A. G. Shur

Rearrangement of ferroelectric domain structure induced by chemical etching

The rearrangement of the domain structure induced by chemical etching has been observed in periodically poled MgO-doped stoichiometric lithium tantalate single crystals. Topographic and piezoresponse scanning probe microscopy have been used for measuring the etching relief height and domain wall position after etching. The considerable shift of the domain wall during etching by pure hydrofluoric acid has been revealed by analysis of the experimental data. We have found that the wall motion proceeded after the termination of the etching procedure. We have shown that the whole consequence of the domain wall positions during etching is recorded in the etching relief height and can be extracted with high spatial and temporal resolution.

Field induced evolution of regular and random 2D domain structures and shape of isolated domains in LiNbO3 and LiTaO3

The shapes of isolated domains produced by application of the uniform external electric field in different experimental conditions were investigated experimentally in single crystalline lithium niobate LiNbO 3 and lithium tantalate LiTaO 3 . The study of the domain kinetics by computer simulation and experimentally by polarization reversal of the model structure using two-dimensional regular electrode pattern confirms applicability of the kinetic approach to explanation of the experimentally observed evolution of the domain shape and geometry of the domain structure. It has been shown that the fast domain walls strictly oriented along X directions appear after domain merging.

Self-Organization in LiNbO3 and LiTaO3: Formation of Micro- and Nano-Scale Domain Patterns

We review the study of self-organized formation of several types of quasi-regular micro- and nano-scale domain patterns in single crystalline LiNbO3 and LiTaO3 samples with artificial surface dielectric layers. The domain images revealed by chemical etching have been visualized using optical, scanning electron and scanning probe microscopy (SPM) in contact atomic force mode. SPM piezoresponse imaging mode allows us to investigate the domain structure under the sample surface. We classify the obtained quasi-regular domain structures and discuss the mechanism of their formation and self-maintained growth.

Shape Evolution of Isolated Micro-Domains in Lithium Niobate

The varieties of domain shapes produced in single crystals of lithium niobate LiNbO 3 family by application of the uniform electric field have been revealed. The crucial role of predetermined nucleation effect representing the step generation at vertices of polygon domain and step growth in three Y directions was discussed. We put emphasis on formation of unusual domain shapes created by switching in non-equilibrium conditions arisen due to retardation of the screening of depolarization field. Formation of oriented fingers and dendrite self-assembled domain structures during switching with artificial surface dielectric layer and during spontaneous backswitching was considered.

Nanoscale Domain Effects in Ferroelectrics. Formation and Evolution of Self-Assembled Structures in LiNbO3 and LiTaO3

We discuss the most interesting nanoscale domain effects resulting in formation and evolution of self-assembled domain structures in various representatives of LiNbO 3 and LiTaO 3 family. Several exotic domain kinetic scenarios for complete suppression of the classical wall motion have been revealed. It has been shown that the modification of the surface layer allows to obtain: (1) the wall motion controlled by merging with nanoscale domains generated in front of the moving wall and (2) the discrete switching by enlargement of the web-like self-assembled ensemble of isolated domains. The formation of nanoscale quasi-periodic and self-similar structures during cooling after pulse heating without any application of external electric field was studied. It has been shown that all experimental results can be explained, if the retardation of the bulk screening of the depolarization field is taken into account.

Fatigue effect in bulk ferroelectrics

We have used a kinetic approach to the fatigue phenomenon in ferroelectrics for the analysis of the evolution of switching current and strain hysteresis loops in bulk PZT ceramics and the switching current in PZN-PT single crystals during cyclic switching. It is proposed that fatigue is due to a redistribution of the local internal bias field during cycling (spatially non-uniform imprint effect). The model considered is based on the fact that during cycling the ratio of the states with opposite direction of polarization ranges over the sample area. The local value of this ratio defines the change of the internal bias field at the given point during the switching cycle considered. Thus the spatial distribution of the internal bias field depends on the domain evolution prehistory. We have investigated by computer simulation the self-consistent change of the internal bias field distribution function with cycling, which leads to fatigue. The mathematical treatment of the switching current data allows us to extract the information about the evolution of the field distribution function. The fatigue-induced change of the strain loops is explained by a strong unipolarity of the growing frozen domain area, which has been predicted by our simulations. The analysis of experimental data confirms the validity of our model.

