Sidewise Motion Research Articles

An optical method for characterizing domain wall motions and ferroelectric hysteresis in tetragonal Mn:Fe:KTN co-doped crystals

An optical method is proposed to extract the displacement vector of domain wall (DW) sidewise motion from ferroelectric domain configuration pattern on a tetragonal Mn:Fe:KTN crystal. The ferroelectric domain configuration evolution under an external electric field is observed in situ using optical microscope imaging system, and the relative displacement of DW sideways motion between two adjacent electric fields is extracted. By the combination of the new domain length vector extracted, the ferroelectric domain displacement vector as a function of field strength can be obtained; what is more, the hysteresis loop can be achieved during field cycling. The method provides an access to directly manipulating DW motion and exploring the properties of ferroelectric materials from ferroelectric domain configuration pattern.

Eliminating and Modelling Non-metric Camera Sensor Distortions Caused by Sidewise and Forward Motion of the UAV

Abstract. This paper explains the critical importance of modelling and eliminating the effect of motion of an Unmanned Aerial Vehicle (UAV) as a result of air turbulence and unstable flight conditions on a camera sensor and the image geometry. A new method for improving the geometrical distortions caused by this motion is introduced. We have developed a hardware and software tool to minimize and model the geometric distortion of the image from commercial off-the-shelf (COTS) cameras which are commonly being used in aerial mapping UAVs. Due to the rolling shutter mechanism of the most common SLR cameras, sideway and forward motions of the UAV during image capture will have a strong effect on the image geometry and final product accuracies. As the amount of this random distortion varies from one photo to the next, a unique and robust camera calibration model cannot be established for interior orientation and image processing using photogrammetric methods, even by self-calibration. To achieve the highest possible accuracy, we also consider temperature effects on the camera calibration parameters. In this paper we show the results, accuracies and benefits of using this method compared with a typical UAV mapping system. To the best of our knowledge this is the first time that this method has been implemented in a UAV mapping system.

IN SITU INVESTIGATION OF RETENTION PROPERTIES OF POLYDOMAIN FERROELECTRIC THIN FILMS BY MULTIMODE SCANNING FORCE MICROSCOPY

ABSTRACT The domain structures and retention properties of the sandwich structure PT/PZT/PT thin films with pure perovskite structure, strong (111)-preferred orientation and excellent ferroelectric properties were investigated in situ by piezoresponse force microscope (PFM) and electrostatic force microscope (EFM) synchronously. The piezoresponse domain images and the profiles of piezoresponse with various times exhibit that the forward backswitching and the sidewise motion of the domain walls occurred synchronously in the backswitching of the written domain. The time-dependent surface potential images and line potential profiles show that the potential decay with time. The tendency of decay becomes slower as time goes on, and the highest decay rate is within the first 15 min.

Domain Dynamics of C-Axis Polarization in Bismuth Titanate Crystals

Polarization switching and domain dynamics in unpoled and poled crystals of bismuth titanate by applying electric field along the crystallographic c axis were investigated through polarization measurements and domain observations by optical microscope and piezoelectric force microscope. Poled crystals showed a well-saturated polarization hysteresis with a remanent polarization of 4.4 μC/cm2 and a coercive field of 4.7 kV/cm. Domain observations reveal that lenticular domain acts as an initial nucleus during polarization switching. The sidewise motion of the lenticular-domain walls and resultant single domain state were easily established for the poled crystals, while the lenticular domains observed in unpoled crystals were clamped even though a high electric field was applied to them.

Domain Dynamics in Unpoled and Poled Bismuth Titanate Crystals

Domain switching process of bismuth titanate single crystals was investigated under application of electric field along the crystallographic c axis through polarization measurements and domain observations by optical microscope and piezoelectric force microscope. While unpoled crystals exhibited a poor polarization hysteresis, the crystals which were poled at 150°C showed a well-saturated polarization hysteresis with a remanent polarization of 4.4 micro C/cm2 and a coercive field of 4.7 kV/cm. Domain observations reveal that lenticular domain acts as an initial nucleus both in the poled and unpoled crystals during polarization switching of the c-axis component. The sidewise motion of the lenticular-domain walls and resultant single domain state were easily established for the poled crystals, while the lenticular domains observed in unpoled crystals were clamped even though a high electric field was applied to them.

