Dielectric Mismatch Research Articles

Regulating the interfacial structure in percolating graphite nanoplate/PVDF composites via TiO2 as an interlayer towards meliorative dielectric performances

Polymer nanocomposites combining large dielectric permittivity (ε′) but low loss along with high breakdown strength (Eb) have garnered significant attention in the fields of electronic devices and power systems. To concurrently accomplish these desirable performances in pristine graphite nanoplates (GNP)/poly(vinylidene fluoride, PVDF) composites, the GNP were initially encased by a layer of anatase-type titanium dioxide (TiO2) shell, and then incorporated into PVDF to investigate the effect of TiO2 interlayer on the dielectric properties of the nanocomposites, specifically in relation to the thickness of the TiO2 shell and the nanofiller concentration. The TiO2 shell acts as a barrier layer prohibiting the electronic percolating, thus significantly reducing the dielectric loss and leakage conductivity of the GNP@TiO2/PVDF. Moreover, it not only alleviates the strong dielectric mismatch between GNP and PVDF, which restrains local electric field distortion, but also introduces charge traps, raising the energy barrier height for captured charge detrapping and preventing the growth of electric trees and subsequently promoting the Eb. For example, the PVDF with 20 wt% of GNP@TiO2 exhibited good comprehensive dielectric performances: ε′ of 50.63, loss factor of 0.071 (100 Hz) and Eb of 7.89 kV/mm. Additionally, tailoring the TiO2’s thickness can simultaneously modulate the overall dielectric parameters in the GNP@TiO2/PVDF. Theoretical fitting of experimental data via Havriliak-Negami equation uncovers the underlying polarization mechanism and the interlayer’s impact on charge migration. This work provides an efficient method for developing and producing polymeric nanodielectrics that simultaneously incorporate increased Eb with high ε′ but low loss for potential use in power devices and microelectronic devices.

Preparation and Electrorheological Behavior of Rare‐Earth La Ion Doping MIL‐125 Nanoparticles

Herein, rare‐earth element (lanthanum)‐doped MIL‐125 is synthesized via the solvothermal method. The morphology, physicochemical structure, specific surface area, and other characteristics of the synthesized material are characterized via scanning electron microscopy, transmission electron microscopy, X‐ray diffraction, Fourier transform infrared spectroscopy, Brunauer Emmett Teller, X‐ray photoelectron spectroscopy, element mapping, etc. It is observed that appropriate La doping enhances the dielectric mismatch and conductive mismatch levels of the material. This enhancement leads to a stronger interface polarization capability, thereby influencing the material's dielectric properties. Ultimately, the electrorheological fluids with La‐doped MIL‐125 as the dispersive phase show an obvious electrorheological effect.

Significantly enhanced high-temperature energy storage performance for polymer composite films with gradient distribution of organic fillers

Film capacitors as one of the most important electronic devices are heading in large capacity, heightened integration and excellent extreme-condition tolerance, which faces the challenges in maintaining outstanding performance under harsh conditions of high temperature and large electric field. Nonetheless, polymer capacitive films, which are renowned for their exceptional thermal stability, experience an escalation in conduction losses at elevated temperatures, resulting in degradation of energy storage performance. This study presents the gradient distribution of organic fillers content in all-organic polymer capacitive films utilizing electrospinning technique, the significantly improved high-temperature energy storage performance has been achieved. Glucose (GLC), a weak polar molecule rich in hydroxyl groups, is blended with the most promising polyetherimide (PEI). Experimental and theoretical calculations confirm that the formed hydrogen bond between GLC and PEI acts as a trapping site for capturing carriers and suppressing conduction losses. Furthermore, the spatial distribution of organic fillers was designed on the basis of direct mixing. The results demonstrate that the gradient composite film introduces interlayer interfacial polarization, while the dielectric mismatch between adjacent layers increases the height of potential barriers for the charge carriers across the interfaces, thereby achieving a synergistic enhancement of dielectric response and insulation strength. The maximum discharge energy density of 6.52 J/cm3 with an efficiency of 85.6 % has been achieved at 150℃ for the modified capacitive films. This work establishes a decoupling relationship between permittivity and electric breakdown strength, offering insights for the advancement of polymer films with outstanding energy storage capabilities in extreme environments.

