Complex Dielectric Spectra Research Articles

Low-Frequency Spectra of Metallocenium Ionic Liquids Studied by Terahertz Time-Domain Spectroscopy

Terahertz (THz) time-domain spectroscopic measurements have been done on five novel metallocenium ionic liquids based on the electro-optic sampling method. The study covered the spectral range from 10 to 85 cm(-1). The complex dielectric spectra were broad and dispersive in nature, and the imaginary part of the dielectric constant consisting of part of the dielectric constant was simulated with different combinations of model functions to unravel the intermolecular dynamics. We compared our results with the previous results on the other ionic liquid. It was revealed that the librational motion of the cations as well as the interion vibration between the cations and the anions are responsible for observed dynamics in THz region. No intramolecular vibrational mode has been found in the low-frequency region.

Dielectric behaviour of aqueous CsCl solutions

Complex dielectric permittivity spectra, in the frequency range 10 MHz to 20 GHz are reported for aqueous cesium chloride (CsCl) solutions at 250C using time domain reflectometry technique. The static dielectric constant, relaxation time and conductivity have been determined using nonlinear least squares fit method. From the static dielectric constant, hydration numbers were determined by using measured solutions density at different concentrations.

Investigations of intermolecular interactions between 2-methoxyethanol and nitrobenzene through dielectric relaxation study

Complex dielectric spectra e*(ω) = e' − ie of binary mixture of 2-methoxyethanol with nitrobenzene were obtained in the frequency range of 10 MHz to 20 GHz over the volume fraction range 0 < v < 1 and at different temperatures of 288, 298, 308, and 318 K using the time domain reflectometry (TDR) technique. The static dielectric constant s and relaxation time have been obtained. These values are used to obtain the excess permittivity eEs , excess inverse relaxation time (1/τ)E, Kirkwood correlation factor geff , Bruggeman factor fB, and thermodynamic parameters. On the basis of above parameters, intermolecular interaction and dynamics of molecules at molecular level are predicated. Keywords: dielectric relaxation, excess parameters, Kirkwood correlation factor, thermodynamic parameters, time domain reflectometry

Investigations of intermolecular interactions between 2-methoxyethanol and nitrobenzene through dielectric relaxation study

Complex dielectric spectra e*(ω) = e' − ie" of binary mixture of 2-methoxyethanol with nitrobenzene were obtained in the frequency range of 10 MHz to 20 GHz over the volume fraction range 0 < v < 1 and at different temperatures of 288, 298, 308, and 318 K using the time domain reflectometry (TDR) technique. The static dielectric constant "s and relaxation time have been obtained. These values are used to obtain the excess permittivity eEs , excess inverse relaxation time (1/τ)E, Kirkwood correlation factor geff , Bruggeman factor fB, and thermodynamic parameters. On the basis of above parameters, intermolecular interaction and dynamics of molecules at molecular level are predicated. Keywords: dielectric relaxation, excess parameters, Kirkwood correlation factor, thermodynamic parameters, time domain reflectometry

First-principles calculation on the electronic structure and optical properties of laB&amp;lt;sub&amp;gt;6&amp;lt;/sub&amp;gt;

The electronic structure and optical properties of laB6 have been calculated using the first-principle density function theory molecular dynamics method. The results of band structure show that laB6 is a conductor material at 313K. The density of state of laB6 is mainly composed of La 5d, 6s and B 2p with the static dielectric function e1(0) of 213.7, the reflectivity n(0) of 14.803, and the minimum absorption coefficient of 21585 cm?1 in the visible range. Moreover, the complex dielectric functions, refractive index, reflection spectra, absorption spectra, optical conductivity and energy loss function of laB6 are analyzed in terms of calculated band structure and density of state. The transmittance of laB6 is high in the visible range, however, it is nearly equal to zero in the UV and NIR ranges. The results offer theoretical data for the application of the insulating material for use with windows．

Infrared optical constants, molar absorption coefficients, dielectric constants, molar polarisabilities, transition moments and dipole moment derivatives of liquid N, N-dimethylacetamide–carbon tetrachloride mixtures

Mid-infrared spectra of the DMA–carbon tetrachloride system by transmission and single- and multiple-reflection ATR technique in the whole composition range (0 < x DMA ≤ 1), recorded at room temperature between 5000 and 850 cm −1 are presented. The complex optical constant, molar absorption coefficient, complex dielectric constant and complex molar polarisability spectra are determined. The wavenumber × imaginary molar polarisability spectra were fitted to classical damped oscillator model, which gives intensities, vibrational transition moments, and dipole moment derivatives with respect to normal coordinates of the corresponding vibrations.

