Electric Polarization Research Articles

A Bond-Based Machine Learning Model for Molecular Polarizabilities and A Priori Raman Spectra.

The use of machine learning (ML) algorithms in molecular simulations has become commonplace in recent years. There now exists, for instance, a multitude of ML force field algorithms that have enabled simulations approaching ab initio level accuracy at time scales and system sizes that significantly exceed what is otherwise possible with traditional methods. Far fewer algorithms exist for predicting rotationally equivariant, tensorial properties such as the electric polarizability. Here, we introduce a kernel ridge regression algorithm for machine learning of the polarizability tensor. This algorithm is based on the bond polarizability model and allows prediction of the tensor components at the cost similar to that of scalar quantities. We subsequently show the utility of this algorithm by simulating gas phase Raman spectra of biphenyl and malonaldehyde using classical molecular dynamics simulations of these systems performed with the recently developed MACE-OFF23 potential. The calculated spectra are shown to agree very well with the experiments and thus confirm the expediency of our algorithm as well as the accuracy of the used force field. More generally, this work demonstrates the potential of physics-informed approaches to yield simple yet effective machine learning algorithms for molecular properties.

Longitudinal Piezoelectricity and Polarization-Insensitive Oxidation in Janus vdWs Nb3SeI7.

As a newly discovered Janus van der Waals (vdW) material, semiconducting Nb3SeI7 offers several notable advantages, including spontaneous out-of-plane polarization, facile exfoliation to the monolayer limit, and significant out-of-plane emission dipole in second harmonic generation. These properties make it a promising candidate for piezoelectric and piezophototronic applications in highly efficient energy conversion. However, Nb3SeI7 is prone to oxidation when exposed to oxygen, which can severely limit the exploration and utilization of these intriguing physical properties. Therefore, understanding the oxidation mechanism of pristine Nb3SeI7 and its correlation with electrical polarization-an area that remains largely unexplored-is highly significant. In this study, the out-of-plane piezoelectricity of Nb3SeI7 is experimentally demonstrated, with a piezoelectric coefficient (|d33 eff|) of 0.76nmV-1. Furthermore, by combining near ambient-pressure X-ray photoelectron spectroscopy (NAP-XPS), Time-of-Flight secondary ion mass spectrometry (ToF-SIMS), and Density functional theory (DFT)calculations, it is revealed that the oxidation of Nb3SeI7 is self-limiting and independent of its electrical polarization, owing to the similar defect formation energies of Se and I atoms. This self-limiting and polarization-insensitive oxidation provides valuable insights into the stabilization mechanisms and expands the potential applications of out-of-plane piezoelectricity and other intriguing physical properties in Janus vdW Nb3SeI7.

Effects of boron and manganese doping on electrical poling and properties of 0.94(Bi0.5Na0.5)TiO3-0.06BaTiO3 piezoelectric ceramics

Effects of boron and manganese doping on electrical poling and properties of 0.94(Bi0.5Na0.5)TiO3-0.06BaTiO3 piezoelectric ceramics

Effect of Low Electric Field Polarization Condition on Properties of Cement-based Piezoelectric Ceramic Composite

Effect of Low Electric Field Polarization Condition on Properties of Cement-based Piezoelectric Ceramic Composite

Anti-plane Yoffe-type crack in flexoelectric material

This work investigates the deformation and polarization fields around a finite anti-plane shear (mode III) crack growing dynamically under steady-state conditions. The leading tip of this finite crack breaks the material while the trailing tip heals it. This fast moving finite crack (referred to as a rupture “pulse” in the geophysics literature) propagates with a constant velocity and with the mechanical and the electrical fields that remain invariant with respect to an observer moving with the crack-tips. This problem belongs to the first type of steady state crack growth problems according to the classification of Freund. The “prototype” problem which refers to an isotropic, body subjected to fracture under tensile loading was first proposed and solved by Yoffe, while finite cracks (or shear pulses) were also analyzed by Freund and by Rice. In the above cases the material was assumed to be linear elastic. Our analysis extends these studies to flexoelectric materials, and it is both theoretical and numerical. It discusses the asymptotic structure of the crack-tip displacement and the polarization fields; it calculates the dynamic energy release rate and presents their dependence on crack-tip velocity. Comparisons are made to the available, classical, elasto-dynamic solutions and to the static case. The influence of the electrical properties of the material on strengthening is also analyzed. Dynamic fracture of flexoelectric materials is of relevance to both the study of earthquake source mechanics and to the analysis of the reliability of micro-electronic devices. This is because both rocks and ceramics are flexoelectric. Indeed, during earthquake rupture processes, dynamic, in-plane shear (Mode-II) and out of plane shear (Mode-III), cracks propagate along faults and exhibit both mechanical and electrical polarization signatures. At an entirely different length scale, flexoelectric ceramics are currently used as sensors and transducers and can experience dynamic shear failure along interfaces when subjected to dynamic loading (e.g. impact.). Failure by dynamic fracture can be detrimental to both their mechanical reliability and electrical functionality.

