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Ferroelectric materials undergo a phenomenon called domain switching when subjected to electric fields exceeding a critical yielding value: an irreversible polarisation arises, that can be removed only by applying an appropriate electric field in the opposite sense. Under a cyclic electric field, this results in a hysteretic behaviour in the relation between the electric field and the polarisation. The hysteresis loop is a measure of the energy dissipated in the ferroelectric switching process. In this study, we introduce a rate-independent model of ferroelectricity, inspired by small-deformation elastoplasticity models. Analogously to the yielding surface in elastoplasticity, we define the switching surface, the boundary of the domain of the admissible states of the system. States in the interior of the domain are reversible, while states on the surface can be either reversible or irreversible, based on the relation between the electric field and the derivative of the yielding function with respect to the electric field. We solve a two-dimensional benchmark boundary-value problem by applying two numerical methods, Finite Differences and Finite Elements. Our results demonstrate the effectiveness of both methods in capturing the nonlinearities and reproducing the electrical hysteresis loops typical of ferroelectric materials. This work establishes a foundational framework for modelling rate-independent ferroelectricity and paves the way for future research on comprehensive elastoplastic-ferroelectric models for piezoelectric materials. [ABSTRACT FROM AUTHOR]

In this work, a multi-stage material design framework combining machine learning techniques with density functional theory is established to reveal the mechanism of phase stabilization in HfO2 based ferroelectric materials. The ferroelectric phase fractions based on a more stringent relationship of phase energy differences is proposed as an evaluation criterion for the ferroelectric performance of hafnium-based materials. Based on the Boltzmann distribution theory, the abstract phase energy difference is converted into an intuitive phase fraction distribution mapping. A large-scale prediction of unknown dopants is conducted within the material design framework, and gallium (Ga) is identified as a new dopant for HfO2. Both experiments and density functional theory calculations demonstrate that Ga is an excellent dopant for ferroelectric hafnium oxide, especially, the experimentally determined variation trends of ferroelectric phase fraction and polarization properties with Ga doping concentration are in good agreement with the predictions given by machine learning. This work provides a new perspective from machine learning to deepen the understanding of the ferroelectric properties of HfO2 materials, offering fresh insights into the design and performance prediction of HfO2 ferroelectric thin films. [ABSTRACT FROM AUTHOR]

In recent years, Bismuth Ferrite (BiFeO3, BFO) has emerged as a promising multiferroic material due to its high antiferromagnetic Néel temperature (TN ~ 623–643 K) and ferroelectric Curie temperature (TC ~ 1083–1103 K). These properties make BFO a strong candidate for exhibiting a magnetoelectric effect even at room temperature. Understanding the temperature-dependent ferroelectric behavior of BFO is crucial for optimizing its performance in applications where stable ferroelectric behavior at operational temperatures is essential for enhancing device efficiency, stability, and functionality. This study investigates the impact of temperature on the crystallographic characteristics (unit cell type, bond lengths, and dimensions) and ferroelectric performance of BFO. X-ray diffraction and electrical hysteresis measurements confirm the presence of a ferroelectric phase with a rhombohedral R3c structure, along with two phase transitions: the first around 600 K from ferroelectric to paraelectric, and the second near 1050 K from paraelectric back to ferroelectric. [ABSTRACT FROM AUTHOR]

Polar topologies, such as vortex and skyrmion, have attracted significant interest due to their unique physical properties and promising applications in high-density memory devices. To date, all known polar vortices are present in or induced by ferroelectric materials. In this study, we find polar vortex arrays in paraelectric SrTiO3. Using multislice electron ptychography, the evolution of vorticity along the vortex axis is revealed in twisted bilayers of SrTiO3 with deep-sub-angstrom resolution and one picometer accuracy. The surprising finding of polar vortices in a paraelectric crystal opens up opportunities for polarization physics and corresponding new devices. The authors find polar vortex arrays in twisted paraelectric SrTiO3. By employing multislice electron ptychography, the atomic structures of different layers are effectively resolved, allowing for the identification of depth-dependent rotation reversal of the in-plane polarization. [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]

Intergrowth Aurivillius structure materials are found to be attractive owing to its complex nature and scientific point of view. Lanthanum (La) modified intergrowth compound was prepared by mixing the two-layered (LaxBi3-xTiNbO9: LBTN-x where, x = 0.25, 0.50 and 0.75) and three-layered (LayBi4-yTi3O12: LBT-y, where y = 0.25, 0.50 and 0.75) compounds in a stoichiometric ratio. The resultant novel intergrowth compound, represented as BLTNO-(x + y), where, x + y = 0, 0.50, 1.0 and 1.5), is prepared by solid state route. From the scanning electron microscope pictures, the average grain size is found to increase with the increasing of La substitution, and possessing a plate-like morphology. The X-ray diffraction (XRD) patterns and transmission electron microscopy (TEM) images confirm the formation of six-layered phase with orthorhombic crystal structure. Impedance data was measured as a function of frequency at different temperatures. From the combined ac-conductivity and master (scaling) plots it is revealed that the conduction mechanism belongs to thermally activated process. The variation of imaginary part of modulus (complimentary to dielectric) with temperature has shown anomalies near 350o C and the peak maximum is found to shift towards higher temperature, indicates the dielectric relaxation of the sample. The ac-conductivity data obeys Johnscher's law and the isotherms appear to fall onto a single curve. The results were corroborated to defect based hopping mechanism. The remnant polarization (Pr) is found to decrease with increasing the lanthanum concentration. The overall result from the structural, Raman and impedance spectroscopic data revealed that the intergrowth is a layered-engineered method and one can improve ferroelectric properties, arises from strain-induced lattice distortions at the interfaces. [ABSTRACT FROM AUTHOR]

In this paper, the thin-film ferroelectric material equation which enables a propagation of solitary polarization in thin-film ferroelectric materials, and it also can be described using the nonlinear evolution equations. Ferroelectrics are dielectric materials explain wave propagation nonlinear behaviors. Thin films made from the ferroelectric materials are used in various modern electronics devices. The Paul-Painlevé approach is adopted for the first time to solve these nonlinear thin-film equation analytically. To investigate the characterizations of new waves, the solitary wave dynamics of the thin-film ferroelectric material equation are obtained using the standard -expansion technique and generalized G-expansion method. The bright and periodic solutions are obtained by semi-inverse variational principle scheme. Many alternative responses are achieved utilizing various formulaes; each of these solutions is shown by a distinct graph. The validity of such methods and solutions are demonstrated by assessing how well the relevant techniques and solutions match up. Three novel analytical and numerical techniques provide new, dependable approaches for determining and estimating responses. The effect of the free variables on the behavior of reached solutions to a few of graphs on the exact solutions is also explored depending upon the nature of nonlinearities. The simulations, which are exhibited in both two-dimensional (2D) and three-dimensional (3D), depict the behavior of a solitary solution in both the natural and digital worlds. These findings demonstrate that this strategy is the most effective way to solve nonlinear mathematical physics problems. [ABSTRACT FROM AUTHOR]

