Temperature dependence of the dielectric constant of acrylic dielectric elastomer

The dielectric constant is an essential electrical parameter to the achievable voltage-induced deformation of the dielectric elastomer. This paper primarily focuses on the temperature dependence of the dielectric constant (within the range of 173 K to 373 K) for the most widely used acrylic dielectric elastomer (VHB 4910). First the dielectric constant was investigated experimentally with the broadband dielectric spectrometer (BDS). Results showed that the dielectric constant first increased with temperature up to a peak value and then dropped to a relative small value. Then by analyzing the fitted curves, the Cole–Cole dispersion equation was found better to characterize the rising process before the peak values than the Debye dispersion equation, while the decrease process afterward can be well described by the simple Debye model. Finally, a mathematical model of dielectric constant of VHB 4910 was obtained from the fitted results which can be used to further probe the electromechanical stability of the dielectric elastomers.     

The dependence of dielectric properties on the thickness of (Ba,Sr)TiO3 thin films

In the dielectric (Ba,Sr)TiO₃ thin films, the correlation between the film thickness and the dielectric properties was investigated. The dielectric properties such as the dielectric constant (ε) and dielectric loss (tan δ) were measured using the capacitor geometry. As the film thickness increased, the dielectric constant also increased due to the reduction of the interfacial dead-layer effect. However, the dielectric loss did not show a monotonous variation with the increasing film thickness. It was found that the dielectric loss correlated well with the non-uniform distribution of local strain, as analyzed by X-ray diffraction, according to the Curie–von Schweidler relaxation law.     

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.     

Combined dielectric and plasmon resonance for giant enhancement of Raman scattering

Combined dielectric/metal resonators for colossal enhancement of inelastic light scattering are developed and their properties are investigated. It is shown that a record enhancement factor of 2 × 10⁸ can be obtained using these structures. The dielectric resonators are fabricated on Si/SiO₂ substrates where periodic arrays of square 10- to 200-nm-high dielectric pillars are produced via electron-beam lithography and plasma etching. The lateral size a of the pillars varies between 50 and 1500 nm, and their period in the array is 2a. To make a combined dielectric/metal resonator, a nanostructured layer of silver is deposited onto the fabricated periodic dielectric structure by thermal evaporation. It is established that, for a fixed height of the dielectric pillars, the Raman scattering enhancement factor experiences pronounced oscillations as a function of the period (and size) of the pillars. It is shown that these oscillations are determined by the modes of the dielectric resonator and governed by the relation between the excitation laser wavelength and the planar size of the dielectric pillars.     

Electrochemical characteristics of alumina dielectric layers

The electrochemical characteristics of alumina dielectric layers were studied using a surface roughness factor and an impedance spectroscopy. From the limiting diffusion current method, the surface area factor of the dielectric anodic layer with low electrical conductivity was estimated to be 1.03. As alumina dielectric films on Al have a variable stoichiometry, the electrochemical behavior of Al₂O₃ layer can be monitored by evaluating an equivalent circuit with Young impedance of dielectric constant with a vertical decay of conductivity.     

Temperature studies of dielectric permittivity and mass density pretransitional anomalies in binary mixtures

Results of temperature studies of dielectric permittivity and mass density in binary mixtures are presented. The anomaly of dielectric permittivity as a function of temperature in nitrobenzene-n-alkanes binary mixtures has been studied. Molar dielectric permittivity which takes into account the anomaly of dielectric permittivity and the mass density anomaly has been introduced.     

Effects of the dielectric discontinuity on the photodetachment of H− ion

Using the closed orbit theory, we studied the effects of dielectric discontinuity on the photodetachment of H^? ions. The photodetachment cross-section of H^? in a medium with dielectric discontinuity was derived and calculated. The results have shown that the relative dielectric constants of the medium have a significant influence on the photodetachment of H^?. If H^? is kept in a medium with a relative small dielectric constant, the photodetachment cross-section of H^? becomes oscillating only in a small region above the ionization threshold. However, if H^? is kept in a medium with a relative large dielectric constant, the oscillation in the photodetachment cross-section becomes much stronger. Besides, the distance between H^? and the dielectric dividing interface also influences the photodetachment of H^?. For a given dielectric medium, the oscillation in the cross-section decreased with increasing distance between H^? and the dielectric dividing interface. Therefore, we can control the photodetachment of a negative ion by changing the dielectric constant and the ion–interface distance. This study provides a new understanding of the photodetachment process of negative ions in the presence of a dielectric medium.     

