Dielectric behaviour of polycrystalline lead germanate

The dielectric behaviour of ferroelectric Lead Germanate (Pb₅Ge₃O₁₁) is reported in the frequency region 60 Hz-100 KHz for various particle size ranges from 40 to 300 μ m. The dielectric constant and conductivity decrease with decreasing particle size. The dielectric anomaly in small particle size unsintered samples disappears at lower frequencies, while at 100 KHz a broad diffuse phase transition is observed for all the samples, irrespective of particle size. A strong dielectric dispersion has been observed in the frequency range 60 Hz–100 KHz. The dielectric constant of sintered samples for the same panicle size range, and the dielectric anomaly which was absent at lower frequencies for unsintered samples re-appears in sintered samples. These results have been explained by assuming a high resistivity surface layer having a lower dielectric constant than the bulk at the boundary of particles.     

Kramers Kronig analysis of the optical properties of small silver particles

In order to complete a preceding paper the dielectric constant? of the particle material of small silver particles with diameters between 210 and 25 Å is computed in the wavelength region 365≦λ≦455 nm from the measured spectra of thesmall particle plasma reasonance absorption. For this purpose a properKramers Kronig relation is derived, and is checked by applying to particles with Drude free electron gas. The results, concerning the silver particles, are that the real part of? changes slightly, whereas the imaginary part is markedly enhanced (up to the ten-fold of the bulk values) if the particle size decreases. This size dependence of? can quantitatively be described with thefree path effect within the accuracy of the measured values. Conversely, thebulk dielectric constant of silver is obtained by applying the free path effect to the measured dielectric constant of the small particles.     

Improved Dielectric Breakdown Strength of Covalently-Bonded Interface Polymer–Particle Nanocomposites

Interfacial covalent bonding is an effective approach to increase the electrical resistance of a polymer–particle composite to charge flow and dielectric breakdown. A bifunctional tether reagent bonded to an inorganic oxide particle surface assists with particle dispersion within a thermosetting epoxy polymer matrix but then also reacts covalently with the polymer matrix. Bonding the particle surface to the polymer matrix resulted in a composite that maintained the pure polymer glass transition temperature, compared to modified or unmodified particle dispersions that lacked covalent bonding to the polymer matrix, which depressed the polymer glass transition to lower temperatures. The added interfacial control, directly bonding the particle to the polymer matrix, appears to prevent conductive percolation across particle surfaces that results in a reduced Maxwell–Wagner relaxation of the polymer–particle composite and a reduced sensitivity to a dielectric breakdown event. The inclusion of 5 vol% particles of higher permittivity produces a composite of enhanced dielectric constant and, with surface modification to permit surface cross-linking into the polymer, a polymer–particle composite with a Weibull E ₀ dielectric breakdown strength of 25% greater than that of the pure polymer resulted. The estimated energy density for the cross-linked interface composite was improved 260% compared to the polymer alone, 560% better than a polymer–particle composite synthesized using bare particles, and 80% better than a polymer–particle composite utilizing bare particles with a dispersant.     

Optical absorption of ultrafine metal spheres with dielectric cores

We compute the optical absorption of a glass containing a small fraction of silver particles with dielectric cores. The results are based on the Maxwell Garnett formalism. The dielectric permeability of the metallic shells is obtained by modifying experimental data for bulk silver to account for size dependent scattering of the conduction electrons. We find an absorption maximum in the visible range at a wavelength which, for sufficiently minute particles, depends rather strongly on the size of the cores and on their dielectric constant. The relevance of these results to recent experimental data by Smithard and by Genzel et al. is pointed out. We argue that their observed absorption maxima can be explained without invoking any quantum effects.     

金红石相纳米块材TiO2的介电特性

研究了不同制备压力下成型的以金红石相为主的纳米二氧化钛介电常数的频率谱和温度谱。在频率谱上发现,当频率ω<0.1kHz时,随着测量频率的下降,介电常数迅速升高,低频下的介电常数比高频区的介电常数高1—2个数量级。并且随着样品加压压力的提高,介电常数升高,在与之相对应的介电损耗谱上,随着样品加压压力的提高,损耗值下降,损耗峰向低频区位移。对1.0GPa压力下成型的样品,其介电常数随测量温度的升高,分别在50℃和300℃出现两个峰值。经分析得出,影响金红石相纳米二氧化钛介电行为的微观机制主要为晶粒内部的电子松弛极化和界面中的电偶极矩的转向极化,50℃峰对应于电于松弛极化,而300℃峰则对应于电偶极矩的转向极化。 关键词：     

Theoretical Studies on Photoionization Cross Sections of Solid Gold

Accurate expression for photoabsorption (photoionization) cross sections of high density system proposed recently is used to study the photoionization of solid gold. The results show that the present theoretical photoionization cross sections have good agreement both in structure and in magnitude with the experimental results of gold crystal. The studies also indicate that both the real part ε' and the imaginary part ε" of the complex dielectric constant ε, and the dielectric influence function of a nonideal system have rich structures in low energy side with a range about 50 eV, and suggest that the influence of particle interactions of surrounding particles with the photoionized particle on the photoionization cross sections can be easily investigated using the dielectric influence function. The electron overlap effects are suggested to be implemented in the future studies to improve the accuracy of theoretical photoionization cross sections of a solid system.     