Low-loss plasmonic waveguide based on gain-assisted periodic metal nanosphere chains

We propose a low-loss nanoscale waveguide based on gain-assisted plasmonic resonance metallic nanosphere chain. We demonstrate that by employing a gain material or even an appropriate dielectric for the host environment, waveguide loss can be reduced dramatically. A highly efficient pseudo-orthonormal basis expansion method for obtaining the complex dielectric spectra of the low-loss transmission has been developed. Eigenmode analysis revealed the physical origin of those low-loss waveguiding modes, which opens the possibility to achieve waveguiding other than using conventional dipolar resonances of individual particles. A scheme based on electron beam lithography and chemically synthesized nanoparticles has been proposed to fabricate the device.

Spin Spray‐Deposited Nickel Manganite Thermistor Films For Microbolometer Applications

Nickel manganite thin films are good candidates for thermal imaging applications because of their large temperature coefficient of resistance (TCR), (&gt;−3%/K) and good environmental stability. To enable low‐temperature deposition (90°C) on preexisting circuitry, a spin spray technique was developed for these materials. As‐deposited manganese oxide films show well‐developed X‐ray diffraction patterns, while as‐deposited nickel manganite films exhibit a nanocrystalline spinel structure. Low‐temperature (400°C) postdeposition annealing leads to densification of the nanocrystalline nickel manganite spinel films. Spectroscopic ellipsometry measurements on annealed films provide complex dielectric function spectra over a range from 0.75 to 5.15 eV with comparable features with those found in films prepared by a chemical solution method. Energy‐dispersive X‐ray spectroscopy indicates that the final composition of the films is Ni deficient relative to the starting solution composition. The TCR of the nickel manganite films annealed at 400°C in an argon atmosphere is −3.6%/K. Doping the nickel manganite films with zinc results in an improvement of crystallinity, but leads to substantial increases in the electrical resistivity. Copper doping reduces the resistivity of the films to &lt;1.0 kΩ·cm without degrading the crystalline quality, thus resulting in films suitable for microbolometer applications.

Dielectric properties of montmorillonite clay filled poly(vinyl alcohol)/poly(ethylene oxide) blend nanocomposites

Organic–inorganic nanocomposites of poly(vinyl alcohol) (PVA)–poly(ethylene oxide) (PEO) blend filled with montmorillonite (MMT) nanoclay up to 10 wt.% concentration were synthesized by aqueous solution-cast technique. The complex dielectric function, electrical conductivity, electric modulus and impedance spectra of the nanocomposites were measured in the frequency range 20 Hz–1 MHz at ambient temperature. A direct correlation was observed between the real part of dielectric function and the mean relaxation time of the polymer chain segmental dynamics, with the exfoliated and intercalated MMT clay structures, and the extent of miscibility between PVA and PEO due to hydrogen bonded bridging through exfoliated MMT clay nanosheets. The large increase of dielectric relaxation time revealed that the dispersed exfoliated nanoscale MMT clay in the polymers blend matrix produces a large hindrance to the polymer chain dynamics. Results confirm that the real part of dielectric function of the nanocomposites can be tailored by varying amount of MMT clay filler for their use as nanodielectric materials in the microelectronic technology.

Hydration Analysis on Atp Hydrolysis by Microwave Dielectric Spectroscopy

Recent theoretical works reveiled that the hydration energies of nucleotides and inporganic phosphates are one of important factors in the ATP hydrolysis energy. Here we have measured the hydration states of the reactants and the products of ATP hydrolysis reaction by precesion microwave dielectric relaxation spectroscopy. The complex dielectric spectra of hydrated solutes, such as sodium salts of ATP4-, ADP3- , HPO42-, were measured. We detected constrained water and hyper-mobile water around nucleotides and phosphates. Hydration change upon the neutralization reaction of phosphate, H2PO4- + OH- ◊ HPO42- + H2O, was investigated by measuring high-resolution complex dielectric spectra of mono- and di-sodium phosphate solutions at 20°C to understand the hydration effect on the thermodynamics of phosphate buffer reaction. From each solution spectrum the dielectric spectrum of a spherical volume containing each hydrated solute in water was derived based on a suspension theory. Each spectrum was decomposed into a bulk water (fcw ∼ 17 GHz) component and two Debye dispersion components, assigned as constrained water (fc2 ∼ 6.4GHz fcw), respectively. The dielectric dispersion of hyper-mobile water was about five times stronger than the constrained one. The strengths of these two Debye dispersions decreased by 20% (ΔN2 = −7) for the constrained water number and by 10% (ΔN1 = −15) for the hyper-mobile water number upon the neutralization reaction, while those decrements were compensated by an increase of dispersion strength of bulk water. It is thought that the entropy changes corresponding to the number increases of constrained water and hyper-mobile water molecules are negative and positive, respectively. So the present result provides us a physical explanation of the small effect of hydration change on the total entropy change upon the reaction.

