Charge Polarization Research Articles

Impact of Ag2O on physical and electrical properties of Li2O-MgO-Bi2O3-SiO2 glass system as promising solid state electrolytes

The intrinsic aim of this work is to understand the influence of composition change on the physical-electrical parameters of glasses with the composition (20-Y) Li2O-YAg2O–20MgO–10Bi2O3-50SiO2 (Y = 0.25, 0.5, 1.0, 2.0 and 4.0 mol%). The results of the physical parameters indicate a growth in the strength of the glass structure with the increase replacement of Li2O by Ag2O. However, the decrease in loss factor ε″, and AC conductivity σac of glasses may be attributed to the decrease in the space charge polarization (scp). AC conductivities exhibit simple power law variation. The s values essentially lie in the range of 0.67–0.92, which is typical of conductors in Jonscher regime. Dielectric properties (constant ε′, loss ε″ and ac conductivity σac, over a range of frequency 100–100 kHz and temperature RT (Room Temperature)–200 °C and frequency exponent s) of these glasses have been studied The results indicate a great potential of the prepared glasses as promising materials that can be used for solid state electrolytes.

Nonvolatile Reconfigurable Transistor via Ferroelectrically Induced Current Modulation.

New logic in memory (LiM) architectures, able to unify memory and logic functionalities into a single component, are highly promising for executing self-learning algorithms such as artificial neural networks (ANNs), with lower energy requirements. The multigated reconfigurable field effect transistor (RFET) is a novel type of logic device that can be fully reconfigured at run-time, promising to be a very versatile platform for logic applications. If equipped with a memory element, then it would represent the ideal building block for LiM-enabling hardware with embedded self-learning capabilities. To reach this goal, here we investigate the integration of a ferroelectric Hf0.5Zr0.5O2 (HZO) layer onto dual top gated RFETs. We demonstrate that HZO polarization charges can be successfully employed to tune the height of the two Schottky barriers, influencing the injection behavior and allowing the selection of the majority carriers, thus defining the transistor mode and switching it between a fully p-type transport to a prevalently n-type one. Moreover, we show that the modulation strength is strongly dependent on the height of the pulse used to polarize the ferroelectric domains, allowing for the selection of different current levels. All the different achievable states show a good retention over time, owing to the stability of the HZO polarization. The limitations of the produced devices are discussed, alongside possible mitigation strategies. The presented results demonstrate that ferroelectric HZO can modulate the carrier injection across Schottky barriers in RFET devices. This approach paves the way for the future realization of a fully optimized nonvolatile RFET, an ideal building block for novel LiM hardware, enabling low-power circuits for ANN execution.

Insights into Co-Catalytic Single-Atom-Support Interactions for Boosting Sulfur Reduction Electrocatalysis.

The use of single-atom catalysts (SACs) with abundant electrocatalytic centers has been identified as the most desirable strategy to inhibit the shuttle effect in lithium-sulfur batteries. However, the co-contribution from SAC and its support via their interactions for accelerating the sulfur reduction reactions (SRR) has so far received little attention, since the underlying mechanism remains elusive. Herein, guided by density functional theory calculations, Cobalt-SACs supported on a graphitic carbon nitride substrate (Co-GCN), are selected to elucidate the co-catalytic role in enhancing the SRR. The inherent high charge polarity of GCN, combined with its unique tri-s-triazine structure, offers multiple binding sites for lithium polysulfides (LiPSs) through Li-N bonds, as well as N/C-coordinated frameworks for anchoring Co-SACs. This structural configuration further amplifies the interaction with LiPSs via Co-S bonds. Consequently, both Co-SACs and GCN actively participate in sulfur reduction electrocatalysis by binding LiPS intermediates, lowering the conversion energy barrier of SRR. Benefitting from such unique synergy, the battery demonstrates outstanding rate performance (718.9 mAh g-1 at 5.0 C) and yields a high areal capacity of up to 13.8 mAh cm-2 (1584.3 mAh g-1) under a high areal sulfur loading of 8.7 mg cm-2 but a low electrolyte/sulfur ratio of 5.0 μL mg-1.