Deaging in Gd2(MoO4)3 by cyclic motion of a single planar domain wall

The motion of a single planar 180° domain wall was studied in single-crystalline gadolinium molybdate, Gd2(MoO4)3. The switching current and the instantaneous wall positions were recorded using polarized light in an optical microscope and subsequent image processing. A pronounced deaging (wake-up) effect is observed represented by an increase of domain-wall shift during cyclic switching at constant voltage amplitude. The experimental data are compared to computer simulations taking into account the kinetic imprint effect under ac cycling. The latter is the change of the spatial distribution of the internal bias field during cycling. It is shown that deaging (wake-up) arises for aged (screened) initial states. After long enough cycling, the spatial distribution of the internal bias field becomes steady state and the wall motion becomes reproducible in all its details. The final distribution of the internal bias field does not depend on the initial state of the sample. The activation energies for deaging an...

Dynamics of a single-planar domain wall in ferroelectric–ferroelastic Gd2(MoO4)3

The field-induced jump-like dynamics of a single planar domain wall are investigated in single crystal uniaxial ferroelectric–ferroelastic Gd2(MoO4)3 containing extended bulk defects. The kind and location of the defects interfering with the free motion of the domain wall determines which type of elastic vibration is excited by the discontinuous jump of the domain wall. Time coincidence between optically observed jumps, Barkhausen pulses, and acoustic emissions each occur for particular jumps only. The time coincidence conditions correlate with the vibration spectra and differ for the initial release of the wall, large domain wall jumps, and clamped motions.

The Dynamics of Domain Walls Determined from Acoustic Emission Measurements

The field-induced jump-like dynamics of a single planar domain wall in single crystalline uniaxial ferroelectric-ferroelastic Gd 2 (MoO 4 ) 3 and needle domains in the perovskite BaTiO 3 are compared. Acoustic emission as well as ferroelectric Barkhausen pulse measurements were performed in order to investigate time coincidences with optically observed jumps. In both crystals significant amounts of acoustic emissions occur. The coincidences of both event types in Gd 2 (MoO 4 ) 3 are determined by the particular character of extended defects in the crystal and the relative orientation of the acoustic sensor. Hardly any Barkhausen pulses but huge amounts of acoustic pulses are observed for the annihilation of needle domains. The underlying microscopic mechanisms are discussed.

Formation of self-assembled micro- and nano-domain structures in uniaxial ferroelectrics

We present the experimental study of appearance of domain wall shape instabilities and self-assembled domain structures in uniaxial ferroelectrics lithium niobate and lithium tantalate covered by artificial dielectric layer. The domain structure evolution has been considered as a manifestation of nucleation processes similar to the first order phase transformation. The necessary conditions for formation of self-assembled domain structures including the highly non-equilibrium switching conditions and stability of concave angles were proposed. The formation of the self-assembled domain shape instabilities under application of the uniform external electric field during switching (domain growth) and backswitching (domain shrinkage) has been studied experimentally with these conditions fulfilled. The formation of the bumps at the vortexes of hexagon domain for diameter above 3 - 5 μm with subsequent oriented growth was obtained in stoichiometric lithium tantalate. The formation of quasi-regular fish-bone domain structure has been revealed during spontaneous backswitching in Mg doped lithium niobate. The resulted structure consisted of the narrow residual domains with width from 200 to 500 nm appeared as a result of finger growth to the center of hexagon domain. The obtained decreasing of the number of the residual domains during growth has been attributed to strong electrostatic interaction of domain walls.