Frequency Dependent Dielectric Behavior Research Articles

Synthesis, structural, dielectric and magnetic properties of spinel structure of Ca2+ substitute in Cobalt ferrites (Co1−xCaxFe2O4)

Non magnetic material Ca2+ as a substitute in Cobalt ferrite (Co1−xCaxFe2O4x = 0.00, 0.05, 0.10 & 0.15) is prepared by self auto combustion method. The synthesized samples were carried out for various characterizations such as X-ray diffraction, Field emission scanning electron microscope (FE-SEM), Dielectric measurement and Magnetic property. X-ray diffraction reveals the values of crystalline size, lattice parameter and x-ray density by using the standard formula. The saturation magnetization (Ms) decreases from 63.92 to 43.17 emu/g for x = 0.00 to 0.15 and the coercivity (Hc) increases gradually from 819.85 to 1312.32 Oe with the increase in Ca2+ concentration. The dielectric properties of synthesized nano materials were carried out at room temperature. The dielectric parameters such as tangent loss, Cole–Cole plot (Impedance, Modulus), and AC Conductivity were determined for various Ca2+ concentration. The frequency dependent dielectric dispersion behaviour of all the samples can be explained by the Maxwell–Wagner two-layer model along with Koop's phenomenological theory. As a result, Ca2+ substituted Cobalt ferrite is enhanced with their dielectric and magnetic property which is suitable for a memory device, recording media application and high frequency device.

Effect of Swift Heavy Ion Irradiation on Dielectric Properties of Manganite Based Thin Films

In this communication, we report the results of the investigations on the structural, microstructural and electrical properties of Y0.95Sr0.05MnO3 (YSMO) thin films with 100 nm thickness grown on (100) single crystalline SrNb0.002Ti0.998O3 (SNTO) substrates using pulsed laser deposition (PLD) technique. YSMO films were irradiated using 100 MeV O+7 swift heavy ions (SHI) with different fluence using 15 UD Tandem Accelerator, IUAC, New Delhi facility. Structural investigations using θ – 2θ X – ray diffraction (XRD) reveal that all the films crystallize in single phasic nature. With increase in ion fluence, structural strain is found to increase upon the irradiation using lower fluence of 1 × 1011 ions/cm2 which can be ascribed to the irradiation induced creation of defects at the interface. Further increase in ion fluence up to 1×1012 ions/cm2 can create more defects resulting in the degradation in lattice structure and hence strain gets enhanced. For the higher ion fluence of 1×1013 ions/cm2, local annealing takes place at the interface which in turn results in the improved structural strain and recrystallization process. To study the surface morphology of the pristine and irradiated films, atomic force microscopy (AFM) measurement was performed. To understand the electrical properties of presently studied YSMO / SNTO pristine and irradiated films, frequency dependent dielectric behavior was studied. It is seen that dielectric constant increases upon irradiation using the fluence of 1 × 1011 ions/cm2 and 1 × 1012 ions/cm2 while gets suppressed for 1 × 1013 ions/cm2 fluence. Variation in dielectric behavior with different ion fluence has been discussed on the basic of lattice strain and universal dielectric response (UDR) model.

Theoretical Modeling of Dielectric Properties of Artificial Shales

Accurately modeling the anisotropic dielectric properties of shales is important for the interpretation of dielectric data acquired from shales as source rocks and unconventional reservoirs. We have developed a multiphase incremental model for the frequency dependent anisotropic dielectric properties of sedimentary rocks and presented an approach based on the developed model to simulate the measured anisotropic dielectric behaviors of artificial shales. The new model was built based on the theoretical basis of differential effective medium models for any number of mineral grain components aligned in any direction and was shown to be independent of the mixing order. The model incorporates the measured orientation distribution function of the clay particles to determine the shale dielectric anisotropy, and the frequency dependent dielectric behaviors of the wet clay minerals are obtained by inverting the dielectric properties of the artificial sample composed of clay and the same brine as in other artificial shales. The modeling technique combined important polarization mechanisms in the intermediate frequency range and was shown to give satisfactory fit to the measured frequency dependent anisotropic relative permittivity and conductivity of the artificial shales with varying silt contents by using a reasonable aspect ratio and constant dielectric parameters for the silt grains.

