Dielectric properties and ac-conductivity analysis of Bi3.25La0.75Ti3O12 ceramic using impedance spectroscopy

Investigations have been performed on lanthanum-modified layered ferroelectric bismuth titanate for composition Bi_3.25La_0.75Ti₃O₁₂ (BLT) using impedance spectroscopy to understand the role of microstructure on the dielectric properties of this important material. A wide range of frequency and a wide range of temperature passing through the Curie point were chosen for the measurement. The frequency dependence suggested an interfacial polarization controlled Maxwell–Wagner type relaxation at low frequencies, and the impedance spectrum correlated with the mathematical fitting indicated the presence of two types of interfaces, which were attributed to the metallurgical boundaries and the twinned planes parallel to the bismuth oxide layers inherent to the crystal structure within the metallurgical grains. A careful analysis of the dielectric properties, particularly the ac-conductivity analysis revealed that the grain boundaries did also follow their own Jonscher-like relaxation, and the overall relaxation of the sample changed to a purely grain boundary-limited response at low frequency to a pure grain-limited response at higher frequencies. And overall admittance of the ceramic sample neither follow unmodified nor modified Jonscher's law rather its behaviour can be well described by series addition of Jonscher's admittance corresponding to grain boundary and grain. It was demonstrated that the frequency response of the ac conductivity was related to the microstructure exactly in the same way as any other dielectric function, like the impedance or dielectric constant, a fact, which is not much emphasized in the open literature.     

Surface impedance of a spatially dispersive medium

The surface impedance for non-normal specular reflection from a spatially dispersive medium is calculated using the additional boundary condition of vanishing polarization at the surface. There is no dependence on the longitudinal dielectric constant for either polarization directions of the electric field in contrast to the formula derived by Kliewer and Fuchs.     

Numerical analysis of complex impedance and microwave absorption of metamaterials composed of split cut wires on grounded dielectric substrate

The microwave absorption of metamaterials composed of split cut wire (SCW) on grounded dielectric substrate has been investigated on the basis of equivalent transmission line circuit. S-parameters (S ₁₁ and S ₂₁) and input impedance are numerically simulated with variations of the thickness and dielectric loss of the substrate and the geometry of the SCW. Magnetic resonance resulting from antiparallel currents between SCW and ground plane was observed at the frequency of minimum reflection loss. The simulated resonance frequency and reflection loss can be explained well on the basis of the circuit theory of an LC resonator. Analysis of the input impedance of the high impedance surface has shown that perfect absorption can be obtained at the optimized impedance-matching condition, which is dependent on SCW width, thickness and the dielectric loss of the substrate. Better insight into the absorption mechanism of metamaterial absorbers can be attained through the parametric analysis on complex impedance of SCW and its relationship with reflection loss.     

巨介电常数氧化物CaCu3Ti4O12的介电和阻抗特性

采用固相烧结法合成了单相巨介电常数氧化物CaCu₃Ti₄O₁₂（CCTO）.用阻抗分析仪分析了10—420 K温度范围内的介电频谱和阻抗谱特性,并结合ZVIEW软件进行了模拟.结果表明：温度高于室温时,频谱出现两个明显的弛豫台阶,低频弛豫介电常数随温度升高而显著增大,表现出热离子极化特点;温度低于室温时,频谱表现出类德拜弛豫,且高、低平台介电常数值基本不随温度变化,表现出界面极化特点和较好的温度稳定性.频谱中依次出现的介电弛豫对应于阻抗谱中 关键词： 3Ti₄O₁₂')" href="#">CaCu₃Ti₄O₁₂ 介电频谱 阻抗谱 Cole-Cole半圆弧     

Theoretical analysis of the characteristic impedance in metal-insulator-metal plasmonic transmission lines

We propose a closed form formulation for the impedance of the metal-insulator-metal (MIM) plasmonic transmission lines by solving the Maxwell's equations. We provide approximations for thin and thick insulator layers sandwiched between metallic layers. In the case of very thin dielectric layer, the surface waves on both interfaces are strongly coupled resulting in an almost linear dependence of the impedance of the plasmonic transmission line on the thickness of the insulator layer. On the other hand, for very thick insulator layer, the impedance does not vary with the insulator layer thickness due to the weak-coupling/decoupling of the surface waves on each metal-insulator interface. We demonstrate the effectiveness of our proposed formulation using two test scenarios, namely, almost zero reflection in T-junction and reflection from line discontinuity in the design of Bragg reflectors, where we compare our formulation against previously published results.     

