Activation Energy Of Dc Conductivity Research Articles

Investigation of structural and electrical transport properties of nano-flower shaped NiCo2O4 supercapacitor electrode materials

Nickel cobaltite nano-flower was synthesized via temperature dependent co-precipitation techniques and its single phase formation, vibrational spectra and nanostructured with flower-like morphology were confirmed by XRD, FTIR, Raman and TEM micrographs. The electrical transport properties and conduction mechanism of NiCo2O4 were studied first time using complex impedance spectroscopy in frequency range 100 Hz-1 MHz and wide temperature range 25 °C-300 °C. Poor grain relaxation was observed from RT to 75 °C whereas interface (both grain boundary and electrode effect) plays a dominant role above 75 °C are ascertained from Nyquist plot of impedance and modulus spectra. The utmost dielectric constant (6.8 × 102) and loss (540) was observed at high temperature (300 °C) and low frequency (100 Hz) regime and gradually diminished with high-frequency evolution and low-temperature approach. Finally, the ac and dc conduction mechanism were examined individually in details by the help of hooping relaxation model and overlapping large polaron tunneling (OLPT) concept for supercapacitor application. The calculated value of activation energy for dc conduction (0.63 eV) is larger than ac conduction (0.36 eV) as the ac conductivity is thermally activated.

Study on electrical and structural properties in SiO2 substituted Li2O-Al2O3-GeO2-P2O5 glass-ceramic systems

Two different LAGP glasses with nominal compositions a) Li1.5Al0.5Ge1.5P2.9Si0.1O12 (LAGP1) b) Li1.5Al0.5Ge1.5P2.5Si0.5O12 (LAGP2) were prepared to see the effect of SiO2 substitution in place of P2O5 on their phase formation and electrical properties. Different heat schedules were applied to see the phase evolution in these glass-ceramics (GC). The electrical conductivity of the glass-ceramics samples was measured using impedance analyzer in the frequency range of 0.1–106 Hz and temperature range of 300–373 K. XRD confirm presence of pure LiGe2(PO4)3 in LAGP1 GC sample whereas LAGP2 shows additional minor phases along with LiGe2(PO4)3. In LAGP2 GC XRD patterns showed a little shift in peak position as compared to LAGP1 GC because of SiO2 substitution. LAGP1 shows ionic conductivity value of around 2.45 ×10−4 S/cm at room temperature (RT) for the sample heat treated at 750 oC whereas the LAGP2 GC sample shows maximum conductivity of 8.95 ×10−6 S/cm for the sample heat treated at 700 °C. The conductivity value increased to nearly one order higher with increase in temperature upto 333 K. The lower conductivity value of LAGP2 sample is due to presence of additional minor insulating phases in the sample. The activation energies for dc conductivity was calculated as 0.43 eV and 0.48 eV for LAGP1 and LAGP2, respectively. Ionic mobility of these samples were determined using the permittivity and loss factor and the mobility value is higher for LAGP1 GC (1.34 ×10−3 cm2/V-s) as compared to LAGP2 GC sample (3.56 ×10−6 cm2/V-s). Microstructure of glass- ceramics samples shows growth of very fine structure of around 100 nm size in LAGP1 GC where as in LAGP2 GC microstructures are looking like small globules of less than 100 nm sizes and are interconnected to form a chain like structure. LAGP1 GC with high ionic conductivity is found to have more potential advantages over LAGP2 GC for use in Li-ion battery.