Nanocrystalline Ni0.70−xCuxZn0.30Fe2O4 with 0 ≤ x ≤ 0.25 prepared by nitrate-citrate route: structure, morphology and electrical investigations

The structure, morphology, temperature dependent electrical and frequency dependent dielectric behavior of Cu2+ substituted Ni–Zn spinel ferrite nanoparticles having generic formula Ni0.70−xCuxZn0.30Fe2O4 (x = 0.00, 0.05, 0.15 and 0.25) prepared by sol–gel auto combustion technique with citric acid as a chelating agent is reported here. The XRD patterns revealed the presence of cubic spinel structure. The crystallite size was obtained using Scherrer’s formula which varies between 29 and 34 nm. The lattice parameter was found to increase with an increase in copper concentration. FTIR spectra show the characteristic bands for tetrahedral and octahedral sites. The morphology investigated by SEM technique demonstrates the nanocrystalline grain formation with almost spherical geometry. The grain size obtained from SEM analysis is in the range of 69–88 nm. The particle size obtained through TEM image analysis varies from 30 to 35 nm. The electrical and dielectric behavior was studied using a two-probe technique as a function of temperature and frequency respectively. Various electrical parameters like DC resistivity, activation energy, drift mobility, charge carrier concentration, diffusion coefficient were obtained as a function of copper concentration ‘x’. Arrhenius plot indicates the semiconducting nature of Cu2+ substituted Ni–Zn spinel ferrite. The dielectric constant and dielectric loss tangent both decreases with increase in frequency and concentration of Cu2+.

Synthesis and characterization of Ni-Cu-Zn ferrites by microwave reactive sintering technique

ABSTRACTNi0.3Cu0.08Zn0.62Fe2O4 (NCZF) ceramics were prepared by solid state reaction route and calcined at temperatures at (i) 600°C for 30 minutes and (ii) 900°C for 15 minutes in microwave furnace. Room temperature X-ray diffraction analysis of microwave sintered samples calcined at 900°C showed single phase cubic structure while, secondary peaks of iron oxide (Fe2O3) were found in sample calcined at 600°C. Single phase cubic structure of the sintered calcined at 600°C confirmed the microwave reactive sintering. Frequency and temperature dependent dielectric behavior and magneto-dielectric study showed comparable properties of both the microwave sintered samples.

Structural and dielectric properties of the fluorite-type LaxCe1−xO2−δ ceramics

High density (95–97%) Lax () ceramics were tested for structural and dielectric properties. Dense microstructure and controlled phase-purity were obtained for all the -doped samples. A surprising three-fold increase was noticed in the frequency dependent dielectric permittivity behavior for the ceramic, associated with the space-charge polarization at grain boundaries or inhomogeneous microstructure of the ceramic. High resistivity (∼108 Ωm) at room temperature was noticed for the ceramics (at 100 Hz). Hopping of electrons within the oxygen vacancies were noted as the main transport mechanism; strong localization of charge carriers were noticed at high frequencies. The temperature dependent ac-resistivity analysis (T) provides strong evidence for Mott’s variable range hopping process of charge carriers, between the localized states with an average hopping length of RH of 3 nm and hopping energy of WH of 0.67 eV. Moreover, the effect of grains and grain boundaries on the correlation between ac-conductivity and angular-frequency ω has been discussed in detail.

Strain and morphology control over electrical behavior of pulsed laser deposited BiFeO3 films

In this communication, we report the results of the studies on thickness dependent electrical behavior of pulsed laser deposited (PLD) BiFeO3 (BFO) thin films grown on (100) single crystalline Si substrates. X–ray diffraction (XRD) measurement reveals the single phasic nature with polycrystalline growth for all the films. Atomic force microscopy (AFM) images reveal that grain size and granular morphology are highly influenced by the thickness of the films. Frequency dependent dielectric behavior at different temperatures suggests the ferroelectric nature of the films. Variation in dielectric constant with frequency, temperature and film thickness has been discussed in the context of dipole relaxation, ferroelectric nature, structural strain, granular morphology and possible oxygen vacancies in the lattice. P–E loop measurement verifies the ferroelectric nature of the films understudy and its strong dependence on the film thickness. UDR model and dipole relaxation relation were used to understand the dielectric behavior of the films understudy.

