Ferroelectric Domain Structure Research Articles

4D-STEM Study on Ferroelectric Domain Structure within Biaxially-Strained BiFeO3 Film

4D-STEM Study on Ferroelectric Domain Structure within Biaxially-Strained BiFeO3 Film

Giant electrocaloric effect and breakdown field strength in ferroelectric terpolymer nanocomposites by morphologically diverse nanostructures

Electrocaloric cooling is a method for flexible electronics and compact chips with a promising ability to subvert traditional vapor compression refrigeration technology. Nevertheless, most reported EC materials exhibit relatively low adiabatic temperature (ΔT) and low breakdown field strength (Eb) at room temperature, limiting their further applications. Here, we develop a ferroelectric nanocomposite, composed of relaxor terpolymer poly(vinylidene fluoride-trifluoroethylen-chlorofluoroethylene) (PVTC), ceramic nanofillers [0.68(BaZr0.2Ti0.8O3)-0.32(Ba0.7Ca0.3TiO3)] (BCZT), boron nitride nanosheets (BNNSs), and BiFeO3 nanofibers (BFO NFs) with different morphologies and vary components ratios. The most optimal 12BBBP nanocomposite demonstrates gigantic ECE values including an isothermal entropy change (ΔS) of 94.5 J·kg−1·K−1 and a ΔT of 13.5 K under 220 MV/m electric field at 303 K, ΔS and ΔT are 3.5 times and 2.2 times larger than PVTC under 100 MV/m. It also exhibits an excellent Eb with a value of 290 MV/m. The phase-field simulation is used to simulate Eb behavior of nanocomposites with fillers of different nano-morphologies under an electrostatic field. Simultaneously, the interfacial coupling and ferroelectric domain structures are also simulated based on the time-dependent Landau-Ginzburg-Devonshire (TLGD) theory through finite element analysis (FEA) to present a better explanation for ECE performance. The experimental and simulation results simultaneously denote the ferroelectric nanocomposite possesses outstanding ECE and high Eb performance, laying foundation for the ferroelectrics in fields of flexible electronics and compact chip cooling. Coupled with the facile processability of terpolymer and lead-free nature of electroactive ceramics, this work paves a new way to develop a scalable, environmentally friendly and high-performance EC materials for next generation of refrigeration.

Reversible flexoelectric domain engineering at the nanoscale in van der Waals ferroelectrics

The universal flexoelectric effect in solids provides a mechanical pathway for controlling electric polarization in ultrathin ferroelectrics, eliminating potential material breakdown from a giant electric field at the nanoscale. One challenge of this approach is arbitrary implementation, which is strongly hindered by one-way switching capability. Here, utilizing the innate flexibility of van der Waals materials, we demonstrate that ferroelectric polarization and domain structures can be mechanically, reversibly, and arbitrarily switched in two-dimensional CuInP2S6 via the nano-tip imprinting technique. The bidirectional flexoelectric control is attributed to the extended tip-induced deformation in two-dimensional systems with innate flexibility at the atomic scale. By employing an elastic substrate, artificial ferroelectric nanodomains with lateral sizes as small as ~80 nm are noninvasively generated in an area of 1 μm2, equal to a density of 31.4 Gbit/in2. Our results highlight the potential applications of van der Waals ferroelectrics in data storage and flexoelectronics.

High-efficiency nonlinear frequency conversion enabled by optimizing the ferroelectric domain structure in x-cut LNOI ridge waveguide

Abstract Photonic devices based on ferroelectric domain engineering in thin film lithium niobate are key components for both classical and quantum information processing. Periodic poling of ridge waveguide can avoid the selective etching effect of lithium niobate, however, the fabrication of high-quality ferroelectric domain is still a challenge. In this work, we optimized the applied electric field distribution, and rectangular inverted domain structure was obtained in the ridge waveguide which is beneficial for efficient nonlinear frequency conversions. Second harmonic confocal microscope, piezoresponse force microscopy, and chemical selective etching were used to characterize the inverted domain in the ridge waveguide. In addition, the performance of nonlinear frequency conversion of the periodically poled nano-waveguide was investigated through second harmonic generation, and the normalized conversion efficiency was measured to be 1,720 % W−1 cm−2, which is close to 60 % that of the theoretical value. The fabrication technique described in this work will pave the way for the development of high-efficiency, low-loss lithium niobate nonlinear photonic devices.

