Ferroelectric Research Articles

Intermediate multidomain state in single-crystalline Mn-doped BiFeO3 thin films during ferroelectric polarization switching

A intermediate multidomain state and large crystallographic tilting of 1.78° for the (hh0)pc planes of a (001)pc-oriented single-domain Mn-doped BiFeO3 (BFMO) thin film were found when an electric field was applied along the [110]pc direction. The anomalous crystallographic tilting was caused by ferroelastic domain switching of the 109° domain switching. In addition, ferroelastic domain switching occurred via an intermediate multidomain state. To investigate these switching dynamics under an electric field, we used in situ fluorescent X-ray induced Kossel line pattern measurements with synchrotron radiation. In addition, in situ inverse X-ray fluorescence holography (XFH) experiments revealed that atomic displacement occurred under an applied electric field. We attributed the atomic displacement to crystallographic tilting induced by a converse piezoelectric effect. Our findings provide important insights for the design of piezoelectric and ferroelectric materials and devices.

Optical Control of In-Plane Domain Configuration and Domain Wall Motion in Ferroelectric and Ferroelastic Materials.

The sensitivity of ferroelectric domain walls to external stimuli makes them functional entities in nanoelectronic devices. Specifically, optically driven domain reconfiguration with in-plane polarization is advantageous and thus is highly sought. Here, we show the existence of in-plane polarized subdomains imitating a single domain state and reversible optical control of its domain wall movement in a single-crystal of ferroelectric BaTiO3. Similar optical control in the domain configuration of nonpolar ferroelastic material indicates that long-range ferroelectric polarization is not essential for the optical control of domain wall movement. Instead, flexoelectricity is found to be an essential ingredient for the optical control of the domain configuration, and hence, ferroelastic materials would be another possible candidate for nanoelectronic device applications.

0.98(K0.5Na0.5)NbO3–0.02(Bi0.5Na0.5)(Zr0.85Sn0.15)O3 Single Crystals Grown by the Seed-Free Solid-State Crystal Growth Method and Their Characterization

(K0.5Na0.5)NbO3-based single crystals are of interest as high-performance lead-free piezoelectric materials, but conventional crystal growth methods have some disadvantages such as the requirement for expensive Pt crucibles and difficulty in controlling the composition of the crystals. Recently, (K0.5Na0.5)NbO3-based single crystals have been grown by the seed-free solid-state crystal growth method, which can avoid these problems. In the present work, 0.98(K0.5Na0.5)NbO3–0.02(Bi0.5Na0.5)(Zr0.85Sn0.15)O3 single crystals were grown by the seed-free solid-state crystal growth method. Sintering aids of 0.15 mol% Li2CO3 and 0.15 mol% Bi2O3 were added to promote single crystal growth. Pellets were sintered at 1150 °C for 15–50 h. Single crystals started to appear from 20 h. The single crystals grown for 50 h were studied in detail. Single crystal microstructure was studied by scanning electron microscopy of the as-grown surface and cross-section of the sample and revealed porosity in the crystals. Electron probe microanalysis indicated a slight reduction in K and Na content of a single crystal as compared to the nominal composition. X-ray diffraction shows that the single crystals contain mixed orthorhombic and tetragonal phases at room temperature. Raman scattering and impedance spectroscopy at different temperatures observed rhombohedral–orthorhombic, orthorhombic–tetragonal and tetragonal–cubic phase transitions. Polarization–electric field (P–E) hysteresis loops show that the single crystal is a normal ferroelectric material with a remanent polarization (Pr) of 18.5 μC/cm2 and a coercive electrical field (Ec) of 10.7 kV/cm. A single crystal presents d33 = 362 pC/N as measured by a d33 meter. Such a single crystal with a large d33 and high Curie temperature (~370 °C) can be a promising candidate for piezoelectric devices.

Pulsed Force Kelvin Probe Force Microscopy-A New Type of Kelvin Probe Force Microscopy under Ambient Conditions.