The Evaluation of Dielectric Resonators Containing H2O or D2O as RF Coils for High-Field MR Imaging and Spectroscopy

Electromagnetic resonators consisting of low-loss dielectric material and/or metallic boundaries are widely used in microwave technologies. These dielectric resonators usually have high Q factors and well-defined field distributions. Magnetic resonance imaging was shown as a way of visualizing the magnetic field distribution of the resonant modes of these resonators, if the dielectric body contains NMR sensitive nuclei. Dielectric resonators have also been proposed as RF coils for magnetic resonance experiments. The feasibility of this idea in high-field MR is discussed here. Specifically, the dielectric resonances of cylindrical water columns were characterized at 170.7 MHz (4 T¹H Larmor frequency), and evaluated as NMR transmit and receive coils. The dielectric resonance of a cylindrical volume of D₂O was used to image a hand at 170.7 MHz. This study demonstrated that MRI is an effective way of visualizing the magnetic field in dielectric structures such as a water cylinder, and can potentially be generalized to solid-state dielectric devices. The possible applications of dielectric resonators other than simple cylindrical volumes in MRI and MR solution spectroscopy at high field strengths are also discussed.     

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.     

薄板型介质材料复介电常数的无损测量

采用带法兰结构的TE01n圆柱谐振腔,用无损检测的方法测量薄板型微波介质材料的复介电常数。利用轴向模式匹配法对谐振腔内的电磁场进行了求解,给出了相对介电常数和损耗角正切的计算公式,并利用矢量网络分析仪对几种常用微波介质材料进行了测量,其结果表明:该测量方法对相对介电常数的测量误差不超过1%,而对损耗角正切的测量误差不超过10%。该方法还具备一腔多模的测试能力,测量频率可调,可用于介质材料频率特性的测量。     

Dielectric properties of several liquid crystalline esters

A dielectric study has indicated that the inherent dielectric anisotropy (measured at 10 kHz) for the liquid crystals derived from hydroquinone or terephthalic acid is negative whereas it is positive for the phenyl benzoyloxybenzoate system. The dielectric anisotropy of these systems can be changed by appropriate structural modifications, for example, liquid crystals with negative dielectric anisotropies can be obtained by the incorporation of a cyano group in a lateral position or a cyanomethoxy group in a para position of the molecule.     

Fe-Ni-BaTiO3复合材料的介电行为及其机理研究

利用金属铁、镍(Fe与Ni保持mol比为22∶78不变)与钛酸钡复合，在保护气氛下成功烧结制备了高介电常数Fe-Ni-BaTiO₃复合陶瓷材料，并研究了该复合材料的电导和介电性能及其物理机理.分析结果表明，由于渗流效应，随着陶瓷中金属含量的增加，材料经历了绝缘体—导体突变.同时，在渗流阈值附近，材料的介电常数有了极大的提高.当金属体积含量为0.23时，即在绝缘体向导体转变的渗流阈值附近，复合材料的介电常数达到了22000，为同条件下制备的纯钛酸钡陶瓷体介电常数的12倍，同时材料的介电 关键词： 3')" href="#">Fe-Ni-BaTiO₃ 渗流理论 介电性能 Maxwell-Wagner效应     

Dielectric properties of a hydrated sulfonated poly(styrene-ethylene/butylenes-styrene) triblock copolymer

The present study showed that sulfonated poly(styrene-ethylene/butylenes-styrene) (S-SEBS) triblock copolymer ionomers can be made to exhibit dielectric constants on the order of a hundreds thousand. Although they are too lossy at this point to use as dielectric materials in capacitors or as electrostrictive Maxwell effect transducer materials because of their high hydrogen ion conductivity, the results of these initial dielectric studies as a function of ion content were used to try to understand the effects of a polar plasticizer, water, on dielectric properties of the acid form of this ionomer. This was done before moving on to more tightly bound ions (rather than the hydrogen ions of the sulfonic acid groups used here) and to other polar, less mobile plasticizers (which also interact strongly with the ionic dipoles). The discovery of such high dielectric constants suggested the possibility that low dielectric loss versions of this type of polymer, as well as other members of the class known as ionomers, might find future applications as extremely high dielectric constant materials in capacitors or transducers. Experimental results for films with degrees of sulfonation on the order of 10% or more showed dielectric constants on the order of ?′ ∼ 100,000 but dielectric loss tangents near D = tan δ ∼ 0.3, when the materials were exposed to high humidity conditions. Experiments to determine the effects of water content on the material's dielectric response showed that water can easily move into and out of the films studied and that this transport behavior is strongly correlated to the relative humidity of the environment and to the degree of sulfonation. Water content, in this case, was thus the primary consideration when attempting to understand the observed high dielectric constants in films with degree of sulfonation greater than 5.5%. However, vacuum-dried films were, also, examined and observed to exhibit a dielectric constant on the order of 2 until the degree of sulfonation was greater than 11%. Above this value, the dielectric constant increased by approximately 100% to a value on the order of 4.     

Dielectric properties of electrolytic solutions

The variation in dielectric properties of water with the addition of ionic salts have been measured using automated frequency domain experimental microwave C-band. The dielectric properties, that is dielectric constant (ε′) and dielectric loss (ε″) of two electrolyte solutions for various concentrations have been measured at 5-GHz frequency at room temperature. It has been observed that for concentration between 0.2 to 1.0 mole the dielectric constant of water is smaller and some larger than that of pure water and dielectric loss increases with increasing concentration of these salts. It has been also observed that the variation in dielectric loss is different, though the ionic concentration of the two salts are equal.     

