Ferroelectric Domain Reversal Research Articles

Electrostatic conductive disc singularity resolved

The conventional electrostatic solutions for two-dimensional (2D) electrodes possess edge singularities for the surface charge density σ and the normal component of the electric field En. These singularities are generally non-physical because they admit infinite gradients of the concentration of free charge carriers. In particular, they are unacceptable in the studies of the local field sensitive effects, such as the electric breakdown and the ferroelectric domain reversal. We claim that account for diffusion of free charge carriers leads to the disappearance of the edge singularities. This generalization occurs consistently within the same basic concept of conduction. Specifically, we consider the case of U-biased circular disc electrode of radius a. Account for diffusion leads here to a strongly nonlinear integral 2D equation for the electrostatic potential φ(r). Numerical solution of this equation shows that the law σ(a)∝U2/a takes place. Outside a close vicinity of the disc edge, we stay close to the conventional electrostatic solution for φ and σ.

Effect of domain wall conductivity on domain formation energy

Domain wall (DW) conductivity is nowadays considered as a general ferroelectric phenomenon. As applied to ferroelectric domain reversal, it is capable of providing a strong and instantaneous compensation of the bound polarization charge on DWs by free charges coming from electrodes. We claim that account for this compensation can strongly lower the domain formation energy as compared to that known from the Landauer theory. This facilitates the domain reversal process and resolves the problem of an excessively large depolarization energy. We provide a derivation and detailed analysis of the domain formation energy in the presence of the DW conduction; this is relevant to both the capacitor and atomic force microscopy experimental configurations.

Insights into improved ferroelectric and electrocaloric performance of Ba0.85Ca0.15Ti0.9Zr0.1O3 thick films grown by the electrophoretic deposition

Lead-free Ba0.85Ca0.15Ti0.9Zr0.1O3 (BCZT) bulk ceramics have recently gained attention as one of the attractive candidates for electrocaloric cooling due to their large heat absorption capacity induced by electro-structural phase transition near room temperature. However, adiabatic temperature change (ΔT) at room temperature in ceramics has been limited by their relatively low dielectric breakdown strength. Thick films, in this respect, possess the advantages of ceramics (volume) and thin films (thickness). In this work, a systematic ferroelectric and electrocaloric investigation of BCZT thick films, fabricated by electrophoretic deposition combined with laser annealing, has been carried out. Laser annealing at an optimized energy density of 398 W/cm2 has resulted in densely packed grain morphology with no compositional heterogeneities. Analysis of the scaling behavior of dynamic hysteresis revealed that ferroelectric domain reversal in BCZT/Pt has good stability and low energy consumption in the saturation region. The present thick films exhibited larger breakdown strength of 294 kV/cm and recoverable energy storage density of ∼7.3 J/cm3, at least five-fold enhancement compared to the bulk which is stable up to a 4 mm bending radius. The indirect electrocaloric measurements displayed parameters such as a ΔT and entropy change (ΔS) of 2.94 K and 3.1 J kg−1 K−1 respectively, for 205 kV/cm which are more than two orders increased compared to the bulk. Higher values of ΔT (1.9 K) at 25 °C, refrigerant capacity of 249 J/kg, and responsivity of 0.143 K mm/kV for BCZT/Pt film compared to relevant lead-free ferroelectric thick films elucidate the potential use of these films for solid-state refrigeration applications. The work also presents electrophoretic deposition with laser annealing as an alternative technique to widely studied tape-casting of thick films for electrocaloric studies.

Ferroelectric Domain Reversal: The Role of Domain Wall Conduction

Ferroelectric domain reversal is a vast research area relevant to the fundamental science and applications as well as to macro- and nanoscales. An instantaneous compensation of typically huge depolarizing electric fields is a key element here. On the other hand, the domain wall (DW) conduction is now regarded as a general ferroelectric phenomenon. Being often separated by big surface energy barriers in macroscopic experiments, the DW conduction becomes easily available under the conditions of atomic-force microscopy. We claim that the DW conduction has to be regarded as a crucial and general ingredient of the domain reversal processes. Its importance is in providing an automatic compensation of the depolarizing electric fields. The presence of DW conduction essentially modifies the basics of domain reversal processes, including the relations for domain nucleus energies, the domain grows velocities, and the domain shapes. Concerning atomic-force microscopy applications, domain reversal theories have to include injection models from conductive tip electrodes. Below we provide specific primary results relevant to the basics of DW conduction mediated ferroelectric domain reversal.

Ferroelectric Domain Reversal Dynamics in LiNbO3 Optical Superlattice Investigated with a Real‐Time Monitoring System (Small 32/2022)

Ferroelectric Domain Reversal Dynamics in LiNbO₃ Optical Superlattice Investigated with a Real‐Time Monitoring System (Small 32/2022)

Ferroelectric Domain Reversal Dynamics in LiNbO3 Optical Superlattice Investigated with a Real-Time Monitoring System.