Broken symmetries in quasi-2D charged systems via negative dielectric confinement

We report spontaneous symmetry breaking (SSB) phenomena in symmetrically charged binary particle systems under planar nanoconfinement with negative dielectric constants. The SSB is triggered solely via the dielectric confinement effect, without any external fields. The mechanism of SSB is found to be caused by the strong polarization field enhanced by nanoconfinement, giving rise to charge/field oscillations in the transverse directions. Interestingly, dielectric contrast can even determine the degree of SSB in transverse and longitudinal dimensions, forming charge-separated interfacial liquids and clusters on square lattices. Furthermore, we analytically show that the formed lattice constant is determined by the dielectric mismatch and the length scale of confinement, which is validated via molecular dynamics simulations. The novel broken symmetry mechanism may provide new insights into the study of quasi-2D systems and the design of future nanodevices.

Synergistically depressed dielectric loss and elevated breakdown strength in core@double-shell structured Cu@CuO@MgO/PVDF nanocomposites

To synergistically bolster breakdown strength (Eb) and restrain dielectric loss in the copper (Cu)/poly(vinylidene fluoride, PVDF) presenting a giant dielectric constant (ε), we explore the PVDF nanocomposites with a serial of core@double-shell Cu@CuO (copper oxide)@MgO (magnesium oxide) nanofillers with various MgO shell thicknesses. The double-shell CuO@MgO not only improves the interface compatibility between filler and matrix but also increases the energy barrier height for charge migration across the nanocomposites and facilitates the formation of charge traps, thus impeding long-distance carrier transport and resulting in restrained dielectric loss. Further, the MgO shell with appropriate ε and wide bandgap effectively alleviates the strong dielectric mismatch between neat Cu and PVDF, which significantly lessens the local electric field distortion thereby resulting in elevated Eb. Moreover, the overall dielectric performances of the Cu@CuO@MgO/PVDF can be modulated via altering the MgO shell thickness. This core@double-shell strategy offers a new paradigm for the design and preparation of percolating nanocomposites with desirable integrated dielectric performances.

Core-shell engineering of graphite nanosheets reinforced PVDF toward synchronously enhanced dielectric properties and thermal conductivity

Polymer composites integrating high dielectric permittivity (ε′) but low loss, large breakdown strength (Eb) and thermal conductivity (TC), have attracted widespread attention in electronic devices and power systems. To simultaneously achieve these properties in graphite nanosheet (GNS)/poly(vinylidene fluoride, PVDF), the GNS were first encapsulated by a layer of aluminum oxide (Al2O3), and then incorporated into PVDF, and the resulting PVDF nanocomposites’ dielectric properties and TC were explored in terms of the Al2O3 shell thickness and filler loading. The insulating Al2O3 shell serves as a barrier layer for the formation of leakage current and long-distance electron migration thus resulting in much lower dielectric loss and conductivity of the GNS@Al2O3/PVDF. It effectively mitigates the dielectric mismatch between the filler and host matrix, further introduces more traps that can capture charge carriers, and increases the barrier height for electron detrapping subsequently preventing the growth of electric trees and elevating the Eb. Moreover, the Al2O3 interlayer alleviates both the phonon density state and phonon impedance mismatches between the filler and matrix and facilitates the interfacial phonon transport thus leading to improved TC. The dielectric parameters and TC of the GNS@Al2O3/PVDF can be simultaneously modulated by optimizing the Al2O3′s thickness. This work offers an effective approach for designing and fabricating the polymeric nanodielectrics concurrently integrating high ε′ but low loss, enhanced Eb, and TC for prospective applications in power equipment and microelectronic devices.

