AC Conductivity Behavior Research Articles

Size and Temperature Effect on Electrical Conductivity, Dielectric Properties, and Electrical Switching Memory Application of Nanocrystalline Na-DDQ (Metal-Organic Frameworks) Thin Films

Organometallic Sodium-2,3-Dichloro-5,6-dicyano-p-benzoquinone (Na-DDQ) films were synthesized using a conventional thermal vacuum deposition technique at ambient temperature. DC electrical resistivity was measured over a wide range of thicknesses and temperatures. This helps in investigating the different size-effect parameters, for instance the bulk mean free path (λ o ), bulk resistivity (ρ o ), grain-boundary transmission coefficient (t), surface scattering factor (p), external surface parameters (U), and grain-boundary parameter (V) in specular and non-specular conditions. The contribution of grain-boundary and surface resistivity to total resistivity was then estimated. Additionally, the AC conductivity (σ ac ) and dielectric (ε) behavior of Na-DDQ films were examined at the same temperature in the frequency range (50 Hz-5 MHz). Thus, the temperature dependence of frequency exponent factor (s) was calculated and interpreted in terms of various conduction models. The AC activation energy and its frequency dependence were extracted. The dielectric properties were attributed using electric modulus and complex permittivity of the studied films. Finally, Na-DDQ films showed a memory and switching behavior during the I–V characterization, the On-Off states were observed by applying an external electric field. Hence, the switching parameters for instance threshold voltage (Vth), switching time (τ s) and delay time (τ d) of samples were evaluated.

Structural, AC conductivity, dielectric and catalytic behavior of calcium oxide nanoparticles derived from waste eggshells

Calcium Oxide (CaO) nanoparticles have been synthesized from waste eggshells (ES) as a source of calcium by solution combustion technique using muffle furnace and microwave oven. CaO nanoparticles obtained using muffle furnace (CaO-F) and via microwave oven (CaO-M) were characterized using X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, AC conductivity and dielectric studies to correlate the physico-chemical behavior. The frequency dependence of AC conductivity, the permittivity (ε′) and dielectric loss tangent (D) studies have been undertaken in the frequency range 50 Hz–5 MHz at room temperature. AC conductivity was found to enhance with an increase in the frequency. The ε′ was found to decrease initially with the frequency and finally reaching a constant value at higher frequencies. The frequency dependence of D was found to exhibit a resonance peak in the studied frequency region. Catalytic activity of CaO-M was correlated with its dielectric behavior.

Vibrational analysis and AC electrical conduction behavior of lithium zinc orthogermanate

The lithium zinc orthogermanate, Li2ZnGeO4, was synthesized by the solid-state reaction and characterized by X-ray diffraction (XRD) and electrical technique. Li2ZnGeO4 is of monoclinic symmetry with the space group P n. The unit cell parameters are as follows: a = 6.368(2)A, b = 5.438(2)A, c = 5.034(1)A, β = 90.191(0)°, and V=174.360(1)A3. The electrical measurements were carried out by impedance spectroscopy in the temperature and frequency range (553–653)K and (40 Hz to 1 MHz), respectively. The AC conductivity was interpreted using Jonscher’s law. s parameter decreases while the temperature increases indicating that the CBH model is the most reasonable mechanism of AC conduction behavior. Thermodynamic parameters such as the enthalpy ΔH and the change in entropy ΔS have been calculated. The negative value of ΔS may be due to the existence of dipole-dipole interactions and suggests that the molecules are more nearly aligned with each other in the activated state.

Effect of Fe Substitution on Dielectric, Electrical and Photocatalytic Behavior of ZnO Nanoparticles

