Nucleation Of New Domains Research Articles

Mechanism of nucleation in ferroelastic domain switching

The mechanism of domain nucleation during ferroelastic domain switching is revealed by utilizing phase-field simulations. A complete compression-tension hysteresis loop is simulated, and the results show the nucleation of new domains at domain walls (DW). Due to relaxation of strain energy, the coherent DWs of the surviving domains often form features like steps, crevices and corners, and nucleation of new domains primarily takes place at these sites in a repeated fashion. The change in elastic strain energy around these sites is sufficient to provide the energy necessary for ferroelastic domain nucleation (FDN). The present simulations reveal that the apparent ellipsoidal shape of a nucleus might be an oblate spheroid when the nucleation takes place at a crevice. The present work also reveals that nucleation of triangular shaped domains is equally probable, and they take place at the steps or corners of DWs.

A phase-field model for study of ferroelastic deformation behavior in yttria stabilized zirconia

A modified phase-field model coupled with linear elasticity is formulated to study the effect of ferroelastic domain switching on the deformation behavior of tetragonal-prime yttria-stabilized zirconia. Simulations are performed under uniaxial tension and compression using realistic domain microstructures. This work provides new insights into the mechanism of ferroelastic deformation by studying the evolution of domains under different loading directions and strain rates. The model predicts realistic stress-strain curves consisting of stress-plateaus with accurate domain switching behavior without setting a switching criterion based on a critical stress for nucleation of new domains. The results reveal that the origin of coercive stress lies in the balance between the energy absorbed by the domain switching process and the externally applied energy. Loading in different directions but parallel to the spontaneous strain results in different levels of coercive stress as domain switching absorbs different amounts of energy. For the same reason when the strain-rate increases, the coercive stress also increases. This work establishes the relation between the coercive stress and microstructural changes during ferroelastic domain switching.

Observation of Micro-Scale Domain Structure Evolution under Electric Bias in Relaxor-Based PIN-PMN-PT Single Crystals

Relaxor ferroelectrics play a vital role as functional components in electromechanical devices. The observation of micro-scale domain structure evolution under electric bias in relaxor ferroelectrics has posed challenges due to their complex domain morphology characterized by small-sized domains. The present study aims to investigate the dielectric diffusion–relaxation characteristics, domain structure, and domain switching evolution under electric bias in high-performance single crystals of Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-33PbTiO3. The findings reveal the presence of strip-like domain patterns that interlock irregular small-sized nanodomains in PIN-PMN-33PT single crystals. Furthermore, the sample undergoes three distinct stages under electric bias, including the nucleation of new domains, the gradual forward expansion of domains, and the lateral expansion of domains. These observations provide valuable insights for understanding and exploring domain engineering techniques in relaxor ferroelectrics.

Voltage-driven ferroelectric domain dynamics in (K,Na)NbO3 investigated by in situ transmission electron microscopy

Ferroelectric domain dynamics is at the heart of any ferroelectric-based application. In situ transmission electron microscopy (TEM) offers an exciting opportunity to directly image ferroelectric switching and domain dynamics, revealing phenomena that might be concealed in macroscopic measurements. Here, we investigate the voltage-driven response of the mobile, needlelike domains and domain walls (DWs) of a (K,Na)NbO3 single crystal (KNNsc) using in situ TEM in a miniaturized capacitor. Our experimental results reveal that the immobile DWs can act as random bound pinning centers, pinning an area of up to 0.35 μm2. The edge of the sample can promote the nucleation of new domains. Domain growth and coalescence are not always continuous but can be interrupted at a certain voltage in favor of fine domain splitting and the formation of nanoscale domains. Other discontinuities are generated in the functional response when two orthogonal, needlelike domains meet and soft-pinning events occur. These findings shed light on the kinetics of ferroelectric domains and are probably not limited to KNNsc, being applicable to other perovskite-based ferroelectric materials where a needlelike domain morphology is present or where mobile and immobile DWs coexist.