Theoretical insights into size and dielectric confinement: Unraveling real and imaginary parts of the effective complex dielectric function in spherical multilayered quantum dots with oxide interfaces

A quantitative numerical exploration is conducted to scrutinize the combined effects of size and dielectric confinement consequences on the electronic and optical characteristics of spherical multilayered quantum dot CdSe/ZnS/CdSe/ZnS (SMLQD) and its inverted configuration ZnS/CdSe/ZnS/CdSe (ISMLQD) buried into two oxides: HfO2 and SiO2. By employing the effective mass approximation (EMA) and the density matrix approach (DMA), the derived quantized electron energy states and their associated wave functions were obtained by solving the Schrödinger equation in a spherical coordinates. The dipole transition element, both real and imaginary parts of the effective complex dielectric function (ECDF) as well as its linear, nonlinear and total counterparts are brought out for various values of inner core radii, number density of QDs and incident photon intensity. In addition, a specific analysis of electron probability distributions is provided to gain a clearer understanding of the underlying physical factors. Our findings point to a notable influence of these mentionned factors on the computed coefficients. The study unveils that the dielectric mismatch occurring at the system/oxide interfaces plays a crucial role in modifying the electronic structure and a substantial impact on both linear and third-order nonlinear components is witnessed.

Is Dielectric Mismatch Actually Important in 2D Perovskites?

Understanding and controlling exciton properties are important for the design of 2D semiconductors, such as monolayer transition metal dichalcogenides (TMDCs) and 2D halide perovskites (HPs). This paper demonstrates that the widespread strategy used for the exciton engineering of 2D HPs, based on dielectric mismatch, is flawed since dielectric mismatch has very little correlation with exciton properties. For monolayer TMDCs, however, the dielectric mismatch is shown to be more important.

Exploring the microscopic effects of surrounding matrices (HfO2 and SiO2) on CdSe/ZnS and ZnS/CdSe cylindrical core/shell quantum dot for microelectronic transport applications

The primary goal of this study is to comprehensively describe the physical impact of surrounding dielectrix oxides on the electronic and optical properties of a confined electron within CdSe/ZnS and ZnS/CdSe cylindrical core/shell quantum dot (CCSQD). The effective mass approximation and the compact density matrix approach have been employed to compute the energy eigenvalues as well as the optical absorption coefficients (OACs) and the refractive index changes (RICs). Our calculations revealed that the presence of enveloping oxides acts as an additional confinement tool altering the electron energy spectrum. The ZnS/CdSe CCSQD exhibited more pronounced response and the exploitation of the local electric factor can effectively enhance the optical nonlinearity of OACs and RICs. We demonstrated that confined electrons within the ZnS/CdSe CCSQD are subjected to an intense interaction at the microscopic scale with the host medium. In addition, saturation effects in the nonlinear computed coefficients have been meticulously analyzed in terms of size and dielectric surroundings. Our findings demonstrated that electronic band edge states are heavily impacted by the sharp dielectric mismatch occurring at QD/matrix interface which could be exploited for the creation of novel optoelectronic devices in the future.

Ultralow-content Co decoration on Ti3C2Tx MXene induced electromagnetic characteristic modulation for efficient microwave absorption

Ti3C2Tx MXene has been regarded as a promising candidate for advanced microwave absorption materials. However, the microwave absorbing performance of Ti3C2Tx MXene is suppressed by the single dielectric loss mechanism and impedance mismatch because of the high conductivity. To effectuate a good absorption capability of Ti3C2Tx MXene, this paper constructs a heterostructured Co/Ti3C2Tx hybrid by atomic layer deposition of magnetic Co nanoparticles on Ti3C2Tx nanosheets. The microstructures, magnetism, and microwave absorption behaviors of the Co/Ti3C2Tx hybrids are investigated systematically. The results show that the frequency-dependent electromagnetic parameters of the Ti3C2Tx MXene become tunable by controlling the content of Co decorations, which are conducive to both magnetic loss and impedance matching. The Co/Ti3C2Tx hybrid with ultralow Co decoration content (only 1.52 wt%) achieves the minimum reflect loss of −54.32 dB at a thin matched thickness of 1.29 mm, and the corresponding effective absorption bandwidth with reflection loss below −10 dB reaches 4.29 GHz. The atomic layer deposited magnetic metal nanostructures provides an effective strategy for preparing MXene-based hybrids which not only have high absorption efficiency but also significantly reduce the use of magnetic metals.

