Search

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]

In this paper, structural, microstructure, electrical (impedance, conductivity), and dielectric properties (dielectric constant, tangent loss, and polarization) of a new ferroelectric ceramic (SrTi2O5) synthesized by a high-temperature solid-state reaction method have been reported. The crystallization of the compound in orthorhombic symmetry is confirmed by analyzing the room-temperature X-ray diffraction profile. The scanning electron micrograph displays nearly square and/or spherical grains with varying dimension. The energy-dispersive spectrograph displays desired stoichiometry of the prepared sample. The room-temperature hysteresis loop provides a saturation polarization of about 7.95 µC/cm2 suggesting the existence of ferroelectricity in the compound. In the temperature regime of 25–500 °C, at different frequency (1 kHz–1 MHz), the electrical and dielectric properties have been investigated. The average normalized change of impedance in the above temperature range signifies the footprint of different conduction processes above 250 °C. The Nyquist plots show non-Debye-type semicircular arc for each selected temperature. The grains and grain boundaries' contributions are found on fitting these arcs to the (Rg Qg) (Rgb Qgb) circuit. The conductivity study reveals the existence of distinct conduction processes in the grains and grain boundary regions. The dielectric constant increases with temperature rise at selected frequencies. The dielectric loss first increases with temperature, and about 270 °C, it follows relaxation phenomena in the low-frequency regime. In the high-frequency regime, its value increases with temperature rise. A low value of dielectric loss in the high-frequency regime nominates its possible application in microwave devices. [ABSTRACT FROM AUTHOR]

The paper discusses the features of the effect of modification with lithium carbonate on the dielectric dispersion of lead ferroniobate ceramics. The modifier has been previously shown to change the ways of the recrystallization sintering and therefore reduce the sintering temperature of the ceramics, increase their average grain size, and improve their dielectric and piezoelectric properties. In this study, the emphasis is placed on the analysis of the diffusion effects of the ferroelectric phase transition upon such modification considered from the standpoint of the chemical specifics of the modifier and its location in the structure of the parent compound. [ABSTRACT FROM AUTHOR]

The original definition of multiferroics is that one owns two or three "ferro" properties, such as ferroelectricity, ferroelasticity, and ferromagnetism. Furthermore, novel effects would be generated by the cross-coupling effect among various orders of multiferroic materials, and it has a broad application prospect in electronic information, sensing, storage, wireless network and other fields. At present, researchers are still focus on the multiferroic materials with strong magnetoelectric coupling effect at room temperature. However, the realization and application of devices based on multiferroics are still on the way. Strain engineering is an effective way that can influence the physical properties of multiferroic materials. The physical properties of materials such as electricity, magnetism, and photoacoustic could be influenced by strain engineering through the interaction of lattice with electrons, spins, and orbits. Tuning the structural and physical properties of ferroelectric thin films by strain has been paid extensive attention. Through investigating the research of strain engineering in multiferroic materials in this paper, herein, the strain engineering in multiferroics are summarized and effect of strain engineering on the physical properties of multiferroics is reviewed. It is prospected that the current work may provide research ideas for the investigation and development of multiferroic materials. [ABSTRACT FROM AUTHOR]

Molecular ferroelectric materials have been widely used in capacitors and sensors due to their low cost, light weight, flexibility and good biocompatibility. Organic–inorganic hybrid complexes, on the other hand, have received a great deal of attention in the luminescence field due to their low cost and simple preparation. The combination of ferroelectricity and photoluminescence in organic–inorganic hybrid materials not only leads to tunable optical properties, but also enriches potential applications of multifunctional ferroelectrics in optoelectronic devices. Here, we report a new luminescent ferroelectric material (1,3-dicyclohexylimidazole)2MnCl4 (DHIMC). Thermogravimetric analysis (TGA) was used to measure the mass change of the material at a measurement rate of 20 K min−1 from room temperature to 900 K, and we found that this material has good thermostability, which is up to 383 K. Meanwhile, UV-vis measurements showed that it is also a fluorescent material emitting a strong green fluorescence at the wavelength of 525 nm. The ferroelectricity of the crystal was determined by two different methods: the Sawyer–Tower method and the double-wave method (DWM). Particularly, the single crystal experiences a phase transition from the ferroelectric phase to the paraelectric phase during the heating/cooling process at 318 K/313 K and the space group changes from P1¯ (centrosymmetric) to P1 (non-centrosymmetric). This work will enrich multifunctional luminescent ferroelectric materials and their application in display and sensing. [ABSTRACT FROM AUTHOR]

Improper ferroelectrics are a class of materials with the potential to design multiferroic properties. In this paper, we report on the effect of defect dipoles on the ferromagnetic and ferroelectric properties of Ca 3 Mn 2 O 7 improper ferroelectric thin films. Two kinds of defects dipoles, Mn3+-oxygen vacancy (Mn3+- V O ∙ ∙ ) and Li+-Al3+ doping, were studied. The experimental results show that both Mn3+- V O ∙ ∙ and Li+-Al3+ defect dipoles can introduce ferromagnetism in the films, and Li+-Al3+ defect dipole can also improve ferroelectricity with self-polarization. The first-principle calculations based on local density approximation demonstrate the local lattice distortion, including title MnO 6 octahedron and off-center displacement of Mn ion, plays crucial role in multiferroic properties of the film. This work gives an effective method to design the ferroelectricity and ferromagnetic properties in improper ferroelectric oxides with layered structure through constructing defect dipoles. [ABSTRACT FROM AUTHOR]

