Polarization Electric Field Research Articles

Electric double layer-mediated polarization field for optimizing photogenerated carrier dynamics and thermodynamics

Photocatalytic hydrogen evolution efficiency is limited due to unfavorable carrier dynamics and thermodynamic performance. Here, we propose to introduce electronegative molecules to build an electric double layer (EDL) to generate a polarization field instead of the traditional built-in electric field to improve carrier dynamics, and optimize the thermodynamics by regulating the chemical coordination of surface atoms. Based on theoretical simulation, we designed CuNi@EDL and applied it as the cocatalyst of semiconductor photocatalysts, finally achieved a hydrogen evolution rate of 249.6 mmol h−1 g−1 and remained stable after storing under environmental conditions for more than 300 days. The high H2 yield is mainly due to the perfect work function, Fermi level and Gibbs free energy of hydrogen adsorption, improved light absorption ability, enhanced electron transfer dynamics, decreased HER overpotential and effective carrier transfer channel arose by EDL. Here, our work opens up new perspectives for the design and optimization of photosystems.

Electrical and optical properties of a lead-free complex double perovskite BaNaFeMoO6: Photovoltaic and thermistor applications

In this communication, synthesis (solid-state reaction) and characterizations of a complex double perovskite BaNaFeMoO6 are reported. X-ray diffraction analysis (structure and lattice parameters) adopts a monoclinic structure while Raman spectroscopy provides information about the vibrational characteristics. Homogenous distribution of the grains is observed from the scanning electron microscope (SEM) whereas energy dispersive X-ray analysis (EDX) supports compositional consistency. Ultraviolet–visible (UV–vis) data provides a direct energy bandgap of 2.75 eV, which may be suitable for photovoltaic applications. The analysis of Maxwell-Wagner type of dielectric dispersion, resistance, relaxation, and transport mechanism are carried out using dielectric, impedance, modulus, and conductivity data recorded within an available range of frequency (1 kHz – 1 MHz) and temperature (25 °C – 500 °C). Both the theoretical fit of the Nyquist data using ZSIMPWIN software as well as temperature-dependent conductivity support a negative temperature coefficient of resistance (NTCR) nature. The scaling nature of modulus data supports the non-Debye type of relaxation. The obtained temperature-dependent thermistor constant (β), sensitivity factor (α), and activation energy make the prepared material suitable for thermistor-related device application. The study of polarization–electric field (P-E) loop suggests the possibility of ferroelectric nature in the reported material.

Structure and electrical conductivity of nanocomposite SiOxNy(Si) and SiAlzOxNy(Si) films

In this study, the peculiarities of the structure and electrical conductivity of nanocomposite SiOxNy(Si) and SiAlzOxNy(Si) films in the temperature range of 95 – 340 K are determined. The composite films were obtained by ion-plasma sputtering of Si and co-sputtering of Si and Al targets in oxygen and nitrogen containing atmosphere (Ar+O2 +N2) followed by high temperature annealing. During the annealing of the deposited Si rich oxynitride films, Si nanoinclusions were formed in an amorphous dielectric matrix due to phase separation. Al atoms are found to be in the bound state (no Al metal nanoparticles present). The films have low absorbance and considerable transparency in the ultraviolet – visible – near infrared spectral region. Reduction of some part of Si-O bonds by Al during annealing the Al-containing samples leads to the separation of higher Si concentration as compared to the Al-free samples. The electrical conductivity of the films at low electric fields is found to be by variable-range electron hopping through the traps near the Fermi level. The characteristics of the traps and transport process such as the density of electron traps near the Fermi level, the activation energy of hopping and the hopping length are determined. It is found that the electrical conductivity of the SiAlzOxNy(Si) films annealed in argon is higher as compared to the films annealed in nitrogen and the Al-free films due to higher concentration of electron traps. The region of the conductivity decrease with the increase of electric field is revealed on the current-voltage characteristics of both the SiAlzOxNy(Si) films annealed both in nitrogen and argon and the SiOxNy(Si) films annealed in nitrogen. This effect is explained based on the peculiarities of electric field polarization in the films. The important role is played by the interface traps at the Si nanoparticle / amorphous matrix interfaces that capture electrons. At high electric fields, the film conductivity corresponds to the space charge limited current mechanism with the exponential distribution of the traps in the energy gap.

