Dielectric Constant Of Medium Research Articles

Solid-state structural transformation triggered by water in zinc(Ⅱ) coordination polymers based on 3,5-ditertbutyl-2-hydroxybenzoic acid:Structural characterization and dielectric properties

Single-crystal-to-single-crystal (SCSC) transformation provides a good platform for obtaining new functional coordination polymers. In this study, we demonstrate a violent and rapid structural transformation between two d10 coordination polymers (CPs). The complex 1 [Zn(3,5-thbzc)2(C2H6O)2] transformed into the complex 2 {[Zn(3,5-thbzc)2(H2O)2]·C3H7NO·2H2O} (where t = tbutyl, hbzc− = 2-Hydroxybenzoato) triggered by deionized water under standard temperature and pressure conditions in solid state. The transformation reaction was confirmed using single-crystal XRD, PXRD and SEM. The results showed that complex 1 adopts a bidentate chelate six-coordination mode, and complex 2 adopts a monodentate four-coordination mode. SEM clearly showed that complex 2 was in the form of random nanowire clusters, suggesting that their transformation required degradation of the entire crystal structure. UV–Vis–NIR spectra were used to calculate the band gaps of complexes 1 and 2, which demonstrated wide-bandgap semiconductor-like materials with ∼3.2 eV band gap widths. The results of dielectric studies of complex 1 revealed that it possessed a medium dielectric constant (κ = 6.08 at 1 kHz), while complex 2 displayed an even higher dielectric constant (κ = 7.97 at 1 kHz) at room temperature. Interestingly, parent complex 1 exhibited a small ladder-like dielectric anomaly at 188 °C, while progeny complex 2 did not. This paper describes a new strategy for preparing adjustable functional dielectric materials.

The study of BMN cubic pyrochlores based multi-layer capacitors

The multi-layer ceramic capacitor (MLCC) is prepared with Bi1.5MgNb1.5O7 (BMN) pyrochlores, which has medium dielectric constant, large dielectric tunability, and especially the very small dielectric loss. The multilayer ceramic capacitors with Bi1.5MgNb1.5O7 as the dielectric material are prepared by a tape-casting method. The dielectric constant of the BMN thick film was observed to be superior to that of the bulk material, indicating its potential application in electronic devices. The increase in dielectric constant during the preparation of multilayer ceramic capacitors was explained by investigating the interdiffusion between the ceramic thick films and the electrodes. The BMN thick films and Ag0.7/Pd0.3 electrodes showed a dense microstructure and serial interfaces when sintering at 1050 °C for 1.5 h. The capacitor exhibited good temperature stability with a dielectric constant temperature coefficient of −249.94 ppm/°C, a relative dielectric constant of 216, and a dielectric loss of 0.00036. Provides insights for the development and optimization of high-performance dielectric tunable electronic device.

The effect of Ti/Ba ratio on the microstructures and microwave dielectric properties of BaTi4O9–Ba2Ti9O20 composite ceramics

Considering the strengths and weaknesses of the two distinct physical phases of BaTi4O9 and Ba2Ti9O20, we opted to combine them in order to harness the synergistic effects of their properties. In contrast to conventional two-phase composites, we synthesized BaTi4O9–Ba2Ti9O20 microwave ceramics with varying Ti/Ba ratios utilizing the solid-state reaction method. The phase compositions, surface morphologies, microwave dielectric properties and impedance analyses of the composite ceramics with different Ti/Ba ratios were systematically investigated. The X-ray diffractograms showed that the content of BaTi4O9 decreases rapidly as the Ti/Ba ratio increases from 4.15 to 4.35 and Ba2Ti9O20 becomes the main phase when Ti/Ba = 4.25. From complex impedance spectra, it can be seen that the arc gradually compresses as the Ti/Ba ratio increases, representing a decrease in the resistance. The ceramic possessing a Ti/Ba ratio of 4.15 exhibited superior microwave dielectric properties, characterized by Q × f = 16,622 GHz, εr = 38.01, and τf = 10.37 ppm/°C. These results provide guidance for the future design of high-performance microwave ceramics with medium dielectric constant.