The optical superlattice structure derived from a periodic poling process endows ferroelectric crystals with tunable optical property regulation, which has become one of the most efficient strategies for fabricating high-efficiency optical devices. Achieving a precise superlattice structure has been the main barrier for preparation of specific optical applications due to the unclear dynamics of domain structure regulation. Herein, a real-time monitoring system for the in situ observation of periodic poling of lithium niobate is established to investigate ferroelectric domain reversal dynamics. The formation of reversed domain nuclei, growth, and expansion of the domain are monitored, which is highly related to domain growth dynamics. The nucleation and growth of domain are discussed combined with the monition of domain reversal and the variation of local electric field distribution along with finite element analysis. An electrode configuration with multiholes is proposed to use the local electric field more efficiently and controllably, which could achieve a higher domain nucleus density with high uniformity. Two-mm-thick periodically poled LiNbO3 crystals with high quality are achieved. A nonlinear light conversion from 1064.2 to 3402.4nm is realized by the single-resonance optical parameter oscillator with a nonlinear optical efficiency up to 26.2%.

Temperature dependent scaling behavior of 0.67PMN–0.33PT relaxor ferroelectric ceramics

Polarization reversal mechanisms are the key to understand the ferroelectric properties. The scaling behaviors of ferroelectric loops reveal the dynamic processes of ferroelectric domain's nucleation, growth, and reversal. Pb(Mg1/3Nb2/3)O3–PbTiO3 (PMN-PT) at morphotropic phase boundary (MPB) exhibits excellent piezoelectric and electromechanical properties. In this paper, the dynamic scaling behaviors of 0.67PMN-0.33PT ceramics at variable temperatures were investigated. Results indicate that, at the high electric field, the remanent polarization Pr, coercive field Ec, and hysteresis loops area <A> decrease monotonically with the increase of temperature. While at a low electric field, they first increase and then decrease with increasing temperature. The scaling exponents a and b increase with the increase of temperature, indicating that the frequency and electric amplitude dependence of polarization reversal is enhanced with temperature.

Wake-up Free Ferroelectric Rhombohedral Phase in Epitaxially Strained ZrO2 Thin Films.

Zirconia- and hafnia-based thin films have attracted tremendous attention in the past decade because of their unexpected ferroelectric behavior at the nanoscale, which enables the downscaling of ferroelectric devices. The present work reports an unprecedented ferroelectric rhombohedral phase of ZrO2 that can be achieved in thin films grown directly on (111)-Nb:SrTiO3 substrates by ion-beam sputtering. Structural and ferroelectric characterizations reveal (111)-oriented ZrO2 films under epitaxial compressive strain exhibiting switchable ferroelectric polarization of about 20.2 μC/cm2 with a coercive field of 1.5 MV/cm. Moreover, the time-dependent polarization reversal characteristics of Nb:SrTiO3/ZrO2/Au film capacitors exhibit typical bell-shaped curve features associated with the ferroelectric domain reversal and agree well with the nucleation limited switching (NLS) model. The polarization-electric field hysteresis loops point to an activation field comparable to the coercive field. Interestingly, the studied films show ferroelectric behavior per se, without the need to apply the wake-up cycle found in the orthorhombic phase of ZrO2. Overall, the rhombohedral ferroelectric ZrO2 films present technological advantages over the previously studied zirconia- and hafnia-based thin films and may be attractive for nanoscale ferroelectric devices.

Enhanced ferroelectric and dielectric behaviors of PZT/BFO heterostructure via compositional development

Phase-pure perovskite structure Pb(Zr, Ti)O3 (PZT) thin films are successfully prepared on FTO/glass substrate via magnetron sputtering process, acting as buffer layers for the sol–gel-derived BiFeO3 (BFO) thin film. The existence of compressive strain of PZT buffer layer with various thicknesses was demonstrated through qualitative analysis, which can make the Gibbs-free energy flat and then reduce the ferroelectric domain reversal barrier, thereby influencing the ferroelectric performances. It showed that 100-nm PZT buffer layer is an optimal thickness, and the leakage current density of 100-nm PZT/BFO thin film is significantly decreased by 1–2 orders of magnitudes and the lowest value is obtained. And then BFO/PZT heterostructures in different modes are constructed and the related insulating, ferroelectric and dielectric performance are explored. With 100 nm PZT acting as buffer, enhanced ferroelectricity (at ± 490 kV/cm, Pr = 39.48 µC/cm2, Ec = 125.48 kV/cm) is obtained by modulating the number of interface between BFO and PZT to 7 (marked with Y-7), which is highly related to the reduced leakage current density (at ± 300 kV/cm, 10−5 A/cm2). It can be accounted for existence of compressive stress flattened Gibbs-free energy and increased interfaces number strengthened interfacial polarization. All these indicate that the formation of different heterostructures is promising for obtaining enhanced ferroelectricity.