Ferroelectricity in biological system has been anticipated both theoretically and experimentally over the past few decades. Claims of ferroelectricity in biological systems have given rise to confusion and methodological controversy. Over the years, a “loop” of induced polarization in response to a varying applied electrical field and a consequent polarization reversal has prompted many researchers to claim ferroelectricity in biological structures and their building blocks. Other observers were skeptical about the methodology adopted in generating the data and questioned the validity of the claimed ferroelectricity as such, “loop” can also be obtained from linear capacitors. In a paper with somewhat tongue-in-cheek title, Jim Scott showed that ordinary banana peels could exhibit closed loops of electrical charge which closely resemble and thus could be misinterpreted as ferroelectric hysteresis loops in barium sodium niobate, BNN paraphrasing it as “banana”. In this paper, we critically review ferroelectricity in biological system and argue that knowing the molecular and crystalline structure of biological building blocks and experimenting on such building blocks may be the way forward in revealing the “true” nature of ferroelectricity in biological systems.

κ-Ga2O3 has been predicted to be a potential ferroelectric material. In this work, undoped Ga2O3 films were grown by either plasma-enhanced atomic layer deposition (PEALD) or metal organic chemical vapor deposition (MOCVD) on platinized sapphire substrates. 50 nm thick PEALD films with a mixture of κ-Ga2O3 and β-Ga2O3 had a relative permittivity of ∼27, a loss tangent below 2%, and high electrical resistivity up to ∼1.5 MV/cm. 700 nm thick MOCVD films with predominantly the κ-Ga2O3 phase had relative permittivities of ∼18 and a loss tangent of 1% at 10 kHz. Neither film showed compelling evidence for ferroelectricity measured at fields up to 1.5 MV/cm, even after hundreds of cycles. Piezoresponse force microscopy measurements on bare κ-Ga2O3 showed a finite piezoelectric response that could not be reoriented for electric fields up to 1.33 MV/cm. [ABSTRACT FROM AUTHOR]

We conducted a comprehensive investigation on the influence of TiN thickness and stress on the ferroelectric properties of Hf 0.5 Zr 0.5 O 2 thin films. TiN top electrode layers with varying thicknesses of 2, 5, 10, 30, 50, 75, and 100 nm were deposited and analyzed. It was observed that the in-plane tensile stress in TiN films increased with the thickness of the TiN top electrode. This is expected to elevate the tensile stress in the Hf 0.5 Zr 0.5 O 2 film, consequently leading to an enhancement in ferroelectric polarization. However, the effect of stress on the ferroelectric behavior of Hf 0.5 Zr 0.5 O 2 films exhibited distinct stages: improvement, saturation, and degradation. Our study presents novel findings revealing a saturation and degradation phenomenon of in-plane tensile stress on the ferroelectric properties of polycrystalline Hf 0.5 Zr 0.5 O 2 films, thereby partially resolving the discrepancies between experimental observations and theoretical predictions. The observed phase transformation induced by tensile stress in Hf 0.5 Zr 0.5 O 2 films played a crucial role in these effects. Furthermore, we found that the impact of the TiN top electrode thickness on other factors influencing ferroelectricity, such as grain size and oxygen vacancies, was negligible. These comprehensive results offer valuable insights into the influence of stress and TiN top electrode thickness on the ferroelectric behavior of Hf 0.5 Zr 0.5 O 2 films. [ABSTRACT FROM AUTHOR]

Ferroelectric (FE) electrocaloric materials research has been blossoming worldwide for solid-state refrigeration and potential cooling systems replacing thermoelectric Peltier coolers in microelectronics. In this work, we report the outcomes from a systematic study of combined phase transition (thermodynamics) based on the phenomenological Landau theory and distributed electric field (electrostatics of thin film interfaces) in FE bilayer films. Specifically, the compositional variation of ferroelectric bilayers results in broken spatial inversion symmetry leading to asymmetric thermodynamic potentials due to a combination of normal (first- and second-order phase transition) and relaxor (dispersive dielectric constant) ferroelectric behaviors devised for efficient electrocaloric cooling effects. Extensive theoretical analyses conducted for bilayers consisting of insulating materials highlight modified phase transition temperature behavior and self-poling by effective electric field amplification arising due to bilayers' electrostatic coupling yielding significant changes in isothermal entropy (ΔS) and adiabatic temperature (ΔT). The theoretical calculation insights supported with experimental results signify, through case studies for a combination of materials experimental parameters, that amplification of the local electric field and materials engineering maximize the number of coexisting phases at or away from the morphotropic phase boundary of constituent layers in bilayer thin film architectures, which can be applicable toward other classes of materials and multilayer systems. These are effective ways for efficient cooling, in general, and for microelectronics thermal management either directly or by developing a thermal switch with phase change materials integrated with thermoelectric coolers for residual heat dissipation, both at the system and on-chip levels. [ABSTRACT FROM AUTHOR]