Low-cost, simple preparation and outstanding energy density of glass fiber reinforced PVDF polymer flexible composites

To make the product commercially viable and applicable, the inclusion of glass fiber filler with a low cost and medium dielectric constant (ε) is adopted as the filler. Synchronously, representative polyvinylidene fluoride (PVDF) with high permittivity and breakdown strength is selected as optimal polymer matrix. And surface modifying agent is employed as organic coatings to weaken the surface energy of glass fiber and boost the interfacial inter-action. An investigation of dielectric properties was conducted by preparing flexible composites consisting of various content of glass fiber. The ε of composites can be significantly enhanced in the PVDF composites with glass fiber, and the breakdown strength (BDS) is remained at a high level. Moreover, within a specific content range, glass fiber makes the ε and BDS of the material increase synchronously. This work provides a facile strategy for the development of excellent performance, simple preparation and low-cost flexible composites.

Unveiling the impact of exchange-correlation functionals on the description of key electronic properties of non-fullerene acceptors in organic photovoltaics.

Non-fullerene electron acceptors have emerged as promising alternatives to traditional electron-acceptors in the active layers of organic photovoltaics. This is due to their tunable energy levels, optical response in the visible light spectrum, high electron mobility, and photochemical stability. In this study, the electronic properties of two representative non-fullerene acceptors, ITIC and Y5, have been calculated within the framework of density functional theory using a range of hybrid and non-hybrid density functionals. Screened range-separated hybrid (SRSH) approaches were also tested. The results are analyzed in light of the previously reported experimental outcomes. Specifically, we have calculated the oxidation and reduction potentials, fundamental and optical gaps, the highest occupied molecular orbital and lowest unoccupied molecular orbital energies, and exciton binding energies. Additionally, we have investigated the effects of the medium dielectric constant on these properties employing a universal implicit solvent model. It was found that hybrid functionals generally perform poorly in predicting oxidation potentials, while non-hybrid functionals tend to overestimate reduction potentials. The inclusion of a large Hartree-Fock contribution to the global or long range was identified as the source of inaccuracy for many hybrid functionals in predicting both redox potentials and the fundamental and optical gaps. Corroborating with the available literature, ∼50% of all tested functionals predicted very small exciton binding energies, within the range of ±0.1eV, that become even smaller by increasing the dielectric constant of the material. Finally, the OHSE2PBE and tHCTHhyb functionals and the optimal tuning SRSH approach emerged as the best-performing methods, with good accuracy in the description of the electronic properties of interest.

Improving the optoelectronic properties of monolayer MoS2 field effect transistor through dielectric engineering

The reduced dielectric screening in atomically thin two-dimensional materials makes them very sensitive to the surrounding environment, which can be modulated to tune their optoelectronic properties. In this study, we significantly improved the optoelectronic properties of monolayer MoS2 by varying the surrounding environment using different liquid dielectrics, each with a specific dielectric constant ranging from 1.89 to 18. Liquid mediums offer the possibility of environment tunability on the same device. For a back-gated field effect transistor, the field effect mobility exhibited more than two-order enhancement when exposed to a high dielectric constant medium. Further investigation into the effect of the dielectric environment on the optoelectronic properties demonstrated a variation in photoresponse relaxation time with the dielectric medium. The rise and decay times were observed to increase and decrease, respectively, with an increase in the dielectric constant of the medium. These results can be attributed to the dielectric screening provided by the surrounding medium, which strongly modifies the charged impurity scattering, the band gap, and defect levels of monolayer MoS2. These findings have important implications for the design of biological and chemical sensors, particularly those operating in a liquid environment. By leveraging the tunability of the dielectric medium, we can optimize the performance of such sensors and enhance their detection capabilities.

Kinetic and mechanistic study of oxidation of valine by pyridinium chlorochromate in aqueous DMF medium

Oxidative transformation of Valine by pyridinium chlorochromate in aqueous DMF medium, containing perchloric acid has been studied at 40 ℃. The rate of reaction was found to be of first order dependence on Oxidant, Valine, and H+ ion Concentration. The increase in the rate of reaction with increase in acidity indicates the involvement of a protonated chromium(VI) species in the rate-determining step. The product of oxidation has been identified as aldehyde. The rate of reaction decreased with increase in the polarity (dielectric constant of medium) of solvent, which indicates that there is involvement of an ion–dipole type of interaction in the rate-determining step. The activation parameters have been evaluated. On the basis of the experimental findings, a suitable mechanism and rate law has been proposed.

