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Monoclinic ferroelectric phases are prevalent in various functional materials, most notably mixed‐ion perovskite oxides. These phases can manifest as regularly ordered long‐range crystallographic structures or as macroscopic averages of the self‐assembled tetragonal/rhombohedral nanodomains. The structural and physical properties of monoclinic ferroelectric phases play a pivotal role when exploring the interplay between ferroelectricity, ferroelasticity, giant piezoelectricity and multiferroicity in crystals, ceramics and epitaxial thin films. However, the complex nature of this subject presents challenges, particularly in deciphering the microstructures of monoclinic domains. In Paper I [Biran & Gorfman (2024). Acta Cryst. A80, 112–128] the geometrical principles governing the connection of domain microstructures formed by pairing MAB type monoclinic domains were elucidated. Specifically, a catalog was established of 'permissible domain walls', where 'permissible', as originally introduced by Fousek & Janovec [J. Appl. Phys. (1969), 40, 135–142], denotes a mismatch‐free connection between two monoclinic domains along the corresponding domain wall. The present article continues the prior work by elaborating on the formalisms of permissible domain walls to describe domain microstructures formed by pairing the MC type monoclinic domains. Similarly to Paper I, 84 permissible domain walls are presented for MC type domains. Each permissible domain wall is characterized by Miller indices, the transformation matrix between the crystallographic basis vectors of the domains and, crucially, the expected separation of Bragg peaks diffracted from the matched pair of domains. All these parameters are provided in an analytical form for easy and intuitive interpretation of the results. Additionally, 2D illustrations are provided for selected instances of permissible domain walls. The findings can prove valuable for various domain‐related calculations, investigations involving X‐ray diffraction for domain analysis and the description of domain‐related physical properties. [ABSTRACT FROM AUTHOR]

Ferroelectric field effect transistors (FeFETs), characterized by their low power consumption and polarization effect, can be employed in photodetectors based on 2D materials. In this paper, a MoS2 phototransistor with epitaxial ferroelectric (Hf0.5Zr0.5)O2 (HZO) is reported as a gate dielectric layer. Gate‐dielectric‐polarization‐dependent ambipolar behavior is observed in the FET, and relatively low power consumption and hysteresis‐free loop are achieved in the FeFET. The anomalous negative photoconductivity (NPC) is observed as well. Possible reasons for such phenomenon are clarified including the photogating effect originating from the interface traps and the polarization‐dependent electric‐field control through ferroelectric gating. The high responsivity of −8.44 × 103 A W−1 in the negative photoconductivity as well as the response time of 500 ms are reported. The demonstrated Molybdenum disulfide (MoS2) FeFET photodetectors show great potential in the on‐chip complementary metal‐oxide semiconductor (CMOS)‐compatible circuits for multifunctional devices. [ABSTRACT FROM AUTHOR]

Bismuth layer structured ferroelectrics (BLSFs) have drawn much attention due to their great potential for high‐temperature applications. It is generally accepted that BLSFs with small orthorhombic distortion should have low TC. In this paper, we report an anomalous example Li0.5Bi2.5Nb2O9 (LBN), which has small orthorhombic distortion but very high TC. LBN shows the highest TC (834°C) among currently reported prototype alkali‐metal BLSFs, which is attributed to its small tolerance factor. However, the refinement result reveals that LBN is orthorhombic with the space group of A21am, and the orthorhombic distortion of LBN a/b is merely 1.0019. The measurement of piezoelectric coefficient (d33 ∼ 6 pC/N) and observation of striped domain structure confirm the ferroelectricity nature of LBN. This work deepens our understanding of BLSFs and may lead to the finding of more novel BLSFs with high performance. [ABSTRACT FROM AUTHOR]

In this paper, barium titanate nanoparticles (BaTiO3, BT) were incorporated into the polyurethane (TPU) matrix to prepare dielectric elastomer composites. Then, the composites were thermal treated to improve the interfacial compatibility between TPU and BT, enhance the interface polarization, and improve the dielectric properties. The results showed that the dielectric constant of the composites after thermal treatment at 150°C reached to 7.3 at 1 kHz, the elongation at break remained 1934%, and the elastic modulus (Y) dropped to 4.4 MPa. In addition, the discharge energy density reached 73 mJ/cm3 under an electric field of 300 kV/cm, and charge–discharge energy conversion efficiency was up to 84%. More importantly, the electrically actuated displacement of 2.61 mm at electric field of 160 kV/cm was 1.7 times greater than that of untreated composites. The composites worked stably under the action of the circulating electric field. This study provided a new strategy for obtaining high‐performance dielectric elastomer actuators, which were expected to be applied to biomimetic robots, human skin, or dielectric energy storage devices. [ABSTRACT FROM AUTHOR]

The present paper reports the multifunctional properties of lead‐free BiFeO3–La (BFO–La) thin films. The structural, microstructural, and optical properties have been investigated as a function of the lanthanum doping concentration. The structural properties at room temperature showed the formation of the perovskite structure, thus suggesting the high quality of the obtained thin film compositions. Raman spectroscopy analysis revealed a slight variation in both the peak position and absolute intensity for the Raman active modes, as lanthanum content increases in BiFeO3–La. Crystallized thin films with well‐defined grains as well as crack‐free surfaces have been obtained, for all the studied compositions, as inferred from atomic force microscopy images. The optical properties have been measured, and the values for the direct bandgap was significantly lower than those reported for other BFO‐based systems, being the lowest ∼1.87 eV for the Bi0.90La0.10FeO3 composition. Results revealed a noteworthy effect of the defect concentrations induced by the lanthanum doping on the long‐range crystallinity and directly affecting the polarizability of the A–O bond as well as the Fe–O and Fe–O–Fe bond lengths in the perovskite structure. The enhanced optical absorption properties registered for the Bi1–xLaxFeO3 (x = 0–20) compositions make these perovskite multiferroic thin films as a potential candidate material for the high‐performance photovoltaic device applications. [ABSTRACT FROM AUTHOR]

Electrically switchable bistable conductance that occurs in ferroelectric materials has attracted growing interest due to its promising applications in data storage and in‐memory computing. Sc‐alloyed III‐nitrides have emerged as a new class of ferroelectrics, which not only enable seamless integration with III‐nitride technology but also provide an alternative solution for CMOS back end of line integration. In this paper, the resistive switching behavior and memory effect in an ultrawide‐bandgap, high Curie temperature, fully epitaxial ferroelectric ScAlN/GaN heterostructure is reported for the first time. The structure exhibits robust ON and OFF states that last for months at room temperature with rectifying ratios of 60–210, and further shows stable operation at high temperatures (≈670 K) that are close to or even above the Curie temperature of most conventional ferroelectrics. Detailed studies suggest that the underlying mechanism is directly related to a ferroelectric field effect induced charge reconstruction at the hetero‐interface. The robust resistive switching landscape and the electrical polarization engineering capability in the polar heterostructure, together with the promise to integrate with both silicon and GaN technologies, can pave the way for next‐generation memristors and further enable a broad range of multifunctional and cross‐field applications. [ABSTRACT FROM AUTHOR]

