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Research and development of antimicrobial technology are critical for safeguarding human life and health. Ferroelectric materials, materials with spontaneous polarization, can adjust their direction of spontaneous polarization in response to an external electric field. When subjected to this applied field, the ordered arrangement of electric dipoles within the ferroelectric material becomes disrupted. This disruption causes the bound charges on the surface to redistribute, and the released positive and negative charges react with the oxygen and water in the surrounding medium. This reaction forms active substances with powerful oxidant properties (such as OH, \begin{document}$\cdot {\text{O}}_2^ - $\end{document}). These highly oxidizing active substances can destroy the cell wall of bacterial cells, enter the cell to damage DNA, leak proteins, and render them inactive, thereby inactivating the bacteria. Ferroelectric materials are not only excellent for their piezoelectric, pyroelectric, and photovoltaic properties but also possess the unique ability to convert mechanical, thermal, and optical energy in nature into electrical and chemical energy. Coupled with their fast response speed (10−6 s) and high electromechanical coupling coefficients, the development of ferroelectric materials in conjunction with catalytic technology has emerged as a new sterilization technique. However, achieving high antimicrobial efficiencies is closely related to carrier utilization in the catalytic process and the catalyst activity. This holds true regardless of whether mechanical, thermal, or optical energy is used as the driving source to stimulate ferroelectric materials for catalytic antimicrobials. When using ferroelectric materials as catalysts, the spontaneous polarization properties of these materials can be harnessed to reduce the electron–hole pair combination rate through the internal electric field. This action increases the yield of active substances, thereby improving the efficiency of catalytic antibacterial agents. In addition, high-performance ferroelectric materials have a high internal electric field potential after polarization treatment, which can accelerate carrier separation during the catalytic process. As a result, ferroelectric materials have great potential for catalytic antimicrobial applications under environmentally friendly and safe conditions. In this review, we begin with an introduction to the ferroelectric properties of these materials and their relationship with piezoelectric and pyroelectric materials. We then summarize and organize previous work reported on the catalytic antimicrobial properties of ferroelectric materials. This summary includes discussions on photocatalytic, piezocatalytic, and pyrocatalytic antimicrobial properties and descriptions of the antimicrobial mechanisms of ferroelectric materials in different types of catalytic processes. The aim is to provide a reference for future research into the catalytic antimicrobial properties of ferroelectric materials.

Abstract The discovery of nanoscale ferroelectricity in hafnia (HfO2) has paved the way for next generation high‐density, non‐volatile devices. Although the surface conditions of nanoscale HfO2 present one of the fundamental mechanism origins, the impact of external environment on HfO2 ferroelectricity remains unknown. In this study, the deleterious effect of ambient moisture is examined on the stability of ferroelectricity using Hf0.5Zr0.5O2 (HZO) films as a model system. It is found that the development of an intrinsic electric field due to the adsorption of atmospheric water molecules onto the film's surface significantly impairs the properties of domain retention and polarization stability. Nonetheless, vacuum heating efficiently counteracts the adverse effects of water adsorption, which restores the symmetric electrical characteristics and polarization stability. This work furnishes a novel perspective on previous extensive studies, demonstrating significant impact of surface water on HfO2‐based ferroelectrics, and establishes the design paradigm for the future evolution of HfO2‐based multifunctional electronic devices.

Abstract The critical challenges of the energy crisis and environmental degradation promote innovative approaches for energy conversion. Semiconductor‐based photocatalytic technology, which transforms solar energy into chemical energy, emerges as a promising solution. However, the practical application of this technology faces several challenges, such as the rapid recombination of photogenerated electrons and holes, significantly limiting photocatalytic efficiency. In this review, we provide a detailed discussion, an insightful perspective, and a critical evaluation of recent advances, challenges, and opportunities in the field of photocatalysis using polar materials. We present a comprehensive examination of the photocatalytic mechanisms, activity, and diverse applications of photocatalysts based on polar materials. We also briefly discuss the engineering design of polar photocatalysis in experiments and its scalability in the industry. This review outlines future trends and potential breakthroughs in the photocatalytic field using polar materials, projecting their transformative impact on environmental chemistry and energy engineering.

Abstract The silicon (Si) anode is prone to forming a high electric field gradient and concentration gradient on the electrode surface under high‐rate conditions, which may destroy the surface structure and decrease cycling stability. In this study, a ferroelectric (BaTiO3) interlayer and field polarization treatment are introduced to set up a built‐in field, which optimizes the transport mechanisms of Li+ in solid and liquid phases and thus enhances the rate performance and cycling stability of Si anodes. Also, a fast discharging and slow charging phenomenon is observed in a half‐cell with a high reversible capacity of 1500.8 mAh g−1 when controlling the polarization direction of the interlayer, which means a fast charging and slow discharging property in a full battery and thus is valuable for potential applications in commercial batteries. Simulation results demonstrated that the built‐in field plays a key role in regulating the Li+ concentration distribution in the electrolyte and the Li+ diffusion behavior inside particles, leading to more uniform Li+ diffusion from local high‐concentration sites to surrounding regions. The assembled lithium‐ion battery with a BaTiO3 interlayer exhibited superior electrochemical performance and long‐term cycling life (915.6 mAh g−1 after 300 cycles at a high current density of 4.2 A g−1). The significance of this research lies in exploring a new approach to improve the performance of lithium‐ion batteries and providing new ideas and pathways for addressing the challenges faced by Si‐based anodes.