Phase-field modeling of domain evolution in ferroelectric materials in the presence of defects

The properties of ferroelectric devices are strongly influenced, besides crystallographic features, by defects in the material. To study this effect, a fully coupled electromechanical phase-field model for 2D ferroelectric volume elements has been developed and implemented in a Finite Element code. Different kinds of defects were considered: holes, point charges and polarization pinning in single crystals, as well as grain boundaries in polycrystals, without and with additional dielectric interphase. The impact of the various types of defects on the domain configuration and the overall coercive field strength is discussed in detail. It can be seen that defects lead to nucleation of new domains. Compared to the energy barrier for switching in an ideal single crystal, the overall coercive field strength is significantly reduced towards realistic values as they are found in ferroelectric devices. Also the simulated hysteresis loops show a more realistic shape in the presence of defects.

Patterned nano-domains in PMN-PT single crystals

The domain structure, dielectric, and piezoelectric properties of 0.7 Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 (PMN-PT) single crystals with nanocomposite electrode, which includes MnOx semiconductor nanogratings and a Ti/Au conductive layer, were studied in this paper. These artificial MnOx nanogratings can alter the electric field distribution and then enhance the domain density. PMN-PT crystals with Ti/Au-MnOx nanocomposite electrodes showed high piezoelectric constant of 2250 p.m./V and dielectric constant of 5400 at 1 kHz, respectively. Compared to ones with conventional planar electrodes, the piezoelectric and dielectric constants of the samples with nanocomposite electrodes were increased 36.7% and 38.3%, respectively. Piezoresponse force microscopy (PFM) images revealed the domain pattern near the electrode/single crystal interface. A linear domain structure induced by the MnOx nanocomposite electrode was found in the samples with thickness less than 200 μm. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) results showed the diffusion of Mn about 300 nm in depth in PMNPT crystal after heat treatment during MnOx nanocomposite electrode. It is believed that the localized high electric fields induced by fringe effects caused by the nanocomposite electrode can enhance nucleation of new domains, and that diffusion from the patterned Mn layer may also lead to an enhancement in domain wall mobility. Our findings open up a new domain engineering technique for tailoring the dielectric and piezoelectric properties of PMN-PT single crystals.

A magnetic shift register with out-of-plane magnetized layers

Using out-of-plane magnetized layers, a lateral shift register made from discrete elements is demonstrated. By carefully designing the in-plane shape of the elements which make up the shift register, both the position of nucleation of new domains and the coercivity of the element can be controlled. The dipole field from a neighboring element, placed tens of nanometers away, creates a bias field on the nucleation site, which can be used to create a NOT gate. By chaining these NOT gates together, a shift register can be created where data bits consisting of neighboring layers with aligned magnetization are propagated synchronously under a symmetric applied magnetic field. The operation of a 16 element shift register is shown, including field coupled data injection.

Molecular dynamics study of ferroelectric domain nucleation and domain switching dynamics

Ferroelectric materials contain domains of ordered electric dipoles, separated by domain walls, that can undergo polarisation switching under externally applied electric fields. The domain switching dynamics in ferroelectric materials plays an essential role in their application to electronic and electro-optic de- vices. Previous studies suggest that the switching occurs largely through domain wall motion which is explained from the viewpoint of statistical physics on surface growth as the behaviour of a pinned elas- tic interface. We perform molecular dynamics simulations to investigate the domain switching process and quantitatively estimate the switching speed of anti-parallel 180° domains in ferroelectric, tetragonal BaTiO3 perfect single crystals at room temperature using the core-shell model. We observe an unprece- dented, non-linear increase in the domain switching speed caused by the nucleation of new domains within the switching domain. We determine the strength of the electric field to evoke nucleation of new domains and show that the nucleated domains diffuse into nearby favourable domains when the electric field is removed. Furthermore, we discuss the prominence of domain nucleations during ferroelectric switching.

Direct Imaging of the Electrochemical Deposition of Poly(3,4-ethylenedioxythiophene) by Transmission Electron Microscopy.