Noncollinear dipole textures greatly extend the scientific merits and application perspective of ferroic materials. In fact, noncollinear spin textures have been well recognized as one of the core issues of condensed matter, e.g. cycloidal/conical magnets with multiferroicity and magnetic skyrmions with topological properties. However, the counterparts in electrical polarized materials are less studied and thus urgently needed, since electric dipoles are usually aligned collinearly in most ferroelectrics/antiferroelectrics. Molecular crystals with electric dipoles provide a rich ore to explore the noncollinear polarity. Here we report an organic salt (H2Dabco)BrClO4 (H2Dabco = N,N'−1,4-diazabicyclo[2.2.2]octonium) that shows a transition between the ferroelectric and antiferroelectric phases. Based on experimental characterizations and ab initio calculations, it is found that its electric dipoles present nontrivial noncollinear textures with 60o-twisting angle between the neighbors. Then the ferroelectric-antiferroelectric transition can be understood as the coding of twisting angle sequence. Our study reveals the unique science of noncollinear electric polarity. The authors find that the electric dipoles of a hybrid molecular material exhibit two kinds of intrinsic noncollinear textures, corresponding to its ferroelectric and antiferroelectric states. [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]

A fascinating aspect of nanoscale ferroelectric materials is the emergence of topological polar textures, which include various complex and stable polarization configurations. The manipulation of such topological textures through external stimuli like electric fields holds promise for advanced nanoelectronics applications. There are, however, several challenges to reach potential applications, among which reliably creating and controlling these textures at the nanoscale on silicon, and with lead-free compounds. We report the realization of epitaxial BaTiO3 nanoislands on silicon, with a lateral size as small as 30-60 nm, and demonstrate stable center down-convergent polarization domains that can be reversibly switched by an electric field to center up-divergent domains. Piezoresponse force microscopy data reconstruction and phase field modeling give insight into the 3D patterns. The trapezoidal-shape nanoislands give rise to center down-convergent lateral swirling polarization component with respect to the nanoisland axis, which prevents the formation of bound charges on the side walls, therefore minimizing depolarization fields. The texture resembles a swirling vortex of liquid flowing into a narrowing funnel. Chirality emerges from the whirling polarization configurations. The ability to create and electrically manipulate chiral whirling polar textures in BaTiO3 nanostructures grown monolithically on silicon holds promise for applications in future topological nanoelectronics. Epitaxial BaTiO3 ultra scaled nanoislands (30−60 nm) on Si exhibit an electrically switchable topological center down-convergent polar pattern. The peculiar island shape induces a lateral swirling component, which confers chirality to the polar domains. [ABSTRACT FROM AUTHOR]

This study investigated the piezoelectric properties of BaTiO3 ceramics with different sizes through molecular dynamics simulations. The results show that all samples reached thermal equilibrium at 300 K and equilibrium in potential energy within 10 ns, confirming effective equilibration. As the size of the ceramics increased, the mean square displacement and diffusion coefficients decreased from 0.217 and 0.0034 to 0.1934 Å2 and 0.003 Å2/ns, attributed to a more uniform microstructure with fewer defects, resulting in reduced ion mobility. Furthermore, saturation polarization, residual polarization, and coercive field values increased from 0.35, 0.1, and 0.175 to 0.42 C/m2, 0.16 C/m2, and 0.282 MV/m, respectively, with increasing sample size, highlighting enhanced polarization responses due to a greater volume of ferroelectric material. Larger barium titanate (BaTiO3) crystals can have better polarization due to more domains aligning, but they may not deform as much (lower strain) because the walls among those domains can't move freely. While improved domain alignment contributed to higher polarization, the increased stress can restrict the mobility of the domain walls. These findings provided valuable insights into the size-dependent behavior of BaTiO3 ceramics, essential for optimizing their applications in electronic devices and sensors. The study underscored the importance of understanding microstructural effects on material properties for future advancements in ferroelectric technology. [ABSTRACT FROM AUTHOR]

Background: The unique non-uniform polar nanoregions and complex phase structure near morphotropic phase boundaries (MPBs) in relaxor ferroelectric materials lead to rich microstructure changes (domain transition, phase transition) under external field stimulation. This not only results in the material with extremely high electromechanical properties, but also greatly affects their mechanical properties and stability. Objective: This study investigated the fundamental mechanical properties of the rhombohedral phase (R-phase) and tetragonal phase (T-phase) structures of the relaxor ferroelectric single crystal PMN-PT material using the nanoindentation with different shapes of indenters. Methods: The basic mechanical properties of the material were measured by nanoindentation, and the fracture caused by indentation was analyzed by scanning electron microscopy. Results: The elastic modulus of R-phase relaxed ferroelectric materials showed a significant dependence on the indentation depth, and the hardness of different phases (R, T-phase) materials all show obvious indentation size effects (ISE). Under the loading of the spherical indenter, both R and T phase materials exhibited a pop-in phenomenon caused by the transition from elastic to inelastic. Under the loading of the Berkovich indenter, the R and T phase materials showed different fracture characteristics of crack propagation response with the increase of the indentation depth. Conclusions: The result demonstrate that the mechanical properties of relaxor ferroelectric materials are significantly related to their phase structure, providing guidance for the design of load bearing and material selection in the practical application of related ferroelectric devices. [ABSTRACT FROM AUTHOR]

Intrinsic ferroelectric materials play a critical role in the development of high-density integrated device. Despite some two-dimensional (2D) ferroelectrics have been reported, the research on one-dimensional (1D) intrinsic ferroelectric materials remains relatively scare since 1D atomic structures limit their van der Waals (vdW) epitaxy growth. Here, we report the synthesis of 1D intrinsic vdW ferroelectric SbSI nanowires via a confined-space chemical vapor deposition. By precisely controlling the partial vapor pressure of I2 and reaction temperature, we can effectively manipulate kinetics and thermodynamics processes, and thus obtain high quality of SbSI nanowires, which is determined by Raman spectroscopy and high-resolution scanning transmission electron microscopy characterizations. The ferroelectricity in SbSI is confirmed by piezo-response force microscopy measurements and the ferroelectric transition temperature of 300 K is demonstrated by second harmonic generation. Moreover, the in-plane polarization switching can be maintained in the thin SbSI nanowires with a thickness of 20 nm. Our prepared 1D vdW ferroelectric SbSI nanowires not only enrich the vdW ferroelectric systems, but also open a new possibility for high-power energy storage nanodevices. [ABSTRACT FROM AUTHOR]

