Frequency Dependent Dielectric Spectra Research Articles

Dielectric relaxation and dielectric decrement in ionic acetamide deep eutectic solvents: Spectral decomposition and comparison with experiments.

Frequency-dependent dielectric relaxation in three deep eutectic solvents (DESs), (acetamide+LiClO4/NO3/Br), was investigated in the temperature range, 329 ≤ T/K ≤ 358, via molecular dynamics simulations. Subsequently, decomposition of the real and the imaginary components of the simulated dielectric spectra was carried out to separate the rotational (dipole-dipole), translational (ion-ion), and ro-translational (dipole-ion) contributions. The dipolar contribution, as expected, was found to dominate all the frequency-dependent dielectric spectra over the entire frequency regime, while the other two components together made tiny contributions only. The translational (ion-ion) and the cross ro-translational contributions appeared in the THz regime in contrast to the viscosity-dependent dipolar relaxations that dominated the MHz-GHz frequency window. Our simulations predicted, in agreement with experiments, anion-dependent decrement of the static dielectric constant (ɛs ∼ 20 to 30) for acetamide (ɛs ∼ 66) in these ionic DESs. Simulated dipole-correlations (Kirkwood g factor) indicated significant orientational frustrations. The frustrated orientational structure was found to be associated with the anion-dependent damage of the acetamide H-bond network. Single dipole reorientation time distributions suggested slowed down acetamide rotations but did not indicate presence of any "rotationally frozen" molecule. The dielectric decrement is, therefore, largely static in origin. This provides a new insight into the ion dependence of the dielectric behavior of these ionic DESs. A good agreement between the simulated and the experimental timescales was also noticed.

Lead-free flexible Bismuth Titanate-PDMS composites: A multifunctional colossal dielectric material for hybrid piezo-triboelectric nanogenerator to sustainably power portable electronics

This study presents a multiunit hybrid piezo-triboelectric nanogenerator (HNG), utilizing both the triboelectric and piezoelectric effects, constructed from Bismuth Titanate, Bi 4 Ti 3 O 12 (BiTO)/polydimethylsiloxane (PDMS) composite films through a simple and cost-effective fabrication technique. The BiTO samples synthesized by a mixed oxide route crystallize in the orthorhombic symmetry, as confirmed by the Rietveld refinement of the structural data. The temperature- and frequency-dependent dielectric spectra elucidate the colossal dielectric properties of BiTO, originating from the combined effects of interfacial polarization, hopping polarization, and extrinsic electrode effect. The colossal dielectric BiTO leads to the amplification of internal polarization, providing enhanced output performance of the HNG device. As a result, the HNG devices exhibit multiple folds improvement in terms of power density compared to individual PDMS-BiTO composite-based PENG and TENG devices. Subsequently, a new design of device structure comprising a multiunit HNG device is constructed with the help of a 3D printed structure and a ball, delivering the voltage and current output of 300 V and 4.7 μA, respectively. Finally, the HNG device is utilized for biomechanical energy harvesting and powering various electronics like LEDs, a calculator, and a wristwatch. • Internal hybridization of piezoelectric-triboelectric boost the power density. • Bismuth titanate possesses multiferroic behavior and colossal permittivity. • Internal polarization amplification of a dielectric polymer is achieved. • New device structure for energy harvesting and power up the electronics.

A phenomenological approach to study the magnetoelectric (ME) response of lead free magnetostrictive NiFe2O4–Piezoelectric BaZr0.2Ti0.8O3 particulate composites

Lead-free magnetoelectric (ME) composites comprises NiFe2O4 (NFO) and BaZr0.2Ti0.8O3 (BZT) were synthesized by using conventional double sintering solid-state reaction technique and it's structural, electric, dielectric, magnetic and ME properties were studied. The spectra of X-ray diffraction displayed the formation of parent phase and presence of two phases within the composites (ferrite-ferroelectric). DC resistivity as a function of temperature has been studied, it indicates the semiconducting behavior. Frequency dependent dielectric spectra of the composites indicates small polaron hopping model of conduction mechanism. Magnetic measurements at room temperature shows the composites are soft magnetic and such materials reveals M-H hysteresis type behavior. The composite with x = 0.3 showed the highest value of ME voltage coefficient ~3.82 mV/cmOe. Such ME composite materials furnish fabulous chances as prospective lead-free systems for multifunctional device applications.

