Frequency Dependent Dielectric Properties Research Articles

Investigation on Temperature-Dependent Electrical Transport Behavior of Cobalt Ferrite (CoFe2O4) for Thermistor Applications

This paper discusses the temperature and frequency-dependent dielectric and electrical transport properties of cobalt ferrite (CoFe2O4) and its suitability for thermistor applications. The material is prepared through a high-temperature solid-state reaction route. The formation of the materials is checked by using an X-ray diffraction. Microstructure study is done through SEM analysis. Analysis of dielectric data shows a thermally activated relaxation process occuring in the material within the studied frequency range. Analysis of complex impedance (Nyquist) plots at different temperatures reveal the contribution of grain to the overall electrical response of the compound. The variation of dc conductivity with temperature shows the NTCR behavior of the material. Looking into the strong dependence of resistivity on temperature, the thermistor parameters are evaluated using the grain resistance at different temperatures, which suggest the possible application for thermistor-based devices as well as a temperature sensor. The temperature-dependent ac conductivity (σ ac) fits well with Jonscher’s universal power law. The activation energy calculated from the temperature-dependent spectroscopic plots of impedance and conductivity suggests the charge carriers involved in deciding transport properties.

The investigation of frequency dependent dielectric properties and ac conductivity by impedance spectroscopy in the Al/(Cu-doped Diamond Like Carbon)/Au structures

The investigation of frequency dependent dielectric properties and ac conductivity by impedance spectroscopy in the Al/(Cu-doped Diamond Like Carbon)/Au structures

Investigation of frequency dependent dielectric properties of La-doped BaSnO3-ZnSnO3 solid-solutions

In this study, we report the structural, optical, and dielectric properties for La-doped BaSnO3 and ZnSnO3 solid solutions, La0.03(Ba1−xZnx)0.97SnO3 (x = 0,0.1,0.5,1) prepared at 1100 °C by isovalent substitution of Zn+2 at the Ba+2 site using the conventional solid-state reaction route. Structural data shows the transformation from cubic perovskite to orthorhombic perovskite structure as the amount of Zn increases in La-doped BSO samples. A minor pyrochlore phases, La2Sn2O7 and Ba2SnO4 were found in the XRD. This paper mainly focuses on understanding the contribution of physical phenomena of ac conductivity in terms of dielectric properties. The dielectric properties of the composites follow non-Debye type behavior. There was a moderate increase in the dielectric constant from 10.07 to 334 at 20 Hz, and 2.99–133 at 1 kHz, respectively, as we increased the amount of Zn, which is high as compared with other reported dielectric materials. By using Jonscher's power law, ac conductivity was found to increase in LZSO samples. This conduction mechanism due to the hopping of ions between coordination sites present in the composite and can be understood by the classically correlated barrier hopping phenomenon. Furthermore, the trivial loss of electromagnetic waves over a given frequency range demonstrates the great potential of La-doped ZnSnO3 materials to be utilized in ground penetrating radar systems, communication systems, and energy storage devices.

Structural, optical, and electrical properties of Mn0.9La0.1Fe2O4 nanocrystalline ferrites and its synthesis through sol-gel method

This work reports the formation of La-doped nano-crystalline manganese ferrite Mn0.9La0.1Fe2O4 through sol–gel route and examined using XRD and dielectric spectroscopy techniques. The single-phased cubic spinel structure of the ferrite is supported by X-ray diffraction (XRD). The mean crystallite dimension appraised from XRD data has been found to be 21 nm and 11 nm for un-doped and La3+ doped MnFe2O4, respectively, along with a significant rebate in the optical band gap. At room temperature, the frequency-dependent dielectric properties were studied in the frequency range (42 Hz − 5 MHz). The dielectric constant of both the samples narrowly lowers with enhancing frequency and, consequently, shows exemplary dielectric dispersion. The AC-conductivity of the un-doped samples enhances with increasing frequency while it decreases with doping. The dispersion in ac-conductivity (σac) and dielectric properties imply the ordinary dispersion of Maxwell-Wagner type due to the process of hopping of electrons between the Fe2+ and Fe3+ ions and interfacial polarization. The band gap of energy is evaluated with the help of the UV–visible spectra and found to be decreased when La3+ doped with MnFe2O4 ferrite.