Information industry is one of the major drivers of the world economy. Its rapid growth, however, leads to severe heat problem which strongly hinders further development. This calls for a non-charge-based technology. Magnon, capable of transmitting spin information without electron movement, holds tremendous potential in post-Moore era. Given the cornerstone role of the field effect transistor in modern electronics, creating its magnonic equivalent is highly desired but remains a challenge. Here, we demonstrate a nonvolatile three-terminal lateral magnon field effect transistor operating at room temperature. The device consists of a ferrimagnetic insulator (Y3Fe5O12) deposited on a ferroelectric material [Pb(Mg1/3Nb2/3)0.7Ti0.3O3 or Pb(Zr0.52Ti0.48)O3], with three Pt stripes patterned on Y3Fe5O12 as the injector, gate, and detector, respectively. The magnon transport in Y3Fe5O12 can be regulated by the gate voltage pulses in a nonvolatile manner with a high on/off ratio. Our findings provide a solid foundation for designing energy-efficient magnon-based devices. Searching non-charge-based devices is crucial for sustainable information processing. Here, the authors make a nonvolatile magnon field effect transistor at room temperature, enabling efficient magnon transport control via the gate voltage pulses. [ABSTRACT FROM AUTHOR]

BiFeO3 (BFO) application in flexible wearable devices is garnering interest because of its unique ferroelectric and magnetic properties. However, the integration of high-quality BFO films onto flexible substrates presents significant technical challenges. Here, we successfully fabricated high-quality BFO films on mica substrates by using pulsed laser deposition, and report the fatigue characteristics of BFO films on flexible substrates for the first time. The results demonstrated that, after 108 bipolar switching cycles, the polarization only degraded by 0.28%, indicating superior fatigue characteristics compared to previously reported BFO films. Additionally, the device ferroelectric properties remained largely unchanged, with a bending radius of 3.5 mm. The fabricated flexible Pt/BFO/La0.65Sr0.35MnO3(LSMO)/SrTiO3(STO)/mica non-volatile memory devices exhibited mechanical flexibility and fatigue resistance. These findings not only highlight the potential of flexible BFO films for wearable electronic devices and flexible memory devices, they also provide valuable insight for the future development of high-performance flexible ferroelectric materials. [ABSTRACT FROM AUTHOR]

We investigated the multi-domain states of a multiferroic La-doped BiFeO3 (BLFO) thin film by examining diffraction patterns in optical second-harmonic generation (SHG) measurement. By directing a laser onto the domain wall within the domain-patterned sample, we observed clear diffraction signatures of SHG waves generated from two ferroelectric domains. We explained the experimental results of the diffraction patterns, including the intensity distribution and the polarization characteristics, using Fresnel propagation of SHG waves. From this, we could determine the amplitude and phase of the SHG waves generated from each domain, and figure out not only the polarization direction of each ferroelectric domain but also the phase related to the complex-valued second-order susceptibility tensor. Consequently, we could present SHG diffractometry as an effective measurement method to reveal the phase details of electric polarization of the multi-domain states of ferroic materials. [ABSTRACT FROM AUTHOR]

Compared to single-phase multiferroic materials, multiferroic (MF)-magnetoelectric (ME) composites, which combine magnetic and ferroelectric materials, show improved (many orders of magnitude) ME coupling and a higher operating temperature (beyond room temperature). In the present study, lead-free multiferroic Ni0.5Co0.5Fe2O4/BaTiO3 (NCFO/BTO) composites with different weight percentages were prepared through the solid-state reaction approach. The phase purity and structural confirmation were carried out using X-ray diffractograms. The XRD peak shifting in the composites has been observed, and it is attributed to the formation of residual stresses/strains during the sample's grinding, heating, and freezing processes. Fourier-transformative infrared spectroscopy confirmed the presence of metal-oxygen bonds in spinel NCFO and Ti-O and Ba-O bonds in perovskite BaTiO3. UV-vis spectra disclose the energy gap values of the magnetoelectric composites. It has been found that the energy gap values for pure ferrite are 1.53 eV, the pure ferroelectric phase is 2.99 eV, and the composites possess the Eg values of 1.78 eV, 2.33 eV, 2.77 eV with decreasing ferrite concentration. The M-H hysteresis loops reveal the ferromagnetic nature of pure ferrite as well as the presence of ferromagnetism in composites. The magnetic moment of the NCFO has been found as 2.26 µB and it further decreased to 0.59 µB for the 0.25NCFO-0.75BTO compound. The magneto crystalline anisotropy has been calculated using the law of approach (LA) method and the details are discussed in the paper. [ABSTRACT FROM AUTHOR]

The solid-state reaction approach was used to synthesize Ba0.95Sr0.05Ca5Ti2−xMxNb8O30 (where M represents Fe and Mn and x is 0 and 0.05) in order to compare the variations in the structural and dielectric properties of the ferroelectric material. The structural investigation was carried out using x-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. The orthorhombic structure with Pbcn space group revealed by the XRD investigation was validated by Rietveld refinement. The FTIR spectroscopy results were in good agreement with the reported phase. Analysis of the electrical properties was carried out by complex impedance spectroscopy. The results of transition metal doping with both Fe and Mn with regard to the dielectric permittivity as a function of frequency showed an improvement in the dielectric characteristics, while Mn exhibited a higher dielectric constant than Fe. The pure sample showed a lower transition temperature than the Fe- and Mn-doped sample. Analysis of the magnetic characteristics obtained from vibrating-sample magnetometry (VSM) revealed that doping enhanced the magnetic properties. This approach thus shows excellent potential for high-temperature operation, achieving good temperature stability via transition metal doping. [ABSTRACT FROM AUTHOR]

The piezotronics effect utilizes a piezopotential to modulate and control current in piezo-semiconductors. Ferroelectric materials, as a type of piezoelectric materials, possess piezoelectric coefficients that are significantly larger than those found in conventional piezoelectric materials. Here, we propose a strain modulated ferroelectric field-effect transistor (St-FeFET) utilizing external strain instead of gate voltage to achieve ferroelectric modulation, which eliminates the need for gate voltage. By applying a very small strain (0.01%), the St-FeFET can achieve a maximum on-off current ratio of 1250% and realizes a gauge factor (GF) of 1.19 × 106, which is much higher than that of conventional strain sensors. This work proposes a new method for realizing highly sensitive strain sensors and presents innovative approaches to the operation methods of ferroelectric field-effect transistors as well as potential applications for coupling of strain sensors and various devices across different fields. [ABSTRACT FROM AUTHOR]

In the past decade, ferroelectric materials have been intensively explored as promising photocatalysts. An intriguing ability of ferroelectrics is to directly sperate the photogenerated electrons and holes, which is believed to arise from a spontaneous polarization. Understanding how polarization affects the photocatalytic performance is vital to design high-efficiency photocatalysts. In this work, we report a size effect of ferroelectric polarization on regulating the photocatalytic overall water splitting of SrTiO3/PbTiO3 nanoplate heterostructures for the first time. This was realized hydrothermally by controlling the thickness and thus spontaneous polarization strength of single-crystal and single-domain PbTiO3 nanoplates, which served as the substrate for selective heteroepitaxial growth of SrTiO3. An enhancement of 22 times in the photocatalytic overall water splitting performance of the heterostructures has been achieved when the average thickness of the nanoplate increases from 30 to 107 nm. A combined experimental investigation revealed that the incompletely compensated depolarization filed is the dominated driving force for the photogenerated carrier separation within heterostructures, and its increase with the thickness of the nanoplates accounts for the enhancement of photocatalytic activity. Moreover, the concentration of oxygen vacancies for negative polarization compensation has been found to grow as the thickness of the nanoplates increases, which promotes oxygen evolution reaction and reduces the stoichiometric ratio of H2/O2. These findings may provide the opportunity to design and develop high-efficiency ferroelectric photocatalysts. [ABSTRACT FROM AUTHOR]

