Close-circuit domain quadruplets in BaTiO3_3 nanorods embedded in SrTiO3_3 film

Cylindrical BaTiO3 nanorods embedded in (100)-oriented SrTiO3 epitaxial film in a brush-like configuration are investigated in the framework of the Ginzburg-Landau-Devonshire model. It is shown that strain compatibility at BaTiO3/SrTiO3 interfaces keeps BaTiO3 nanorods in the rhombohedral phase even at room temperature. Depolarization field at the BaTiO3/SrTiO3 interfaces is reduced by an emission of the 109-degree or 71-degree domain boundaries. In case of nanorods of about 10-80 nm diameter, the ferroelectric domains are found to form a quadruplet with a robust flux-closure arrangement of the in-plane components of the spontaneous polarization. The out-of-plane components of the polarization are either balanced or oriented up or down along the nanorod axis. Switching of the out-of-plane polarization with coercive field of about $5.10^6$ V/m occurs as a collapse of a 71-degree cylindrical domain boundary formed at the curved circumference surface of the nanorod. The remnant domain quadruplet configuration is chiral, with the $C_4$ macroscopic symmetry. More complex stable domain configurations with coexisting clockwise and anticlockwise quadruplets contain interesting arrangement of strongly curved 71-degree boundaries.Comment: Erratta - corrected error in Fig.

Migration kinetic of primary radiation defects at nonuniform irradiation

The migration of interstitial atoms and vacancies under nonuniform irradiation is theoretically studied. The possibility of the formation of regions with increased concentration of point defects of certain kind in crystalls with low concentration of dislocatios at the surface and at Bragg peak is demonstrated. The region of the penetration of interstitials beyond the irradiated area is estimated. It might be of order of 0.02 sm at the dislocation density 104 cm-2. The difference of the flows of interstitials and vacancies changes its sign in process of irradiation which can lead to different processes of macroscopic defect formation at the imitial stages of irradiation and in the stationary state