Formation Of Domain Structures Research Articles

Domain evolution in BiFeO3 epitaxial nanoisland array via post-annealing

We describe the impact of post-annealing on ferroelectric-domain structures in arrays of BiFeO3 (BFO) epitaxial nanoislands, which exhibit a domain evolution from an initial 71° stripe/vortex domains to center-convergent topological domains. These results suggest that the increase and redistribution of charged defects, e.g., oxygen vacancies, in BFO nanoislands play a crucial role in driving the formation of center-type domain structures. The observation of defect-driven domain evolution in BFO nanoislands provides a path for further exploring their formation mechanism, topological properties, novel functionalities, and potential applications.

Impact of defect concentration on piezoelectricity in Mn/Fe-doped KTN crystals

Defect engineering via doping exhibits considerable potential for improving the performance of environment-friendly lead-free piezoelectric materials. Owing to the susceptibility to lattice vibrations and the micro-local chemical environment, the readily available Mn/Fe transition metal elements (TMEs) facilitate the construction of defect structures. However, the role of TMEs in shaping the domain structures and the corresponding promotional mechanism of piezoelectricity need to be further decoded. Herein, we propose the different influence mechanisms of Mn and Fe ions on the ferroelectric domain and piezoelectric properties. Different concentrations of (MnNb/Ta′-VO••)• and (FeNb/Ta″-VO••)× defect dipoles are obtained based on the synergy of Mn/Fe ions with oxygen vacancies. Diverse ferroelectric behaviors resulting from (MnNb/Ta′-VO••)• and (FeNb/Ta″-VO••)× defect dipoles are observed. Furthermore, the variation of the dielectric diffusiveness with the defect dipole concentration is investigated. Trace concentration of (MnNb/Ta′-VO••)• generates strong diffusiveness. With the characterization of the ferroelectric domain, this strong diffusiveness is attributed to the lattice-like domain structure. Thereafter, the mechanisms of Mn/Fe defect dipoles on the formation of domain structures are clarified. Macroscopically, the dielectric and piezoelectric properties are measured with Mn/Fe ion components. Trace Mn doping and the resulting lattice-like domain significantly enhance the piezoelectric coefficient, resulting in an increase of nearly 50% for K(Ta,Nb)O3 single crystals. This work highlights the tremendous potential of TME-induced defect dipoles for modifying the ferroelectric domain and provides a reference paradigm for improving piezoelectricity through defect engineering.

Growth of submicron domain structures in electric field at elevated temperatures in lithium niobate with surface dielectric layer

The formation of submicron stripe domain structures was studied during two-stage switching with a change in the dimensionality of domain growth in congruent lithium niobate with a dielectric layer on the polar surface at elevated temperature. At the first stage, a two-dimensional hexagonal microdomain lattice representing a structure of isolated domains was created using the photoresist mask. After that, the polar surface was covered by solid dielectric layer. Thus, switching at the second stage was carried out under inefficient screening of depolarization field leading to growth of the stripe domains only. Self-organized formation of domain stars and snowflakes was demonstrated.

Universal kinetics of the stochastic formation of polarization domain structures in a uniaxial single-crystal ferroelectric

Universal kinetics of the stochastic formation of polarization domain structures in a uniaxial single-crystal ferroelectric

Vortex switching in epitaxial nanodot under uniform electric field: The effect of misfit strain

Epitaxial strain plays an extraordinary role in the formation, evolution, and phase transition of topological domain structures in nanoscale ferroelectrics. Unfortunately, how vortex switching reacts to misfit strain in epitaxial nanodots remains unclear. Based on phase-field simulations, the reversal of vortex chirality in an epitaxial triangular nanodot induced by a uniform electric field applied along various directions is systematically investigated as a function of misfit strain. The results indicate that three basic types of vortex switching exist in an epitaxial triangular nanodot: type I under compressive strain, type II under tensile strain, and a narrow transition type with the characteristics of types I and II. The results show that misfit strain plays a crucial role in determining the type of vortex switching. This work, thus, clarifies the role of misfit strain and could be conducive to facilitating the mechanical manipulation of ferroelectric nanoelectronic devices.