It is well known that electronic energy bands are split by spin‐orbit coupling in a system that lacks inversion center, and the bulk Rashba effect in ferroelectric semiconductor GeTe has attracted intensive attention due to its giant Rashba coefficient. However, the Rashba effect in GeTe film will disappear below a critical thickness due to the occurrence of centrosymmetric structure with decreasing thickness. In this paper, GeTe/In2Se3$_2\text{Se}_3$ heterostructures are investigated by means of first‐principle calculations, and it is found that the Rashba effect not only can be revived for the nonpolar‐GeTe film, but also can be enhanced for the ultrathin polar‐GeTe film. The variation of the bias field within the GeTe film in the heterostructure in contrast with that within the isolated GeTe film may be employed to explain the remarkable improvement of Rashba effect and the spin textures around the spin‐split band. Furthermore, the influence of the In2Se3$_2\text{Se}_3$ polarization on the Rashba coefficient is also discussed. With the increasing demands of device miniaturization, the authors hope that the method of constructing heterostructure may be an alternative route to enable large Rashba effect surviving down to the ultrathin film limit. [ABSTRACT FROM AUTHOR]

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 FROM AUTHOR]

Polymer‐dispersed liquid crystals (PDLCs) with nano‐phase‐separated structures, in which nanometer‐sized liquid crystal (LC) domains are dispersed within a polymer matrix (nano‐PDLCs), are transparent solid materials whose optical properties can be modulated by applying an electric field (E‐field). Because the proportion of LC that can respond to an electric field is small, the specific surface area of the phase‐separated interface of nano‐PDLCs is larger than that of conventional PDLCs, resulting in higher drive voltages than those of conventional PDLCs. To lower the driving voltage of nano‐PDLCs, highly polar LCs (C3DIO) are used with a large dielectric anisotropy (>10000), and prepared nano‐PDLCs using DIO mixtures obtained by mixing them with related compounds as the host LC. Nano‐PDLCs employing DIO mixtures exhibit higher E‐field responsivity than those using conventional LC. In addition, the electro‐optical Kerr coefficient at visible wavelength is significantly high, reaching 10−8 m V−2. Furthermore, nano‐PDLCs using the DIO mixture exhibit a memory effect in which the induced birefringence remains even after the removal of the in‐plane E‐field. Memorized birefringence can be erased by heating or applying an E‐field perpendicular to the substrate surface. Nano‐PDLCs using a DIO mixture can be rewritable electro‐birefringence‐responsive materials that can memorize arbitrary birefringence values. [ABSTRACT FROM AUTHOR]

Chemical Solution Deposition enables low‐cost fabrication of ferroelectric HfO2 films suitable for piezoelectric applications. Control of processing parameters is of utmost importance to obtain high‐quality functional films. However, the impact of the annealing atmosphere on ferroelectric properties of solution‐processed HfO2 films is not clear. In this work, the influence of annealing atmosphere and growth methods on orientation, density and electrical properties of La:HfO2 films is studied. The 45 nm‐thick films are grown by two routes, conventional (crystallization of the final 45 nm‐thick film) and layer‐by‐layer (intermediate crystallizations of 5 nm‐thick films). Annealing is performed in N2:O2 and Ar atmosphere. Films grown by layer‐by‐layer method in an oxygen‐rich atmosphere tend to have higher density (87% of theoretical density) and remanent polarization (15 µC cm–2) than the conventional films (density and remanent polarization of 80% and 7.5 µC cm‐2). Secondary ion mass spectrometry reveals higher amounts of carbon presence in the conventional films annealed in Ar. For layer‐by‐layer films, the ability to control the preferential out‐of‐plane orientation from (111) to (002) simply by changing the annealing atmosphere, is demonstrated. The results can guide the path toward high‐quality thicker films for piezoelectric applications. [ABSTRACT FROM AUTHOR]

Recently, HfO2‐based ferroelectric thin films have attracted widespread interest in developing next‐generation nonvolatile memories. To form a metastable ferroelectric orthorhombic phase in HfO2, a post‐annealing process is typically necessary. However, the microscopic mechanism underlying the effect of annealing temperature on ferroelectric domain nucleation and growth is still obscure, despite its importance in optimizing the operation speed of HfO2‐based devices. In this study, the ferroelectric properties and polarization switching of Hf0.5Zr0.5O2 thin films annealed at different temperatures (550–700 °C) are systematically investigated. Evidently, the crystal structure, remnant polarization, and dielectric constant monotonically change with annealing temperature. However, microscopic piezoresponse force microscopy images as well as macroscopic switching current measurements reveal non‐monotonic changes in the polarization switching speed with annealing temperature. This intriguing behavior is ascribed to the difference in the ferroelectric‐domain nucleation process induced by the amount of oxygen vacancies in the Hf0.5Zr0.5O2 thin films annealed at different temperatures. This work demonstrates that controlling the defect concentration of ferroelectric HfO2 by tuning the post‐annealing process is critical for optimizing device performance, particularly polarization switching speed. [ABSTRACT FROM AUTHOR]

The well‐developed high‐k technologies ease the integration complexity for HfO2‐based ferroelectric (FE) devices in the complementary metal‐oxide semiconductor processes. Sputtered HfxZr(1‐x)O2 (HZO) FEs have proven their thermal compatibility in back‐end‐of‐line (BEOL) integration processes with high remanent polarization (Pr) and a high cycling endurance. With the help of a tungsten oxide (WOx) bottom electrode, the sputtered HZO's FE properties are further advanced in this work. WOx is used to tune the oxygen content in the HZO film, providing an FE performance with a maximum 2Pr of 46 µC cm−2 and an endurance of 108 cycles. Based on this, sputtered HZO can compete with the atomic layer deposited HZO in the BEOL processes. In addition, WOx bottom electrodes enhance the FE capacitor behavior in a broad processing window, which relaxes the manufacturing restrictions. [ABSTRACT FROM AUTHOR]

The preparation of 2D magnetoelectric (ME) nanomaterials with strong ME coupling is crucial for the fast reading and writing processes in the next generation of storage devices. Herein, 2D BaTiO3 (BTO)‐CoFe2O4 (CFO) ME nanocomposites are prepared through a substrate‐free coupling strategy using supercritical CO2. Such 2D BTO‐CFO with strong coupling is built through alternating in‐plane and out‐of‐plane epitaxy stacking, leading to remarkable mutual biaxial strain effects for spin‐lattice coupling. As a results, such strain effect significantly enhances the ferroelectricity of BTO and the ferrimagnetism of CFO, where an unexceptionally high ME coupling coefficient of (325.8 mV cm−1 Oe−1) is obtained for the BTO‐CFO nanocomposites. [ABSTRACT FROM AUTHOR]

