Dielectric Effect Research Articles

Composition-Related Dielectric, Ferroelectric and Electrocaloric Properties of Pb5Ge3O11 Single Crystals Modified by Ba Ions

In this paper, we studied some ferroelectric properties of archetypal oxide uniaxial ferroelectric single crystals of Pb5Ge3O11 modified by Ba ions. They include dielectric, DSC, ferroelectric polarization, and electrocaloric effect (ECE) measurements. The measurements show that increasing Ba doping considerably influences all the measured parameters, mainly by lowering the Curie temperature, gradually diffusing the phase transition, and decreasing values of polarization as well as the coercive field. The decrease in overall ECE is influenced by decreasing polarization. Compared with the pure PGO single crystals, this decrease is from 1.2 K to 0.2 K. However, the effect of diffusing the phase transition increases the range of its occurrence (up to 30 K), which might be beneficial in applications.

Theoretical models of modulated nematic phases.

Novel modulated nematic phases, such as twist-bend nematics, splay-bend nematics and splay nematics, are an important subject of research in the field of liquid crystals. In this article fundamental information about the discovery, structure and properties of these phases is presented. Various theoretical models of elastic properties are compared, especially the proposed formulae for the free energy density of modulated nematic phases and the conditions for their stability. The emphasis is put on the variety of material parameters and variables in the mathematical description of the structures. The elastic models are classified according to a few criteria. Flexopolarisation is indicated as a main phenomenon responsible for the formation of modulated nematic phases. The elastic models are used for analysing the deformations of the twist-bend nematic structure in external fields. Dielectric, flexoelectric, ferroelectric and magnetic effects are considered. Two types of distortions are distinguished: microscopic (connected with the deformation of the director distribution) and macroscopic (related to the change of the optic axis direction). This review can be a starting point for further studies, for example computer simulations of modulated phases and design of liquid crystalline devices.

Photogenerated charge transfer in Dion-Jacobson type layered perovskite based on naphthalene diimide.

Incorporating organic semiconducting spacer cations into layered lead halide perovskite structures provides a powerful approach to mitigate the typical strong dielectric and quantum confinement effects by inducing charge-transfer between the organic and inorganic layers. Herein we report the synthesis and characterization of thin films of novel DJ-phase organic-inorganic layered perovskite semiconductors using a naphthalene diimide (NDI) based divalent spacer cation, which is shown to accept photogenerated electrons from the inorganic layer. With alkyl chain lengths of 6 carbons, an NDI-based thin film exhibited electron mobility (based on space charge-limited current for quasi-layered 〈n〉 = 5 material) was found to be as high as 0.03 cm2 V-1 s-1 with no observable trap-filling region suggesting trap passivation by the NDI spacer cation.

Overall performance improvement of direct-current triboelectric nanogenerators by charge leakage and ternary dielectric evaluation

By coupling the charge leakage effect and the ternary dielectric triboelectrification effect, our work improves the overall performance of DC-TENGs and creates new records in average power density, peak factor and output charge density.

Theoretical study on regulatory mechanism of dielectric environmental screening effects on binding energy of two-dimensional In<i>X </i>(<i>X</i> = Se, Te) exciton

The calculations using GW method based on Green’s function show that two-dimensional monolayer InSe and InTe have desired electronic band gaps for absorbing visible light, high electron mobilities, and suitable electronic band structures for water splitting, and that the spin orbit coupling (SOC) leads to an indirect-to -direct band gap transition for monolayer InTe. On the basis of quasi-particle energy levels, the calculations via solving Bethe-Salpter equation (BSE) show that the exciton binding energy of isolated monolayer InSe and InTe are much higher than that of the dissociation energy of exciton at room temperature. On the other hand, two-dimensional semiconductors in laboratory are often supported by substrates for mechanical stability, and the atomic thickness values of two-dimensional semiconductors are also various in different experiments. These factors will change the dielectric environments of two-dimensional semiconductor, and the further calculations show that the exciton binding energy of InSe and InTe decrease with the increase of the thickness of InSe and InTe and also the thickness of their substrates, also revealing that the exciton binding energy can be accurately controlled by engineering the thickness of two-dimensional semiconductors and the substrates. Our results provide important theoretical basis for accurately controlling the binding energy of two-dimensional InSe and InTe.