Ferromagnetic materials show magnetic structures with domains and walls. Thanks to decades of research regarding the origin and behaviour of magnetic domains, we now possess a general foundation which has been verified experimentally in single crystals and powders. The governing equations at the microscopic scale were built in the 1960 s when Brown published calculations of the magnetic moments distribution inside domain walls. This micromagnetic theory uses the so called LLG ‘Landau-Lifshitz-Gilbert’ equation and can include the damping effects. The LLG equation requires a coupling to the field derived from energy contributions: exchange, anisotropy, magnetostriction, stray-field … and the anti-eddy field. At the macroscopic scale, such behaviours are lumped in a homogenized magnetization law for the electromagnetic field equations inside larger polycrystals. Therefore, the inhomogeneous magnetic material nature is always ignored. The Tensor Magnetic Phase Theory (TMPT) describes the magnetic structure and the magnetization thanks to a tensor variable at a mesoscopic scale. The material structuring is then explained thanks to an energy balance which will be discussed.This paper presents the results of investigations on entangled relationships between the micromagnetic theory, the electromagnetic theory and what is called the Tensor Magnetic Phase Theory (TMPT), which statistically describes the magnetic structures of soft ferromagnetic materials. It examines a connection between the TMPT and the LLG by deriving the main energy terms. Then, the TMPT must stay compatible and coupled to the Maxwell equations at low frequencies with volume and surface connections. Additionally, this paper investigates the way to derive the domains structuring and magnetization laws through the Lagrange principle and the corresponding conservation laws with invariants linked to the Nœther theorem. Finally, the TMPT must be discussed while checking its coherence and formulation when changing the reference frame.

We propose a one-millimeter-scale linear ultrasonic motor and its feedback control system with a Hall sensor. The size of the stator measures 1.6 mm in height, 1.6 mm in width, and 0.3 mm in thickness, and there is a hole with a diameter of 0.6 mm at the center, which is one of the smallest linear motors reported to date. A similar-sized Hall sensor detects the displacement of the slider inserted into the stator hole for position control. In this paper, we build the prototype motor and evaluate its basic performance measures, such as electrical impedance characteristics and mechanical output characteristics. The optimization of the preload between the stator and slider has improved the thrust force of the motor to the maximum value of 7.6 mN, resulting in a higher force-to-volume ratio than existing miniature linear motors. We combine the motor with a Hall sensor having a similar scale to the motor and construct a feedback system with a burst-wave control. The feedback control succeeded in removing the steady-state error that remains in the open-loop system.

Abstract We have witnessed the flourish of bioelectronics, brain–computer interface, and brain science programme in recent decades. In this review, the up‐to‐date advances of dielectric, piezoelectric, and ferroelectric nanomaterials in the biomedical applications are summarised. Biomolecular detection methods have been developed, including dielectric‐gated field‐effect transistor, dielectrophoresis, non‐linear dielectric response, and optical tweezer. Endogenous bioelectricity is a crucial in cell proliferation, migration, differentiation, intracellular communication, neuronal activity, tissue growth. Piezoelectric and ferroelectric materials can be utilised as energy transducer to monitor physiological signal, such as blood pressure or respiration, and directly stimulate cell differentiation, neuronal regeneration, tissue repairment etc. They can also catalyse the electrochemical reaction of organisms through piezoelectricity. The intrinsic relevance between neuronal and ferroelectric polarisation signals inspires the application of the ferroelectrics in the modern intelligent bioelectronics like the artificial retina.

Abstract Piezoelectrets, also called ferroelectrets, can exhibit promising piezoelectric properties and have plenty of applications in wearable health monitoring. Usually, the cellular structure of piezoelectrets is of outstanding importance for their sensing properties, and structure improvement and optimisation would be a possible way to realise high‐performance piezoelectrets. The authors proposed a compound‐structured piezoelectret system, where a layer of polypropylene foam was sandwiched between two layers of solid polytetrafluoroethylene, resulting in a combination of a foam‐structured and a layer‐structured piezoelectrets. The compound systems are thin and flexible, they can exhibit stable electrical outputs, they have relatively broader linear working range under pressure, and promising mechanical sustainability for multiple testing. The results reveal that the compound system can be considered as a simple addition of both components, and each component contributes linearly and independently to the whole system. The application potential of this proposed compound system has been demonstrated by sleep monitoring together with carotid and radial pulse recordings, where many useful physiological information including breath, heartbeat, and pulse details can be extracted from the signals acquired by the compound system. A type of flexible sensor system that is very competitive for future portable and wearable applications may be provided.

Copolymers based on vinylidene fluoride are potential materials for ferroelectric memory elements. The trend in studies showing that a decrease in the degree of crystallinity can lead to an unexpected increase in the electric breakdown field is noted. An analysis of the literature data reveals that in fluorine-containing ferroelectric polymers, when using a bipolar triangular field, the hysteresis loop has an unclosed shape, with each subsequent loop being accompanied by a decrease in the dielectric response. In this work, the effect of the structure of self-polarized films of copolymers of vinylidene fluoride with tetrafluoroethylene and hexafluoropropylene on breakdown processes was studied. The structure of the polymer films was monitored using infrared spectroscopy (IR) and X-ray diffraction. Kelvin probe force microscopy (KPFM) was applied to characterize the local electrical properties of the polymers. For the films of the first copolymer, which crystallize in the polar β-phase, asymmetry in the dielectric response was observed at fields greater than the coercive field. For the films of the copolymers of vinylidene fluoride with hexafluoropropylene, which crystallize predominantly in the nonpolar α-phase, polarization switching processes have also been observed, but at lower electric fields. The noted phenomena will help to identify the influence of the structure of ferroelectric polymers on their electrical properties.

