Ferroelectric Domain Dynamics Research Articles

Physical discovery in representation learning via conditioning on prior knowledge

Recent advances in electron, scanning probe, optical, and chemical imaging and spectroscopy yield bespoke data sets containing the information of structure and functionality of complex systems. In many cases, the resulting data sets are underpinned by low-dimensional simple representations encoding the factors of variability within the data. The representation learning methods seek to discover these factors of variability, ideally further connecting them with relevant physical mechanisms. However, generally, the task of identifying the latent variables corresponding to actual physical mechanisms is extremely complex. Here, we present an empirical study of an approach based on conditioning the data on the known (continuous) physical parameters and systematically compare it with the previously introduced approach based on the invariant variational autoencoders. The conditional variational autoencoder (cVAE) approach does not rely on the existence of the invariant transforms and hence allows for much greater flexibility and applicability. Interestingly, cVAE allows for limited extrapolation outside of the original domain of the conditional variable. However, this extrapolation is limited compared to the cases when true physical mechanisms are known, and the physical factor of variability can be disentangled in full. We further show that introducing the known conditioning results in the simplification of the latent distribution if the conditioning vector is correlated with the factor of variability in the data, thus allowing us to separate relevant physical factors. We initially demonstrate this approach using 1D and 2D examples on a synthetic data set and then extend it to the analysis of experimental data on ferroelectric domain dynamics visualized via piezoresponse force microscopy.

The Investigation of Neuromimetic Dynamics in Ferroelectrics via In Situ TEM.

The core task of neuromorphic devices is to effectively simulate the behavior of neurons and synapses. Based on the functionality of ferroelectric domains with the advantages of low power consumption and high-speed response, great progress has been made in realizing neuromimetic behaviors such as ferroelectric synaptic devices. However, the correlation between the ferroelectric domain dynamics and neuromimetic behavior remains unclear. Here, we reveal the correlation between domain/domain wall dynamics and neuromimetic behaviors from a microscopic perspective in real-time by using high temporal and spatial resolution in situ transmission electron microscopy. Furthermore, we propose utilizing ferroelectric microstructures for the simultaneous simulation of neuronal and synaptic plasticity, which is expected to improve the integration and performance of ferroelectric neuromorphic devices. We believe that this work to study neuromimetic behavior from the perspective of domain dynamics is instructive for the development of ferroelectric neuromorphic devices.

Examination of Ferroelectric Domain Dynamics in HZO Under Endurance Cycling Stress

Examination of Ferroelectric Domain Dynamics in HZO Under Endurance Cycling Stress

Signs of dynamic nonlinearity of the coal dielectrics depolarization upon excitation in electric and magnetic field

The authors conducted a series of experiments on samples treated immediately before measurements with a constant magnetic field of a neodymium magnet and/or an alternating electric field. The experiment has shown complex dynamics of electric potential with alternating polarity relative to the base exponential depolarization curve. The variety of responses to different types of excitation, and the irregular and unpredictable nature of fluctuations suggest that these are varieties of the same phenomenon – the nonlinear dynamics of ferroelectric domains. The applied methods of statistical processing of the cumulative data array suggest that the invariance of the relaxation dynamics of the accumulated electric potential after excitation can be characterized by three related nonlinear differential equations of the first order. The impact of an alternating electric field may consist in bringing the dipoles of ferroelectric domains in the molecular coal structure into a state of unstable equilibrium with their slow return to their original position. The impact of a constant magnetic field is determined by the interaction of the external magnetic field with the magnetization induced due to time-varying electric polarization. In any case, the observed fluctuations are due to changes in the domain structure topology of the condenser with coal matter.

Data-Driven Analysis of High-Resolution Hyperspectral Image Data Sets through Nanoscale Capacitance–Voltage Measurements to Visualize Ferroelectric Domain Dynamics

Data-Driven Analysis of High-Resolution Hyperspectral Image Data Sets through Nanoscale Capacitance–Voltage Measurements to Visualize Ferroelectric Domain Dynamics

Investigation on degree of non-ergodicity and local piezoelectric properties in Na0.5Bi0.5TiO3–BiFeO3–PbTiO3 system

