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1.
TiC/PVDF nanocomposite is prepared via simple blending and hot pressing route. Percolation theory was employed to explain the dielectric behavior of the TiC/PVDF composites. The dependence of the dielectric properties of the composite on both volume fraction of the filler and frequency is investigated. High dielectric constant (? = 540) and low loss (tan δ = 0.48) of the composites at 100 Hz have been observed near the percolation threshold (0.12). The composites show a weak frequency dependence towards the high frequency range (10–100 kHz), regardless of the TiC content. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
2.
We consider the influence of an ω-dependent ionic dielectric constant ?(ω) on the properties of a superconductor. Assuming that the pairing interaction is proportional to ?2 we have solved the Eliashberg equations for this case, both for imaginary and real frequencies. The interaction potential depends on a coupling constant λ and on a longitudinal phonon frequency Ω. The dielectric constant is assumed to be independent of wavevector q, and to depend on frequency through the expression: ?(ω) = (ω2 - ω2long)/(ω2 - ω2trans), where ωlong, ωtrans are the frequencies of optical phonons of the dielectric. We find that along the imaginary frequency axis (but not for real frequencies) the weighted phonon propagator can be modeled by an appropriate choice of a cutoff frequency and an effective coupling constant. The influence of ?(ω) on Tc, the gap δ(ω), and the renormalization function Z(ω) are studied and it is found that these quantities increase significantly with the dielectric constant. 相似文献
3.
In this paper we report the effect of Pb incorporation in the dielectric properties of a-Se75In25 glassy alloy. The temperature and frequency dependence of the dielectric constants and the dielectric losses in glassy Se75In25
−x
Pb
x
(x = 0, 5, 10 and 15) alloys in the frequency range (1 kHz-5 MHz) and temperature range (300–340 K) have been measured. A detailed
analysis shows that the dielectric losses are dipolar in nature and can be understood in terms of hopping of charge carriers
over a potential barrier as suggested by Elliott for the case of chalcogenide glasses. It has been found that both dielectric
constant and the dielectric loss are highly dependent on frequency and temperature and also found to increase with increasing
concentration of Pb in binary a-Se75In25 glassy system. The results have been interpreted in terms of increase in the density of defect states by the incorporation
of Pb as a metallic additive in the aforesaid glassy system. 相似文献
4.
Confinement of massless particles in a suitably chosen dielectric medium is considered. Light waves of selected frequencies
are shown to be confined in a medium with dielectric constantε(r)=a/r−b
2. A wave theoretical analysis gives equispaced frequency spectrum for the confined light, the radial dependence of its electric
wave vector resembling that of hydrogen atom wave functions. In the large frequency limit an eikonal approximation of the
problem gives elliptic orbits for the confined rays. Higher frequency orbits are shown to be closer to the centre of the medium
than the lower frequency ones. 相似文献
5.
Dielectric properties of binary mixtures of anisole with methanol (MeOH), 1-propanol (1-PrOH), 1-butanol (1-BuOH) and 1-heptanol (1-HeOH) over an entire concentration range have been studied at a fixed temperature 40°C. The dielectric constant (ε′) and dielectric loss (ε″) of the binary mixtures of polar liquids have been determined at a microwave frequency of 9.1?GHz. The static dielectric permittivity (ε 0) of the liquid samples was also determined using a precision LCR meter. Determined values of static dielectric permittivity (ε 0) and dielectric permittivity (ε*) at 9.1?GHz frequency were used to evaluate relaxation time (τ) and high frequency limit dielectric permittivity (ε ∞). Dielectric parameters were interpreted in terms of molecular interaction between the anisole and alcohol molecules. 相似文献
6.
7.
Dielectric spectroscopy investigations in the frequency range 50?Hz to 1?MHz have been carried out on a new ferroelectric liquid-crystalline material (S-(-)-4-(2-n-hexylpropionyloxy)biphenyl-4′-(3-methyl-4-decyloxy)benzoate) possessing a relatively large spontaneous polarization (P s?~?240?nC?cm?2) and containing a lateral methyl group on the aromatic ring of the alkoxybenzoate unit. The effect of temperature on the dielectric relaxation modes has been investigated in the SmC* and N* phases. From dielectric dispersion data, relaxation frequency and dielectric strength of all detected relaxation modes have been evaluated and discussed. A new surface-like mode of relaxation frequency ~11?kHz and dielectric strength 3.8, is seen to appear in the SmC* phase. 相似文献
8.