Effect of TiO2 crystalline composition on the dielectric properties of TiO2/P(VDF‐TrFE) composites

In order to study the effect of the TiO₂ particle crystalline composition (with different proportions of rutile and anatase crystals) on the dielectric properties of the composite, titanium dioxide (TiO₂) particles and TiO₂/poly(vinylidene fluoride‐co‐trifluoroethylene) [P(VDF‐TrFE)] composites were synthesized by a reflux method and the solution route, respectively. The results indicated that the optimum TiO₂ particle crystalline composition is anatase content of 37% and rutile content of 63% for dielectric‐constant modifier applications. Furthermore, a dielectric constant of 25.7 with dielectric loss of 0.17 at 100 Hz at room temperature were obtained in the composite with 40 wt% TiO₂ particles. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Dielectric constant of a highly polarizable atomic fluid: the clausius–mossotti versus the onsager relation

The relation between the dielectric constant and the particle polarizability for a polarizable liquid composed of Lennard-Jones particles carrying a saturable induced dipole is studied by computer simulations. It is shown that the widely accepted Clausius–Mossotti relation is only valid for low polarizabilities and fails for high polarizabilities. The results can be fitted accurately by an Onsager-like relation using an effective particle radius measured in the simulations which is larger than the equivalent hard-sphere radius defined conventionally. Furthermore, the orientational ordering transition found at high polarizabilities is shown to be of anti-ferroelectric type.     

The optical properties in a chain waveguide of an array of silver nanoshell with dielectric holes

Plasmonic chain waveguide by employing an array of silver nanoshell with dielectric holes that interact with incident plane wave of transverse magnetic polarization are simulated by use of the finite element method. Results show that the working wavelength of the system is highly tunable by using the nanoshell instead of solid particles and by varying the dielectric constant of the core. Besides, chain waveguides that are operated on resonant multipolar modes can provide longer propagation lengths, which is beyond what is maximally achieved by conventional solid particle chains.     

固态高压脉冲形成线研究

 为了实现高压脉冲形成线小型化,开展了平板固态脉冲形成线研究。实验研究了两种作为储能介质的固态材料的高压体击穿特性、沿面闪络特性和频率响应特性,一种是特种复合材料,其相对介电常数在50～250之间,另一种是功能陶瓷,其相对介电常数在200～1 000之间。在此基础上,研制了两种平板固态脉冲形成线。特种复合介质固态脉冲形成线试验电压为3 kV左右,输出电压脉冲半高全宽（FWHM）可以达到58 ns;功能陶瓷介质固态脉冲形成线的试验充电电压超过120 kV,输出电压脉冲半高全宽为92 ns。     

固态高压脉冲形成线研究

为了实现高压脉冲形成线小型化,开展了平板固态脉冲形成线研究。实验研究了两种作为储能介质的固态材料的高压体击穿特性、沿面闪络特性和频率响应特性,一种是特种复合材料,其相对介电常数在50～250之间,另一种是功能陶瓷,其相对介电常数在200～1 000之间。在此基础上,研制了两种平板固态脉冲形成线。特种复合介质固态脉冲形成线试验电压为3 kV左右,输出电压脉冲半高全宽（FWHM）可以达到58 ns;功能陶瓷介质固态脉冲形成线的试验充电电压超过120 kV,输出电压脉冲半高全宽为92 ns。     

Particle transport by standing waves on an electric curtain

Discrete-element simulations are performed to study particle transport by standing waves on an electric curtain. An electric curtain consists of a series of parallel electrodes with oscillating potential field embedded in a dielectric surface. The study shows that particles can be transported in two different modes under excitation by standing waves. In the first mode, particles roll along the surface in a constant direction with average velocity equal to the wave speed. In the second mode, particles hop along the surface in a manner akin to a Brownian motion. Effect of particle collisions on these transport modes is evaluated.     

Wake potential with mobile positive/negative ions in multicomponent dusty plasmas

We employ the test charge approach to calculate the electrostatic potential for a test charge in a multicomponent dusty plasma, whose constituents are the Boltzmann distributed electrons, mobile positive and negative ions, and immobile positive/negative charged dust particles. By using the modified dielectric constant of the dust-ion-acoustic (DIA) waves, the Debye screening and wake potentials are obtained. It is found that the presence of mobile negative ions significantly modify the DIA speed and the wake potential. The present results are relevant to polar mesosphere and microelectronic in the context of charged particle attraction and repulsion.     