The possibility to engineer (GeTe)m(Sb2Te3)n phase‐change materials to co‐host ferroelectricity is extremely attractive. The combination of these functionalities holds great technological impact, potentially enabling the design of novel multifunctional devices. Here an experimental and theoretical study of epitaxial (GeTe)m(Sb2Te3)n with GeTe‐rich composition is presented. These layered films feature a tunable distribution of (GeTe)m(Sb2Te3)1 blocks of different sizes. Breakthrough evidence of ferroelectric displacement in thick (GeTe)m(Sb2Te3)1 lamellae is provided. The density functional theory calculations suggest the formation of a tilted (GeTe)m slab sandwiched in GeTe‐rich blocks. That is, the net ferroelectric polarization is confined almost in‐plane, representing an unprecedented case between 2D and bulk ferroelectric materials. The ferroelectric behavior is confirmed by piezoresponse force microscopy and electroresistive measurements. The resilience of the quasi van der Waals character of the films, regardless of their composition, is also demonstrated. Hence, the material developed hereby gathers in a unique 2D platform the phase‐change and ferroelectric switching properties, paving the way for the conception of innovative device architectures. [ABSTRACT FROM AUTHOR]

Thermally triggered spatial symmetry breaking in traditional ferroelectrics has been extensively studied for manipulation of the ferroelectricity. However, photoinduced molecular orbital breaking, which is promising for optical control of ferroelectric polarization, has been rarely explored. Herein, for the first time, we synthesized a homochiral fulgide organic ferroelectric crystal (E)‐(R)‐3‐methyl‐3‐cyclohexylidene‐4‐(diphenylmethylene)dihydro‐2,5‐furandione (1), which exhibits both ferroelectricity and photoisomerization. Significantly, 1 shows a photoinduced reversible change in its molecular orbitals from the 3 π molecular orbitals in the open‐ring isomer to 2 π and 1 σ molecular orbitals in the closed‐ring isomer, which enables reversible ferroelectric domain switching by optical manipulation. To our knowledge, this is the first report revealing the manipulation of ferroelectric polarization in homochiral ferroelectric crystal by photoinduced breaking of molecular orbitals. This finding sheds light on the exploration of molecular orbital breaking in ferroelectrics for optical manipulation of ferroelectricity. [ABSTRACT FROM AUTHOR]

In recent years, multiferroic (MF) materials have attained remarkable attention because of their exceptional ability to demonstrate both ferroelectric (FE) and magnetic properties simultaneously which has lead to their applications in memory, sensors, and energy storage devices. Here, a simple synthesis approach is used to enhance the ferroelectricity and induce the multiferroicity in double transition metal carbide (DTM) MXene film. The successful synthesis is confirmed by X‐ray Diffraction (XRD), Raman Spectroscopy, and Scanning Electron Microscopy (SEM) analysis. In addition, the FE and magnetic hysteresis (MH) loops are conducted to observe the nature of synthesized materials. Furthermore, the magnetoelectric (ME) effect is also examined to explore its significance in data storage and ME signal generation devices. Thus, the findings reveal the first report on the co‐existence of FE and magnetic properties of DTM MXene for potential applications in nano‐electronic devices of future technology. [ABSTRACT FROM AUTHOR]

Crosslinked liquid crystal polymers (CLCPs) are smart materials that combine the anisotropy of liquid crystals (LCs) with the elasticity of rubber. When subjected to external stimuli, they exhibit exceptional two-way shape memory behavior. Among the various stimuli, electrical energy has the advantages of cleanliness, stability, and high controllability; hence, it is widely used for controlling CLCP-based soft actuators, thus presenting potential for application in diverse, complex scenarios. By combining electrically driven mode and sensor equipment, precise control of CLCPs can be achieved, and the electrically driven CLCPs can accomplish more intricate and sophisticated tasks. This study presents a comprehensive review of electrically driven CLCPs with various driving mechanisms, including the electroclinic effect of ferroelectric CLCPs, the reorganization of LC molecules, the Maxwell effect of dielectric CLCPs, and the Joule heating effect of electrothermally responsive CLCP systems. In addition, a detailed analysis of the applications of electrically driven CLCPs in various research fields is presented. Finally, the current challenges in the field of electrically driven CLCP technology are summarized, along with predictions for future prospects. [ABSTRACT FROM AUTHOR]

Ferroelectric materials are considered ideal for emerging memory devices owing to their characteristic remanent polarization, which can be switched by applying a sufficient electric field. However, even several decades after the initial conceptualization of ferroelectric memory, its applications are limited to a niche market. The slow advancement of ferroelectric memories can be attributed to several extant issues, such as the absence of ferroelectric materials with complementary metal–oxide–semiconductor (CMOS) compatibility and scalability. Since the 2010s, ferroelectric memories have attracted increasing interest because of newly discovered ferroelectricity in well‐established CMOS‐compatible materials, which are previously known to be non‐ferroelectric, such as fluorite‐structured (Hf,Zr)O2 and wurtzite‐structured (Al,Sc)N. With advancing material fabrication technologies, for example, accurate chemical doping and atomic‐level thickness control, a metastable polar phase, and switchable polarization with a reasonable electric field can be induced in (Hf,Zr)O2 and (Al,Sc)N. Nonetheless, various issues still exist that urgently require solutions to facilitate the use of the ferroelectric (Hf,Zr)O2 and (Al,Sc)N in emerging memory devices. Thus, ferroelectric (Hf,Zr)O2 and (Al,Sc)N are comprehensively reviewed herein, including their fundamental science and practical applications. [ABSTRACT FROM AUTHOR]

A lead‐free tetragonal‐phase (Ba0.94Ca0.06)(Ti0.95Zr0.05)O3 (BCTZ) micro sheet is prepared by molten‐salt growth method, which exhibits a polarizing behavior of relaxor ferroelectricity and possesses a high dielectric constant (εr) of ~2400. Subsequently, the BCTZ sheet is evenly doped into ferroelectric copolymer P(VDF‐TrFE)55/45 mol% with different mass fractions, and the flexible BCTZ/P(VDF‐TrFE) composite films are prepared using a conventional solution casting process. εr of BCTZ/P(VDF‐TrFE) increases with the mass content of BCTZ, and reaches 23.8 in 20 wt% BCTZ sample. Meanwhile, at a high electrical field of 30 MV/m, the strain and electric field of BCTZ/P(VDF‐TrFE) are in the opposite direction, indicating a negative value of piezoelectric strain coefficient (d33) caused by inverse piezoelectric effect. In addition, d33 of different BCTZ/P(VDF‐TrFE) films are fitted using a strain‐electrical field curve, which firstly increases and then decreases with increases in BCTZ content. As such, a high d33 of −47.3 pC/N is obtained in BCTZ/P(VDF‐TrFE)15/85 wt% film. Thus, this research concerning the inverse piezoelectric effect may provide a reference for designing a piezoelectric composite using in transducers and actuators. [ABSTRACT FROM AUTHOR]