Actively-monitored periodic-poling in thin-film lithium niobate photonic waveguides with ultrahigh nonlinear conversion efficiency of 4600 %W-1cm-2.

Chip-scale implementations of second-order nonlinear optics benefit from increased optical confinement that can lead to nonlinear interaction strengths that are orders of magnitude higher than bulk free-space configurations. Here, we present thin-film-based ultraefficient periodically-poled lithium niobate nonlinear waveguides, leveraging actively-monitored ferroelectric domain reversal engineering and nanophotonic confinement. The devices exhibit up to 4600 %W-1cm-2 conversion efficiency for second-harmonic generation, pumped around 1540 nm. In addition, we measure broadband sum-frequency generation across multiple telecom bands, from 1460 to 1620 nm. As an immediate application of the devices, we use pulses of picojoule-level energy to demonstrate second-harmonic generation with over 10% conversion in a 0.6-mm-long waveguide. Our ultracompact and highly efficient devices address growing demands in integrated-photonic frequency conversion, frequency metrology, atomic physics, and quantum optics, while offering a coherent link between the telecom and visible bands.

Narrow optical gap ferroelectric Bi2ZnTiO6 thin films deposited by RF sputtering

Thriving ferroelectric oxide Bi2ZnTiO6 thin films with a 1.48 eV optical gap.

Preparation and characterization of thick stoichiometric lithium tantalate crystals by vapor transport equilibration method

A stoichiometric lithium tantalate (SLT) crystal, 3.2 mm in the thickness and approximate 56 mm in the diameter, was prepared employing improved vapor transport equilibration (VTE) method. The chemical composition in SLT crystals is about 49.99 mol%. The compositional depth profile and uniformity along the radial direction were characterized. The composition deviation in the whole wafer is less than 0.02 mol%. The poling fields for ferroelectric domain reversal of SLT crystals were measured by applying ramped voltages using liquid electrodes. The forward and reverse poling fields are 159 V/mm and 145 V/mm, respectively, and their uniformity in the whole SLT crystal is promising.

Ferroelectric domain switching dynamics and memristive behaviors in BiFeO3-based magnetoelectric heterojunctions

The ferroelectric domain reversal dynamics and the corresponding resistance switching as well as the memristive behaviors in epitaxial BiFeO3 (BFO, ~150 nm) based multiferroic heterojunctions were systematically investigated. The ferroelectric domain reversal dynamics could be described by the nucleation-limited-switching model with the Lorentzian distribution of logarithmic domain-switching times. By engineering the domain states, multi and even continuously tunable resistances states, i.e. memristive states, could be non-volatilely achieved. The resistance switching speed can be as fast as 30 ns in the BFO-based multiferroic heterojunctions with a write voltage of ~20 V. By reducing the thickness of BFO, the La0.6Sr0.4MnO3/BFO (~5 nm)/La0.6Sr0.4MnO3 multiferroic tunnel junction (MFTJ) shows an even a quicker switching speed (20 ns) with a much lower operation voltage (~4 V). Importantly, the MFTJ exhibits a tunable interfacial magnetoelectric coupling related to the ferroelectric domain switching dynamics. These findings enrich the potential applications of multiferroic BFO based devices in high-speed, low-power, and high-density memories as well as future neuromorphic computational architectures.

A High‐Speed and Low‐Power Multistate Memory Based on Multiferroic Tunnel Junctions

AbstractFerroic‐order‐based devices are emerging as alternatives to high density, high switching speed, and low‐power memories. Here, multi‐nonvolatile resistive states with a switching speed of 6 ns and a write current density of about 3 × 103 A cm−2 are demonstrated in crossbar‐structured memories based on all‐oxide La0.7Sr0.3MnO3/BaTiO3/La0.7Sr0.3MnO3 multiferroic tunnel junctions. The tunneling resistive switching as a function of voltage pulse duration time, associated with the ferroelectric domain reversal dynamics, is ruled by the Kolmogorov–Avrami–Ishibashi switching model with a Lorentzian distribution of characteristic switching time. It is found that the characteristic resistance switching time decreases with increasing voltage pulse amplitude following Merz's law and the estimated write speed can be less than 6 ns at a relatively higher voltage. These findings highlight the potential application of multiferroic devices in high speed, low power, and high‐density memories.

Solid-State Synapse Based on Magnetoelectrically Coupled Memristor.