Thermodynamics and Ferroelectric Properties of Pb1-xSrxTiO3 Solid Solutions

Pb1-xSrxTiO3 solid solutions have been utilized to compositionally tune the phase transitions and ferroelectric properties and thus are attractive for potential applications in tunable microwave devices and pyroelectric energy harvesters. However, a reliable thermodynamic description of the Pb1-xSrxTiO3 system is currently lacking. Here, we establish a thermodynamic free energy density function for the Pb1-xSrxTiO3 solid solution system taking into account both the polarization and octahedral tilt, and validated it by reproducing the experimentally measured polarization, lattice parameters, and dielectric constant values. Based on the thermodynamic model, we successfully explain the experimentally observed dielectric anomalies by analyzing the interactions between ferroelectric and octahedral tilt order parameters and constructed a comprehensive temperature-composition Pb1-xSrxTiO3 phase diagram which can be used to guide future experimental synthesis and thin film growth. The thermodynamic model developed in this work can be employed not only to predict the ferroelectric and structural states and their properties for compositions that have not yet been synthesized but also used as input to model the formation of mesoscale domain structures using the phase-field method.

Collective Magnetic Behavior in Vanadium Telluride Induced by Self-Intercalation

Self-intercalation of native magnetic atoms within the van der Waals (vdW) gap of layered two-dimensional (2D) materials provides a degree of freedom to manipulate magnetism in low-dimensional systems. Among various vdW magnets, the vanadium telluride is an interesting system to explore the interlayer order-disorder transition of magnetic impurities due to its flexibility in taking nonstoichiometric compositions. In this work, we combine high-resolution scanning transmission electron microscopy (STEM) analysis with density functional theory (DFT) calculations and magnetometry measurements, to unveil the local atomic structure and magnetic behavior of V-rich V1+xTe2 nanoplates with embedded V3Te4 nanoclusters grown by chemical vapor deposition (CVD). The segregation of V intercalations locally stabilizes the self-intercalated V3Te4 magnetic phase, which possesses a distorted 1T'-like monoclinic structure. This phase transition is controlled by the electron doping from the intercalant V ions. The magnetic hysteresis loops show that the nanoplates exhibit superparamagnetism, while the temperature-dependent magnetization curves evidence a collective superspin-glass magnetic behavior of the nanoclusters at low temperature. Using four-dimensional (4D) STEM diffraction imaging, we reveal the formation of collective diffuse magnetic domain structures within the sample under the high magnetic fields inside the electron microscope. Our results shed light on the studies of dilute magnetism at the 2D limit and on strategies for the manipulation of magnetism for spintronic applications.

Technology for the creation of ferroelectric regular domain structures using interfering elastic waves

Objectives. In many laboratories around the world, work is underway in the field of domain engineering of ferroelectrics. For a number of years, RTU MIREA has been conducting research on the creation of a high-performance technology for the formation of ferroelectric photonic and phononic crystals. The technology is characterized by a short duration of the technological cycle and provides the necessary depth of spatially periodic domain inversion. The key element of the technology is the combined effect of a uniform electric field and interfering high-frequency elastic waves that create a temperature grating. The technology is universal in relation to ferroelectrics of varying degrees of acoustic transparency, which is achieved by using highly dissipative liquid electrodes of a certain thickness. In this case, the energy of elastic waves practically does not penetrate into the ferroelectric, so the manifestation of undesirable effects is excluded. The purpose of this review article is to analyze the results of work carried out at RTU MIREA in the field of technology for the formation of ferroelectric regular domain structures (RDSs) during the period from 2008 to the present.Methods. Provisions of the theory of propagation, refraction and interference of elastic waves in condensed media are used, in particular, the Newtonian model of a liquid as applied to shear waves, as well as computer simulation. When considering the main stages of the Double Pulse heterothermal technology for the formation of RDSs, methods of analysis and synthesis were applied.Results. The possibility of forming not only micro-, but also submicron RDSs is shown. Recommendations are given on the choice of the type and specific properties of liquid electrodes, the angles between the direction of propagation of interfering waves, and their frequency. It is shown, in particular, that the use of highly dissipative ionic liquids as liquid electrodes creates favorable conditions for the formation of an RDS with a short period at room temperature. Thus, on shear waves with electrodes based on LiPF6-PC at a frequency of 300 MHz, RDS with a period of about 2 цт can be created. The main technological parameters are determined both for the case of the action of longitudinal elastic waves and for the case of shear waves with horizontal polarization. The results are applicable to ferroelectrics such as lithium niobate, potassium titanyl phosphate, and lead zirconate titanate.Conclusions. The proposed and studied methods are focused on the mass production of devices based on RDSs, in particular, on the manufacturing of optical parametric oscillators, acoustoelectronic devices, as well as terahertz wave generators and second harmonic oscillators. The technology has a short duration of the technological cycle, comparable to the polarization switching time in the used ferroelectric.