While the influence of various fabrication parameters during deposition on the ferroelectricity of hafnium oxide has been extensively studied, the effect of different atmospheres on the actual switching process has not yet been investigated. In this work, we characterized the ferroelectric properties of undoped hafnium oxide prepared by reactive sputtering under three different atmospheres: dry oxygen/nitrogen, wet nitrogen, and vacuum conditions. We found a significant correlation between dry and wet atmospheres and resulting polarization. Specifically, we observed a direct effect on ferroelectric switching when the film was exposed to dry atmospheres and vacuum, resulting in a higher electric field necessary to initialize the wake-up effect due to an initial imprint effect. Increasing the amount of wet nitrogen during switching decreased the imprint and lowered the necessary voltage required for the wake up. We present a simple model that explains and discusses the incorporation of moisture and its resulting consequences on the ferroelectric properties of hafnium oxide. Additionally, kinetic Monte Carlo simulations showed that the addition of protons to the oxide thin film leads to a lowering of the potential and to a redistribution of protons and oxygen vacancies, which reduces the initial imprint. [ABSTRACT FROM AUTHOR]

Ferroelectric oxide becomes the focus of memory industry again after the discovery of ferroelectricity in doped-HfO 2 polycrystalline films. Thermal stress is an important factor for the variation of ferroelectric phase content. In this paper, the effect of film stress induced by Y 2 O 3 interlayer in the ferroelectric properties of Y-doped HfO 2 (Y: HfO 2) ferroelectric films, which is deposited by chemical solution deposition (CSD), is investigated systematically by polarization-voltage measurement. Compared with Y-doped HfO 2 film without interlayer, 1 nm Y 2 O 3 interlayer enhances the remanent polarization of Y: HfO 2 film due to the effects of film stress and surface energy. And thick Y 2 O 3 interlayer benefits to reduce leakage current density. But polarization switching of HfO 2 film is restrained due to the capacitor voltage divider caused by thick Y 2 O 3 interlayer. The obvious enhance effect of Y 2 O 3 interlayer still exists in Y: HfO 2 film at high voltage due to the breakdown of Y 2 O 3 interlayer, realizing a huge remanent polarization (P r) of 22.8 μC/cm2 in Y: HfO 2 film (doping content: 4 at %). It is 3.6 times than that of ferroelectric doped-HfO 2 film without Y 2 O 3 interlayer. [ABSTRACT FROM AUTHOR]

BiFeO 3 (BFO), as a kind of narrow band-gap semiconductor material, has gradually emerged advantages in the application of photocatalysis. In this paper, Ca doped BFO nanoparticles Bi 0.9 Ca 0.1 FeO 3 (BCFO) were prepared by sol-gel method. And BCFO and CdS nanocomposites with two morphologies were obtained by controlling the time of loading CdS under a low temperature liquid phase process. It is found that the band gap becomes narrower after doping Ca into BFO, which is conducive to the absorption of visible light. Among all the samples, the composite of CdS nanowires and BCFO nanoparticles obtained by reaction time of 10 min has the best photocatalytic performance. The degradation rate of Methyl Orange solution was 94% after 90 min under visible light irradiation, which was much higher than that of pure BCFO and CdS. Furthermore, significant enhancement in the degradation rate (100% degradation in 60 min) can be achieved in poled samples after electric polarization process. The highest degradation rate is due to the promoted separation of photogenerated carriers induced by the internal polarization field and the formation of S-scheme heterostructure between BCFO and CdS. Such BCFO-CdS nanocomposites may bring new insights into designing highly efficient photocatalyst. [Display omitted]. [ABSTRACT FROM AUTHOR]

The first-principles calculations are employed to investigate the Ce doping effects on the ferroelectricity of the Aurivillius-structured CaBi 2 Nb 2 O 9 (CBN). The formation energy is calculated for the Ce substituting the Bi site model and the Ce substituting the Ca site model, it is noted that the former is more stable than the latter. The NbO 6 octahedron distortion of the Ce/Bi model is increased due to the long-range effect of the Ce doping. By analyzing the partial density of states (PDOS), the Bader charge and the electron localization function (ELF), it is found that the extra electrons are introduced by the Ce doping, and transferred to the atoms of O2, O5, Nb and Bi. Thus, the electronic orbital hybridizations of O2-Nb, O5-Bi, and O2-Bi are enhanced by the extra electrons, and the enhancement of the orbital hybridization is the main reason of the enhancement of the spontaneous polarization (P s) comparing with intrinsic CBN. These findings could be used as a theoretical reference for future researches on the bismuth layer-structured ferroelectrics (BLSFs). In this paper, there are the following two highlights. • Comparing the formation energy of the Ce substituting the Bi site of CBN (Ce/Bi) model and that of the Ce doping in the Ca site of CBN (Ce/Ca) model, it is found that the former is more stable than the latter. Our calculations clarify the long time puzzle of the substituting of the Ce doping in CBN. • By analyzing the PDOS, the Bader charge and the ELF, it is found that extra electrons are introduced in the Ce/Bi model by the Ce doping, and are transferred to the atoms of O2, O5, Nb, and Bi. The electronic orbital hybridizations of the Ce/Bi model are enhanced due to the introduction of the extra electrons, and the enhancement of the orbital hybridization is just the reason of the enhancement of the spontaneous polarization comparing with intrinsic CBN. [ABSTRACT FROM AUTHOR]

