Dependent Ac Conductivity Research Articles

Dielectric properties and study of AC electrical conduction mechanisms by non-overlapping small polaron tunneling model in Bis(4-acetylanilinium) tetrachlorocuprate(II) compound

In the present work, the synthesis and characterization of the Bis(4-acetylanilinium) tetrachlorocuprate(II) compound are presented. The structure of this compound is analyzed by X-ray diffraction which confirms the formation of single phase and is in good agreement the literature. Indeed, the Thermo gravimetric Analysis (TGA) shows that the decomposition of the compound is observed in the range of 420–520K. However, the differential thermal analysis (DTA) indicates the presence of a phase transition at T=363k. Furthermore, the dielectric properties and AC conductivity were studied over a temperature range (338–413K) and frequency range (200Hz–5MHz) using complex impedance spectroscopy. Dielectric measurements confirmed such thermal analyses by exhibiting the presence of an anomaly in the temperature range of 358–373K. The complex impedance plots are analyzed by an electrical equivalent circuit consisting of resistance, constant phase element (CPE) and capacitance. The activation energy values of two distinct regions are obtained from logσT vs 1000/T plot and are found to be E=1.27eV (T<363K) and E=1.09eV (363K<T).The frequency dependence of ac conductivity, σac, has been analyzed by Jonscher's universal power law σ(ω)=σdc+Aωs. The value of s is to be temperature-dependent, which has a tendency to increase with temperature and the non-overlapping small polaron tunneling (NSPT) model is the most applicable conduction mechanism in the title compound.

Electrical and dielectric properties of In2S3 synthesized by solid state reaction

Indium sulfide (In2S3) material was synthesized by solid state reaction technique. The obtained powder was characterized by means of X-ray diffraction (XRD) and impedance spectroscopy. X-ray analysis shows that the obtained phase is β-In2S3 with cubic structure. The average grain size is about 42.6 nm, indicating the nanocrystalline nature of In2S3 material. The ac conductivity and dielectric properties of In2S3 have been investigated in a wide frequency (10 Hz–1 MHz) and temperature (0°C–100 °C) ranges.We found that the electrical conductance of In2S3 material is frequency and temperature dependent. The frequency dependence of ac conductivity follows the Jonscher's universal dynamic law. The variation of ac conductivity and the frequency exponent ‘s’ are interpreted by the correlated barrier hopping (CBH) model. Activation energy value inferred from conductance spectrum matches very well with the value estimated from relaxation time, indicating that the relaxation process and conductivity have the same origin. In addition, the electronic conduction appears to be dominated by thermally activated hopping of small polaron (SPH) at high temperatures and by variable range hopping (VRH) at low temperatures. Values of dielectric constants ε′ and ε″ were found to decrease with frequency and increase with temperature. Such an observation is interpreted by Maxwell-Wagner-Sillars model (MWS).

Structural, dielectric and impedance characteristics of CoTiO3

The present work reports the synthesis and characterization of the ilmenite-type rhombohedral structured CoTiO3 ceramic. The polycrystalline powder of CoTiO3 was prepared by the mixed-oxide technique. X-ray structural analysis of the compound confirmed the formation of a single-phase compound. The study of microstructure by scanning electron microscopy shows that the compound has well defined grains which are distributed uniformly throughout the surface. It shows that the grain size lies in the range of 8–10 μm. The Fourier transform infrared spectroscopy (FTIR) studies confirm the presence of TiO, TiOTi, TiOO, CoO bond in the studied compound. The frequency dependence of dielectric constant was explained on the basis of Maxwell–Wagner mechanism and Koop's phenomenological theory. The frequency-temperature dependence of impedance analysis shows that the bulk effect dominates up to 250 °C, and the appearance of second semicircular arc above 280 °C indicates the presence of grain boundary effect in the sample. The depressed semicircles in Nyquist plot with depression angles clearly indicate the distribution of relaxation times in the ceramic samples. It also shows that the material has negative temperature co-efficient of resistance similar to that of semiconductors. Similar behavior has also been observed in the study of IV characteristics of the material. Through the study of dc conductivity of CoTiO3 and using the relation; ln σdc α Ea/KBT, activation energy of the compound was calculated. The frequency dependence of ac conductivity is explained on the basis of Correlated barrier Hopping Model.