Harnessing ferroic ordering in thin film devices for analog memory and neuromorphic computing applications down to deep cryogenic temperatures

The future computing beyond von Neumann era relies heavily on emerging devices that can extensively harness material and device physics to bring novel functionalities and can perform power-efficient and real time computing for artificial intelligence (AI) tasks. Additionally, brain-like computing demands large scale integration of synapses and neurons in practical circuits that requires the nanotechnology to support this hardware development, and all these should come at an affordable process complexity and cost to bring the solutions close to market rather soon. For bringing AI closer to quantum computing and space technologies, additional requirements are operation at cryogenic temperatures and radiation hardening. Considering all these requirements, nanoelectronic devices utilizing ferroic ordering has emerged as one promising alternative. The current review discusses the basic architectures of spintronic and ferroelectric devices for their integration in neuromorphic and analog memory applications, ferromagnetic and ferroelectric domain structures and control of their dynamics for reliable multibit memory operation, synaptic and neuronal leaky-integrate-and-fire (LIF) functions, concluding with their large-scale integration possibilities, challenges and future research directions.

Achieving large strain and low hysteresis in BiFeO3-BaTiO3-based piezoelectric ceramics

The high strain hysteresis has impeded lead-free piezoelectric ceramics to replace lead zirconate titanate ceramics applied in actuators. In this study, we report a significant advancement with the synthesis of a novel BiFeO3-BaTiO3-(Ba0.6Sr0.4)TiO3 (BF-BT-BST) system. The optimal composition has demonstrated a remarkable strain of 0.42 % coupled with a notably low hysteresis of 21 %. It is found that the incorporation of BST into BF-BT facilitates the transition from the rhombohedral phase to the pseudo-cubic phase, which in turn significantly enhances the relaxor ferroelectric characteristics of the ceramic. Through adjusting the composition proportion of BST, a unique ferroelectric domain structure is established for the BF-BT-0.04BST ceramic, where polar nanoregions (PNRs) are surrounded by ferroelectric macrodomains. The domain structure enables the ceramic to have the ability to respond the external electric field quickly compared to the PNRs for typical relaxor composition, thereby leading to large strain and low hysteresis simultaneously. Hence, it is inferred that the ferroelectric macrodomains simplify the response process of the PNRs under electric field. This study provides an efficient strategy to break through the bottleneck of large strain hysteresis for BF-BT ceramic, and gives a deep comprehension for the improvement of the strain characteristics.

Three-dimensional domain identification in a single hexagonal manganite nanocrystal

The three-dimensional domain structure of ferroelectric materials significantly influences their properties. The ferroelectric domain structure of improper multiferroics, such as YMnO3, is driven by a non-ferroelectric order parameter, leading to unique hexagonal vortex patterns and topologically protected domain walls. Characterizing the three-dimensional structure of these domains and domain walls has been elusive, however, due to a lack of suitable imaging techniques. Here, we present a multi-peak Bragg coherent x-ray diffraction imaging determination of the domain structure in single YMnO3 nanocrystals. We resolve two ferroelectric domains separated by a domain wall and confirm that the primary atomic displacements occur along the crystallographic c-axis. Correlation with atomistic simulations confirms the Mexican hat symmetry model of domain formation, identifying two domains with opposite ferroelectric polarization and adjacent trimerization, manifesting in a clockwise arrangement around the hat’s brim.

Room-Temperature Ferroelectric Epitaxial Nanowire Arrays with Photoluminescence.

The development of large-scale, high-quality ferroelectric semiconductor nanowire arrays with interesting light-emitting properties can address limitations in traditional wide-bandgap ferroelectrics, thus serving as building blocks for innovative device architectures and next-generation high-density optoelectronics. Here, we investigate the optical properties of ferroelectric CsGeX3 (X = Br, I) halide perovskite nanowires that are epitaxially grown on muscovite mica substrates by vapor phase deposition. Detailed structural characterizations reveal an incommensurate heteroepitaxial relationship with the mica substrate. Furthermore, photoluminescence that can be tuned from yellow-green to red emissions by varying the halide composition demonstrates that these nanowire networks can serve as platforms for future optoelectronic applications. In addition, the room-temperature ferroelectricity and ferroelectric domain structures of these nanowires are characterized using second harmonic generation (SHG) polarimetry. The combination of room-temperature ferroelectricity with photoluminescence in these nanowire arrays unlocks new avenues for the design of novel multifunctional materials.