The origin of piezoelectric enhancement in compositionally graded ferroelectrics with sinusoidal variation

The direct piezoelectric effect of BaTiO3↔ Ba1−xSrxTiO3 graded ferroelectrics, whose compositions change in a sinusoidal form, is investigated via an extended phase-field method. The obtained results demonstrate that the piezoelectric coefficient can be significantly enhanced by controlling the amplitude of sinusoidal variation. The origin of piezoelectric enhancement is investigated by considering the formation of polarization domain structures and their behaviors under strain. Although a ferroelectric tetragonal phase or a paraelectric cubic phase primarily form in homogeneous Ba1−xSrxTiO3 ferroelectrics with a different content x, interestingly, an unusual ferroelectric monoclinic phase can be formed in compositionally graded ferroelectrics, giving rise to the coexistence of multiple phases. The monoclinic phase emerges as a result of the process that reduces built-in electric potential induced by a large gradient of polarization. In turn, the formation of the monoclinic phase gives rise to transient zones that make the polarization field more susceptible to external strains, thereby enhancing the piezoelectric response. We further demonstrate that the piezoelectric enhancement strongly depends on the volume fraction of the monoclinic phase in compositionally graded ferroelectrics, suggesting a route for the rational design of polarization domains and piezoelectric effects.

Formation of regular domain structures using interfering laser beams and liquid electrodes with a giant extinction coefficient

A method is proposed for formation of regular domain structures in ferroelectrics using interfering laser beams, a uniform electric field, and liquid electrodes with a giant extinction coefficient. It is shown that when using liquid electrodes, for example, based on a CdI2 aqueous solution with a 248 ÷ 266 nm photonic band gap, it is possible to create domain structures with a period of 6 ÷ 8 µm. The method is versatile for ferroelectrics of various degrees of transparency and birefringence, and is also characterized by a short duration of the process of formation of structures in ferroelectrics, such as LiNbO3, KTiOPO4, and PZT.

The role of cysteine in the formation of domain structures of papain and legumin in peas, involved in limited proteolysis

The limited use of plant proteins for food is explained by their low bioavailability and poor digestibility by enzymes of the gastrointestinal tract. Partially reproduced enzymatic processes of limited proteolysis that occur during seed germination are used to modify and improve the edibility characteristics of seed proteins. The present work discusses the possibility of reducing the duration of seed germination processes by optimising the conditions and parameters of limited proteolysis. To optimise manufacturing high-quality final product, enzymes (additional to the natural enzymes in the seed) and proteolysis conditions (in this case, temperature), as well as added substances (hydrolysis activators), were selected. The influence of cysteine on the formation of domain structures of proteins (enzymes and globulins) was evaluated. The proposed expressions can be used to determine those fragments of protein molecules that form stable domains and become unstructured when exposed to enzymes. Optimal conditions for limited proteolysis were identified based on the physical mechanism of action of papain-like proteolytic enzymes on pea legumin LegA (3KSC, CAA10722). It is shown that the decomposition of protein secondary structures takes 6–8 times longer, since the formed hydrogen bonds limit the access of enzymes to the corresponding amino-acid residues. It is also demonstrated that the decomposition of hydrogen bonds, e.g. by preliminary heat treatment of proteins, will broaden the prospects for limited proteolysis.