A novel way to prepare PbZrO3 nanocomposite films for increasing electrical properties and energy storage performance

The energy storage performance of dielectric materials depends largely on their polarization properties and electric breakdown strength. Nanocomposites have emerged as an effective method for improving these properties. In this study, we propose a novel method to prepare PbZrO3-Al2O3 nanocomposite films by combining chemical solution deposition with thermal evaporation of a metal Al layer. The resulting composite films exhibit a layered distribution of Al2O3 nanoparticles (NPs) on the PbZrO3 matrix, which can be used to control the shape and characteristics of the polarization-electric field (P-E) hysteresis loop by varying the thickness of the Al layer. We thoroughly investigated the effects of Al2O3 NPs on the microstructure, polarization, leakage current, and energy storage properties of the composite films. Our results show that as the content of Al2O3 NPs increases, the property of the composite films gradually evolves from antiferroelectric characteristics to ferroelectric characteristics. Specifically, the maximum polarization, remanent polarization, and electrical breakdown strength increase, while the leakage current decreases. Compared to PbZrO3 thin films, the electrical breakdown strength (1850 kV/cm) and energy storage density (25.0 J/cm3) of the nanocomposite thin films increased by 189% and 93%, respectively. Our study presents a new method to prepare dielectric nanocomposite films and opens up a new avenue for designing energy storage capacitor materials using nanocomposites.

Alternating current polarization to enhance piezoelectric performance of single crystal composites

Pb-based relaxor piezoelectric single crystal composites (PSCCs) have attracted widespread attention for improving the bandwidth and sensitivity performance of acoustic transducers due to their excellent electromechanical and piezoelectric properties. Alternating current polarization (ACP) has been proven as an effective method for enhancing the dielectric and piezoelectric properties of relaxor-PbTiO3 single crystals. Herein, we investigated the effects of the amplitude, frequency, and cycle number of the poling electric field on the piezoelectric and dielectric performances of PSCCs and obtained the optimum poling condition of ACP. Compared with the traditional direct current poling method, both the dielectric permittivity (ε33T/ε0) and piezoelectric coefficient (d33) of the AC-poled PSCCs were both increased by up to 20%. Notably, the ACP PSCC with a volume fraction of 60% exhibited a high d33 of 1610 pC/N, which is superior to values previously reported for PSCCs. This work provides an alternative strategy for enhancing the properties of PSCCs and may contribute to the further development of piezoelectric applications.

Soft actuators based on piezoelectric composites for nanoscale self-bending

Nano/microscale objects would be far less damaged by soft actuators than rigid actuators in the mechanical nano/micromanipulation, but the precision of most soft actuators cannot meet the requirements. In this work, a kind of soft actuators which can realize nanoscale self-bending are developed on the basis of lead zirconate titanate (PZT)/shape memory polyurethane (SMPU) composites. The self-bending ability is the result of the weak polarization electric fields produced by the combination of the microstructures of particulate composites and the fringe effect of electric fields. However, unlike common piezoelectric actuators, strong polarization electric fields would weaken the actuation ability (self-bending ability). The PZT/SMPU actuators are able to generate nanoscale self-bending displacements with the maximum error of ± 8 nm in a common condition without controlling any environmental parameter. This work provides a helpful reference for the design of soft self-bending actuators based on piezoelectric particulate composites.

Structure, Antiferroelectricity and Energy-Storage Performance of Lead Hafnate in a Wide Temperature Range.