Analysis of the conduction mechanism and dielectric properties of N, N’, N” tris(4-methylphenyl)phosphoric triamide

The structure for the powder of N,N’, N”-tris(4-methylphenyl)phosphoric triamide, TMP-TA, was characterized using X-ray diffraction (XRD) and differential thermal analysis (DTA) techniques. The ac conductivity and dielectric properties were measured in the frequency range of 42-\(10^{5}\) Hz for the bulk TMP-TA in a pellet form at different temperatures. The frequency dependence of ac conductivity was expressed by a Jonscher’s universal power law. The frequency exponent (s) was determined from the fitting of experimental data of ac conductivity. The correlated barrier hopping (CBH) model was found to be responsible for the ac conduction mechanism in TMP-TA. The activation energy was calculated from the temperature dependence of ac conductivity. The values of the density of states at the Fermi level were determined for different frequencies. The components of the electric modulus (M’ and M”) were calculated and used to estimate the relaxation time.

Superlinear frequency dependence of AC conductivity and its scaling behavior in xAgI-(1 − x) AgPO3 glass superionic conductors

Low temperature AC conductivity studies on melt quenched xAgI-(1−x) AgPO3 glass electrolytes are presented. It is observed that doped glasses show Jonscher power law behavior at all temperatures, however, undoped AgPO3 glass also shows superlinear frequency-dependent conductivity at very low temperatures apart from the usual Jonscher power law behavior. This behavior in undoped AgPO3 glass is not yet reported in literature. The Summerfield scaling law is used to demonstrate that Jonscher power law behavior and superlinear power law behavior have different physical origins as scaling law is not followed in the superlinear regime. Moreover, scaling behavior of AC conductivity also indicates that conduction mechanisms are slightly different in doped and undoped glasses. However, scaling behavior provides only qualitative information about the conduction mechanisms. The conductivity spectra of doped and undoped glasses can be merged into a super-master conductivity curve except in the transition zone (where AC conductivity starts dominating over DC conductivity) where the conductivity master plots of doped and undoped glasses do not merge.

Structural, dielectric, impedance and magneto-electric properties of mechanically synthesized (Bi0.5Ba0.25Sr0.25) (Fe0.5Ti0.5)O3 nano- electronic system

Structural, electrical, magnetic and magneto-electric properties of (Bi0.5Ba0.25Sr0.25) (Fe0.5Ti0.5) O3 nanoceramic synthesized by the mechanical alloying method were studied. Structural analysis was studied by Rietveld refinement of room temperature XRD data. The temperature and frequency dependent dielectric data were explained using the different mechanism. The grain and grain boundary effect of the material on the electrical properties has been explained using the existed mechanism. The impedance study reveals a semi conducting grain and insulating grain boundary resulting in the formation of surface and internal barrier layer capacitors leading to the high value of dielectric constant. The frequency dependence of AC conductivity at two different regions can be explained on the basis of correlated barrier Hopping model and quantum mechanical tunneling model. The value of the magneto-electric voltage coupling coefficient, α, of (Bi0.5Ba0.25Sr0.25) (Fe0.5Ti0.5)O3 ceramic is obtained as 2.56 mV cm−1 Oe−1.

Electrical conductivity and dielectric studies of MnO2 doped V2O5

The investigation on electrical conductivity and dielectric properties of mixed oxide of manganese (Mn) and vanadium (V) was carried out to study the mixed oxides response to different frequencies and different measuring temperatures. The frequency and temperature dependence of AC conductivity, dielectric constant and dielectric loss factor of mixed oxides were studied in the frequency range of 40Hz–1MHz and a temperature range of 30–250°C. Since the mixed oxides are multi phase materials, hence the properties of the pure oxides are also presented in this study to discuss the multi phase behaviour of the mixed oxides. The XRD pattern shows the Mn–V oxide is multiphase and quantitative phase analysis was performed to determine the relative phases. The overall results indicate that with increasing temperature, the AC conductivity, dielectric constant, dielectric loss factor and loss tangent of the Mn–V mixed oxide increases. However, it shows an overlap in the dielectric constant at 225°C and 250°C due to the V2O5 phase in the mixed oxide. From the AC activation energy, the mixed oxides underwent conduction mechanism transition from band to hopping in the investigated frequency range. The MnV2O6 has relatively good resistivity, therefore the mixed oxide sintered at 550°C with the highest composition of MnV2O6 gives the highest dielectric constant of 9845 at 1kHz, and at 250°C.