An impedance spectroscopy study in poly(butylene adipate) ionomers

Poly(butylenes adipate) ionomers (PBAi) were synthesized using dimethyl 5‐sulfoisophthalate sodium salt (DMSI) up to 5 mol% of diacid monomer. We have investigated electrical and dielectric properties of the ionomers to evaluate alternating current (AC) parameters such as impedance, conductance, dielectric constant, admittance, susceptance, dielectric loss, and resistance by an impedance spectroscopy. It is seen that the ionic conductances of the ionomers increase with increasing content of DMSI. The AC conductance for the ionomers was found to vary as ω^s with the index s ≥ 1. A decrease in the relative dielectric constant of the ionomers is observed with the increase in the ionic content. The electrical relaxation in the dielectric spectra of the ionomers was not observed due to the orientation polarization of the dipoles. It is also observed that the tangent loss increases with the increase in the ionic content.     

Electrical and dielectric characterization of Au/ZnO/n-Si device depending frequency and voltage

Au/Zn O/n-type Si device is obtained using atomic layer deposition(ALD) for Zn O layer, and some main electrical parameters are investigated, such as surface/interface state(Nss), barrier height(Φb), series resistance(Rs), donor concentration(Nd), and dielectric characterization depending on frequency or voltage. These parameters are acquired by use of impedance spectroscopy measurements at frequencies ranging from 10 k Hz to 1 MHz and the direct current(DC) bias voltages in a range from-2 V to +2 V at room temperature are used. The main electrical parameters and dielectric parameters,such as dielectric constant(ε"), dielectric loss(ε"), loss tangent(tan δ), the real and imaginary parts of electric modulus(M and M), and alternating current(AC) electrical conductivity(σ) are affected by changing voltage and frequency. The characterizations show that some main electrical parameters usually decrease with increasing frequency because charge carriers at surface states have not enough time to fallow an external AC signal at high frequencies, and all dielectric parameters strongly depend on the voltage and frequency especially in the depletion and accumulation regions. Consequently, it can be concluded that interfacial polarization and interface charges can easily follow AC signal at low frequencies.     

Chiral planar waveguide for guiding single-mode backward wave

Single-mode backward wave is shown to be guided in a planar dielectric waveguide with a strong chiral core. The significant difference of such a waveguide from the traditional one is the guidance of single-mode backward wave, without using negative permittivity and/or negative permeability. In the design, we generalize the idea of total internal reflection to the chiral medium and make a numerical analysis on the reflection with oblique incidence. We deduce rigorously a general solution of incident wave on the boundary of two arbitrary chiral magneto-electric media. We observe that the impedance matching can eliminate the coupling between two eigenwaves in chiral media. With strong chiral core and the matched impedance with cladding, one eigenwave becomes a backward wave and can be guided without transferring to the other eigenwave. If a single-mode propagation condition is satisfied, we will get single-mode backward guided wave. A special interface has been designed to prevent the forward wave entering the waveguide from the source.     

Effective dielectric constant model of electromagnetic backscattering from stratified air–sea surface film–sea water medium

Studies of surface film medium on the sea surface are carried out in this paper for developing the technology to automatically detect and classify sea surface films, and an effective dielectric constant model of electromagnetic backscattering from a stratified air–ocean interface. Numerical results of the new model show the characteristics of effective dielectric constants for the air–sea surface film–sea water medium as follows. The effective dielectric constants decrease with increasing relative dielectric constants of the sea surface films. The effective dielectric constants decrease in horizontal polarization(abbr. HH polarization) and increase in VV vertical polarization(abbr. VV polarization) with increasing radar incident angle. Effective dielectric constants vary with relative sea surface film thickness as a cosinusoidal function of sea surface film thickness. Effective dielectric constant of VV polarization is larger than that of HH polarization. Two potential applications are found with our model, i.e., the retrieval of dielectric constants from the sea surface film, and the film thickness retrieval with our model. Our model has a highly significant influence on improving the technology related to the remote sensing of sea surface films.     