Rajesh Kumar S. Asad Ali Udayan De D. K. Avasthi Rajendra Prasad 《Indian Journal of Physics》2009,83(7):963-968
The passage of heavy ions in a track detector polymeric material produces lattice deformations. These deformations may be
in the form of latent tracks or may vanish by self annealing in time. Heavy ion irradiation produces modifications in polymers
in their relevant electrical, chemical and optical properties in the form of rearrangement of bonding, cross-linking, chain
scission, formation of carbon rich clusters and changes in dielectric properties etc. Modification depends on the ion, its energy and fluence and the polymeric material. In the present work, a study of the dielectric
response of pristine and heavy ion irradiated Makrofol-KG polycarbonate is carried out. 40 μm thick Makrofol-KG polycarbonate
films were irradiated to various fluences with Si8+ ions of 100 MeV energy from Pelletron at Inter University Accelerator Centre (IUAC), New Delhi and Ne6+ ions of 145 MeV from Variable Energy Cyclotron Centre, Kolkata. On irradiation with heavy ions dielectric constant (ɛ′) decreases with frequency where ɛ′ increases with fluence for both the ions. Variation of loss factor (tan δ) with frequency for pristine and irradiated with Si ions reveals that tan δ increases as the frequency increases. Tan δ also increases with fluence. While Ne irradiated samples tan δ shows slight variation with frequency as well as with fluence. Tan δ has positive values indicating the dominance of inductive behavior.
相似文献
9.
Electroluminescence in PbTiO3 single crystals is studied with variation in applied electric field, frequency (20 Hz to 5 kHz) and temperature. The EL onset
depends on the rate at which the dipole switches. Extremely sharp upward rising nature of the pulses of micro second duration
suggest that there is a self maintained discharge in the dielectric due to secondaryγ
p mechanism. Frequency dependence of EL suggests that both the secondary mechanisms, viz. theγ
p andγ
i are active after the application of a high field and the critical field at which this occurs decreases with increase in the
frequency of the applied voltage. Similarly the onset voltage decreases with increase in frequency. The temperature dependence
of EL at the applied frequency of 50 Hz shows that the onset voltage is intimately connected with the coercive field of the
crystal and it is minimum at the Curie point. The study suggests that EL occurs in the bulk and there is a breakdown in the
dielectric due to an avalanche formation. 相似文献
10.
Temperature-dependent dielectric characterization of 4-hexyl-4′-[2-(4-isothiocyanatophenyl)ethyl]-1,1′-biphenyl (HIEB), which exhibits smectic B and nematic phases, has been carried out over the frequency range of 1 Hz to 10 MHz for homeotropic and planar alignment of sample molecules. This compound shows positive dielectric anisotropy (Δε = ε ∥ ? ε ⊥ > 0) in the nematic (N) phase. One mode of dielectric relaxation showing Arrhenius behaviour has been detected in the hexatic smectic B (SmB) phase. Various electrical parameters, namely, dielectric anisotropy, relaxation frequency and activation energy, have been determined in the N and SmB phases. 相似文献
11.
B. Lalevic N. Fuschillo B. Kuliyev W. Wang 《Applied Physics A: Materials Science & Processing》1974,5(2):127-132
Transport and dielectric properties of polycrystalline CoO films were studied as functions of the applied field, frequency
and temperature. TheI–V plots showed that the Poole-Frenkel field emission mechanism is responsible for conduction at fields>105 V/cm. The ac conductivity σ(ω), the imaginary part of the dielectric constantε
2, and tan δ plots as functions of frequency revealed three dispersion regions. The σ(ω) andε
2 frequency dependence indicates a non-adiabatic hopping of charge carriers at low frequencies and adiabatic hopping at high
frequencies. The activation energy of a dielectric oscillator is 0.15 eV.
Work supported by the Office of Naval Research. 相似文献
12.
The distribution of relaxation times approach, a less frequently employed dielectric data analysis technique, is utilized to better understand the relaxation characteristics of composites consisting of metal-coated, hollow glass spheres dispersed in a paraffin wax matrix. The dielectric properties of the composite samples are measured by means of impedance spectroscopy in the frequency range 0.1?mHz to 10?MHz. The application of a mixture law is not appropriate for the analysis of the frequency-dependent properties of the considered system on this broad frequency range. However, utilization of the distribution of relaxation times procedure to study the dielectric behaviour shows clear trends in the mixtures’ relaxation spectra. Relaxation processes of the paraffin wax and those specific to the composites are found from the extracted distribution of relaxation times spectra. The influence of the filler concentration, q, on the dielectric properties is examined; a relaxation with a narrow distribution at intermediate frequencies becomes broad with the addition of the filler. This relaxation, in the form of the low-frequency-dispersions (also known as constant phase angle) phenomenon, dominates the dielectric properties of the composites with high bead concentration, q>0.15. The variation in dielectric properties of individual samples whose bead concentrations q are nominally the same is discussed in terms of possible microstructural variations. 相似文献
13.
K. J. Hameeuw F. Brosens J. T. Devreese 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,35(1):93-101
Dynamical exchange interactions can be introduced in the dielectric function via a dynamic local field factor. We study the effects of this inclusion on both the static and the frequency dependent dielectric function of a two-dimensional electron gas, using the dynamic local field factor that we derived recently via the dynamical exchange decoupling method. The results are compared with the dielectric function in the Random Phase Approximation and with different dynamic and static approximations of the local field factor.Received: 7 May 2003, Published online: 22 September 2003PACS:
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons - 77.22.Ch Permittivity (dielectric function) - 77.55.+f Dielectric thin filmsJ.T. Devreese: , jtd@uia.ua.ac.be 相似文献
14.
