Fine mechanisms of polarization switching in KTiOPO₄ ferroelectric crystals

Highly anisotropic ferroelectric domain structure was observed in KTiOPO 4 (KTP) crystals reversed in low electric field. The applied Miller-Weinreich model for sidewise motion of domain walls indicates that the origin of this anisotropy is peculiarities of the KTP crystal lattice. The domain nuclei of sub-micron size imaged by atomic force microscopy method, demonstrate regular hexagonal forms. Domain inversion in non-uniform electric field has shown that when KTP sample is in the superionic state, nucleation of new domains occurs in the bulk of the crystal. When a KTP sample is in the dielectric state, nucleation in the crystal bulk is not observed. In this case domains nucleate under the top electrode and grow straightforward to the bottom electrode. The effect of bulk nucleation may be explained by effective compensation of depolarization field by the mobile ions when the crystal is in the superionic state. The observed effects allow to improve tailoring of ferroelectric domain engineered structures for nonlinear optical converters.