Electrode polarization and interface effects in liquid crystal systems with mobile ions: development of a model of bipolar diffusion

The influence of mobile ions on the results of impedance spectroscopy (dielectric spectroscopy) measurements performed on a liquid crystal cell using the new mathematical model recently described was investigated. This mathematical model reformulates the fundamental equation system of continuity for mobile charge carriers and the Poisson equation using new variables. One makes the following assumptions: ions have different mobilities and diffusion coefficients, there is no generation-recombination process, the equilibrium carrier concentrations are uniform and equal each other, the electrodes are either completely blocking or blocked with adsorption-desorption processes. The final result is the analytical expression of the equivalent admittance for the system, allowing to have a clearer picture of the mobile ions and of the processes that occur at the electrode interface influencing the dielectric behavior.     

An Ultra-Broadband Chirality Selective Metastructure Absorber using High Impedance Surface

In this paper, an ultra-wideband chirality selective metastructure absorber is proposed that enables differential absorption and reflection of circularly polarized waves in the terahertz (THz) range. The structure achieves circular dichroism (CD) by using asymmetrically split metal rings as fundamental meta-atoms. Most critically, the high impedance surface and air-resonant cavities are inserted separately in the meta-atoms and dielectric substrate to enhance CD and broaden the bandwidth of absorption. The metastructure absorber can achieve more than 90% absorption of right circularly polarized waves at 0.675–1.244 THz, and it can maintain more than 90% reflection of left circularly polarized waves at 0.607–1.229 THz without changing the direction of rotation. Besides, its CD can reach more than 80% at 0.687–1.213 THz with a relative bandwidth of 55.3%. Spin-selective absorption, which is closely related to breaking chiral symmetry, is investigated through power loss distribution, wide-angle incidence, and scan parameter optimization. The proposed strategy is further validated in the THz band, and the polarization selection and manipulation techniques can be applied to chiral sensing/radio-thermometry, circular polarization detectors/lasers, and molecular spectroscopy.     

AC conductivity and relaxation behavior in ion conducting polymer nanocomposite

We report the ac conductivity and relaxation behavior analysis for a heterogeneous polymer–clay nanocomposite (PNC) having composition (polyacrylonitrile)₈LiCF₃SO₃ + x wt.% dodecylamine modified montmorillonite. Charge transport behavior in an ionically conducting PNC has been analyzed systematically and correlated with the macroscopic parameters like polymer glass transition temperature and available free mobile charge carriers. Intercalation of cation coordinated polymer into the nanometric clay channels has been confirmed by high-resolution transmission electron microscopy. The electrical properties of the intercalated PNC films have been studied using complex impedance/admittance spectroscopy. Excellent correlation of relaxation behavior with polymer glass transition temperature (T _g) confirmed the objectives of the work. An analysis of dielectric relaxation indicates that PNC films are lossy when compared with polymer–salt film. This result is a direct outcome of faster ion dynamics leading to strong electrode polarization effect due to the accumulation of charge carriers at the interface.     

Negative refraction and rough surfaces: A new regime for lensing

The action of a rough, but differentiable, interface upon the passage of rays between air and a left-handed medium is considered. It is shown that negative refraction brings rays to a focus at distances closer to the boundary than can be attained by conventional refraction. This effect enables a new mechanism for reflection to occur, even in media that are impedance matched, caused principally by rays undergoing two interactions with the interface via paths that pass exclusively through air or the left-handed medium.     