The trade-off between electrostrain and strain hysteresis for piezo/ferroelectric materials largely restrains the development of high precision actuators and remains unresolved over the past few decades. Here, a simple composition of (Bi0.5Na0.5)1-x/100Srx/100TiO3 in the ergodic relaxor state is collaboratively designed through the segregated domain structure with the ferroelectric core, local polarization heterogeneity, and defect engineering. The ferroelectric core can act as a seed to facilitate the field-induced nonpolar-to-polar transition. Together with the internal bias field caused by defect dipoles and adjusted through electric field cycling and heat treatment technology, a giant unipolar strain of 1.03% is achieved in the x = 30 ceramic with a low hysteresis of 27%, while the electric-field-independent large-signal piezoelectric strain coefficient of ~1000 pm/V and ultralow hysteresis of <10% can be obtained in the x = 35 ceramic. Intriguingly, the low-hysteresis high strain also exhibits near-zero remnant strain, excellent temperature and cycling stability. The development of precision piezo/ferroelectric actuators is hindered by the trade-off between electrostrain and strain hysteresis. Here, the authors report ferroelectric cores embedded into ergodic relaxor phase shells, showing giant unipolar strain and low hysteresis. [ABSTRACT FROM AUTHOR]

The effect of randomly distributed Ca dopants within the BaTiO3 lattice was investigated using first principle calculations. We examined electronic properties to understand how different orbitals contribute to the conduction and valence bands in doped materials. Our findings indicate that the valence band is primarily composed of Ti-3d and O-2p orbital states, while the conduction band is influenced by the collective contributions of Ba-4d, Ti-3d, and Ca-3d orbital states. Additionally, our results demonstrate a reduction in the bandgap due to Ca doping, with the extent of variation depending on the substituted sites of the Ca atoms. Furthermore, we investigated modifications in optical properties such as absorption, conductivity, dielectric function, refractive index, extinction coefficient, loss function, and reflectivity in the energy range from 0 to 40 eV. The findings reveal the stability of these characteristics in the infrared and visible light regions, and they also depend on the site substitution of Ca cations within the BaTiO3 lattice. We expected that our findings would deepen the understanding of the mechanism and site effect of Ca dopant on the properties of BaTiO3 materials, thereby contributing to the development of lead-free ferroelectric materials with enhanced properties for multifunctional applications. [ABSTRACT FROM AUTHOR]

Re-poling of unexpected partially depoled piezoelectric materials conventionally needs to be first fully depoled through annealing above their Curie temperature to revive piezoelectric performances. Here, we investigated de-poling and re-poling of Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 single crystals under electric fields at room temperature. We found that alternating current electric fields with amplitudes near the coercive field at low frequencies (<10 Hz) can be employed to successfully depolarize poled crystals at room temperature. We also demonstrated a reversible polarization switching process with a relaxor-PbTiO3 single crystal ultrasound transducer without device performance degradations. This experimental observation is supported by phase-field simulation, showing that alternating current electric fields can readily induce de-poling at room temperature, while direct current electric fields induce a transient depoled state only within an uncontrollable short period of time. The findings suggest new strategies for unprecedented in-device tailoring of the polarization states of ferroelectric materials. The authors find that alternating current electric fields with amplitudes near the coercive field at low frequencies (<10 Hz) can be employed to depolarize poled relaxor-PbTiO3 single crystals at room temperature, without conventional heat treatment. [ABSTRACT FROM AUTHOR]

The metastable nature of the ferroelectric phase of HfO2 is a significant impediment to its industrial application as a functional ferroelectric material. In fact, no polar phases exist in the bulk phase diagram of HfO2, which shows a dominant non-polar monoclinic ground state. As a consequence, ferroelectric orthorhombic HfO2 is stabilized either kinetically or via epitaxial strain. Here, we propose an alternative approach, demonstrating the feasibility of thermodynamically stabilizing polar HfO2 in superlattices with other simple oxides. Using the composition and stacking direction of the superlattice as design parameters, we obtain heterostructures that can be fully polar, fully antipolar or mixed, with improved thermodynamic stability compared to the orthorhombic polar HfO2 in bulk form. Our results suggest that combining HfO2 with an oxide that does not have a monoclinic ground state generally drives the superlattice away from this non-polar phase, favoring the stability of the ferroelectric structures that minimize the elastic and electrostatic penalties. As such, these diverse and tunable superlattices hold promise for various applications in thin-film ferroelectric devices [ABSTRACT FROM AUTHOR]

Electrocaloric refrigeration which is environmentally benign has attracted considerable attention. In distinction to ferroelectric materials, which exhibit an extremely high positive electrocaloric effect near the Curie temperature, antiferroelectric materials represented by PbZrO3 have a specific negative electrocaloric effect, i.e., electric field decreases the temperature of the materials. However, the explanation of the microscopic mechanism of the negative electrocaloric effect is still unclear, and further research is still needed to provide a theoretical basis for the negative electrocaloric effect enhancement. Herein, the antiferroelectric phase-field model has been proposed to design polar boundaries enhancing antiferroelectric negative electrocaloric performance in PbZrO3-based materials. Based on this, we have simulated the polarization response and domain switching process of the temperature and electric field-induced antiferroelectric—ferroelectric phase transition. It is shown that the temperature range tends to increase as the density of polar boundaries increases from the antiferroelectric stripe domain, polymorphic domain to the nanodomain. Among them, the peak adiabatic temperature change of antiferroelectric nanodomains can reach −13.05 K at 84 kV/cm, and a wide temperature range of about 75 K can be realized at 42 kV/cm. We expect these discoveries to spur further interest in the potential applications of antiferroelectric materials for next-generation refrigeration devices. [ABSTRACT FROM AUTHOR]

A review of dielectric materials with high (exceeding 10,000) values of relative permittivity is presented. Most of the compositions of these materials are based on systems that include ferroelectric and non-ferroelectric components, as well as solid solutions based thereon. Various approaches to increasing the permittivity of materials are considered, including doping, sintering atmosphere, grinding time, sintering temperature, and grain size. The effect of dopants and the synthesis method on the characteristics of capacitor ceramics that can be used in the low-frequency and high-frequency range are compared. [ABSTRACT FROM AUTHOR]