Optical and dielectric realisation of biomolecular detection using gold nanoparticles bio-conjugate with liquid crystal

Dielectric biosensor based on nematic liquid crystal platform has been fabricated using sandwich immunoassay technique for the detection of a biomolecule, human cardiac troponin I (cTnI). The optical response of Liquid crystal (LC) biosensor and its corresponding frequency-dependent dielectric properties have been investigated as a function of cTnI concentration. Gold nanoparticles conjugate with detection antibody (AB-GNP) is used for the enhancement of both the optical and dielectric signal of the biosensor. AB-GNP binding with cTnI alter the surface energy of the substrate causing disturbances in LC alignment resulting in a change in transmission. The transmission of the LC cell has been found to be varying from dark to bright texture under polarized microscope as a function of cTnI concentration. A change in low-frequency permittivity with increasing cTnI concentration that forms an increasing order of sandwich immunocomplex with AB-GNP revealed an interfacial surface phenomenon. A positive shift in the onset frequency of permittivity is observed due accumulation of immunocomplex with increasing concentration of cTnI at electrode/LC interface. The dielectric response ε′ of the biosensor is fitted with Hill-Langmuir equation over a concentration range of 0.01 to 10 ng mL−1 cTnI. The dissociation constant ‘Kd’ of 1.02 ± 0.24 ng/mL−1 indicates strong cTnI binding affinity for substrate antibody. A nearby value of 1, calculated for Hill coefficient ‘n’ revealed no co-operativity characteristic of cTnI binding to the primary capture antibody, wherein each binding site of the antibody functions independently at the electrode surface, causing accumulation of charged species revealing LC interfacial surface electrical property.

Frequency dependent electrical and dielectric properties of the Au/(RuO2:PVC)/n-Si (MPS) structures

In this study, the electrical and dielectric characteristics of the Au/(RuO2:PVC)/n-Si structures were analyzed using the impedance spectroscopy method, including capacitance/conductance (C - G/ω) measurements in wide voltage and frequency ranges (±4 V, 5 kHz – 5 MHz) at room temperature. The main electrical parameters such as concentration of donor atoms (ND), diffusion potential (VD), depletion layer thickness (WD), Fermi energy level (EF), barrier height (ΦB), and maximum electric field (Em) were extracted for each measured frequency. The ΦB, WD, and EF values are increasing with increased frequency, while ND and Em exponentially decrease. The surface-states (NSS) were evaluated using the low–high-frequency capacitance technique. Furthermore, the basic dielectric parameters such as tangent-loss (tan δ), electrical conductivity (σac), real and imaginary parts of ε*, electric-modulus (M*), and complex impedance (Z*) were investigated. The obtained results indicate that the NSS, and RuO2:PVC organic interlayer are more effective on C and G/ω measurements.

Improved dielectric performance of polyvinylidene fluoride (PVDF) - Carbon dots composites

Polymer nanocomposites with high dielectric constant and low-loss tangent materials have been extensively used in devices. Polyvinylidene fluoride (PVDF)-carbon dot (C-dot) nanocomposites have been synthesized to investigate the effect of C-dot on AC conductivity and dielectric properties. The FTIR spectra of synthesized samples confirm the formation of composites. The broadening of the peak in XRD patterns with an increase in the C-dot concentration has been observed, indicating the interaction of PVDF with C-dot. Morphological studies were carried out using Scanning electron microscopy (SEM). Frequency-dependent conductivity and dielectric properties were studied in the frequency range of 10 Hz to 8 MHz. AC conductivity graphs were found to obey Jonscher's power law and show no contact loss behavior. Prepared samples show improved dielectric constant with an increase in C-dot filler concentrations. Moreover, all samples show tangent loss of less than 0.015 at 1 kHz frequency. These results demonstrate that composite possesses broad application prospects in device electronics.