Brain-inspired computing architectures attempt to emulate the computations performed in the neurons and the synapses in the human brain. Memristors with continuously tunable resistances are ideal building blocks for artificial synapses. Through investigating the memristor behaviors in a La0.7Sr0.3MnO3/BaTiO3/La0.7Sr0.3MnO3 multiferroic tunnel junction, it was found that the ferroelectric domain dynamics characteristics are influenced by the relative magnetization alignment of the electrodes, and the interfacial spin polarization is manipulated continuously by ferroelectric domain reversal, enriching our understanding of the magnetoelectric coupling fundamentally. This creates a functionality that not only the resistance of the memristor but also the synaptic plasticity form can be further manipulated, as demonstrated by the spike-timing-dependent plasticity investigations. Density functional theory calculations are carried out to describe the obtained magnetoelectric coupling, which is probably related to the Mn-Ti intermixing at the interfaces. The multiple and controllable plasticity characteristic in a single artificial synapse, to resemble the synaptic morphological alteration property in a biological synapse, will be conducive to the development of artificial intelligence.

Highly Textured BaTiO3 via Templated Grain Growth and Resulting Polarization Reversal Dynamics

Samples of bulk textured polycrystalline BaTiO3 ceramics were fabricated using a templated grain growth (TGG) approach in order to investigate effects of polycrystallinity and texture related to ferroelectric domain reversal under high‐power drive conditions. Barium titanate platelets were formed via two‐step topochemical conversion of bismuth titanate platelets grown via molten salt synthesis, then aligned via tape casting within a matrix of fine BaTiO3 powder. The coarse‐grained parts showed a high degree of crystallographic texture after sintering. Combined with ceramics of similar density and polycrystallinity, but random orientation and commercial single‐crystal specimens, this sample set enabled direct isolation of crystallographic texture and polycrystallinity as the primary variables for high‐power polarization reversal studies. These studies have also demonstrated a link between grain size and polarization reversal time that strongly suggests that grain boundaries serve effectively as nucleation sites during the ferroelectric switching process.

Micro-spectroscopic characterization of ferroelectric domain structures in Yb^3+:LiNbO_3 prepared by electron beam writing

Sub-micrometer inverted domains in Yb3+ doped bulk LiNbO3 crystals are reported by using direct electron beam writing (DEBW) as a tool to reverse the spontaneous polarization in a two dimensional geometry. The effect of electron bombardment within the domain inversion process is analyzed at the micrometer scale by combining spatially resolved confocal Raman, Fluorescence and Second Harmonic Generation (SHG) imaging techniques. The obtained results not only confirms the feasibility of DEBW on the inversion procedure -the linear and nonlinear optical properties of the system remain unaltered after the process, but they also show that the slight structural changes associated with the polarization reversal in LiNbO3 are independent on the employed switching mechanism. The possibility of obtaining complementary non-destructive spectroscopic images of domains is also shown. Together, the results highlight the outstanding opportunities offered by confocal spectroscopy as a non invasive tool to probe the interaction between intrinsic defects and ferroelectric domain reversal structures in LiNbO3. Additionally, they provide valuable information to further decrease the size and distance between adjacent inverted domains in a solid state system in which, IR laser action, self-frequency conversion processes and laser tunability have been demonstrated.

Electric field driven variation in magnetoresistance of Co/Cu/Fe/BaTiO3 heterostructure

We demonstrate control of the magnetoresistance of Co/Cu/Fe giant magnetoresistance structures on BaTiO3(001) by electric field. The magnetoresistance clearly increases with electric field strength in the three different ferroelectric phases of BaTiO3, while the electric field dependence is more significant in the orthorhombic and rhombohedral phases with hysteretic behaviors, associated with the different ferroelectric domain reversal processes of BaTiO3. The results clearly show that electrically induced lattice distortion at the Fe/BaTiO3 interface can provide an alternative means to manipulating the electronic structure of the Fe layer by electric field.

Determination of the effective coercive field of ferroelectrics by piezoresponse force microscopy

The effective coercive field Ec for ferroelectric domain reversal is usually determined in a capacitor-like geometry by increasing an applied electric field until poling occurs. Here we present a different method based on local poling with the tip of a scanning force microscope and analyzing the dependence of the domain size on the poling parameters. This method for determining Ec is of importance because for many samples the standard technique fails, either because they are too small in size, or because they are slightly conductive. Results obtained on lithium niobate crystals of different composition conform to literature values.

Direct writing of ferroelectric domains on the x- and y-faces of lithium niobate using a continuous wave ultraviolet laser

Ferroelectric domain reversal has been achieved by scanning a tightly focused, strongly absorbed ultraviolet laser beam across the x- and y-faces of lithium niobate crystals. The domains were investigated by piezoresponse force microscopy. The emergence and width of any domain was found to depend on the scanning direction of the irradiating laser beam with respect to the polar z-axis. Full width and half width domains or no domain formation at all could be achieved for scanning along specific directions. We interpret the results by a direct correlation between the local temperature gradient and the resulting polarization direction.