Aims: To develop a simple and cost effective synthetic strategy for the preparation of Fe substituted ZnO nanoparticles. Background: The optoelectronic, electrical, dielectric, optical and magnetic properties of nanocrystalline transition metal substituted ZnO are being explored worldwide for a variety of applications in optoelectronic devices, solar cells, transparent thin film transistors, ultraviolet photodetector, piezoelectric devices, light emitting diodes as well as in the biomedical field. Fe substituted ZnO nanoparticles are being looked upon as promising material in dilute magnetic semiconductor system. Objective: To establish chemical identity and purity in order to ensure the complete substitution of Fe3+ in ZnO lattice and study the effect of Fe substitution on dielectric, electrical and photocatalytic behavior of ZnO nanoparticles. Methods: The nearly spherical ZnO and Fe substituted ZnO nanoparticles were synthesized at a low temperature via solution combustion synthesis employing metal nitrate and sucrose. Results: The powder X-ray diffraction measurement has revealed the monophasic character and complete substitution of Fe in the wurtzitic ZnO lattice. The lattice constants and aspect ratio of Fe substituted ZnO were nearly constant and comparable to that of pristine ZnO. The average crystallite size was found to decrease with increasing Fe substitution. SEM images revealed porous spongy network like morphology. TEM measurements revealed a nearly spherical particle with narrow size distribution between 10 nm - 25 nm. Conclusion: The dielectric constant and dielectric loss decrease upto x = 0.04 and increases with further increase in Fe concentration. The lower value of dielectric loss in the higher frequency region indicates the less lossy nature of Fe substituted samples. AC conductivity behaviour suggests small polaron hopping type of conduction mechanism. The RT DC resistivity was found to decrease with increasing Fe substitution. Pristine ZnO displayed very high degradation efficiency for photodegradation of MB dye. The photodegradation efficiency was found to decrease considerably with increasing Fe substitution.

Effect of Polaron formation in conduction and dielectric behavior in La0.7Sr0.25K0.05MnO3 oxide

The purpose of this paper is to analyze the dielectric properties of La0.7Sr0.25K0.05MnO3 (LSKM) using impedance spectroscopy over the frequency range of 100 Hz to 1 MHz at different temperatures from 260 to 380 K. In fact, the dielectric analyses of the sample showed two relaxation processes at different relaxation times related to the effect of microstructural inhomogeneities and the contribution of grain and gain boundaries. However, Ac conductivity behavior reveals a metal–semiconductor phase transition at a specific temperature TM-S = 260 K and showed an important impact of the electron–lattice interaction in polaron formation. Also, the conductivity curve is analyzed by Johnscher’s universal power law and the variation of the exponent ‘n’ with temperature suggests the domination of small polaron hopping (SPH) model governed by an activation energy Ea = 0.12 eV. Further investigations using modulus formalism proved the presence of electrical relaxation, which is in good agreement with impedance results. The dielectric poly-dispersive behavior is related to the conduction process and the large value of the dielectric constant $$\varepsilon^{\prime\prime}(\omega )$$ in the order of 106 is correlated to the Maxwell–Wagner relaxation.

AC conductivity and dielectric properties of 98[20Li2O-xBi2O3-(80-x)TeO2]-2Ag mixed ionic-electronic glasses

Mixed ionic-electronic 98[20Li2O-xBi2O3-(80-x)TeO2]-2Ag (x = 3, 5, 7, 11, 13 and 15 mol%) glasses were prepared by melt-quenching technique to investigate their AC conductivity and dielectric properties. Structural analysis revealed the increase of non-bridging oxygen (NBO) up to x = 5 mol% before dropping at x = 7 mol% followed by a further increase at x > 7 mol%. The nonlinear behaviour of AC conductivity with Bi2O3 showed an initial increase in $$\sigma$$ AC until reaching a minimum at x = 7 and 11 mol% before increasing again at x > 11 mol%. The minimum is suggested to be due to the blocking effects of Bi2O3 towards ionic conduction caused by mixed ionic-electronic (MIE) effect. Other than that, dielectric constant displayed an anomalous decrease at x = 7 mol% followed by a steep increase at x > 7 mol%. This decrease could also be related to blocking effects induced by MIE that contributes to a reduction of space charge polarization. The anomalous decrease at x = 7 mol% coincided with a minimum of $$\sigma$$ AC for the same glass composition. Meanwhile, another nonlinear behaviour is observed on M′ with a maximum at x = 7 and 11 mol% which coincided with the location of $$\sigma$$ AC minimum that may be due to MIE effect attributed to the blocking effect of Bi2O3 to migrating ions which then led to high resistance. Electrical modulus analysis reveals the non-Debye relaxation nature for the glass samples indicating the presence of dynamic ions processes.