Conducting polymers IX: Optical properties, dielectric constants and conduction mechanism of poly(N,N′-Bis-salphinyl 2,6-diaminipyridine-3,5-diamini-1,2,4-trizole)

Poly(N,N′-Bis-salphinyl 2,6-diaminipyridine-3,5-diamini-1,2,4-trizole) (PBDPT) is synthesized starting with 2,6-diamino-pyridine using thionyl chloride (SOCl2) as an oxidizing agent and then is polymerized with 3,5-diamino-1,2,4-triazole. The chemical structure of the produced PBDPT is confirmed by spectroscopic analyses techniques. The average molecular weight of PBDPT is determined using 1H NMR technique. The optical investigations of PBDPT showed two absorption peaks and two remarkable emission peaks. The oscillator strength of the absorption peaks is calculated and is found to be 4.4×1012 and 1.96×1012 for the peaks at 9.19×1014 and 7.54×1014Hz, respectively. The energy gap (Eg) is found to be 2.66eV. Direct current electrical conductivity (σDC), alternating current electrical conductivity (σAC) and conduction mechanisms are investigated in the temperature range 298–373K. The thermal activation energy for DC conductivity, ΔEDC, is determined and found to be 0.54eV while the thermal activation energy for AC conductivity, ΔEAC, is found to be in the range 0.09–0.17eV; depending on the test frequency. The semi-circle behavior of the impedance spectra confirmed that the equivalent circuit of the sample can be represented by a resistor Rp in parallel with a capacitor Cp.

Temperature-dependence of electrical properties for the ceramic composites based on potassium polytitanates of different chemical composition

The samples of ceramic materials based on potassium polytitanate (PPT) characterized with various TiO2/K2O molar ratio, are produced by calcination at 900 °C and investigated. AC conductivity (σ ac ) of the obtained ceramics is measured at different temperatures between 200 and 800 °C in frequency range of 0.1 Hz–1 MHz. The method of combined impedance and modulus spectroscopy is used to analyze the obtained results. The activation energies of DC conductivity, bulk and grain-boundary conductivity as well as relaxation frequency for studied composites are estimated. Using the correlated barrier hopping (CBH) model, the energies of potential barrier between neighboring defect sites for all kinds of investigated materials are presented. The bulk and grain boundary parameters of the produced ceramic materials based on potassium polytitanates are calculated. The mechanism of different vacancies formation in the investigated ceramic system is discussed. The influence of precursor chemical composition on electrical properties for the ceramic composites based on potassium polytitanates is studied.

Thermal and electrical properties of (B2O3-TeO2-Li2O-CoO) glasses

Borotellurite glasses in the composition, (B2O3)0.2–(TeO2)0.3–(CoO)x–(Li2O)0.5-x; x = 0.05, 0.10, 0.15, 0.20, 0.25, 0.30, 0.35, 0.40, 0.45 and 0.50 have been synthesized and their non-crystalline nature confirmed by XRD. Density of the glasses increased and molar volume decreased up to x = 0.3 and reversed their trends for x > 0.3. The glass transition temperature is increased up to x = 0.30 and decreased for x > 0.3. Changes in density, molar volume and glass transition temperature around x = 0.3 may be ascribed to structural/topological modifications occurring in the glasses. Polaron parameters have been determined. Thermal stability is found to increase with increasing x. Activation energy for dc conduction at high temperature has been determined by applying Mott's small polaron hopping model. Conductivity and activation energy were found to pass through minimum and maximum respectively for x around 0.30, which may be due to a changeover of conduction mechanism from predominantly ionic regime to electronic regime. This transition can be attributed to the interaction between electrons and alkali ions. This result is of significance both scientifically and technologically. Mott's variable range hopping model has been employed to understand conductivity at low temperature for the present glasses.

Microstructural, magnetic and electrical properties of Zn0.4M0.3Co0.3Fe2O4 (M = Ni and Cu) ferrites synthesized by sol–gel method