A micromechanics-based thermodynamic model for the domain switch in ferroelectric crystals

In this work we take the view that domain switch in ferroelectric crystals is a thermodynamics-driven process. In this light we first consider the micromechanics of domain switch to derive the Gibbs free energy of the heterogeneous system and the corresponding thermodynamic driving force at a given level of switched domain concentration f p , applied stress σ ij , and applied electric field E i . Then in conjunction with Miller and Weinreich's [Phys. Rev. 117 (1960) 1460] resistance force for the sidewise motion of 180° domain walls, a kinetic equation is established to calculate the evolution of new domains under a reversed electric field for a BaTiO 3 crystal. The calculated results show that, as the field increases, the switching process is initially rapid, and then becomes quite slow as it approaches the saturation state. The calculated polarization versus the electric field relation ( P– E relation) is found to agree with the measured characteristics. The effect of porosity on the switching processes is also examined. It is found that, due to the lower level of Gibbs free energy in the presence of pores, a higher field is required to overcome the energy resistance of domain switch. On the other hand, due to the lower initial parent domain concentration, the level of electric field to cause a complete reversal of the domains decreases with porosity.

Forward motion of ferroelectric domain walls

A theory is presented for the forward growth of ferroelectric domains taking place during polarization reversal. A faster forward motion in comparison with a sidewise motion is explained in terms of forces arising from the depolarization field of the growing domain. Dynamic equations for the time dependence of the domain length and radius are derived and solved. The calculation shows that in a strong electric field the forward velocity of the domain in barium titanate exceeds the lateral velocity by a large factor. This explains the observed rapid growth of new domains throughout the sample thickness without significant changes in their lateral sizes.

Dynamic process of domain switching in ferroelectric films

In this article, a general variational formulation is established for the dynamics of domain switching in ferroelectric thin films. By incorporating the kinetic energy in the Landau free energy expansion, we obtain a second-order time-dependent Ginzburg–Landau evolution equation, which can be used to analyze the frequency-dependent dielectric and ferroelectric properties of the materials. A numerical model is developed to calculate the time-dependent polarization and electric-field distribution during the domain switching process. As an example of practical importance, a ferroelectric film with 180° domain boundaries perpendicular to the film surface is studied. Domain switching is found to proceed in two stages, the initial nucleation and growth of the ferroelectric domain, followed by the expansion of the domain through the sidewise motion of the 180° domain walls, until the spontaneous polarization in the entire electrified area is reversed.

Dynamics of nanoscale polarization backswitching in tetragonal lead zirconate titanate thin film

The dynamics of polarization backswitching in highly oriented Pb(Zr0.3Ti0.7)O3 (PZT) thin films has been studied in nanoscale using piezoresponse scanning force microscopy (SFM). Our measurements reveal that a SFM-written domain with diameter about 200 nm in PZT films loses its polarization through both the sidewise and forward backswitching. Both of these sidewise and forward domain wall motions follow a stretched exponential law. However, the characteristic time τ of forward backswitching are about ten times of that sidewise motion. The time dependence of sidewise domain wall velocity indicates that there is a time dependence of activation energy of the barrier that domain motions encounter.

Fine Mechanisms of Polarization Switching in KTiOPO 4 Ferroelectric Crystals

Highly anisotropic ferroelectric domain structure was observed in KTiOPO 4 (KTP) crystals reversed in low electric field. The applied Miller-Weinreich model for sidewise motion of domain walls indicates that the origin of this anisotropy is peculiarities of the KTP crystal lattice. The domain nuclei of sub-micron size imaged by atomic force microscopy method, demonstrate regular hexagonal forms. Domain inversion in non-uniform electric field has shown that when KTP sample is in the superionic state, nucleation of new domains occurs in the bulk of the crystal. When a KTP sample is in the dielectric state, nucleation in the crystal bulk is not observed. In this case domains nucleate under the top electrode and grow straightforward to the bottom electrode. The effect of bulk nucleation may be explained by effective compensation of depolarization field by the mobile ions when the crystal is in the superionic state. The observed effects allow to improve tailoring of ferroelectric domain engineered structures for nonlinear optical converters.

Anisotropic domain structure of KTiOPO4 crystals

Highly anisotropic ferroelectric domain structure is observed in KTiOPO4 (KTP) crystals reversed by low electric field. The applied Miller–Weinreich model for sidewise motion of domain walls indicates that this anisotropy results from the peculiarities of KTP crystal lattice. The domain nuclei of dozen nanometer size, imaged by atomic force microscopy method, demonstrate regular hexagonal forms. The orientation of domain walls of the elementary nuclei coincides with the orientation of the facets of macroscopic KTP crystals. The observed strong domain elongation along one principal crystal axis allows us to improve tailoring of ferroelectric domain engineered structures for nonlinear optical converters.