In-situ study of phase changes in glass by impedance spectroscopy and scaling

Transformation in “evolving glass” in ion-conducting silicate glasses, glass ceramics or ceramics containing an intergranular glass is studied by in-situ impedance spectroscopy and scaling laws. Approaches are developed to scale frequency-dependent electrical conductivity and dielectric properties of multiphase ion-conducting materials to derive temperature-independent information on bulk phases and interfaces in presence. A material's scaled electric conductivity provides a unique response over a range of temperature, if the material remains unaltered, but changes, once modifications in the material occur. Therefore, impedance spectroscopy in combination with scaling can be used for tracking modifications in structure, organization, chemistry and microstructure in “evolving (ion-conducting) glass”.In a first part of this work, our approach is validated through application to stable silicate glasses and glass ceramics. Then “evolving glass” is studied in bulk glasses and ceramics with intergranular glass. Examples include ceramming of glass under formation of a glass ceramic, glass-glass phase separation, modification of intergranular glass in ceramics as result of chemical reactions or melt corrosion.Our approach allows to determine onset of phase separation, nucleation or reaction with high precision. It further reveals that nucleation in our exemplary lithium aluminum silicate glass starts with formation of interfaces (phase separation) prior to forming a well-organized crystal lattice. During phase separation in glass, early capacitive contributions in the impedance spectra indicate that the formation of glass-glass interface precedes the compositional changes in the bulk glass.Impedance of refractories is monitored during thermal treatments or corrosion in glass melt at temperatures up to 1600 °C, and glass characteristics of refractories with glass content as low as 3% are extracted. Conductivity and/or level and/or interconnectivity of the refractory's glass are shown to change during thermal treatments due to reactions between glass and crystalline refractory phases, due to phase transformation or, in case of melt corrosion, due to melt infiltration and ion exchange with the melt.In-situ tracking of impedance and application of scaling laws is shown to be able to reveal changes in bulk glass and intergranular glass.

Cationic distributions and dielectric properties of magnesium ferrites fabricated by sol-gel route and photocatalytic activity evaluation

Abstract Sol-gel auto combustion method was adopted to fabricate magnesium ferrite (MgFe2O4) nanoparticles. The structural and morphological properties was studied by XRD, FTIR, and SEM analysis. The average particle sizes of MgFe2O4 was in the range of 35–55 nm. The octahedral & Tetrahedral bond lengths, R AE (tetrahedral edge length), R BE (shared octahedral edge length) and R BEU (individual octahedral edge length), cationic radii (tetra and octa-sites) were also determined. The magnetic strength also showed direct reliance on bond angle and indirect to bond length. Hoping length L a and L b and bond angles are also measured. The frequency dependent conductivity and dielectric properties of MgFe2O4 were investigated by Impedance analyzer. The photocatalytic activity (PCA) is appraised against MB (methylene blue) dye and MgFe2O4 calcined at 800 °C showed promising degradation (78%) under visible light irradiation. The findings revealed that MgFe2O4 is can harvest the solar light, which could be employed for the remediation of wastewater contains textile dyes.

Temperature and frequency dependent dielectric and electrical properties of relaxor (Ca1/2W1/2)(Pb1/2Ni1/2)O3 electronic material

In the present study, a solid-state reaction technique is used to formulate and synthesize the (Ca0.5W0.5)(Pb0.5Ni0.5)O3, [CWPN] relaxor perovskite composite. Its structural, morphological, and electrical characteristics have all been revealed so that they may be studied for potential use in electronics and sensors. X-ray diffraction analyses have confirmed the structure to be combination of primary tetragonal along with secondary rhombohedral and orthorhombic phase. Throughout a wide temperature and frequency range (25° – 500° C and 1 kHz–1 MHz), the impedance spectroscopy, dielectric, and a.c. conductivity have all been analyzed. The sample's dielectric spectroscopy confirmed its relaxor properties. On a Nyquist plot, the sample's grain contribution is represented by a single semicircular arc. A replica of a similar circuit was constructed so that its electrical characteristics could be studied. Both the activation energy and the mobility of the charge carriers have been evaluated. Conducting systematic studies of dielectric properties at elevated temperatures is crucial for fundamental characterization and device development, as it allows for the analysis of electrical parameters associated with surfaces, grain borders, or grains.