Dielectric Properties of Heterogeneous Mineral Compositions Based on Bentonite and Gypsum

To interpret the well-known experimental fact of reducing the depth of GPR diagnostics of railway subgrades in arid regions, the properties of model samples of mineral compositions formed by adding gypsum to bentonite at low moisture were studied. Using electron microscopy, the microstructure of bentonite and the compositions of bentonite and gypsum were studied with various methods of introduction of gypsum. Dielectric permittivity is studied by the microwave resonance method in the GPR frequency range of 1200 - 1700 MHz. The influence of the interaction of water and gypsum, as well as the Maxwell-Wagner dielectric effect on dielectric permittivity of heterogeneous mineral compositions, depending on the concentration of the components, is estimated.

Synergistic magnetic/dielectric loss of Fe3Si/SiC composites for efficient electromagnetic wave absorption

It is confirmed that the multi-component strategy of combining magnetic and dielectric components with different dielectric properties is still challenging to achieve efficient electromagnetic wave (EMW) absorbing (strong absorption and a broad effective absorption bandwidth at a low filling level). Herein, a magnetic/dielectric multi-component of Fe3Si/SiC composites is constructed via an in-situ carbothermal reduction strategy. The heterogeneous magnetic/dielectric multi-component benefit to superior EMW absorption performance through forming multiple polarizations, magnetic loss, and dielectric loss effects. Especially, when the carbothermal reduction temperature is 1400 °C, the prepared Fe3Si/SiC composites exhibit the best EMW absorption performance at a very low filler loading of 10 wt%, with a minimum reflection loss (RLmin) of −61.67 dB and an effective bandwidth (EAB) for RLmin < −10 dB reaches 6.96 GHz. Additionally, the radar cross section (RCS) can be reduced to 17.08 dB m2 and the RCS value is completely lower than −5.98 dB m2 in the range of −60° to 60°, which signified the high attenuation performance of radar wave. This work guides to design an efficient EMW absorber with lightweight and strong absorption.

Study of dielectric and magnetodielectric behavior of flexible PVA-NiNdxFe2-X O4 film for EMI shielding application

We have reported dielectric and magnetocaloric effects in flexible Neodymium (Nd) doped nickel ferrite (NiNdxFe2-xO4) - polyvinyl-alcohol nanocomposite films. The samples are characterized by X-ray diffraction, scanning electron microscopy, vibrating sample magnetometer and broadband dielectric spectroscopy. The dielectric permittivity is enhanced in the composite for a particular filler concentration. The magnetic entropy change decreases by higher doping in the polymer chain. The magnetodielectric coefficient is enhanced in higher frequency and with the rise in doping concentration. The observed skin depth value of the polymer nanocomposite is lower than the film's thickness which is suitable for electromagnetic shielding.

Electrorheological and dielectric analysis of self-crosslinked poly(ionic liquid)s with different flexible chain spacer

Three kinds of self-crosslinked poly(ionic liquid)s (S-PILs) with different flexible chain spacers, namely P[B2V][TFSI], P[C8DVIM][TFSI] and P[TEGDVIM][TFSI], were prepared. The influence of flexible chain spacer on electrorheological (ER) effect of S-PIL suspension in silicone oil under electric fields was studied by rheological method and dielectric spectroscopy. It is found that as the flexibility of chain spacer increases, the ER effect increases. However, the dielectric spectrum shows that the variation of ER effect is not completely consistent with that of interfacial polarization but is related to the competition between interfacial polarization induced by ion motion and electrode polarization formed by ion leakage. By combining wide-angle X-ray scattering spectra and ion activation energy analysis, we further clarify that the reason for the inconsistence of dielectric property and ER effect is not only related to the flexibility of chain spacer but also related to the interaction between oxygen on chain spacer and counter-anions in the S-PILs. The result provides an insight for the molecular design of S-PIL ER materials.

Large Harvested Energy by Self-Excited Liquid Suspension Triboelectric Nanogenerator with Optimized Charge Transportation Behavior.