Polarization retention in SrBi2Ta2O9 thin films investigated at nanoscale

The nanoscale mechanism of retention behavior in SrBi2Ta2O9 (SBT) thin films has been investigated by means of piezoresponse scanning force microscopy. It has been found that SBT films with Pt electrodes (SBT/Pt) exhibit a strong dependence of retention characteristics upon domain polarity: positive domains with the polarization vector pointing to the bottom electrode exhibit excellent stability in sharp contrast to the negative domains which show poor retention. The backswitching of the negative domains proceeds via sidewise motion of the domain walls and shows a log-time dependence. The strong effect of the poling voltage parameters (duration and amplitude) and the previous switching pattern on domain retention behavior is reported. On the other hand, in SBT films with IrO2 electrodes (SBT/IrO2), the written domains of both polarities show no sign of relaxation to the original state irrespective of the parameters of the poling voltage. The difference in retention behavior of opposite domains in SBT/Pt films is explained by the presence of the polarization-independent built-in bias at the SBT/Pt interface pointing to the bottom electrode. This built-in bias triggers the backswitching of a negative domain by generating positive nuclei at the interface. The forward growth of the nuclei is further governed by the field of the space charge which screens the original polarization state. The symmetric retention behavior and the stability of domain in SBT films with IrO2 electrodes are attributed to the inhibition of the nucleation process at the SBT/IrO2 interface.

Dynamical Process of Domain Pattern Coarsening in Ferroelectric Sodium Nitrite I. Microscopic Observation

The process of domain pattern coarsening in sodium nitrite has been studied by microscopic observation. The domain pattern was delineated by rubbing the b -face on deer's buff wetted with ethanol. Starting from a nearly one-dimensional domain pattern whose average domain width is 0.6 µm, the pattern coarsens initially through nucleation and growth of antistripples. The antistripples are shaped like a dagger elongated in the b -direction. They are nucleated even between two adjacent walls separated as wide as 2 µm. In the late stage the pattern coarsens through the backward motion of the fronts of wedge-shaped domains which have been formed by combined growth processes of antistripples. The sidewise motion of the planar walls was not observed in either of the initial or late stage. The one-dimensional character of the pattern is retained throughout the whole coarsening process.

T.E.M. study of 3-q modulated phase of quartz-type under electric field

Abstract Since the 3-q modulated phase of quartz-type (existing in quartz and berlinite) can be predicted to be polar (ferroelectric or pyroelectric) we have performed T.E.M. experiments under an applied external field along z. We observe that ferroelectric switching does occur, the mechanism being a sidewise motion of the ferroelectric walls, the block boundaries. Under the field, there occurs also a slight distortion of the sample inconsistent with symmetries of α or β phases but in agreement with the predicted symmetry 6′ of the 3-q modulated phase.

Amplitude internal friction peaks associated with the interaction between dislocation kinks and solute atoms in aluminium

Early in 1950, Kê observed in slightly cold-worked dilute aluminium-copper solid solutions a pronounced low-frequency internal friction peak around room temperature as a function of strain amplitude in which the high-amplitude side of the peak decreases rapidly to a very small value. This paper reviews the experimental results since the work of Kê, with emphasis on cold-worked aluminium containing Cu or Mg as substitutional solute atoms. A dislocation kink dragging and break away model is suggested. The latest results show that this internal friction peak around room temperature consists of two separate peaks. The amplitude peak accompanying the lower temperature peak shifts toward lower amplitudes and that accompanying the higher temperature peak shifts toward higher amplitudes with an increase of temperature of measurement. The former amplitude peak appears at an amplitude range lower than that of the former peak. A mechanism of the double amplitude peaks is suggested in terms of the simultaneous occurrence of longitudinal core diffusion (LCD) and transverse core diffusion (TCD) of the solute atoms during the to and fro sidewise motion of the dislocation kinks. Some conclusions concerning the mechanism of Hasiguti peaks are drawn from the comparison with studies on the internal friction peaks associated with the interaction between dislocation kinks and solute atoms.