Characterisation of pore fluid salinity dependent evaporative dewatering of kaolin using dielectric spectroscopy

Realising the importance of pore fluid salinity on the dewatering behaviour of fine-grained porous systems, the present study systematically investigated such impacts on temporal moisture dynamics of kaolin subjected to evaporative dewatering. A detailed discussion is provided pertaining to the background processes dictating evaporative dewatering response and corresponding alterations in the dielectric behaviour of kaolin. Frequency dependent dielectric spectra of soil, which can be considered as the fingerprint of the transient changes in the condition of water phase within the pore system of the soil and associated densification, are monitored in real time during dewatering using an open-ended coaxial probe with a vector network analyser. The spatial sensitivity of the coaxial probe has been quantified through layered media approach. Combining the results of volume change behaviour of the material along with its moisture loss response, the study characterised the hydro-mechanical response of the material from the windows of frequency dependent dielectric spectroscopy.

Preparation and Dielectric Characterization of P(VDF–TrFE) Copolymer-Based Composites Containing Metal–Formate Frameworks

We report the synthesis and dielectric characterization of novel polyvinylidene fluoride-trifluoroethylene P(VDF-TrFE) composite films containing [(CH3)2NH2][Mg(HCOO)3] (DMAMg) and [NH4][Zn(HCOO)3] (AmZn) dense metal-organic frameworks (MOFs). The optical camera and Raman microscopies are used to map the distribution of the MOF fillers in the prepared films. The dielectric spectroscopy experiments of the DMAMg/P(VDF-TrFE) composite performed in a broad temperature range demonstrate rich dielectric behavior originating from the dipolar dynamics of the (CH3)2NH2+ molecular cations and glassy behavior of the copolymer matrix. An anomalous behavior of the complex dielectric permittivity is also observed because of the structural phase transition of DMAMg fillers. The dielectric properties of the AmZn/P(VDF-TrFE) composite film are mainly determined by the dipolar glass relaxation of the P(VDF-TrFE) polymer. The frequency-dependent dielectric spectra of both composites allow us to characterize the observed dipolar relaxation processes. The (CH3)2NH2+ cation dynamics follows the Arrhenius law, whereas the glassy behavior of P(VDF-TrFE) is described by the Vogel-Fulcher equation. For both composites, we observe a significant increase of the dielectric permittivity compared with the P(VDF-TrFE) film without MOF fillers.

Molecular dynamics simulation of microwave heating of liquid monoethanolamine (MEA): An evaluation of existing force fields.

We present a complete classical molecular dynamics (MD) study of the dielectric heating of liquid monoethanolamine (MEA) at microwave (MW) frequencies ranging from 1.0 to 10.0 GHz. The detailed dielectric properties predicted by a series of existing empirical force fields of MEA were carefully compared to experimental results. We find that all the evaluated force fields were unable to accurately predict experimental static dielectric constant, frequency-dependent dielectric spectra, and MW heating profiles of liquid MEA, although GROMOS-aa (all-atom GROningen molecular simulation) is the most accurate of those tested. With an isotropic scaling of partial atomic charges, the modified GROMOS-aa and OPLS-aa (all-atom optimized potentials for liquid simulations) force fields could accurately reproduce the experimental static dielectric constant and frequency-dependent dielectric spectra, but they failed to predict MW heating rates directly from MD heating simulations. Thus, the recently presented approach [F. J. Salas et al., J. Chem. Theory Comput. 11, 683 (2015); A. P. de la Luz et al., ibid. 11, 2792 (2015)] to tune existing force fields is not an ideal approach to produce force fields suitable for accurate dielectric heating studies.