Insights into Co‐Catalytic Single‐Atom‐Support Interactions for Boosting Sulfur Reduction Electrocatalysis

The use of single‐atom catalysts (SACs) with abundant electrocatalytic centers has been identified as the most desirable strategy to inhibit the shuttle effect in lithium‐sulfur batteries. However, the co‐contribution from SAC and its support via their interactions for accelerating the sulfur reduction reactions (SRR) has so far received little attention, since the underlying mechanism remains elusive. Herein, guided by density functional theory calculations, Cobalt‐SACs supported on a graphitic carbon nitride substrate (Co‐GCN), are selected to elucidate the co‐catalytic role in enhancing the SRR. The inherent high charge polarity of GCN, combined with its unique tri‐s‐triazine structure, offers multiple binding sites for lithium polysulfides (LiPSs) through Li‐N bonds, as well as N/C‐coordinated frameworks for anchoring Co‐SACs. This structural configuration further amplifies the interaction with LiPSs via Co‐S bonds. Consequently, both Co‐SACs and GCN actively participate in sulfur reduction electrocatalysis by binding LiPS intermediates, lowering the conversion energy barrier of SRR. Benefitting from such unique synergy, the battery demonstrates outstanding rate performance (718.9 mAh g‐1 at 5.0 C) and yields a high areal capacity of up to 13.8 mAh cm‐2 (1584.3 mAh g‐1) under a high areal sulfur loading of 8.7 mg cm‐2 but a low electrolyte/sulfur ratio of 5.0 μL mg‐1.

Sulfur Vacancy-Induced Enhancement of Piezocatalytic H2 Production in MoS2.

This study explores the role of S vacancies in MoS2 in enhancing its piezocatalytic efficiency. Sulfur vacancies in the crystal lattice introduce localized changes in the electronic structure and charge distribution, improving the material's piezoelectric response. Characterization of the catalysts involved techniques like field-emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). Electrochemical measurements, including impedance spectroscopy (EIS) and Mott-Schottky (M-S) analysis, are performed to assess the piezocatalytic performance. The study also employed density functional theory (DFT) calculations to investigate the electronic structure and hydrogen adsorption properties of MoS2 with S vacancies. The results demonstrated that S-deficient MoS2 significantly enhanced piezocatalytic H2 evolution. The piezocatalytic H2 production rates of MoS2 with different vacancy concentrations are measured under ultrasonic vibration. The sample with an optimal vacancy concentration (MS-1) exhibited the highest H2 production rate of 1423.29µmol g-1 h-1, compared to 439.06µmol g-1 h-1 for pristine MoS2 (MS-0). The improved performance is attributed to the increased piezoelectric polarization and efficient charge separation facilitated by S vacancies.

Synergy of Ni single atoms and NiO nanoclusters in carbon nitride to create local charge polarization for enhanced CO2 photoreduction

Synergy of Ni single atoms and NiO nanoclusters in carbon nitride to create local charge polarization for enhanced CO2 photoreduction

Overcoming Energy Storage-Loss Trade-Offs in Polymer Dielectrics Through the Synergistic Tuning of Electronic Effects in π-Conjugated Polystyrenes.

Achieving high-performance dielectric materials remains a significant challenge due to the inherent trade-offs between high energy storage density and low energy loss. A central difficulty lies in identifying a suitable dipolar unit that can enhance the polarity and dielectric constant of the material while effectively suppressing the high energy losses associated with polarization relaxation, charge injection, and conduction. To address this, a novel strategy is proposed that introduces electron-donating and electron-withdrawing substituents on the benzene ring of polystyrene-based polymers, creating bulky dipole groups that are resistant to reorientation under an electric field. This approach mitigates relaxation losses associated with dipole reorientation and manipulates the band structure via substituent modification to suppress conduction losses. Additionally, the deformation of the π-electron cloud under an electric field enhances the dielectric constant and energy storage density. Ultimately, the optimized chlorostyrene-methyl methacrylate (MMA) copolymer exhibits an 85% discharge efficiency and an energy storage density of 18.3 J cm- 3, nearly three times that of styrene-based copolymers under the same conditions. This study introduces a new approach for designing high-energy density, low-loss polymer dielectric materials by precisely controlling electron-donating and electron-withdrawing effects to modulate the distribution of π-conjugated electron clouds.