Effect of MgO and Nb2O5 co-doping on the microwave dielectric properties of Y2Ti2O7 ceramics

This study investigated the effects of MgO and Nb2O5 co-doping on the microwave dielectric properties of Y2Ti2O7 ceramics with a medium dielectric constant. Substituting (Mg1/3Nb2/3)4+ for Ti4+ in Y2Ti2O7 ceramics effectively enhanced the quality factor Qf. The interrelationship among the crystalline structure, microstructure, and microwave properties of Y2(Ti1-x(Nb2/3Mg1/3)x)2O7 (0 ≤ x ≤ 0.15) sintered at 1500 °C with different holding times were examined using XRD, SEM, TEM, XPS, Raman, and network analyzer. The research findings indicate that all samples exhibited a single cubic pyrochlore phase without a second phase. Moreover, the densification temperature increased with an increase in (Mg1/3Nb2/3)4+ content, and the relative density could be increased by increasing the sintering dwell time. The sample with x = 0.025 demonstrated an optimal densification temperature of 1500 °C. TEM/SAED pattern analysis revealed the existence of a "superlattice" due to the occurrence of a 1:2 cation ordering structure at high temperatures. As the dwell time was extended from 4 h to 12 h, the quality factor Qf increased from 10,830 GHz to 46,068 GHz. The sample with x = 0.025 sintered at 1500 °C for 12 h exhibited the best microwave dielectric properties (permittivity(εr) = 62.5, Qf = 46,068 GHz, and the temperature coefficient of frequency (TCF) = 290.8 ppm/°C).

Comparison of the Electrical Performance of AlN and HfO<sub>2 </sub>Passivation Layer in AlGaN/GaN HEMT

Different material thickness with medium and high dielectric constant can impact the performance and reliability of high electron mobility transistor device. With varying the thickness of the passivation layer, the effect of it towards the device performance is still unclear. Two different insulator layers with a medium dielectric and a high dielectric constant namely Aluminium Nitride and Hafnium Oxide are used as passivation layer in AlGaN/GaN HEMT. Both material performance was simulated via COMSOL software by varying the thickness and the drain current output were compared. The passivation layer thickness of 10nm at Vds=6 V and Vgs=5 V, HfO2 outperforms AlN with the output drain current of 39 mA compared to 35 mA respectively. It was observed that HfO2 can attain higher threshold voltage, Vth as compared to the AlN because of the influence of its material properties that shows a direct proportional relationship between Vth and dielectric constant. Using high dielectric constant material like HfO2, we observe the ON-voltage gradually decreases as the thickness of the passivation layer increased. Out of all the thickness simulated for HfO2 and AlN, 10nm produced the highest drain current output instead of layer thickness of 20nm.

Measurement of two‐layer medium dielectric property using a novel parameters model in radio frequency

SummaryThe RLCG parameters model and one‐port measurement model of the closed‐double ring electrodes have been established to obtain the dielectric properties of two‐layer medium in radio frequency. The accuracy of these models was verified by electromagnetic simulation experiments and the permittivity measurement experiments under 160 MHz. Results showed that (1) When the medium dielectric constant , the calculation values based on the models and the real values, have a determination coefficient using the quadratic regression function fitting; (2) the effective sensing depth of the ring electrodes was about the structural wavelength of the ring electrodes; (3) the measuring permittivity of the intact mature corn ear were in good agreement with the results in the literatures. This study demonstrates a practical technique to extract the permittivity of two‐layer medium with the ring electrodes, and will provide a new way to in situ monitoring the physiological changes of two‐layer medium and environmental parameters.