Lead hafnate (PbHfO3) has attracted a lot of renewed interest due to its potential as antiferroelectric (AFE) material for energy storage. However, its room temperature (RT) energy-storage performance has not been well established and no reports on the energy-storage feature of its high-temperature intermediate phase (IM) are available. In this work, high-quality PbHfO3 ceramics were prepared via the solid-state synthesis route. Based on high-temperature X-ray diffraction data, the IM of PbHfO3 was found to be orthorhombic, Imma space group, with antiparallel alignment of Pb2+ ions along the [001]cubic directions. The polarization-electric field (P-E) relation of PbHfO3 is displayed at RT as well as in the temperature range of the IM. A typical AFE loop revealed an optimal recoverable energy-storage density (Wrec) of 2.7 J/cm3, which is 286% higher than the reported data with an efficiency (η) of 65% at 235 kV/cm at RT. A relatively high Wrec value of 0.7 J/cm3 was found at 190 °C with an η of 89% at 65 kV/cm. These results demonstrate that PbHfO3 is a prototypical AFE from RT up to 200 °C, making it a suitable material for energy-storage applications in a wide temperature range.

Role of interfacial electric field on thermal conductivity of In x Al1−x N/GaN superlattice (x = 0.17)

Abstract In this paper, we report the role of the interfacial polarization electrical field in thermal conductivity of In x Al1−x N/GaN superlattice. Thermal conductivity reduction is one recent effort to improve thermoelectric device efficiency because a small reduction in thermal conductivity can enhance the figure of merit significantly. Quantum size effect and thermal boundary resistance are responsible for this reduction. The theoretical results demonstrate that the interfacial polarization electric field modifies acoustic phonon properties through elastic moduli and phonon group velocity as a result of the inverse piezoelectric effect. This enhances phonon scattering and thermal boundary resistance. Consequently, the thermal conductivity of the superlattice is reduced. Room temperature thermal conductivity is found to be 2.94 (3.35) W m−1 K−1 for In x Al1−x N/GaN superlattice (x = 0.17) in the presence (absence) of an electric field.

Dynamic Behavior and Residence Characteristics of Space Charge in Oil-Paper Insulation Under Polarity–Reversal Electric Field

As one of the core components of the direct current (dc) transmission system, the converter transformer bears not only the alternate current (ac) electric field but also complex electric fields, such as polarity reversal. In the process of polarity reversal, the phenomenon of space charge residence occurs in the oil-paper insulation inside the converter transformer, which distorts the internal electric field, leading to insulation deterioration or even failure. However, studies on the dynamic characteristics of space charge during the reversal process and the mechanism of insulation degradation are not comprehensive. Therefore, in this study, a test pulse matching circuit was developed to accurately match the test pulse with the polarization voltage of polarity reversal and perform the multi-point rapid test of the space charge transient characteristics during polarity reversal. The space charge tests (of the unaged specimen) were performed at the polarity–reversal time of 60, 30, and 10 s, and the influence of polarity–reversal time on the charge residence characteristics of oil-paper insulation was compared and analyzed. Additionally, space charge tests were performed on oil-paper insulation samples with accelerated electro–thermal–mechanical aging treatment for 0, 2.5, 5, 10, and 15 days to compare and analyze the influence of oil-paper insulation aging degree on charge residence characteristics under the action of multi-physical field coupling. Research results indicate that the shorter the reversal time, the shorter the time required for the charge to dissipate, and the more the charge resides, the stronger its enhancement effect on the electric field. As the aging degree of the sample increases, the dissipation rate of the resident charge becomes slower during the reversal process, and the resident charge increases, so that the maximum electric field intensity inside the sample increases under the same polarization electric field. The study of the charge residence characteristics and the dynamic charge behavior during the polarity inversion process has important guiding significance for clarifying the deterioration mechanism of the converter transformer oil-paper insulation under polarity–reversal electric field.