Volatile Resistive Switching and Short-Term Synaptic Plasticity in a Ferroelectric-Modulated SrFeOx Memristor.

SrFeOx (SFO) offers a topotactic phase transformation between an insulating brownmillerite SrFeO2.5 (BM-SFO) phase and a conductive perovskite SrFeO3 (PV-SFO) phase, making it a competitive candidate for use in resistive memory and neuromorphic computing. However, most of existing SFO-based memristors are nonvolatile devices which struggle to achieve short-term synaptic plasticity (STP). To address this issue and realize STP, we propose to leverage ferroelectric polarization to effectively draw ions across the interface so that the PV-SFO conductive filaments (CFs) can be ruptured in absence of an external field. As a proof of concept, we fabricate ferroelectric Pb(Zr0.2Ti0.8)O3 (PZT)/BM-SFO bilayer films with Au top electrodes and SrRuO3 bottom electrodes. The device exhibits the desired volatile resistive switching behavior, with its low resistance state decaying over time. Such volatility is attributed to the positive polarization charge near the PZT/SFO interface, which can attract the oxygen ions from SFO to PZT and hence lead to the rupture of CFs. Moreover, this volatile device successfully emulates STP-related synaptic functions, including excitatory postsynaptic current, paired-pulse facilitation, learning-experience behavior, associative learning, and reservoir computing. Our study showcases an effective method for achieving volatile resistive switching and STP, which may be applied to various systems beyond SFO-based memristors.

Fluoropolymer-Single Crystal Nanocomposite Based Transducer Fabrication for Bio-Imaging.

Fluoropolymer alone, as an alternative to lead-based piezoelectric materials, has shown multiple challenges to develop useful sensors for solving real-world problems such as photoacoustic, ultrasound pulse echo, and other non-destructive testing. This work demonstrates the fabrication of high frequency and wide bandwidth transducers with fluoropolymer and highly polarizing cubic single crystal Barium titanate (BaTiO3) ceramic composite for high resolution in-vivo photo-acoustic and ultrasound imaging. For transducer fabrication, a customized bio-compatible nanocomposite sensor film of PVDF-TrFE (Polyvinylidene fluoride trifluoroethylene)/BaTiO3 (BTO) is synthesized by drop and dry in heating-cum-electro-poling system for advancing polarization, crystallinity, and higher charge generation. The ratio of nanofiller cubic single crystal BTO and PVDF-TrFE is optimized using characterization techniques such as FTIR, XRD and electrometer. Thereafter, SEM and TGA analyses are performed to study the surface morphology and thermal stability of the sensing film. Transducers with central frequencies varying from 17 to 42MHz are fabricated and tested for both pulse-echo mode and receiving photoacoustic signals. These transducers are used for sensing photoacoustic signals generated from hemoglobin and eumelanin and further for ultrasound and photoacoustic imaging. The imaging results are compared with the results obtained using a commercial ultrasound and photoacoustic imaging device. To the best of the knowledge and available literature, for the first time, the fabrication of ultrasound/photoacoustic transducers with cubic single-crystal nanofiller and fluoropolymer nanocomposite is showed. The detailed transducer fabrication method, characterization results, and imaging of biological tissue using photoacoustic and ultrasound are presented.

Nitrogen Modified Linear Polythiophene Derivatives with Polarized Charge Distribution for Red Light-Induced Photocatalysis.