Dielectric response and alternating current conductivity in (Co,Ni)Al2O4 nano-spinel

The dielectric behavior and alternating current conduction mechanism of nanocrystalline (Co,Ni)Al2O4 aluminate spinel have been investigated over a broad frequency range (1kHz to 1MHz) for different temperatures i.e. 50°C to 90°C. The low cost and environmental friendly method has been used to developed the nanocrystalline (Co,Ni)Al2O4 spinel phase. The formation of homogeneous single phase of nanocrystalline (Co,Ni)Al2O4 spinel has been confirmed by X-ray diffraction, transmission electron microscopy and scanning electron microscopy. The dielectric response and alternating current conductivity have been observed by inductance, capacitance and resistance bridge which confirms traditional dielectric behavior of (Co,Ni)Al2O4. The frequency dependent complex dielectric impedance behavior has also been explored. The activation energy of (Co,Ni)Al2O4 has been found nearly 0.3–0.1eV b/w the frequency range 1kHz to 1MHz. The alternating current conduction mechanism reveals the signature of correlated barrier hopping by following the power law where the maximum barrier length has been found 144 ± 0.25MeV. This alternating current conduction also follows the Meyer-Neldel rule in the low frequency region.

Effect of annealing process on dielectric and multiferroic properties of Sol-Gel derived bismuth chromate thin films

ABSTRACTMultiferroic materials such as BiCrO3, uniquely exhibit ferroelectricity and ferromagnetism simultaneously have been extensively studied for spintronics device applications. Conversely, the origin of multiferroicity remains poorly understood. In this paper, the structural phases of BiCrO3 over Pt (111)/Ti/SiO2/Si substrate and their lattice distortions after careful annealing were carefully investigated to explain their multiferroicity. Structural transition and different phases was studied from X-ray diffraction at different annealing temperature from 400°C to 700°C and the size of the grains were calculated from Scherrer's equation. SEM and AFM reveal nano-rod formation and the size and density of nano-rods tends to increase with increase of temperature. The step height variation and surface outgrowth of the films at different annealing temperature were further studied by measuring root mean square (RMS) and roughness (Rq) values. The frequency dependent dielectric behavior with terrific dielectric constant and dielectric loss were observed using LCRQ meter. Structural transformation also results an improved (well saturated) ferromagnetism at 700°C from weak ferromagnetism at 400°C due to addition of extra phases. This kind of approach could be used to probe the origin of multiferroic properties in rare-earth materials for device applications.

AC conductivity and dielectric relaxation of bulk tris (8-hydroxyquinoline) aluminum organic semiconductor

The frequency dependent conductivity and dielectric behavior of bulk tris (8-hydroxyquinoline) aluminium(III) (Alq3) have been studied in the temperature range (293–473 K) and frequency range (102–5 MHz). The AC conductivity, σac, was found to be proportional to ωs (where ω is the angular frequency). The exponent frequencies was found to be less than unity and decreased by increasing temperature. This behavior suggests that the correlated barrier hopping (CBH) model is the most predominated conduction mechanism. Both the dielectric constant e1 (ω) and dielectric loss e2 (ω) are decreased with the increase of frequency while they are increased with the increase of temperature in the investigated ranges. The complex diagram of electric modulus gives an evidence of existence of the type of Debye relaxation. The relaxation time (τ) and activation energy for relaxation (Ea) were determined.

Frequency Dependent Conductivity and Dielectric Behavior Studies of Cu Doped Polyindole in Presence of Poly(Vinyl Acetate)

In this article we present results of frequency dependent conductivity and dielectric behavior investigation of Cu doped polyindole in presence of poly(vinyl acetate). As-synthesized composites were analyzed via X-ray diffractometer, fourier transform infrared spectra spectrum, dielectric behavior and ac conductivity measurements. The Cu doped PIN/PVAc composites represent semi-crystalline nature confirmed through X-ray diffraction analysis. The dielectric behavior study of prepared composites reveals that dielectric constants and dielectric loss decreases with increase in frequency. The highest ac conductivity value of composites was estimated as 2.97 × 10−5 S/cm at frequency 1 MHz.

Temperature- and frequency-dependent dielectric behaviors of insulator/semiconductor (Al2O3/ZnO) nanolaminates with various ZnO thicknesses

Al2O3/ZnO nanolaminates (NLs) with various ZnO sublayer thicknesses were prepared by atomic layer deposition. The Al2O3 sublayers are characterized as amorphous and the ZnO sublayers have an oriented polycrystalline structure. As the ZnO thickness decreases to a certain value, each NL exhibits a critical temperature at which its dielectric constant starts to rise quickly. Moreover, this temperature increases as the ZnO thickness is decreased further. On the other hand, the permittivity demonstrates a large value of several hundred at a frequency ⩽1000 Hz, followed by a steplike decrease at a higher frequency. The change in the cut-off frequency with ZnO thickness is characterized by a hook function. It is revealed that the Coulomb confinement effect becomes predominant in the dielectric behaviors of the NLs with very thin ZnO. As the ZnO thickness decreases to about the same as or even smaller than the Bohr radius of ZnO, a great change in the carrier concentration and effective mass of ZnO is induced, which is shown to be responsible for the peculiar dielectric behaviors of Al2O3/ZnO with very thin ZnO. These findings provide insight into the prevailing mechanisms to optimize the dielectric properties of semiconductor/insulator laminates with nanoscale sublayer thickness.

