Dc Activation Energy Research Articles

Dielectric, impedance and modulus spectroscopy of Ta-based layered perovskite

ABSTRACTPbBi2Ta2O9 ceramic samples were fabricated by high-temperature mixed oxide method. X-ray diffraction determines the structure as orthorhombic. The scanning electron microscopy confirms the formation of densely packed grains in the sample. The dielectric measurements, complex impedance and complex modulus study were carried out in a frequency range of 1 kHz–1 MHz and a temperature rangeof 25–500°C. The conduction mechanism of the material is discussed in details using variable range hoping, nearest neighbor hopping relaxation model and dc activation energy at two different temperature regimes. From the J-E characteristics studies, the occurrence of non-linear curves endorses the non-Ohmic nature of the material.

Effect of neodymium doping on electrical properties and relaxor ferroelectric behavior of YCrO3 nanoparticles

In this research paper we have discussed the electrical, relaxor ferroelectric and ferromagnetic properties of Neodymium (Nd) doped YCrO3 nanomaterial prepared by sol-gel method. The characterization of the samples is followed by X-ray diffraction (XRD) and Transmission electron microscope (TEM). Upon Nd doping the conductivity of the YCrO3 enhances and the samples show semiconducting behavior. It is also found that the dc activation energy is decreased with the increasing doping concentration. Dielectric permittivity supports the modified Cole-Cole model with dc conductivity contribution correction. Both the space charge and free charge carrier dependent conductivity values increase with the increase of doping content. The frequency dependent conductivity study suggests the Dyre's free energy barrier model. Diffused relaxation peak has been observed in different doped samples. The diffuseness factor γ increases with increasing Nd doping concentration. Enhanced relaxer ferroelectric behavior has been noticed with the increasing Neodymium doping content in YCrO3.

Phase formation process of AlSb thick films prepared by screen printing and sintering method

Aluminum antimonide (AlSb) is a promising semiconductor candidate for photovoltaic and opto-electronic applications. In this study, ∼200 μm thick AlSb films were prepared by screen printing and sintering method. To clarify the phase formation process during sintering, TG/DSC analysis, XRD analysis, SEM observations (combined with EDS line scans) and DC conductivity measurements were carried out. DSC curves and XRD patterns confirmed that the solid–solid reaction, Sb melting, solid–liquid reaction, Al melting, liquid–liquid reaction occurred in sequence with increasing temperature within the Al-Sb system, and AlSb phase was mainly generated at the liquid–liquid reaction stage. Moreover, SEM characterizations illustrated that the films sintered at liquid-liquid stage showed extremely different morphologies with the films sintered at solid–solid and solid–liquid reaction stages, the films were highly developed and large AlSb particles distributed in them. Finally, the semiconducting nature of the films was affirmed by DC conductivity measurements, both resistivity and activation energy increased with increasing sintering temperature owing to the formation of more AlSb phase under higher sintering temperatures.

Electrical conductivity and dielectric behaviour of lithium diborate glasses containing Gd3+ ions

The electrical conductivity and dielectric characteristics of gadolinium doped lithium diborate samples were analysed by the impedance spectroscopic method in temperature and frequency range of 393 K–573 K and 100 Hz–5 MHz respectively. Obtained dc activation energy values with Arrhenius plots vary non-linearly with Gd3+ ions. Increase in dielectric loss and dielectric permittivity were observed with temperature variation and results were analysed on the basis of frequency dependent electron hopping in addition to the electron polarization. Modified KWW model was fitted on account of asymmetric nature in the frequency response of shape parameters. The imaginary part of complex electric modulus obtained from the fit were found to be consistent with glass composition. The conductivity modulus was reasonably fitted with stretched exponential relaxation functions and the stretched exponential values were found to be independent of temperature.

Influence of La3+ and V5+ doping on the polarization and impedance behaviour of BaBi2Nb2O9 nano-ceramics prepared by chemical route

The effect after the incorporation of La3+ and V5+ on BaBi2Nb2O9 ceramics was investigated by the analysis of structural and electrical studies. The materials are synthesized using chemical precursor solution decomposition method. Single orthorhombic phase was established after calcined the precursor mass at 700 °C for 3 h studied using X-ray diffraction study. The morphology of the samples was studied using scanning electron micrograph and transmission electron micrograph. The Curie temperature was increased with increasing substitution. High relaxation behaviour was observed during impedance spectroscopy study. For higher substitution both grain and grain boundary conductivity appears in the samples. The dc activation energy was in the range of 1.13–1.43 eV which are lower than the relaxation activation energy. The polarization of all the samples increases with increasing electric field. BBLNV0.5 showed the highest energy efficiency about 86%.