Kelvin probe force microscopy (KPFM) is an increasingly popular scanning probe microscopy technique used for nanoscale imaging of surface potential for various materials, such as metals, semiconductors, biological samples, and photovoltaics, to reveal their surface work function and/or local accumulation of charges. This featured review outlines the operation principles and applications of KPFM, including several typical commercially available variants. We highlight the significance of surface potential measurements, present the details of the method operation, and discuss the causes of the limitation on spatial resolution. Then, we present the pulsed force Kelvin probe force microscopy (PF-KPFM) as an innovative improvement to KPFM, which provides an enhanced spatial resolution of <10 nm under ambient conditions. PF-KPFM is promising for the characterization of heterogeneous materials with spatial variations of electrical properties. It will be especially instrumental for investigating emerging perovskite photovoltaics, heterogeneous catalysts, 2D materials, and ferroelectric materials, among others.

Pyroelectric effect in high detectivity self-powered photodetector based on Cs2AgBiBr6

The ferroelectric perovskite material Cs2AgBiBr6 has received much attention because of its low poisonous nature and environmental stability. In this paper, we prepared high-quality Cs2AgBiBr6 thin films for self-powered photodetectors using a low-pressure-assisted method, investigated their optical, electrical, and pyroelectric properties, and characterized the film morphology and crystallization. The device modulates the photoelectric process without an external power supply, and has a maximum switching ratio of 1.72 × 106, a response rate of 0.158 A/W, a specific detectivity of 1.39 × 1011 Jones, an external quantum efficiency of 52.8 %, and a fast response time of 15.4/16.8 μs when irradiated with 532 nm light, which is much better than that of previous self-powered devices with the same material on/off ratio and specific detectivity. It is worth mentioning that the pyroelectric effect was observed in the infrared band. In addition, the devices exhibited high stability to water and oxygen in an air environment (25 °C, 60 % humidity), retaining more than 95 % of the initial performance after one month of placement. Our study demonstrates that the lead-free perovskite Cs2AgBiBr6 is a promising and environmentally friendly alternative for the preparation of highly stable self-powered photodetectors and is also of great research value in the field of pyroelectric detection.

Exploring Disturb Characteristics in 2D and 3D Ferroelectric NAND Memory Arrays for Next-Generation Memory Technology.

Ferroelectric transistors are considered promising for next-generation 3D NAND technology due to their lower power consumption and faster operation compared to conventional charge-trap flash memories. However, ensuring their suitability for such applications requires a thorough investigation of array-scale reliability. This study specifically examines the suitability of hafnia-based ferroelectric transistors for advanced 3D NAND applications, with a specific focus on establishing a disturb-free voltage scheme to ensure the reliability of ferroelectric transistors within the array. Our key finding highlights the crucial role of optimal pass voltage in achieving disturb-free operation in both 2D and 3D ferroelectric NAND arrays. Additionally, the study indicates that read disturb remains negligible when an appropriate read voltage is applied. These insights provide a practical strategy for achieving reliable operation in 2D and 3D ferroelectric NAND, highlighting the potential of hafnia-based ferroelectric materials to meet the evolving requirements of high-density and reliable NAND flash memory applications.

Evaporation Dynamics on a Lithium Niobate Surface.

Manipulating the water evaporation dynamics is a prerequisite in various modern-day applications like DNA stretching, rapid disease diagnostics, and inkjet printing. One method to affect the evaporation dynamics of droplets is to externally apply electric fields. However, surfaces that bear an intrinsic surface charge have not yet been investigated with respect to their evaporation behavior. In this study, we investigate water droplet evaporation on lithium niobate (LN), a ferroelectric material with a very high spontaneous polarization of 0.7 . Our results show that a droplet deposited on an LN surface evaporates in three stages: (i) constant contact radius (ii) mixed phase (iii) stick-slip, which is likely originating from the intrinsic surface charge. The influence of the polarization direction of the LN surface as well as the relative humidity of the environment on various evaporation characteristics were studied. The results suggest that the specific adsorption layers forming on charged surfaces, e. g. from the humidity of the surrounding air, play a key role in the evaporation process. Furthermore, compared to other materials with similar contact angles, LN demonstrated a significantly large evaporation rate. This property might also be attributed to the intrinsic surface charge and could be exploited in heat transfer applications.