This article presents a study on the subthreshold swing (SS) and the ON–OFF current ratio of a negative capacitance source pocket double-gate tunnel field-effect transistor (NC-SP-DGTFET). In this analysis, a novel device is developed that integrates gate and channel engineering techniques. The combination of the ferroelectric material hafnium zirconium oxide (HZO) with the dielectric material SiO2 generates a negative capacitance (NC) effect. Additionally, the incorporation of a totally depleted source pocket into the DGTFET reduces the tunneling width. The addition of NC has the potential to improve the SS through the amplification of the electric field at the tunnel junction. Moreover, it has been observed that a fully depleted source pocket within the source/channel region significantly enhances the ION current when compared to the double-gate tunnel field-effect transistor (DGTFET). Following thorough device optimization, there has been a notable enhancement in the ION/IOFF current ratio, SS, and transconductance (gm) by a factor of 1.54 × 1013, 20.8 mV/dec, and 5.102 × 10−4 S/µm, respectively. These improvements signify superior energy efficiency and enhanced performance when compared to both DGTFET and source pocket based DGTFET (SP-DGTFET) configurations. Furthermore, substantial research has been conducted on the variation in electrical properties in relation to the thickness of ferroelectric materials. The findings indicate that the proposed device exhibits considerable potential as a viable option for applications requiring both low power consumption and high operational speed. [ABSTRACT FROM AUTHOR]

Highlights: Ferroelectricity and domain dynamics of emerging ferroelectric AlScN films were discussed. The performance optimization of ferroelectric AlScN films grown by different deposition techniques was comprehensively analyzed. The challenges and perspectives regarding the commercial avenue of AlScN-based memories and in-memory computing applications were summarized. Ferroelectrics have great potential in the field of nonvolatile memory due to programmable polarization states by external electric field in nonvolatile manner. However, complementary metal oxide semiconductor compatibility and uniformity of ferroelectric performance after size scaling have always been two thorny issues hindering practical application of ferroelectric memory devices. The emerging ferroelectricity of wurtzite structure nitride offers opportunities to circumvent the dilemma. This review covers the mechanism of ferroelectricity and domain dynamics in ferroelectric AlScN films. The performance optimization of AlScN films grown by different techniques is summarized and their applications for memories and emerging in-memory computing are illustrated. Finally, the challenges and perspectives regarding the commercial avenue of ferroelectric AlScN are discussed. [ABSTRACT FROM AUTHOR]

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

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

This study highlights the effect of copper oxide (CuO) doping on electrocaloric (EC) and energy storage (ES) properties of solid state synthesised 1-x(0.6[Ba(Zr0.2Ti0.8)O3]-0.4[(Ba0.7Ca0.3)TiO3])-xCuO (1-xBZCT-xCuO) ceramics with x = 0.005 to 0.05. The x-ray diffraction (XRD) analysis evidences the formation of impurity free 1-xBZCT-xCuO ceramics. Further, XRD, Raman and temperature dependent dielectric studies reveal that the inclusion of CuO into the BZCT lattice suppresses the morphotropic phase boundary (MPB) and reduces the tetragonality (c/a ratio) and consequently enhances the diffused phase transition (DPT) behaviour. The Curie temperature (Tc) shifted towards lower temperature, as the CuO content increases in 1-xBZCT-xCuO ceramics. Significantly, 0.995BZCT-0.005CuO ceramics demonstrated a maximum recoverable energy density (Wr) of 398 mJ/cm3 with an efficiency of 90 % under electric field of 100 kV/cm with an excellent heat stability. Moreover, EC effect exhibited a temperature change of 1.02 K at 30 kV/cm and a responsivity of 0.03 Kcm/kV near Tc. [ABSTRACT FROM AUTHOR]

Magnetoelectric composite materials, which exhibit both ferroelectric and ferromagnetic properties simultaneously, have attracted considerable interest for their potential in various applications such as microelectronics, memory devices, and spintronics. In this study, we investigated the synthesis, structural, morphological, electrical, and magnetic properties of multiferroic CoFe2O4/0.65BiFeO3-0.35PbTiO3 (CFO/65BF-35PT) composite thin films. These films were prepared using a high ferroelectric, morphotropic phase boundary (MPB) composition, 65BF-35PT, combined with a high magnetostrictive compound, CFO. Multilayered CFO/65BF-35PT composite films were spin-coated onto fluorine-doped tin oxide (FTO)/glass substrates using the sol-gel method, with variation in the solution molarity to achieve different layer thicknesses. Structural analysis revealed a perovskite phase for 65BF-35PT and a spinal structure for CFO, with the presence of rhombohedral and tetragonal polymorphs confirming MPB composition. Scanning electron microscope images demonstrated uniform growth of 1 μm thick composite films. Ferroelectric hysteresis loops exhibited considerable leakage current at room temperature, increasing with higher CFO content, while current versus voltage plots revealed ohmic conduction at low applied fields and space charge limited current (SCLC) conduction at high fields in all composite films. The crossover field between ohmic and SCLC conduction decreased with increasing CFO content. Moreover, room-temperature magnetic hysteresis loops showed a decrease in saturation and coercive field with increasing CFO concentration, and the temperature-dependent magnetization response indicated a monotonic decrease, with magnetization vanishing around 800 K, confirming the magnetic order of CFO. Our findings demonstrate that stable ferroelectric and ferromagnetic phases can be achieved at low temperatures by depositing composite films containing CFO/MPB on a low-cost FTO substrate. [ABSTRACT FROM AUTHOR]

Materials with field-tunable polarization are of broad interest to condensed matter sciences and solid-state device technologies. Here, using hydrogen (H) donor doping, we modify the room temperature metallic phase of a perovskite nickelate NdNiO3 into an insulating phase with both metastable dipolar polarization and space-charge polarization. We then demonstrate transient negative differential capacitance in thin film capacitors. The space-charge polarization caused by long-range movement and trapping of protons dominates when the electric field exceeds the threshold value. First-principles calculations suggest the polarization originates from the polar structure created by H doping. We find that polarization decays within ~1 second which is an interesting temporal regime for neuromorphic computing hardware design, and we implement the transient characteristics in a neural network to demonstrate unsupervised learning. These discoveries open new avenues for designing ferroelectric materials and electrets using light-ion doping. Hydrogen-doping driven metal to ferroelectric phase transition in a complex oxide NdNiO3 is demonstrated. Transient negative differential capacitance and implementation of polarization decay into neural network for learning are then presented. [ABSTRACT FROM AUTHOR]

Van der Waals heterostructures have opened new opportunities to develop atomically thin (opto)electronic devices with a wide range of functionalities. The recent focus on manipulating the interlayer twist angle has led to the observation of out-of-plane room temperature ferroelectricity in twisted rhombohedral bilayers of transition metal dichalcogenides. Here we explore the switching behaviour of sliding ferroelectricity using scanning probe microscopy domain mapping and tunnelling transport measurements. We observe well-pronounced ambipolar switching behaviour in ferroelectric tunnelling junctions with composite ferroelectric/non-polar insulator barriers and support our experimental results with complementary theoretical modelling. Furthermore, we show that the switching behaviour is strongly influenced by the underlying domain structure, allowing the fabrication of diverse ferroelectric tunnelling junction devices with various functionalities. We show that to observe the polarisation reversal, at least one partial dislocation must be present in the device area. This behaviour is drastically different from that of conventional ferroelectric materials, and its understanding is an important milestone for the future development of optoelectronic devices based on sliding ferroelectricity. The authors study tunneling junctions in rhombohedral MoS2 bilayers and correlate their performance with the local domain layout. They show that the switching behavior in sliding ferroelectrics is strongly dependent on the pre-existing domain structure. [ABSTRACT FROM AUTHOR]