Vortex Structures and Momentum Sharing in Dynamic Sauter-Schwinger Process

Vortex pattern formation in electron-positron pair creation from vacuum by a time-dependent electric field of linear polarization is analyzed. It is demonstrated that in such scenario the momentum distributions of created particles exhibit vortex-antivortex pairs. Their sensitivity to the laser field parameters such as the field frequency and intensity is also studied. Specifically, it is shown that with increasing field frequency accross the one-photon threshold additional vortex-antivortex pairs appear. Their location in the momentum space is consistent with a general threshold behavior of probability distributions of created electrons (positrons). Namely, while for small field frequencies the particles tend to be created along the field polarization direction, for large enough frequencies they are predominantly generated in the perpendicular direction. Such change in longitudinal and transverse momentum sharing of created particles occurs accross the one-photon threshold.

A case study on multiple self-interactions of MSTID bands: New insights

In this study, we report a special event of nighttime southwestward propagating medium scale traveling ionospheric disturbances (MSTIDs) observed in O(1D) 630.0 nm airglow images from an all-sky imager at Hanle (32.7°N, 78.9°E; Mlat. ∼ 24.1°N), Leh Ladakh, India on a geomagnetically quiet (Ap = 7) night of 15 September 2018. The time sequence of airglow images unveiled two dynamic interactions between multiple dark bands of MSTID. Following the first interaction, one of the interacting bands decayed possibly due to the entrance of plasma from the ambient higher plasma density region. Shortly after this interaction, the other interacting dark band was involved in the second interaction with a third dark band which resulted in the co-alignment of the two interacting bands. Following this co-alignment, one of the bands started rotating prominently that led to further separation of these two co-aligned bands. These changes in the MSTID phase fronts (bands) are explained based on the development of the polarization electric fields arising out of the interactions. This investigation combines the all-sky 630.0 nm airglow imaging observations with TEC maps constructed, for the first time over the Indian sector, from 67 Global Navigation Satellite System (GNSS) measurements to capture the MSTID over this region. The investigation reveals a few important features of self-interactions of MSTID bands over the geomagnetic low-mid latitude transition region which is important to assess their impact over low latitudes.

MOF-Derived Tourmaline@ZnO Nanostructure as a High-Response Sensing Material of Gas Sensors toward n-Butanol

Herein, in order to efficiently enhance the sensing properties based on zinc oxide (ZnO) sensors toward n-butanol, a series of MOF ZIF-8 (zeolite imidazolate framework-8)-derived Tourmaline@ZnO core–shell nanostructures were prepared with a facile solution mixing method and an after-treatment calcination process, and the gas sensing performances were systematically characterized. The results exhibited that the paucity of tourmaline introduction could significantly improve the gas sensitivity for n-butanol, simultaneously increasing the gas selectivity and reducing the response–recovery times. In particular, the sensor based on 5 wt % Tourmaline@ZnO nanocomposites achieved a superior response value, reaching up to 294.4 for 100 ppm n-butanol at 320 °C. Through the integrated testing and analyses of BET, XPS, PL, and UV, it has been confirmed that the introduction of tourmaline can not only enlarge the specific surface area and enrich the surface defects of the ZnO matrix, but its unique spontaneous polarization electric field can also reduce the recombination rate of electron–hole pair efficiency, promoting the efficiency of electron transport and accelerating the gas sensing process ultimately. The enhancement mechanism of the nanostructured Tourmaline@ZnO core–shell gas sensing material was also elucidated from the perspective of the energy band theory at length.

Determination of Vibrational Modes of l-Alanine Single Crystals by a Combination of Terahertz Spectroscopy Measurements and Density Functional Calculations.

Density-functional theory may be used to predict both the frequency and the dipole moment of the fundamental oscillations of molecular crystals. Suitably polarized photons at those frequencies excite such oscillations. Thus, in principle, terahertz spectroscopy may confirm the calculated fundamental modes of amino acids. However, reports to date have multiple shortcomings: (a)material of uncertain purity and morphology and diluted in a binder material is employed; (b)consequently, vibrations along all crystal axes are excited simultaneously; (c)data are restricted to room temperature, where resonances are broad and the background dominant; and (d)comparison with theory has been unsatisfactory (in part because the theory assumes zero temperature). Here, we overcome all four obstacles, in reporting detailed low-temperature polarized THz spectra of single-crystal l-alanine, assigning vibrational modes using density-functional theory, and comparing the calculated dipole moment vector direction to the electric field polarization of the measured spectra. Our direct and detailed comparison of theory with experiment corrects previous mode assignments for l-alanine, and reveals unreported modes, previously obscured by closely spaced spectral absorptions. The fundamental modes are thereby determined.