Frequency-dependent dielectric properties of BTO/parylene nanocomposites with layered structure

First the frequency-dependent dielectric spectrum of a self-assembled pure $$\hbox {BaTiO}_{3}$$ (BTO) nanocrystalline thin film with consideration of the packing density is studied using the Lichtenecker logarithmic rule and the modified Kerner model. Then the Wiener lower bound is modified to evaluate the overall effective dielectric properties for 2–2 type of layered nanocomposites within a large frequency range, and a simple rule of mixture is found to be suitable for predicting the dielectric permittivity of multi-layered composites. The calculated dielectric properties of the BTO/parylene nanocomposites agree reasonably well with the experimental data, whereas a little discrepancy in the dielectric loss tangent is shown in the frequency range beyond $$10^{5 }\hbox {Hz}$$ .

Classical molecular dynamics simulation of microwave heating of liquids: The case of water.

We perform a complete classical molecular dynamics study of the dielectric heating of water in the microwave (MW) region. MW frequencies ranging from 1.0 to 15.0 GHz are used together with a series of well-known empirical force fields. We show that the ability of an empirical force field to correctly predict the dielectric response of liquids to MW radiation should be evaluated on the basis of a joint comparison of the predicted and experimental static dielectric constant, frequency-dependent dielectric spectra, and heating profiles. We argue that this is essential when multicomponent liquids are studied. We find that both the three-site OPC3 and four-site TIP4P-ϵ empirical force fields of water are equally superior for reproducing dielectric properties at a range of MW frequencies. Despite its poor prediction of the static dielectric constant, the well-known SPCE force field can be used to accurately describe dielectric heating of water at low MW frequencies.

Synthesis, structural and dielectric characterization of lead free x[(Ba0.7Ca0.3)TiO3]–(1 − x)[Ba(Zr0.2Ti0.8)O3] composite

Lead free x[(Ba0.7Ca0.3)TiO3]–(1 − x)[Ba(Zr0.2Ti0.8)O3] where x = 0.4 and 0.5 ceramic solid solution system were prepared by hydroxide co-precipitation method. These solid solution ceramics were sintered using the microwave sintering technique. The structural, dielectric and ferroelectric properties were analyzed by X-ray diffraction, scanning electron microscope, dielectric impedance spectroscopy and polarization with applied electric field measurements. From the X-ray analysis it is seen that there is formation of pure perovskite phase with coexistence of tetragonal and rhombohedral structures. Dielectric constant and loss tangent were studied as a function of frequency and temperature. Temperature dependant dielectric properties are measured in the frequency range between 1 kHz and 1 MHz. The well known diffuse phase transition (DPT) behavior of the ferroelectric material exists near the room temperature which is also confirmed from the frequency dependent dielectric spectra. The gamma (γ) values were 1.32 and 1.61 for x = 0.4 and 0.5 respectively. It confirms the ferroelectric nature of materials which is in between the normal ferroelectrics and relaxor ferroelectrics. Saturation polarization values were observed 1.28 and 1.95 µC/cm2 for x = 0.4 and 0.5 respectively with the promising coercive field.

Structural and dielectric relaxor behavior of Ba1−xNdxBi4Ti4O15 ceramics

Abstract Ba 1− x Nd x Bi 4 Ti 4 O 14 (BNBT) ceramics were prepared by the convention solid state reaction method. Effect of neodymium substitution on the structural and dielectric properties of the BBT ceramic was investigated. Phase structure was characterized by using X-ray diffraction analysis (XRD). A broaden dielectric peak in frequency dependent dielectric spectrum is observed during the phase transition of the BNBT ceramics. The modified Curie-Weiss and Lorentz-type relationship were used to describe the phase transition behavior. The relaxor behavior could be described well by the Lorentz-type relationship. Effect of neodymium substitution on the Curie temperatures and degree of the diffuseness in the BNBT ceramics was discussed.