Ferroelectric materials, whose electrical polarization can be switched under external stimuli, have been widely used in sensors, data storage, and energy conversion. Molecular orbital breaking can result in switchable structural and physical bistability in ferroelectric materials as traditional spatial symmetry breaking does. Differently, molecular orbital breaking interprets the phase transition mechanism from the perspective of electronics and sheds new light on manipulating the physical properties of ferroelectrics. Here, we synthesize a pair of organosilicon Schiff base ferroelectric crystals, (R)- and (S)-N-(3,5-di-tert-butylbenzylidene)-1-((triphenylsilyl)oxy)ethanamine, which show optically controlled phase transition accompanying the molecular orbital breaking. The molecular orbital breaking is manifested as the breaking and reformation of covalent bonds during the phase transition process, that is, the conversion between C = N and C–O in the enol form and C–N and C = O in the keto form. This process brings about photo-mediated bistability with multiple physical channels such as dielectric, second-harmonic generation, and ferroelectric polarization. This work further explores this newly developed mechanism of ferroelectric phase transition and highlights the significance of photo-mediated ferroelectric materials for photo-controlled smart devices and bio-sensors. Switchable structural and physical bistability in ferroelectric materials can be achieved as result of molecular orbital breaking. Here, the authors describe the photo-mediated bistability in organosilicon Schiff base ferroelectric crystals for the modulation of dielectric, second-harmonic generation, and ferroelectric polarization and showing good in vitro biocompatibility. [ABSTRACT FROM AUTHOR]

Ferroelectric materials have important applications in transduction, data storage, and nonlinear optics. Inorganic ferroelectrics such as lead zirconate titanate possess large polarization, though they are rigid and brittle. Ferroelectric polymers are light weight and flexible, yet their polarization is low, bottlenecked at 10 μC cm−2. Here we show poly(vinylidene fluoride) nanocomposite with only 0.94% of self-nucleated CH3NH3PbBr3 nanocrystals exhibits anomalously large polarization (~19.6 μC cm−2) while retaining superior stretchability and photoluminance, resulting in unprecedented electromechanical figures of merit among ferroelectrics. Comprehensive analysis suggests the enhancement is accomplished via delicate defect engineering, with field-induced Frenkel pairs in halide perovskite stabilized by the poled ferroelectric polymer through interfacial coupling. The strategy is general, working in poly(vinylidene fluoride-co-hexafluoropropylene) as well, and the nanocomposite is stable. The study thus presents a solution for overcoming the electromechanical dilemma of ferroelectrics while enabling additional optic-activity, ideal for multifunctional flexible electronics applications. Wang et al. report large nonvolatile polarization in stretchable polymer ferroelectrics incorporating perovskite nanocrystals. The built-in electric field from poled ferroelectrics stabilises Frenkel defects via interfacial coupling, which can also enhance the polarization of nonferroelectrics. [ABSTRACT FROM AUTHOR]

A nonvolatile optical phase shifter is a critical component for enabling the fabrication of programmable photonic integrated circuits on a Si photonics platform, facilitating communication, computing, and sensing. Although ferroelectric materials such as BaTiO3 offer nonvolatile optical phase shift capabilities, their compatibility with complementary metal-oxide-semiconductor fabs is limited. Hf0.5Zr0.5O2 is an emerging ferroelectric material, which exhibits complementary metal-oxide-semiconductor compatibility. Although extensively studied for ferroelectric transistors and memories, its application to photonics remains relatively unexplored. Here, we show the optical phase shift induced by ferroelectric Hf0.5Zr0.5O2. We observed a negative change in refractive index at a 1.55 μm wavelength in a pristine device regardless of the direction of the applied electric field. The nonvolatile phase shift was only observed once in a pristine device. This non-reversible phase shift can be attributed to the spontaneous polarization within the Hf0.5Zr0.5O2 film along the external electric field. The authors present nonvolatile optical phase shift induced by ferroelectric hafnium zirconium oxide deposited on a SiN waveguide. This finding paves the way for largescale programmable photonic circuits for communication, computing, and sensing. [ABSTRACT FROM AUTHOR]

The unique spontaneous polarization property of ferroelectric material makes it to be a special catalyst in photocatalysis. The spontaneous polarization property can induce the formation of built-in electric field, which can improve the separation of photoelectrons and holes to affect photocatalytic performance. The internal electric field induced by spontaneous polarization can be influenced by multiple factors such as the morphology, the concentration of defect, the type of doped heteroatoms, as well as the composition of heterostructures. Besides, the preparation method, pretreating temperature, the strength of prepolarized external electric field of ferroelectric-based photocatalysts as well as the strength of external mechanical force or external magnetic field in photocatalytic reactions can influence the photocatalytic effectivity via influencing spontaneous polarization-induced internal electric field. Thus, it is urgently to unveil the mystery of structure-activity relationships for ferroelectric materials-based photocatalysts, which is usually uncertain. With this in mind, this review was provided for the role of various complex influencing factors on ferroelectric materials-based photocatalysis based on the latest advancement in the fields of new energy development, environmental remediation. In the beginning, the basic structure and properties of ferroelectric material are given. Then, popular synthesis methods of ferroelectric-based photocatalysts are summarized. After that, two main mechanisms of ferroelectric photocatalysis are discussed. The research progress of ferroelectric photocatalysis is then given emphatically according to the classification of photocatalytic reactions. Finally, the problems existing nowadays and the challenges facing in the future on the application of ferroelectric materials-based photocatalysts are outlined in the summary and outlook section. [ABSTRACT FROM AUTHOR]

This paper proposes a compact model for a top-gated negative capacitance-based carbon nanotube field-effect transistor (NC-CNTFET). The proposed model relies on a metal–ferroelectric–metal–insulator–semiconductor (MFMIS) configuration. A charge-based modelling approach is used for the top-gated CNTFET, where the surface charge of the CNT is calculated from chirality and gate bias. This charge is the same as the NC-CNTFET device's total charge, based on which the compact model for the proposed device is developed. The ferroelectric material of choice is hafnium silicon oxide (HfSiO). A comparison of the NC-CNTFET with the top-gated CNTFET (TG-CNTFET) is also shown. The results show an improved subthreshold slope and ON/OFF-current ratio in the NC-CNTFET because of the negative capacitance effect of the ferroelectric layer. The impact of different ferroelectric thicknesses is also shown, which suggests further improvement in device performance as the ferroelectric thickness increases. [ABSTRACT FROM AUTHOR]