Elevating the long-wavelength activation of photocatalysts represents a formidable approach to optimizing sunlight utilization. Polythiophene (PTh), although renowned for its robust light absorption and excellent conductivity, is largely overlooked for its potential as a photocatalyst due to the swift recombination of photogenerated charge carriers. Herein, we unveil that the strategic introduction of an aromatic ring containing varying nitrogen content into PTh instigates polarized charge distribution and facilitates the narrowing of the band gap, thereby achieving efficient photocatalytic activities for both hydrogen and hydrogen peroxide generation. Notably, the best sample, PTh-N2, even demonstrates photocatalytic activity in the red light region (600-700 nm). This study offers a promising avenue for the development of polymer photocatalysts with efficient photocatalytic performance for red light-induced photocatalysis.

Investigation on coupling between ferro-orderings and energy harvesting properties of nickel ferrite and strontium modified barium titanate composites

Environment-friendly, low power-consuming magnetoelectric composites possess the interesting coupling between various ferro-order parameters and find applications in magnetic sensors, waveguides, transducers, spintronics, four-state memory devices, etc. The particulate composites (x)NiFe2O4–(1 − x)Ba0.9Sr0.1TiO3 were prepared using the hybrid sol-gel method using the conventional ceramic double-sintering method. The ferromagnetic nickel ferrite crystallized into a cubic crystal structure whose x-ray diffraction (XRD) peaks could be indexed to Fd3¯m space group. The ferroelectric strontium-substituted barium titanate crystallized to a tetragonal crystal structure with P4mm space group. Presence of both crystal symmetries and elemental compositions as per the proposed stoichimetry were observed from experimental results (XRD and electron microscopy techniques). Koop's phenomenological theory could be employed to explain the impedance spectra in the range of 1 kHz to 1 MHz. The effect of Maxwell–Wagner polarization and space charge polarization on the dielectric properties of composites have been observed. The Arrott plot technique successfully explains the suitability of composites for high-energy storage applications. The coupling between both ferro-orderings has been revealed from the magneto-dielectric curves and its dependency on the microstructure has been observed. The magnetocapacitance increased with the increase in NiFe2O4 composition in the (x)NiFe2O4–(1 − x)Ba0.9Sr0.1TiO3 composite. The 30% NiFe2O4 in (x)NiFe2O4–(1 − x)Ba0.9Sr0.1TiO3 composite exhibited overall better energy harvesting (η = 62.9%) and magnetodielectric properties (MC = 1.4%, MI = 20% at 1 kHz).

Atomic Decompositions of Periodic Electronic-Structure Simulations.

We present a new theory for partitioning simulations of periodic and solid-state systems into physically sound atomic contributions at the level of Kohn-Sham density functional theory. Our theory is based on spatially localized linear combinations of crystalline Gaussian-type orbitals and, as such, capable of exposing local features within periodic electronic structures in a more intuitive and robust manner than alternatives based on the spatial distribution of atomic basis functions alone. Early decomposed cohesive energies of both molecular polymers and different crystalline polymorphs demonstrate how the atomic properties yielded by our theory convincingly align with the expected charge polarization in these systems, also whenever partial charges and Madelung energies may lend themselves somewhat ambiguous to interpretation.

Charge Polarity Modulation and Efficient Electron Transport in Quinoid–Donor–Acceptor Polymers by Acceptor Engineering for High-Performance Transistors

Charge Polarity Modulation and Efficient Electron Transport in Quinoid–Donor–Acceptor Polymers by Acceptor Engineering for High-Performance Transistors

Electrostatically tuning radical addition and atom abstraction reactions with distonic radical ions.