The ever-increasing demand for high-speed data transmission in telecommunications and data centers has driven the development of advanced on-chip integrated electro-optic modulators. Silicon modulators, constrained by the relatively weak carrier dispersion effect, face challenges in meeting the stringent requirements of next-generation photonic integrated circuits. Consequently, there has been a growing interest in Pockels effect-based electro-optic modulators, leveraging ferroelectric materials like LiNbO3, BaTiO3, PZT, and LaTiO3. Attributed to the large first-order electro-optic coefficient, researchers have delved into developing modulators with expansive bandwidth, low power consumption, compact size, and linear response. This paper reviews the working principles, fabrication techniques, integration schemes, and recent highlights in Pockels effect-based modulators.

Abstract High‐performance ferroelectric materials are widely used in various electronic devices owing to the function of mutual conversion among different energies, which mainly relates to their special structure gene of polarization configuration. Recent researches show that the high‐entropy strategy has emerged as an effective and flexible approach for boosting physical properties in high‐entropy ferroelectrics via the delicate design of local polarization configurations and other intrinsic effects caused by entropy increment, such as entropy stabilization, lattice disorder, inhibition of grain coarsening, improved mechanical properties, cocktail effect, and so on. In this review, the recent research progress about high‐entropy ferroelectrics has been summarized, especially for the directional design of novel local polarization configurations according to the characteristics of different electrical properties such as high piezoelectricity, high‐efficiency energy storage, and large electrostriction, providing a guidance for designing and exploring more novel local polarization configurations in high‐entropy ferroelectrics for generating higher performance.

Linear piezoelectric materials offer new opportunities for next-generation multifunctional micro/nano systems on chip aside from ferroelectrics. However, the advantage of quantitative pressure sensing of linear piezoelectric materials over ferroelectrics has not been demonstrated, while the thermal stability of linear piezoelectric zinc oxide (ZnO) is yet to be evaluated. In this work, pressure sensors based on linear piezoelectric undoped ZnO and ferroelectric vanadium doped ZnO (V-ZnO) films are studied side by side. Both films possess similar fiber textures oriented along the polar ZnO [002] direction, yet each of the V-ZnO grains consists of strip-like domains observed by SEM. Applying triangular-wave pressures, the linear piezoelectric ZnO sensor generates triangular-wave voltage signals that are one-to-one linearly correlated to the applied pressure, showing decisive advantages for quantitative pressure sensing compared to the ‘sail-like’ voltage signals of the ferroelectric V-ZnO sensor that is many-to-one correlated to the applied pressure. Superior thermal stability is demonstrated in the linear piezoelectric ZnO sensor showing stable pressure sensing properties up to 450 °C compared to the degraded sensing properties of the ferroelectric V-ZnO sensor at 150 °C. The thermally stable piezoelectric sensors for quantitative pressure sensing based on linear piezoelectric ZnO films serve as candidates for high-performance multifunctional micro/nano systems.

Abstract Recently, self‐driven soft robotics based on biomimetics, capable of mimicking biological motion, has attracted attention. Soft actuators using intrinsically soft organic materials are expected to be applied to haptic devices, artificial muscles, and micropumps. Ferroelectric polymers can aid in the realization of such soft actuators. However, actuators using such materials encounter problems in terms of the response frequency to an applied voltage. In this study, a soft actuator is fabricated by a printing process using a unique composite material comprising P(VDF‐TrFE), nano‐carbon material (single‐walled carbon nanotubes (SWCNT) and graphene oxide (GO)), and conductive polymer. To characterize the actuator using a minimum substrate thickness of 25 µm, hysteresis curves in the ferroelectric properties and driving characteristics according to the applied frequency are clarified. In addition, the mechanical life of the actuator under continuous voltage sweep is clarified considering it as a mechanical property. Subsequently, a simple haptics system is constructed using the fabricated actuators, and a human‐sensitive actuator demonstration system is constructed wherein the phase of the sweep frequency is variable.

Bismuth ferrite-barium titanate (BF-BT) solid solutions are lead-free ferroelectrics that show great promise as the basis for high temperature piezoelectric transducers. This article investigates the dielectric properties of such materials using broadband dielectric spectroscopy. The study focuses on the re-entrant relaxor ferroelectric behaviour of Nb-doped BF-BT ceramics, exploring a wide frequency range from approximately 20 Hz to 30 GHz and temperature from 200 to 500 K. The results reveal the presence of thermally induced transitions between ordered and disordered states. Quantitative analysis of the dielectric dispersion is accomplished using the Cole-Cole model, modified to account for the contribution from conduction losses at low frequencies/high temperatures. This analysis revealed that the freezing temperature of the polar nanoregions is around 158 K, with an activation energy of 0.194 eV. The findings contribute to understanding the dielectric relaxation mechanisms and thermal evolution of functional properties in BiFeO _3 -BaTiO _3 ceramics.