Raman, dielectric and variable range hopping nature of Gd2O3-doped K0.5N0.5NbO3 piezoelectric ceramics

(K0.5Na0.5)NbO3 (KNN) + x wt% Gd2O3 (x = 0 -1.5) ceramics have been prepared by conventional solid state reaction method. The effect of Gd2O3 on the structural, microstructural and dielectric properties of KNN ceramics were studied systematically. The effect of Gd2O3 on phase transformation from orthorhombic to psuedocubic structure is explained interms of changes in the internal vibration modes of NbO6 octahedra. The Raman intensity of the stretching mode v1 enhanced and shifted toward higher wavenumber with Gd2O3 concentration, which is attributed to the increase in polarizability and change in the O-Nb-O bond angles. Microstructural analysis revealed that the grain size of the KNN ceramics decreases from 2.26 ± 1.07 μm to 0.35 ± 0.13 μm and becomes homogenous with an increase in Gd2O3 concentration. The frequency dependent dielectric spectra are analyzed by using Havriliak-Negami function. The fitted symmetry parameter and relaxation time (τ) are found to be 0.914 and 8.78 × 10−10 ± 5.5 × 10−11 s, respectively for the sample doped with x = 1.0. The addition of Gd2O3 to the KNN shifted the polymorphic phase transition orthorhombic to tetragonal transition temperature (TO-T) from 199oC to 85oC with enhanced dielectric permittivity (ε′ = 1139 at 1 MHz). The sample with x = 1.0, shown a high dielectric permittivity (ε′ = 879) and low dielectric loss (<5%) in the broad temperature range (-140oC – 150oC) with the Curie temperature 307 oC can have the potential for high temperature piezoelectric and tunable RF circuit applications. The temperature dependent AC-conductivity follows the variable range hopping conduction mechanism by obtaining the slope -0.25 from the ln[ln(ρac)] versus ln(T) graph in the temperature range of 133 K-308 K. The effect of Gd2O3 on the Mott’s parameters such as density of states (N(EF)), hopping length (RH), and hopping energy (WH) have been discussed.

Quantitative description of the phase transition of Aurivillius oxides Sm modified BaBi4Ti4O15 ceramics

BaBi4Ti4O15+xwt.%Sm2O3 (x=0.00, 0.25, 0.50, 0.75) ceramics were prepared by the solid-state reaction method. The effect of samarium additives on the structural and electrical properties of BBT ceramic was investigated. XRD patterns indicate that all ceramics are an m=4 members of Aurivillius oxides and no secondary phases were detected. A broad dielectric peak in frequency dependent dielectric spectrum is observed during the phase transition of all the BBT ceramics. The modified Curie–Weiss law, Vogel–Fucher relationship and Lorentz-type law were used to describe the phase transition behavior. The relaxor behavior was described well by the modified Curie–Weiss law and Vogel–Fucher relation. The effect of samarium additives on the degree of relaxation and diffuseness of BBT ceramics was discussed.

Modeling of high-k dielectric nanocomposites

In this paper, based on recent research on BaTiO3 (BT) nanoparticles, BT/P(VDF-HFP) nanocomposites, frequency-dependent dielectric properties of such a material system with high energy density have been investigated as functions of the volume fraction of the nanoparticles at room temperature by several theoretical models. For single domain and single crystals of BT, a Debye type of dissipation and soft mode theory have been adopted to obtain a more precise frequency-dependent dielectric spectrum of BT. For nanodielectric composites, among the others, Wiener Rule, Lichtenecker model, Maxwell–Wagner model, Yamada, and modified Kerner model were applied to evaluate the frequency-dependent dielectric spectrum of nanocomposites. A simple rule of mixture for the dielectric loss tangent was obtained using Lichtenecker logarithmic rule. The results from theoretical calculations are compared with the experimental data. For the dielectric constant, Lichtenecker model, Maxwell–Wagner model, and Yamada model show reasonable agreements with the experimental data up to 50 % volume fraction of the nanoparticles. At the higher volume fraction of the nanoparticles, the experimental data show a decreasing trend of the dielectric constant of the composites due to an increase in porosity of the system. In this case, a three-phase model (nanoparticles/pores/matrix) was developed to predict dielectric properties of the system at higher volume fraction of the nanoparticles (up to 80 %). The results showed reasonable agreements for a wide range of frequency. This theoretical study provides an essential information on dielectric properties of polymer-based BT nanocomposites with a wide frequency range instead of the trial-and-error strategy of experiments and can be used for designing high energy density dielectric materials in the future.