Complex dielectric and impedance behavior of magnetoelectric Fe2TiO5

We have investigated the complex dielectric and impedance properties of magnetoelectric compound Fe2TiO5 (FTO) as a function of temperature (T) and frequency (f) to understand the grain (G) and grain boundary (Gb) contributions to its dielectric response. The temperature and frequency dependent dielectric permittivity (ε′) data shows a sharp increase in permittivity above 200 K accompanied with a frequency dependent peak in tanδ. At T < 175 K, only G contribution dominates even at lower frequency (∼100 Hz), but for T ≥ 175 K, the Gb contribution starts appearing at low frequency. The value of critical frequency distinguishing these two contributions increases with increasing temperature. The observed non-Debye dielectric relaxation follows thermally activated process and is attributed to polaron hopping. Further the frequency dependence of ac conductivity follows the Jonscher's power-law. The temperature dependency of critical exponent ‘s’ shows that the correlated barrier hopping model is appropriate to explain the conductivity mechanism of FTO in the studied temperature regime.

Structural characterization, thermal, ac conductivity and dielectric properties of (C7H12N2)2[SnCl6]Cl2·1.5H2O

(C7H12N2)2[SnCl6]Cl2·1.5H2O is crystallized at room temperature in the monoclinic system (space group P21/n). The isolated molecules form organic and inorganic layers parallel to the (a, b) plane and alternate along the c-axis. The inorganic layer is built up by isolated SnCl6 octahedrons. Besides, the organic layer is formed by 2,4-diammonium toluene cations, between which the spaces are filled with free Cl− ions and water molecules. The crystal packing is governed by means of the ionic N—H···Cl and Ow—H···Cl hydrogen bonds, forming a three-dimensional network. The thermal study of this compound is reported, revealing two phase transitions around 360(±3) and 412(±3) K. The electrical and dielectric measurements were reported, confirming the transition temperatures detected in the differential scanning calorimetry (DSC). The frequency dependence of ac conductivity at different temperatures indicates that the correlated barrier hopping (CBH) model is the probable mechanism for the ac conduction behavior.

The structural, electrical and magnetoelectric properties of soft-chemically-synthesized SmFeO3 ceramics

The structural, electrical and magnetoelectric properties of SmFeO3 ceramic samples, synthesized using a soft-chemical method, were studied. A structural analysis of the material was carried out by the Rietveld refinement of room temperature x-ray diffraction data. The temperature dependence of the dielectric peaks was analyzed by fitting them with two Gaussian peaks corresponding to two phase transitions—one being electric, and the other being magnetic in nature. The depression angle of the semicircles in a Nyquist plot representing the grain and grain boundary contributions in the sample was estimated. The grain boundary effect, appearing at temperatures above 75 °C, is explained using the Maxwell–Wagner mechanism. The impedance study reveals a semi-conducting grain with an insulating grain boundary, leading to the formation of surface and internal barrier layer capacitors and resulting in a very high dielectric constant. The effect of dc conductivity on the loss tangent at low frequencies and high temperature has been analyzed. The frequency dependence of ac conductivity in the two different regions can be explained on the basis of correlated barrier hopping and quantum mechanical tunneling models. The material is found to exhibit canted antiferromagnetism and improper ferroelectric characteristics. The value of the magnetoelectric voltage-coupling coefficient (α) of a SmFeO3 ceramic is found to be 2.2 mV cm−1 Oe−1.

Development of ilmenite-type electronic material CdTi0&lt;sub&gt;3&lt;/sub&gt; for devices

The correlation between structural and electrical properties of cadmium titanate (CdTiO3) ceramic was established through X-ray diffraction combined with electrical and optical characterization techniques. The compound was prepared using a hightemperature solid-state reaction technique. Preliminary study on some structural aspect of the material using X-ray diffraction pattern showed the formation of singlephase compound in orthorhombic crystal system. Some characteristics of molecular structure of the material were studied by using Fourier transform infrared spectroscopy and ultraviolet visible spectroscopy techniques. The size and distribution of grains in the scanning electron micrograph revealed the polycrystalline nature of the material with size anisotropy and small number of voids. Detailed analysis of temperature-frequency dependence of dielectric parameters (i.e. dielectric constant and tangent loss) has revealed many interesting and important results of the material. The impedance studies of CdTiO3 over a wide range of temperature and frequency in the complex plane formalism with suitable equivalent circuit have shown some correlation between microstructure and electrical properties of the material. From the impedance and dielectric measurements some electrical parameters such as bulk resistance, capacitance, relaxation time and relative dielectric constant were calculated. The variation of DC conductivity with inverse of absolute temperature follows the Arrhenius relation. The study of frequency dependence of AC conductivity suggests that the material obeys Jonscher's universal power law.