Although electrostatic catalysis can enhance the kinetics and selectivity of reactions to produce greener synthetic processes, the highly directional nature of electrostatic interactions has limited widespread application. In this study, the influence of oriented electric fields (OEF) on radical addition and atom abstraction reactions are systematically explored with ion-trap mass spectrometry using structurally diverse distonic radical ions that maintain spatially separated charge and radical moieties. When installed on rigid molecular scaffolds, charged functional groups lock the magnitude and orientation of the internal electric field with respect to the radical site, creating an OEF which tunes the reactivity across the set of gas-phase carbon-centred radical reactions. In the first case, OEFs predictably accelerate and decelerate the rate of molecular oxygen addition to substituted phenyl, adamantyl, and cubyl radicals, depending on the polarity of the charged functional group and dipole orientation. In the second case, OEFs modulate competition between chlorine and hydrogen atom abstraction from chloroform based on interactions between charge polarity, dipole orientation, and radical polarizability. Importantly, this means the same charge polarity can induce different changes to reaction selectivity. Quantum chemical calculations of these reactions with DSD-PBEP86-D3(BJ)/aug-cc-pVTZ show correlations between the barrier heights and the experimentally determined reaction kinetics. Field effects are consistent between phenyl and cubyl scaffolds, pointing to through-space rather than through-bond field effects, congruent with computations showing that the same effects can be mimicked by point charges. These results experimentally demonstrate how internal OEFs generated by carefully placed charged functional groups can systematically control radical reactions.

In situ self-cleaning removal of emerging organic contaminants with covalent organic framework armed with arylbiguanide.

An in situ self-cleaning covalent organic framework featuring arylbiguanide arms (Aryl-BIG-COF) was first developed to remove emerging organic pollutants such as propranolol (PRO) from water. The main breakthroughs addressed the scarcity of functional active sites, the impracticality of ex situ regeneration, and the rapid recombination of electronhole pairs in the application of COFs. Owing to the directional capture ability and electronic structure regulation of the arylbiguanide arms, the adsorption capacity and photocatalytic degradation rate of the newly synthesized COF increased by nearly four and seven times, respectively. Its self-cleaning ability, driven by the photocatalytic regeneration of active sites, enabled in situ removal of PRO and sustained over 90 % removal efficiency after six cycles. Moreover, it demonstrated broad applicability for removing PRO and other emerging pollutants, such as bisphenol A (BPA), tetracycline (TC), and norfloxacin (NOR), across various water matrices with less residual toxicity. The coexisting organic matter and ions in natural water promoted the removal of PRO. The enhancement mechanism involved arylbiguanide arms narrowing the band gap and inducing local charge polarization, thereby increasing the separation efficiency of electronhole pairs. This work provides significant insights into the structural design and practical applications of COFs for purifying water.

Comprehensive Investigation of Ti-Doped Sr3CoSb2O9 Triple Perovskite: Structural, Morphological, Optical, and Dielectric Characteristics

We report a comprehensive investigation of the doped Ti4+ and the pristine Sr3CoSb2O9 triple perovskite material. By conducting a solid-state reaction in the air at room pressure, a stabilized single orthorhombic Immm (SG 71) phase is obtained. For series samples Sr3CoSb2−xTixO9 (x = 0.0, 0.1, 0.3, 0.5), using Rietveld refinements of powdered x-ray patterns, we reach to the conclusion that the Ti4+ doping at B-site has considerable impact on its structural parameters. The microstructure of the series samples was studied using FESEM and associated with EDS mapping for compositional analysis. The optical characteristics studied via optical absorbance measurements indicate that with an increasing doping concentration of Ti4+, the optical bandgap increases for 0.1 sample and then decreases up to 1.50 eV for 0.5 sample. As a result, they can be considered potential candidates for technological applications like photocatalytic systems and solar cells due to their suitable bandgap values and optical absorption-related applications. The FTIR analysis aimed to examine the bond forms and vibrational modes of the synthesized samples. Moreover, the space charge polarization mechanism explains a detailed analysis of temperature-dependent dielectric properties in the 1 KHz-2 MHz frequency range. The dielectric loss behavior is described by the thermally activated relaxation process tailored by the Arrhenius law and characterized by doping Ti4+ ions into the material’s structure. The existence of Co in Co2+ and Co3+ oxidation states, while Sb3+ state is stabilized with doping confirmed by X-ray photoelectron spectroscopy research. The current study thereby advances our knowledge of how these materials’ structural, morphological, optical, and dielectric characteristics are related.

Dielectric and Photocatalytic Performance of Heterostructured Nanocomposites of Cobalt and Nickel Oxides Embedded in Zeolite 4A Matrix.