High-entropy relaxor ferroelectric ceramics for ultrahigh energy storage

Dielectric ceramic capacitors with ultrahigh power densities are fundamental to modern electrical devices. Nonetheless, the poor energy density confined to the low breakdown strength is a long-standing bottleneck in developing desirable dielectric materials for practical applications. In this instance, we present a high-entropy tungsten bronze-type relaxor ferroelectric achieved through an equimolar-ratio element design, which realizes a giant recoverable energy density of 11.0 J·cm−3 and a high efficiency of 81.9%. Moreover, the atomic-scale microstructural study confirms that the excellent comprehensive energy storage performance is attributed to the increased atomic-scale compositional heterogeneity from high configuration entropy, which modulates the relaxor features as well as induces lattice distortion, resulting in reduced polarization hysteresis and enhanced breakdown endurance. This study provides evidence that developing high-entropy relaxor ferroelectric material via equimolar-ratio element design is an effective strategy for achieving ultrahigh energy storage characteristics. Our results also uncover the immense potential of tetragonal tungsten bronze-type materials for advanced energy storage applications.

Free-standing two-dimensional ferro-ionic memristor

Two-dimensional (2D) ferroelectric materials have emerged as significant platforms for multi-functional three-dimensional (3D) integrated electronic devices. Among 2D ferroelectric materials, ferro-ionic CuInP2S6 has the potential to achieve the versatile advances in neuromorphic computing systems due to its phase tunability and ferro-ionic characteristics. As CuInP2S6 exhibits a ferroelectric phase with insulating properties at room temperature, the external temperature and electrical field should be required to activate the ferro-ionic conduction. Nevertheless, such external conditions inevitably facilitate stochastic ionic conduction, which completely limits the practical applications of 2D ferro-ionic materials. Herein, free-standing 2D ferroelectric heterostructure is mechanically manipulated for nano-confined conductive filaments growth in free-standing 2D ferro-ionic memristor. The ultra-high mechanical bending is selectively facilitated at the free-standing area to spatially activate the ferro-ionic conduction, which allows the deterministic local positioning of Cu+ ion transport. According to the local flexoelectric engineering, 5.76×102-fold increased maximum current is observed within vertical shear strain 720 nN, which is theoretically supported by the 3D flexoelectric simulation. In conclusion, we envision that our universal free-standing platform can provide the extendable geometric solution for ultra-efficient self-powered system and reliable neuromorphic device.

Ferroelectric catalytic BaTiO3‐based composite insoles to promote healing of infected wounds: Analysis of antibacterial efficacy and angiogenesis

AbstractOur feet are often subjected to moist and warm environments, which can promote the growth of harmful bacteria and the development of severe infection in wounds located in the foot. As a result, there is a need for new and innovative strategies to safely sterilize feet, when shoes are worn, to prevent any potential foot‐related diseases. In this paper, we have produced a non‐destructive, biocompatible and convenient‐to‐use insole by embedding a BaTiO3 (BT) ferroelectric material into a conventional polydimethylsilane (PDMS) insole material to exploit a ferroelectric catalytic effect to promote the antibacterial and healing of infected wounds via the ferroelectric charges generated during walking. The formation of reactive oxygen species generated through a ferroelectric catalytic effect in the PDMS‐BT composite is shown to increase the oxidative stress on bacteria and decrease both the activity of bacteria and the rate of formation of bacterial biofilms. In addition, the ferroelectric field generated by the PDMS‐BT insole can enhance the level of transforming growth factor‐beta and CD31 by influencing the endogenous electric field of a wound, thereby promoting the proliferation, differentiation of fibroblasts and angiogenesis. This work therefore provides a new route for antimicrobial and tissue reconstruction by integrating a ferroelectric biomaterial into a shoe insole, with significant potential for health‐related applications.