This work systematically studies the TiN, Ru, and RuO2 top electrodes (TEs) effects on the ferroelectric properties of Hf0.5Zr0.5O2 (HZO) films. The Ru top electrode significantly improves the ferroelectric performance even with the conventional TiN bottom electrode. The high two‐remanent polarization (2Pr) value (≈65 µC cm−2) is obtained with the capacitor with Ru TE, which is ≈1.5 times higher than that of the capacitors with the TiN and RuO2 TEs. Moreover, it does not break down to 1 × 109 cycling with a high cycling electric field of 4.0 MV cm−1, while others do lower cycle numbers. Further enhancement can be achieved by inserting a 2‐nm‐thick HfON interfacial layer between the HZO film and TiN bottom electrode while keeping the Ru/HZO top interface structure. The capacitor does not break down even at an electric field strength of 4.8 MV cm−1, at which a 2Pr value of ≈67 µC cm−2 is achieved. Furthermore, it can endure 1 × 1011 switching cycles while a 2Pr value of 45–53 µC cm−2 is retained. Therefore, this study elucidates that interfacial engineering is an important technology that can overcome the trade‐off relationship between Pr and endurance, a critical issue in ferroelectric doped HfO2‐based films. [ABSTRACT FROM AUTHOR]

Several classes of materials manifest displacive phase transitions, including shape memory alloys, many electronically correlated materials, superconductors, and ferroelectrics. Each of these classes of materials displays a wide range of fascinating properties and functionalities that are studied in disparate communities. However, these materials' classes share similar electronic and phononic instabilities in conjunction with microstructural features. Specifically, the common motifs include twinned microstructures, anomalies in the transport behavior, softening of specific phonons, and frequently also (giant) Kohn anomalies, soft phonons, and/or nesting of the Fermi surface. These effects, phenomena, and their applications have until now been discussed in separate communities, which is a missed opportunity. In this perspective a unified framework is presented to understand these materials, by identifying similarities, defining a unified phenomenological description of displacive phase transitions and the associated order parameters, and introducing the main symmetry‐breaking mechanisms. This unified framework aims to bring together experimental and theoretical know‐how and methodologies across disciplines to enable unraveling hitherto missing important mechanistic understanding about the phase transitions in (magnetic) shape memory alloys, superconductors and correlated materials, and ferroelectrics. Connecting structural and electronic phenomena and microstructure to functional properties may offer so‐far unknown pathways to innovate applications based on these materials. [ABSTRACT FROM AUTHOR]

Polycrystalline‐multiferroic Bi0.85Pr0.15‐xEuxFe0.97Mn0.03O3 (0, 0.01, 0.02, 0.03, 0.4, 0.05) thin films were grown on fluorine‐doped tin oxide (FTO)/glass substrate with radio frequency (RF) magnetron sputtering. Rietveld quantitative analysis reveals that whereas the starting materials (nanoparticles [NPs] and ceramics) are composed of tetragonal P4mm symmetry, the thin films can lose 80% of this symmetry to become rhombohedral R3c symmetry. The structure evolution from tetragonal to rhombohedral symmetry indicates that the Eu3+ ion acts positively to reduce the tensile residual stress component from 24 to 1.8 MPa in the thin films. The band gap shifts to 2.17 eV by Eu substitution at the A‐site of the perovskite. Scanning electron microscopy (SEM) results show high‐elongated nanocrystals that share parallel facets without porosity. In that morphology, the Eu has a strong influence on reducing the magnetic coercivity from 10.7 to 6.5 kOe, which has been interpreted in terms of local shape anisotropy. Although the magnetic response increases monotonously, the ferroelectric polarization decreases with doping. These changes are explained through local defects created by the evolution of the VO·· concentration that changes significantly by Eu doping. [ABSTRACT FROM AUTHOR]

The pressure‐driven explosive energy‐conversion (EEC) effect of ferroelectric (FE) materials has been extensively studied in scientific research and high‐tech applications owing to its high pulse‐power output capability. The fundamental principle of this effect is pressure‐driven phase transition and depolarization in FE materials, accompanied by discharging behavior from the charge release upon pressure loading. Pb(Zr,Ti)O3 has been an excellent example of a materials exhibiting these properties. However, recent investigations have been focused on developing other lead‐based or lead‐free materials with a higher energy‐storage ability and better temperature stability. In this article, we review the recent progress achieved in the past decades on different types of lead‐based and lead‐free ceramics, single crystals, and multilayer films, based on their unique pressure‐driven phase transition and energy‐conversion properties. Their pulse power discharging performance under actual shock‐wave compression is also summarized, followed by a detailed discussion of the failure mechanism under shock‐wave compression. Finally, several issues and perspectives are proposed for future investigation in this area. All these not only assist in the design of new materials for high‐performance EEC but are also helpful for the practical application of these promising materials in pulse‐power technologies. [ABSTRACT FROM AUTHOR]

Polarization is one of the unique properties of ferroelectric materials; yet the polarization mechanism for enhancing ferroelectric photovoltaic performance is rarely been investigated, particularly in terms of bandgap variation. In this work, the effect of high‐field polarization on the enhanced photovoltaic performance of a ferroelectric ceramic, 0.98KNbO3–0.02SrCo0.5Hf0.5O3−δ (KNSCH2), was explored in terms of bandgap variation. The bandgap of the KNSCH2 sample shrank after polarization because of the increase in potential energy band overlap and the upward shift of the valence band due to increased oxygen‐vacancy defects. The polarization optimized the energy band structure of KNSCH2, promoting the separation and transport of photoinduced carriers and thus further enhancing its photovoltaic performance. The KNSCH2 sample shows a twofold enhancement in Jsc after 60 kV/cm polarization. The degree of the lattice distortion of KNSNH2 increased following polarization, causing a minute increase in its cell asymmetry. The reasons for the bandgap narrowing and the creation of sub‐bandgaps in the KNSCH samples were also investigated. This work opened new doors to understanding the mechanisms underlying the polarization‐enhanced photovoltaic performance of ferroelectric materials. [ABSTRACT FROM AUTHOR]