Ambient Moisture-Induced Self Alignment of Polarization in Ferroelectric Hafnia.

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.

A Broad-High Temperature Ceramic Capacitor with Local Polymorphic Heterogeneous Structures.

Crafting high-performance dielectrics tailored for pulsed power capacitors, in response to the escalating demands of practical applications, presents a formidable challenge. Herein, this work introduces a novel lineup of lead-free ceramics with local polymorphic heterogeneous structures, defined by the formula (1-x)[0.92BaTiO3-0.08Sr(Mg1/2Ti3/4)O3]-x(Na0.5Bi0.5)TiO3 (BT-SMT-xNBT). This innovative multi-scale synergistic strategy, spanning from the atomic to grain scale, yields materials with a giant recoverable energy density (Wrec) of 10.1 J·cm-3 and an impressive energy efficiency (η) of 95.0%. The integration of linear end elements SMT can significantly mitigate the polarization hysteresis while concurrently boosting the breakdown strength, thus enhancing overall energy efficiency. Furthermore, the inclusion of NBT with high polarization serves to amplify domain size, thereby reinforcing the electric field-induced polarization. This addition also stimulates the creation of polymorphic heterostructures, where tetragonal and rhombohedral nanodomains coexist, as validated by aberration-corrected transmission electron microscopy. Notably, the BT-SMT-0.2NBT ceramics have demonstrated outstanding high-temperature energy storage capabilities, with a Wrec of 7.2 J·cm-3 and an η of 92.2% at 150 °C, along with remarkable broad-temperature stability (ΔWrec, Δη ≤ 4.0%, ≈20-150 °C). These achievements in this work propel the field toward more practical and durable solutions of energy storage dielectrics.

Polar order in a fluid like ferroelectric with a tilted lamellar structure – observation of a polar smectic C (SmCP) phase

The discovery of fluid states of matter with spontaneous bulk polar order is appreciated as a major discovery in the fields of soft matter and liquid crystals. Typically, this manifests as polar order superimposed atop conventional phase structures and is thus far limited to orthogonal phase types. Here we report a family of materials which exhibit a previously unseen state of matter which we conclude is a polar smectic C phase, and so we term it SmCP. The spontaneous polarisation of the SmCP phase is over two orders of magnitude larger than that found in conventional ferroelectric SmC phase of chiral materials used in some LCD devices. Fully atomistic molecular dynamics simulations faithfully and spontaneously reproduce the proposed structure and associated bulk properties; comparison of experimental and simulated X‐ray scattering patterns shows excellent agreement. The materials disclosed here have significantly smaller dipole moments than typical polar liquid crystals such as RM734 which suggests the role of molecular electrical polarity in generating polar order is perhaps overstated, a view supported by consideration of other molecular systems.

Polar order in a fluid like ferroelectric with a tilted lamellar structure - observation of a polar smectic C (SmCP) phase.

The discovery of fluid states of matter with spontaneous bulk polar order is appreciated as a major discovery in the fields of soft matter and liquid crystals. Typically, this manifests as polar order superimposed atop conventional phase structures and is thus far limited to orthogonal phase types. Here we report a family of materials which exhibit a previously unseen state of matter which we conclude is a polar smectic C phase, and so we term it SmCP. The spontaneous polarisation of the SmCP phase is over two orders of magnitude larger than that found in conventional ferroelectric SmC phase of chiral materials used in some LCD devices. Fully atomistic molecular dynamics simulations faithfully and spontaneously reproduce the proposed structure and associated bulk properties; comparison of experimental and simulated X-ray scattering patterns shows excellent agreement. The materials disclosed here have significantly smaller dipole moments than typical polar liquid crystals such as RM734 which suggests the role of molecular electrical polarity in generating polar order is perhaps overstated, a view supported by consideration of other molecular systems.