With the development of wearable devices and hafnium-based ferroelectrics (FE), there is an increasing demand for high-performance flexible ferroelectric memories. However, developing ferroelectric memories that simultaneously exhibit good flexibility and significant performance has proven challenging. Here, we developed a high-performance flexible field-effect transistor (FeFET) device with a thermal budget of less than 400 °C by integrating Zr-doped HfO2 (HZO) and ultra-thin indium tin oxide (ITO). The proposed FeFET has a large memory window (MW) of 2.78 V, a high current on/off ratio (ION/IOFF) of over 108, and high endurance up to 2×107 cycles. In addition, the FeFETs under different bending conditions exhibit excellent neuromorphic properties. The device exhibits excellent bending reliability over 5×105 pulse cycles at a bending radius of 5 mm. The efficient integration of hafnium-based ferroelectric materials with promising ultrathin channel materials (ITO) offers unique opportunities to enable high-performance back-end-of-line (BEOL) compatible wearable FeFETs for edge intelligence applications. Using Zr-doped HfO2 and ultra-thin indium tin oxide, Li et al. develop flexible field-effect transistors with a memory window of 2.78 V and bending reliability to enable high-performance back-end-of-line compatible wearable devices. [ABSTRACT FROM AUTHOR]

Realization of higher-order multistates with mutual interstate switching in ferroelectric materials is a perpetual drive for high-density storage devices and beyond-Moore technologies. Here we demonstrate experimentally that antiferroelectric van der Waals CuInP2S6 films can be controllably stabilized into double, quadruple, and sextuple polarization states, and a system harboring polarization order of six is also reversibly tunable into order of four or two. Furthermore, for a given polarization order, mutual interstate switching can be achieved via moderate electric field modulation. First-principles studies of CuInP2S6 multilayers help to reveal that the double, quadruple, and sextuple states are attributable to the existence of respective single, double, and triple ferroelectric domains with antiferroelectric interdomain coupling and Cu ion migration. These findings offer appealing platforms for developing multistate ferroelectric devices, while the underlining mechanism is transformative to other non-volatile material systems. Materials with higher-order multistates are desired for non-Boolean high-density storage. Here the authors realized sextuple intrinsic polarization states in vdW CuInP2S6, and reversible transformation among sextuple-, quadruple-, and double-polarization orders. [ABSTRACT FROM AUTHOR]

This work highlights the electrocaloric (EC) and energy storage (ES) properties of 1-x(0.6Ba(Zr0.2Ti0.8)O3-0.4(Ba0.7Ca0.3)TiO3)-x(BiTa0.5La0.5)O3 (1-xBZCT-xBTL) ceramics with x = 0 to 0.05. The XRD studies revealed that inclusion of BTL content in BZCT does not induce any impurity phase. The peak splitting of BZCT near 2θ = 45 ∘ and 66 ∘ confirms the presence of morphotropic phase boundary corresponding to tetragonal and rhombohedral phases. Further, the solid solution formation of BZCT-BTL has suppressed its morphotropic phase boundary behaviour. The XRD, Raman and temperature dependent dielectric studies suggest the presence of pseudocubic phase in 1-xBZCT-xBTL at higher values of x = 0.025 and 0.05. Moreover, the inclusion of BTL boosts the diffused phase transition behaviour of BZCT ceramics. Further, BTL strengthened its relaxor nature due to a reduction in grain size as evidenced from SEM analysis. It is observed that the 0.99BZCT-0.01BTL ceramics show 95% efficiency and a maximum recoverable energy density of 479 mJ/cm3 at 100 kV/cm. Moreover, the electrocaloric temperature change and responsivity are found to be 1.06 K and 0.01 Kcm/kV near the transition temperature. [ABSTRACT FROM AUTHOR]

The separation of photogenerated electron–hole pairs is vitally important for photocatalysis, which can be effectively promoted by polarization field. However, it only manifests in piezoelectric/pyroelectric/ferroelectric materials that have a non-centrosymmetric structure. Here, we demonstrate that the polarization enhanced photocatalysis (with wide spectra from ultraviolet (UV) light to visible light) can be achieved in centrosymmetric semiconductors, such as δ-MnO2 and TiO2 nanosheets integrated nanoflowers, by using the strain-gradient-induced flexoelectric polarization that is always overlooked in polarization-enhanced catalysis. Under ultrasonic and illumination excitation, the organic pollutants (methylene blue (MB), etc.) can be effectively degraded within 30 min with excellent stability and repeatability. Compared with photocatalysis, the flexo-photocatalytic performance of above centrosymmetric semiconductors is substantially increased by 85%. Moreover, the factors related to flexo-photocatalysis such as material morphology, mechanical stimuli source, and adsorption are explored to deeply understand the mechanism of flexo-photocatalysis. This work opens up a way for high-performance photocatalysis in centrosymmetric semiconductors. [ABSTRACT FROM AUTHOR]

We present a new ferroelectric nematic material, 4-((4′-((trans)-5-ethyloxan-2-yl)-2′,3,5,6′-tetrafluoro-[1,1′-biphenyl]-4-yl)difluoromethoxy)-2,6-difluorobenzonitrile (AUUQU-2-N) and its higher homologues, the molecular structures of which include fluorinated building blocks, an oxane ring, and a terminal cyano group, all contributing to a large molecular dipole moment of about 12.5 D. We observed that AUUQU-2-N has three distinct liquid crystal phases, two of which were found to be polar phases with a spontaneous electric polarization Ps of up to 6 µC cm–2. The highest temperature phase is a common enantiotropic nematic (N) exhibiting only field-induced polarization. The lowest-temperature, monotropic phase proved to be a new example of the ferroelectric nematic phase (NF), evidenced by a single-peak polarization reversal current response, a giant imaginary dielectric permittivity on the order of 103, and the absence of any smectic layer X-ray diffraction peaks. The ordinary nematic phase N and the ferroelectric nematic phase NF are separated by an antiferroelectric liquid crystal phase which has low permittivity and a polarization reversal current exhibiting a characteristic double-peak response. In the polarizing light microscope, this antiferroelectric phase shows characteristic zig-zag defects, evidence of a layered structure. These observations suggest that this is another example of the recently discovered smectic ZA (SmZA) phase, having smectic layers with the molecular director parallel to the layer planes. The diffraction peaks from the smectic layering have not been observed to date but detailed 2D X-ray studies indicate the presence of additional short-range structures including smectic C-type correlations in all three phases—N, SmZA and NF—which may shed new light on the understanding of polar and antipolar order in these phases. [ABSTRACT FROM AUTHOR]

Understanding the nature of sliding ferroelectricity is of fundamental importance for the discovery and application of two-dimensional ferroelectric materials. In this work, we investigate the phenomenon of switchable polarization in a bilayer MoS2 with natural rhombohedral stacking, where the spontaneous polarization is coupled with excitonic effects through asymmetric interlayer coupling. Using optical spectroscopy and imaging techniques, we observe how a released domain wall switches the polarization of a large single domain. Our results highlight the importance of domain walls in the polarization switching of non-twisted rhombohedral transition metal dichalcogenides and open new opportunities for the non-volatile control of their optical response. Sliding ferroelectricity occurs in stacks of van der Waals materials. Depending on the particular stacking, the system can host a spontaneous polarization, and under an applied electric field, polarization domain walls will propagate transverse to the electric field. Here, Yang et al use an optical approach to directly observe this sliding of domain walls in bilayer MoS2. [ABSTRACT FROM AUTHOR]