Spin polarization and magnetostriction properties in superperiodic Janus twisted bilayer graphenes

The atomic and electronic structure of superperiodic vertical hybrid Janus heterostructures based on doped twisted bilayer graphenes were theoretically developed and studied using electronic structure calculations. Regularly opposed superperiodic sublattices of fluorine and aluminum adatoms were used to induce structural charge polarization, and uncompensated spin moments up to 1.05 µB per unit cell, caused by local intense transverse electric fields generated by ferromagnetically aligned spin polarization of entire lattices. It was shown that spin polarization of the heterostructures is mostly determined by partial carbon and fluorine electronic states localized in the vicinity of the Fermi level, whereas superlattices of Al adatoms mostly determine the rate of charge polarization, the symmetry, and intensity of the internal transverse electric field up to −0.018 e2/Å. It was shown that proposed heterostructures may display advanced electronic spin, entanglement and magnetostriction properties perspective for various spin- and quantum-related applications.

Hybrid improper ferroelectricity and phase transition behavior of Li2Nd2Ti3O10 ceramics with A-site ordered triple-layer Ruddlesden-Popper structure

Hybrid improper ferroelectricity has been extensively reported through theoretical prediction and experimental investigation in the oxides with Ruddlesden-Popper (R–P) structures. However, the experimentally reported ferroelectric materials based on triple-layer R–P structures are rare, and the weak ferroelectricity impedes its practical application. In the present work, the single-phase Li2Nd2Ti3O10 ceramics with A-site cation ordered triple-layer R–P structure was obtained by spark plasma sintering technique, and the crystal structure of P21ab symmetry was revealed by neutron powder diffraction and transmission electron microscope analysis. Furthermore, the switchable ferroelectricity in Li2Nd2Ti3O10 ceramics has been observed at room temperature, and the saturated polarization-electric field hysteresis loop was obtained with Pr = 0.4 μC/cm2 under the electric field of 250 kV/cm. The phase transition behavior of Li2Nd2Ti3O10 oxides was revealed by the temperature-dependence Raman and dielectric spectra combined with the piezoelectric property.

Ferroelectric properties of triglycine sulfate crystals doped with glycine analogs

Single crystals of ferroelectric triglycine sulfate doped with glycine analogs serine, threonine, lactic acid, and alaninol were grown via the slow solvent evaporation method. The resulting ferroelectric domain structures and polarization–electric field hysteresis loops revealed that these dopants caused triglycine sulfate to form a multidomain structure. This was attributed to hydrogen bonds not being formed, which is significant in polarization reversal, due to the side chains and the substituents of the dopant molecules. Therefore, the dopants did not affect the surrounding dipoles enough to cause cooperative phenomena, such as dipole‒dipole interactions, and do not result in the formation of a single- domain, unlike alanine in our previous study.

Electric field and viscous fluid polarity effects on capillary-driven flow dynamics between parallel plates

—Micropumps have attracted considerable interest in micro-electro-mechanical systems (MEMS), microfluidic devices, and biomedical engineering to transfer fluids through capillaries. However, improving the sluggish capillary-driven flow of highly viscous fluids is critical for commercializing MEMS devices, particularly in underfill applications. This study investigated the behavior of different viscous fluid flows under the influence of capillary and electric potential effects. We observed that upon increasing the electric potential to 500 V, the underfill flow length of viscous fluids increased by 45% compared to their capillary flow length. To explore the dynamics of underfill flow under the influence of an electric potential, the polarity of highly viscous fluids was altered by adding NaCl. The results indicated an increase of 20–41% in the underfill flow length of highly viscous conductive fluids (0.5–4% NaCl additives in glycerol) at 500 V compared to that at 0 V. The underfill viscous fluid flow length improved under the electric potential effect owing to the polarity across the substance and increased permittivity of the fluid. A time-dependent simulation, which included a quasi-electrostatic module, level set module, and laminar two-phase flow, was executed using the COMSOL Multiphysics software to analyze the effect of the external electric field on the capillary-driven flow. The numerical simulation results agreed well with the experimental data, with an average deviation of 4–7% at various time steps for different viscous fluids. Our findings demonstrate the potential of utilizing electric fields to control the capillary-driven flow of highly viscous fluids in underfill applications.