Knowledge of the statics and dynamics of ferroelectric domains is of immense importance since they are directly correlated with macroscopic polarization and strain. For the present work, piezoresponse force microscopy (PFM) is used to afford insight into field-induced phase transitions and local switching properties of a (1–2x)Na0.5Bi0.5TiO3–xBiFeO3–xPbTiO3 system for compositions, x = 0.01, 0.03, 0.05, and 0.07. Rietveld analysis of x-ray diffraction data reveals crystallization of the compound in single and dual phases in the chosen compositions. Upon the application of a local electric field, a phase transition from relaxor to normal ferroelectric (FE) is observed for all samples. A decrease in degree of non-ergodicity is realized within this composition range, which is found by analyzing the stability of field-induced ferroelectric domains. The field-induced FE domains for lower concentrations of x are found to be irreversible and a reversible nature was found for higher values of x. In addition, spatial variations of local switching parameters are investigated with the help of switching spectroscopic-PFM and a maximum local d33 was found for compositions having dual phases.

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.

Ultralow-power in-memory computing based on ferroelectric memcapacitor network.

Analog storage through synaptic weights using conductance in resistive neuromorphic systems and devices inevitably generates harmful heat dissipation. This thermal issue not only limits the energy efficiency but also hampers the very-large-scale and highly complicated hardware integration as in the human brain. Here we demonstrate that the synaptic weights can be simulated by reconfigurable non-volatile capacitances of a ferroelectric-based memcapacitor with ultralow-power consumption. The as-designed metal/ferroelectric/metal/insulator/semiconductor memcapacitor shows distinct 3-bit capacitance states controlled by the ferroelectric domain dynamics. These robust memcapacitive states exhibit uniform maintenance of more than 104 s and well endurance of 109 cycles. In a wired memcapacitor crossbar network hardware, analog vector-matrix multiplication is successfully implemented to classify 9-pixel images by collecting the sum of displacement currents (I=C×dV/dt) in each column, which intrinsically consumes zero energy in memcapacitors themselves. Our work sheds light on an ultralow-power neural hardware based on ferroelectric memcapacitors.

Anisotropy free energy contribution of the ferroelectric domain dynamics in PMN‐PT and PIN‐PMN‐PT relaxor ferroelectrics

AbstractA direct correlation between the materials property behavior with its associated ferroelectric domain mechanisms and the anisotropic component of the Landau free energy is established for binary PMN‐PT (generation I) and ternary PIN‐PMN‐PT (generation II) relaxor ferroelectric single crystal material systems. In addition to their trade‐off in material properties, the observed ferroelectric domain dynamic and the determined free energy anisotropies, especially as approaching phase transition, provide direct insights into the materials field‐dependent behavior between the binary and ternary ferroelectric systems. Domain configuration features such as lamellar structures in binary PMN‐PT and concentric oval‐like structures in ternary PIN‐PMN‐PT result in different material responses to external stimuli. Compared to binary PMN‐PT, the concentric oval‐like domain structures of ternary PIN‐PMN‐PT result in a 20°C higher temperature range of field‐dependent linear behavior, 40% increase in coercive electric field higher elastic stiffness during ferroelectric domain switching, and lower electromechanical energy losses. Separation of the isotropic and anisotropic components in the Landau free energy reveals a higher anisotropic free energy contribution from the ternary system, especially at temperature for practical applications. The high anisotropic free energy found in the ternary PIN‐PMN‐PT system implies that the concentric oval‐like domain structure contributes to reduced electromechanical energy losses and enhanced stability under external applied fields.

Domain dynamics in coercive-field engineered sub-µm periodically poled Rb-doped KTiOPO4

Nonlinear optical interactions involving counter-propagating photons are of great interest for both classical and quantum optical applications. However, their use is sparsely spread due to the fact that they require quasi-phase-matched devices with sub-µm periods. A recent breakthrough has been the fabrication of bulk sub-µm domain gratings in Rb-doped KTiOPO4 by creating a grating of low- and high- coercive field regions in the crystal via periodic ion exchange, so-called coercive-field engineering. Here, we investigate the physical mechanisms behind this method and study the interplay between the ion-exchanged grating properties and the ferroelectric domain dynamics. Furthermore, we investigate the scalability of the method by studying the domain morphology of sub-µm periodically poled crystals with periods ranging from 755 to 433 nm and correlating it to that of the ion-exchanged regions. We show that the formation of sub-µm domain gratings is governed by the depth, shape, and critical ion-concentration of the ion-exchanged volume and that it is independent of the poling period. These findings are crucial for further scaling the coercive field engineering technique to even shorter poling periods and larger aperture periodically poled crystals.