Sodium bismuth titanate-based ferroelectric materials have a promising application in modern microdevices due to their strong ferroelectricity and high Curie temperature. The domain structure plays a crucial role in the piezoelectric and ferroelectric properties of (1- x)(Bi 0.5 Na 0.5)TiO 3 - x BaTiO 3 ((1- x)BNT- x BT)(x =0, 0.06, 0.08, 0.10) ceramic coatings. In this paper, (1- x)BNT- x BT ceramic coatings were prepared by supersonic plasma spraying. Piezoresponse-force microscopy (PFM) was employed to gain insight into the microscopic domain evolution of (1- x)BNT- x BT ceramic coatings. Piezoelectric-force Microscopy (PFM) results show that the 0.92BNT-0.08BT ceramic coating exhibits relatively homogeneous striped domains and island domains, as well as a maximum amplitude response with an average amplitude intensity of 67.6 pm, which increases the localized piezoelectric response of the ceramic coating. The switching spectroscopy piezoelectric-force microscopy (SS-PFM) results show that the local piezoelectric coefficient (PR max) of the 0.92BNT-0.08BT ceramic coating reaches 426.5 pm/V at 15 V, and the ferroelectric domains exhibit significant switching behavior. This study provides new ideas to further understand the relationship between microscopic electrical domains and macroscopic properties of these important lead-free piezoelectric ceramics. ● (1- x)(Bi 0.5 Na 0.5)TiO 3 - x BaTiO 3 ceramic coatings were prepared by supersonic plasma spraying. ● When x =0.08, the remnant polarization (P r) of the 0.92BNT-0.08BT ceramic coating reaches 28.9 μC/cm2, the coercive field (E c) is 30.6 kV/cm, and T m is 425.2 ℃. ● The 0.92BNT-0.08BT ceramic coating exhibits relatively homogeneous striped domains and island domains, as well as a maximum amplitude response with an average amplitude intensity of 67.6 pm, which increases the localized piezoelectric response of the ceramic coating. ● The local piezoelectric coefficient (PR max) of the 0.92BNT-0.08BT ceramic coating reaches 426.5 pm/V at 15 V, and the ferroelectric domains exhibit significant switching behavior. [ABSTRACT FROM AUTHOR]

This paper presents a variational modeling framework for investigating the flexoelectricity-driven evolution of remanent polarization in piezoceramics. In small-scale electromechanical systems, strain gradients can exhibit polarization in dielectric materials via the direct flexoelectric effect. In ferroelectrics, it is reasonable to expect that a sufficiently large magnitude of the flexoelectricity leads to a switching of the domain structure and thus the material becomes remanently polarized. It is interesting to note that this means that poling would be able to occur in the absence of any external electrical source. This provides the motivation to gain a better understanding of this effect for a possible technical use in e.g. sensor applications. For this purpose, a macroscopic model is presented that couples flexoelectricity and ferroelectric domain switching processes. By embedding the model in the variational framework of the generalized standard materials (GSM), a minimum-type potential structure and thus a stable and efficient numerical treatment is obtained. A mixed finite element formulation based on the Helmholtz free energy is introduced to solve the higher-order flexoelectric boundary value problem. In order to realistically predict the flexoelectric material behavior, the model response is adapted to experimental results in literature obtained for a piezoceramic in a bending test. By simulations based on the adapted model the evolution of the flexoelectricity-driven remanent polarization in the vicinity of a notch is shown. • A variational modeling framework for flexoelectric problems is introduced. • A mixed finite element formulation based on Helmholtz free energy is used. • The model response is adapted to experimental results on the flexoelectric effect. • The flexoelectricity-driven remanent polarization in piezoceramics is investigated. [ABSTRACT FROM AUTHOR]

Electric polarization typically originates from non-centrosymmetric charge distributions in compounds. In elemental crystalline materials, chemical bonds between atoms of the same element favor symmetrically distributed electron charges and centrosymmetric structures, making elemental ferroelectrics rare. Compared to atoms, elemental clusters are intrinsically less symmetric and can have various preferred orientations when they are assembled to form crystals. Consequently, the assembly of clusters with different orientations tends to break the inversion symmetry. By exploiting this concept, we show that sliding ferroelectricity naturally emerges in trilayer quasi-hexagonal phase (qHP) C60, a cluster-assembled carbon allotrope recently synthesized. Compared to many metallic or semi-metallic elemental ferroelectrics, trilayer qHP C60's have sizable band gaps and several ferroelectric structures, which are distinguishable by measuring their second-harmonic generation (SHG) responses. Some of these phases show both switchable out-of-plane and in-plane polarizations on the order of 0.2 pC/m. The out-of-plane and in-plane polarizations can be switched independently and enable an easy-to-implement construction of Van der Waals homostructures with ferroelectrically switchable chirality. [ABSTRACT FROM AUTHOR]