Poling induced changes in polarization domain structure of polymer ferroelectrics for application in organic thin film transistors

While electrical poling of organic ferroelectrics has been shown to improve device properties, there are challenges in visualizing accompanying structural changes. We observe poling induced changes in ferroelectric domains by applying differential phase contrast (DPC) imaging in the scanning transmission electron microscope, a method that has been used to observe spatial distributions of electromagnetic fields at the atomic scale. In this work, we obtain DPC images from unpoled and electrically poled polyvinylidene fluoride trifluorethylene films and compare their performance in polymer thin film transistors. The vertically poled films show uniform domains throughout the bulk compared to the unpoled film with a significantly higher magnitude of the overall polarization. Thin film transistors comprising a donor–acceptor copolymer as the active semiconductor layer show improved performance with the vertically poled ferroelectric dielectric film compared with the unpoled ferroelectric dielectric film. A poling field of 80–100 MV/m for the dielectric layer yields the best performing transistors; higher than 100 MV/m is seen to degrade the transistor performance. The results are consistent with a reduction in deleterious charge carrier scattering from ferroelectric domain boundaries or interfacial dipoles arising from electrical poling.

Nonlocal erasing and writing of ferroelectric domains using a femtosecond laser in lithium niobate.

We experimentally demonstrate the highly-efficient nonlocal erasing and writing of ferroelectric domains using a femtosecond laser in lithium niobate. Based on the induction of a focused infrared femtosecond laser without any relative displacement or additional treatment, the original multiple ferroelectric domains can be either erased (erasing operation) or elongated (writing operation) simultaneously in the crystal, depending on the laser focusing depth and the laser pulse energy. In the erasing operation, the original multiple ferroelectric domains can be cleared completely by just one laser induction, while in the writing operation, the average length of the ferroelectric domains can be elongated up to 235 µm by three laser inductions. A model has been proposed in which a thermoelectric field and a space charge field are used cooperatively to successfully explain the mechanism of nonlocal erasing and writing. This method greatly improves the efficiency and flexibility of tailoring ferroelectric domain structures, paving the way to large-scale all-optical industrial production for nonlinear photonic crystals and nonvolatile ferroelectric domain wall memories.

Conducting atomic force microscopy studies on domain wall currents of Bi5Ti3FeO15 nanodots fabricated by anodic aluminum oxide nanotemplate and sol-gel process.

We investigated the local current characteristics of Bi5Ti3FeO15 (BTFO) nanodots on Nb-doped SrTiO3 substrates affected by their ferroelectric domain structures and domain walls. The BTFO nanodots with a diameter of about 50 nm were fabricated by anodic aluminum oxide nanotemplates and a BTFO sol-gel process. Based on a piezoresponse force microscope, it was confirmed that domain walls were formed in the ferroelectric domain structures of the epitaxial BTFO nanodots. Current changes due to ferroelectric tunneling junctions according to ferroelectric polarizations in epitaxial BTFO nanodots were confirmed by conduction atomic force microscopy. In particular, the domain walls formed in the epitaxial BTFO nanodots formed high currents compared to the currents in ferroelectric tunneling junctions due to polarizations. RESEARCH HIGHLIGHTS: Ferroelectric Bi5Ti3FeO15 nanodots with a diameter of 50 nm. Ferroelectric domain structures observed with piezoresponse force microscopy. High domain wall currents observed at domain boundaries observed with conducting atomic force microscopy.

Effect of annealing conditions on surface morphology and ferroelectric domain structures of BiFeO3 thin films

Ferroelectric materials are widely used in the applications of electronic devices due to their robust spontaneous polarization. The surface roughness of ferroelectric thin films, which is closely related to the morphology, can play an important role in determining the ferroelectric domain structures. In this work, we have investigated the influence of annealing conditions on the surface morphology of epitaxial BiFeO3 and SrRuO3 thin films prepared by pulsed laser deposition on SrTiO3 (001) substrates. It is found that the morphology of the thin films is sensitive to the annealing time and cooling rate, and the corresponding surface roughness decreases with increasing annealing time and decreasing cooling rate. In addition, the ferroelectric domain structures of BiFeO3 films have been investigated by piezoelectric force microscopy, which shows a significant improvement in domain size and reverse piezoelectric response in the thin films with decreasing surface roughness. This work provides a simple way to predict and improve the ferroelectric domain structures by in situ annealing.