One‐dimensional (1D) magnetoelectric multiferroics are promising multifunctional materials for miniaturized sensors, actuators, and memories. However, 1D materials with both ferroelectricity and ferromagnetism are quite rare. Herein, using first‐principles calculations, a series of fullerene‐based 1D chains, namely U2C@C80‐M (M = Cr, Mn, Mo, and Ru) 1D chains with both ferroelectric (FE) and ferromagnetic (FM) properties is designed. Compared to individual U2C@Ih(7)‐C80, the spontaneous polarization (Ps) in 1D chains is enhanced by about two to four times owing to the interaction between U2C@Ih(7)‐C80 fullerene and M (M = Cr, Mn, Mo, and Ru) atoms. Meanwhile, the introduction of transition metal atoms dopes electrons into U's 5f orbitals, leading to numerous intriguing magnetic properties, such as U2C@C80‐Cr and U2C@C80‐Mo as 1D ferromagnetic semiconductors, U2C@C80‐Ru as 1D ferrimagnetic (FiM) semiconductor, and U2C@C80‐Mn as 1D antiferromagnetic (AFM) semiconductor. Excitingly, it is found that magnetic ordering and electrical polarization can be modulated independently by linking different transition metal atoms. These findings not only broaden the range of 1D multiferroic materials, but also provide promising candidates for novel electronic and spintronic applications. [ABSTRACT FROM AUTHOR]

We show that cation ordering on A site columns, oppositely displaced via coupling to B site octahedral tilts, results in a polar phase of the columnar perovskite (NaY)MnMnTi4O12. This scheme is similar to hybrid improper ferroelectricity found in layered perovskites, and can be considered a realisation of hybrid improper ferroelectricity in columnar perovskites. The cation ordering is controlled by annealing temperature and when present it also polarises the local dipoles associated with pseudo‐Jahn–Teller active Mn2+ ions to establish an additional ferroelectric order out of an otherwise disordered dipolar glass. Below TN≈12 K, Mn2+ spins order, making the columnar perovskites rare systems in which ordered electric and magnetic dipoles may reside on the same transition metal sublattice. [ABSTRACT FROM AUTHOR]

We show that cation ordering on A site columns, oppositely displaced via coupling to B site octahedral tilts, results in a polar phase of the columnar perovskite (NaY)MnMnTi4O12. This scheme is similar to hybrid improper ferroelectricity found in layered perovskites, and can be considered a realisation of hybrid improper ferroelectricity in columnar perovskites. The cation ordering is controlled by annealing temperature and when present it also polarises the local dipoles associated with pseudo‐Jahn–Teller active Mn2+ ions to establish an additional ferroelectric order out of an otherwise disordered dipolar glass. Below TN≈12 K, Mn2+ spins order, making the columnar perovskites rare systems in which ordered electric and magnetic dipoles may reside on the same transition metal sublattice. [ABSTRACT FROM AUTHOR]

Although the monolayers of most 2D materials are non‐ferroelectric with highly symmetric lattices, symmetry breaking may take place in their bilayers upon some stacking configuration, giving rise to so‐called sliding ferroelectricity where the vertical polarizations can be electrically reversed via interlayer translation. However, it is not supposed to appear in systems like graphene bilayer with centro‐symmetry at any stacking configuration, and the origin of the recently reported ferroelectricity (Nature 2020, 588, 71) in graphene bilayer intercalated between h‐BN remains mysterious. Here, a type of across‐layer sliding ferroelectricity that arises from the asymmetry of next‐neighbor interlayer couplings is proposed. The first‐principles evidence is shown that the vertical polarizations in intercalated centro‐symmetric 2D materials like graphene bilayer can be switched via multilayer sliding, which is likely to be the origin of the observed ferroelectric hysteresis. Moreover, such ferroelectricity may exist in a series of other heterolayers with quasi‐degenerate polar states, like graphene bilayer or trilayer on BN substrate, or even with a molecule layer on surface where each molecule can store 1‐bit data independently, resolving the bottleneck issue of sliding ferroelectricity for high‐density data storage. [ABSTRACT FROM AUTHOR]

Complex oxides exhibit a wide range of fascinating functionalities, such as ferroelectricity, piezoelectricity, and pyroelectricity, which are indispensable for cutting‐edge electronics, energy, and information technologies. The intriguing physical properties of these complex oxides arise from the complex interplay between lattice, orbital, charge, and spin degrees of freedom. Here, it is reviewed how electromechanical properties can be achieved/improved by artificially breaking the symmetry of centrosymmetric oxides via engineering thermodynamic variables such as stress, strain, electric field, and chemical potentials. The mechanisms that have been utilized to break the inherent symmetry of conventional materials that lead to novel functionalities and applications are explored. It is highlighted that access to "hidden phases," which otherwise are prohibited, could uncover opportunities to host exotic properties, such as piezoelectricity, pyroelectricity, etc. This review not only reports how to engineer intrinsically nonpolar and centrosymmetric oxides for emergent properties, but also has implications for manipulating polar functional materials for better performance. [ABSTRACT FROM AUTHOR]

Parametric infrared (IR) upconversion is a process in which low‐frequency IR photons are upconverted into high‐frequency ultraviolet/visible photons through a nonlinear optical process. It is of paramount importance for a wide range of security, material science, and healthcare applications. However, in general, the efficiencies of upconversion processes are typically extremely low for nanometer‐scale materials due to the short penetration depth of the excitation fields. Here, parametric IR upconversion processes, including frequency doubling and sum‐frequency generation, are studied in layered van der Waals NbOCl2. An upconversion efficiency of up to 0.004% is attained for the NbOCl2 nanosheets, orders of magnitude higher than previously reported values for nonlinear layered materials. The upconverted signal is sensitive to layer numbers, crystal orientation, excitation wavelength, and temperature, and it can be utilized as an optical cross‐correlator for ultrashort pulse characterization. [ABSTRACT FROM AUTHOR]

A group of ferroelectric polyvinylidene‐trifluoroethylene (P(VDF‐TrFE)) with 6, 9, 20, and 50 mol% trifluoroethylene (TrFE) is synthesized by an hydrogenation process using a new catalyst (SiMe3)3SiH from polyvinylidene‐chlorotrifluoroethylene. We find the crystalline region of hydrogenated P(VDF‐TrFE) 80/20 mol% is β crystal phase predominant, which is responsible to the favorable ferroelectric property. Moreover, polyvinylidene fluoride (PVDF) blending is used to fabricate the ferroelectric and relaxor ferroelectric properties of P(VDF‐TrFE) 80/20 mol%. Interestingly, with the increasing of PVDF content, PVDF/P(VDF‐TrFE) has three successional conversion stages of ferroelectricity, antiferroelectricity, and relaxor ferroelectricity, respectively, indicating that the β crystal domains in hydrogenated P(VDF‐TrFE) films gradually reduces with the introduction of PVDF. Otherwise, after an unidirectional stretching process, the ferroelectricity of relaxor PVDF/P(VDF‐TrFE) blend film is reformed. As such, the maximum polarization (Pm) and remnant polarization (Pr) of stretched PVDF/P(VDF‐TrFE) with 90 wt% PVDF reached to 13.8 and 7.5 μC/cm2 under 200 MV/m, respectively. Thus, the three methods proposed in this work including fabricating configuration by changing TrFE content, physical blending by introduction of PVDF, and simple stretching can modify the ferroelectric performances of this hydrogenated P(VDF‐TrFE), which also provides a reference of application of this polymer on ferroelectric areas. [ABSTRACT FROM AUTHOR]