Electrical, dielectric and electrochemical measurements of bulk aluminum phthalocyanine chloride (AlPcCl)

AC conductivity and the related dielectric properties of bulk aluminum phthalocyanine chloride (AlPcCl) have been studied over a temperature range (303–403 K) and frequency range (42–106 Hz). The universal power law σac(ω)=Aωs has been used to investigate dependence of AC conductivity on frequency. The variation of the frequency exponent (s) with temperature was analyzed in terms of different conduction mechanisms; the predominant conduction mechanism was found to be the correlated barrier hopping (CBH) model. The barrier height was calculated by using (CBH) model, it was found to be 1.41 eV. Dependence of σac(ω) on temperature refers to a linear increase with increasing temperature at different frequencies. The density of states N (EF) was calculated to be equal 4.11×1019 cm−3 using Elliott model. It has been found that AC activation energy decreases with increasing frequency. Dielectric values were analyzed using complex permittivity and complex electric modulus for bulk AlPcCl at different temperatures. The obtained value of HOMO–LUMO energy gap was found to be 1.48 eV.

Crossover between transport mechanisms in the region of the transition from sublinearity to superlinearity of the AC-conductivity frequency dependence for disordered semiconductors

The transition of the frequency dependence of AC conductivity of disordered semiconductors from sublinear to superlinear behavior with an increase in frequency, which is observed for many disordered systems, is investigated. It is shown that the standard approach to calculating the superlinearity of the frequency dependence of the AC hopping conductivity in the form Reσ(ω) ∼ \(\frac{\omega } {{\ln \left( {\omega _{c,ph} /\omega } \right)}}\) (ωc, ph is the characteristic frequency), based on the single-particle density of states with a Coulomb gap, generally cannot be used to calculate high-frequency conductivity. The superlinearity of the experimentally observed frequency dependences of the conductivity Reσ(ω) in the crossover region indicates that the optimal hop length is frequency-independent and that the resonance mechanism of conductivity plays a key role. The resonance mechanism causes abnormally large measured values cot(γ) = Ims/Reσ (γ is the dissipation factor) in the crossover region.

Synthesis, characterization and ionic conductivity of MgAl2O4

Magnesium aluminate nanoparticles have been synthesized by a citrate sol-gel route. X-ray diffraction and IR spectroscopy study confirmed the formation of MgAl 2 O 4 cubic spinel structure without presence of any secondary phase. Crystallite size of the synthesized nanoparticles was found to be equal to 24 nm. The ac conductivity of MgAl 2 O 4 was studied using complex impedance spectroscopy technique in the frequency range from 5 Hz to 13 MHz and temperature range from 673 to 798 K. The temperature and frequency dependence of ac conductivity were highlighted and the activation energies of, respectively, ac conduction and relaxation processes were also calculated.

Synthesis of dye-substituted polyanilines and study of their conducting and antimicrobial behavior

AbstractConducting and antimicrobial properties of chemically synthesized polyanilines was found to be affective by varying the dye moieties. The temperature dependence of AC conductivity was studied by two-probe method to learn about the conduction behavior of the synthesized compounds. The conductivity of the dye-substituted polyanilines was found to be in the range of 10−3 S/cm. For the study of antimicrobial behavior of the synthesized dye-substituted polyanilines, different micro-organisms, namely, the bacteria Escherichia coli (MTCC 442), Pseudomonas aeruginosa (MTCC 441), Staphylococcus aureus (MTCC 96), and Staphylococcus pyogenus (MTCC 443) and fungal strains Candida albicans (MTCC 227), Aspergillus niger (MTCC 282), and Aspergillus clavatus (MTCC 1323), were chosen based on their clinical and pharmacological importance. Antimicrobial properties of dye-substituted polyanilines show very good results as compared to polyanilines and dyes individually.

Dielectric behavior of manganese titanate in the paraelectric phase

Rhombohedral MnTiO3 powder has been synthesized by a high-temperature solid-state reaction method. The formation of single-phase compound is confirmed through XRD, Rietveld refinement and FTIR analysis. The optical band in MnTiO3 obtained from the UV–Vis absorption spectrum has been analyzed. The study of SEM micrographs suggested that the prepared material has good sinter ability and high density with homogeneous grain distribution on the surface and in the bulk. From the impedance and dielectric measurements, the electrical parameters were obtained. It was found that the magnitude of relative dielectric constant (er) was relatively high with low dielectric loss. The study of frequency dependence of AC conductivity suggests that the material obeys Jonscher’s universal power law. The variation of DC conductivity with inverse of absolute temperature follows the Arrhenius relation.