Investigation on the lithium ion dynamics in the context of microscopic length scale in zinc borophosphate glass

Dynamics of lithium ions in lithium borophosphate glass has been investigated. The mean square displacement of the lithium ions in the conduction process through the glass matrix has been estimated by using linear response theory. The lithium ions perform diffusive motion in long time scales but perform non-random correlated motion in short time scale. A new model has been proposed in the context of jump relaxation theory of K. Funke to investigate the time and temperature dependence of the mean square displacement. Experimental data can be successfully fitted with this model. Two types of activation energies such as ac activation energy and dc activation energy play a key role in ion dynamics. Perfect superposition of the mean square displacement curves at different temperatures indicates that the dynamics of the lithium ions is independent of the temperature.

Electronic Transport Mechanisms in PVDF/ZnO Nanocomposite Films

In this report, we present fundamental DC conduction mechanisms of pol-yvinyl difluoride/nano-zinc oxide (PVDF/ZnO) composite films. Nano-composite films of zinc oxide in the PVDF matrix have been fabricated via a solution casting method. Space charge limited conduction (SCLC) was found to be a prominent conduction mechanism in higher voltage region and Schottky- Richardson mechanism was a possible conduction mechanism in a higher temperature region. DC activation energy for composites was found to decrease with increasing concentration of ZnO nanoparticles and reduced graphene oxide (RGO) with 1.41 eV (9.9 wt%), 1.04 eV (33.33 wt%), and 0.95 eV (33.33 wt% RGO), respectively.

Facile Synthesis and Conductivity Studies of Multifunctional [CGN]/[LNS] Composite Material as Relaxor Dielectric

In the present study, a composite material of doped ceria and lithium sodium sulphate for its structural and electrical properties was investigated for multipurpose applications. Analysis revealed composite to be capable of being used as relaxor dielectric, dielectric resonator antenna for radio signals, NTC thermistor, oxygen sensor, MOSFET, humidity sensor, multilayer capacitor, low sintering dielectric and electrolyte material in solid oxide fuel cells (SOFCs). Composite with a ratio of [Ce0.5Gd0.25Nd0.25O2−δ]0.8 (CGN)/[(Li0.8Na0.2)2SO4]0.2 (LNS) was prepared. The composite was sintered at 500 °C for 20 min. X-ray diffraction (XRD) revealed cubic crystal structure of CGN and hexagonal crystal structure of LNS. AC electrical properties including dielectric loss tangent (tanδ), dielectric constant (e′), and ac electrical conductivity (σac), were analysed for CGN and CGN/LNS as a function of frequency (20 Hz–3 MHz) at temperatures 30–400 °C. Moreover, ac electrical properties were also analysed as a function of temperature (30–650 °C) at a fixed frequency. Composite showed dielectric constant of 2.87 × 105 at 400 °C and 1 kHz frequency. Composite showed a relaxor type behaviour. Composite also showed a maximum ac conductivity of 1.23 S m−1 at 480 °C and minimum impedance of 3 Ω at 600 °C. Samples also showed proton conductivity at lower temperatures. Cole–cole plots were also studied for the composite. DC electrical conductivity and activation energy of CGN and CGN/LNS was analysed using two probes method in a temperature regime of 30–600 °C. DC conductivity increased from 0.005 to 0.25 S m−1 in the composite (compared to single phase CGN) at 550 °C. Activation energy of the above-mentioned samples was also determined.

Ionic Conductivity in Lithium-Borate-Tantalate Compound Glasses

We have investigated the ionic conductivity and dielectric relaxation in Li2B4O7 (LBO) and Li2OB2O3-Ta2O5 (LBTO) glasses. The sample was synthesized by using the melt quenching method. The frequency dependence of the electrical data from the LBO and LBTO glasses has been analyzed in the frameworks of the impedance Cole-Cole formalism and the universal power-law representation driven by the modified fractional Rayleigh equation. The potential barriers in the LBO and the LBTO glasses turn out to be the same. Comparing with the dc and ac activation energies of the LBO glass, these energies of the LBTO glass decrease due to the increasing Coulomb interaction of inter-cationic interaction.