High-temperature dielectric behavior of hexagonal HoMnO3

The ac electrical response of hexagonal HoMnO3 was investigated in the temperature range 340≤T≤700K. The combination of impedance and electrical modulus spectra reveal a single dielectric relaxation. However, the ac conductivity in the range 340≤T≤600K revealed two electro-active regions with dissimilar activation energies associated with grain and grain boundary regimes. We suggest that grains have the largest capacitance, whereas grain boundary dominates the overall resistance of the sample. The most interesting was the first-hand observation of a positive temperature coefficient of resistance (PTCR) effect in HoMnO3, and the sample behaves as an extrinsic semiconductor material. Both bulk effects and grain boundary were observed to contribute together to the PTCR phenomena. A correlation between the ac conductivity and dielectric data was built up. Results show that oxygen non-stoichiometry and associated electron holes are liable for the complex dielectric behavior. The scaling behavior of ac conductivity was studied using different formalisms.

Dielectric properties and ac conductivity behavior of rGO incorporated PVP-PVA blended polymer nanocomposites films

We have reported dielectric and ac conductivity investigations on reduced grapheme oxide (rGO) incorporated PVP-PVA blend polymer nanocomposite films (BPNC) prepared via standard solution casting technique. The dielectric properties and ac conductivity have been explored using the complex electrochemical impedance technique that has been studied at room temperatures. The frequency-dependent dielectric constant (εʹ) is maximum at low frequencies region which value increases with increasing rGO concentration, while at higher frequency region their value decreases with increasing frequency for all BPNC films. The appearance of the loss tangent (tanδ) peaks at specific frequency suggested the existence of recline dipoles which has been found to shift towards high frequency side with increasing weight ratios of rGO in all the BPNC films. The fluctation of a.c conductivity behavior as a function of frequency follow Jonscher Power-law model. The a.c. conductivity shows an increasing trend with an increase in the doping concentration of rGO. The electrical modulus has been examined for supporting the complex permittivity part. The relaxation peaks occur in electric modulus (M“) indicates the presence of orientation dipoles in the blend polymer nanocomposites, which support the fast ion conduction.

Development of hydroxyapatite nanoparticles reinforced chlorinated acrylonitrile butadiene rubber/chlorinated ethylene propylene diene monomer rubber blends

AbstractHydroxyapatite nanoparticles (HA) reinforced polymer blend based on chlorinated nitrile rubber (Cl‐NBR) and chlorinated ethylene propylene diene monomer rubber (Cl‐EPDM) were prepared. Resulting blend composites were analyzed with regard to their rheometric processing, crystallinity, glass transition temperature (Tg), mechanical properties, oil resistance, AC conductivity, and transport behavior. The decrease in optimum cure time with the addition of HA is more advantageous for the development of products from these blend nanocomposites. The XRD, FTIR, and SEM confirmed the attachment and uniform dispersion of HA nanoparticles in the Cl‐NBR/Cl‐EPDM blend. The good compatibility between polymer blend and nanoparticles was also deduced by the formation of spherically shaped HA particles in the blend matrix determined by TEM analysis. DSC analysis showed an increase in Tg of the blend with the filler loading. The addition of HA particles to the blend produced a remarkable increase in tensile and tear strength, hardness, AC conductivity, abrasion, and oil resistance. The diffusion of blend composites was decreased with an increase in penetrant size. The diffusion mechanism was found to follow an anomalous trend. Among the blend composites, the sample with 7 phr of HA not only showed good oil and solvent resistance but also a remarkable increase in AC conductivity and mechanical properties.