Conjugated polymers are electronically and ionically active organic materials of interest for use in a variety of devices. Electrochemical deposition is a convenient method for precisely fabricating conjugated polymer thin films, yet a detailed, quantitative understanding of nucleation and growth mechanisms has remained elusive. Here, we report direct imaging of the in situ electrochemical deposition of poly(3,4-ethylenedioxythiophene) (PEDOT) from an aqueous solution of EDOT monomer using Transmission Electron Microscopy with an electrochemical liquid flow cell. We found that PEDOT deposition began preferentially at the edge of the glassy carbon anodes at the beginning of the reaction. Fluctuating clusters of liquid-like oligomers were observed to form near the electrode surfaces. As the reaction continued, both the nucleation of new domains as well as the growth of pre-existing PEDOT deposits were observed, leading to systematic increases in film thickness and roughness.

Effect of grain orientation and grain size on ferroelectric domain switching and evolution: Phase field simulations

Phase field simulations were conducted in order to understand the effect of grain orientation, grain boundary and grain size on ferroelectric domain switching, stress distribution and evolution behavior under an applied electric field. Tetragonal ferroelectric domains were considered. Hysteresis loops were obtained for a single crystal, a bi-crystal and a polycrystal and the differences in their coercive fields were examined. It was found that the magnitude of the coercive field was closely related to the domain structures at the maximum electric field. Nucleation of new domains at a grain boundary led to local high stress. The effect of a reduced ferroelectric transition temperature at the grain boundary on the polarization distribution, domain structure and switching was studied.

Size effects in epitaxial ferroelectric islands and thin films

Size effects on domain configuration and polarization switching in two-dimensional epitaxial ferroelectric islands and in thin films are investigated by using a continuum phase field model that incorporates long-range elastic and electrostatic interactions. The simulations exhibit spatial polarization distributions with different types of domain walls in the epitaxial ferroelectric islands and find two critical thicknesses, at which the simulated material changes from a multidomain state to a single-domain state and from ferroelectric phase to paraelectric phase, respectively. The two critical thicknesses and the domain wall types vary with the length-to-thickness ratio. The simulations show that macroscopic polarization switching in thin films under an external electric field is processed through the nucleation of new domains and domain wall motion. The remanent polarization and the coercive field of the simulated ferroelectric films both decrease with decreasing film thickness.

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.

Barkhausen avalanches in anisotropic ferromagnets with 180 degrees domain walls

We show that Barkhausen noise in two-dimensional disordered ferromagnets with extended domain walls is characterized by the avalanche size exponent tau(s)=1.54 at low disorder. With increasing disorder the characteristic domain size is reduced relative to the system size due to nucleation of new domains and a dynamic phase transition occurs to the scaling behavior with tau(s)=1.30. The exponents decrease at finite driving rate. The results agree with recently observed behavior in amorphous Metglas and Fe-Co-B ribbons when the applied anisotropic stress is varied.

Computer simulations of switching behaviour in an orthorhombic ferroelectric model

Molecular-dynamics simulations of the switching process in the ferroelectric commensurate 1/3 three-dimensional model crystal have been carried on. Three stages of domain kinetics were observed, nucleation of new domains, growth of new domains, and the annealing process which reverses concurrent domains and leads to a single domain. The corresponding relaxation times have been derived from the coercive field as a function of external electric field frequency. We have found also that the time at which the repolarization current reaches a maximum characterizes the moment from which the amount of newly growing domains decreases, but the domain sizes increase.

Thermoremanent magnetization of nonuniformly magnetized grains

A simple and elegant interpretation of thermoremanent magnetization (TRM) in uniformly magnetized single‐domain (SD) grains was given by Néel 50 years ago, but the TRM acquisition processes in larger, nonuniformly magnetized grains are more varied and difficult to describe theoretically. SD TRM is a frozen high‐temperature partition between two microstates: spins parallel or antiparallel to an applied magnetic field. Nonuniformly magnetized grains have a much greater choice of microstates (local energy minimum or LEM states), and partitioning among various LEM states continues to change during cooling. These changes may involve Barkhausen jumps of domain walls between positions of minimum local energy or nucleation of new domains and walls. Because of the lower remanence capacity of nonuniform microstates compared to the uniform SD state, TRM intensity decreases as grain size increases, although certain microstates, e.g., single‐vortex states, seem to contribute little to TRM. Thermal demagnetization of TRM begins just above room temperature and continues to the Curie point, quite unlike the sharp “unblocking” of SD TRM. This continuous demagnetization, resulting from changes in microstates driven by the changing internal demagnetizing field during heating, profoundly affects the separation of different components of natural remanent magnetization and the determination of paleomagnetic field intensity.

