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- 2018
- arbitrary coupling coefficients
- Dielectric resonator
- filtering
- coupler
- filtering balun
- dual-band
- dual-mode dielectric resonator (DR)
- Electronic Science and Technology
- Nantong University
- Sun Yat-Sen University
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Complex Dielectric and Impedance Spectroscopic Studies in a Multiferroic Composite of Bi2Fe4O9-BiFeO3
摘要： Complex dielectric and impedance spectroscopic studies have been carried out in a detailed manner on the system comprising of Bi2Fe4O9-BiFeO3 composite particles dispersed in a α-Fe2O3 matrix as prepared using ball milling and controlled annealing treatments. This multiferroic composite is observed to exhibit a giant dielectric constant associated with a low tangent loss. A non-Debye type of relaxation has been deduced based on complex modulus analysis. Based on these studies, the important role played by bismuth ferrite nanoshell in the core-shell composite of Bi2Fe4O9-BiFeO3 is elucidated for the observed complex impedance spectroscopic properties of the system. Electron hopping across Fe2+/Fe3+ and oxygen vacancies are deduced to be playing an important role in conduction mechanisms based on activation energy analysis of the complex impedance spectroscopy results.
关键词： dielectric,composite,Bi2Fe4O9,multiferroic
更新于2025-09-23 15:23:52
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Time-and-Space Resolved Cathode Plasma Expansion Velocities in Magnetically Insulated Coaxial Diode With a Metal-Dielectric Cathode
摘要： Time-and-space resolved cathode plasma expansion velocities in magnetically insulated coaxial diodes (MICD) with edged cathodes made of bronze dielectric, bronze, and graphite have been compared through optical diagnosis. The voltage and current of the diode pulse of 260 ns are about 400 kV and 2.8 kA, respectively. The axial and radial expansion velocities of the cathode plasma were obtained through the angled lateral view by utilizing high-speed framing camera combined with the digital image processing methods. In addition, the evolution of the cathode and collector plasmas was visible firstly on the front view at the same time. The bronze-dielectric cathode not only showed low expansion velocity of about 0.5 cm/μs but also had other superior characteristics indicated by the strong emission capability, the fast plasma formation and the uniform plasma distribution. Thereby, the metal–dielectric cathode is a good candidate for applications in a long-pulsed MICD.
关键词： Bronze-dielectric cathode,plasma expansion velocities,high-speed framing camera (HSFC),magnetically insulated coaxial diode (MICD)
更新于2025-09-23 15:23:52
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Structural, Optical, and Dielectric Studies on Sr-Doped Biferroic YCrO3
摘要： In this work, the solid-state synthesis of Y1-xSrxCrO3 (x = 0.0, 0.1) samples has been reported. The X-ray diffraction data analysis confirmed that the synthesized samples have crystallized into the orthorhombic phase with the assigned space group Pbnm. The Rietveld refinement of the XRD data confirmed the structure and other related parameters. The slight variation in the lattice parameters and negligible shift in the reflection peaks reveals the uniform dispersion of Sr at Y-site in the parent YCrO3 matrix. The dielectric characterization revealed the good dielectric nature of the prepared samples which decreases with Sr doping. Field emission scanning electron microscopy (FE-SEM) revealed that an agglomeration type process has taken place in the sample preparation. Fourier transform infrared (FTIR) characterization witnessed the formation of orthorhombic phase of the samples under study displaying sharp absorption bands corresponding to Cr–O stretching, Y/Sr–O stretching, and O–Cr–O deformation vibration, respectively. UV-Vis spectroscopy analysis revealed the dual direct allowed bandgap of the samples assigned to the Cr3+ ion transition in the ground level.
关键词： Nanoparticles,Structure,Rietveld refinement,Morphology,Dielectric properties
更新于2025-09-23 15:23:52
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The description of quantum dielectric function for insulators over Bethe surface
摘要： A new expression for the dielectric function is suggested here, which is the Mermin–Belkacem-Sigmund (MBS) model derived from the Belkacem–Sigmund (BS) model based on the conservation of a local particle number in the Mermin model. The energy loss function expressions are reviewed analytically for both models, and these dielectric functions were used to calculate the Bethe sum rule, the energy loss function (ELF), as well as the differential inelastic inverse mean free path (DIIMP) for H2O. The indication from the results is that, compared to the BS dielectric function, the MBS dielectric function is more compatible in its consistency with the exact Bethe sum rule. The ELF for the MBS type is compatible relatively in high and low momentum transfers, while the ELF for the BS type is suitable for high-k. The two models of ELF were also applied to evaluate DIIMP for electron kinetic energy 1 keV, and these were compared with the results predicted in several ways via the SESINIPAC program, using the Mermin dielectric function and the extended Drude and Monte–Carlo method. These predicted results are in reasonable agreement with those estimated from other methods at the range of energy transfer (0–50) eV.