A comparative study of microstructural, magnetic and electrical properties of Zn0.4Ni0.3Co0.3Fe2O4 (ZNCFO) and Zn0.4Cu0.3Co0.3Fe2O4 (ZCCFO) ferrites prepared using sol–gel method have been investigated in this work. X-ray diffraction results indicate that samples have cubic spinel type structure ( $$Fd\bar {3}m$$ space group). Lattice constant, average grain size and X-ray density are higher for ZCCFO than those of ZNCFO. The magnetic parameters such as M s , H c , and M r were found to decrease with the substitution of Ni by Cu. The electrical properties of the samples have been studied using impedance measurements as a function of frequency and temperature. The substitution of Zn–Co ferrite with Cu leads to improve its conductivity that its substitution with Ni. The behaviors of imaginary part of permittivity and loss tangent have been investigated using Maxwell–Wagner’s model and Koop’s theory. The electrical modulus study reveals the presence of the non-Debye type of dielectric relaxation in our samples. Close values of activation energy for dc conduction (E dc ) and for conductivity relaxation (E Mʺ ) were found confirming that the relaxation process and electrical conductivity are attributed to the same defect. Nyquist representations (Z″ vs. Zʹ) were plotted and their characteristic behaviors were analyzed in terms of electrical equivalent circuit.

Hydrothermal synthesis, structural, electrical and magnetic studies of cathode material Li2FeZrO4 for lithium ion batteries

In this present work, Li2FeZrO4 has been synthesized by hydrothermal method. The material is characterized using XRD, TGA, FTIR, UV–Vis, VSM and impedance spectroscopy. The powder XRD patterns of Li2FeZrO4 sintered at 800 °C shows that these crystallites are stable in room temperature with tetragonal structure of space group p141 and the average crystallites size is found to be 38 nm. Due to its structural stability, ac electrical properties in terms of complex Impedance Z*(ω), complex permittivity e*(ω), complex conductivity σ*(ω) and complex electric modulus M*(ω) of the sample have been evaluated as a function of frequency at different temperatures. The shape of the impedance spectra reveals the non-Debye nature of the relaxation processes of the present material. The relaxation process consists of two different polarization processes i.e., hopping charge polarization (“pinned dipole”) and dielectric dipolar like polarization (“free dipole”) mechanism. The dc conductivity activation energy E σ has been calculated for the material along with the activation energy for hopping conduction and dielectric relaxation. Magnetic properties have been investigated by vibrating sample magnetometer (VSM) for the sample at various temperatures.

Characterization and Evaluation of Activation Energy for Dc Conductivity of Polypyrrole/Nickel Zinc Iron Oxide Nanocomposites

Characterization and Evaluation of Activation Energy for Dc Conductivity of Polypyrrole/Nickel Zinc Iron Oxide Nanocomposites

Zinc chloride modified electronic transport and relaxation studies in barium-tellurite glasses

The ac conductivity of halide based tellurium glasses having composition 70 TeO2-(30-x) BaO-x ZnCl2; x = 5, 10, 15, 20 and 25 has been investigated in the frequency range 10-1 Hz to 105Hz and in the temperature range 453 K to 553 K. The frequency and temperature dependent ac conductivity show mixed behaviour with increase in halide content and found to obey Jonscher’s universal power law. The values of dc conductivity, crossover frequency and frequency exponent have been estimated from the fitting of experimental data of ac conductivity with Jonscher’s universal power law. For determining the conduction mechanism in studied glass system, frequency exponent has been analyzed by various theoretical models. In presently studied glasses, the ac conduction takes place via overlapping large polaron tunneling (OLPT). The values of activation energy for dc conduction (W) and the one associated with relaxation process (E R) are found to increase with increase in x up to glass sample with x = 15 and thereafter it decrease with increase in zinc chloride content. DC conduction takes place via variable range hopping (VRH) as proposed by Mott with some modification suggested by Punia et al. The value of real part of modulus (M') is observed to decrease with increase in temperature. The value of stretched exponent (β) obtained from fitting of M'' reveals the presence of non-Debye type of relaxation in presently studied glass samples. Scaling spectra of ac conductivity and values of electric modulus (M' and M'') collapse into a single master curve for all the compositions and temperatures. The values of relaxation energy (E R) for all the studied glass compositions are almost equal to W, suggesting that polarons have to overcome same barrier while relaxing and conducting. The conduction and relaxation processes in the studied glass samples are composition and temperature independent.

