Dielectric permittivity of suspensions

A strict macroscopic analysis of the limiting long-wavelength permittivity of a model suspension is presented in which the suspension is considered as a finely dispersed system consisting of isotropic dielectric balls with piecewise-continuous radial permittivity profile. The analysis is performed within the framework of the notion of compact groups of inhomogeneities and the procedure of field averaging over volumes significantly exceeding the scale of these groups. The indicated value is described by the Lorentz-Lorenz formula. The effective polarizability of balls in the suspension is reconstructed from their parameters and the parameters of the medium by means of integration. The result is valid for any concentration of the balls at which the suspension remains macroscopically homogeneous and isotropic with respect to the field and for an arbitrary difference between the ball and medium permittivities.     

Dielectric permittivity of kaolinite heated to high temperatures

Heating of kaolinite from the room temperature to 600 °C results in a gradual decrease in the dielectric permittivity. However, when the temperature rises to 1000 °C the high frequency permittivity of kaolinite increases surprisingly. We suppose that the decomposition of the material produces imperfections, which liberate a small distance movement of polar groups. Positron annihilation experiments performed in this material confirm the appearance of empty volumes after kaolinite calcination.     

Dielectric permittivity in the smectic a phase of liquid crystals

We propose a functional dependence of the dielectric constant with the smectic order parameter of liquid crystals in their smectic A phase. The proposal is verified by comparing with the published values of heptylazoxybenzene.     

Dielectric permittivity and phase transitions in the SrTiO3-KTaO3 system

The dielectric permittivity and losses of the (SrTiO₃)_0.85(KTaO₃)_0.15 solid solution have revealed an unusual behavior at temperatures of 5–300 K and frequencies ranging from 100 Hz to 1 MHz. The dielectric permittivity exhibits a broad maximum at ≈40 K, which obeys the Curie-Weiss law in the high-temperature wing, and the onset of low-temperature relaxation contributions. Besides, while for T>40 K it is a fully ergodic, uniformly ordering system, the uniform polar ordering is replaced with decreasing temperature by two low-temperature phase transitions to a glass-like state. The proposed mechanism for the dielectric relaxation and the observed phase transformations involves reorientation and ordering in the system of electron and hole polarons, which form in the course of charge compensation of the heterovalent ions Sr²⁺, K⁺ and Ti⁴⁺, Ta⁵⁺ distributed randomly in the sublattices. Fiz. Tverd. Tela (St. Petersburg) 39, 2040–2045 (November 1997)     

Dielectric photonic crystal as medium with negative electric permittivity and magnetic permeability

We show that the two-dimensional photonic crystal (PC) made from a non-magnetic dielectric is a left-handed material in the sense defined by Veselago. Namely, it has negative values for both the electric permittivity ? and the magnetic permeability μ in some frequency range. This follows from a recently proven general theorem. The negative values of ? and μ are found by a numerical simulation. Using values |?| and |μ| for the medium surrounding the PC slab we simulate the Veselago lens, a unique optical device predicted by Veselago. An approximate analytical theory is proposed to calculate the values of ? and μ from the PC band structure. It gives the results that are close to those obtained by the numerical simulation. The theory explains how a non-zero magnetization arises in a non-magnetic PC.     

Dielectric permittivity of nickel ferrites at microwave frequencies 1 MHz to 1.8 GHz

NiFe₂O₄ prepared via the sol–gel technique were pre-sintered at 900 °C and synthesized at different sintering temperatures from 1,000 °C to 1,200 °C at 100 °C intervals. The samples were characterized for microwave dielectric properties. These samples were measured using Agilent Impedance/Material Analyzer at frequencies 1 MHz to 1.8 GHz. Results showed a decrease in the dielectric constant and loss factor with frequency except at the turning point, around 150 MHz, where the loss factor showed a gradual increase. However, both the dielectric constant and loss factor increase with increasing sintering temperature. The grain size and density also increased with increasing sintering temperature, but the porosity and grain boundary density showed a decrease. This paper was presented at the International Conference on Solid State Science and Technology 2006, Kuala Terengganu, Malaysia, Sept. 4–6, 2006.     

Self-organized superlattice formation during crystal growth from continuous beam fluxes

Alloy superlattice structures consisting of alternating Si-rich and C-rich layers form spontaneously during gas-source molecular beam epitaxy of Si(1-y)C(y) on Si(001) from constant Si2H6 and CH3SiH3 precursor fluxes at T(s)=725-750 degrees C. The self-organized patterning is due to a complex interaction among competing surface reactions. During growth of the initial Si-rich layer, strain-driven C segregation to the subsurface results in charge transfer from surface Si atom dangling bonds to C backbonds. This decreases the Si2H6 sticking probability, and, hence, the instantaneous deposition rate, thereby enhancing C segregation. The Si-rich layer continues until a critical C coverage is reached allowing nucleation of a C-rich layer which grows until the excess subsurface C is depleted. The process then repeats with periods tunable through the choice of T(s) and y(avg).     