Amphoteric rare‐earth ion dopants can improve ferroelectric ceramic electrical performance because of their amphoteric ion radius and valences. Herein, Ho3+‐doped Ba0.90Ca0.10(Ti0.95Zr0.05)2O5 ceramics are sintered at 1230 °C with as‐synthesized nanoparticles. The effects of various holmium contents (x) on the phase, structure, dielectric, and piezoelectric characteristics are investigated. For low x (<1.5 mol%), Ho3+ occupies the Ba2+ or/and Ca2+ sites, leading to high dielectric properties due to decreased oxygen vacancies, while the electrical properties weaken with further increase in x. The ferroelectricity and piezoelectricity also deteriorate when x > 1.5 mol% because of the re‐emerged oxygen vacancies and interrupted long‐range ordering with large compositional fluctuations. The defect chemistry mechanism at different x contents is deduced in accordance with the phase and electrical properties. The activation energy initially elevates to 1.56 eV and then decreases to 1.35 eV with increasing x. Results indicate that the ceramics are promising candidates for lead‐free ferroelectric ceramics. [ABSTRACT FROM AUTHOR]

Traditional von Neumann architecture is facing severe challenges due to separated physical structure of memory and processing units, which inspires the development of in‐memory computing electronics. Intriguingly, as a kind of complementary metal‐oxide‐semiconducor compatible ferroelectric material, HfO2 is widely studied based on first‐principles calculation in the semiconductor field, showing great potential in constructing emerging electronics. Different structures including ferroelectric diode, ferroelectric field effect transistor, and ferroelectric tunnel junctions based on HfO2 are proposed for in‐memory computing application. Here, this work reviews the progress of HfO2 from materials to devices, including crystal structure, fatigue mechanism, first‐principles calculation, and neuromorphic computing application of HfO2‐based device. This work can provide a reference for the HfO2 ferroelectric device development for next‐generation in‐memory computing applications. [ABSTRACT FROM AUTHOR]

The presence of the top electrode on hafnium oxide‐based thin films during processing has been shown to drive an increase in the amount of metastable ferroelectric orthorhombic phase and polarization performance. This "Clamping Effect," also referred to as the Capping or Confinement Effect, is attributed to the mechanical stress and confinement from the top electrode layer. However, other contributions to orthorhombic phase stabilization have been experimentally reported, which may also be affected by the presence of a top electrode. In this study, it is shown that the presence of the top electrode during thermal processing results in larger tensile biaxial stress magnitudes and concomitant increases in ferroelectric phase fraction and polarization response, whereas film chemistry, microstructure, and crystallization temperature are not affected. Through etching experiments and measurement of stress evolution for each processing step, it is shown that the top electrode locally inhibits out‐of‐plane expansion in the HZO during crystallization, which prevents equilibrium monoclinic phase formation and stabilizes the orthorhombic phase. This study provides a mechanistic understanding of the clamping effect and orthorhombic phase formation in ferroelectric hafnium oxide‐based thin films, which informs the future design of these materials to maximize ferroelectric phase purity and corresponding polarization behavior. [ABSTRACT FROM AUTHOR]

SmFeO3 has received the increasing scientific attention as a promising room‐temperature single‐phase multiferroic material with great application potential in the next‐generation spintronic devices. However, the ferroelectricity of SmFeO3 has remained as a controversial issue. In the present work, high resistivity incipient ferroelectric CaTiO3 was introduced as a charge blocking layer on an SmFeO3 thin film to suppress the leakage current. CaTiO3/SmFeO3/Nb–SrTiO3 (1 0 0) thin films were prepared by a PLD (pulsed laser deposition) process, and the epitaxial growth of thin films was confirmed by XRD (X‐ray diffraction) and HRTEM (high resolution transmission electron microscope) images. The interface strain resulted in the polar non‐centrosymmetry in space group P42/mc for SmFeO3, and subsequently the room‐temperature ferroelectricity was achieved with a robust remanent polarization of about 4.9 μC/cm2. The 180° switchable domain structure was confirmed by PFM (piezoelectric force microscope). Meanwhile, strong magnetoelectric coupling with magnetoelectric coefficient (αME) of about 2.5 V/(cm Oe) was observed. The present work has revealed the structural origin of ferroelectricity in an SmFeO3 thin film and provided the great reference for its room temperature multiferroic applications. [ABSTRACT FROM AUTHOR]

Harvesting solar energy to solve the energy crisis and environmental pollution is a research hotspot in the photovoltaic industry today. Conventional ferroelectric materials have a bandgap between 3.0 and 3.8 eV, and their low absorption coefficients and photocurrent densities limit the photovoltaic applications of ferroelectric materials. Inorganic ferroelectric thin film materials with narrow bandgap (1.1–2.0 eV) have high optical absorption coefficient and broad spectral response, wide bandgap tuning range (1.2–3.0 eV), as well as high photocurrent density and switchable ferroelectric photoelectric effect, which have great potential for photovoltaic and optoelectronic applications in solar cells, photodetection, photocatalysis. This review summarizes the recent developments of narrow bandgap inorganic ferroelectric thin‐film materials and aims to stimulate research interest and efforts in ferroelectric photovoltaic materials. [ABSTRACT FROM AUTHOR]

Metal halide perovskites (MHPs) have been shown to be key materials for next‐generation photovoltaic energy harvesting, electro‐optic detection, and all‐optical conversion. Room‐temperature tetragonal MAPbI3 has been reported to possess two space groups: polar I4cm and non‐polar I4/mcm. Although the space group of MAPbI3 is still under debate, significant effort has been expended to prove that I4cm MHPs are ferroelectric and I4/mcm MHPs are antiferroelectric. Both structures belong to the ferroelastic point group, and there has been debate regarding whether the domain structures observed on MHPs are ferroelectric or ferroelastic. The relationship between the ferroelectricity and ferroelasticity of MHPs has been discussed, whereas these two properties sometimes are regarded as mutually exclusive in MHPs. In this work, the ferroelectricity and ferroelasticity of MHPs originating from structural symmetry have been reviewed, and the interrelationship between the ferroelectricity and ferroelasticity of MHPs are discussed. [ABSTRACT FROM AUTHOR]