To enhance the durability of triboelectric nanogenerator (TENG), liquid lubrication has been used to reduce mechanical abrasion. However, as the charge transportation behavior in dielectric liquid is not clearly understood, the output energy is still low although some improvements have been reported. Herein, the charge transportation behaviors in dielectric liquid by self-excited liquid suspension triboelectric nanogenerator (LS-TENG) are systematically investigated. The important role of solid-liquid triboelectrification effect, charge-liquid transmission and dissipation effect, and the homogeneous dielectric induction effect in promoting its output performance is found. The LS-TENG with a dual dielectric tribolayer has advantages of slight driving force and long lifetime for harvesting micro energy. The output of LS-TENG remains almost constant for more than 234 k operating cycles. A high charge density of 704 µC m-2 is obtained, 2.7 times as much as that of the current highest record in non-contact TENG. Additionally, the rotary LS-TENG lights up 4200 LEDs and continuously powers a variety of wireless sensors by harvesting wind energy at low wind speed. This work provides an important insight toward the charge transportation mechanism in dielectric liquid, and a prospective strategy for achieving highly robust TENG in micro energy harvesting for practical applications.

Polyaniline-based acid resistant membranes for controllable ion rejection performance

Nanofiltration (NF) membrane with extraordinary acid stability and controllable separation performance is crucial for acidic wastewater treatment. In this study, we reported polyaniline (PANI)-based acid resistant membranes which can realize controllable ion transport under applied potential. To achieve this, electrically conductive membranes (ECMs) were fabricated by incorporating carboxylic multi-walled carbon nanotubes (MWNTs-COOH) and acids doped PANI via in-situ chemical polymerization. The external voltage was applied to manipulate the electrostatic interactions of ECMs with charged ions in order to regulate the ion transport. The results showed that the type of acid dopants (from small acid to polymer acid) affected the physicochemical and electrochemical properties of ECMs, and therefore influenced the ion rejection performance. ECM-PANIPSSA possessed the optimal acid stability performance among the three kinds of ECMs. It was interesting to find that all the ECMs showed elevated ion rejection rate in response to electrical voltage even immersed in the acid solution for different periods. The ion transport behavior in response to applied potential attributed to the interaction of steric hindrance, Donnan effect and dielectric effect. The proposed ion transport mechanism implied that the interaction energy barrier between ions and ECMs showed a significant change as a result of applied potential. For negatively charged membrane, the Donnan potential difference became more obvious under negative voltage, which made ion transfer more difficult. By contrast, negative voltage neutralized part of the positively charged surface, and therefore weakened the electrostatic interaction for positively charged membrane. The ECMs exhibit good ion rejection and membrane permeance by applying electrical voltage, whose performance was comparable to the current acid resistant NF membrane. This work offers a feasible guideline for the development of acid resistant membranes and opens opportunities in controllable ion transport for acidic wastewater treatment.

Synergistically Constructed Electromagnetic Network of Magnetic Particle-Decorated Carbon Nanotubes and MXene for Efficient Electromagnetic Shielding.

Lightweight polymer-based nanostructured aerogels are crucial for electromagnetic interference (EMI) shielding to protect electronic devices and humans from electromagnetic radiation. The construction of three-dimensional (3D) conductive networks is crucial to realize the excellent electromagnetic shielding performance of polymer-based aerogels. However, it is difficult to realize the interconnection of different conductive fillers in the polymer matrix, which limits the further improvement of their performance. Herein, 3D ordered hierarchical porous Fe3O4-decorated carbon nanotube (Fe3O4@CNT)/MXene/cross-linked aramid nanofiber (c-ANF)/polyimide (PI) aerogels were prepared via a unidirectional freezing strategy. Benefiting from the magnetic loss effect of Fe3O4 magnetic nanoparticles, the conductive and dielectric loss effects of CNTs, and the multiple reflections induced by the 3D ordered hierarchical porous structure, the Fe3O4@CNTs/MXene/c-ANFs/PI (FMCP) aerogels with the same contents of 8 wt % of Fe3O4@CNTs and MXene exhibit a high absolute EMI shielding effectiveness (SE) of up to 67.42 dB and a microwave reflection (SER) of 0.60 dB. More importantly, the phase transition of a small amount of MXene to TiO2 optimizes the impedance matching and transmission and then improves the microwave absorption. The FMCP aerogel has an outstanding normalized surface specific SE (SSE/t) which is up to 62,654 dB cm2·g-1. Meantime, the FMCP aerogels also show super-elasticity and could maintain 91.72% of the maximum stress after 1000 cycles of compression release under a fixed deformation of 60%.