Synthesis, Crystal Structure, Intermolecular Interactions, HOMO-LUMO, MEP, NLO Properties, and DFT/TD-DFT Investigation of (Z)-5-(4-Nitrobenzylidene)-3-N(3-Chlorophenyl)-2-Thioxothiazolidin-4-One

A novel heterocyclic compound named (Z)-5-(4-nitrobenzylidene)-3-N(3-chlorophenyl)-2-thioxothiazolidin-4-one (NCTh) was synthesized and analyzed using various techniques, including single crystal X-ray diffraction, FT-IR, UV-Vis, NMR spectroscopy, and mass spectral data methods. NCTh was observed to crystallize in the triclinic crystal system P-1 space group. To validate the experimental findings, density functional theory (DFT) calculations were performed using the B3LYP functional with the 6-311 G(d,p) basis set. The results indicated good agreement in geometrical parameters between the experimental and theoretical outcomes. The study also calculated HOMO-LUMO energies, molecular electrostatic potential (MEP), and global chemical reactivity descriptors to evaluate the compound’s reactivity. Additionally, the study conducted reduced density gradient and Hirshfeld surface analyses to reveal attractive, repulsive, and van der Waals strong and weak interactions. The calculation of thermodynamic parameters was also included. The study focused on investigating the nonlinear optical (NLO) properties of NCTh, which were characterized through key parameters such as the electric dipole moment (µ), polarizability (α), first-order hyperpolarizability (β), and second-order hyperpolarizability (γ). These properties provide insights into the material’s potential applications in optical and photonic technologies. Additionally, a molecular docking study was performed to further explore the structure-activity relationship, particularly in a biological context. The docking results revealed a strong ligand-protein interaction, with a binding energy of −10.3 kcal/mol, indicating significant affinity. Moreover, the inhibition constant (Ki) was calculated to be 0.0281 μM, suggesting a highly potent interaction, which could be relevant for drug design or biochemical applications.

Hybrid topology optimization combining simulated annealing for designing unpolarized high-efficiency freeform metasurface in-coupler for augmented reality waveguide

High-efficiency in-couplers with unpolarized responses are crucial for the performance of waveguide augmented reality displays. Freeform quasi-3D metasurfaces (FQ3DM), which integrate freeform metasurfaces with multilayer films, is one possible solution to achieve this. However, the performance of FQ3DM is limited by the lack of inverse design algorithms capable of optimizing its overall structure. In this work, we proposed a hybrid topology optimization combining simulated annealing (HTO-SA) algorithm that alternates between topology optimization and simulated annealing to find the global optimum for both the shape and thickness of FQ3DM. With the HTO-SA algorithm, we designed an unpolarized high-efficiency in-coupler that achieves an average efficiency of 90% across a 20° field-of-view for both transverse electric and transverse magnetic polarization. We envision that our proposed approach can be generalized to the design of high-performance diffractive optical devices.

One-step high-speed thermal-electric aerosol printing of piezoelectric bio-organic films for wirelessly powering bioelectronics.

Piezoelectric biomaterials hold a pivotal role in the progression of bioelectronics and biomedicine, owing to their remarkable electromechanical properties, biocompatibility, and bioresorbability. However, their technological potential is restrained by certain challenges, including precise manipulation of nanobiomolecules, controlling their growth across nano-to-macro hierarchy, and tuning desirable mechanical properties. We report a high-speed thermal-electric driven aerosol (TEA) printing method capable of fabricating piezoelectric biofilms in a singular step. Electrohydrodynamic aerosolizing and in situ electrical poling allow instantaneous tuning of the spatial organization of biomolecular inks. We demonstrate TEA printing of β-glycine/polyvinylpyrrolidone films, and such films exhibit the piezoelectric voltage coefficient of 190 × 10-3 volt-meters per newton, surpassing that of industry-standard lead zirconate titanate by approximately 10-fold. Furthermore, these films demonstrate nearly two orders of magnitude improvement in mechanical flexibility compared to glycine crystals. We also demonstrate the ultrasonic energy harvesters based on the biofilms, providing the possibility of wirelessly powering bioelectronics.