Low-temperature dielectric and impedance properties of Ba1-xSrxTiO3 and BaTi1-xTaxO3 ceramics

In this work, two series of BaTiO3-based ceramics, Ba1-xSrxTiO3 (x = 0, 0.2, 0.4, 0.6, 0.8) and BaTi1-xTaxO3 (x = 0.03, 0.06, 0.075, 0.09, 0.1), were synthesized by using standard solid-state reaction method at 1350 ?C, and then sintered at 1400 ?C for 10 h in air. Frequency-dependent dielectric and impedance properties were investigated at low temperature range of 100-300K. The changes in dielectric properties of the Ba1-xSrxTiO3 ceramics are believed to originate from the phase transition due to the different A-site Sr2+ doping concentration. The local electron-pinned defect-dipole effect is responsible for the enhancement of dielectric constant observed in the B-site Ta5+ doped BaTi1-xTaxO3 ceramics. The complex impedance analysis was used to discern the temperature and frequency dependence of grains and grain boundaries responses. The results suggest that A- and B-site doped BaTiO3 ceramics can be applied for different dielectric devices at low temperatures.

Investigation of multiferroic properties of dysprosium substituted bismuth ferrite (Bi1-xDyxFeO3) prepared by auto combustion technique

A simple and inexpensive auto combustion procedure was used to create the Bi1-xDyxFeO3 (x=0.0, 0.015, 0.03, 0.045, 0.060) multiferroics samples. In bismuth ferrite, the average crystallite size increased with growing Dy3+ concentration in BFO, revealing a rhombohedral distorted perovskite structure of space group R3c. During morphological analyses of the produced samples, a spherical structure with little aggregation was found. When Dy3+ is substituted at the B-site, the Raman modes widen and the cation site occupancy changes even more. The frequency-dependent dielectric properties (εr, tanδ), electric conductivity (ac), impedance (Z), and electric modulus (M' and M′′) of the samples were assessed using an impedance analyzer at frequencies between 20 Hz and 20 MHz. All samples had the maximum dielectric constant, which was discovered at a relatively low frequency. The highest value of impedance was found at low frequency and it lowers with increasing frequency as a result of the contributions from the grain and grain boundary. It is discovered that the samples' ac conductivity is frequency-dependent and changes depending on how much Dy3+ is doped into the BFO.

Understanding the impact of Gd3+ substitutions on the enhancement of dielectric and electrical behaviour of lead-free Ba0.85Ca0.15Zr0.1Ti0.9O3 ceramics

The present study focuses on the effect of Gadolinium (Gd3+) concentration on the lead-free Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT) ceramics synthesised using conventional solid-state reaction method at high temperature (∼1300). Introducing Gd3+ to the BCZT system influences the properties of the materials. All the compounds were crystallised in tetragonal structure at room temperature. The microstructural study of the compounds has been obtained by scanning electron microscopy (SEM). The frequency and temperature dependent dielectric properties were analysed. The diffusivity of the compounds was investigated using modified Curie-Weiss law. Impedance spectroscopy have been employed for the study of the electrical conduction mechanism. All the compounds display negative temperature coefficient of resistance (NTCR)-type behaviour which indicates its semiconducting characteristic. The existence of non-Debye type relaxation is shown from Nyquist plots. All the synthesised ceramics show enhanced electrical properties which may be utilised in electronic device manufacturing.

Impact of amorphous SiO2 as shell material on superparamagnetic Fe3O4 nanoparticles and investigation of temperature and frequency dependent dielectric properties

In this work, Fe 3 O 4 nanoparticles and amorphous silica coated Fe 3 O 4 @SiO 2 nanocomposites synthesized using solvothermal method and modified Stöber method are reported. Powder XRD analysis, FTIR spectroscopic technique and X-ray photoelectron spectroscopy analyzeswere employed to confirm the structure and formation of Fe 3 O 4 nanoparticles and Fe 3 O 4 @SiO 2 core shell structured nanocomposites. The structural details elucidated from TEM images and SAED patterns are very much in agreement with the XRD results and confirm the formation of Fe 3 O 4 @SiO 2 core shell structured nanocomposites. VSM analysis confirms super paramagnetic features having soft magnetic property in Fe 3 O 4 @SiO 2 albeit with reduction in saturation magnetization. The dielectric behavior was studied at different temperatures in the frequency range between 1 Hz and 1 MHz in the temperature range 373 K to 723 K in steps of 50 K. The modulus spectrum formalism reveals temperature dependent hopping type of mechanism for charge transport and the impedance spectra reveals the contribution of grain effect on the electrical properties. Further, the analysis of dielectric data indicates that the Fe 3 O 4 @SiO 2 displays positive temperature coefficient of resistance type behavior and the frequency dependent ac conductivity obeys the well-known Jonscher’s power law. • Fe 3 O 4 @SiO 2 core shell nanocomposites are prepared using modified Stober process. • The value of magnetic saturation is high for Fe 3 O 4 and low for Fe 3 O 4 @SiO 2 core shell structured nanocomposites. • FTIR, XPS and TEM measurements substantiate the formation of Fe 3 O 4 @SiO 2 core shell structured nanocomposites. • When the temperature is high the dielectric constant is high and the dielectric loss is low at lower frequency region. • The cole-cole plot reveals that the material follows non-Debye type of relaxation.