2D hybrid halide double perovskites (HHDPs) have been demonstrated to be a promising alternative to conventional lead‐based halide perovskites as a new system of photoferroelectrics, due to their unique characteristics of environmental friendliness, favorable stability, and fascinating optoelectronic properties. Herein, for the first time, a 2D iodide double perovskite photoferroelectric is reported based on Ag/Sb ions, (4,4‐DFPD)4AgSbI8 (4,4‐DFPD = 4,4‐difluoropiperidinium), which possesses a high Curie temperature of 414 K (above BaTiO3), a large spontaneous polarization of 9.6 μC cm−2, ferroelectric photovoltaic effect, and photostrictive effect. Notably, to the best of the authors' knowledge, the discovery of photostriction in HHDP photoferroelectrics is unprecedented. Moreover, (4,4‐DFPD)4AgSbI8 exhibits an impressive X‐ray responsivity, with a sensitivity as high as 704.8 μC Gyair−1 cm−2 at 100 V bias and a detection limit as low as 0.36 μGyair s−1 at 10 V bias, both of which outperform the current all HHDP photoferroelectrics. This work enriches the photoferroelectric family, and proves that Ag/Sb‐based HHDP photoferroelectrics are a promising candidate for the next‐generation optoelectronic devices. [ABSTRACT FROM AUTHOR]

Comprehensive Summary: Recently, molecular ferroelectrics have attracted more and more attention due to their structural diversity, low cost of manufacture, and environmental‐friendly processing. However, most of the design strategies for molecular ferroelectrics have focused on the selection and modification of cations, and the use of anions has been rarely reported. Here, introducing distorted [CuBr4]2– tetrahedra, we obtained a high curie temperature (Tc) ferroelectric, [cyclopentylammonium]2CuBr4, with a Tc as high as 393 K, and exceeding commercial and most of reported molecular ferroelectric BaTiO3 (393 K). Variable‐temperature hysteresis loop shows the nonlinear P‐E loop of the crystal under a wide temperature range. Variable‐temperature single‐crystal X‐ray diffraction revealed that the Aizu expression can be written as mmmFmm2. In short, this work will inspire more creative strategies by exploiting the tunability of the anion module. [ABSTRACT FROM AUTHOR]

Ferroelectricity in fluid materials, which allows free rotation of molecules, is an unusual phenomenon raising cutting‐edge questions in science. Conventional ferroelectric liquid crystals have been found in phases with low symmetry that permit the presence of spontaneous polarization. Recently, the discovery of ferroelectricity with high symmetry in the nematic phase has attracted considerable attention. However, the physical mechanism and molecular origin of ferroelectricity are poorly understood and a large domain of macroscopically oriented spontaneous polarization is difficult to fabricate in the ferroelectric nematic phase. This study reports new fluid layered ferroelectrics with the C∞v symmetry in which nearly complete orientation of the spontaneous polarization remains stable under zero electric field without any orientation treatment. These ferroelectrics are obtained by simplifying the molecular structure of a compound with a known ferroelectric nematic phase, although the simplification reduced the dipole moment. The results provide useful insights into the mechanism of ferroelectricity due to dipole–dipole interactions in molecular assemblies. The new ferroelectric materials are promising for a wide range of applications as soft ferroelectrics. [ABSTRACT FROM AUTHOR]

Similar to the canonical antiferroelectric (AFE) compound PbZrO3 in Pb(Zr,Ti)O3 solid‐solutions, the presence of double hysteresis loops and that of electric field–induced phase transitions are important characteristics of NaNbO3 AFE materials; yet the phase transition behavior in the latter system is typically irreversible with the related mechanisms not fully understood. Here, we explore the phase transition mechanism of ferroelectric and AFE phases in NaNbO3 based on measurements of single crystals with different directions in conjunction with density‐functional theory (DFT) calculations. The tilting and distortion behaviors of the [NbO6] octahedra are explained by DFT, and the ion displacement in the lattice is traced. The tilting and distortion behaviors of the [NbO6] octahedra with different orientations are compared. We confirm that the tilt and distortion of the [NbO6] octahedra along the [1 1 1] direction is the main reason to improve the stability of AFE phase. This conclusion is verified by the experimental characterizations of large‐size NaNbO3 single crystals successfully obtained in this study. [ABSTRACT FROM AUTHOR]

Organic–inorganic hybrid perovskites (OIHPs) have gained tremendous interest for their rich functional properties. However, the coexistence of more than one of ferroelectricity, ferromagnetism and ferroelasticity has been rarely found in OIHPs. Herein, we report a two‐dimensional Cr2+‐based OIHP, [3,3‐difluorocyclobutylammonium]2CrCl4 ([DFCBA]2CrCl4), which shows both ferroelectricity and ferromagnetism. It undergoes a 4/mmmFm type ferroelectric phase transition at a temperature as high as 387 K and shows multiaxial ferroelectricity with a saturate polarization of 2.1 μC cm−2. It acts as a soft ferromagnet with a Curie temperature of 32.6 K. This work throws light on the exploration of OIHPs with the coexistence of ferroelectricity and ferromagnetism for applications in future multifunctional smart devices. [ABSTRACT FROM AUTHOR]

Cation ordering in solids is important for controlling physical properties and leads to ilmenite (FeTiO3) and LiNbO3 type derivatives of the corundum structure, with ferroelectricity resulting from breaking of inversion symmetry in the latter. However, a hypothetical third ABO3 derivative with R32 symmetry has never been observed. Here we show that Co2InSbO6 recovered from high pressure has a new, ordered‐R32 A2BCO6 variant of the corundum structure. Co2InSbO6 is also remarkable for showing two cation redistributions, to (Co0.5In0.5)2CoSbO6 and then Co2InSbO6 variants of the ordered‐LiNbO3 A2BCO6 structure on heating. The cation distributions change magnetic properties as the final ordered‐LiNbO3 product has a sharp ferrimagnetic transition unlike the initial ordered‐R32 phase. Future syntheses of metastable corundum derivatives at pressure are likely to reveal other cation‐redistribution pathways, and may enable ABO3 materials with the R32 structure to be discovered. [ABSTRACT FROM AUTHOR]

Cation ordering in solids is important for controlling physical properties and leads to ilmenite (FeTiO3) and LiNbO3 type derivatives of the corundum structure, with ferroelectricity resulting from breaking of inversion symmetry in the latter. However, a hypothetical third ABO3 derivative with R32 symmetry has never been observed. Here we show that Co2InSbO6 recovered from high pressure has a new, ordered‐R32 A2BCO6 variant of the corundum structure. Co2InSbO6 is also remarkable for showing two cation redistributions, to (Co0.5In0.5)2CoSbO6 and then Co2InSbO6 variants of the ordered‐LiNbO3 A2BCO6 structure on heating. The cation distributions change magnetic properties as the final ordered‐LiNbO3 product has a sharp ferrimagnetic transition unlike the initial ordered‐R32 phase. Future syntheses of metastable corundum derivatives at pressure are likely to reveal other cation‐redistribution pathways, and may enable ABO3 materials with the R32 structure to be discovered. [ABSTRACT FROM AUTHOR]