AbstractOrganic pollutants like malachite green pose severe environmental risks due to their toxicity and persistence in water bodies. This study explores an eco‐friendly solution for their removal via photocatalytic degradation using cobalt and nickel oxide‐doped zeolite nanocomposites (CoZ NC & NiZ NC), synthesized through a co‐precipitation method. X‐ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and energy‐dispersive X‐ray (EDX) analyses confirm the formation of FCC‐structured nanometal oxides on the zeolite matrix. Optical spectral analysis reveals low bandgap energies (2.84 eV for CoZ NC and 2.81 eV for NiZ NC), enabling efficient photocatalysis under visible light. These nanocomposites demonstrated effective photodegradation of malachite green, showcasing their environmental remediation potential. Dielectric studies indicate significantly higher dielectric permittivity in CoZ NC and NiZ NC compared to pristine zeolite. This enhancement is attributed to internal barrier layer capacitance arising from variable oxidation states of metal oxide nanoparticles and interfacial space charge polarization between the zeolite matrix and metal dopants. Uniformly distributed cobalt oxide nanoparticles provide superior permittivity in CoZ NC compared to the unevenly arranged nickel oxide in NiZ NC. Additionally, lower dissipation factors in CoZ NC and NiZ NC highlight their suitability as promising k‐dielectric materials for energy storage applications.

Interfacial polarization charge engineering with co-designed LQB and EBL for enhanced EQE of AlGaN DUV LEDs

Abstract In this paper, we propose to modulate the polarization charges at the interface between the last quantum barrier (LQB) and the electron blocking layer (EBL) via strategically adjusting the Al composition in the LQB and EBL simultaneously. With appropriate design of the linear gradient profile in Al composition, the original positive polarization charges at the LQB/EBL interface can be diminished or converted into negative charges, which helps to reduce the positive electric field in EBL, thus adjusting the energy band near the LQB/EBL interface. Enhanced effective barrier height for electrons, decreased effective barrier height for holes, and accumulation of a large number of holes at the LQB/EBL interface are obtained, resulting in improved electron leakage and hole injection. In comparison with the reference deep ultraviolet light-emitting diode (DUV LED), an enhanced external quantum efficiency by 37.5% at an injection current density of 100 A cm−2 is achieved for the device with negative polarization charges. The modulation strategy of polarization charges at the LQB/EBL interface via co-designing the linear gradient of Al composition in LQB and EBL can be a feasible approach for obtaining high-performance DUV LEDs.

Charge-transfer energy through the dipole moment.

The charge-transfer energy contribution is one of the most controversial components of the total interaction energy. Commonly, the energy associate to a charge-transfer process depends on population analysis. Therefore, the results further depend on how the population analysis is defined, and certainly, the results may be arbitrary. Moreover, another important feature of the current methods is the basis sets dependency. The results of methodologies that depend on orbital-based population analyses tend to have a strong dependency on the size of the basis set utilized. This basis set dependency is eliminated by using spatial partitioning population analyses. However, these methodologies still rely on the arbitrary choice of how to divide the space. In this work, we study the use of the molecular dipole moment as a reference to describe the charge transfer-free system, i.e., a system in which the charge-transfer process is avoided. We use the recently developed constrained dipole moment density functional theory methodology to constrain the dipole moment of several systems according to reference values. These dipole moment references do not present charge transfer nor polarization contributions. In this manner, we have calculated the charge-transfer energy contributions and the total interaction energies of 13 non-covalent complexes. In addition, we determined two long range charge-transfer excitations considering the dipole moment as a reference. The calculated charge-transfer energy contributions and excitation energies are in a very good agreement with the fragment-based Hirshfeld methodology. Nevertheless, the constrained dipole moments results do not depend on population analysis. Moreover, the method is robust with respect to the strength of the charge transfer and the basis set size.

Electric field calculation using the induced polarization charge in the tilted dielectric media

Electric field calculation using the induced polarization charge in the tilted dielectric media