Domain boundaries have been intensively investigated in bulk ferroelectric materials and two-dimensional materials. Many methods such as electrical, mechanical and optical approaches have been utilized to probe and manipulate domain boundaries. So far most research focuses on the initial and final states of domain boundaries before and after manipulation, while the microscopic understanding of the evolution of domain boundaries remains elusive. In this paper, we report controllable manipulation of the domain boundaries in two-dimensional ferroelectric In2Se3 with atomic precision using scanning tunneling microscopy. We show that the movements of the domain boundaries can be driven by the electric field from a scanning tunneling microscope tip and proceed by the collective shifting of atoms at the domain boundaries. Our density functional theory calculations reveal the energy path and evolution of the domain boundary movement. The results provide deep insight into domain boundaries in two-dimensional ferroelectric materials and will inspire inventive applications of these materials. Here, the authors realize controllable manipulation of polar domain boundaries in a two-dimensional ferroelectric material In2Se3. It reveals the origin of distinct behaviors for different domain boundaries in combination with density functional theory calculations. [ABSTRACT FROM AUTHOR]

Ferroelectrics are a class of polar and switchable functional materials with diverse applications, from microelectronics to energy conversion. Computational searches for new ferroelectric materials have been constrained by accurate prediction of the polarization and switchability with electric field, properties that, in principle, require a comparison with a nonpolar phase whose atomic-scale unit cell is continuously deformable from the polar ground state. For most polar materials, such a higher-symmetry nonpolar phase does not exist or is unknown. Here, we introduce a general high-throughput workflow that screens polar materials as potential ferroelectrics. We demonstrate our workflow on 1978 polar structures in the Materials Project database, for which we automatically generate a nonpolar reference structure using pseudosymmetries, and then compute the polarization difference and energy barrier between polar and nonpolar phases, comparing the predicted values to known ferroelectrics. Focusing on a subset of 182 potential ferroelectrics, we implement a systematic ranking strategy that prioritizes candidates with large polarization and small polar-nonpolar energy differences. To assess stability and synthesizability, we combine information including the computed formation energy above the convex hull, the Inorganic Crystal Structure Database id number, a previously reported machine learning-based synthesizability score, and ab initio phonon band structures. To distinguish between previously reported ferroelectrics, materials known for alternative applications, and lesser-known materials, we combine this ranking with a survey of the existing literature on these candidates through Google Scholar and Scopus databases, revealing ~130 promising materials uninvestigated as ferroelectric. Our workflow and large-scale high-throughput screening lays the groundwork for the discovery of novel ferroelectrics, revealing numerous candidates materials for future experimental and theoretical endeavors. [ABSTRACT FROM AUTHOR]

Stacking two atomic layers together can induce interlayer (sliding) ferroelectricity that is absent in their naturally occurring crystal forms. With the flexibility of two-dimensional materials, more layers could be assembled to give rise to even richer polarization states. Here, we show that three-layer boron nitride can host ferro- and antiferroelectric domains in the same sample. When used as a tunneling junction, the polarization of these domains could be switched in a layer-by-layer procedure, producing multiple resistance states. Theoretical investigation reveals an important role played by the interaction between the trilayer boron nitride and graphene substrate. These findings reveal the great potential and unique properties of 2D sliding ferroelectric materials. Here, the authors use three-layer boron nitride to construct interfacial ferro- and antiferroelectric tunnel junctions and find that the polarization is flipped in a layer-by-layer way, resulting in multiresistance states. [ABSTRACT FROM AUTHOR]

Ferroelectric materials exhibiting switchable and spontaneous polarization have strong potential to be utilized in various novel electronic devices. Solid solutions of different perovskite structures induce the coexistence of various phases and enhance the physical functionalities around the phase coexistence region. The construction of phase diagrams is important as they describe the material properties, which are linked to the underpinning physics determining the system. Here we present the phase diagram of (K0.5Na0.5NbO3)–(Ba0.5Sr0.5TiO3) (KNN-BST) system as a function of composition and their associated physical properties. Lead-free (1 − x)KNN–xBST (0 ≤ x ≤ 0.3) solid solution ceramics were synthesized by conventional solid-state reaction technique. The X-ray diffraction and Raman spectroscopic studies indicate composition-dependent structural phase transitions from an orthorhombic phase for x = 0 to orthorhombic + tetragonal dual-phase (for 0.025 ≤ x ≤ 0.15), then a tetragonal + cubic dual-phase (x = 0.2) and finally a cubic single phase for x ≥ 0.25 at room temperature (RT). Among these, the orthorhombic + tetragonal dual-phase system shows an enhanced value of the dielectric constant at room temperature. The phase transition temperatures, orthorhombic to tetragonal (TO-T) and tetragonal to cubic (TC), decrease with the increase in BST concentrations. The ferroelectric studies show a decrease of both 2Pr and EC values with a rise in BST concentration and x = 0.025 showed a maximum piezoelectric coefficient. [ABSTRACT FROM AUTHOR]

Ferroelectric ceramics, Ba0.95Sr0.05(Ti0.95Zr0.05)1–xSnxO3 (BSTZS), with varying Sn content (x = 0%, 2.5%, 5%, and 7.5%), were synthesized using the conventional solid-state reaction method. This study delves into the temperature-dependent ferroelectric behavior of BSTZS ceramics, with a focus on their potential for thermal energy conversion, assessed using the Olsen cycle. Operating the cycle within the temperature range of 25 to 110 °C and applying an electric field ranging from 0 to 30 kV/cm, we achieved an impressive maximum energy conversion density of 175 kJ/m3 per cycle for the composition with x = 5%. Notably, when compared to other lead-free ferroelectric materials, these results demonstrate a significantly high energy density, particularly for relatively modest electric fields and temperature gradients. Considering the impact of temperature on hysteresis parameters, we also provide insights into the relationship between remnant polarization (Pr) and temperature (T), along with scaling relations. The power-law exponents for hysteresis parameters in the examined compositions are determined. The scaling relations for coercive field (EC) and remnant polarization (Pr) are expressed with respect to T as follows: EC ∝ T −0.3803, EC ∝ T −0.8806, EC ∝ T −0.6010, and EC ∝ T −0.0389 for x = 0%, 2.5%, 5%, and 7.5%, respectively. Similarly, Pr ∝ T −0.364, Pr ∝ T −0.962, Pr ∝ T −2.170 and Pr ∝ T −4.018 for x = 0%, 2.5%, 5%, and 7.5%, respectively. Furthermore, we have employed the Arrhenius law to calculate the average activation energy for all materials. This calculation helps us estimate the behavior of back-switching polarization (Pbc) as a function of temperature. [ABSTRACT FROM AUTHOR]