Alignment assessment of anisotropic liquid crystals through an automated image processing algorithm

Liquid crystals (LCs) are recognised as an emerging type of responsive and functional materials that exhibit diverse technological applications. The spatial arrangement or alignment of LC molecules creates an optical anisotropy, which influences the propagation of light. This study presents an automated image processing algorithm designed to quantitatively assess LC alignment. The algorithm calculates the image structure tensor and computes a score ranging from 0 to 1 to represent the uniformity of LC alignment. The tool was verified on both artificially generated images of lines with pre-defined orientations and then tested on microscope images of LCs. For the latter, test samples of deformed helix ferroelectric LCs were constructed using three different alignment methods. Analysis of microscopic images of samples prepared utilising photoalignment, polymer rubbing, and oblique evaporation alignment techniques, determined average alignment scores (mean ± standard error of the mean) of 0.44 ± 0.03, 0.26 ± 0.1, and 0.17 ± 0.04, respectively, in comparison to commercially sourced control samples with a score of 0.64 ± 0.03 (n=5 each). This study paves the way for automated objective assessment of LC alignment, a critical aspect to ensure the optimal performance, reliability, and efficiency of various devices and sensors relying on LC technology.

Performance improvement of HfO2-based ferroelectric with 3D cylindrical capacitor stress optimization

To meet commercialization requirements, the distributions of materials in hafnium-based ferroelectric devices—including their phase and orientation—need to be controlled. This article presents a method for improving the ferroelectric phase ratio and orientation by adjusting the stress distribution of the annealing structure in a three-dimensional capacitor. In such a structure, stress can be applied in three directions: tangential, axial, and radial; there are, thus, more ways to regulate stress in three-dimensional structures than in two-dimensional structures. This work sought to clarify the role of the stress direction on the proportions and orientations of ferroelectric phases. The results of stress simulations show that a structure with an internal TiN electrode, but no filling provides greater axial and tangential stresses in the hafnium-oxide layer. In comparison with the case of the hole being filled with tungsten, the proportion of the O phase is increased by approximately 20%, and in experiments, the projection of the polarization direction onto the normal was found to be increased by 5%. Axial and tangential stresses are regarded to be beneficial for the formation of the O phase and for improving the orientation of the polarization direction. This work provides a theoretical basis and guidance for the three-dimensional integration of hafnium-based ferroelectric materials.

Probing the electric and thermoelectric response of ferroelectric 2H and 3R α-In2Se3

Two-dimensional van der Waals ferroelectric materials play an important role in a wide spectrum of semiconductor technologies and device applications. Integration of ferroelectrics into 2D-layered material-based devices is expected to offer intriguing working principles and add desired functionalities for next-generation electronics. Here, we investigate the electric and thermoelectric properties of thin layers of the 2H and 3R polymorphs of α-In2Se3 embedded in solid-state three-terminal devices. Charge transport measurements reveal a hysteretic behavior that can be ascribed to the effect of ferroelectric polarization at the metal electrode/2D semiconductor interfaces. The thermoelectric investigation of the same devices unveils a well-defined negative signal of the order of 100–200 μV/K in absolute value for the 2H polymorph, showing a slight modulation as a function of the gate voltage. An analogous but noisy thermoelectric voltage is measured for devices based on the 3R polymorph, where indeed a constant finite transversal offset in the 100 μV-few mV range is detected, which does not depend on the applied temperature gradient. We argue that these experimental observations are related to a strong residual in-plane ferroelectric polarization in the 3R α-In2Se3 polymorph thin layer. Our results show that the thermoelectric response is a fine probe of the ferroelectric character of 2D layered α-In2Se3.