Improvement in magnetic behaviour of cobalt doped magnesium zinc nano-ferrites via co-precipitation route

Nanoparticles of spinel ferrites have attracted huge interest in various technological applications due to their distinct magnetic behaviour. These magnetic nanoparticles acquire surface and finite size effects. We report an improvement of magnetic characteristics in Co2+ substituted MgZn nano-ferrites synthesized by co-precipitation route. Physical properties have been investigated for Mg0.5Zn0.5−xCoxFe2O4 (x = 0, 0.125, 0.250, 0.375, 0.500) nano ferrites using XRD, FTIR, FESEM, EDS, VSM, photoluminescence and UV spectroscopy. Single phase cubical spinel structure has been observed. A phase transition from superparamagnetic to ferrimagnetic behaviour for x > 0.125 has been observed. Saturation magnetization has been found to be enhanced. Frequency dependent dielectric behaviour shows normal dispersion. Absorption spectra show a shift in position of maximum absorption towards longer wavelength with increasing Co2+ content. Photoluminescence spectroscopy has also confirmed the red shift in band edge emission with increasing Co2+ content. Some theoretical parameters, using proposed cation distribution, like theoretical lattice parameter, oxygen positional parameter, bond length etc., have also been calculated and found to support our experimental results.

Introduction of effective dielectric constant to the Poisson-Nernst-Planck model.

The Poisson-Nernst-Planck (PNP) model has been widely used for analyzing impedance or dielectric spectra observed for dilute electrolytic cells. In the analysis, the behavior of mobile ions in the cell under an external electric field has been explained by a conductive nature regardless of ionic concentrations. However, if the cell has parallel-plate blocking electrodes, the mobile ions may also play a role as a dielectric medium in the cell by the effect of space-charge polarization when the ionic concentration is sufficiently low. Thus the mobile ions confined between the blocking electrodes can have conductive and dielectric natures simultaneously, and their intensities are affected by the ionic concentration and the adsorption of solvent molecules on the electrodes. The balance of the conductive and dielectric natures is quantitatively determined by introducing an effective dielectric constant to the PNP model in the data analysis. The generalized PNP model with the effective dielectric constant successfully explains the anomalous frequency-dependent dielectric behaviors brought about by the mobile ions in dilute electrolytic cells, for which the conventional PNP model fails in interpretation.

Giant dielectric response and magnetoelectric behavior of 95BiFeO3–5BaTiO3 (95BFO–5BT) ceramics

A detailed study of electrical behavior of 95BiFeO3–5BaTiO3 (95BFO–5BT) ceramics through comprehensive analysis of temperature and frequency dependent dielectric behavior, ac impedance and magnetodielectric (MD) properties is reported here. Addition of insulating BaTiO3 into BiFeO3 have exhibited enhanced dielectric and ferromagnetic responses. The remnant polarization (Pr) was found to be 6 µC/cm2, while the dielectric constant was found to be very high ( $$\varepsilon_{\text{r}}^{\prime }$$ ≥ 102, for T ≥ 140 °C). Along with strong conductivity contribution to $$\varepsilon_{\text{r}}^{\prime }$$ , spectroscopic plots of $$\varepsilon_{\text{r}}^{\prime }$$ revealed the Maxwell–Wagner type relaxation in the sample, which ultimately could have led to an apparent high $$\varepsilon_{\text{r}}^{\prime }$$ in 95BFO–5BT ceramics. Origin of such a high $$\varepsilon_{\text{r}}^{\prime }$$ in BFO–BT was further investigated using impedance spectroscopy. MD studies revealed the magneto-electric coupling in the ceramics. The MD studies along with anomaly in dielectric data near antiferromagnetic ordering temperature (TN = 170 °C) of BFO suggests the magnetic bearing on the electrical properties of 95BFO–5BT ceramics.

Relaxation dynamics of liposomes in an aqueous solution.