High energy capability in poly(vinylidene fluoride-co-chlorotrifluoroethylene) nanocomposite incorporated with Ag@polyaniline@covalent organic framework core–shell nanowire

The development of polymer film with large electrical displacement is essential for the applications of lightweight and compact energy storage. The dielectric diversity at interface of polymer composite should be addressed to realize the film capacitor with high energy density and dielectric reliability. In this work, poly(vinylidene fluoride-co-chlorotrifluoroethylene) (P(VDF-CTFE)) nanocomposite was incorporated by core–shell nanowire with covalent organic framework (COF) outer coating to alleviate the dielectric mismatch at interface. After the preparation of Ag nanowire through polyol reduction, polyaniline (PANI) and COF layers were sequentially deposited to construct core–shell Ag@polyaniline@covalent organic framework (Ag@PANI@COF) nanowire. According to the unique core–shell architecture, the COF framework is utilized to suppress the remanent polarization while high electrical displacement is preserved by the center Ag nanowire. The maximum energy density of 25.0 J/cm3 at 425 MV/m is obtained in 0.1 wt% stretched Ag@PANI@COF/P(VDF-CTFE) nanocomposite. The presence of core–shell nanowire depresses the distribution distortion of electric field and the diffusion of charge carriers under high field. This work demonstrates an effective method to develop the polymer film with large electrical displacement, and sheds a light on insightful exploration of interfacial polarized mechanism in polymer dielectric composite.

Construction of three-dimensional porous network Fe-rGO aerogels with monocrystal magnetic Fe3O4@C core-shell structure nanospheres for enhanced microwave absorption

Single dielectric loss material has defects such as strong dielectric properties and impedance mismatch. Hence, developing electromagnetic wave (EMW) absorption materials with both outstanding EMW absorption and favourable impedance matching performances is still a great challenge. A large number of literature have reported that combining dielectric materials with magnetic materials to enhance microwave absorption. However, there is little literature on the effect of crystal structure on the absorbing properties of materials. Owing to the virtues of light weight, low density and thin thickness of aerogel, which has been widely utilized in EMW absorption materials. Herein, Fe-based metal organic framework-reduced graphene oxide (Fe-rGO) aerogel was synthesized via simple hydrothermal method and freeze-drying. Besides, Polyvinyl Pyrrolidone (PVP) was used as a surfactant to endow Fe3O4 nanospheres with uniform size and smooth morphology. Moreover, Fe3O4 nanospheres with different crystal phase (monocrystal and polycrystal) structure were obtained under different carbonization temperatures (600 and 800 °C). Through comparison, the monocrystal Fe3O4 nanospheres show better microwave absorption and impedance matching performance than that of polycrystal Fe3O4 nanospheres. In addition, the electromagnetic parameters can be adjusted by regulating the mass ratio of Fe-based metal organic framework (Fe-MOF) to GO. As a consequence, the prepared 600Fe-rGO 2:1 aerogel achieves the minimum reflection loss (RLmin) of −64.89 dB and a broad effective absorption bandwidth (EAB) of 6.96 GHz with a low filling content of 5 wt%, showing excellent EMW absorption and impedance matching property. In short, the structural design of single crystal magnetic Fe3O4 nanospheres provides inspiration and guidance for future research of enhanced microwave absorption materials.

Theoretical modeling of nonlinear optical properties in spheroidal CdTe/ZnTe core/shell quantum dot embedded in various dielectric matrices

The theoretical investigation of the electronic and nonlinear optical properties in spheroid-shaped CdTe/ZnTe core/shell quantum dots (CSQDs) embedded into two commonly adopted dielectric matrices (PVA, SiO2) is done in the framework of the Effective Mass Approximation (EMA). The discrete intra-band confined energy levels and their matching wave functions were calculated by solving the stationary Schrödinger equation taking into account the Compact Density Matrix (CDM) approach. The effect of the dielectric mismatch between the system and the capped matrix has been studied and discussed. Our numerical results revealed that the third-order nonlinear (TON) optical susceptibility χ3 is strongly influenced by the geometrical parameters and the dielectric environment.