Dielectric permittivity of aqueous solutions of electrolytes probed by THz time-domain and FTIR spectroscopy

We have measured the dielectric permittivity of pure water and aqueous chlorides solutions in the range 0.2-1.5 THz. We considered the relaxation spectral function as the weighted sum of two independent single-parameter Debye functions. Such an approach allowed to drastically reduce the number of the parameters used in the fit which we set only by physical considerations. The resulting functions allow to fit the experimental data for pure water and solutions of LiCl, KCl, NaCl, and CsCl and to predict the excess response on the high frequency side of the relaxation without “ad hoc” corrective terms.     

Dielectric permittivity studies of nematogenic compounds and their binary mixtures showing induced smectic Ad phase

The binary mixture of 4-n-pentyl phenyl 4-n′-hexyloxy benzoate (ME6O.5) and p-cyanophenyl trans-4-pentyl cyclohexane carboxylate (CPPCC) shows the presence of induced Smectic A_d phase. In the present work the phase diagram as well as static dielectric permittivity measurements of different mixtures throughout the composition range, are reported. The observed variation of dielectric anisotropy with molar concentration in the nematic and smectic phases is explained, assuming the formation of both homo- and hetero-dimers in the mixture.     

Infrared study of superlattice formation in Ti1+xSe2

Infrared reflectivity measurements have been made on two Ti_1+xSe₂ crystals of different stoichiometry over the range 200 cm^?1 to 4000 cm^?1 before and after the formation of a 2a_o × 2c_o superlattice. In both crystals at room temperature a heavily damped Drude edge is observed at about 1000 cm^?1. At liquid helium temperatures, below the phase transition, the Drude minimum of a non-stoichiometric crystal ($\text{x ? 0.02, T}{}_{\mathrm{c}}\text{= 155 K}$) is at 750 cm^?1 whereas the low temperature minimum of a more stoichiometric sample (T_c = 198 K) is below 350 cm^?1. Also, new absorption peaks are seen to develop below T_c at about 3700 cm^?1 and 3300 cm^?1 for the non- stoichiometric and stoichiometric-crystals respectively. The observed phenomena are related to the energy gaps which open up in the band structure below the phase transition temperature.     

介质阻挡放电系统中超四边形斑图形成的实验研究

采用水电极介质阻挡放电装置,在氩气和空气的混合气体放电中,对超四边形斑图的形成进行了实验研究.发现随着外加电压的升高,斑图类型经历了四边形斑图、准超点阵斑图、超四边形斑图、条纹斑图或六边形斑图的演化顺序.对这些斑图进行了傅里叶谱分析,得到了空间模式随电压的变化关系.此外,在外加电压升高的过程中,出现了具有不同空间尺度的两种超四边形斑图,它们满足不同的驻波条件.分析了壁电荷在超四边形斑图形成中的作用.实验测量了斑图类型随气隙间距和外加电压变化的相图以及超四边形斑图随气隙间距和气隙气压变化的相图.测量了击穿电 关键词： 介质阻挡放电 斑图 壁电荷 放电参量     

Dielectric permittivity and electric modulus of polyethylene oxide (PEO)-LiClO4 composite electrolytes

Dielectric permittivity and conductivity relaxation in polyethylene oxide (PEO)-LiClO₄ salt polymer electrolytes have been investigated for different lithium ion concentrations. We have observed that imaginary modulus spectra exhibit asymmetric maxima with peak-width much broader than that of the Debye peak and are skewed toward the high frequency sides of the maxima. The charge carriers for the electrolyte having higher lithium salt concentration relax much faster than that for other electrolytes and produces higher conductivity. The modulus data have been fitted using non-exponential Kohlrausch-Williams-Watts (KWW) function φ(t). We have observed that the value of the non-exponential parameter (β) is fairly low and nearly constant for different salt concentrations. The low value of β suggests a wide distribution of non-exponential relaxation times. Using the scaling of modulus data we have observed that the relaxation dynamics of charge carriers in these PEO-Li salt based electrolytes is independent of temperature and salt concentration.     

Phonon-induced optical superlattice

We demonstrate the formation of a dynamic optical superlattice through the modulation of a semiconductor microcavity by stimulated acoustic phonons. The high coherent phonon population produces a folded optical dispersion relation with well-defined energy gaps and renormalized energy levels, which are accessed using reflection and diffraction experiments.     

Conditions for formation and trapping of the two-ion Coulomb cluster in the dissipative optical superlattice

Conditions have been studied under which a polychromatic optical superlattice can form and trap the Coulomb cluster of two strongly interacting ions.In our previous work(Krasnov I V and Kamenshchikov L P 2014 Opt.Comm.312 192)this new all-optical method of obtaining and confining the Coulomb clusters was demonstrated by numerical simulations for special values of the optical superlattice parameters and in the case of Yb ions.In the present paper the conditions are explicitly formulated,under which the long-lived two-ion cluster in the superlattice cell is formed.The peculiarity of these conditions is the renormalization of the ion–ion Coulomb interaction.Notably,the renormalized Coulomb force is determined by the effective charge which depends on the light field parameters and can strongly differ from the bareion charge.This result can be accounted for by the combined manifestation of the quantum fluctuations of optical forces,nonlinear dependence of these forces on the velocity,and non-Maxwellian(Tsallis type) velocity distribution of the ions in the optical superlattice.Explicit analytical formulas are also obtained for the parameters of the optical two-ion cluster.