Electrical and optical properties of new azo dyes derived from m-aminophenol

The electrical and optical absorption properties of 5-amino −2-(aryldiazenyl) phenol (HLn) was investigated. A semiconductor behavior with two thermal activation energies for dc conduction which are in the range 0.11–0.47eV for ΔE1 at the lower region of temperature and 0.77–1.12eV for ΔE2 at higher region of temperature are observed. The ac conductivity measurement showed a dependence of σac on test frequency following the relations σac∝ωS. Temperature dependence of the exponent S recommends different conduction mechanisms depends on the chemical structure. The recommended mechanism are small polaron tunneling (SPT) and quantum-mechanical tunneling mechanism (QMT). The optical absorption investigations for HLn thin films show that the ligands HL1 and HL2 experiences indirect optical transition with energy gap 2.02 and 1.89eV, respectively. The ligands HL3 and HL4 experiences direct optical energy gap with values 2.6 and 2.20eV, respectively.

Structural and electrical properties of La3+-doped Na0.5Bi4.5Ti4O15-Bi4Ti3O12 inter-growth high temperature piezoceramics

New lead-free inter-growth piezoelectric ceramics, Na0.5Bi8.5-xLaxTi7O27 (NBT-BIT-xLa, 0.00≤x≤1.00), were prepared by the conventional solid-state method. Structural and electrical properties of NBT-BIT-xLa were studied. All the NBT-BIT-xLa samples exhibited a single inter-growth structured phase. XRD and Raman spectroscopy revealed a reduced orthorhombicity, which strongly supports the variation of dielectric and ferroelectric properties. Plate-like grains were found to decrease with the increasing x contents. Impedance spectra analysis indicated that oxygen vacancy defects dominated the contributions to the electrical conductivity. The increased activation energies for dc conductivity evidenced the reduction of oxygen vacancy concentration after La substitution, inducing the enhancement in piezoelectric constant (d33) and remanent polarization (2Pr). The studies of thermal depoling indicated that the optimal d33 of NBT-BIT-0.50La ceramics still remained 22 pC/N at 500°C, implying that this ceramics could be potentially applied into high temperature devices.

Morphological and Electrical Conductivity of Novel Nano Lithium Phthalocyanine Complexes

Novel nano-filament lithium phthalocyanine (LiPc) complexes with different concentrations of Li + ions have been prepared successfully via the urea fusion technique. Spectrophotometric measurements such as XRD and SEM are used to characterize the obtained nano-filament complexes. The behavior of electrical conductivity (DC and AC) for the prepared complexes at frequency range 0.1 KHz – 5 MHz and temperature 298 K ≤ T ≤ 423 K is presented. The conduction mechanism is suggested to be a result of thermal hopping of the activated electrons while at low frequency range the electrons may tunnel through the nanoparticles of LiPc complexes. The activation energies of DC-conductivity were calculated from the Arrhenius plot and ranged from 0.314 eV to 1.243 eV. These values show that the rate of electron transport depends on temperature within these ranges.

Electrical transport properties and conduction mechanisms of semiconducting iron bismuth glasses

DCelectrical conductivity measurements were carried out on iron bismuth glasses with the nominal composition (100–x)Bi2O3–x Fe2O3(where x=15, 25, 35and 45mol%) in an attempt to understand the nature of the conduction mechanism governing the DC electrical conductivity and the effect of addition of Fe2O3 on electrical properties in these glasses. The investigated glasses were prepared by a normal melt quenching technique. X-ray diffraction (XRD) patterns confirmed the amorphous nature of the present glasses. DC conductivity measurements showed an enhancement in conductivity by increasing Fe2O3 concentration. The change in activation energy of DC conductivity with temperature reveals the change in conduction mode from small polaron hopping (SPH) at high temperatures (T>θD/2) to variable range hopping (VRH) at low temperatures (T<θD/2). The conductivity results were analyzed in terms of different theoretical models to determine the possible conduction mechanism. The analysis showed that the conductivity data are consistent with Mott's nearest-neighbor SPH model. However, both Mott VRH and Greaves VRH models are suitable to explain the data. Further, Schnakenberg's polaron hopping model is also consistent with the temperature dependence of the activation energy, but the different model parameters, for example, hopping energy and disorder energy determined from the best fits were found not to be in accordance with the prediction of the SPH model.