关键词： Bethe surface,differential inelastic inverse mean free path,local particle number,Energy loss function,dielectric function
更新于2025-09-23 15:23:52
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Influence of Surface Modification and Dispersive Additives on Dielectric and Electrical Properties of BiFeO3/Poly(methyl methacrylate) Composite Films
摘要： Surface modi?cation plays an important role to enhance the dielectric constant and minimize the dielectric loss. In this study, poly(methyl methacrylate) (PMMA) composites ?lled with 2-aminoethanesulfonic acid-modi?ed bismuth ferrite (BiFeO3; BFO) have been prepared via solution casting technique. The surface morphology of the composites provides a better homogeneous dispersion of the particles in the polymer matrix and increases interface compatibility between modi?ed BFO and PMMA matrix. The experimental results show that the composites have high dielectric constant (≈ 147), alternating current (AC) conductivity (1 × 10??) and relatively low loss (< 1) at 100 Hz. The percolation phenomenon is well observed in the composite having less than 30 wt.% of BFO particles. Further, the composites produce passivation layers on the surface of modi?ed BFO particles which might improve the morphology and promote the space charges, interface effects and dielectric properties. Our strategy is to provide a simple and ef?cient approach to fabricate high-performance dielectric composites for energy storage applications.
关键词： dielectric properties,surface treatment,morphology,Poly(methyl methacrylate)
更新于2025-09-23 15:23:52
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Study on Charge transportation and scaling behavior of CsPbI3 microwires
摘要： Cesium lead iodide (CsPbI3) has been prepared by a new experimental hazard free precipitation technique. X-ray diffraction spectra have been interpreted with Rietveld refinement which assures the orthorhombic phase of CsPbI3. Energy dispersive X-ray fluorescence spectra confirms the formation of ternary compound. Orthorhombic to cubic phase transition has been studied by observing hysteresis loop in R(T)-T plot for forward-reverse temperature scan. The intra-grain and inter-grain contribution of CsPbI3 to dielectric relaxation has been accounted by fitting the complex impedance plot (Cole-Cole plot). The value of FWHM in Z″(ω)-lnf or M″(ω)-lnf plot is greater than 1.141 decades which reveals the non-Debye type relaxation within material. The broad relaxation peak signifies that there is a distribution of relaxation time over a mean value. Moreover, Z″ & M″ have been plotted in scaled coordinate to check whether the distribution of relaxation time is temperature dependent or not. The frequency dependent relative permittivity represents the decreases of polarizations with frequency which have been successfully analyzed by Koop’s theory. Here, activation energies are equal for different formalism, suggests that the same type charge carriers involved in conduction as well as relaxation process. Ac conductivity has been interpreted by using Jonncher’s power law and frequency exponent (n) increases with temperature which suggests the presence small polaron hopping mechanism.
关键词： Joncher’s power law,dielectric relaxation,Rietveld,Hysteresis,Cole-Cole plot,CsPbI3 micro-wire
更新于2025-09-23 15:23:52
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Design of high gain, broadband resonant cavity antenna with meta-material inspired superstrate
摘要： A broadband high gain planar meta-material based Resonant Cavity Antenna (RCA) operating at C-band is proposed. The RCA is modeled using simple ray tracing method. The unit cell metamaterial consists of Artificial Magnetic Conductor (AMC) and square patch laminated on either side of a lossy commercial dielectric material of dielectric constant 4.4 & thickness 1.6mm, is used as the superstrate to design RCA. Square patch is the capacitive type and that AMC as inductive. Effects of the reflection phase of the substrate decide the high gain of the antenna. A cylindrical dielectric resonator antenna (CDRA) is embedded into the cavity as a feed. The proposed antenna achieves 22.4dBi gain with 2 layers of 4x4 array superstrate with a bandwidth of around 5.1GHz. The full-wave analysis is performed to extract the impedance matching, radiation pattern & gain of the composite RCA. A prototype antenna is fabricated and tested for verification of experimental results which was found to be well correlated. It also shows that the proposed RCA achieves -10dB impedance bandwidth of 72.72% ranging from 4 to 9.1GHz with a high gain around 22.4dBi.