Geometric interpretation of hadronization model

A hadronization model termed as geometric dielectric confinement model is described. The model describes the charmed meson decays quite successfully. In the model we assume that the non-abelian gauge field describing the colour force simulates the effect of a medium having space-dependent dielectric constant. The quarks produced in weak decays move in the dielectric medium such that they are free in limited region of space (r⋍0) and cannot appear as asymptotic states resulting in hadronization. It is found that the dielectric medium resembles anti-desitter microuniverse and the quarks behave essentially as free particles damped by gaussian distribution. The model reproduces from a single Lagrangian the quark motion as well as the form of dielectric function.     

Natural oscillations of shielded multilayer spherical dielectric resonators

Characteristic equations and analytic expressions for the Q-factors are derived for a three-layer spherical dielectric resonator in a metal shield. The effect of dielectric coatings on the Q-factors of dielectric resonators is examined. The effect of a metal shield on thinning of the spectrum of a hollow spherical dielectric resonator is investigated.Kiev Polytechnic Institute. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 35, No. 6/7, pp. 579–586, June–July, 1992.     

Correlations of structural, magnetic, and dielectric properties of undoped and doped CaCu3Ti4O12

The present work reports synthesis, as well as a detailed and careful characterization of structural, magnetic, and dielectric properties of differently tempered undoped and doped CaCu₃Ti₄O₁₂ (CCTO) ceramics. For this purpose, neutron and X-ray powder diffraction, SQUID measurements, and dielectric spectroscopy have been performed. Mn-, Fe-, and Ni-doped CCTO ceramics were investigated in great detail to document the influence of low-level doping with 3d metals on the antiferromagnetic structure and dielectric properties. In the light of possible magnetoelectric coupling in these doped ceramics, the dielectric measurements were also carried out in external magnetic fields up to 7 T. At low temperatures the dielectric constant shows a minor but significant dependence on the applied magnetic field. Undoped CCTO is well-known for its colossal dielectric constant in a broad frequency and temperature range. With the present extended characterization of doped as well as undoped CCTO, we want to address the question why doping with only 1% Mn or 0.5% Fe decreases the room-temperature dielectric constant of CCTO by a factor of ~100 with a concomitant reduction of the conductivity, whereas 0.5% Ni doping changes the dielectric properties only slightly. In addition, diffraction experiments and magnetic investigations were undertaken to check for possible correlations of the magnitude of the colossal dielectric constants with structural details or with magnetic properties like the magnetic ordering, the Curie-Weiss temperatures, or the paramagnetic moment. It is revealed, that while the magnetic ordering temperature and the effective moment of all investigated CCTO ceramics are rather similar, there is a dramatic influence of doping and tempering time on the Curie-Weiss constant.     

Pressure and temperature dependence of the static dielectric constant of KBr

The static dielectric constant and the temperature and pressure derivatives of the static dielectric constant of KBr have been measured at several temperatures between 4·3°K and room temperature. The sample was prepared in the form of a three-terminal parallel-plate capacitor and the dielectric constant was determined from measurements of the capacitance with a high precision bridge. The dielectric constant decreases with temperature as does the magnitude of the temperature dependence and the magnitude of the pressure dependence. The data were used to calculate the fixed-volume temperature derivative of the dielectric constant. This quantity, (? ln ε/?T)_v, exhibiting lattice-anharmonicity effects, decreases slightly from its room temperature value as the temperature is lowered, rises to a maximum value at about 33°K and then decreases rapidly at lower temperatures.     

Synthesis and dielectric characteristics of La0.5Bi0.5MnO3 ceramics

La_0.5Bi_0.5MnO₃ ceramics with a single phase were prepared by a solid-state reaction method, and their dielectric properties were characterized. Two dielectric relaxations with a giant dielectric constant were identified in the temperature range from 125 to 350 K. The electron hopping between Mn³⁺ and Mn⁴⁺ was found to be the origin of the dielectric relaxation at low temperatures (125–200 K) with an activation energy of 0.18 eV. The high temperature (200–350 K) dielectric relaxation can be attributed to the conduction.     

Effect of modifying a methyl siloxane-based dielectric by a polymer thin film for pentacene thin-film transistors

We report on the fabrication of pentacene thin-film transistors (TFTs) utilizing a spun methyl siloxane-based spin-on-glass (SOG) dielectric and show that these devices can give a similar electrical performance as achieved by using pentacene TFTs with a silicon dioxide (SiO₂) dielectric. To improve the electrical performance of pentacene TFTs with the SOG dielectric, we employed a hybrid dielectric of an SOG/cross-linked poly-4-vinylphenol (PVP) polymer. The PVP film was deposited onto the spun SOG dielectric prior to pentacene evaporation, resulting in an improvement of the saturation field effect mobility (μ_sat) from 0.01 cm²/(V s) to 0.76 cm²/(V s). The good surface morphology and the matching surface energy of the SOG dielectric that was modified with the polymer thin film allow the optimized growth of crystalline pentacene domains whose nuclei are embedded in an amorphous phase.