Microscopic stress-induced magnetization changes in a fracture (1 1 1) surface of Terfenol-D observed with magnetic force microscopy

We have imaged mechanically polished and fractured (1 1 1) surfaces of Terfenol-D using magnetic force microscopy (MFM), and also the fracture surface during application of in situ applied stresses. The theory of James and Kinderlehrer (Phil. Magn. B 68 (1993) 237) has been used to explain some of the observed domain structures. Although some imaged domain structures are not predicted, there is general agreement with the theory. Observations indicate applied stress results in domain wall motion between existing domains as well as nucleation of new domains.

Scanning force microscopy of ferroelectric crystals

Abstract We report on the recent investigations of the surface of ferroelectric crystals with scanning force microscopy. Our inspection of the ferroelectric crystals triglycine-sulphate (TGS) and Barium-titanate (BaTiO3) allowed the simultaneous investigation of topographic surface features and ferroelectric domain structure in these crystals. Ferroelectric domains are clearly discernible in the non-contact mode as well as the friction force mode of imaging. In-situ investigations are demonstrated for temperatures T above the transition temperature Tc for TGS and BaTiO3 (Tc , TGS = 49°C, Tc , BaTiO3 = 126°C). We directly observed transition from the ferroelectric into the paraelectric phase. Upon cooling, new domains were formed indicating no memory effect, i.e. new domains grew on other spots than before heating. Further, a significantly different type of surface decoration was found for positively and negatively charged surface domains in TGS. This allows the in-situ observation of both domain wall motion and the nucleation of new domains.

Thermal stability of deformation substructure of cyclically deformed TiAl PST crystals

The effect of deformation mode on the deformation substructure and its thermal stability of TiAl polysynthetically twinned (PST) crystals was investigated using cyclically deformed and monotonically compressed crystals. In the fatigued TiAl PST crystals, two types of deformation substructure of deformation twins and a vein-like structure containing very tangled ordinary dislocations were formed depending on the type of ordered domains in γ phase. In contrast, numerous deformation twins and a large number of homogeneously distributed dislocations were observed in the compressed crystals. There was a great difference in the softening process and the thermal stability of deformation substructure between the fatigued and compressed crystals. Recovery occurred in the fatigued crystals even at low temperature (~400 °C) due to the climb motion of dislocations assisted by vacancy diffusion but recrystallisation could not be confirmed after annealing at 1000 °C for 105 s. In contrast, recrystallisation was observed in the compressed crystals at 1000 °C and deformation twins had an important role in the nucleation of new domains.

Drift and nucleation of magnetic domains in weak ferromagnet DyFeO3

The behavior of weak ferromagnetic strip domain structures is studied in ac and pulse magnetic fields in the presence of an external field gradient. Directed domains motion and the related process of nucleation of new domains are observed as the magnetic field reaches its threshold value.

Random Nucleation of New Domains in BaTiO3 Crystals at 20 kV/cm

The locations of domains appearing on the surface of a BaTiO3 crystal have been observed by repeated partial switching and etching to determine how frequently the domains appear at the same location on successive applied pulses. The ratio of the number of repeating locations to that of all locations is (10±1.6) % for a series of six pulses at 20 kV/cm on crystals with a positive internal bias and (28±5) % on crystals with a negative bias. The simplest interpretation of the results is that new domains can nucleate at points in the crystal remote from imperfections. This interpretation is in rough agreement with Landauer's calculation of the probability of thermally activated new domains for a 180° wall energy of 0.4 erg/cm2.