Varenyk O. The modeling of the local polar and electrochemical properties of the ferroelectrics and size effects in nanostructures based on them.

This thesis deals with the research of local polar and electrochemical properties of the ferroelectrics and size effects in different nanostructures based on them. Self-consistent modeling of the electrotransport and electrochemical response of solid electrolyte thin films was performed allowing for the steric effects of mobile ions, electron degeneration and Vegard coupling. It was shown that internal electric fields, both built-in and depolarization ones, lead to a strong accumulation of screening space charges near the film interfaces. Mobile defects dynamics, kinetics of polarization and electric current reversal are defined by the complex interplay between the donor, electron and phonon relaxation times, misfit strain, finite size effect and Vegard stresses. Heterostructure "domain patterned ferroelectric film - ultra-thin dielectric layer - semiconductor" was studied. It was find out that in such heterostructures multiple size effects appearance and manifestation are defined by the relationship between dielectric layer thickness, domain structure period and semiconductor screening radius. Theory of the mechanism of the tip-induced polarization switching at non-polar cuts of uniaxial lithium niobate crystal was built. Formation and growth of isolated domains on the surface of the non-polar cut of lithium niobate single crystal was studied systematically. Theoretical calculations and computer simulations by Landau-Ginzburg-Devonshire model allowed to describe kinetics of formation and growth of the wedge-shaped domain and showed good agreement with experiments. The self-consistent modeling of dynamic electrochemical strain microscopy (ESM) for mixed ion-electronic conductors was performed. 2D maps of the strain and concentration distribution across the mixed ionic-electronic conductor and bias-induced surface displacements for ESM microscopy were calculated. Results show significant impact of the nonlinear effects on the ESM image formation mechanism. It was found that Vegard mechanism plays a key role in the mechanisms of the ESM image formation at low voltages less than 1V, but electrostriction contribution dominates with voltage increase.