Domain structure of lead germanate

With the help of selective etchants as-grown domain structure arising as a result of the phase transition and its restruction in electric field is investigated in lead germanate single crystals. It is shown that this structure consists of small counter domains which are enlarged in electric field. By the use of stroboscopic lighting the domain dynamics under applied electric field is studied. It is shown that the influence of growth layers upon forward domain growth can be explained by the relative variation of the spontaneous polarization in the layers of the order of 0,1%. The observed peculiarities of sidewise motion of plane domain wall are explained by the presence of dielectric gap and by the influence of bulk screening. It is supposed that in low-field region domain wall motion occurs through the one-dimensional nucleation at the wall. Within this model it is possible to qualitatively explain the domain shape dependence on the switching conditions.

The change of the activation field in tgs crystal

Abstract In the Miller and Weinreich model the apparent sidewise motion of a domain wall was realized by forming a nucleus, of opposite polarization one lattice constant thick, and then spreading it along the domain wall. Assuming the layer formation to be controlled by nucleation mechanism they got for the switching time of the crystal the following relations ts too exp/ ∞oC/E /, where ∞ is the activation field, E is the applied field. Assuming the nucleation is taking place at random sites on the domain wall and assuming the growth rate of a nucleus to be isotropic, for the time t1needed to spread it on the layer we get: tl ≅ u-2/3 exp/ ∞/3E /. For this process we observe the activation field to be diminished three times as compared to the situation, when nucleation rate is much smaller than the growth rate. In order to compute reliable values of the layer switching time from the crystal switching time, the measurements were carried out for an aged periodical domain structure. In this case, the domain shift is the same for all domain walls and the proportionality between ts and tl is readily established.

DISLOCATION INTERNAL FRICTION PEAKS WITH ANOR- MALOUS AMPLITUDE EFFECT IN Al-Mg ALLOY

Two low frequency internal friction peaks have been observed at 243 K and 333 K respectively in Al-0.03 at% Mg alloy during the process of temperature going up after the specimen was stretched in situ with a tensile strain of 0.5% at 208 K. Such two peaks appeared also at the same temperatures when the measurement was made in the subsequent cooling from 353 K. The dependence of internal friction on the amplitude was determined and the amplitude internal friction peaks were observed in the temperature range of the peaks. The relationship between these two kinds of peaks was analysed and the effective activation energies of the temperature internal friction peaks were found to be about 0.32 eV for the 243 K peak and 0.22 eV for the 333 K peak. It was suggested that the two peaks at 333 K and 243 K may be respectively associated with the dragging of the solute atoms and the "Mg atom-vacancy" pairs, which may be produced through the sidewise motion of the kinks on the dislocations formed during the low temperature cold working.

On Polarization Reversal and Surface Neutralization in BaTiO3 Crystal

Polarization reversal in BaTiO 3 is discussed taking account of neutralizing electrons or ions upon the crystal surface. The neutralizing charges spread on the surface of one c -domain from another one separated by the 180°-type domain wall, and build up there a kind of wall of moderate or large (especially in liquid electrode) thickness, which plays an important role in the side-wise motion of the wall during the reversal process. Since the property of electrodes has a great influence upon the creation of the wall, the behaviour of the side-wise motion has the great difference among metal, semiconductor and liquid. The rapid side-wise motion in liquid electode can be attributed to the extensive thickness of the wall in this case. The origin of the central peak in neutron diffraction is discussed from the scope of the displacement of front walls and also the side-wise motion of this walls.

Equivalent Circuit Analysis of a Ferroelectric-Photoconductor Memory Device

An analysis of an equivalent circuit representing a ferroelectric photoconductor memory device has been performed. The purpose of this work is to provide a basis for describing the transient switching characteristics of the ferroelectricphotoconductor memory element. Two models describing the polarization reversal in the ferroelectric have been investigated. The first model assumes that the polarization charge is a nonlinear function of the voltage that is applied to the ferroelectric. This represents a simple generalization of an RC model for which the ferroelectric is assumed to have a well defined threshold field and allows one to qualitatively describe the partial switching of the ferroelectric. The second model of polarization reversal assumes that domain wall motion is activated. described adequately by the sidewise motion of domains, and dependent upon the instantaneous electric field in the ferroelectric domain. Domain statistics involving domain overlap as well as polarization reversal conditions are imposed to realistically describe the state of the ferroelectric as it traverses a hysteresis loop. The time dependence of the polari7ation, current, and voltage is examined and voltage is examined and attention focussed on polarization switching time as an important device parameter. Nonsaturated switching increases this speed and the feasibility of operating the device in this mode is discussed.