At present, the research on ferroelectric photovoltaic materials mainly focuses on photoelectric detection. In the context of the rapid development of the Internet of Things (IoT), it is particularly important to use smaller thin-film devices as sensors. In this work, an indium tin oxide/bismuth ferrite (BFO)/lanthanum nickelate device has been fabricated on an F-doped tin oxide glass substrate using the sol–gel method. The sensor can continuously output photoelectric signals with little environmental impact. Compared to other types of sensors, this photoelectric sensor has an ultra-low response time of 1.25 ms and ultra-high sensitivity. Furthermore, a material recognition system based on a BFO sensor is developed. It can effectively identify eight kinds of materials that are difficult for human eyes to distinguish. This provides new ideas and methods for developing the IoT in material identification.

Relaxor ferroelectrics play a vital role as functional components in electromechanical devices. The observation of micro-scale domain structure evolution under electric bias in relaxor ferroelectrics has posed challenges due to their complex domain morphology characterized by small-sized domains. The present study aims to investigate the dielectric diffusion–relaxation characteristics, domain structure, and domain switching evolution under electric bias in high-performance single crystals of Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-33PbTiO3. The findings reveal the presence of strip-like domain patterns that interlock irregular small-sized nanodomains in PIN-PMN-33PT single crystals. Furthermore, the sample undergoes three distinct stages under electric bias, including the nucleation of new domains, the gradual forward expansion of domains, and the lateral expansion of domains. These observations provide valuable insights for understanding and exploring domain engineering techniques in relaxor ferroelectrics.

The paper reports results on the complex study on ferroelectric ceramics that represent solid solutions containing components with a perovskite-type or columbite-type structure. Solid solutions of a three-component (1[Formula: see text])[Formula: see text][Formula: see text]CdNb2O6 system are manufactured at [Formula: see text] = 0.05–0.20 and [Formula: see text] = 0.10. Domain structures in ceramic grains are studied. The consistency between experimental and calculated results is examined for coexisting phases split into non-180[Formula: see text] domains (mechanical twins) in the solid solution with [Formula: see text] = 0.15. A correlation between the internal structure (crystal, domain, granular, and defect) and fundamental electromechanical and polarization properties is stated for the studied three-component solid solutions.

Abstract 2D ferroelectrics provide great promise for future electronics owing to their unique properties at 2D limit. Although simple perovskite oxides (such as BaTiO3 and PbTiO3) are an important target for 2D ferroelectrics, controlled synthesis of 2D nanosheets still remains a challenge. Here, this issue is addressed by using a new chemical protocol; unilamellar Ti0.87O2 nanosheets can serve as templates, guiding the solvothermal synthesis of 2D BaTiO3 nanosheets with a molecularly thin thickness (< 3 nm). Raman spectroscopy, second‐harmonic generation, and transmission electron microscopy characterizations suggest the formation of tetragonal ferroelectric BaTiO3 nanosheets. Based on piezoresponse force microscopy, BaTiO3 nanosheets exhibit a clear ferroelectric response with a high Curie temperature (≈100 °C) even down to 1.8 nm thickness. This study provides new opportunities to investigate perovskite ferroelectrics with the critical thickness.

The values of the surface potentials of two sides of films of polyvinylidene fluoride, and its copolymers with tetrafluoroethylene and hexafluoropropylene, were measured by the Kelvin probe method. The microstructures of the chains in the surfaces on these sides were evaluated by ATR IR spectroscopy. It was found that the observed surface potentials differed in the studied films. Simultaneously, it was observed from the IR spectroscopy data that the microstructures of the chains on both sides of the films also differed. It is concluded that the formation of the surface potential in (self-polarized) ferroelectric polymers is controlled by the microstructure of the surface layer. The reasons for the formation of a different microstructure on both sides of the films are suggested on the basis of the general regularities of structure formation in flexible-chain crystallizing polymers.

Abstract Investigation and analysis of a ferroelectric material–based dopingless nanotube tunnel field‐effect transistor are conducted using a lead zirconate titanate (PZT) gate stack to induce negative capacitance in the device. Landau–Khalatnikov equations are used in deriving the parameter values of the ferroelectric material to ensure accurate results. The nanotube structure of the tunnel field‐effect transistor allows for better electrostatic control owing to its gate‐all‐around structure. Incorporation of negative capacitance further reduces the voltage supply requirement and power consumption of the structure while simultaneously improving switching. In addition, the device is studied for varying thicknesses of the dielectric PZT material. The threshold voltage of the device under study was calculated as 0.281 V, and the average subthreshold slope of the device was reduced to 18.271 mV/decade, far below the thermionic limit of 60 mV/decade.

