I. S. Baturin

Kinetic approach to fatigue phenomenon in ferroelectrics

We propose an approach to the explanation of the fatigue effect as an evolution of the switching area during cyclic switching as a result of self-organized domain kinetics due to retardation of bulk screening of the depolarization field. The formation of spatially nonuniform internal bias field during cycling (kinetic imprint effect) slows the domain kinetics in some regions leading to formation of the kinetically frozen domains. Presented fatigue and rejuvenation experimental data measured in sol-gel PbZrxTi1−xO3 thin films are in accordance with the results of computer simulation.

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.

Evolution of bias field and offset piezoelectric coefficient in bulk lead zirconate titanate with fatigue

Hysteresis loops of the piezoelectric coefficient, d33=f(E3), are measured on virgin and fatigued lead zirconate titanate ceramics. Four parameters are directly extracted from the measurements: internal bias field Eb, offset piezoelectric coefficient doffset, coercive field Ec, and remnant piezoelectric coefficient dr. The reduction in dr displays the decreasing switchable polarization with fatigue cycling. Eb and doffset are found to be linearly related. After thermal annealing, both offsets disappear, while the increase in Ec and the reduction in dr withstand annealing. The microscopic entities responsible for the offsets are less stable than those for reduced switching.

Polarization fatigue in PbZr0.45Ti0.55O3-based capacitors studied from high resolution synchrotron x-ray diffraction

High resolution synchrotron x-ray diffraction experiments were performed on (111)-oriented PbZr0.45Ti0.55O3-based capacitors with a composition in the morphotropic region. Diffraction analyzes were done after bipolar pulses were applied and removed, representing several places in the cyclic switching. Microstructural changes were evidenced from relative diffracted intensities variations of several Bragg reflections and a correlation with the evolution of the ferroelectric responses has been established. First, a peculiar microstructural evolution was observed during the first 3×104 switching cycles and was attributed to the so-called “wake-up” effect. On the other hand, the onset of the fatigue phenomenon was accompanied by significant variations on integrated diffraction intensities. Several mechanisms are proposed and discussed to explain such variations. Finally, the ferroelectric responses were analyzed after x-ray diffraction experiments and compared with those measured before exposure. A detailed an...

Investigation of Jerky Domain Wall Motion in Lithium Niobate

Jerky domain wall motion during merging of neighboring domains in lithium niobate single crystals was studied in details by using synchronized in-situ optical visualization and recording of switching current shape. Several scenarios of domain structure transformation were revealed and classified. It has been shown that predetermined nucleation and layer-by-layer mechanism are main reasons for observed jerky domain wall motion. On the basis of the analysis of the current pulse shape the step growth velocity was estimated to be about 1 m/s. This value is several orders of magnitude higher than the averaged visible domain wall velocity in lithium niobate.

Complex study of bulk screening processes in single crystals of lithium niobate and lithium tantalate family

Comprehensive study of depolarization field bulk screening was carried out in lithium niobate and lithium tantalate single crystals with various stoichiometry. Three used complementary methods are based on: 1) dependence of coercive field on delay time; 2) decrease of optical contrast of domain wall trace; 3) relaxation of light diffraction intensity on domain walls. The following parameters of bulk screening process were obtained: relaxation time constants, type of relaxation law, maximal value of bias field and “true” value of coercive field. Advantages and disadvantages of used experimental methods were analyzed.

Characterization of Bulk Screening in Single Crystals of Lithium Niobate and Lithium Tantalate Family

Kinetics of bulk screening of depolarization field was studied in single crystalline lithium niobate and lithium tantalate of various compositions by analysis of the switching current, birefringence contrast, and diffraction of coherent light on the domain walls. The bulk screening process was quantitatively characterized by several essential parameters, such as a type of relaxation law, relaxation time constants, and maximum value of bulk screening field. Advantages and disadvantages of used experimental methods were discussed. The comparison of the obtained and previously published results was carried out.

Kinetic approach for describing the fatigue effect in ferroelectrics

A new kinetic approach is proposed for explaining the fatigue effect in ferroelectrics. A self-consistent variation in the area and geometry of the switching region of a sample upon a cyclic switching accompanied by the formation and growth of kinetically frozen domains is considered. It is assumed that fatigue is due to self-organized formation of a spatially inhomogeneous internal bias field due to retardation of bulk screening of the depolarization field. Variations in the switching charge and in the amplitude of switching current, which are calculated with the help of computer simulation of domain kinetics upon cyclic switching, are in good agreement with experimental data obtained for thin lead zirconate-titanate (PZT) thin films.

New Approach to Analysis of the Switching Current Data, Recorded During Conventional Hysteresis Measurements

The explanation of fatigue as a spatially non-uniform kinetic imprint due to evolution of the local threshold field distribution function has been proposed by us recently. In this paper we propose a new switching current analysis which allows to extract the distribution function from the data of conventional hysteresis loop measurements. Domain kinetics in slow-increasing field in spatially inhomogeneous ferroelectric was investigated by computer simulation. Domain arising and growth were considered under assumption that the threshold field for appearance of isolated nuclei is essentially higher than for nuclei at the domain wall. The obtained approach essentially differs from Preisach one. The proposed method has been applied for analysis of the switching current data measured during fatigue cycling in PZT and PLZT thin films. The fitting formula for dependence of switching charge and current maximum on the cycle number has been proposed and successively used for experimental data. The proposed method can accelerate the fatigue testing.

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.