells on one edge, clusters with g//[111], g//[110], and g//[001] were stable in this order. In the interior of the nanoclusters, ferroelectric domain walls (FDWs) were formed. We confirmed that the cluster with g//[111] consisted of 71 degrees FDWs, a lowest energy FDW of the rhombohedral phase. We found that higher energy clusters consisted of higher energy FDWs. For smaller clusters with n < 6, the toroidal moment vanished for all the clusters.