Optimized energy storage properties of Bi0.5Na0.5TiO3-based lead-free ceramics by composition regulation

To meet the demand for miniaturization and integration of electronic and electrical equipments, developing dielectric capacitors with excellent energy storage properties is of utmost importance. Bi0.5Na0.5TiO3-based ceramics have been investigated extensively for potential energy storage applications. However, its low breakdown strength Eb and high remnant polarization Pr limit the energy storage density and efficiency (η). Therefore, we explored a synergistic design strategy of domain control and grain size adjustment via La doping to successfully synthesize 0.8Bi0.5Na0.5TiO3-0.2NaNbO3-xLa2O3 (0.8BNT-0.2NN-xLa2O3) ceramics with superior energy storage properties to overcome above issues. It shows that the composition regulation by antiferroelectric NaNbO3 results in improved disrupted long rang order ferroelectric domain structure, effectively promoting the formation of polar nanoregions, subsequently weakening Pr and enhancing relaxation behavior. The introduction of antiferroelectric NaNbO3 effectively improves the η of the system. Moreover, the grain size is decreased and densification is enhanced after La tailoring, which is beneficial for the Eb and recyclable energy storage density (Wrec). Finally, a high Wrec of 4.40 ± 0.20 J/cm3 and η of 80.1 ± 2.1% at 450 kV/cm are obtained in 0.8BNT-0.2NN-0.07La2O3 ceramic. Besides, the sample demonstrates admirable temperature stability (25–175 °C) and frequency stability (10–100 Hz). Simultaneously, it displays stable discharge energy density, rapid discharge time of 0.36 μs, and good fatigue endurance (105 cycles). The results offer useful guidance for the design of novel ceramic capacitors with comprehensive energy storage performance.

Effect of Thickness on Ferroelectric Properties of Bi3.25La0.75Ti3O12 Thin Films

The pursuit of low-power/low-voltage operation in devices has prompted a keen interest in the mesoscale effects within ferroelectric thin films. The downsizing of ferroelectrics can significantly influence performance; for instance, the remanent polarization and coercive field are susceptible to alterations based on thickness. In this study, randomly oriented Bi3.25La0.75Ti3O12 thin films were fabricated on Pt/Ti/SiO2/Si substrates using the sol–gel method, and SEM observations revealed rod-like grains in all thin films. The investigation delved into the correlation between dielectric and ferroelectric properties with thin film thickness. The thin film exhibited an increased remanent polarization and a reduced coercive electric field. Additionally, the ferroelectric domain structure was scrutinized through PFM, and the resistor properties of the BLT4 thin film were studied, which shows the potential of BLT thin films in non-volatile memory and memristor.

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.

Manipulation of BiFeO3 nanostructure by substrate terrace morphology

Topological domain structures, such as vortex and center domain have been found in BiFeO3 nanoislands fabricated by self-assemble approaches, which exhibit great application potential in nonvolatile storage. However, how to control the self-assembled nanostructure during preparation process is still an open question. Here, we successfully grew BiFeO3 films with nano-stripe, nano-maze and dense nanoisland structures on LaAlO3 (001) substrate by pulsed laser deposition. We found the formation of different nanostructures is related to the terrace morphology of the substrate. Nano-stripe structure with strip domain and high conduction tail-to-tail domain wall preferred to form on wide terrace, nano-maze structure with three-fold or four-fold center-type domain usually form on bunched terrace, while dense nanoisland structure with two/three-fold domain preferred to from on the narrow or rough terrace LaAlO3 substrate. These findings provide guidance for manipulating the ferroelectric topological domain structure during film preparation process.