Enhancement in magnetic and electrical properties of Ni substituted Mg ferrite

Abstract In this work, Ni substituted magnesium spinel ferrites having general formula Mg1−xNixFe2O4 (where x = 0.0, 0.1, 0.15, 0.2, 0.25 and 0.3) were synthesized by standard solid state reaction method. All the samples were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), vibrating sample magnetometer (VSM), DC resistivity measurements. X-ray diffraction analysis confirmed the single spinel phase. The lattice constant decreased with increasing Ni content due to the difference in the ionic radii of Mg2+ and Ni2+ ions. The FT-IR spectra reveled two prominent frequency bands in the wave number range of 400 cm−1 to 600 cm−1, which confirmed the cubic spinel structure of obtained compound and completion of chemical reaction. Magnetic studies revealed that the saturation magnetization increased with the substitution of Ni. The increase in magnetization was explained on the basis of distribution of magnetic and non-magnetic cations among A and B sites of the spinel lattice. A significant influence of cation distribution on DC electrical resistivity and activation energy was observed.

Almond-West type grain and grain boundary conduction-modified dielectric relaxation in NdCoO3

In this present work, the bulk NdCoO3 was prepared via conventional solid-state synthesis route and its single-phase formation with a cubic crystal structure of space group Pm$$\bar {3}$$m [No. 221] were investigated with a perspective to understand its grain and grain-boundary contribution in dielectric and conduction processes. A general equation for grain and grain-boundary contribution in conduction-modified dielectric relaxation processes for ionically conducting material was proposed the first time and also correlated with our experimental observation, $$\epsilon {\left( \omega \right)_{total}}={\epsilon _\infty }+\frac{{{\epsilon _{\text{s}}} - {\epsilon _\infty }}}{{1+{{\left( {\frac{{i\omega }}{{{\omega _r}}}} \right)}^{1 - \alpha }}}}+\frac{{{\sigma _0}}}{{{\epsilon _{0{{{\omega}}}}}}}\left[ {1+i{{\left( {\frac{\omega }{{{\omega _h}}}} \right)}^{{n_1}}}+i{{\left( {\frac{\omega }{{{\omega _h}}}} \right)}^{{n_2}}}} \right]$$where (ωr, α), (ωh, n1) and (ωh, n2) couples explain the lattice and charge carriers responses for grain and grain boundary respectively. The relaxation-type conduction-modified dielectric behavior was observed from low to high-frequency region (100 Hz–1 MHz) and fitted conduction spectra with modified Jonscher power law which reveals the existence of grain and grain boundary effect with dc activation energy 0.86 eV. The impedance response was resolved into two contributions associated with intra-grain (bulk) and inter-grains (grain boundary) and the grain boundary resistance and capacitance exhibit a higher value than its grain counterparts. The suppressed and asymmetric semicircle in the Cole–Cole plot of impedance confirms the existence of the non-Debye-type of relaxation in NdCoO3.

Facile synthesis, structural, electrical and dielectric properties of CdSe/CdS core-shell quantum dots

Quantum dots (QDs) consisting of CdSe (core) with CdS (shell) were synthesized by an organometallic precursors method. The average sizes of CdSe/CdS core-shell quantum dots were estimated from X-ray diffraction by Debye-Scherer formula and compared with high resolution electron microscopy (HRTEM). The shape of CdSe/CdS QDs was nearly spherical and reveals that the CdS shell almost fully cover the CdSe core with thickness of 0.7 nm. DC and AC conductivity, dielectric loss, and dielectric constant of CdSe/CdS core-shell QDs were described. The electrical properties of nanoparticles pellet of CdSe/CdS core-shell QDs were studied over a temperature range from 323 to 453 K. The values of dc activation energy and the pre-exponential were determined. The ac conductivity was found to increase with the increase of both the temperature and the frequency, and follows the power low. The frequency exponent s was found to decrease with the increase of temperature. The correlated barrier hopping (CBH) model was found to be applying to the ac conductivity data. The observed properties of the prepared CdSe/CdS core-shell QDs demonstrated the capabilities of these nanomaterials as a good candidate in the optoelectronics and photonics devices.