The electrical, dielectric and magnetic effect of MgFe2O4–polypyrrole and its composites

The electrical, dielectric and magnetic effect of MgFe2O4–polypyrrole and its composites

Light-induced reversible reorganizations in closed Type II reaction centre complexes: physiological roles and physical mechanisms.

The purpose of this review is to outline our understanding of the nature, mechanism and physiological significance of light-induced reversible reorganizations in closed Type II reaction centre (RC) complexes. In the so-called 'closed' state, purple bacterial RC (bRC) and photosystem II (PSII) RC complexes are incapable of generating additional stable charge separation. Yet, upon continued excitation they display well-discernible changes in their photophysical and photochemical parameters. Substantial stabilization of their charge-separated states has been thoroughly documented-uncovering light-induced reorganizations in closed RCs and revealing their physiological importance in gradually optimizing the operation of the photosynthetic machinery during the dark-to-light transition. A range of subtle light-induced conformational changes has indeed been detected experimentally in different laboratories using different bRC and PSII-containing preparations. In general, the presently available data strongly suggest similar structural dynamics of closed bRC and PSII RC complexes, and similar physical mechanisms, in which dielectric relaxation processes and structural memory effects of proteins are proposed to play important roles.

SeO2 Microwires Designed as Low‐Temperature Abrupt Microelectronic Switches, Negative Resistance, and Negative Dielectric Constant Sources

Herein, the structural, morphological, compositional, and electrical properties of SeO2 microwires are studied and analyzed. Microwires of SeO2 with dimensions of 460 m are electrically characterized in the temperature range of 17–300 K. SeO2 microwires are observed exhibiting nanocrystalline structures relating to a tetragonal phase. The microwires contained excess oxygen leading to some Se vacancies. The current–voltage (I–V) characteristics of the microwires displayed temperature‐dependent abrupt switching property revealing an “ON/OFF” current ratio of ≈90 at a threshold voltage of 0.48 V at 300 K. These features of the microwires remained down to 250 K. In addition, the temperature‐dependent electrical resistivity measurement showed that the microwires perform as a degenerate (metal like) semiconductors with quadratic temperature dependence (ρ ). Moreover, impedance spectra analysis has shown that SeO2 microwires exhibit negative resistance and negative dielectric constant effects in the spectral ranges of 20–1800 MHz. The work here indicates that SeO2 microwires can perform much better than powders in pellets form or in thin‐film form. The resonance–antiresonance of dielectric constant and abrupt switching properties are accounted as remarkable features of the SeO2 microwires nominating them as abrupt electronic switches and signal amplifiers at workable in microelectronics.

Water dopant control of structural stability and charge recombination of perovskite solar cells: A first-principles study

Humidity is a key factor in affecting the long-term stability of perovskite solar cells. However, how water interacts with the perovskite film and influences the individual energy conversion process in perovskite solar cells remains virtually unexplored. By using ab initio molecular dynamics and nonadiabatic molecular dynamics, we reveal that the MAX-terminated surface is more susceptible to water erosion. The intrusion of water brings in severe lattice distortion, whose degree follows the law of MAPbI3 > MAPbBr3 > MAPbCl3, thereby leading to attenuation in optical absorbance. Unexpectedly, the carrier lifetimes of hydrated MAX-terminated systems are prolonged, while the PbX-terminated surfaces are largely unaffected. This is due to the dielectric shielding effect of invading water molecules, hindering electron-hole recombination. Our results shed light on a comprehensive understanding of the complex effect of humidity on the perovskite performance, rationalize the contradictory experimental observations, and provide novel insights for further optimization of renewable energy devices.