关键词： Cylindrical Dielectric Resonator Antenna (CDRA),Metamaterials (MTM),Resonant Cavity Antenna (RCA)
更新于2025-09-23 15:23:52
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A simple, low cost ink system for Drop-On-Demand printing high performance metal oxide dielectric film at low temperature
摘要： We have successfully developed an ink system containing cheap raw materials through a simple process and have printed ZrOx dielectric film at a relatively low annealing temperature of 250 °C. The ZrOx dielectric film afforded a leakage current density of 5.4×10-6 A/cm2 at 1 MV/cm and a dielectric constant of 10, which shows promising future for flexible electronics. The ink system shows a temperature-induced gelation behavior and gel network is formed when temperature rises. A high concentration of oxide precursors is obtained near the network area through the absorption function of polymer groups, and thus oxide structure can be formed at a relatively low temperature due to the shorter diffusion path of precursor polymerization. The microstructure of printed ZrOx film was investigated by High Resolution Transmission Electron Microscope (HRTEM), Fourier-transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS), and the effect of annealing temperature on film structure was studied.
关键词： dielectric film,low temperature,Low cost,ink system,Drop-On-Demand printing
更新于2025-09-23 15:23:52
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Effects of Ge substrate on the structural and optical conductivity parameters of Bi2O3 thin films
摘要： In this article the structural, optical and dielectric properties of a 200 nm thick Bi2O3 thin films which are deposited onto amorphous germanium substrate are reported. Both of the Ge and Bi2O3 thin films are prepared by the thermal evaporation technique under vacuum pressure of 10^-5 mbar. Bi2O3 thin films are found to prefer the monoclinic nature of structure with larger values of microstrain, dislocation density, stacking faults and smaller grain sizes upon replacement of the glass substrate by germanium. Optically, significant redshift in the energy band gap is observed when the films are grown onto Ge. The Ge/Bi2O3 heterojunctions exhibit a conduction and valence band offsets of value of 0.81 and 1.38 eV, respectively. In addition to the enhancement in the dielectric constant near the IR region, the Drude-Lorentz modeling of the Ge/Bi2O3 heterojunctions has shown remarkable effect of the Ge substrate on the optical conductivity parameters of Bi2O3. Particularly, the drift mobility increased by about one order of magnitude, the free hole density decreased by ~24 times and the plasmon frequency ranges extended from 5.21 to 11.0 GHz to 2.59–12.80 GHz when germanium substrate is used. The optical features of the heterojunction nominate it for visible light communication technology.
关键词： Ge/Bi2O3,Band offsets,X-ray,Heterojunction,Plasmon,Dielectric
更新于2025-09-23 15:23:52
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Heat-Assisted Photoacidic Oxidation Method for Tailoring the Surface Chemistry of Polymer Dielectrics for Low-Power Organic Soft Electronics
摘要： The use in low-power soft electronics of the appropriate insulating polymer materials with a high dielectric constant (k) is considered a practical alternative to that of inorganic dielectric materials, which are brittle and have high processing temperatures. However, the polar surfaces of typical high-k polymer insulators are problematic. Further, it is a huge challenge to control their surface properties without damage because of their soft and chemically fragile nature. Here, a heat-assisted photoacidic oxidation method that can be used to effectively oxidize the outermost surfaces of high-k rubbery polymer films without degradation is presented. The oxidized surfaces prepared with the developed method contain large numbers of hydroxyl groups that enable the subsequent growth of dense and ordered self-assembled monolayers (SAMs) consisting of organosilanes. The whole process modifies the surface characteristics of polymer dielectrics effectively. The mechanisms of the oxidation of polymer surfaces and the subsequent SAM growth process are investigated. The resulting surface-tailored rubbery dielectrics exhibit superior electrical characteristics when used in organic transistors. These results demonstrate that this method can be used to realize practical soft organic electronics based on high-k polymer dielectrics.
关键词： self-assembled monolayers,organic semiconductors,polymer gate dielectric,polymer oxidation,surface chemistry
更新于2025-09-23 15:23:52