Influence of Zn/Co ratio on dielectric behavior of Na2Zn1 ‐ xCoxP2O7 glasses

A series of zinc phosphate glass doped with cobalt Na2Zn(1 − x)CoxP2O7 (x = 0, 1, 2 and 5 mol%) was synthesized. These glasses were characterized by both infrared and large broadband dielectric spectroscopy. Infrared spectra indicate the increase of Zn/Co ratio creates defect in phosphate network due to the depolymeration of phosphate anions. The dc conductivity increases and activation energy decreases with the amount of cobalt ions in the glass network. The impedance measurements reveal that the total conductivity follows Jonscher’s power law. The dielectric constant and dielectric loss increased with the temperature and decreased with the frequency whatever the cobalt proportion.

Study of spinel-type ZnNixCo2⿿xO4 nano-particles, synthesised by thermal decomposition of ternary metal nitrate solutions

We report the structural, magnetic and electrical properties of new composition of spinel-type ZnNixCo2⿿xO4 (0.1⿤x⿤0.6) nano-particles. The X-ray diffraction and Fourier transform infrared spectroscopy studies reveal that the ZnNixCo2⿿xO4 nano-crystals show pure cubic spinal for all compositions wherein Co ions are systematically replaced by Ni ions. The electron microscopic studies reveal the nanoparticle sizes are of well-defined spherical shape and the magnetometry studies show superparamagnetic like behaviour with smaller values of coercive fields. The maximum dc conductivity at 30°C is found to be 0.03S/cm for ZnNi0.6Co1.4O4. Activation energies of dc conductivity obtained from Arrhenius plots are within the range of 0.12⿿0.35eV for extrinsic and 0.13⿿0.78eV for intrinsic regions and are affected by Ni concentration. Overall results suggest that these nano-particles are of high crystalline quality and electrical properties are dominated by holes as major charge carriers.

Dielectric and Conduction Processes and Behaviours in Ni&lt;sub&gt;0.3&lt;/sub&gt;Zn&lt;sub&gt;0.7&lt;/sub&gt;Fe&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;4&lt;/sub&gt;

Dielectric relaxation and conductivity of Ni0.3Zn0.7Fe2O4 (NZF) were studied in the frequency range between 0.01 Hz to 3 MHz and temperature range within 313 K to 473 K. The sample was prepared by mixing Zinc Oxide, Nickel Oxide and Iron Oxide and sintered at 1573 K for 10 hours long. Dielectric properties were studied using Novo Control Dielectric Spectrometer. Dielectric relaxation and conductivity phenomena were discussed using an empirical model to key out the dielectric relaxation process. Analyze peak frequency relaxation process consist of four slopes to explain the dielectric relaxation process. The conductivity of the sample indicates an activated process and activation energy of dc conductivity is 0.44 ± 0.01 eV.

Conductivity and modulus formulation in lithium modified bismuth zinc borate glasses