Domain patterning in nonpolar cut PMN–PT by focused ion beam

The formation of the ferroelectric domain structure as a result of irradiation by focused ion beam of [100]-cut 0.61Pb(Mg[Formula: see text]Nb[Formula: see text]O3–0.39PbTiO3 (PMN–PT) single crystals covered by surface artificial dielectric layer and with free surface was investigated. The dot irradiation resulted in formation of the wedge-like domains grown along [00[Formula: see text]] direction. For irradiation of the free surface, the domains are mainly located under the surface, while at the irradiated surface with an artificial dielectric layer the domains are located at the surface. It was shown that the subsurface wedge-shaped part of the domain is unstable and completely disappears after a month due to spontaneous backswitching under the action of the residual depolarization field. The revealed nonlinear dose dependence of the domain sizes was attributed to the distribution of the electric field using the point charge model. The domain interaction for the distance between irradiated dots below 30[Formula: see text][Formula: see text]m has been revealed in all samples. It was shown that the decrease of the distance between irradiated dots in the created domain row leads to an increase in the length of the central domains, which is explained by the contribution of all injected charges to the switching field.

Theoretical and numerical study of the Landau-Khalatnikov model describing a formation of 2D domain patterns in ferroelectrics

Among the numerous applications of the Ginzburg-Landau theory to the analysis of significant reaction-diffusion systems, modeling of the behavior of promising polar dielectric materials should be especially highlighted. The paper is devoted to the theoretical and numerical analysis of the Landau-Khalatnikov model describing the dynamics of 2D domain pattern formation in ferroelectrics. The unique solvability of the initial-boundary value problem for the system of 2D cubic-quintic Landau-Khalatnikov equations is proved. The proof is based on the derivation of new a priori estimates for the solution of the system of nonlinear parabolic equations. A series of computational experiments are conducted to examine both spontaneous and polar-induced domain pattern formation in biaxial ferroelectrics. Finite-element simulations allow us to visualize different types of ferroelectric domain structures depending on the varying boundary conditions.

Leakage current characteristics affected by crystallinity and domain wall current of epitaxial Bi5Ti3FeO15 thin films

We investigated leakage current characteristics affected by crystallinity and domain wall currents of epitaxial Bi5Ti3FeO15 (BTFO) thin films on Nb-doped SrTiO3 substrates. Highly a-oriented BTFO thin films, highly c-oriented BTFO thin films, and BTFO thin films with a mixture of a-oriented and c-oriented crystallinity were prepared by controlling the substrate temperature and the pulsed laser deposition deposition rate. Highly c-oriented BTFO thin films exhibited the best leakage current characteristics because the Bi2O2 layers were placed perpendicular to the c-axis to reduce leakage currents. The BTFO thin films with a mixture of a-oriented and c-oriented crystallinity showed larger leakage currents compared to highly c-oriented BTFO thin films. The current domains of the BTFO thin films corresponding to the ferroelectric domain structures were observed by a conducting atomic force microscope, and it was observed that leakage currents were formed around the domain walls. In particular, the largest leakage currents are formed at the boundaries of c-oriented domains and a-oriented domains, and these domain boundaries confirmed that the BTFO thin films with a mixture of a-oriented and c-oriented crystallinity were responsible for the largest leakage currents.

Large bi-axial tensile strain effect in epitaxial BiFeO3 film grown on single crystal PrScO3

A BiFeO3 film is grown epitaxially on a PrScO3 single crystal substrate which imparts ~ 1.45% of biaxial tensile strain to BiFeO3 resulting from lattice misfit. The biaxial tensile strain effect on BiFeO3 is investigated in terms of crystal structure, Poisson ratio, and ferroelectric domain structure. Lattice resolution scanning transmission electron microscopy, precession electron diffraction, and X-ray diffraction results clearly show that in-plane interplanar distance of BiFeO3 is the same as that of PrScO3 with no sign of misfit dislocations, indicating that the biaxial tensile strain caused by lattice mismatch between BiFeO3 and PrScO3 are stored as elastic energy within BiFeO3 film. Nano-beam electron diffraction patterns compared with structure factor calculation found that the BiFeO3 maintains rhombohedral symmetry, i.e., space group of R3c. The pattern analysis also revealed two crystallographically distinguishable domains. Their relations with ferroelectric domain structures in terms of size and spontaneous polarization orientations within the domains are further understood using four-dimensional scanning transmission electron microscopy technique.