Gate-all-around (GAA) field effect transistors (FETs) have appeared as one of the potential candidates for the electrostatic integrity required to reduce MOSFETs to minimum channel lengths. Meanwhile, the negative capacitance effect of ferroelectrics is known as a remarkable quality enhancer for MOSFETs in terms of reducing sub-threshold slope (SS), supply voltage, and power consumption by utilizing the gate voltage amplification phenomenon. In this work, combining these two phenomena we numerically design a cylindrical GAA NCFET where promising two-dimensional WSe2 is used as a channel material. We have suggested a high-K dielectric consisting of a tri-layer HfO2/TiO2/HfO2 and lead zirconate titanate (PZT) as a ferroelectric layer in the gate stacking. The extremely high $I_{on}/I_{off}$ ratio on the order of 1012 (six order higher than conventional FET), and the high on-state current of $119~\mu \text{A}$ are the most remarkable findings of this device which exceeds all the earlier results. The integration of the NC effect utilizing a 20 nm PZT offers lowest $SS$ of 18.9 mV/dec. Moreover, a large transconductance ( $g_{m}$ ) of $117~\mu \text{S}$ and a higher current cut-off frequency ( $f_{T}$ ) of 335 GHz were reported from the output characteristics. These outcomes allude that the suggested device structure may create a new path for electronic devices; therefore, it can be used for high speed operation with low power consumption.

Information storage relies on the fast and reversible memory devices, which can read and write data easily with low energy input. In addition, in order to pursue high data storage density and miniaturizing device size, low-dimensional materials with large area to volume ratio would be preferable. Up to date, there are already a lot of explorations of two-dimensional functional material based devices with interesting phase transitions. According to Ginzburg-Landau theory, phase transition occurs when order parameter changes, under external stimuli such as temperature, electric field, or external stress. Other than these, novel phase transition mechanisms under low-frequency light irradiation has been recently proposed. The light frequency is below the corresponding energy bandgap of the semiconductors, which intuitively has very small scattering cross sections. However, according to thermodynamic theory, there could have light-matter interactions. Geometric structure can be changed and manipulated under light illumination. If ion displacements are strong enough, phase transition could occur. This optically driven phase transition approach requires no direct contacts with the sample, so that this procedure is easily controlled. In this mini-review, we briefly summarize the basic theory, computational predictions and some very recent experiments on low-frequency light induced phase transition in various systems.

Crystals of PbTiO3 and 0.9PbTiO3-0.1(Na0.5Bi0.5)TiO3 were obtained by the flux growth method whereas crystals of (Na0.5Bi0.5)TiO3 were growth by the Czochralski method. Raman spectroscopy and polarized light microscopy were performed at room temperature. The Raman spectra of 0.9PbTiO3-0.1(Na0.5Bi0.5)TiO3 shown significant changes comparing to the base materials PbTiO3 and (Na0.5Bi0.5)TiO3. A domain structure was investigated by use polarized light microscopy. Dielectric permittivity measurements were carried out in the temperature range from 20°C to 550°C and a frequency from 1 kHz to 1 MHz. These showed higher dielectric permittivity for the crystals 0.9PbTiO3-0.1(Na0.5Bi0.5)TiO3 than the source materials PbTiO3 and (Na0.5Bi0.5)TiO3. The high value of dielectric constant makes it possible to applied 0.9PbTiO3-0.1(Na0.5Bi0.5)TiO3 as efficient dielectric medium in a capacitors. The small size of the domain structure with the easy possibility of switching by application of an external electric field, give opportunities to apply these materials to FRAM memory applications. Moreover, the high sensitivity of these materials to the surrounding gases e.g. ammonia, chlorine, hydrogen, etc., allows the construction of sensor devices.

The flexoelectric effect, which exists in all dielectrics, is an electromechanical effect that arises due to the coupling of strain gradients (or electric field gradients) with electric polarization (or mechanical stress). Numerous experimental studies have demonstrated that ferroelectric materials possess a larger flexoelectric coefficient than other dielectric materials; thus, the flexoelectric response becomes significant. In this review, we will first summarize the measurement methods and magnitudes of the flexoelectric coefficients of ferroelectric materials. Theoretical studies of the flexoelectric coefficients of ferroelectric materials will be addressed in this review. The scaling effect, where the flexoelectric effect dramatically increases when reducing the material dimension, will also be discussed. Because of their large electromechanical response and scaling effect, ferroelectric materials offer vast potential for the application of the flexoelectric effect in various physical phenomena, including sensors, actuators, and transducers. Finally, this review will briefly discuss some perspectives on the flexoelectric effect and address some pressing questions that need to be considered to further develop this phenomenon.

In recent years, hafnia-based ferroelectrics have attracted enormous attention due to their capability of maintaining ferroelectricity below 10 nm thickness and excellent compatibility with microelectronics flow lines. However, the physical origin of their ferroelectricity is still not fully clear, although it is commonly attributed to a polar Pca 2 _1 orthorhombic phase. The high-temperature paraelectric phases (the tetragonal phase or the cubic phase) do not possess a soft mode at the Brillouin zone center, thus the ferroelectric distortion has to be explained in terms of trilinear coupling among three phonon modes in the tetragonal phase. It is necessary to explore new materials with possible ferroelectricity due to the polar Pca 2 _1 phase, which in turn should be very helpful in evaluating the microscopic theory for ferroelectric hafnia. In this work, based on the idea of the Materials Genome Engineering, a series of hafnia-like ferroelectrics have been found, exemplified by LaSeCl, LaSeBr, LuOF and YOF, which possess adequate spontaneous polarization values and also relatively favorable free energies for the polar phase. Their common features and individual differences are discussed in detail. In particular, a promising potential ferroelectric material, Pca 2 _1 phase LuOF, is predicted and recommended for further experimental synthesis and investigation.