Optical constants of gold and silver clusters in the spectral range between 1.5 eV and 4.5 eV

Optical constants of gold and silver clusters of various sizes are determined from measurements of their optical extinction in the range from 1.5 eV to 4.5 eV photon energy. For this purpose, it is shown that the optical extinction by spherical clusters satisfies a Kramers-Kronig relation, yielding the second quantity needed for the determination of the complex dielectric constant ε of the cluster material. The dielectric constant is then obtained applying a generalized Newton-Raphson iteration method on the measured extinction data and the Kramers-Kronig data. The results show a clear dependence on cluster size, and also deviations from bulk dielectric constants in the range of the interband transitions. From the various ε-data, a “bulk” dielectric constant of gold and silver is obtained, which fits the positions of the cluster plasmons more precisely than bulk dielectric constants from the literature.     

球形粒子的近场辐射换热研究

近场辐射引起的能量交换可以比远场辐射高若干个数量级.本文计算了SiC和Cu两种球形颗粒的近场辐射换热,发现当颗粒间距非常小时,辐射换热会大大强化.颗粒直径、颗粒间距以及颗粒的介电常数是决定近场辐射换热大小的重要因素,而颗粒温度对近场辐射换热的影响较小.     

Dielectric characteristics of CaCu3Ti4O12/P(VDF-TrFE) nanocomposites

Composite thin film is highly desirable for the dielectric applications. In order to develop composite thin film, a nanocomposite, in which nanosized CaCu₃Ti₄O₁₂ (CCTO) particles are used as filler and P(VDF?CTrFE) 55/45 mol% copolymer is used as polymer matrix, is investigated. The contents of CCTO in the nanocomposites range from 0% to 50?vol%. The dielectric property of these nanocomposites was characterized at frequencies ranging from 100 Hz to 1 MHz and at temperatures ranging from 200 K to 370 K. A dielectric constant of 62 with a loss of 0.05 was obtained in nanocomposite with 50?vol% CCTO at room temperature at 1 kHz. At the phase transition temperature (??340?K) of the copolymer, a dielectric constant of 150 with a loss less than 0.1 was obtained in this nanocomposite. It is found that the dielectric loss of the nanocomposites is dominated by the polymer which has a relaxation process. Comparing to composites made using microsized CCTO, the nanocomposites exhibit a much lower dielectric loss and a lower dielectric constant. This indicates that the nanosized CCTO particles have a lower dielectric constant than the microsized CCTO particles.     

Synthesis modified structural and dielectric properties of semiconducting zinc ferrospinels

The influence of preparation techniques on structural and dielectric properties of ZnCr_xFe_1−xO₄ (x=0, 0.1 abbreviated as Z and ZC) ferrite nano-particles synthesized using chemical co-precipitation (CCP), sol-gel (SG) and solid state reaction (SS) techniques is discussed. XRD profiles are used to confirm the single phase spinel ferrite formation. TEM images indicate the change in size and shape of particles on changing either the composition or the synthesis methodology. The TEM micrograph of samples obtained through CCP shows uniform particle size formation compared to those obtained through SG and SS. Sample prepared through CCP possess porosity >70% making these materials suitable for sensing applications. The dielectric loss, dielectric constant and ac conductivity are analyzed as a function of frequency, temperature and composition using impedance spectroscopy. A universal dielectric behavior has been predicted through temperature and frequency variations of different parameters. Dielectric constant is found to possess highest value for sample synthesized through SG which marks the possibility of using the SG derived ferrospinels as microwave device components.     

Measurement of the complex dielectric constant of a single gold nanoparticle

A differential interference contrast microscopy technique that employs a photonic crystal fiber as a white-light source is used to measure both the real and the imaginary part of the complex dielectric constant of single 10 and 15 nm gold nanoparticles over a wavelength range of 480 to 610 nm. Noticeable deviations from bulk gold measurements are observed at short wavelengths and for individual particles even after taking into account finite-size surface damping effects.     

Activation energy of etching for CR-39 as a function of linear energy transfer of the incident particles

In this work, we have studied the effect of the radiation damage caused by the incident particles on the activation energy of etching for CR-39 samples. The damage produced by the incident particle is expressed in terms of the linear energy transfer (LET). CR-39 samples from American Acrylic were irradiated to three different LET particles. These are N (LET₂₀₀ = 20 KeV/μm) as a light particle, Fe (LET₂₀₀ = 110 KeV/μm) as a medium particle and fission fragments (ff) from a ²⁵²Cf source as heavy particles. In general the bulk etch rate was calculated using the weight difference method and the track etch rate was determined using the track geometry at various temperatures (50–90 °C) and concentrations (4–9 N) of the NaOH etchant. The average activation energy F_b related to the bulk etch rate v_b was calculated from ln v_b vs. l/T. The average activation energy E_t related to the track etch rate v_t was estimated from ln v_t vs. l/T. It is shown that activation energy of etching is a constant value for CR-39 detector where E_t was found to be independent on the damage produced by the incident particle.     

Light scattering by slightly nonspherical particles on surfaces

We investigate the shape dependence of the scattering by dielectric and metallic particles on surfaces by considering particles whose free-space scattering properties are nearly identical. The scattering by metallic particles is strongly dependent on the shape of the particle in the region near where the particle touches the surface. The scattering by dielectric particles displays a weaker, but nonetheless significant, dependence on particle shape. These results have a significant effect on the use of light scattering to size and identify particles on surfaces.