High‐throughput combinatorial approach expedites the synthesis of a lead‐free relaxor ferroelectric system

AbstractDeveloping novel lead‐free ferroelectric materials is crucial for next‐generation microelectronic technologies that are energy efficient and environment friendly. However, materials discovery and property optimization are typically time‐consuming due to the limited throughput of traditional synthesis methods. In this work, we use a high‐throughput combinatorial synthesis approach to fabricate lead‐free ferroelectric superlattices and solid solutions of (Ba0.7Ca0.3)TiO3 (BCT) and Ba(Zr0.2Ti0.8)O3 (BZT) phases with continuous variation of composition and layer thickness. High‐resolution x‐ray diffraction (XRD) and analytical scanning transmission electron microscopy (STEM) demonstrate high film quality and well‐controlled compositional gradients. Ferroelectric and dielectric property measurements identify the “optimal property point” achieved at the composition of 48BZT–52BCT. Displacement vector maps reveal that ferroelectric domain sizes are tunable by varying {BCT–BZT}N superlattice geometry. This high‐throughput synthesis approach can be applied to many other material systems to expedite new materials discovery and properties optimization, allowing for the exploration of a large area of phase space within a single growth.image

Tunable entangled photon-pair generation in a liquid crystal

Liquid crystals, with their ability to self-assemble, strong response to an electric field and integrability into complex systems, are key materials in light-beam manipulation1. The recently discovered ferroelectric nematic liquid crystals2,3 also have considerable second-order optical nonlinearity, making them a potential material for nonlinear optics4,5. Their use as sources of quantum light could considerably extend the boundaries of photonic quantum technologies6. However, spontaneous parametric down-conversion, the basic source of entangled photons7, heralded single photons8 and squeezed light9, has so far not been observed in liquid crystals—or in any liquids or organic materials. Here we implement spontaneous parametric down-conversion in a ferroelectric nematic liquid crystal and demonstrate electric-field tunable broadband generation of entangled photons, with an efficiency comparable to that of the best nonlinear crystals. The emission rate and polarization state of photon pairs is markedly varied by applying a few volts or twisting the molecular orientation along the sample. A liquid-crystal source enables a special type of quasi-phase matching10, which is based on the molecular twist structure and is therefore reconfigurable for the desired spectral and polarization properties of photon pairs. Such sources promise to outperform standard nonlinear optical materials in terms of functionality, brightness and the tunability of the generated quantum state. The concepts developed here can be extended to complex topological structures, macroscopic devices and multi-pixel tunable quantum light sources.

Ferroelectric Material in Triboelectric Nanogenerator.

Ferroelectric materials, with their spontaneous electric polarization, are renewing research enthusiasm for their deployment in high-performance micro/nano energy harvesting devices such as triboelectric nanogenerators (TENGs). Here, the introduction of ferroelectric materials into the triboelectric interface not only significantly enhances the energy harvesting efficiency, but also drives TENGs into the era of intelligence and integration. The primary objective of the following paper is to tackle the newest innovations in TENGs based on ferroelectric materials. For this purpose, we begin with discussing the fundamental idea and then introduce the current progress with TENGs that are built on the base of ferroelectric materials. Various strategies, such as surface engineering, either in the micro or nano scale, are discussed, along with the environmental factors. Although our focus is on the enhancement of energy harvesting efficiency and output power density by utilizing ferroelectric materials, we also highlight their incorporation in self-powered electronics and sensing systems, where we analyze the most favorable and currently accessible options in attaining device intelligence and multifunctionality. Finally, we present a detailed outlook on TENGs that are based on ferroelectric materials.

Free‐standing 0.9Na0.5Bi0.5TiO3‐0.1Sr0.7Bi0.2TiO3 thick films produced by water‐based tape‐casting method

Abstract(1‐x)Na0.5Bi0.5TiO3‐xSr1‐1.5yBiyTiO3 solid solutions attract increased interest as lead‐free ferroelectrics perspective for sensors, actuators, and energy storage applications. However, thick films of this composition are of great demand, as they could serve as a good compromise between the bulk ceramics and thin films—due to the advantage in realization of miniaturized devices without reducing the power and sensitivity of target devices, as in the case of thin films, and ability to accommodate application of much higher electric fields compared to bulk ceramics. In the present research, for the first time, we have produced free‐standing 0.9Na0.5Bi0.5TiO3‐0.1Sr0.7Bi0.2TiO3 thick films by water‐based tape‐casting method, using just two organic chemicals, which is an eco‐friendly production approach having only several successful attempts in the case of ferroelectric materials before. We conducted a detailed study focusing on development of microstructure at various sintering temperatures and consequences of evaporation of Bi during the production. Our findings show how the choice of the sintering temperature can help in improvement of density of the thick films, reaching 98.9%, and changing the grain size. It is demonstrated that a secondary phase appears predominantly on the free surface of the films. We propose a method for effective minimization of its formation—by the choice of appropriate embedding powder media during the sintering.