Enhanced magnetic modulation at a border of magnetic ordering in La1−xSrxMnO3/BaTiO3(100) heterostructure

In La1−xSrxMnO3 (LSMO)/BaTiO3 (BTO) heterostructures with a multiferroic interface, an artificial modulation of the magnetic structure is observed. The saturation magnetization of La1−xSrxMnO3 changes discontinuously due to in-plane distortions caused by a structural phase transition of a BaTiO3 substrate. Polarity reversal of the external electric field also causes a reversible switching in the magnetization. The magnitude of both magnetic modulations, due to the magnetoelastic and electric field effects, is concomitantly enhanced at a critical composition xc∼0.55, locating at a border of the magnetic phase transition. The polarity-dependent change in magnetization is possibly attributed to a change in the concentration of oxygen ions at the LSMO/BTO interface, indicating that the exchange interaction is reciprocally driven from being ferromagnetic to antiferromagnetic by the electric field polarity.

Piezoelectric polarization and interfacial electric field synergistically promote piezo-photocatalysis of in-situ transformed heterojunction

Photocatalysis is a promising approach for purifying water pollutants resources, but is greatly restricted by rapid photogenerated charges recombination. Herein, Bi2O2(OH)NO3-Bi2MoO6 heterojunction photocatalysts with strong interfacial electric field are synthesized via in situ transformation method with using Bi2O2(OH)NO3 as a self-sacrificial template. The intimate interface interaction renders a large interfacial potential, which allows efficient charge separation within the heterojunction. Thus, the photocatalytic activity was well optimized compared with the pristine catalyst and composite counterpart prepared by in situ growth route. Then, the piezoelectric polarization induced by ultrasonic vibration is introduced in the photocatalytic system, which yields a piezocatalytic activity and enhancement on the separation and transfer of photogenerated charge carriers. Benefiting from the piezoelectric polarization and interfacial electric field, the in situ transformed Bi2O2(OH)NO3-Bi2MoO6 heterojunction exhibits a prominent piezo-photocatalytic performance for degradation of tetracycline, much higher than that under sole light or ultrasound irradiation source as well as the individual catalyst. This work reveals the potential of the collaboration of piezoelectric polarization and interfacial electric field in photocatalysis.

Ferroelectric phase transitions in epitaxial antiferroelectric PbZrO3 thin films

The archetypical antiferroelectric, PbZrO3, is currently attracting a lot of interest, but no consensus can be clearly established on the nature of its ground state as well as on the influence of external stimuli over its physical properties. Here, the antiferroelectric state of 45-nm-thick epitaxial thin films of PbZrO3 is established by observing the characteristic structural periodicity of antiparallel dipoles at the atomic scale, combined with clear double hysteresis of the polarization-electric field response related to antiferroelectric–to–ferroelectric phase transitions. Surprisingly, while the antiferroelectric state is identified as the ground state, temperature-dependent measurements show that a transition to a ferroelectric-like state appears in a large temperature window (100 K). Atomistic simulations further confirm the existence, and provides the origin, of such ferroelectric state in the films. Electric-field-induced ferroelectric transitions are also detected by the divergence of the piezoresponse force microscopy response. Using this technique, we further reveal the signature of a ferroelectric ground state for 4-nm-thick PbZrO3 films. Compared with bulk crystals, these results suggest a more complex competition between ferroelectric and antiferroelectric phases in epitaxial thin films of PbZrO3.