Ac Conductivity Data Research Articles

Effect of substrate temperature on the structural and electrical properties of La and Mn co-doped BiFeO3 thin films

The effect of substrate temperature on the structural and electrical properties of multiferroic Bi0.90La0.10Fe0.95Mn0.05O3 (BLFMO) thin films deposited on Pt (111)/Ti/SiO2/Si substrate using pulsed laser deposition (PLD) has been investigated. Films with substrate temperature ranging from 450°C to 650°C have been deposited. The grain size and roughness are found to increase with substrate temperature. The film deposited at 575°C exhibits maximum remnant polarization around 39μC/cm2 and a coercive field of 400kV/cm. The cyclic fatigue study of the sample shows only 4% loss after 108cycles. Complex impedance study of the BLFMO thin films demonstrates electrical homogeneity of the sample. AC conductivity data has been fitted using Jonscher single power law, and value of n found to be <1 indicating translational hopping conduction mechanism. The lowest leakage current found is 4.37×10−6A/cm2 at 575°C. The leakage current mechanism is found to be dominated by space charge limited current and Fowler-Nordheim conduction mechanism.

Dc conductivity of two-temperature warm dense gold.

Using recently obtained ac conductivity data we have derived dc conductivity together with free electron density and electron momentum relaxation time in two-temperature warm dense gold with energy density up to 4.1 MJ/kg (0.8×10^{11}J/m^{3}). The derivation is based on a Drude interpretation of the dielectric function that takes into account contributions of intraband and interband transitions as well as atomic polarizability. The results provide valuable benchmarks for assessing the extended Ziman formula for electrical resistivity and an accompanying average atom model.

Bottle-necked ionic transport in Li2ZrO3: high temperature neutron diffraction and impedance spectroscopy

We present a study of the crystal structure, ionic conductivity and Li migration map in a wide temperature range for the Li2ZrO3 and Li1.8ZrO3-δ samples synthesized by the solid state reaction and soft chemistry methods, respectively. Both samples were found to be Li-deficient at room temperature with the partially vacant Li[1] sites. Thermally activated redistribution of Li+ ions between two lithium sites has been revealed by high temperature neutron diffraction. The redistribution of lithium results in rise of the ionic conductivity and drop of the activation energy observed on the AC conductivity data at the temperatures above 740K for Li2ZrO3 and 710K for Li1.8ZrO3-δ. It has been found that more deficient Li1.8ZrO3-δ sample prepared by the soft chemistry method exhibits enhanced ionic conductivity. Three-dimensional lithium migration map composed of the stripe-like migration pathways has been constructed. Most of the elementary channels composing lithium migration map were found to be probabilistic ones, which indicates bottle-necked ionic transport in both compounds.

Structural and ion transport properties of [(AgI)x(AgBr)0.4−x](LiPO3)0.6 and (AgBr)x(LiPO3)(1−x) solid electrolytes

AbstractThe (AgBr)x(LiPO3)(1−x) (x=0.4 and 0.5) and [(AgI)x(AgBr)0.4−x](LiPO3)0.6 (x=0.1, 0.2, and 0.3) superionic electrolytes have been prepared by conventional melt quenching using a twin roller. These electrolytes are characterized by X‐ray diffraction, SEM, and energy dispersive X‐ray analysis (EDAX) for structural investigation. Electrical characterizations have been carried out by the AC impedance analysis. The conductivity of LiPO3 glassy system at room temperature is improved by doping with the silver bromide (AgBr)x(LiPO3)(1−x) and the mixture of silver iodide, silver bromide (AgI‐AgBr‐LiPO3 system) up to 10−5 and 10−3 Ω−1 cm−1, respectively (improvements by four or five orders of magnitude). The frequency response of ionic conductivity has been analyzed by universal dynamic response model (Jonscher's law) and AC conductivity data are fitted using the Jonscher's power law. The conductivity values obtained by the power law and impedance plots are comparable. The frequency exponent (n) has a value between 0 and 1. The AgI‐AgBr‐LiPO3 system shows the mixed alkali effect. Summerfield scaling master curve is temperature dependent, which may be due to the contribution of the both lithium and silver ions to ionic conduction.

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.

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.

Electrical, dielectric and photocatalytic properties of Fe-doped ZnO nanomaterials synthesized by sol gel method

Fe-doped ZnO nanoparticles were synthesized by sol gel technique. Fine-scale and single phase hexagonal wurtzite structure in all samples were confirmed by SEM and XRD, respectively. The band gap energy depends on the amount of Fe and was found to be in the range of 3.11-2.53 eV. The electric and dielectric properties were investigated using complex impedance spectroscopy. AC conductivity data were correlated with the barrier hopping (CBH) model to evaluate the binding energy (Wm), the minimum hopping distance (Rmin) and the density of states at Fermi level, N(EF). Fe doping in ZnO also improved the photocatalytic activity. Thus, the sample Zn0.95Fe0.05O showed high degradation potential towards methylene blue (MB), i.e. it degrades 90% of BM in 90min under UV light.