Electrical conduction and switching properties of As2O3·V2O5·FeO glasses

Electrical conductivity, negative resistance and joule heating characteristics for x%As2O3·(80-x)%V2O5·20%FeO bulk glasses with (25 ≤ x ≤ 45), have been investigated at various temperatures, frequencies and thicknesses. Electrical conductivity is found to increase from 3 × 10−5 to 0.012 Ω−1 m−1 depending on the composition. The experimental results for electrical conductivity has been analyzed using varies models. The dc activation energy (Edc) is estimated to be in the range 0.25–0.5 eV depending on the value of x. According to the multi phonon hopping model, the dc conductivity is found to be relative to Tp with the exponent p between 8.2 and 10.5. The fitted data of the ac conductivity according to Dyre’s percolation path approximation and Almond–West power law equation showed an excellent collapse to a single master curve. This indicates that there is a good time–temperature superposition in these glasses. Threshold switching type is detected in all the samples with maximum current of about 3 mA. The threshold voltage Vth values are affected by ambient temperature, sample thickness and sample composition ratios. The activation energy for switching is found to decrease with increasing the percentage of As2O3. Variations of the surface temperature during the switching cycles suggest the applicability of the electrothermal mechanism.

Conductivity spectra of silver-phosphate glass nanocomposites: Frequency and temperature dependency

A series of glass nanocomposite systems of the composition xAgI–(1 − x) (0.5Ag2O–0.5P2O5) for x = 0.1, 0.2, 0.3 and 0.4 have been prepared by conventional melt quenching route. The X-ray diffraction patterns indicate the amorphous nature of all the glassy samples with the presence of a certain amount of crystallinity, superposing over broad peaks. Different types of bonds, existing within present system have been identified by FT-IR measurement. The dc and ac conductivity decreases with AgI content. The values of activation energy for dc conductivity and activation energy for crossover frequency are very close to each other, which specify that the same mechanism is responsible for the electrical conduction. The ionic conduction depends on the Agion–Agion separation (R), which increases with a rise in AgI content. The absence of grain boundary effect is observed from complex impedance plots. The formation of the cation-electron pair with increasing AgI content is expected to block the diffusive or hopping path, which indicates fall in conductivity. Correlated barrier hopping (CBH) model is the appropriate mechanism for ac conduction process. The temperature and composition scaling of conductivity spectra reveals that the conductivity relaxation is independent of temperature but depend on composition i.e., the structure of the glass nanocomposites.

Investigation of optical, electrical and magnetic properties of hexagonal NiTiO3 nanoparticles prepared via ultrasonic dispersion techniques for high power applications

Nickel titanate (NiTiO3) nanoparticles were synthesized by ultrasonic dispersion techniques using ethylene glycol monoetheline ether as a solvent. The x-ray diffraction (XRD), Raman, transmission electron micrographs (TEM) exhibit pure phase formation, fine hexagonal nanostructure, agglomerated and inhomogeneous grain growth in nm range (26.5 nm) of as-prepared NiTiO3 nanoparticles. Raman studies on NiTiO3 nanoparticles exposed almost all the active vibrational modes (5Ag + 5Eg) of its crystalline structure. A wide optical band gap (3.02 eV) was observed from UV-DRS spectra which arises from the hybridized Ni- 3d and O- 2p orbitals to the Ti -3d orbitals. The characteristics vibration bands of M-O (Ni–O, and Ti–O) were also analyzed using Fourier Transform Infrared spectrum. The antiferromagnetic (AFM) properties were examined from M-H loop with coercive field 75.02 ± 0.05 Oe and saturation magnetization 0.418 ± 0.05 emu gm−1. respectively. The dielectrics constant and loss decays with high frequency evaluation and Maxwell–Wagner type of polarization were responsible for its dielectric behavior. The total conductivity was explained using NNH and VRH hopping relaxation model and dc activation energy (0.81 eV) were calculated from Arrhenius plot.

Synthesis and study the physical properties of the nanosized Li0.5AlxFe2.5-xO4 samples

Nanoparticles of Li0.5AlxFe2.5-xO4 (x = 0.00, 0.15, 0.25, 0.35, 0.45) have been synthesized by using a chemical auto-combustion method. The effect of varying Al3+ ions content on the microstructure, magnetic, thermal, and dc electrical conductivity, mobility and activation energy of the as-prepared nanosamples have been studied. The obviously low loss thin hysteresis curve of the M-H relation reveals that the present materials are classified soft magnetic. The dependence of magnetic properties on adding Al3+ ions is explained as due to many factors such as crystallite size, measured density, porosity, expected cation distribution, and magnetocrystalline anisotropy. The cation distributions for all samples have been suggested such that the experimental and theoretical values of magnetic moments and lattice constants are in good consistency. Moreover, the pure Li-ferrite sample of (x = 0) has lower values of thermal conductivity, specific heat capacity, and thermal effusivity; and higher values of thermal diffusivity than those of the Al substituted Liferrite samples. The reasons of this behavior have been discussed. Also, the temperature and the chemical composition dependence of dc conductivity and drift mobility of the prepared samples have been studied.