On the Neel temperature and magnetic domain wall movements of Ga2−xFexO3 single crystals grown by floating-zone technique

Single crystals of piezoelectric ferrimagnet, Gallium ferrite Ga2−xFexO3 (x=0.8, 1.0 and 1.2) were grown by optical floating zone technique. Phase confirmation was done by X-ray diffraction and the lattice parameters were determined via Rietveld refinement which shows a linear variation. Composition of the grown crystals was confirmed by energy dispersive X-ray spectra. Temperature and frequency dependent dielectric spectra have been used to explain the conduction mechanism in Ga2−xFexO3 single crystals. Dielectric constant of 1610 was obtained for GaFeO3 (x=1) and increases with x. With increasing iron concentration, a linear increase in TN is observed and the crystals transform as softer magnets.

On the theory of dielectric spectroscopy of protein solutions

We present a theory of the dielectric response of solutions containing large solutes, of the nanometer size, in a molecular solvent. It combines the molecular dipole moment of the solute with the polarization of a large subensemble of solvent molecules at the solute–solvent interface. The goal of the theory is two-fold: (i) to formulate the problem of the dielectric response avoiding the reliance on the cavity-field susceptibility of dielectric theories and (ii) to separate the non-additive polarization of the interface, jointly produced by the external field of the laboratory experiment and the solute, from specific solute–solvent interactions contributing to the dielectric signal. The theory is applied to experimentally reported frequency-dependent dielectric spectra of lysozyme in solution. The analysis of the data in the broad range of frequencies up to 700 GHz shows that the cavity-field susceptibility, critical for the theory formulation, is consistent with the prediction of Maxwell’s electrostatics in the frequency range of 10–200 GHz, but deviates from it outside this range. In particular, it becomes much smaller than the Maxwell result, and shifts to negative values, at small frequencies. The latter observation implies a dia-electric response, or negative dielectrophoresis, of hydrated lysozyme. It also implies that the effective protein dipole recorded by dielectric spectroscopy is much smaller than the value calculated from the protein’s charge distribution. We suggest an empirical equation that describes both the increment of the static dielectric constant and the decrement of the Debye water peak with increasing protein concentration. It gives fair agreement with broad-band dispersion and loss spectra of protein solutions, but misses the δ-dispersion region.

The Evidence for Ferroelectricity on Magnetite Ceramics below the Verwey Transition

We report the temperature- and frequency-dependent dielectric spectrum of magnetite ceramic single phase samples at 77.4–300K and 200Hz–1 MHz. In temperature-dependent dc resistivity, the sharp transition expected in single crystals is much suppressed. At higher temperatures, the grain boundaries contribute to the relaxation process. Below 120K, the temperature-dependent dielectric constant reveals a weak broadened peak as cooling, from our analysis this behavior may be intrinsically correlated with the charge ordering of Fe3+ and Fe2+. Under a relatively low dc bias at 77.4 K, the polarization of the magnetite ceramic decreases, while under a much stronger electrical field, the dielectric spectrum in the lower frequency region is suppressed remarkably for the excitation of carriers bounded by grain boundaries.

Barium zirconate-titanate/barium calcium-titanate ceramics via sol–gel process: novel high-energy-density capacitors

Lead-free barium zirconate-titanate/barium calcium-titanate, [(BaZr0.2Ti0.80)O3]1−x–[(Ba0.70Ca0.30)TiO3]x (x = 0.10, 0.15, 0.20) (BZT–BCT) ceramics with high dielectric constant, low dielectric loss and moderate electric breakdown field were prepared by the sol–gel synthesis technique. X-ray diffraction patterns revealed tetragonal crystal structure and this was further confirmed by Raman spectra. Well-behaved ferroelectric hysteresis loops and moderate polarizations (spontaneous polarization, Ps ∼ 3–6 µC cm−2) were obtained in these BZT–BCT ceramics. Frequency-dependent dielectric spectra confirmed that ferroelectric diffuse phase transition (DPT) exists near room temperature. Scanning electron microscope images revealed monolithic grain growth in samples sintered at 1280 °C. 1000/ε versus (T) plots revealed ferroelectric DPT behaviour with estimated γ values of ∼1.52, 1.51 and 1.88, respectively, for the studied BZT–BCT compositions. All three compositions showed packing-limited breakdown fields of ∼47–73 kV cm−1 with an energy density of 0.05–0.6 J cm−3 for thick ceramics (>1 mm). Therefore these compositions might be useful in Y5V-type capacitor applications.