The conductivity and modulus formulation in lithium modified bismuth zinc borate glasses with compositions xLi2O–(50-x) Bi2O3–10ZnO–40B2O3 has been studied in the frequency range 0.1 Hz–1.5 × 105 Hz in the temperature range 573 K–693 K. The temperature and frequency dependent conductivity is found to obey Jonscher's universal power law for all the studied compositions, the dc conductivity (σdc), crossover frequency (ωH), and frequency exponent (s) have been estimated from the fitting of the experimental data of ac conductivity with Jonscher's universal power law. Enthalpy to dissociate the cation from its original site next to a charge compensating centre (Hf) and enthalpy of migration (Hm) have been estimated. It has been observed that number of charge carriers and ac conductivity in the lithium modified bismuth zinc borate glasses increases with increase in Li2O content. Further, the conduction mechanism in the glass sample with x = 0 may be due to overlapping large polaron tunneling, whereas, conduction mechanism in other studied glass samples more or less follows diffusion controlled relaxation model. The ac conductivity is scaled using σdc and ωH as the scaling parameter and is found that these are suitable scaling parameter for conductivity scaling. Non-Debye type relaxation is found prevalent in the studied glass system. Scaling of ac conductivity as well as electric modulus confirms the presence of different type of conduction mechanism in the glass samples with x = 0 and 5 from other studied samples. The activation energy of relaxation (ER) and dc conductivity (Edc) are almost equal, suggesting that polarons/ions have to overcome same barrier while relaxing and conducting.

Dielectric response and electric conductivity of ceramics obtained from BiFeO3 synthesized by microwave hydrothermal method

BiFeO3 powder which formed ball-like structures resembling flowers was obtained by microwave hydrothermal synthesis. The flowers were of a dozen or so μm in diameter and the thickness of the crystallites forming petals could be controlled. The material was characterized by X-ray diffraction, scanning electron microscopy and X-ray photoelectron spectroscopy. Dielectric response of ceramics obtained from the powder contained three extrinsic contributions, which could be correlated with the differences in temperature variation of the ac conductivity. The dielectric relaxation between 150 K and 300 K was related to reorientations of Fe3+–Fe2+ dipoles and characterized by an activation energy of 0.4 eV, which was independent of the petal thickness. The dielectric and electric response in the range 300 K ÷ 450 K usually ascribed to the grain boundary and interfacial polarization effect was diffused and could not be characterized. Above 450 K the activation energy of dc conductivity was 1.73 eV and 1.52 eV for ceramics consisting of crystallites of mean thickness of 160 nm and 260 nm, respectively. The energies, which are considerably higher than those reported earlier for BFO nanoceramics, were discussed considering the interactions between oxygen vacancies and size scaled ferroelectric domain walls, which in BiFeO3 are associated with electrostatic potential steps.

Study of conduction mechanism in Fe2O3 doped Na2O·Bi2O3·B2O3 semiconducting glasses

Conduction mechanism in Fe2O3 doped Na2O·Bi2O3·B2O3 semiconducting glass system was studied in frequency range 10Hz to 1MHz and at temperatures between room temperature and 663K. The total conductivity spectrum follows universal power law with frequency exponent ‘s’ value less than unity and lies in the range 0.51≤s≤0.78. These ranges of ‘s’ values indicate that the carrier transport is predominately due to hopping electrons between charged defects and show temperature dependence as predicted by correlated barrier hopping (CBH) model. The change in activation energy of dc conductivity with temperature reveals the change in conduction mode from small polaron hopping (SPH) at high temperatures (T>θD/2) to variable range hopping (VRH) at low temperatures (T<θD/2). The range of density of states at Fermi level N (EF)=7.25×1021–1.32×1021eV−1cm−3 at temperatures below θD/2 corresponds to localized states near Fermi level. The large values of activation energy W2 (0.067–0.155eV) dominated the conduction may results in high range of temperature (T=503– 423K) for variable-range hopping conduction in these glasses.

Effect of sulfur on dielectric properties of Cd–Se Glassy system

Cd4Se96−xSx with x = 0, 4, 8, 12 amorphous semiconductor has been prepared by melt-quenching technique. Bulk samples in the form of powder were characterized by XRD which shows the amorphous nature of the prepared samples. The dielectric parameters were studied in the temperature range of 300–350 K and in the frequency range of 20 Hz–1 MHz. Dielectric dispersion are observed in the Cd–Se–S system, these results are explained on the basis of dipolar type of dielectric dispersion. It is also observed that DC conductivity increases and activation energy decrease with increase of sulfur concentration, which is mainly due to increase in the density of localized state in the mobility gap or decrease in the band gap.