In this work, explicitly pyro-catalytic performance is observed in sol-gel-synthesized ferroelectric Bi0.5Na0.5TiO3 lead-free nanomaterials, and its application for dye wastewater purification is also actualized under temperature fluctuations varying from 23 °C to 63 °C. The decomposition ratios of the pyro-catalytic Bi0.5Na0.5TiO3 nanomaterials on Rhodamine B, methyl blue and methyl orange can reach 96.75%, 98.35% and 19.97%, respectively. In the pyro-catalytic process, the probed active species such as hydroxyl radicals, superoxide radicals and holes play an extremely important role in decomposing dye molecules. The ferroelectric Bi0.5Na0.5TiO3 lead-free nanomaterials will have an excellent prospect for dye wastewater purification due to its explicit pyro-catalysis.

Electrocaloric effect (ECE) of ferroelectrics has attracted considerable interest due to its potential application in environmentally friendly solid-state refrigeration. The discovery of giant ECE in ferroelectric thin films has greatly renewed the research activities and significantly stimulated experimental and theoretical investigations. In this review, the recent progress on the theoretical modeling of ECE in ferroelectric and antiferroelectric materials are introduced, which mainly focuses on the phase field modeling and first-principles based effective Hamiltonian method. We firstly provide the theoretical foundation and technique details for each method. Then a comprehensive review on the progress in the application of two methods and the strategies to tune the ECE are presented. Finally, we outline the practical procedure on the development of multi-scale computational method without experiemtal parameters for the screening of optimized electrocaloric materials.

Abstract Investigations focusing on electrical energy storage capacitors especially the dielectric ceramic capacitors for high energy storage density are attracting more and more attention in the recent years. Ceramic capacitors possess a faster charge‐discharge rate and improved mechanical and thermal properties compared with other energy storage devices such as batteries. The challenge is to obtain ceramic capacitors with outstanding mechanical, thermal and storage properties over large temperature and frequencies ranges. ABO3 as a type of perovskites showed a strong piezoelectric, dielectric, pyroelectric, and electro‐optic properties useful as energy storage and environmental devices. CaCu3Ti4O12 (CCTO) perovskite with cubic lattice (Im3 symmetry) was discovered to have a colossal dielectric constant (104) that is stable over a wide range of frequencies (10 Hz–1 MHz) and temperature independence (100–300 K). The origin of this high dielectric constant is not fully established, specially because it is the same for single crystal and thin films. In this review, the history of CCTO will be introduced. The synthesis and the sintering approaches, the dopant elements used as well as the applications of CCTO will be reported. In addition to dielectrical properties useful to energy storage devices; CCTO could serve as photocatalytic materials with a very good performance in visible light.

The 1980s saw the development of ferroelectric chiral smectic C (SmC*) liquid crystals (FLCs) with a clear focus on their application in fast electro-optic devices. However, as the only known fluid ferroelectric materials, they also have potential in other applications, one of which is in heat-exchange devices based on the electrocaloric effect. In particular, ferroelectric liquid crystals can be both the electrocaloric material and the heat exchanging fluid in an electrocaloric device, significantly simplifying some of the design constraints associated with solid dielectrics. In this paper, we consider the electrocaloric potential of three SmC* ferroelectric liquid crystal systems, two of which are pure materials that exhibit ferroelectric, antiferroelectric, and intermediate phases and one that was developed as a room-temperature SmC* material for electro-optic applications. We report the field-induced temperature changes of these selected materials, measured indirectly using the Maxwell method. The maximum induced temperature change determined, 0.37 K, is currently record-breaking for an FLC and is sufficiently large to make these materials interesting candidates for the development for electrocaloric applications. Using the electrocaloric temperature change normalised as a function of electric field strength, as a function of merit, the performances of FLCs are compared with ferroelectric ceramics and polymers.

Abstract Ferroelectric materials (FEMs), possessing piezoelectric, pyroelectric, inverse piezoelectric, nonlinear optic, ferroelectric‐photovoltaic, and many other properties, are attracting increasing attention in the field of biomedicine in recent years. Because of their versatile ability of interacting with force, heat, electricity, and light to generate electrical, mechanical, and optical signals, FEMs are demonstrating their unique advantages for biosensing, acoustics tweezer, bioimaging, therapeutics, tissue engineering, as well as stimulating biological functions. This review summarizes the current‐available FEMs and their state‐of‐the‐art fabrication techniques, as well as provides an overview of FEMs‐based applications in the field of biomedicine. Challenges and prospects for future development of FEMs for biomedical applications are also outlined.

Abstract Ferroelectric memories with ultralow‐power‐consumption are attracting a great deal of interest with the ever‐increasing demand for information storage in wearable electronics. However, sufficient scalability, semiconducting compatibility, and robust flexibility of the ferroelectric memories remain great challenges, e.g., owing to Pb‐containing materials, oxide electrode, and limited thermal stability. Here, high‐performance flexible nonvolatile memories based on ferroelectric Hf0.5Zr0.5O2 (HZO) via quasi‐van der Waals heteroepitaxy are reported. The flexible ferroelectric HZO exhibits not only high remanent polarization up to 32.6 µC cm−2 without a wake‐up effect during cycling, but also remarkably robust mechanical properties, degradation‐free retention, and endurance performance under a series of bent deformations and cycling tests. Intriguingly, using HZO as a gate, flexible ferroelectric thin‐film transistors with a low operating voltage of ±3 V, high on/off ratio of 6.5 × 105, and a small subthreshold slope of about 100 mV dec−1, which outperform reported flexible ferroelectric transistors, are demonstrated. The results make ferroelectric HZO a promising candidate for the next‐generation of wearable, low‐power, and nonvolatile memories with manufacturability and scalability.