The influence of polarizability on the dielectric spectrum of the ionic liquid 1-ethyl-3-methylimidazolium triflate

This work reports for the first time the computational, frequency-dependent dielectric spectrum of the polarizable molecular ionic liquid 1-ethyl-3-methylimidazolium triflate as well as its experimental analogue. In the frequency range from 500 MHz up to 20 GHz the agreement between the computational and the experimental spectrum is quantitative. For higher frequencies up to 10 THz the agreement is still remarkably good. The experimental asymptotic limit ε(∞) is 2.3. The difference in the computational value of 1.9 comes solely from the neglect of polarizability of the hydrogen atoms. For reasons of efficiency the simulations are based on the Lagrangian algorithm for the Drude oscillator model which cannot handle polarizable hydrogens. In the computational analysis the complete spectrum of the generalized dielectric constant ∑(0)*(ν) is splitted into its translational and non-translational components, called dielectric conductivity ϑ(0)(ν) and dielectric permittivity ε(ν). For 1-ethyl-3-methylimidazolium triflate both components contribute with equal weight and overlap in the complete frequency range. The inclusion of polarization forces, however, is quite different for the two components: the collective non-translational dynamics is accelerated and hence the dielectric permittivity is shifted to higher frequencies. The low frequency region of the dielectric conductivity is also affected while its high frequency part remains almost unchanged. Inductive effects are not only visible at high frequencies but also contribute in the sub-GHz region. The computational peak found in this region correlates with the experimental OKE-spectrum. It may be interpreted as the correlation between the induced dipole moment of the cations and the local electric field exerted by the anionic cage.

Calculating van der Waals-London dispersion spectra and Hamaker coefficients of carbon nanotubes in water fromab initiooptical properties

The van der Waals-London dispersion (vdW-Ld) spectra are calculated for the [9,3,m] metallic and [6,5,s] semiconducting single wall carbon nanotubes (SWCNTs), graphite, and graphene (a single carbon sheet of the graphite structure) using uniaxial optical properties determined from ab initio band structure calculations. The [9,3,m], exhibiting metallic optical properties in the axial direction versus semiconducting optical properties in the radial direction, highlights the strong anisotropic nature of metallic SWCNTs. Availability of both efficient ab initio local density band structure codes and sufficient computational power has allowed us to calculate the imaginary parts of the frequency dependent dielectric spectra, which are then easily converted to the required vdW-Ld spectra for Hamaker coefficient calculations. The resulting Hamaker coefficients, calculated from the Lifshitz quantum electrodynamic theory, show that neither graphite nor graphene are accurate model materials for estimating the Hamaker coefficients of SWCNTs. Additionally, Hamaker coefficients were calculated between pure radial-radial, radial-axial, and axial-axial components of both SWCNTs. Analysis of these coefficients reveals that the vdW-Ld interactions will depend on both chirality and the particular orientation between neighboring SWCNTs. The minimization of energy, with respect to orientation, predicts that vdW-Ld alignment forces will arise as a result of the anisotropic optical properties of SWCNTs.

The Dielectric Spectrum of Ubiquitin in Aqueous Solution

We report on frequency-dependent dielectric spectra (1 MHz < ν < 2 GHz) at 298.15 K of aqueous solutions of the globular protein ubiquitin at weight fractions of the protein up to wp = 0.03, corresponding to concentrations up to about 3.4 mmol dm-3. The spectra show a bimodal structure with two dominant dispersion/loss regimes near 20 MHz and 10 GHz, corresponding to the so-called β- and γ-processes found for other proteins. We establish a minor contribution near 100 MHz, which corresponds to the familiar δ-process. The static dielectric constant shows a comparatively large increment. By comparison with results from recent computer simulations, we confirm the usual interpretation of the β- and γ- processes in terms of protein tumbling and reorientation of bulk waters, respectively. The δ-process is attributed to protein−water cross interactions. The results contradict a recently developed microscopic theory in which cross interactions between hydration and bulk water due to exchange processes are responsi...