Study of dielectric properties of meta-aramid fibers by molecular dynamics methods using modified OPLSAA force field

The dielectric properties of materials have been a prevalent subject in dielectric physics research. However, the theoretical calculation of the dielectric properties of polymer insulating materials remains challenging. Taking meta-aramid fiber (PMIA) as the research object, the micro-dielectric relaxation process of the PMIA system was studied by molecular dynamics and the polarization frequency response theory. The OPLSAA force field was optimized based on the density functional theory B3LYP/6-31G. Using calculations of the spatial structure, chain motion, basic physical and chemical properties, and dielectric properties of PMIA, it was found that the optimized OPLSAA force field accurately indicated the dielectric properties of PMIA. The frequency-dependent dielectric properties of PMIA calculated by the optimized OPLSAA force field were consistent with the polarization frequency response theory, and the simulation results agreed with the Debye model theory. The theoretical calculation process of polymer dielectric properties based on molecular dynamics presented in this paper provides a new avenue to improve the prediction accuracy of polymer dielectric properties. • The optimized OPLSAA can accurately indicated the dielectric properties of PMIA. • Intermolecular hydrogen bonds obstruct the dielectric relaxation of PMIA molecules. • The minimum degree of polymerization to build a PMIA model is 10.

Dielectric property measurement of human sweat using attenuated total reflection terahertz time domain spectroscopy.

Sweat is one of the essential biofluids produced by the human body, and it contains various physiological biomarkers. These biomarkers can indicate human health conditions such as disease and illness. In particular, imbalances in the concentration of electrolytes can indicate the onset of disease. These same imbalances affect the dielectric properties of sweat. In this study, we used attenuated total reflection terahertz time domain spectroscopy to obtain the frequency-dependent dielectric properties of human sweat in a frequency range from 200 GHz to 2.5 THz. We have investigated the variation of dielectric properties of sweat collected from different regions of the human body, and we have observed that the real and imaginary part of dielectric permittivity decreases with the increase in frequency. A combination of left-hand Jonscher and Havriliak-Negami processes is used to model the results and reveal the presence of relaxation processes related to sodium and calcium ions concentrations. This information may help design novel biosensors to understand the human health condition and provide a hydration assessment.

Dielectric properties of porous rocks with partially saturated fractures from finite-difference modeling

Fractures are common features of geologic rocks, and they have a profound influence on the fluid flow and transport characteristics as well as physical properties of the fracture-bearing rocks. Fractures are frequently partially saturated in hydrocarbon reservoirs, and the dielectric properties that are highly sensitive to the fluid types and concentrations are useful tools for the quantitative characterization of reservoir rocks with partially saturated fractures. However, the effects of partially saturated fractures on the dielectric properties of the porous rock are still poorly understood. Based on a 3D finite-difference model, we have bridged this knowledge gap by studying the frequency-dependent dielectric properties of a porous carbonate rock with partially saturated fractures obtained by the brine-displacing oil simulation. We find that the conductivity and high-frequency (higher than approximately 1 MHz) relative permittivity generally increase, whereas the low-frequency relative permittivity and peak dielectric loss decrease with the increasing brine saturation. We also find that the partially saturated fractured rock with lower brine saturation exhibits a greater low-frequency relative permittivity and maximum dielectric loss factor than the cases in which the fractures are completely filled with oil. A systematic investigation based on simplified intersecting fracture models suggests that the oil-brine distribution is the main reason for the abnormal dielectric responses of the low-frequency relative permittivity and the maximum dielectric loss factor at low brine saturations. The results provide new insights for the comprehensive understanding of the frequency-dependent dielectric responses of fractured sedimentary rocks and will pave the way for the quantification of the brine saturation in partially saturated fractures.