Pb(In1∕2Nb1∕2)O3-Pb(Mg1∕3Nb2∕3)O3-PbTiO3 (PIN-PMN-PT) relaxor ferroelectric crystals in 5″ diameter by 5″ length were grown by the Bridgman (BR) method for the first time. Typical issues in the crystal growth concerning large volume of the melt, high density of the crystal and corrosion of the melt on the wall of Pt crucible are discussed.

In this paper, a brief review of the current state of research on ferroelectric, ferromagnetic, and multiferroic materials in the microwave range is given, and the main research methods are described. The main areas of application of functional materials in radio electronics are outlined. Multicomponent ferroelectric media based on ferroelectric (PbTiO3), antiferroelectric (PbZrO3), and relaxors (PbMg1/3Nb2/3O3) are considered promising radio-absorbing materials. A method for comparing the electrical parameters of samples using a microstrip line and a network analyzer is described in detail, in which cylindrical samples were placed on a microstrip line. The measurements were carried out in the frequency range 10 MHz–20 GHz. Based on the frequency dependences of the S parameters, the relationships between the resonant frequencies of the samples and their composition were determined. The frequency dependences of the absorption coefficient were calculated for materials of various compositions. For each composition, the effective absorption band was calculated, and a pattern of its distribution over the concentrations of the system components was plotted. For empty areas of the phase diagram, interpolation was performed using the obtained results, which made it possible to obtain a qualitative idea of the radio-absorbing properties of the entire system. It was revealed that the compositions with the greatest variety of different phases had the widest absorption band. The results obtained will help in future research and composition selection for further development of microwave devices such as dielectric resonators, filters, and attenuators.

The present work highlights a new general method devoted to computations of the clamped linear electro-optical coefficients from the measured fundamental vibrational frequencies and the nonlinear dielectric susceptibility constants. The calculations are based on the formula analog to that of the Lyddane–Sachs–Teller relation, which is systematically used for the calculations of the clamped linear electro-optical coefficient of oxide ferroelectric crystals such as LiNbO3, LiTaO3, BaTiO3, PbTiO3, and KNbO3. The computed electro-optical coefficients are in good agreement with those obtained from direct measurements and the first-principles calculations or other semi-empirical models. In addition, the famous r51 or r42 coefficients of the tetragonal BaTiO3, PbTiO3, and KNbO3 crystals are finally calculated with high accuracy and discussed in connection with the soft mode behavior.

Flexoelectricity is a gradient electromechanical effect that exists in all solid dielectrics. The effect was first predicted in the late 1950s, but received little interest because it was expected to be small. The experimentally measured large flexoelectric response in ferroelectric ceramics led to the revival of the field in the early 2000s. In this study, the progress made in the flexoelectric field is reviewed. The authors’ focus will be primarily on the experimental studies related to the flexoelectric effect. The techniques employed to measure the flexoelectric coefficients are first summarised. A compilation of the flexoelectric coefficients of different ferroelectrics reported in the literature will be presented. An unresolved issue in this field is that the measured flexoelectric coefficients in ferroelectric materials are normally much greater than the theoretically predicted values, and the mechanisms proposed to explain this issue are discussed. Finally, the efforts toward the applications of the flexoelectric effect are reviewed.

Dielectric capacitors are widely used in pulse power systems, electric vehicles, aerospace, and defense technology as they are crucial for electronic components. Compact, lightweight, and diversified designs of electronic components are prerequisites for dielectric capacitors. Additionally, wide temperature stability and high energy storage density are equally important for dielectric materials. Ferroelectric materials, as special (spontaneously polarized) dielectric materials, show great potential in the field of pulse power capacitors having high dielectric breakdown strength, high polarization, low-temperature dependence and high energy storage density. The first part of this review briefly introduces dielectric materials and their energy storage performance. The second part elaborates performance characteristics of various ferroelectric materials in energy storage and refrigeration based on electrocaloric effect and briefly shed light on advantages and disadvantages of various common ferroelectric materials. Especially, we summarize the polarization effects of underlying substrates (such as GaN and Si) on the performance characteristics of ferroelectric materials. Finally, the review will be concluded with an outlook, discussing current challenges in the field of dielectric materials and prospective opportunities to assess their future progress.

In recent years, the development of implantable electronics has been driven by the motivation to expand their field of application. The main intention is to implement advanced functionalities while increasing the degree of miniaturization and maintaining reliability. The intrinsic nonlinear properties of the electronic components, to be used anyway, could be utilized to resolve this issue. To master the implementation of functionalities in implantable electronics using the nonlinear properties of its electronic components, simulation models are of utmost importance. In this paper, we present a simulation model that is optimized in terms of consistency, computing time and memory consumption. Three circuit topologies of nonlinear capacitors, including hysteresis losses, are investigated. An inductively coupled measurement setup was realized to validate the calculations. The best results were obtained using the Trapezoid method in ANSYS with a constant step size and a resolution of 500 k points and using the Adams method in Mathcad with a resolution of 50 k points. An inductive coupling factor between 7% and 10% leads to a significant improvement in consistency compared to lower coupling factors. Finally, our results indicate that the nonlinear properties of the voltage rectifier capacitor can be neglected since these do not significantly affect the simulation results.