Effects of sintering temperature on ac conductivity, permittivity, and permeability of manganese doped cobalt ferrite nanoparticles

This paper reports on the effects of magnetic and electric properties of a non-stoichiometric composition of cobalt ferrite nanoparticles doped with manganese content at the weight percent 0.25. Its toroid and disc-shaped samples were sintered at two different temperatures 750 °C and 1050 °C. The studied results show the dependence of the permittivity and permeability on the microstructural features, particularly crystallite/grain size that change with the sintering temperature. The anomalous behavior of ac conductivity is marked outside a hump region with a decreased sintering temperature. A rightward shift of the characteristic frequency in the absorption of electric modulus is observed with the increased sintering temperature. Similarly, a rightward shift of the resonance frequency in the spectra of the imaginary part of the magnetic modulus is marked with the increased sintering temperature. The higher magnitude of the imaginary part of the electric modulus at the characteristic frequency is expected to dissipate as eddy current loss. Similarly, the higher magnitude of the imaginary part of the magnetic modulus at the resonance frequency is assumed to dissipate as a residual loss. Both of them are selectable by the sintering temperature. This behavior may make this material suitable to be used in thermoelectric and thermomagnetic sensors/switches.

Noticeable impact of Er doping on structural, vibrational, optical, dielectric and electrical parameters of flash combustion synthesized NiO NPs for optoelectronic applications

A facile synthesis of erbium doped nickel oxide (Er@NiO) was accomplished via combustion route at 550 °C within 2 h. Cubic phase of all Er@NiO samples was confirmed by X-ray diffraction (XRD) and Rietveld refinement methods. All XRD profiles were fitted well by Rietveld. XRD data was used to determine the values of size, dislocations, strain and the size was reduced from 26 to 8 nm on rising the Er content in NiO. Vibrational spectroscopy also approved the synthesis of NiO without any impurity content at all Er concentrations. The composition of Ni, O and Er was evaluated by EDX and their uniform dispersal in final product was confirmed by SEM e-mapping. Further, SEM study confirms very compact nanostructure of final products and the size reduction was observed by Er content. Kubelka-Munk methodology was employed to attain the bandgap of all Er@NiO NPs and lies between 3.17 and 3.50 eV. The ε' values are lies between 65–115 at 3 kHz and 18–36 at 3 MHz, however, it was higher for 5 wt% Er@NiO NPs compare to other at 3 kHz and lower after 7 kHz. The ac conductivity and conduction behaviour were also inveterate and conferred.

Dielectric and Thermal Properties of Tetragonal PbTiO3 Nanoparticles/Clusters Embedded in Lithium Tetraborate Glass Matrix

PbTiO3 nanoparticles/clusters embedded in lithium tetraborate glass matrix (glass nanocomposite (GNCs)) of composition (100-x) Li2B4O7-xPbTiO3 (where x = 5, 10, 15 and 20 in mol %) were synthesized. The presence of glassy phase in all GNCs samples was identified by X-ray diffraction (XRD) and differential scanning calorimetric (DSC) studies. The structure of PbTiO3 used in the preparation of these samples is a ferroelectric tetragonal phase (space group P4mm) which is confirmed by Rietveld refinement of XRD data. Transmission electron microscopic (TEM) images exhibit PbTiO3 nanoparticles/clusters phase embedded in lithium tetraborate glass matrix. The ferroelectric to paraelectric phase transition of PbTiO3 nanoparticles/clusters in the GNCs samples was established from DSC and dielectric studies. The thermal, density, dielectric and Ac conductivity behavior of the GNCs samples depends on the change in the coordination number of the network former and the concentration of PbTiO3 in the glass matrix.

AC conductivity and dielectric behaviour of NaNbO3 ceramic polymer composites

The sodium niobate (NN) polymer composites of different compositions were prepared using solution casting method. The prepared polymer composite film samples were characterized by XRD to study the microstructure of the composites. The SEM studies on composite films revealed a better dispersion of ceramic crystallites in the host matrix. The dielectric constant (∊r) and the ac conductivity of the composites with different concentrations at various frequencies (100 Hz–5 MHz) were investigated. The results showed an increment of dielectric constant of NN-PVA (polyvinyl alcohol) composites with ceramic concentration and ac conductivity of the sodium niobate composites increased with increasing frequency. The complex impedance of the composites were also calculated to understand the dielectric behaviour of the composites.

