Photorefractive effects in ferroelectrics as manifestation of structural violations on mesoscales

The nature of violations in ferroelectric structures that lead to emergence of direct photocurrents without application of external fields is discussed. We suppose that the main role in transfer processes and photovoltaic effect emergence belongs to macro- and meso-scopic inhomogeneities of the crystal. The boundaries between fairly perfect crystallites have the size of several constants of the crystal lattice and strongly changes the group (pyro-, piezo-, and ferroelectric) properties of the crystal. The presence of inhomogeneities and local electric fields in them determines the charge transfer mechanism: affected by light, the electrons are generated in discretely distributed defect regions and transported from one inhomogeneity to another laking into account the magnitude and sign of the held. In the framework of new concepts, experimental data on recording of the shifted and nonshifted holograms in LiNbO3 crystals are analyzed.