Structure characteristics and microwave dielectric properties of novel Re2Ce6O15 (Re[dbnd]Y, Sm, Nd, La) ceramics

Based on the cubic fluorite structure, novel ceramic series with Re2Ce6O15 (ReY, Sm, Nd, La) formula had been designed and prepared successfully using solid-state reaction method. The new Re2Ce6O15 (ReY, Sm, Nd, La) ceramics all presented a single phase indexed as CeO2-type structure, belonged to Fm-3m space. The formation mechanism and lattice constant of the crystal structure had been investigated using Rietveld structural refine method. The microstructure of the Re2Ce6O15 (ReY, Sm, Nd, La) ceramics had been evaluated by pores, grain size and its distribution. The dielectric constant had been corrected for the exclusion of pores and depended on the ionic polarizability. The quality factors of the Re2Ce6O15 (ReY, Sm, Nd, La) ceramics had been investigated by packing fraction related to the phonon vibration. The temperature coefficient of resonance frequency had been analyzed using the bond valence theory. The Re2Ce6O15 (ReY, Sm, Nd, La) ceramics exhibited excellent microwave dielectric properties with medium dielectric constant, high quality factors and stable resonant frequency temperature coefficient.

Equilibrium Studies on Pd(II)–Amine Complexes with Bio-Relevant Ligands in Reference to Their Antitumor Activity

This review article presents an overview of the equilibrium studies on Pd-amine complexes with bio-relevant ligands in reference to their antitumor activity. Pd(II) complexes with amines of different functional groups, were synthesized and characterized in many studies. The complex formation equilibria of Pd(amine)2+ complexes with amino acids, peptides, dicarboxylic acids and DNA constituents, were extensively investigated. Such systems may be considered as one of the models for the possible reactions occurring with antitumor drugs in biological systems. The stability of the formed complexes depends on the structural parameters of the amines and the bio-relevant ligands. The evaluated speciation curves can help to provide a pictorial presentation of the reactions in solutions of different pH values. The stability data of complexes with sulfur donor ligands compared with those of DNA constituents, can reveal information regarding the deactivation caused by sulfur donors. The formation equilibria of binuclear complexes of Pd(II) with DNA constituents was investigated to support the biological significance of this class of complexes. Most of the Pd(amine)2+ complexes investigated were studied in a low dielectric constant medium, resembling that of a biological medium. Investigations of the thermodynamic parameters reveal that the formation of the Pd(amine)2+ complex species is exothermic.

Real-Time Optical Measurements of Nanoparticle-Induced Melting and Resolidification Dynamics

The photothermally induced nanoscale dynamics of rapid melting and resolidification of a thin layer of molecular material surrounding a nanoparticle is examined in real time by an all-optical approach. The method employs pulsed periodic modulation of the medium's dielectric constant through absorption of a low-duty-cycle laser pulse train by a single nanoparticle that acts as a localized heating source. Interpretation of experimental data, including inference of a phase change and of the liquid/solid interface dynamics, is obtained by comparing experimental data with results from coupled optical-thermal numerical simulations. The combined experimental/computational workflow presented in this proof-of-principle study will enable future explorations of material parameters at nanoscale, which are often different from their bulk values and in many cases difficult to infer from macroscopic measurements.

Energy Storage Properties of Sol-Gel-Processed SrTiO3 Films.

Dielectric films with a high energy storage density and a large breakdown strength are promising material candidates for pulsed power electrical and electronic applications. Perovskite-type dielectric SrTiO3 (STO) has demonstrated interesting properties desirable for capacitive energy storage, including a high dielectric constant, a wide bandgap and a size-induced paraelectric-to-ferroelectric transition. To pave a way toward large-scale production, STO film capacitors were deposited on Pt(111)/Ti/SiO2/Si(100) substrates by the sol-gel method in this paper, and their electrical properties including the energy storage performance were studied as a function of the annealing temperature in the postgrowth rapid thermal annealing (RTA) process. The appearance of a ferroelectric phase at a high annealing temperature of 750 °C was revealed by X-ray diffraction and electrical characterizations (ferroelectric P-E loop). However, this high dielectric constant phase came at the cost of a low breakdown strength and a large hysteresis loss, which are not desirable for the energy storage application. On the other hand, when the RTA process was performed at a low temperature of 550 °C, a poorly crystallized perovskite phase together with a substantial amount of impurity phases appeared, resulting in a low breakdown strength as well as a very low dielectric constant. It is revealed that the best energy storage performance, which corresponds to a large breakdown strength and a medium dielectric constant, is achieved in STO films annealed at 650 °C, which showed a large energy density of 55 J/cm3 and an outstanding energy efficiency of 94.7% (@ 6.5 MV/cm). These findings lay out the foundation for processing high-quality STO film capacitors via the manufacturing-friendly sol-gel method.