Formation of ferroelectric regular domain structures using shear elastic waves

By simulating the effect of interfering shear waves on a ferroelectric through a layer of a liquid electrode, it was shown that it is possible to form not only micro-, but also submicron domain structures at frequencies below 1000 MHz at room temperature. The frequency dependences of the domain structure period and the angles of incidence of shear waves are obtained for frequencies limited by the framework of the Newtonian fluid model. The method has a short technological cycle, provides the necessary depth of domain inversion, and does not depend on the degree of acoustic transparency.

Influence of asymmetric surface screening conditions on vortex switching in a ferroelectric nanodot

The behaviors of vortex switching in a ferroelectric nanodot on different surface screening conditions are investigated by phase-field simulations. It is found that asymmetric electrical boundary conditions have a significant effect on the formation of vortex domain structures and play a deterministic role in manipulating the vortex chirality by a homogeneous electrostatic field. The results indicate that the critical electric field for vortex switching can be greatly reduced by engineering the asymmetric surface screening conditions in a ferroelectric nanodot with a regular structure and uniform composition.

Effects of anisotropic misfit strains on equilibrium phases and domain structures in (111)-oriented ferroelectric PbTiO3 films

Advances in high-index-oriented ferroelectric films offer the exciting possibility of utilizing strain engineering to tune the desired properties related to the nanostructures. Previous studies often considered ferroelectric films grown on cubic substrates (isotropic strain), while the effects of anisotropic strains introduced by orthorhombic substrates are still not well understood. In our recent work, we grew (111)-oriented PbTiO3 (PTO) films on orthorhombic GdScO3 substrates and studied the domain structure evolution with film thickness. However, the theoretical understanding is lacking. In this work, the physical mechanism of the formation and evolution of domain structures was clearly revealed from the viewpoint of energy competition. Moreover, through the stereographic projection (SP) analysis of polarization vectors, a wide variety of ferroelectric phases for (111)-oriented PTO films under anisotropic strains were identified, and the misfit strain-misfit strain domain stability diagram was then constructed at room temperature. It was indicated that anisotropic misfit strains not only lead to the separation of ferroelectric domain variants that could co-exist under isotropic strain states for tetragonal-like d and monoclinic ma phases, but also stabilize the monoclinic mb phase. Their representative domain morphologies with separated domain variants under different anisotropic strains were analyzed in detail. These results provide guidance for interpreting and understanding more experimental data as well as the designing of (111)-oriented epitaxial ferroelectrics under anisotropic strains.

The study of the interaction of quantum dots with phosphatidylcholine to create hybrid functional materials

Quantum dots (QDs) are widely used as biomarkers that has both fundamental and applied importance. Since cell membranes are mainly composed of lipids such as phosphatidylcholine (PC) and its derivatives, it is important to investigate the interaction of QDs with PC in monolayers to understand the penetration mechanism. This work is devoted to the study of the interaction of QDs with PC by determining their surface-active properties at various interfaces by dynamic surface tension. The isotherms of the surface tension of 5 μg/L QDs solution or 0.17 mM (0.86 mM) PC solutions, as well as the solutions of the mixtures of QDs and PC: 0.17 mM (0.86 mM) PC and 5 μg/L QDs or 0.17 mM (0.86 mM) PC and 15 μg/L QDs were obtained. The mixed QDs/PC monolayers (at low content of QDs equal to 1:100) were characterized by the formation of a stable domain structures. An adsorption of PC at QDs allows to vary the degree of surface modification by changing the amount of the lipid. Such nanoparticles have dimensions not very different from the sizes of the initial QDs, due to the small size of lipids and are well suited for incorporation into biomembrane models.