Non-toxic molecular ferroelectrics have attracted significant interest due to their unique flexibility, low costs, and environmental friendliness. However, such materials with narrow bandgaps and ferroelectricity above room temperature (RT) are still scarce. Herein, we present a brand-new lead-free molecular ferroelectric [C8N2H22]1.5[Bi2I9] synthesized hydrothermally. [C8N2H22]1.5[Bi2I9] features a zero-dimensional (0D) structure with a polar space group of Pc, as confirmed by single-crystal X-ray diffraction and second-harmonic generation (SHG) analyses. The RT hysteresis loop reveals the intrinsic ferroelectricity of [C8N2H22]1.5[Bi2I9] with a spontaneous polarization (Ps) of 1.3 μC cm−2. A visible-light optical bandgap has been confirmed by UV-vis spectroscopy and theoretical calculations. A notable ferroelectric photovoltaic (PV) effect has been revealed in [C8N2H22]1.5[Bi2I9]-based photoelectric devices with an open-circuit voltage (Voc) of 0.39 V and a short-circuit current density (Jsc) of 2.3 μA cm−2 under AM 1.5G illumination. The PV performance can be significantly enhanced by tuning the ferroelectric polarization, achieving a maximum Voc of 0.47 V and Jsc of about 50 μA cm−2. This study offers a novel member of the 0D lead-free hybrid organic–inorganic molecular ferroelectric family possessing great promise for optoelectronic devices. [ABSTRACT FROM AUTHOR]

Extending ferroelectric materials to two-dimensional limit provides versatile applications for the development of next-generation nonvolatile devices. Conventional ferroelectricity requires materials consisting of at least two constituent elements associated with polar crystalline structures. Monolayer graphene as an elementary two-dimensional material unlikely exhibits ferroelectric order due to its highly centrosymmetric hexagonal lattices. Here, we report the observations of electronic ferroelectricity in monolayer graphene by introducing asymmetric moiré superlattice at the graphene/h-BN interface, in which the electric polarization stems from electron-hole dipoles. The polarization switching is probed through the measurements of itinerant Hall carrier density up to room temperature, manifesting as standard polarization-electric field hysteresis loops. We find ferroelectricity in graphene moiré systems exhibits generally similar characteristics in monolayer, bilayer, and trilayer graphene, which indicates layer polarization is not essential to observe the ferroelectricity. Furthermore, we demonstrate the applications of this ferroelectric moiré structures in multi-state nonvolatile data storage with high retention and the emulation of versatile synaptic behaviors. Our work not only provides insights into the fundamental understanding of ferroelectricity, but also demonstrates the potential of graphene for high-speed and multi-state nonvolatile memory applications. Monolayer graphene, with its highly centrosymmetric hexagonal lattice, is typically not considered ferroelectric. Here, the authors observe ferroelectricity in monolayer graphene by introducing asymmetric moiré superlattices, where polarization arises from electron-hole dipoles. [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]

In this study, in situ piezoelectricity was incorporated into the photoactive region to prepare a self-powered deep-ultraviolet photodetector based on a mixture of polyvinylidene fluoride (PVDF)@Ga2O3 and polyethyleneimine (PEI)/carbon quantum dots (CQDs). A ferroelectric composite layer was prepared using β-Ga2O3 as a filler, and the β-phase of PVDF was used as the polymer matrix. The strong piezoelectricity of β-PVDF can facilitate the separation and transport of photogenerated carriers in the depletion region and significantly reduce the dark current when the device is biased with an external bias, resulting in a high on/off ratio and high detection capability. The self-powered PD exhibited specific detectivity (D* = 3.5 × 1010 Jones), an on/off ratio of 2.7, and a response speed of 0.11/0.33 s. Furthermore, the prepared PD exhibits excellent photoresponse stability under continuous UV light, with the photocurrent retaining 83% of its initial value after about 500 s of irradiation. Our findings suggest a new approach for developing cost-effective UV PDs for optoelectronic applications in related fields. [ABSTRACT FROM AUTHOR]

In this study, a passive control strategy of inductive power transfer (IPT) using ferroelectric multilayer ceramic chip capacitors (MLCCs) is presented. The required system parameters, i.e., ferroelectric hysteresis, frequency of the IPT, and voltage range across the MLCCs are reported. The receiver circuit consists only of a parallel resonant circuit, a halfwave rectifier and a load; the passive control of the IPT is achieved exclusively by the nonlinear properties of the ferroelectric MLCCs. The stabilization of the secondary output voltage ULoad at constant load is experimentally evaluated for an inductive coupling factor k between 10 % and 30 % for three nonlinear MLCCs #1, #2 and #3. With our proposed passive control strategy ULoad is maintained at -1.2 % and +0.6 % around a median value of 17.3 V (17.1 - 17.4 V) for k ∈ [20 %, 30 %] using MLCC #1, ±0.9 % around a median value of 11.2 V (11.1 - 11.3 V) for k ∈ [10 %, 18 %] using MLCC #2, and -1.6% and +2.6 % around a median value of 5.03 V (4.95 - 5.16 V) for k ∈ [16 %, 30 %] using MLCC #3. The proposed control principle is particularly advantageous for highly miniaturized microimplants, as it allows IPT control without additional semiconductors, sensors and vulnerable communication channels. [ABSTRACT FROM AUTHOR]