Study of optical properties of Ag ellipsoid nanostructures by discrete dipole approximation method

In this paper, we investigate optical properties of silver ellipsoid nanostructures (SENs) by means of discrete dipole approximation (DDA), when these nanoparticles are embedded into the water. Absorption, scattering and extinction cross-sections of the SENs were calculated by change of incident wavelength in visible and near infrared region. Moreover, height, wavelength and full width at half maximum (FWHM) of extinction cross-section peaks (due to plasmon resonances) were studied by change of nanostructure's size and dielectric constant of medium. Our results show that, there are only two peaks of transverse dipole and longitudinal dipole modes in this spectrum.

Effect of polyol type on the structure and properties of lecithin liposomes prepared using the polyol dilution method

The polyol dilution (PD) method is an approach for preparing liposomes by pre-mixing a lipid/polyol binary mixture, followed by hydration, and is widely used in the cosmetics industry. In this method, polyols play an important role in the formulation design and application, however, the effect of the polyol type on liposomes (PD-liposomes) is yet to be understood. In this study, we investigated the effect of three types of polyols—glycerol (Gly), propylene glycol (PG), and 1,3-butylene glycol (BG)—on the physicochemical properties of PD-liposomes composed of hydrogenated egg yolk lecithin (EL). The particle size of PD-liposomes was controlled by adjusting the type and concentration of the polyols. Furthermore, the addition of polyols improved the dispersion stability, indicating that PD-liposomes are suitable for industrial applications. The morphology of lipid/polyol binary mixture was the determining factor of the liposome structure, and the formation region of unilamellar vesicles (ULVs) and multilamellar vesicles (MLVs) was closely related to the dielectric constant of the dispersion medium. ULVs were formed using a high dielectric constant dispersion medium, such as Gly, and MLVs were formed using a low dielectric constant dispersion medium, such as PG and BG at high concentrations. This study showed that the addition of polyols improves the phase homogeneity of the bilayer and that PG or BG is more effective than Gly. The control of the homogeneity of the bilayer phase is an effective technique to prevent leakage and control the sustained release of the active ingredient; thus, this method enhances the efficacy of the active ingredient. This study is the first to systematically elucidate the control mechanisms of the physicochemical properties of PD-liposomes, including the particle size, dispersion stability, shape, and phase state of the bilayer. Our findings will contribute to the wide range of applications of PD-liposomes.

T-matrix simulations of the optical response of gold nanorods: Impact of dielectric function of nanorods on the simulated optical properties and their sensitivity to the dielectric environment

The T-matrix approach is used to elucidate the influence of the dielectric function of gold nanorods on their optical response. On the basis of extensive and systematic numerical simulations, we follow the spectral variations of extinction efficiency and field enhancement as a function of the nanorod’s dielectric properties, medium dielectric constant, and aspect ratio. Simulations with six available tabulated gold dielectric functions show different locations of the longitudinal localized surface plasmon resonance (LSPR). A shift of up to 50 nm is found and compared with experimental data available in the literature. With the increasing refractive index of the ambient medium, the peaks red shift to higher wavelengths, which can be understood in terms of the reduced plasmon energy due to the reduced restoring forces of the plasmon oscillations. A linear correlation exists between the relative shift of the resonance wavelength and the relative increment of the medium refractive index. The correlation coefficient represents the sensitivity of the resonance to the dielectric environment and is more dependent on the aspect ratio than the dielectric properties of nanorods. However, a non-linear correlation is observed between the relative changes in the resonance extinction peak and the relative refractive index increment of the medium, which is considerably affected by the dielectric properties of nanorods. Results reveal that the field enhancement is influenced primarily by the dielectric environment and the aspect ratio. Simulations with the size-corrected dielectric functions show a broadening of the LSPR with no significant shift, in addition to a reduced extinction efficiency and field enhancement.