The gel-liquid crystal phase transition has been studied by the temperature and frequency dependent dielectric relaxation behavior of liposomes in an aqueous solution (40 g L(-1) DPPC-water mixture). Four relaxation processes were observed in the frequency range from 40 Hz to 30 GHz which were ascribed to different molecular mechanisms, related to the structural units of the system. The gel-liquid crystal phase transition was also described very accurately from the temperature-dependent dielectric relaxation strength, relaxation time and symmetric shape parameter of the relaxation functions obtained from the fitting procedure. Relaxation process 3, obtained from the dielectric fitting procedure, was confirmed by dielectric modulus analysis. A comparison of the lipid membrane with non-biological systems like liquid crystals was performed. It was determined that the lipid membrane has a ferroelectric liquid crystal like behavior. Process 3 is comparable to the soft mode relaxation process observed in ferroelectric liquid crystals which was detected close to the smectic-C*-smectic-A phase transition. Differential scanning calorimetry was also used to confirm the gel-liquid crystal phase transition of this mixture.

Preparation and Electrical Properties of Ba2TiOSi2−xGexO7 (x=0.0 and 0.2) Ferroelectric Ceramics

Polycrystalline ceramic samples of pure and germanium (Ge4+) doped fresnoite of general formula Ba2TiOSi2−xGexO7 (x=0.0 and 0.2) have been prepared by solid state reaction technique. The formation of the single phase compound was confirmed by X-ray diffraction and the structural parameters were refined by the Rietveld refinement technique. The dc conductivity of both the materials has been measured as a function of temperature from room temperature to 753 K and activation energy was calculated using the relation σ = σoexp(-Ea/kt). The activation energy 4.74 eV obtained for the pure compound is very high in comparison with 1.47 eV of Ge4+-substituted compound. The frequency and temperature dependent dielectric behavior of both the compounds have been studied. The real and imaginary parts of the dielectric constant increase with the increase of temperature.

Surface Modification and Dielectric Response Investigation of Cellulose Acetate Membrane Treated by ArF Excimer Laser

Lasers are used to modify the surface morphology, crystallinity, chemical composition, reactivity and resistivity of polymer surfaces. In this work, several cellulose acetate membranes were exposed by ArF excimer laser, 193 nm, at 2 - 20 UV pulses, with 100 - 350 mJ/pulse energy, at 1 Hz pulse repetition rate. Characterization techniques viz. Fourier transform infrared spectroscopy (FTIR), Contact angle measurement, Scanning electron microscopy (SEM), Atomic force microscopy (AFM) with roughness analysis, Water Flux measurement was exploited to understand the induced changes in the surface properties of the polymer. The contact angle measurement was done here, to determine hydrophilicity of the irradiated polymer at various doses. The frequency dependent dielectric behavior was studied both in reference and irradiated samples in the frequency range from 75 KHz - 30 MHz. Results showed that the morphological surface changes with laser irradiation, and the water contact angle alters as the surface of the membrane is modified.

Modeling of electrode polarization for electrolytic cells with a limited ionic adsorption

Dilute electrolytic cells filled with chlorobenzene containing small amounts of tetrabutylammonium tetraphenylborate show anomalous dielectric dispersions in low-frequency regions. We propose a new model for electrode polarization in order to analyze the dielectric behavior of the dilute electrolytic cells. The model comprises two capacitive components: One is the space-charge polarization accompanied with a specific ionic adsorption on electrodes, and the other is the electrode capacitance which is brought about by an electronic spillover from the electrode surface. This model can primarily explain the anomalous frequency-dependent dielectric behavior of the electrolytic cells not only with low electrolyte concentrations, but also with high concentrations and can correctly describe the characteristics of the electrode polarization reflected in the dielectric spectra.

Biomedical Sensing with Hydroxyapatite Ceramics in GHz Frequency Range

Hydroxyapatite (HA) is a leading biocompatible material extensively used for bone implants as a porous ceramic graft and as a bioactive coating. Electrical characteristics of HA can be employed in implantable devices for real-time in vivo pressure sensor applications such as in knee or hip prosthesis. In particular, high piezo and pyroelectricity of HA, its polarisation by electron beam and selective adsorption of proteins on polarised domains indicate the potential for real-time biosensing applications of HA. For this purpose, a comprehensive understanding of the dielectric behaviour of different forms of HA over a frequency range relevant for biomedical sensing is critical. Such information for HA, especially its frequency dependent dielectric behaviour over the GHz range, is rare. To this end, we report on novel investigations of properties of HA in powder and film forms in the GHz frequency range.