CuInP2S6 (CIPS) is an emerging 2D ferroelectric material known for disrupting spatial inversion symmetry due to Cu(I) position switching. Its ferroelectricity strongly relies on the Cu(I) atom/ion occupation ordering and dynamics. Nevertheless, the accurate Cu(I) occupations and correlated migration dynamics under the externally applied energy, which are key to unlocking ferroelectric properties, remain controversial and unresolved. Herein, an atomic-level direct imaging through aberration-corrected scanning transmission electron microscopy is performed to precisely trace the Cu(I) dynamic behaviours under electron-beam irradiation along (100)-CIPS. It clearly demonstrates that Cu(I) possesses multiple occupations, and Cu(I) could migrate to the lattice, vacancy, interstitial and interlayer sites between the InS6 octahedral skeletons of CIPS to form local CuxInP2S6 (x = 2-4) structure. Cu(I) multi-occupations induced lattice stress results in a layer sliding along the b-axis direction generating a sliding size of 1/6 b lattice constant. The CuxInP2S6 (x = 2-4) exists in a type of dynamic structure, only metastable with electron dose over 50 e− Å−2, thus generating a dynamic process of C u x In P 2 S 6 (x = 2 − 4) ⇌ CuIn P 2 S 6 , a completely unreported phenomenon. These findings shed light on the unveiled mechanism underlying Cu(I) migration in CIPS, providing crucial insights into the fundamental processes that govern its ferroelectric properties. The authors demonstrate that Cu(I) possesses multiple occupations, and Cu(I) migrate to the lattice, vacancy, interstitial and interlayer sites between the InS6 octahedral skeletons of CuInP2S6 to form local CuxInP2S6 (x = 2-4) structure. [ABSTRACT FROM AUTHOR]

Kaolinite possesses a structure with asymmetrically layered 1 : 1 dioctahedral aluminum silicate, and this structural property provides a useful platform for creating new cost-efficient functional materials that require noncentrosymmetric crystal packing. In this study, we prepared three covalently grafted kaolinites of propanediol (PD)/butanediol (BD)/glycerol (GL) by forming Al−O−C bonds between the OH groups of PD/BD/GL and the surface of kaolinite (K). Three covalently grafted kaolinites (K-PD, K-BD and K-GL) were characterized by X-ray diffraction, infrared spectroscopy, thermogravimetric analysis, scanning electron microscopy and microanalysis for C, H and N elements. The test of K-PD, K-BD and K-GL stirred with water at ambient conditions for 3 days demonstrated these hybrids showing extra high chemical stability to water. The dielectric spectra of three hybrids show two-step dielectric relaxation in the range of 1–107 Hz, and the P−E measurements revealed the existence of ferroelectricity at room temperature with the spontaneous polarization, the remanent polarization and the coercive field of ∼0.014 μC cm−2, ∼0.008 μC cm−2 and ∼0.426 kV cm−1 for K-PD, ∼0.017 μC cm−2, ∼0.011 μC cm−2 and ∼0.645 kV cm−1 for K-BD, and ∼0.018 μC cm−2, ∼0.011 μC cm−2 and ∼0.141 kV cm−1 for K-GL, respectively. [ABSTRACT FROM AUTHOR]

Nano-ferroelectric materials have excellent piezoelectric performance and can degrade organic dye by ultrasonic vibration in an aqueous solution. Here, BaTiO3 (BT) nanoparticles were prepared by a sol–gel/hydrothermal method and further applied in dye degradation in wastewater. BT nanoparticles exhibited excellent catalytic performance for organic dye molecule degradation through the piezo–Fenton synergistic effect. It was found that both the degradation efficiency and reaction rate were boosted by the increase of the molecular weight of organic dyes. The degradation efficiency toward different organic dyes exhibited a trend of CR > ABK > TH > RhB > MB > MO. For example, a high piezo–Fenton-catalytic degradation ratio of 82.8% at 5 min and 0.337 min−1 rate constant were achieved for the CR dye solution (10 mg L−1), which were 3.2 and 6.4 times the corresponding values of piezo-catalytic only degradation. These results mainly originate from the intrinsic properties of BT nanoparticles that can enhance the separation of charge and promote the formation of hydrogen peroxide (H2O2) and hydroxyl radicals (·OH) under ultrasonic vibration. Furthermore, the reaction of Fe(II) with H2O2 can further enhance the formation of ·OH, which can accelerate the degradation of organic dyes. These results indicate that the piezo–Fenton synergistic effect may provide a new clue for the development of the wastewater treatment field under mechanical vibration. [ABSTRACT FROM AUTHOR]

The growing contamination of water with endocrine-disrupting compounds (EDCs) is posing a serious threat to the reproductive, neuro, and other endocrine-related functions in humans and animals. One of the promising approach for degrading EDCs is photocatalytic degradation, because of its low energy consumption, mild reaction conditions and the absence of any secondary pollution. The visible light-active perovskite photocatalyst- bismuth ferrite (BiFeO3) possesses distinctive intrinsic polarization properties and its modification to design heterostructured BiFeO3–NiS2, BiFeO3–Bi2S3, and BiFeO3–NaNbO3 photocatalysts for EDCs degradation is reported. Upon modification of BiFeO3 with Bi2S3, the morphology changes from nanoparticles to rod-like structures. The BiFeO3–Bi2S3 photocatalyst exhibits higher degradation efficiency (98% and 96% for 17-β-estradiol and estrone, respectively, at pH 8) as compared to those of bare and modified BiFeO3 and follows pseudo-first-order kinetics. The dielectric constant (57 300) and polarization measurements undertaken demonstrate that the high dipole constant and high degree of polarization observed in the case of BiFeO3–Bi2S3 facilitate efficient separation of excitons and high dielectric loss owing to better conductivity enabling faster charge-carrier transfer kinetics, which eventually give rise to improved degradation of EDCs. Such improvement in the EDCs degradation efficacy is ascribed to the synergized effect of enhanced visible light harvesting, faster charge transfer kinetics, greater degree of excitons separation, and higher dielectric constant. [ABSTRACT FROM AUTHOR]