Crystal structures, bond characteristics, and dielectric properties of novel middle-εr Ln3NbO7 (Ln = Nd, Sm) microwave dielectric ceramics with opposite temperature coefficients

This study synthesized two novel middle-εr Ln3NbO7 (Ln = Nd, Sm; named NNO and SNO) microwave dielectric ceramics through the classic solid-state process. The results of XRD and Rietveld refinement show that NNO and SNO ceramics formed pure phases with the space group Cmcm (63) and C2221 (20), respectively. The properties of Ln-O and Nb–O bonds of NNO and SNO ceramics were calculated based on the P–V–L theory. The Nb–O bonds positively affect the crystal structure stability of the two ceramics. The optimum microwave dielectric properties were obtained (NNO: εr = 31.61, Q·f = 6,615 GHz (at 6.10 GHz), and τf = −455.70 ppm/°C; SNO: εr = 34.55, Q·f = 11,625 GHz (at 5.77 GHz) and τf = 72.59 ppm/°C) when the samples sintered at 1550 °C. Notably, SNO ceramic shows a low dielectric loss and medium dielectric constant, and the opposite τf of NNO and SNO ceramics provide the possibility to fabricate microwave dielectric devices with good temperature stability.

Probing Electrolyte Influence on CO2 Reduction in Aprotic Solvents

Selective CO2 capture and electrochemical conversion are important tools in the fight against climate change. Industrially, CO2 is captured using a variety of aprotic solvents due to their high CO2 solubility. However, most research efforts on electrochemical CO2 conversion use aqueous media and are plagued by competing hydrogen evolution reaction (HER) from water breakdown. Fortunately, aprotic solvents can circumvent HER, making it important to develop strategies that enable integrated CO2 capture and conversion. However, the influence of ion solvation and solvent selection within nonaqueous electrolytes for efficient and selective CO2 reduction is unclear. In this work, we show that the bulk solvation behavior within the nonaqueous electrolyte can control the CO2 reduction reaction and product distribution occurring at the catalyst–electrolyte interface. We study different tetrabutylammonium (TBA) salts in two electrolyte systems with glyme ethers (e.g., 1,2 dimethoxyethane or DME) and dimethyl sulfoxide (DMSO) as a low and high dielectric constant medium, respectively. Using spectroscopic tools, we quantify the fraction of ion pairs that forms within the electrolyte. Also, we show how ion pair formation is prevalent in DME and is dependent on the anion type. More importantly, we show that as ion pair formation decreases within the electrolyte, CO2 current densities increase, and a higher CO Faradaic efficiency is observed at low overpotentials. Meanwhile, in an electrolyte medium where the ion pair fraction does not change with the anion type (such as in DMSO), a smaller influence of solvation is observed on CO2 current densities and product distribution. By directly coupling bulk solvation to interfacial reactions and product distribution, we showcase the importance and utility of controlling the reaction microenvironment in tuning the electrocatalytic reaction pathways. Insights gained from this work will enable novel electrolyte designs for efficient and selective CO2 conversion to desired fuels and chemicals.

Enhanced energy storage density in poly(vinylidene fluoride-hexafluoropropylene) nanocomposites by filling with core-shell structured BaTiO3@MgO nanoparticals

Filling with high dielectric constant inorganic nanoparticles is an effective approach to enhance the energy storage performance of an organic dielectric. However, the dielectric mismatch between ceramic and polymer causes early breakdown, which limits the storage density of ceramic/polymer nanocomposites in the application of dielectric capacitors. Herein, we employed MgO as a buffer barrier to mitigate the mismatched dielectric characteristics among BaTiO3 (BT) nanoparticles and poly(vinylidene fluoride-hexafluoropropylene) (P(VDF-HFP)) substrate considering its high insulation and medium dielectric constant. The alien oxide was coated on the spherical BT by a simple chemical precipitation process, forming a BaTiO3@MgO (BT@MgO) core-shell nanostructure, which has been carefully examined by TEM and EDS. The BT-MgO heterogeneous interfacial region provides channels for carriers and promotes charge movement, and therefore the dielectric constant and potential shift have been significantly enhanced. The BT@MgO/P(VDF-HFP) nanocomposite with 1 vol% filling ratio delivered a maximum energy density Ud, and the value reaches up to 5.6 J/cm3 that is 40.0 % and 55.6 % greater than that of the host matrix and BT-filled counterpart with the same filler amount. The BT@MgO core-shell nanostructure demonstrates an alternative way to effectively heighten the energy storage performance of ceramic/polymer composite dielectrics.