Lanthanide doping is widely employed to tune structural change temperature and electrical properties in ABO3-type perovskite ferroelectric materials. However, the reason that A-site lanthanide doping leads to the decrease of the Curie temperature is still not clear. Based on the reported Curie temperature of lanthanides (Ln) doped in two classic ferroelectrics PbTiO3 and BaTiO3 with A2+B4+O3-type perovskite structure, we discussed the relationship between the decrease rate of Curie temperature (ΔTC) and the bond strength variance of A-site cation (σ). For Nd ion doped Pb(Mg1/3Nb2/3)O3-PbTiO3 (Nd-PMNT) ferroelectric crystal as an example, the internal factors of the dramatic decline of the Curie temperature induced by A-site Nd doping were investigated under a systematic study. The strong covalent bonds of Ln-O play an important role in A-site Ln composition-induced structural change from ferroelectric to paraelectric phase, and it is responsible for the significant decrease in the Curie temperature. It is proposed that the cells become cubic around the Ln ions due to the strong covalent energy of Ln-O bonding in A-site Ln doped A2+B4+O3 perovskite ferroelectrics.

Ferroelectric materials have been applied in the photocatalytic field due to the internal electric field generated by the spontaneous polarisation. In this study, it is found that the ferroelectric BaTiO(3) catalysts exhibit the excellent photocatalytic property and cycle stability under ultrasonic vibration. In addition, the degraded photocatalytic activity after several cycling tests can resurrect if the BaTiO(3) sample is treated by ultrasonic before photocatalytic reaction. The enhanced photocatalytic activity and cycle stability are ascribed to the variational spontaneous polarisation under external strain for ferroelectric materials. Under ultrasonic vibration, the high-frequency alternating strain applied on the BaTiO(3) grain changes the internal polarisation electric field. Due to the fast changing polarisation electric field, there is no enough time to form the depolarisation electric field in the BaTiO(3) grain. Therefore, the effective electric field existed in BaTiO(3) grain is large and can effectively promote the separation the photo-generated electrons/holes; thus improving the photocatalytic activity. It is suggested that ultrasonic vibration is an efficient method to improve the photocatalytic properties and cycle stability of the ferroelectric photocatalysts.

Due to the appealing piezoelectric, pyroelectric, and ferroelectric (FE) properties, poly(vinylidene fluoride) (PVDF)-based dielectric polymers have been attracting great attention from both the academic and industrial communities. Depending on the molecular structure and the processing method, PVDF-based dielectric polymers can exhibit rich dielectric polarisation behaviours covering normal FE, relaxor FE, anti-FE-like and linear dielectric responses, which enables a wide spectrum of application fields such as non-volatile memories, piezoelectric and pyroelectric sensors, actuators, electrocaloric refrigeration, and film capacitors. In this study, the authors first briefly introduce the current practical/promising applications of PVDF-based dielectric polymers, and the corresponding optimum dielectric polarisation behaviour and crystal structure are proposed accordingly. The chemical synthesis and modification strategies for obtaining various fluoropolymers beyond PVDF homopolymer are then summarised with an emphasis on the relationship between the molecular structure and the dielectric polarisation behaviour. In addition, the effect of processing methods on the crystal structure and dielectric properties of the PVDF-based polymers is discussed. Finally, some newly developed processing techniques applicable to PVDF-based polymers are described.

A single crystal with nominal composition Pb(Mg1/3Nb2/3)O3-32PbTiO3 (PMN-32PT) was grown by the Bridgman technique. Crystal orientation was determined using the rotating orientation X-ray diffraction (RO-XRD). Element distribution was measured along different directions using inductively coupled plasma-mass spectrometry (ICP-MS). The effect of the element segregation along axial and radial directions on the electrical properties of the PMN-32PT crystal was investigated. It is indicated that the electrical properties of the samples along the axial direction were strongly dependent on the PT (PbTiO3) content. With the increase of the PT content, the piezoelectric coefficient and remnant polarization were improved. Differently, the electrical properties of the samples along the radial direction were mainly determined by the ratio of the Nb and Mg. The reasons for the element segregation and electrical properties varied with the composition were discussed.

The scientific community has shown a growing interest in relating to the ferroelectric materials and it has made an effort to develop them. Among these several ferroelectric materials, we proposed to investigated Pb(ZrTi)O3 doped with distinct Er+3 concentrations. Our aim was to investigate how the erbium affects the PZT electrical properties. To determine the ideal sintering temperature of our ceramic samples, the dilatometry tests were performed. These results have showed that the erbium caused a change in sample densities (91.9% < ρ < 99.0%) as compared to undoped PZT sample. Furthermore, the X-ray diffraction results indicated that all samples are monophasic and peaks are indexed to tetragonal crystalline structure. According to these also results, there was an increment of the parameter a and a reduction of parameter c as compared to undoped PZT sample. On the other hand, the average grain size have decreased with the increment of erbium content. The electrical characterization of ours ceramics showed a peculiar ferrelectric-paraeletric phase transition around 390 ºC. Finally, the ferroelectric hysteresis measurements for doped samples in site A have revealed that remnant polarization and coercive field values depend on content. Whereas, doped samples in site B, the corresponding values are similar.