The stacking order and twist angle provide abundant opportunities for engineering band structures of two-dimensional materials, including the formation of moiré bands, flat bands, and topologically nontrivial bands. The inversion symmetry breaking in rhombohedral-stacked transitional metal dichalcogenides endows them with an interfacial ferroelectricity associated with an out-of-plane electric polarization. By utilizing twist angle as a knob to construct rhombohedral-stacked transitional metal dichalcogenides, antiferroelectric domain networks with alternating out-of-plane polarization can be generated. Here, we demonstrate that such spatially periodic ferroelectric polarizations in parallel-stacked twisted WSe2 can imprint their moiré potential onto a remote bilayer graphene. This remote moiré potential gives rise to pronounced satellite resistance peaks besides the charge-neutrality point in graphene, which are tunable by the twist angle of WSe2. Our observations of ferroelectric hysteresis at finite displacement fields suggest the moiré is delivered by a long-range electrostatic potential. The constructed superlattices by moiré ferroelectricity represent a highly flexible approach, as they involve the separation of the moiré construction layer from the electronic transport layer. This remote moiré is identified as a weak potential and can coexist with conventional moiré. Our results offer a comprehensive strategy for engineering band structures and properties of two-dimensional materials by utilizing moiré ferroelectricity. The authors demonstrate that ferroelectric polarizations in parallel-stacked twisted WSe2 can imprint their moiré potential onto a remote bilayer graphene, providing a comprehensive strategy for engineering band structures. [ABSTRACT FROM AUTHOR]

Multiferroic materials have been intensively pursued to achieve the mutual control of electric and magnetic properties. The breakthrough progress in 2D magnets and ferroelectrics encourages the exploration of low-dimensional multiferroics, which holds the promise of understanding inscrutable magnetoelectric coupling and inventing advanced spintronic devices. However, confirming ferroelectricity with optical techniques is challenging in 2D materials, particularly in conjunction with antiferromagnetic orders in single- and few-layer multiferroics. Here, we report the discovery of 2D vdW multiferroic with out-of-plane ferroelectric polarization in trilayer NiI2 device, as revealed by scanning reflective magnetic circular dichroism microscopy and ferroelectric hysteresis loops. The evolution between ferroelectric and antiferroelectric phases has been unambiguously observed. Moreover, the magnetoelectric interaction is directly probed by magnetic control of the multiferroic domain switching. This work opens up opportunities for exploring multiferroic orders and multiferroic physics at the limit of single or few atomic layers, and for creating advanced magnetoelectronic devices. The authors find the coexistence of ferroelectric and antiferroelectric states induced by chiral degeneracy in helical magnetic order in trilayer NiI2, along with the emergence of exotic magnetoelectric coupling. [ABSTRACT FROM AUTHOR]

Using a microscopic model and Green's function theory, we have investigated the co-doping effect on ferroelectric KNbO3 nanoparticles. Let us emphasize that while the doping with transition metal ions at the Nb site leads an increase in the ferromagnetism and a reduction the band gap, it also decreases the ferroelectricity. On the other hand, doping with La or Ba at the K site leads to enhanced polarization, but does not lead to the appearance of ferromagnetism and reduction in the band gap. Therefore, we have studied co-doping with La/Cr and La/Co ions, which leads to increasing the magnetization and polarization as well as to strongly decreasing the band gap energy. Thus, we observe a multiferroic material with room-temperature ferromagnetism and ferroelectricity as well as small band gap energy which can be tuned using various co-doping ions. There is a good agreement with the existing experimental data. [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]

Since the first report of ferroelectricity in nanoscale HfO2-based thin films in 2011, this silicon-compatible binary oxide has quickly garnered intense interest in academia and industry, and continues to do so. Despite its deceivingly simple chemical composition, the ferroelectric physics supported by HfO2 is remarkably complex, arguably rivaling that of perovskite ferroelectrics. Computational investigations, especially those utilizing first-principles density functional theory (DFT), have significantly advanced our understanding of the nature of ferroelectricity in these thin films. In this review, we provide an in-depth discussion of the computational efforts to understand ferroelectric hafnia, comparing various metastable polar phases and examining the critical factors necessary for their stabilization. The intricate nature of HfO2 is intimately related to the complex interplay among diverse structural polymorphs, dopants and their charge-compensating oxygen vacancies, and unconventional switching mechanisms of domains and domain walls, which can sometimes yield conflicting theoretical predictions and theoretical-experimental discrepancies. We also discuss opportunities enabled by machine-learning-assisted molecular dynamics and phase-field simulations to go beyond DFT modeling, probing the dynamical properties of ferroelectric HfO2 and tackling pressing issues such as high coercive fields. [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]