The Discovery of Polarized Water Vapor Megamaser Emission in a Molecular Accretion Disk

For the first time in an extragalactic source, we detect linearly polarized H2O maser emission associated with the molecular accretion disk of NGC 1068. The position angles of the electric polarization vectors are perpendicular to the axes of filamentary structures in the molecular accretion disk. The inferred magnetic field threading the molecular disk must lie within ∼35° of the sky plane. The orientation of the magnetic fields relative to the disk plane implies that the maser region is unstable to hydromagnetically powered outflow; we speculate that the maser region may be the source of the larger-scale molecular outflow found in Atacama Large Millimeter/submillimeter Array studies. The new very long baseline interferometry observations also reveal a compact radio continuum source, NGC 1068*, aligned with the near-systemic maser spots. The molecular accretion disk must be viewed nearly edge on, and the revised central mass is M = (16.6 ± 0.1) × 106 M ☉.

Observation of converse flexoelectric effect in topological semimetals

A strong coupling between electric polarization and elastic deformation in solids is an important factor in creating useful electromechanical nanodevices. Such coupling is typically allowed in insulating materials with inversion symmetry breaking as exemplified by the piezoelectric effect in ferroelectric materials. Therefore, materials with metallicity and centrosymmetry have tended to be out of scope in this perspective. Here, we report the observation of giant elastic deformation by the application of an alternating electric current in topological semimetals (V,Mo)Te2, regardless of the centrosymmetry. Considering the crystal and band structures and the asymmetric measurement configurations in addition to the absence of the electromechanical effect in a trivial semimetal TiTe2, the observed effect is discussed in terms of a Berry-phase-derived converse flexoelectric effect in metals. The observation of the flexoelectric effect in topological semimetals paves a way for a new type of nanoscale electromechanical sensors and energy harvesting.

Oxygen vacancy induced defect dipoles in BiVO4 for photoelectrocatalytic partial oxidation of methane

A strong driving force for charge separation and transfer in semiconductors is essential for designing effective photoelectrodes for solar energy conversion. While defect engineering and polarization alignment can enhance this process, their potential interference within a photoelectrode remains unclear. Here we show that oxygen vacancies in bismuth vanadate (BiVO4) can create defect dipoles due to a disruption of symmetry. The modified photoelectrodes exhibit a strong correlation between charge separation and transfer capability and external electrical poling, which is not seen in unmodified samples. Applying poling at −150 Volt boosts charge separation and transfer efficiency to over 90%. A photocurrent density of 6.3 mA cm−2 is achieved on the photoelectrode after loading with a nickel-iron oxide-based cocatalyst. Furthermore, using generated holes for methane partial oxidation can produce methanol with a Faradaic efficiency of approximately 6%. These findings provide valuable insights into the photoelectrocatalytic conversion of greenhouse gases into valuable chemical products.

Submillisecond Electric Field Sensing with an Individual Rare-Earth Doped Ferroelectric Nanocrystal.

Understanding the dynamics of electrical signals within neuronal assemblies is crucial to unraveling complex brain functions. Despite recent advances in employing optically active nanostructures in transmembrane potential sensing, there remains room for improvement in terms of response time and sensitivity. Here, we report the development of such a nanosensor capable of detecting electric fields with a submillisecond response time at the single-particle level. We achieve this by using ferroelectric nanocrystals doped with rare-earth ions that produce upconversion (UC). When such a nanocrystal experiences a variation of surrounding electric potential, its surface charge density changes, inducing electric polarization modifications that vary, via a converse piezoelectric effect, the crystal field around the ions. The latter variation is finally converted into UC spectral changes, enabling optical detection of the electric potential. To develop such a sensor, we synthesized erbium and ytterbium-doped barium titanate crystals of ≈160 nm in size. We observed distinct changes in the UC spectrum when individual nanocrystals were subjected to an external field via a conductive atomic force microscope tip, with a response time of 100 μs. Furthermore, our sensor exhibits a remarkable sensitivity of 4.8 kV/cm/, enabling time-resolved detection of a fast-changing electric field of amplitude comparable to that generated during a neuron action potential.