Influence of growth temperature of KTiOAsO4 single crystals on their physicochemical parameters and formation of domain structures

A potassium titanyl arsenate (KTiOAsO4, KTA) crystal 50 × 80 × 60 mm in size has been grown by upgraded Czochralski method from flux (TGGS) with a decrease in temperature from 900 to 770 °C during pulling. It is shown that the spectroscopic properties of the parts of KTA crystals grown at 900 and 770 °C are close, whereas the electrical conductivity of the low-temperature (770 °C) KTA part turned out to be an order of magnitude lower than that of the high-temperature part. Visualisation of the domain structure by second-harmonic generation microscopy revealed a more efficient domain intergrowth (throughout the sample) in the low-temperature KTA, which is important for forming a regular domain structure (RDS) in a KTA-based nonlinear optical element. It is established that the quantum efficiency of parametric generation of light in the RDS formed in low-temperature KTA is several times higher than in the case of high-temperature KTA. The results obtained are important for optimising RDS parameters.

A technique for the formation of ferroelectric regular domain structures using highly dissipative electrically conductive liquids at room temperature

A technique for the formation of ferroelectric regular domain structures using interfering ultrasonic waves, a uniform electric field, and liquid electrodes based on ionic liquids has been proposed. The technique has a short duration of the technological cycle and provides the necessary depth of domain inversion. Based on the simulation results, recommendations are given for choosing the type of ionic liquid and the main parameters of ultrasonic pulses. The results are applicable to ferroelectrics, such as LiNbO3, KTiOPO4, and PZT.

Self-assembled shape evolution of the domain wall and formation of nanodomain wall traces induced by multiple IR laser pulse irradiation in lithium niobate

The formation of the domain structure in congruent lithium niobate crystals by multiple pulse irradiation using an infrared laser was studied experimentally. The qualitative change of the domain wall shape with an increase of the pulse number was revealed. The chains of isolated nanodomains representing the domain wall traces appeared after each laser pulse irradiation in the samples with an irradiated polar surface covered by an indium–tin oxide layer. This effect allowed extraction of the detailed information about the evolution of the domain wall shape. The domain kinetics under the action of the pyroelectric field has been considered. The mechanism of the self-assembled shape evolution of the moving domain wall as a result of the local wall accelerations and retardations caused by the shape fluctuations (bumps and valleys) was proposed. The experimentally observed formation of the quasi-regular comb-like domain structures with randomly distributed bumps and valleys was confirmed by computer simulation. The discovered effects allowed us to create the stable random and quasi-regular domain structures and open the way for further development of the domain engineering methods.

Simulated disordered-to-ordered phase transition of nonadecane

Nonadecane, normal alkane C19H40, has an orientationally disordered phase (rotator phase) between the melting point (305 K) and the transition temperature (293 K). The phase transition from the disordered phase to the ordered phase during the cooling process beyond the transition temperature was simulated based on the rate equation focusing on the state of molecules rotating or fixed. An experimental time profile curve of the disordered-ordered phase transition progression obtained by terahertz spectroscopy was reproduced successfully, allowing visualization of the transition and the formation of orientational domain structures in computer simulations.

An efficient space-time phase field discretization for ferroelectrics

Recent developments of phase field model based on the Ginzburg–Landau theory have provided an unprecedented look at the formation of polarization domain structures and rich phenomena of polarization behaviors in nanoscale ferroelectrics under electrical and mechanical multi-fields. However, the phase field simulations are often computationally expensive. One of the major reasons behind this inefficiency is due to the complex spatio-temporal effects on the dynamical behavior of polarization. In this work, an efficient scheme with error control and adaptive time-stepping is introduced to the phase field model in the context of Ginzburg–Landau theory. The proposed time adaptivity algorithm is based on the discrete maximum norm of the difference in numerical solutions at three consecutive time steps. In addition, the energy stability of the proposed scheme is demonstrated. Several benchmarks of convergence tests are presented to validate the model. The performance of proposed technique is illustrated through numerical examples involving behaviors of polarization in complex ferroelectric nanostructures in three dimensions.