Effects of the magnetic field and the off-center displacement on the third-order nonlinear optical susceptibility of inverted core/shell spherical one-electron quantum dots

The third order nonlinear optical susceptibility (TONOS) of an inverted ZnS/CdSe core–shell spherical quantum dot embedded in SiO 2-matrix with or without impurity, and subjected to an external magnetic field is investigated. Within the framework of effective mass approximation and using B-splines basis functions, the energy levels, the dipole matrix elements and the TONOS are computed. The dielectric mismatch in the interface dots as well as the effective mass dependence on the core and shell regions are taken into account. It is revealed that, simultaneously the shell size, magnetic field and off-center displacement have a noticeable effect on the positions and the heights of the peaks of the TONOS. Moreover, we have shown that, due to the magnetic field and the off-center displacement effects, the TONOS takes different profiles associated with the polarization direction (parallel and perpendicular). In the perpendicular polarization, two peaks of the nonlinear optical properties appear for each off-center displacement value corresponding to the two transversal allowed transitions. The shift towards higher energies of the peak position and the reduction of the intensity of the peak when the magnetic field increases are recorded in the transversal transition case. Furthermore, in the longitudinal transition, as increasing the magnetic field strength, the intensity of the peak of the TONOS grows and the position of the peak is shifted towards lower frequencies. The dielectric constant, effective mass and conduction band offset of the materials that constitute the core and shell are equally found to modify significantly the main features of the susceptibility.

Corona: An effective polarization strategy of polymer composites with high-k filler for piezoelectric nanogenerators

Piezoelectric nanogenerators (PENGs) are mushrooming owing to demand of swift transformation of power supply from fossil fuel to green energy. Piezoelectric ceramics are enthusiastically chased because glorious PENGs demand for high piezoelectricity. Generally, brittleness of ceramics can be compensated by polymer, while the dielectric mismatch between low permittivity of polymer and high permittivity of ceramics plaguing researchers so long. Traditional contact poling is always interrupted by abrupt dielectric breakdown due to electric field concentration at interface between polymer and fillers. Here, we propose a strategy of using corona polarization instead of traditional contact polarization to insistently polarize large-area polymer composite films with high-k filler. The corona polarization technique can ignore the negative effect of local short circuit on polarization failure owing to prominent lateral insulation between deposited charges on surface of composites film, consequently obtaining well-performed piezoelectricity. Henceforth, polarization failure did not occur using corona even under poling voltage of 26 kV. The corona-poled PVDF/Y-ZnO PENG with only 15 wt% content of fillers generated output power density of ∼1064 μW/cm3. Our work will pilot the development of polymer composites with high-k filler and piezoelectric nanogenerators.

Effect of Al2O3 insertion layer on ferroelectricity in HfO2/ZrO2 nanolaminates

Ferroelectric HfO2 with excellent scaling capability and good complementary-metal-oxide-semiconductor (CMOS) technology compatibility has triggered the interest in nonvolatile memories. Here, (HfO2−ZrO2)3/mAl2O3/ (HfO2−ZrO2)3 (m donate the Al2O3 (AO) thickness) nanolaminates with different AO thicknesses were fabricated using atomic layer deposition method. Ferroelectricity and reliability were investigated by varying AO thickness in the deposition process. The highest remnant polarization (Pr) of 23.87 μC/cm2 is obtained in (HZO)3/1AO/(HZO)3 nanolaminate with 1 nm-thick AO dielectric layer. The leakage current can be decreased by 2−3 orders of magnitude with the increase of AO thickness. The performance enhancement is ascribed to the interfacial polarization because of the dielectric mismatch between AO and HfO2−ZrO2 (HZO) and high breakdown strength of AO. The insertion of lower-permittivity AO can effectively modulate the distribution of electric field in nanolaminates and achieves a significant improvement in reliability. Improved ferroelectricity and reliability in ferroelectric/dielectric/ferroelectric structure pave a new way for the designation of HfO2-based ferroelectric memories with broader thickness range.

Selenophene-Based 2D Ruddlesden-Popper Perovskite Solar Cells with an Efficiency Exceeding 19.