Flexible Composites with Rare-Earth Element Doped Polycrystalline Particles for Piezoelectric Nanogenerators

Energy harvesting plays an important role in advancing personalized wearables by enabling continuous monitoring, enhancing wearable functionality and facilitating sustainable solutions. We aimed to develop a flexible piezoelectric energy harvesting system based on inorganic piezoelectric materials that convert mechanical energy into electricity to power a wide range of mobile and portable electronic devices. There is significant interest in flexible piezoelectric energy harvesting systems that use inorganic piezoelectric materials due to their exceptional physical features and prospective applications. Herein, we successfully demonstrated a flexible piezoelectric nanogenerator (PENG) designed by the co-doped rare-earth element ceramics (RE-PMN-PT) embedded in PVDF and PDMS composite film and attained a significant output performance while avoiding electrical poling process. The impact of dielectric characteristics on the electrical output of nanogenerators was investigated, together with the structure of the composites. The Sm/La-PMN-PT particles effectively amplify both the voltage and current output, showcasing their potential to power portable and wearable devices, as demonstrated by their capacity to illuminate LEDs. The maximal output power of 2 mW was correlated with the high voltage (220 V) and current (90 µA) of Sm/La-PMN-PT/PVDF, which demonstrated that the device has the potential for energy harvesting in biomedical applications.

Size Effect of Negative Capacitance State and Subthreshold Swing in Van der Waals Ferrielectric Field‐Effect Transistors

AbstractAnalytical calculations corroborated by the finite element modeling show that thin films of Van der Waals ferrielectrics covered by a 2D‐semiconductor are promising candidates for the controllable reduction of the dielectric layer capacitance due to the negative capacitance (NC) effect emerging in the thin films. The NC state is conditioned by energy‐degenerated poly‐domain states of the ferrielectric polarization induced in the films under incomplete screening conditions in the presence of a dielectric layer. Calculations performed for the FET‐type heterostructure “ferrielectric CuInP2S6 film—2D‐MoS2 single‐layer—SiO2 dielectric layer” reveal the pronounced size effect of the multilayer capacitance. Derived analytical expressions for the electric polarization and multilayer capacitance allow to predict the thickness range of the dielectric layer and ferrielectric film for which the NC effect is the most pronounced in various Van der Waals ferrielectrics, and the corresponding subthreshold swing becomes much less than the Boltzmann's limit. Obtained results can be useful for the size and temperature control of the NC effect in the steep‐slope ferrielectric FETs.

Engineering band structures of two-dimensional materials with remote moiré ferroelectricity.

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.

Rationally designed photothermal-pyroelectric Fe0.9Ni0.1S2/ZnSnO3 Z-scheme heterojunction for promoting electrical charge polarization towards optimized photocatalytic H2 evolution and intermolecular N-N coupling reaction

Developing a photocatalytic composite system that can couple hydrogen (H2) evolution and benzylamine (BA) oxidation is a challenging task, especially while avoiding sacrificial agents and value-added chemicals. Here, a practical approach is reported to develop a photothermal-pyroelectric-Fe0.9Ni0.1S2/ZnSnO3 photocatalytic system with core–shell and Z-scheme heterostructure via hydrothermal and annealing methods. Although Fe0.9Ni0.1S2 nanoparticles (NPs) could convert most of near-infrared (NIR) light energy into heat energy to drive the pyroelectric effect of ZnSnO3, it also results in temperature fluctuations (ΔT) in the system, causing natural polarization and thermoelectric effects under the condensed water circulation. As a result, the as-designed Fe0.9Ni0.1S2/ZnSnO3-2 composites could yield up to 7.194 mmol g-1h−1 with exceptional photocatalytic H2 evolution under simulated sunlight. This result is 5.41 and 4.92-fold those of Fe0.9Ni0.1S2 and ZnSnO3, respectively, with 16.66 % apparent quantum yield (AQY) under 365 nm monochromatic light. At the same time, the composites could also oxidize BA and yield up to 6.640 mmol g-1h-1n-benzylidene benzylamine (NBBA) with a 90.2 % selectivity. Due to the synergistic effect of Z-scheme’s built-in electric field and photothermal-pyroelectric of Fe0.9Ni0.1S2/ZnSnO3, the surface charges released on them could direct the charge transfer pathways and restrain their recombination with accelerated electron transfer kinetics, thus extending the carrier lifetime. This work offers a new perspective for designing electrical charge polarized by the photothermal-pyroelectric effect, which can enhance H2 evolution and BA oxidation concurrently.