Structural, optical and photoelectrical properties of thermally annealed amorphous In15Sb15Se70 chalcogenide films

In this work, the effect of annealing on the structure and photoelectrical properties of In15Sb15Se70 films has been investigated. The annealed films (333–453 K) were characterized by XRD, SEM, TEM, optical absorption, Raman spectroscopy and photoconductivity measurements. The amorphous/crystalline structure of as-prepared and annealed samples was confirmed by XRD and SEM/TEM studies. The crystallization of Se, Sb2Se3 and In4Se3 phases has been observed upon annealing of the film samples. The position and shape of Raman bands have been significantly altered with annealing temperature. The indirect optical gap varies from 1.53 to 1.08 eV which is very useful for solar cell applications. DC activation energy and photosensitivity were found to decrease with annealing temperature. The decay of photocurrents was well fitted to stretched exponential function and the minimum value for fit parameters for the sample annealed at 373 K has revealed least defect states in mobility gap for In15Sb15Se70 films.

Influence of Zn Substitution on Structural, Magnetic and Electrical Properties of MgFe2O4

Polycrystalline spinel ferrites Zn x Mg1−xFe2O4 (where x = 0.0, 0.1, 0.15, 0.2, 0.25 and 0.3) were prepared by standard ceramic method and characterized by x-ray diffraction, Fourier transform infrared spectroscopy (FTIR), and vibrating sample magnetometer. Structural, electric and magnetic properties have been discussed in detail on the basis of Zn composition. The composition shows formation of a single-phase cubic spinel structure and the lattice constant ‘a’ increases with increasing Zn concentration. FTIR spectra show two prominent frequency bands in the wave number range 400–600 cm−1, which further confirms the cubic spinel structure and completion of chemical reaction. Magnetic studies revealed that the saturation magnetization increases with increasing the substitution of Zn. Cation distribution for the present system was estimated by comparing observed and calculated x-ray line intensities. From this it is observed that Zn2+ ions prefer to occupy A sites, and Mg2+ and Fe3+ ions distributed into both A and B sites. The observed variation in magnetization has been explained on the basis of distribution of cations among A and B sites of the spinel lattice. A significant influence of cation distribution is observed on DC electrical resistivity and activation energy.

Optical and Electrical Properties of Nd3+ Doped TeBiY Borate Glasses

60B2O3-30Bi2O3-5TeO2-(5–x)Y2O3-xNd2O3 mole% (0 ≤ × ≤ 4) glasses were prepared by the usual experimental glass-melting procedures. This work was carried out to study the effect of Nd2 O 3 on the properties of the glasses studied and thereby their structure. The effect of the replacement of Y2O3 by Nd2O3 on the optical and electrical properties of the glass samples was studied. The results obtained showed that the values of density, oxygen packing density, concentration of Nd ions and field strength were found to increase with increase of the Nd2O3. On the other hand the molar volume, inter-nuclear distance and polaron radius showed the opposite behavior with increasing Nd2O3 content. The results also showed that the direct and indirect optical band gap were found to increase which indicate that increasing the concentration of Nd2O3 leads to a change in the structure of glasses induced by Nd2O3. Dc and ac conductivities values were found to increase, whereas the dc activation energy decreases, with increasing Nd2O3 concentration. An increase in the dielectric constant values with increasing Nd2O3 content is observed. The results suggest that the CBH model seems to be the appropriate model for the ac conductivity in the studied glasses.

Electric transport and enhanced dielectric permittivity in pure and Al doped NiO nanostructures

In this paper, we have studied the electrical and transport properties of Ni1-xAlxO(x = 0.00, 0.01, 0.03, 0.05) nanoparticles which have been synthesized through wet chemical route via a sol-gel method at 600 °C. The XRD patterns reveal that the NiO nanoparticles have a cubic polycrystalline crystal structure with average crystallite size ranging from 18.20 nm to 9.54 nm and 17.20 nm to 11.53 nm which are calculated by Debye-Sherrer and William Hall method, respectively. The morphology and size of the nanoparticles have also been observed by Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) for pure and Al-doped (5%) NiO nanoparticles. We have also studied the DC resistivity and activation energy (0.19 eV-0.49 eV) of our samples using two probe measurement. It is observed that pure and Al-doped NiO nanoparticles exhibit a giant value of dielectric permittivity (103-104). The high value of dielectric constant of Al-doped NiO nanoparticles depends on Al concentration and can be ascribed to the thermally activated and Maxwell–Wagner polarization mechanism.