Electrical Conductivity and Dielectric Relaxation in Ag1−xLixNbO3

The broadband electrical properties of Ag1−xLixNbO3 (ALNx) ceramics (x ≤ 0.1) together with AgNbO3 (AN) crystals were studied over a wide temperature interval of 20–800 K. For ALNx with x ≤ 0.05, a very diffused ferroelectric phase transition was observed. The position of the dielectric permittivity maximum in this phase transition is strongly frequency-dependent and is described well by the Vogel–Fulcher law. The freezing temperature decreases when the lithium concentration increases. Below the ferroelectric phase transition temperature, the dielectric dispersion is mainly caused by ferroelectric domain dynamics. Moreover, for ALN3 and ALN5 ceramics at very low temperatures (below 100 K), behavior typical of dipolar glasses is observed. At higher temperatures (above 650 K for ALN5), electrical conductivity effects become important. The DC conductivity increases with temperature according to the Arhenius law and the activation energy is highest in the antiferroelectric phase. Moreover, the activation energy is strongly dependent on the lithium concentration and it is greatest when x = 0.02.

Domain switching dynamics in relaxor ferroelectric Pb(Mg1/3Nb2/3)O3–PbTiO3 revealed by time-resolved high-voltage electron microscopy

Ferroelectric domain dynamics in Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 single crystals have been studied by in situ biasing high-voltage transmission electron microscopy with a direct electron detection camera. We have achieved time-resolved recording of polarization switching in real space on a 2.5 ms time scale. The reversible response of micrometer-scale domains was observed by applying an electric field of 1 kV/mm. Detailed analyses on smaller sized domains 100–500 nm in size revealed that the domain switching initiated at a corner of a rectangular domain and propagated inward rapidly. The switching proceeded within 60 ms and the maximum switching rate, as fast as 6–8 μm/s, was observed. The domain switching kinetics was classified as two-dimensional nucleation and growth mode based on the Kolmogolov–Avrami–Ishibashi model.

Effect of Humidity on the Writing Speed and Domain Wall Dynamics of Ferroelectric Domains

AbstractThe switching dynamics of ferroelectric polarization under electric fields depends on the availability of screening charges in order to stabilize the switched polarization. In ferroelectrics, thin films with exposed surfaces investigated by piezoresponse force microscopy (PFM), the main source of external screening charges is the atmosphere and the water neck, and therefore relative humidity (RH) plays a major role. Here, it is shown how the dynamic writing of domains in BaTiO3 thin films changes by varying scanning speeds in the range of RH between 2.5% and 60%. The measurements reveal that the critical speed for domain writing, which is defined as the highest speed at which electrical writing of a continuous stripe domain is possible, increases non‐monotonically with RH. Additionally, the width of line domains shows a power law dependence on the writing speed, with a growth rate coefficient decreasing with RH. The size of the written domains at a constant speed as well as the creep‐factor μ describing the domain wall kinetics follow the behavior of water adsorption represented by the adsorption isotherm, indicating that the screening mechanism dominating the switching dynamics is the thickness and the structure of adsorbed water structure and its associated dielectric constant and ionic mobility.

High-precision local C–V mapping for ferroelectrics using principal component analysis

Local C–V mapping based on scanning nonlinear dielectric microscopy (SNDM) is a useful tool for characterizing ferroelectric domain dynamics at the nanoscale. In this study, we realized high-precision C–V mapping through an improved measurement system that introduces a digitizer and post-signal processing. Coupled with the high capacitance detection sensitivity of SNDM, nontrivial patterns corresponding to the polarization response were observed even in harmonic images with an order as high as thirty. Using these high-order harmonic components for the C–V curve resynthesis led to improved measurement accuracy. In addition, further improvement was achieved by introducing noise reduction based on principal component analysis. From the C–V curves resynthesized in this manner, parameters that represent the curve features could be extracted and subsequently displayed in two-dimensional maps. Detailed analyses of the datasets obtained with a ferroelectric HfO2 film revealed interesting distributions concerning local polarization switching dynamics.

Ferroelectric Synaptic Transistor Network for Associative Memory

AbstractBrain‐inspired associative memory is meaningful for pattern recognitions and image/speech processing. Here, a ferroelectric synaptic transistor network is proposed that is capable of associative learning and one‐step recalling of a whole set of data from only partial information. The competition between an external field and the internal depolarization field governs the ferroelectric creep of domain walls and offers each single ferroelectric synapse a full and subfemtojoule‐energy‐cost Hebbian synaptic plasticity, including short‐term memory (STM) to long‐term memory (LTM) transition, and remarkably both spike‐timing‐dependent plasticity (STDP) and spike‐rate‐dependent plasticity (SRDP). Assisted by the third terminal to control the ferroelectric domain dynamics, self‐adaptive coupling between neurons is realized by updating synaptic weight concurrently. Pavlov's dog experiment and multiassociative memories are demonstrated in this ferroelectric synaptic transistor network. Such ferroelectric synaptic transistor network is available for building multilayer neural networks and provides new avenues for associative‐memory information processing.