Nonvolatile ferroelectric control of both magnetic anisotropy and half-metallicity in multiferroic heterostructures GdI2/Al2Te3

Nonvolatile all-electric spin manipulation is optimal for low-power and compact spintronic devices. Herein, using first-principles density functional theory, we propose a bilayer van der Waals (vdW) multiferroic heterostructure (HS) GdI2/Al2Te3 constructed of ferromagnetic electride GdI2 and ferroelectric (FE) semiconductor Al2Te3 to possess robust magnetoelectric coupling near room temperature. By reversing the electrical polarization states in Al2Te3, the magnetoelectric coupling not only allows the reversible switch of GdI2 from semiconductor to half-metal but also promotes the reversible transition of magnetocrystalline anisotropy from in-plane to out-of-plane. More importantly, the high Curie temperature (TC) of GdI2 and the unspoiled semiconducting nature of Al2Te3 in the HS predict the practical feasibility of this spin manipulation. Additionally, GdI2 exhibits substantial valley polarization when its magnetization direction changes to out-of-plane. These findings pave the way for achieving robust and efficient spin manipulation through all-electric control and also provide implications for multiferroic memory devices with highly efficient data reading and writing based on the HS.

Ferroelectric Domain Intrinsic Radiation Resistance of Lithium Niobate Ferroelectric Single−Crystal Film

The study of the properties of ferroelectric materials against irradiation has a long history. However, anti−irradiation research on the ferroelectric domain has not been carried out. In this paper, the irradiation of switched domain structure is innovatively proposed. The switched domain of 700 nm lithium niobate (LiNbO3, LN) thin film remains stable after gamma irradiation from 1 krad to 10 Mrad, which was prepared by piezoresponse force microscopy (PFM). In addition, the changing law of domain wall resistivity is explored through different sample voltages, and it is verified that the irradiated domain wall conductivity is still larger than the domain. This domain wall current (DWC) property can be applied to storage, logic, sensing, and other devices. Based on these, a ferroelectric domain irradiation resistance model is established, which explains the reason at an atomic level. The results open a possibility for exploiting ferroelectric materials as the foundation in the application of space and nuclear fields.

Realization of 2D multiferroic with strong magnetoelectric coupling by intercalation: a first-principles high-throughput prediction

The discovery of novel two-dimensional (2D) multiferroic materials is attractive due to their potential for the realization of information storage and logic devices. Although many approaches have been explored to simultaneously introduce ferromagnetic (FM) and ferroelectric (FE) orders into a 2D material, the resulting systems are often plagued by weak magnetoelectric (ME) coupling or limited room-temperature stability. Here, we present a superlattice strategy to construct non-centrosymmetric AM2X4 multiferroic monolayers, i.e., intercalating transition metal ions (A) into the tetragonal-like vacancies of transition metal dichalcogenide bilayers (MX2). Starting from 960 intercalated AM2X4 compounds, our high-throughput calculations have identified 21 multiferroics with robust magnetic order, large FE polarization, low transition barrier, high FE/FM transition temperature, and strong ME coupling. According to the origin of magnetism, we have classified them into twelve type-a, seven type-b, and two type-c multiferroics, which exhibit different ME coupling behavior. During the switching of polarization, the reversal of skyrmions chirality, the transition of the magnetic ground state from FM to antiferromagnetic, and the changes in spin-polarized electron distribution were observed in type-a, type-b, and type-c 2D multiferroic materials, respectively. These results substantially expand the family of 2D ferroic materials and pave an avenue for designing and implementing nonvolatile logic and memory devices.