The promising candidate for designing a highly sensitive biosensor is the negative capacitance tunneling field effect transistor (NCTFET). In this paper, to enhance the sensitivity and performance of the biosensor, we combined inverted T-shaped structure with NCTFET. We introduce negative capacitance effects by stacking ferroelectric materials on the gate dielectric layer. This paper presents a detailed comparative analysis of the proposed inverted T-shaped-NCTFET and TFET based biosensors for different dielectric constants and charge densities of the nano-cavity between the channel and source region locations of biosensor. Sensitivity has been measured in terms of drain current, on-state current, current switching ratio, electric field, and transconductance sensitivity. To establish a benchmark, the sensitivity of the proposed biosensor is also compared with the published literature in order to determine its effectiveness. It is conferred from the results that our biosensor can be a better alternative for the detection of the various neutral and charged biomolecules. All the device simulations are performed in a TCAD environment using a well-calibrated structure. [ABSTRACT FROM AUTHOR]

Geometrically frustrated kagome materials reveal many novel states of matter ranging from quantum spin liquids to multiferroics. Herein, we study the compound CaFe3O(PO4)3, which has a quasi-two-dimensional lattice of Fe3+ ions with spin S = 5/2. Electrical and magnetic properties have been investigated on polycrystalline specimens of CaFe3O(PO4)3 using magnetization, pyroelectric, and magnetoelectric current measurements. The system undergoes a weak ferromagnetic-type ordering at TC1 ∼ 19.5 K, followed by another transition at TC2 ∼ 9 K. While no ferroelectric polarization (P) is observed at a zero magnetic field (H), the applied H induces P below TC2. At the temperature of 2.5 K, P starts to increase above H of 1 T, shows a maximum value at 3.15 T, and then decreases at higher H regions. The observed results suggest that CaFe3O(PO4)3 should be a magnetic-field-induced ferroelectric compound with frustrated magnetic couplings. [ABSTRACT FROM AUTHOR]

They found that metal contacts can facilitate the stabilization of the ferroelectric phase, enabling aggressive scaling of 2D ferroelectrics.[13] As a recently discovered vdW ferroelectric, -In SB 2 sb Se SB 3 sb exhibits inter-correlated in-plane and out-of-plane polarization.[[17]] Unlike traditional ferroelectric materials, which are usually insulators, -In SB 2 sb Se SB 3 sb is a semiconductor with a band gap of 1.36 eV (bulk). In recent years, a range of two-dimensional (2D) layered materials have been experimentally confirmed or theoretically predicted to be piezoelectric, pyroelectric, or ferroelectric.[[1], [3], [5], [7], [9]] Compared to their bulk counterparts, 2D piezoelectric, pyroelectric, and ferroelectric materials exhibit many intriguing properties, such as excellent size scaling, tunable bandgap, negative piezoelectric coefficient, and high mechanical flexibility.[[1], [3], [5], [7], [9]] Furthermore, the stackable nature of 2D layered materials makes them promising building blocks for designing functional heterostructures, where the 2D layers can be integrated with conventional piezoelectric, pyroelectric, and ferroelectric oxides and polymers. Piezoelectric, pyroelectric, and ferroelectric materials have attracted tremendous attention owing to their potential applications in nonvolatile memories, logic devices, photodetectors, sensors, actuators, transducers, and energy harvesting devices. 10.1063/5.0116445 40 X. Hong, A. Posadas, K. Zou, C. H. Ahn, and J. Zhu, "High mobility few layer graphene field effect transistors fabricated on epitaxial ferroelectric gate oxides", Phys. [Extracted from the article]

Ferroelectricity in thin films of HfO2 has been the subject of extensive studies in materials science as well as device applications. The emergence of ferroelectricity is attributable to the orthorhombic phase (Pca21) of HfO2, stabilized in the films by metal-element doping, strains from substrates and electrode films, and oxygen deficiency. Recently, ferroelectricity has been reported in nanolaminates of HfO2 with other oxides such as ZrO2 and Al2O3, implying that nanolaminates are another effective way to bring about ferroelectricity in HfO2. However, the mechanism of orthorhombic phase stabilization in nanolaminates is not fully understood. In this study, we demonstrated that ferroelectricity emerges in nanolaminates consisting of undoped HfO2 and perovskite SrHfO3 deposited on Sn-doped In2O3 bottom electrodes, when the thickness of HfO2 layers was ≥6 nm. For nanolaminates in which the thickness of the HfO2 layers was ≤5 nm, ferroelectricity was remarkably suppressed due to Sr-incorporation into the HfO2 layers at the interface. In those nanolaminates, the crystal orientations of HfO2 grains were well aligned throughout the HfO2 layers, indicating that the HfO2 layers grew in a pseudo-coherent manner. This study aids to understand the stabilization of the ferroelectric orthorhombic phase in nanolaminates in terms of their structural properties. [ABSTRACT FROM AUTHOR]

The double-wave method is widely used in ferroelectric measurements to eliminate the effects of conductance and capacitance components while preserving the ferroelectric domain contribution. However, in polycrystalline ferroelectric material, the assumption of the evolution of domains by the double-wave method no longer applies due to the domain back switch of de-field, and the domain contribution calculated by the current subtraction method is also problematic. Therefore, we proposed a new method to calculate the charge contribution of conductance and eliminate the conductance interference in the hysteresis loop. Finally, the feasibility of this new method is verified in many typical polycrystalline ferroelectric materials. This work provides a path for the study of ferroelectric properties of some high conductivity materials. [ABSTRACT FROM AUTHOR]