Reflected and refracted electromagnetic fields in a semi-infinite body

We compute the reflected and refracted electromagnetic fields for an ideal semi-infinite body (either a plasma or a dielectric), as well as the reflection coefficient, by using a general approach based on the polarization equation of motion and electromagnetic potentials. The method consists of representing the charge disturbances by a displacement field in the positions of the moving charges. The propagation of an electromagnetic wave in matter is treated by means of the retarded electromagnetic potentials, and the resulting integral equations are solved. Generalized Fresnel’s relations are thereby obtained for any incidence angle and polarization and the angles of total polarization and total reflection are derived (the latter for the plasma). Bulk and surface plasmon–polariton modes are also identified for the plasma. As it is well known, the field inside the plasma is either damped (evanescent) or propagating (transparency regime), and the reflection coefficient exhibits an abrupt enhancement on passing from the propagating regime to the damped one (total reflection).     

Studies on frequency and gate voltage effects on the dielectric properties of Au/n-Si (110) structure with PVA–nickel acetate composite film interfacial layer

The admittance technique was used in order to investigate the frequency dependence of dielectric constant (????), dielectric loss (????), dielectric loss tangent (tan??), the ac electrical conductivity (?? _ac), and the electric modulus of PVA (Ni-doped) structure. Experimental results revealed that the values of ???? , ????, (tan??), ?? _ac and the electric modulus show fairly large frequency and gate bias dispersion due to the interface charges and polarization. The ?? _ac is found to increase with both increasing frequency and voltage. It can be concluded that the interface charges and interfacial polarization have strong influence on the dielectric properties of metal?Cpolymer?Csemiconductor (MIS) structures especially at low frequencies and in depletion and accumulation regions. The results of this study indicate that the ???? values of Au/PVA/n-Si with Nickel-doped PVA interfacial layer are quite higher compared to those with pure and other dopant/mixture??s of PVA.     

Modification of Classical SPM for Slightly Rough Surface Scattering with Low Grazing Angle Incidence

Based on the impedance/admittance rough boundaries, the reflection coefficients and the scattering cross section with low grazing angle incidence are obtained for both VV and HH polarizations. The error of the classical perturbation method at grazing angle is overcome for the vertical polarization at a rough Neumann boundary of infinite extent. The derivation of the formulae and the numerical results show that the backscattering cross section depends on the grazing angle to the fourth power for both Neumann and Dirichlet boundary conditions with low grazing angle incidence. Our results can reduce to that of the classical small perturbation method by neglecting the Neumann and Dirichlet boundary conditions.     

Modification of Classical SPM for Slightly Rough Surface Scattering with Low Grazing Angle Incidence

Based on the impedance/admittance rough boundaries, the reflection coefficients and the scattering cross section with low grazing angle incidence are obtained for both VV and HH polarizations. The error of the classical perturbation method at grazing angle is overcome for the vertical polarization at a rough Neumann boundary of infinite extent. The derivation of the formulae and the numerical results show that the backscattering cross section depends on the grazing angle to the fourth power for both Neumann and Dirichlet boundary conditions with low grazing angle incidence. Our results can reduce to that of the classical small perturbation method by neglecting the Neumann and Dirichlet boundary conditions.     

Method of polarization reflection matrix measurement in the submillimeter wave range

Homodyne method of measurement of polarization reflection matrix, providing the possibility of simultaneous measurement of all four complex coefficients of polarization reflection matrix in submillimeter quasi-optical (QO) circuits is presented. Technical realizability of the method for QO waveguides of the class of "hollow dielectric wavequide" is shown.     

Dielectric behavior of BaTiO<Subscript>3</Subscript>–Ni composite ferroic films

Composite ferroic BaTiO₃–Ni films with different Ni content were fabricated by radio frequency (RF) cosputtering method. Complex impedance analysis indicates that the addition of Ni has greatly reduced the resistivity of the Ni-enriched boundaries. All the composite films exhibit room temperature ferromagnetism, while the ferroelectricity of the films is degrading with increasing Ni content. Dielectric measurements reveal that below the Ni content of 22.7 at.%, the dielectric response follows the general percolation theory and the increase of dielectric constant and loss tangent with Ni addition is mainly associated with the microstructure induced nanocapacitor effect and Maxwell–Wagner interface polarization which also induces significant dielectric anomaly at low frequency range.