Dielectric relaxation study of diethylsulfoxide/water mixtures

Complex dielectric spectra of diethylsulfoxide (DESO)/water mixtures at 25°C over the entire concentration range of DESO, in the frequency range 0.2 ≤ ν/GHz ≤ 89 have been measured. In general, a description of the complex permittivity spectra requires a consideration of different types of relaxation processes depending upon DESO concentration. For the lower DESO concentration range the relaxation contribution to the spectrum is described by two Debye terms, whereas for higher concentration three Debye terms are used. For both at mol fraction equals to 0.9 and pure DESO as well Cole–Davidson type is valid. In addition, the data on the dimethylsulfoxide (DMSO)/water system obtained in this work well agree with those known from literature. The concentration dependent excess dielectric constant, excess inverse relaxation time and Kirkwood correlation factor of the mixtures have been determined.

Time Domain Reflectometry Studies on a Nematic Liquid Crystal

The complex dielectric permittivity spectra of p-pentyl phenyl-p-propylbenzoate (PPPB) , of a nematic liquid crystal are obtained using Time Domain Reflectometry (TDR) method over a frequency range 10 MHz–10 GHz at various temperatures covering both nematic and isotropic phases. The relaxation behavior at different temperatures was studied through cole–cole arc. The dielectric behavior in nematic (N) phase could be described by the Cole–Davidson model, while isotropic (I) phase is found to obey to a large extent Debye model. Two relaxation times, τ1 and τ2, are obtained for N phase which are the characteristic of Cole–Davidson model. τ1 and τ2 are interpreted as corresponding to different degrees of freedom in different direction in liquid crystalline state. The fact that τ1 and τ2 obtained for the I phase are almost equal favors Debye model. The results are presented over a temperature range, and these results are discussed to understand the phase transition involved. The work included in this article is useful as it provides information about the macroscopic structure of the liquid crystals in general and PPPB in particular. The N phase is the least ordered of liquid crystalline phases, and hence the studies even on an unaligned samples give information that is very close to aligned ones as far as those properties which are due to overall effects like dielectric behavior.

Dielectric properties of acetic acid and vinegar in the microwave frequencies range 1–20 GHz

Complex dielectric spectra of acetic acid solutions were measured at frequencies in the range of 1–20 GHz using an automatic network analyser at room temperature. The spectra of different commercial vinegars were also measured. All spectra follow a Debye relation for both the real and imaginary parts of permittivity. The Debye relation, with an additional term for ionic conduction losses, was fitted to the data, and six parameters were extracted. Quantitative relations between the parameters that define Debye relations and the acid contents in solution were obtained.

First-principles study on the electronic and optical properties of BiFeO 3

The structural, electronic, and optical properties of multiferroic bismuth ferrite (BiFeO 3) are investigated using density functional theory within generalized gradient approximation (GGA). The calculated lattice parameters are in good agreement with the experimental data. The electronic structure shows that BiFeO 3 has an indirect (very close to direct) band gap of 1.06 eV. The complex dielectric function, absorption spectra, refractive index, extinction coefficient, energy-loss spectrum and reflectivity are calculated, and the results are compared with the available experimental data. Finally, the optical properties of BiFeO 3 are discussed based on the band structure calculations.

Slowing down in lipid bilayers: domain structure fluctuations and axial diffusion

Ultrasonic spectra (2×105Hz to 2×109 Hz) and complex dielectric spectra (104 Hz to 4×1010 Hz) are reported for aqueous solutions of vesicles from lipid mixtures near their main phase transition temperature Tm. The results are compared to such for 1,2-dimyristoyl-L-3-phosphatidylcholine systems. Various relaxation terms are identified. One term results from the domain structure fluctuations of the membranes. It features critical point characteristics. Another term is due to the axial diffusion of the lipid molecules within the membrane. It also reveals substantial effects of slowing near Tm. Relaxation times reflecting the zwitterionic head group reorientational motions and the alkyl chain structural isomerisation display step like changes at the phase transition. An additional relaxation term exists close to Tm only. It is assumed to indicate small-area deformations of the vesicles.

The Calibration Technique for Moist Soils Complex Permittivity Measurements in the Microwave Band

In the present work, the calibration method of waveguide in measurement of com- plex dielectric permittivity spectrum of wet soils with coaxial sample holder in microwave fre- quency range is proposed. This method is convenient for soil measurement. With the view of efiect of transition units connecting waveguide to sample holder, the approach includes calibra- tion procedure by the use of measurement of S-scattering matrix for two empty sample holders of difierent lengths. As an example, the results of measurement of complex dielectric permittivity spectrum of loam soil at positive and negative temperature are given.