Non-linear dielectric response of layered CuInP2S6 and Cu0.9Ag0.1InP2S6 crystals

In this work, we report on the results of the examination of the nonlinear dielectric response of layered ferrielectic CuInP2S6 and Cu0.9Ag0.1InP2S6 crystals. The temperature behaviour of the nonlinear dielectric properties of ferrielectic CuInP2S6 and Cu0.9Ag0.1InP2S6 is found to be consistent with Landau theory. The additional peak of the third-order nonlinear susceptibility in these crystals, below the phase transition temperature, is strongly influenced by the electric field amplitude, and it is caused by the ferroelectric domain dynamics. The nonzero value of the second-order susceptibility and the mismatch between the temperatures of linear and third-order susceptibilities indicate that some polarisation exists above the phase transition temperature.

Retraction: “Magnetic-field-induced ferroelectric domain dynamics and in-plane polarization in odd and mixed layered Aurivillius structures” [J. Appl. Phys. 126, 084104 (2019)

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Distinct ferroelectric domain switching dynamics in epitaxial BiFeO3 (001) capacitors depending on the bias polarity

Understanding ferroelectric domain switching dynamics at the nanoscale is a great of importance in the viewpoints of fundamental physics and technological applications. Here, we investigated the intriguing polarity-dependent switching dynamics of ferroelectric domains in epitaxial BiFeO3 (001) capacitors using transient switching current measurement and piezoresponse force microscopy. We observed the distinct behavior of nucleation and domain wall motion depending on the polarity of external electric bias. When applying the negative bias to the top electrode, the sideways domain wall motion initiated by only few nuclei was dominant to polarization switching. However, when applying the positive bias, most of domains started to grow from the pre-existed pinned domains and their growth velocity was much smaller. We suggest that the observed two distinct domain switching behavior is ascribed to the interfacial defect layer.

High piezoelectric response and excellent fatigue resistance in Rb-substituted BNT–BKT–BT ceramics

Lead-free piezoelectric ceramics featuring high piezoelectricity and fatigue resistance are extremely important in practical applications. In this work, 0.85Bi0.5Na0.5TiO3–0.11Bi0.5K0.5−xRbxTiO3–0.04BaTiO3 (x = 0–0.20) ceramics are developed, and the effects of Rb content on the crystalline phase, domain structure, electric property, and fatigue resistance are investigated. XRD results show that all the ceramics exhibit the rhombohedral/tetragonal morphotropic phase boundary. The introduction of Rb at A-sites induces enhanced relaxor characteristics. Increasing the Rb content leads to apparently decreased size and increased dynamics of ferroelectric domains, as revealed by the PFM and TEM observations. Notably, the fatigue resistance of ceramics is greatly improved with the introduction of Rb. In particular, the composition of x = 0.10 exhibits almost fatigue-free behaviors in conjunction with high piezoelectricity of d33 ~ 203 pC/N, which can be attributed to the formation of tweed-like nanodomains with a size of 10–20 nm and stripe-like nanodomains with an average width of ~ 3.5 nm.

Domain Dynamics under Ultrafast Electric-Field Pulses.

Exploring the dynamic responses of a material is of importance to both understanding its fundamental physics at high frequencies and potential device applications. Here we develop a phase-field model for predicting the dynamics of ferroelectric materials and study the dynamic responses of ferroelectric domains and domain walls subjected to an ultrafast electric-field pulse. We discover a transition of domain evolution mechanisms from pure domain growth at a relatively low field to combined nucleation and growth of domains at a high field. We derive analytical models for the two regimes which allow us to extract the effective mass and damping coefficient of ferroelectric domain walls. The exhibition of two regimes for the ferroelectric domain dynamics at low and high electric fields is expected to be a general phenomenon that would appear for ferroic domains under other ultrafast stimuli. The present Letter also offers a general framework for studying domain dynamics and obtaining fundamental properties of domain walls and thus for manipulating the dynamic functionalities of ferroelectric materials.