Dielectric, impedance and transport characteristics of (Bi0.6Pb0.4Fe0.6Ti0.4)O3

Single-phase polycrystalline sample of (Bi0.6Pb0.4Fe0.6Ti0.4)O3 was synthesized by a standard high-temperature solid-state reaction method. Preliminary structural analysis of the material using room temperature X-rays diffraction data and pattern exhibits its tetragonal structure. Detailed studies of frequency and temperature dependence of dielectric, impedance and transport properties of (Bi0.6Pb0.4Fe0.6Ti0.4)O3 in the wide range of frequency (103–106 Hz) at different temperature (25–500 °C) have provided many interesting results useful for device applications. The frequency dependence of ac conductivity of the material obeys Jonscher’s universal power law. The results obtained on transport properties of the materials have been interpreted in terms of a two-layer model with conducting grains partitioned from each other by poorly conducting grain boundaries. Based on this model, the two electrical responses in impedance and modulus formalisms have been suggested to investigate the effect of grain and grain-boundary.

Dielectric relaxation and magnetic characteristics of (La1/2Li1/2)(Fe1/2V1/2)O3 multiferroics

In this study we have synthesized lead-free polycrystalline sample of (La1/2Li1/2)(Fe1/2V1/2)O3 multiferroic by a standard high-temperature solid-state reaction technique. TGA has been carried out to observe the weight loss of the material with rise in temperature. The formation of the material has been confirmed by preliminary structural analysis using X-ray diffraction data. The dielectric permittivity (constant), loss tangent, impedance, and electric modulus of silver coated pellet sample were measured in a wide frequency range (1 kHz–1 MHz) at different temperatures (30–375 °C). The Nyquist plots show the contributions of grain and grain boundary effect in the impedance characteristics of the material. The bulk resistance calculated from the impedance data decreases with increase in temperature showing negative temperature coefficient of resistance (NTCR)-type behaviour of the material. The frequency dependence of ac conductivity at different temperature indicates that the material obeys Jonscher’s universal power law. The nature of variation of dc conductivity follows Arrhenius law. Detailed studies of modulus spectrum suggest that the material exhibits non-Debye type of relaxation mechanism, which is consistent with the impedance data. The room temperature magnetic (M-H) and ferroelectric (P-E) loops confirm the ferromagnetic and ferroelectric ordering present in the prepared material.

Electrical transport in titania nanoparticles embedded in conducting polymer matrix

Abstract Conducting polymer-wide band gap semiconductor nanocomposites are prepared by polymerizing pyrrole in the presence of colloidal titanium dioxide (TiO2) sol. Characterizations of nanocomposites are carried out by Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM) and X-ray diffraction (XRD). Direct current (dc) and alternating current (ac) conductivities of nanocomposites have been investigated as a function of temperature and frequency for different concentrations of polypyrrole (PPY). The temperature dependence of ac conductivity suggests that small polaron tunneling occurs in the charge transfer process. A very large dielectric constant of about 13,000 at room temperature has been observed. The interface between PPY and TiO2 plays an important role in yielding a large dielectric constant in the composite.

Effect of cadmium doping on electrical properties of lead nickel niobate–lead zirconate titanate [Pb1.0(Ni0.167Nb0.333Zr0.155Ti0.345)O3] ceramics

Lead nickel niobate–lead zirconate titanate (PNNZT) and cadmium doped (CdPNNZT) with general composition Pb1.0(Ni0.167Nb0.333Zr0.155Ti0.345)O3 (PNNZT), Pb0.98Cd0.02(Ni0.167Nb0.333Zr0.155Ti0.345)O3 (CdPNNZT) respectively were prepared by conventional solid state reaction. Microstructural and compositional analyses have been carried out by X-ray diffraction and scanning electron microscopy. With cadmium doping there is an increase in both the perovskite phase and in grain size. The effect of cadmium doping on the structural and dielectric properties has been investigated. An increase in the dielectric constant was observed with cadmium doping in PNNZT. Complex impedance analysis suggests poly-dispersive non-Debye type relaxation to occur in the material. The frequency dependence of AC conductivity obeys the universal double power law. The value of activation energy depends on increase in frequency as well as on cadmium doping.