Stimulation-induced changes at the electrode–tissue interface and their influence on deep brain stimulation

Objective. During deep brain stimulation (DBS) the electrode–tissue interface (ETI) forms a critical path between device and brain tissue. Although changes in the electrical double layer (EDL) and glial scar can impact stimulation efficacy, the effects of chronic DBS on the ETI have not yet been established. Approach. In this study, we characterised the ETI surrounding chronically implanted DBS electrodes in rats and compared the impedance and histological properties at the electrode interface in animals that received daily stimulation and in those where no stimulation was applied, up to 8 weeks post-surgery. A computational model was developed based on the experimental data, which allowed the dispersive electrical properties of the surrounding encapsulation tissue to be estimated. The model was then used to study the effect of stimulation-induced changes in the ETI on the electric field and neural activation during voltage- and current-controlled stimulation. Main results. Incorporating the observed changes in simulations in silico, we estimated the frequency-dependent dielectric properties of the EDL and surrounding encapsulation tissue. Through simulations we show how stimulation-induced changes in the properties of the ETI influence the electric field and alter neural activation during voltage-controlled stimulation. A substantial increase in the number of stimulated collaterals, and their distance from the electrode, was observed during voltage-controlled stimulation with stimulated ETI properties. In vitro examination of stimulated electrodes confirmed that high frequency stimulation leads to desorption of proteins at the electrode interface, with a concomitant reduction in impedance. Significance. The demonstration of stimulation-induced changes in the ETI has important implications for future DBS systems including closed-loop systems where the applied stimulation may change over time. Understanding these changes is particularly important for systems incorporating simultaneous stimulation and sensing, which interact dynamically with brain networks.

Frequency and temperature dependent dielectric properties of polyvinyl alcohol/polystyrene sulfonic acid/cobalt oxide nanocomposite films

ABSTRACT Polyvinyl alcohol (PVA), polystyrene sulfonic acid (PSSA), and cobalt oxide (Co3O4) nanoparticles are used in the ease and low-cost solution casting method to prepare flexible nanocomposite films. Structural and morphological studies were carried out for the nanocomposites. Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD) studies revealed an excellent interaction between the host polymer and Co3O4 nanoparticles. Scanning electron microscopy (SEM) was employed to study the surface morphology of the PVA/PSSA/Co3O4 nanocomposite films, which exhibited homogeneous dispersion of nanoparticles within the host matrix. Stress–strain curves were obtained to evaluate the mechanical properties of PVA/PSSA/Co3O4 nanocomposite films. The dielectric behavior of PVA/PSSA/Co3O4 nanocomposite films was examined by varying the content of Co3O4 nanoparticles in the frequency and temperature range of 100 Hz–1 MHz and 30–150°C, respectively. The 15 wt% of Co3O4 nanoparticles in the PVA/PSSA/Co3O4 nanocomposite films have a high dielectric constant (ɛ) of 511.66 and a relatively high dielectric loss (tan δ) of 1440.25 at low frequency and at 60°C, respectively. In addition, the high AC conductivity (σac) obtained for the 15 wt% of Co3O4 nanoparticles was found to be 1.66 × 10−5 Scm−1. The improvement in the dielectric performance of PVA/PSSA/Co3O4 nanocomposite films evidenced that they could be promising materials for microwave absorption applications.

Investigation of large dielectric permittivity and relaxation behavior of DyMnO[formula omitted] single crystal

We have investigated the frequency-dependent dielectric properties of DyMnO3 single crystal in the temperature region from 100 K to 320 K. The material shows a large dielectric permittivity in the low-frequency range around room temperature. The dielectric permittivity exhibits a strong temperature dependence at all frequency and two anomalies which can be associated with the Debye-type relaxation with activation energies of 0.66 eV and 0.23 eV in the higher (around 300 K) and lower (around 150 K) temperature regions, respectively. The high value of activation energy around room temperature suggests that the relaxation is associated to the charge carriers hopping resulting from the second ionization of oxygen vacancies. However, the impedance analysis suggests that the low-temperature relaxation is due to the Maxwell–Wagner type effects originating from the dipoles at the surface.