X-Band Microwave Absorption in Nd³⁺-Substituted Mg–Cd Spinel Ferrites Synthesized Under Microwave Sintering

The electromagnetic parameters and microwave-absorbing properties of Nd3+-substituted Mg–Cd spinel ferrites with the chemical formula Mg x Cd1– x Nd0.03Fe1.97O4 (where $x = 0$ , 0.2, 0.4, 0.6, 0.8, and 1.0) were investigated using vector network analyzer (VNA) in conjunction with the material measurement software. The permittivity of all the ferrites follows the usual dispersion behavior in the microwave frequency range. The behavior of ac conductivity and dielectric losses with frequency for various Mg content is quite similar. The variations in permeability with frequency for compositions with $x = 0.4$ , 0.6, and 1 in the frequency range of 10–12.4 GHz obeys Snoek’s law. The peaks observed in the magnetic loss tangent spectra may be due to spin rotation created in the ferrites. With an increase in magnesium content, the reflection loss peak gets deepened, signifying the increased improvement in the absorption properties. Thus, it can be stated that Mg-substituted Cd–Nd ferrites have better performance when compared with pure Cd–Nd ferrite, proposing it to be a suitable material for electromagnetic shielding applications in the $X$ -band.

Development of novel elastomeric blends derived from chlorinated nitrile rubber and chlorinated ethylene propylene diene rubber

Chlorinated nitrile rubber (Cl-NBR) has been blended with chlorinated ethylene propylene diene rubber (Cl-EPDM) in different ratios by a conventional mill mixing method. The effect of the blend ratio on processing characteristics, mechanical properties (such as tensile and tear strength, elongation at break, hardness, abrasion resistance, heat build-up and resilience), structure, morphology, glass transition temperature (Tg), thermal stability, flame retardancy, oil resistance, AC conductivity, dielectric properties and transport behavior of petrol, diesel and kerosene were investigated. The shift in absorption bands of blends studied from FTIR spectra, single Tg from DSC analysis and decrease in amorphous nature from XRD showed the molecular miscibility in Cl-NBR/Cl-EPDM blends. SEM images showed the uniform mixing of both Cl-NBR and Cl-EPDM in a 50/50 blend ratio. The TGA curves indicated the better thermal stability of the polymer blend. The elongation at break, heat build-up, resilience and hardness of the polymer blend decreases with an increase in Cl-NBR content in the blend whereas the flame and oil resistance were increased with increase in Cl-NBR content. Among the polymer blends, the maximum torque, tensile strength, tear and abrasion resistance was obtained for the 50/50 blend ratio because of the effective interfacial interactions between the blend components. AC conductivity and dielectric properties of polymer blend increased with increase in the ratio of Cl-NBR in the blend. Different transport properties such as diffusion, permeation and sorption coefficient were measured with respect to nature of solvent and different blend ratios. Temperature dependence of diffusion was used to estimate the activation parameters and the mechanism of transport found to be anomalous.

Polarization induced dielectric and electrical response of electrovector hydroxyapatite and ferroelectric sodium potassium niobate ceramics

The ability of hydroxyapatite (HA) to convert readily into an electret under low polarizing fields (⩽1 kV cm−1) makes it as an excellent substitute for electro-active prosthetic implants. In the present study, compacts of electrovector HA and ferroelectric Na0.5K0.5NbO3 (NKN) were developed via the spark plasma sintering route. The compacts were then polarized at various polarizing fields of 30, 50, and 90 kV cm−1, respectively, at 150 °C, for 1 h. Thereafter, samples were depolarized at heating rates of 1, 5, and 10 °C min−1, respectively. The thermally stimulated depolarization current (TSDC) measurement reveals that the charge density in HA increases from ∼0.2 nC cm−2 to ∼2 µC cm−2 with an increase in the polarizing field from 30 to 90 kV cm−1. The dielectric (ϵ), as well as the ac conductivity behaviour of unpolarized and polarized (90 kV cm−1) HA, are compared. The activation energy is measured to be in the range of 0.6–0.7 eV, which is mainly associated with proton (H+) migration. For NKN, TSDC spectra reveal a slight shift in the phase transition temperatures (TO−T, TC) towards higher temperatures, with an increase in the polarizing field (30–90 kV cm−1) as well as the heating rate. The dielectric and ac conductivity measurements suggest that the polarization of NKN slightly decreases TO−T and TC, as compared to its unpolarized counterpart. The conductivity in NKN is mainly attributed to the migration of oxygen vacancies and n-type charge carriers. Furthermore, x-ray photoelectron spectroscopy analyses suggest that the polarization of HA at such a high field (90 kV cm−1) does not alter its surface chemistry.