S. O. Gladkov 《Technical Physics》1999,44(3):291-294
It is predicted that at room temperatures a hopping mechanism of charge transfer plays a very important role and leads to
temperature oscillations of the conductivity σ(T) of a dielectric composite. The dependence of the conductivity σ(ω) on the frequency of an alternating electric field is calculated. The relation obtained can be used to determine, first,
the electron relaxation times and, second, and more importantly, the frequency of electron tunneling through the dielectric
matrix from measurements of the conductivity in various frequency ranges.
Zh. Tekh. Fiz. 69, 31–34 (March 1999) 相似文献
15.
Anomalous infrared monochromatic transmission through superconducting cylinders embedded in a dielectric and dielectric cylinders
embedded in a superconductor is found. The transmitted frequency corresponds to the localized photonic mode in the forbidden
photonic band. This localized mode appears when the symmetry of the photonic crystal is broken by a defect. This defect can
be formed when supercon-ducting cylinder is removed from the node of the ideal two-dimensional lattice of superconducting
cylinders in dielectric medium or one dielectric cylinder placed out of the node of the lattice of the dielectric cylinders
in superconducting medium. The corresponding frequency was calculated for the YBa2Cu3O7 − δ
supercon-ducting cylinders in vacuum. 相似文献
16.
A mode-coupling theory (MCT) is presented for the spin-boson model with a spectral density which accounts for a heat bath made up of lattice vibrations of a dielectric solid (superohmic dissipation). A usual decoupling approximation provides a set of non-linear integral equations which are solved both numerically by iteration on a computer and analytically by means of a frequency dependent ansatz for the memory functions. There is a transition to incoherent motion at a temperatureT
* where the bare two-level energy is equal to the damping rate, in contradiction to results obtained previously from a path integral formulation. The discrepancy arises since in the MCT the relevant self-energy function does not exhibit a 1/z-pole atz=0. For tunnelling systems in dielectrics this yields a new relaxation mechanism due to incoherent tunnelling: the present results might require to modify some of the basic assumptions of the standard tunnelling model for dielectric glasses. 相似文献
17.
本文研究了DCEL器件在AC条件下,亮度、效率、有功电流、无功电流及损耗角正切与频率的关系.指出了发光区有效电场强度、发光区的宽度及电压分配系数等都是与频率有关的物理量.证明了有功电流和损耗角正切随频率的变化可分为两个区,在低于1kHz的低频区,有功电流和介质损耗分别以漏导电流和漏导损耗为主,可称为漏导电流区.在大于1kHz的高频区,有功电流中与各种松弛极化形式有关的吸收电流占主导且随频率增加较快.与其相关的,和各种极化有关的介质损耗急剧增加并超过漏导损耗而成为损耗的的主要成分,从而导致发光效率下降.这一区域可称为吸收电流区. 相似文献
18.
This work is a contribution to the understanding of the dielectric properties of nanofluids prepared by dispersing multiwalled carbon nanotubes in transformer oil. The dielectric measurements were carried out in the frequency range 100 Hz–1 MHz at constant temperature, T = 300 K, for several volume fractions of the nanotubes in the base fluid. A relaxation phenomenon was induced in the nanofluid comparing to the base fluid. In addition, both the real and imaginary part of the dielectric permittivity changed with volume fraction of the nanotubes. These results suggest that the presence of the nanotubes greatly affect the dielectric properties of the oil as a result of polarization phenomenon induced by these nanoparticles.It was found that the measured effective dielectric permittivity follows the empirical Havriliak–Negami model. Nevertheless to take into account the electrode polarization effects, we rewrote this model, with a new term, which fits accurately the experimental data. 相似文献
19.
采用固相反应法制备了不同含氧量的BiFeOδ多晶陶瓷样品,利用HP4294A阻抗分析仪测量了样品的介电特性随频率和氧含量的变化,用正电子湮没寿命谱学的方法研究了样品中因氧含量的变化所引起的结构缺陷. 实验结果表明:引入氧空位和氧填隙离子缺陷都会使介电常数减小,而介电损耗则随氧含量的增加而增加,二者的变化范围均在10%—35%之间;对不同氧含量的BiFeOδ样品,介电常数和介电损耗随测量频率的增加而减小. 氧空位的引入使得局域电子密度变小,正电子平均寿命τm增加. 在氧含量δ=2.99时电子密度最大(ne=3.90×1023/cm3),继续增加氧含量对正电子寿命与局域电子密度的影响不大. BiFeOδ样品的介电常数和介电损耗随氧含量的变化可以在空间电荷限制电导的框架下来理解. 相似文献
20.
This paper presents the results of the investigation of dielectric dispersion in semiconductive ferroelectric Sn2P2S6 crystals over the frequency range 1 kHz to 78.5 GHz. The main dielectric dispersion in Sn2P2S6 is caused by the soft ferroelectric Bu mode and in the vicinity of the Curie point it occurs in the millimeter region. The frequency of the soft mode in the paraelectric phase varies according to vs = 35 (T-Tc )½ GHz on approaching the Curie point. The soft mode is strongly overdamped. Close to Tc the relative damping is y/vs = 14. The dielectric contribution of the soft mode is equal to the static dielectric permittivity and it explains its whole temperature-dependence. 相似文献