Two-dimensional (2D) Ruddlesden-Popper (RP) perovskites have emerged as attractive candidates for high-performance perovskite solar cells (PSCs) thanks to their superior environmental and structural stability. However, 2D RP PSCs exhibit larger exciton binding energy due to the dielectric mismatch between the organic and inorganic layers, resulting in poorer photovoltaic performance compared to their 3D analogs. Here, we developed a selenophene-based spacer, namely, 2-selenophenemethylammonium (SeMA), for stable and efficient 2D RP PSCs. The 2D perovskite film using methylammonium (MA) as the A-site cation (nominal n = 5) shows excellent film quality with large grain size and a preferred vertical orientation relative to the substrate. Furthermore, we have successfully demonstrated the effectiveness of a predeposition transport layer (PDTL) consisting of [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) in passivating surface defects of the perovskite film and inducing densification of the upper PCBM electron transport layer. This densification promotes efficient extraction and transport of electrons. The optimized PSCs based on 2D RP perovskite using MA as A-site cation (nominal n = 5) achieved a power conversion efficiency (PCE) of 17.25%, which was further boosted to 19.03% when using formamidinium (FA) as A-site cation. This represents a record PCE of 2D RP PSCs by using the selenophene-based spacer. Moreover, these 2D RP PSCs significantly improve thermal, moisture, and light stability. Our results provide significant implications for the synergistic strategy of developing selenophene-based spacers and device engineering methods for achieving highly efficient and stable 2D RP perovskite solar cells.

Dielectric Mismatch Effects on Polyelectrolyte Solutions in Electrified Nanopores: Insights from Mean-Field Theory

We utilize the self-consistent field theory to explore the mechanical and electrical properties of charged surfaces immersed in polyelectrolyte solutions that could be potentially useful for electrochemical applications. Our research focuses on how the dielectric heterogeneity of the solution could affect the disjoining pressure and differential capacitance of the electric double layer. Relying on the developed theoretical framework, based on the Noether’s theorem, we calculate the stress tensor, containing the term, arising from the conformational entropy of the polymer chains. With its help we compute the disjoining pressure in polyelectrolyte solution confined between two parallel charged surfaces and analyze its behavior as a function of separation between the surfaces for different values of dielectric mismatch parameter. We also calculate the differential capacitance of the electric double layer and discuss how dielectric heterogeneity of the polyelectrolyte solution influences its values.

Renormalized charge and dielectric effects in colloidal interactions: a numerical solution of the nonlinear Poisson–Boltzmann equation for unknown boundary conditions

The Derjaguin–Landau–Verwey–Overbeek (DLVO) theory, introduced more than 70 years ago, is a hallmark of colloidal particle modeling. For highly charged particles in the dilute regime, it is often supplemented by Alexander’s prescription (Alexander et al. in J Chem Phys 80:5776, 1984) for using a renormalized charge. Here, we solve the problem of the interaction between two charged colloids at finite ionic strength, including dielectric mismatch effects, using an efficient numerical scheme to solve the nonlinear Poisson–Boltzmann (NPB) equation with unknown boundary conditions. Our results perfectly match the analytical predictions for the renormalized charge by Trizac and coworkers (Aubouy et al. in J Phys A 36:5835, 2003). Moreover, they allow us to reinterpret previous molecular dynamics (MD) simulation results by Kreer et al. (Phys Rev E 74:021401, 2006), rendering them now in agreement with the expected behavior. We furthermore find that the influence of polarization becomes important only when the Debye layers overlap significantly.Graphical

Nonempirical Range-Separated Hybrid Functional with Spatially Dependent Screened Exchange.

Electronic structure calculations based on density functional theory (DFT) have successfully predicted numerous ground-state properties of a variety of molecules and materials. However, exchange and correlation functionals currently used in the literature, including semilocal and hybrid functionals, are often inaccurate to describe the electronic properties of heterogeneous solids, especially systems composed of building blocks with large dielectric mismatch. Here, we present a dielectric-dependent range-separated hybrid functional, screened-exchange range-separated hybrid (SE-RSH), for the investigation of heterogeneous materials. We define a spatially dependent fraction of exact exchange inspired by the static Coulomb-hole and screened-exchange (COHSEX) approximation used in many-body perturbation theory, and we show that the proposed functional accurately predicts the electronic structure of several nonmetallic interfaces, three- and two-dimensional, pristine, and defective solids and nanoparticles.