Dielectric dispersion and ac conductivity behavior in tin-modified lead zirconate antiferroelectric single crystals

Frequency and temperature dielectric response and electrical conductivity behavior around the antiferroelectric–paraelectric phase transition temperature were studied in PbZr0.93Sn0.07O3 antiferroelectric single crystals. The contribution of conductive processes to dielectric relaxation for the studied frequency range is discussed, considering oxygen vacancies and electronic transport. The relaxation processes below the transition temperature are associated with short-range polaronic hopping due to the interaction of the charge carriers (trapped electrons) with the distorted crystal lattice. Based on the specific coupling between electrons and phonons in the largely distorted oxygen octahedral sublattice of PbZr1−xSnxO3 crystals, an attempt to explain the formation of the incommensurate phase was undertaken.

Grain size engineering in nanocrystalline Y2Zr2O7: A detailed study on the grain size correlated electrical properties

Abstract A set of nanocrystalline Y2Zr2O7 (YZO) ceramic materials possessing grain sizes ranging from 7 nm to 65 nm was prepared by chemical co-precipitation technique followed by conventional sintering at various temperatures. Evolution of structure and grain growth was investigated by XRD and TEM analysis. Disordered pyrochlore phase of YZO was obtained. Electrical conductivity of YZO has been increased with increasing measuring temperature as well as grain size. The behavior of total electrical conductivity comprising grain interior and grain boundary components was studied. When the grain size was increased, the activation energy for grain boundary and total ionic conduction has been decreased from 1.59 to 1.51 eV whereas the same for bulk grain conductivity remained more or less the same near to 1.43 ± 0.01 eV. The Jonscher’s universal law had explained the behavior of ac conductivity suggesting a long-range hopping of mobile ions-based conduction in YZO. In addition, Maxwell–Wagner model had explained the dielectric behavior of YZO and showed an increasing dielectric constant with increasing grain size. Electric modulus, analysed by Kohlrausch-Williams-Watts function, showed an increasing relaxation frequency at higher grain sizes. A complete electrical characterization of YZO ceramics with good correlation with their grain size is reported.

Polyethylene Composites with Segregated Carbon Nanotubes Network: Low Frequency Plasmons and High Electromagnetic Interference Shielding Efficiency.

Polyethylene (PE) based composites with segregated carbon nanotubes (CNTs) network was successfully prepared by hot compressing of a mechanical mixture of PE and CNT powders. Through comparison with a composite comprising randomly distributed carbon nanotubes of the same concentration, we prove that namely the segregated CNT network is responsible for the excellent electrical properties, i.e., 10−1 S/m at 0.5–1% and 10 S/m at 6–12% of CNT. The investigation of the complex impedance in the frequency range 1 kHz–2 MHz shows that the sign of real part of the dielectric permittivity changes from positive to negative in electrically percolated composites indicating metal-like behavior of CNT segregated network. The obtained negative permittivity and AC conductivity behavior versus frequency for high CNT content (3–12%) are described by the Drude model. At the same time, in contrast to reflective metals, high electromagnetic shielding efficiency of fabricated PE composites in the frequency range 40–60 GHz, i.e., close to 100% at 1 mm thick sample, was due to absorption coursed by multiple reflection on every PE-CNT segregated network interface followed by electromagnetic radiation absorbed in each isolated PE granule surrounded by conductive CNT shells.

AC CONDUCTIVITY AND DIELECTRIC PROPERTIES OF AMORPHOUS Se69Sn10Ge21-xSbx (6≤ x ≤14) GLASSY SYSTEM

The glassy network system under investigation is prepared by using melt quench technique. The ac conductivity and dielectric behavior studied in ac frequency range (500Hz–1MHz) below glass transformation region. The correlated barrier hopping (CBH) model is used for interpreting the relation between the frequency exponent and temperature. The equation based on the Guintini model gives the value of maximum barrier height from the dielectric measurements. The compositional variation of conduction mechanism and dielectric parameters is studied to explore material’s nature.