Bismuth containing hybrid molecular ferroelectrics are receiving tremendous attention in recent years owing to their stable and non‐toxic composition. However, these perovskite‐like structures are primarily limited to ammonium cations. Herein, we report a new phosphonium based discrete perovskite‐like hybrid ferroelectric with a formula [Me(Ph)3P]3[Bi2Br9] (MTPBB) and its mechanical energy harvesting capability. The Polarization‐Electric field (P‐E) measurements resulted in a well‐defined ferroelectric hysteresis loop with a remnant polarization value of 2.1 μC cm−2. Piezoresponse force microscopy experiments enabled visualization of the ferroelectric domain structure and evaluation of the piezoelectric strain coefficient (d33) for an MTPBB single crystal and thin film sample. Furthermore, flexible devices incorporating MTPBB in polydimethylsiloxane (PDMS) matrix at various concentrations were fabricated and explored for their mechanical energy harvesting properties. The champion device with 20 wt % of MTPBB in PDMS rendered a maximum peak‐to‐peak open‐circuit voltage of 22.9 V and a maximum power density of 7 μW cm−2 at an optimal load of 4 MΩ. Moreover, the potential of MTPBB‐based devices in low power electronics was demonstrated by storing the harvested energy in various electrolytic capacitors. [ABSTRACT FROM AUTHOR]

Plastic/ferroelectric crystals have attracted increasing attention as emerging functional molecular materials with unique features. In this study, a new plastic/ferroelectric crystal is developed from ionic molecules, which exhibits three solid phases: a paraelectric plastic crystal phase and two ferroelectric phases. Owing to the malleability in the plastic crystal phase, by applying pressure to the powder at a high temperature, transparent polycrystalline films are easily fabricated, exhibiting ferroelectric performance at room temperature. The crystal structures of the three solid phases are determined by single‐crystal X‐ray diffraction analysis. The arrangement of anions and cations in the ferroelectric crystal is significantly distorted from the CsCl‐type structure in the paraelectric cubic crystal. The large distortion results in distinct splitting of the diffraction peaks that are equivalent in the cubic phase, which enables the observation of electric‐field‐induced lattice reorientation using powder X‐ray diffraction measurements. These results broaden the range of compounds for which plastic/ferroelectric crystals can be developed and provide a solid understanding of the switching process in their bulk polycrystals, which will facilitate their application to a variety of device elements. [ABSTRACT FROM AUTHOR]

With the urgent need to explore low‐cost, high‐efficiency solid‐state refrigeration technology, the electrocaloric effects of ferroelectric materials have attracted much attention in the past decades. With the development of modern computing technology, the phase‐field method is widely used to simulate the evolution of microstructure at mesoscale and predict the properties of different types of ferroelectric materials. In this article, we review the recent progress of electrocaloric effects from phenomenological Landau thermodynamics theory to phase‐field simulation by discussing the microcosmic composition, mesoscopic domain structures, macroscopic size/shape, and external stimulus of strain/stress. More importantly, in searching for new ferroelectric electrocaloric cooling materials, it is possible to find materials whose free energy barrier height changes rapidly with temperature, such materials have a faster change rate with polarization temperature in terms of ferroelectric macroscopic properties, from them could get superior electrocaloric effects. We compile a relatively comprehensive computational design on the high performance of electrocaloric effects in different types of ferroelectrics and offer a perspective on the computational design of electrocaloric refrigeration materials at the mesoscale microstructure level. [ABSTRACT FROM AUTHOR]

The tendency of zinc (Zn) anodes to form uncontrolled Zn electrodeposits and the occurrence of side-reactions at Zn-electrolyte interfaces are a fundamental barrier hampering broad applications of aqueous rechargeable Zn-based batteries. Herein, a ferroelectric domain-mediated strategy is proposed to manipulate the Zn plating behavior and achieve controllable Zn growth orientation by coating Zn foil with a ferroelectric tetragonal KTN (t-KTN) layer. The ferroelectric domain of t-KTN single crystals exhibits periodic distribution of upward and downward polarizations, corresponding to alternating positively and negatively charged surfaces. The charged ferroelectric surfaces can manipulate the transfer kinetics of Zn ions and the concentration distribution of anions via the interplay between ferroelectric dipoles and adsorbed ions. With the synergistic effect of the ferroelectric polarization and domain configurations, the well-aligned interlamellar arrays composed of electrodeposited Zn are formed in the initial deposition process, which enable selective deposition within interlamellar arrays and eliminate the dendrite growth during the following plating process. As a result, the t-KTN layer-modified Zn anode enables reversible Zn plating/stripping with low voltage hysteresis for over 1200 h at 1 mA cm-2 in symmetric cells, and the assembled full cell exhibits a significantly enhanced cycling stability of over 5500 cycles at 5 A g-1. [ABSTRACT FROM AUTHOR]

This article provides a comprehensive overview of piezo‐ and ferro‐electric materials based on organic molecules and organic–inorganic hybrids for mechanical energy harvesting. Molecular (organic and organic–inorganic hybrid) piezo‐ and ferroelectric materials exhibit significant advantages over traditional materials due to their simple solution‐phase synthesis, light‐weight nature, thermal stability, mechanical flexibility, high Curie temperature, and attractive piezo‐ and ferroelectric properties. However, the design and understanding of piezo‐ and ferroelectricity in organic and organic–inorganic hybrid materials for piezoelectric energy harvesting applications is less well developed. This review describes the fundamental characterization of piezo‐ and ferroelectricity for a range of recently reported organic and organic–inorganic hybrid materials. The limits of traditional piezoelectric harvesting materials are outlined, followed by an overview of the piezo‐ and ferroelectric properties of organic and organic–inorganic hybrid materials, and their composites, for mechanical energy harvesting. An extensive description of peptide‐based and other biomolecular piezo‐ and ferroelectric materials as a biofriendly alternative to current materials is also provided. Finally, current limitations and future perspectives in this emerging area of research are highlighted. This perspective aims to guide chemists, materials scientists, and engineers in the design of practically useful organic and organic–inorganic hybrid piezo‐ and ferroelectric materials and composites for mechanical energy harvesting. [ABSTRACT FROM AUTHOR]

The search for ultrathin and robust ferroelectrics leads to few promising two‐dimensional (2D) materials. In2Se3 has drawn special attention owing to the existence of intercoupled in‐plane (IP) and out‐of‐plane (OOP) ferroelectricity in monolayer form, which makes it a potential candidate for emerging artificial intelligence, information processing and memory applications. In addition, the high optical absorption and phase‐dependent visible to infrared bandgap become advantageous from optoelectronics point‐of‐view. This unique ferroelectric and optoelectronic coupling further leads to explore atomic‐scale multifunctional devices. In this review, we summarized the progress of non‐volatile memory (NVM) and photodetector devices, and their intercoupled applications using 2D In2Se3. We expect that this review will provide an insight towards the promising future of 2D ferroelectric‐(opto)electronics and motivate researchers for further development towards industrial scale. [ABSTRACT FROM AUTHOR]