Study of an asymmetry tunnel FET biosensor using junctionless heterostructure and dual material gate

In recent years, label-free sensors have been studied extensively for biomolecule detections. Label-free biosensors based on MOSFETs could achieve high detection sensitivity, the subthreshold swing of such sensors cannot break the limitation of 60 mV Dec−1 due to the physical mechanism of thermal electron emission. However, subthreshold swing less than 60 mV Dec−1 can be achieved in biosensors based on tunnel FETs working in band to band tunneling (BTBT) mode. Usually, label-free biosensors have a nanogap under the gate electrode both in MOSFET and tunnel FET (TFET), which can electrically sense the characteristics of biomolecules by dielectric constant modulation effect. In this article, we propose a novel nanogap embedded and dielectric modulated asymmetry tunnel FET biosensor with junctionless heterostructure and dual material gate, where different biomolecules can be detected effectively by adjusting the workfunctions for gate electrodes. Influences of tunnel gate, auxiliary gate and back gate workfunctions on sensitivities are explored. In addition, device-level gate effects are simulated by considering neutral and charged biomolecules. The influence of different dielectric constant at fixed charge density is also studied. Simulation results show that asymmetry dual material gate junctionless heterostructure tunnel FET (ADMG-HJLTFET) biosensor can provide higher switch ratio and higher sensitivity.

A Robust Constant–Voltage DC Triboelectric Nanogenerator Using the Ternary Dielectric Triboelectrification Effect

AbstractNowadays, the development of direct current triboelectric nanogenerators (DC‐TENGs) is oriented toward practical applications such as real‐time efficient harvesting and supplying energy. This demands DC‐TENGs with a low loss factor, high energy utilization efficiency, device portability, and output stability. Herein, a constant‐voltage DC‐TENG (C‐DC‐TENG) with robust output performance, using the ternary dielectric triboelectrification effect is demonstrated, which gives a crest factor of 1.0082. The key to improving the output charge density is the number of subdivision units, a result of theoretical simulations and experiments of C‐DC‐TENG. The optimized C‐DC‐TENG achieves not only an output charge density of 3.902 mC m−2 per round but also an average power density of 8.77 W m−2 (3.508 W m−2 Hz−1), which both set a new record for the rotary DC‐TENG. Moreover, introducing soft polyester fur enables C‐DC‐TENG to maintain 100% output without wear after 800 000 cycles. This C‐DC‐TENG is faultlessly competent for powering 2784 LEDs in series and 25 parallel‐connected hygrothermographs continuously. This work provides a promising technique for large‐scale clean energy harvesting, accelerating the progress toward practical applications of DC‐TENG.

Dynamic quantification of the overall effect of dielectric polarization

Due to the significance and universality of dielectric polarization, a quantitative assessment of this phenomenon is crucial for the sake of whether to avoid or exploit it. While triboelectrification and electrostatic induction have a direct relationship with dielectric polarization, there has been no prior work on bridging triboelectrification and dielectric polarization. To investigate the dielectric polarization effect, a dielectric-adjustable nanogenerator is built and the interplay of dielectric constant, electrical output, and surface charge is thoroughly investigated. After confirming the occurrence of self-polarization and polarization reversal during device operation, the surface charge accumulation and decay times are studied to understand the impact of dielectric polarization on prolonging the charge decay time and shortening the charge accumulation time, which are responsible for the device electrical output. Consequently, the feasibility of using the dynamic behavior of surface charge to quantify dielectric polarization is systematically studied.

Photoluminescence Polarization of MAPbBr3 Perovskite Nanostructures. Can the Dielectric Contrast Effect Explain It?

The dielectric contrast effect is usually evoked to explain anisotropy of optical properties of elongated nanoobjects, for example, semiconductor nanowires. We applied two-dimensional polarization imaging microscopy to measure the polarization of photoluminescence (PL) excitation and PL intensity of nanoaggregates of in-situ formed MAPbBr3 perovskite nanoparticles in a stretched polymeric matrix. Scanning electron microscopy images of these objects were also acquired to characterize their sizes and shapes. We find that individual perovskite aggregates with sizes of 100–300 nm often possess a PL excitation polarization degree as high as 0.5–0.9, which is up to three times higher than the polarization degree of absorption predicted by the dielectric contrast effect. Small aggregates of nanoparticles possess an emission polarization degree substantially higher than that of excitation. Computer simulations of many possible scenarios show that the dielectric contrast alone cannot quantitatively explain the polarization properties of the studied objects. We propose energy transfer to localized emitting sites and the dependence of PL yield on excitation power density as possible factors strongly influencing the polarization properties of PL emission and PL excitation, respectively.