Temperature and Mineralogy Dependable Model for Microwave Dielectric Spectra of Moist Soils

In this paper, a physically based dielectric model in microwave band for moist soils is developed to account for both the temperature and granulometric mineralogy of the soil. The generalized refractive mixing dielectric model (GRMDM) previously developed by V. L. Mironov etal. was used as a mean to determine the spectroscopic parameters for 5 soils which complex dielectric constant spectra were measured and presented in Technical Report EL-95-34, December 1995 by J. O. Curtis etal. The measurement results used covered the temperatures of 10, 20, 30, and 40 - C, gravimetric clay contents from 0 to 0.76g/g, and frequencies from 0.3 to 26.5GHz. Relating to each individual soil, such GRMDM spectroscopic parameters as dielectric constants in low frequency limit, relaxation times, and ohmic conductivities, pertaining to both bound and unbound soil water, were fltted as functions of temperature with the Clausiuss- Mossotii, Debye and linear equations, respectively. As a result, a set of physical parameters for a temperature dependable generalized refractive mixing dielectric model (TD GRMDM), consisting of the volumetric expansion coe-cients, activation energies, enthropies of activation and others, were obtained. Finally, the parameters of the TD GRMDM as functions of gravimetric clay content were fltted to yield the closing set of polinomial formulas, which, in conjunction with the TD GRMDM, represent a temperature and mineralogy dependable soil dielectric model (TMD SDM). Thus developed, the TMD SDM provides for predictions of the complex dielectric constant of moist soils as a function of moisture, wave frequency, temperature and gravimetric clay content. Further the TMD SDM prediction error was estimated with the use of the ndependent dielectric data.

Millimeter- and Submillimeter-Wave Dielectric Measurements of Household Powders Using Fourier Transform Spectroscopy

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> This paper presents the first step in characterizing and detecting common household powders as hoax materials by investigating their broadband dielectric characteristics. Pesticide is also studied due to its similarities to anthrax. A modified two-beam polarizing interferometer and custom-made sample holders were utilized to obtain the refractive index (RFI), absorption coefficient, complex real and imaginary permittivity, and loss tangent of flour, dry milk, cornstarch, pesticide, baking soda, and talc as a continuous function of frequency in the range of 400–1200 GHz. Dispersive Fourier transform spectroscopy was employed to provide phase and amplitude information, leading to the accurate and direct acquisition of the complex RFI and complex dielectric permittivity spectra. It is the first time that such measurements were carried out over such an extended frequency range for common powders to reveal marked variation in absorption and RFI values for different powders. The powders exhibit high-absorption characteristics, and the RFI values lie between 2.4 and 3.4 in this spectral range. A unique resonance signature for talc was detected at 1135 GHz with an associated anomalous dispersion. Parameters such as grain size and orientation were analyzed for their effect on the dielectric properties of powders. Relationships between density, permittivity, and RFI are explored to provide the ability to extrapolate results for other densities. The RFI and the real part of the dielectric permittivity were found to be the most reliable for identification and detection purposes. </para>

State of Water in Perfluorosulfonic Ionomer (Nafion 117) Proton Exchange Membranes

The nature of water in acid-form Nafion 117 was quantified at several hydration levels by dielectric relaxation spectroscopy. Two independent experimental setups were used to collect complex dielectric permittivity spectra at low frequencies ( at to ) and in the microwave region ( at ). We directly observed the states of water, manifested through three population averages with distinctly resolved dynamical behaviors, and their changes with temperature and hydration level. The fastest process observed was identified as the cooperative picosecond relaxation of free (isotropic, bulklike) water, whereas the slowest process (microsecond relaxation times) corresponded to water molecules strongly bound to the charged sulfonic groups. A third type of water was also observed, also characterized by picosecond relaxation times, close to and about three times slower than those of bulk water, which was attributed to loosely bound water and may contain substantial dynamical heterogeneities.

Dielectric spectroscopy of low-loss sugar lyophiles: II. Relaxation mechanisms in freeze-dried lactose and lactose monohydrate

This article presents an analysis of the dielectric relaxation mechanisms of the disaccharide lactose, in both the freeze-dried state and the crystalline monohydrate. Complex dielectric permittivity spectra for both forms of lactose were measured over wide ranges of frequency (0.1Hz to 1MHz) and temperature (−120°C to +100°C). The crystalline monohydrate displays a sharp peak in the temperature domain which was ascribed to the percolation of migrating protons over the surfaces of the crystals. The freeze-dried material displayed three relaxation processes. The first (γ) and second (β) processes were observed at low temperature and present as very broad relaxations with low dielectric strength. The relaxation times for both processes showed Arrhenius temperature-dependencies, with activation energies of 52kJ/mol and 72kJ/mol, respectively. The mechanisms of dielectric relaxation were ascribed to the motion of the pendant hydroxymethyl group and the relative motion of the pair of saccharide rings, respectively. Analysis and discussion of the third relaxation process is beyond of the scope of this article.