Influence Of Gd On Structural And Impedance Properties Of Multiferroic Composites: BiFeO3-PbTiO3

The Gd-modified BiFeO3-PbTiO3 composites i.e. 0.5BiGdxFe1-xO3-0.5PbTiO3 (BGxF1-x-PT) with x=0.00, 0.05, 0.10, 0.15, 0.20, were prepared by mixed oxide method at high temperature. The structural study reveals that the composites showed tetragonal crystal structure at room temperature and tetragonality (c/a ratio) of composites decrease with increase in Gd concentration. The average crystallite size of the composites was found to be in the range of 30-89 nm. Surface morphology of the composites was studied by scanning electron microscopy (SEM). The Goldschmidt tolerance factors of the composites were found to be in the range of 0.989-0.976. The nature of Nyquist plot confirmed the presence of both bulk and grain boundary effects, and non-Debye type of relaxation process occur in the composites. The activation energy of the composites was found to be in the range 0.13-1.38eV. The analyses of ac conductivity data obey the universal agreement with Jonscher’s power law. Further, the explanation of conduction mechanism through correlated barrier hopping (CBH) model was discussed.

Electrical and structure properties for the alloy system CexLa1−xOy nanostructure thin films

The CexLa1−xOy samples are synthesized, characterized and their electrical properties are reported at different molar ratios in the frequency range of 10−1–10+5Hz. Ac conductivity and permittivity data are analyzed by using conductivity formalism. The values of capacitance and tan(δ) were recorded with respect to different frequencies and temperatures. X-ray diffraction (XRD) patterns of the films show that the films posses crystalline phases. Surface morphology of the films is analyzed by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The energy dispersive X-ray (EDX) and X-ray photoelectron spectroscopy (XPS) analyses reveal that elemental composition is in right stoichiometry. Electrical characterizations of the CexLa1−xOy samples were done by capacitance–voltage (C–V) and current density–voltage (J–V) measurements of MOS structures. Investigation showed high value of k=44.80 and low leakage current (∼1×10−5A/cm2) of the Ce0.4La0.6Oy film.

Temperature dependent dielectric and conductivity studies of polyvinyl alcohol-ZnO nanocomposite films by impedance spectroscopy

Dielectric and conductivity behaviors of nano ZnO doped polyvinyl alcohol (PVA) composites for various concentrations of dopant were investigated using impedance spectroscopy for a wide range of temperatures (303 K–423 K) and frequencies (5 Hz–30 MHZ). The dielectric properties of host polymer matrix have been improved by the addition of nano ZnO and are found to be highly temperature dependent. Anomalous dielectric behavior was observed in the frequency range of 2.5 MHz–5 MHz. Increase in dielectric permittivity and dielectric loss was observed with respect to temperature. The Cole-Cole plot could be modeled by low resistance regions in a high resistance matrix and the lowest resistance was observed for the 10 mol. % films. The imaginary part of the electric modulus showed asymmetric peaks with the relaxation following Debye nature below and non-Debye nature above the peaks. The ac conductivity is found to obey Jonscher's power law, whereas the variation of dc conductivity with temperature was found to follow Arrhenius behavior. Two different activation energy values were obtained from Arrhenius plot indicating that two conduction mechanisms are involved in the composite films. Fitting the ac conductivity data to Jonscher's law indicates that large polaron assisted tunneling is the most likely conduction mechanism in the composites. Maximum conductivity is observed at 423 K for all the samples and it is optimum for 10 mol. % ZnO doped PVA composite film. Significant increase in dc and ac conductivities in these composite films makes them a potential candidate for application in electronic devices.

Effects of curing agent on conductivity, structural and dielectric properties of an epoxy polymer

Two epoxy polymers were prepared by curing the diglycidyl ether of bisphenol A (DGEBA) epoxy resin with two hardeners: the ethylenediamine (EDA) and the 3,3′-diaminodiphenyl sulfone (33′DDS) which are respectively aliphatic and aromatic. Structural properties of DGEBA/EDA and DGEBA/33′DDS polymers were investigated by means of grazing incidence X-ray reflectometry. Their dielectric properties were studied using the dielectric relaxation spectroscopy (DRS) over wide ranges of temperature (from −80 to 200 °C) and frequency (from 10−1–106 Hz), and thermally stimulated depolarization current (TSDC) technique. X-ray data revealed the presence of a locally periodic nanostructure in polymer cured with the aromatic hardener (DGEBA/33′DDS). γ and α dipolar relaxations were highlighted for the two polymers while the Maxwell–Wagner–Sillars (MWS) relaxation appears only in the DGEBA/33′DDS. The electric modulus data were fitted using Havriliak–Negami approch. Conductive properties of epoxies were investigated. Ac conductivity data reveal that DGEBA/EDA is more conductive than the DGEBA/33′DDS.

DC conductivity and study of AC electrical conduction mechanisms by non-overlapping small polaron tunneling model in LiFeP2O7 ceramic

A lithium iron diphosphate LiFeP2O7 ceramic was synthesized by the conventional solid state technique. X-ray diffraction analysis indicates the formation of a single-phase monoclinic structure. Electrical properties were studied using complex impedance spectroscopy as a function of frequency (200Hz to 5MHz) at various temperatures (573–708K). As a result, an electrical equivalent circuit has been proposed. The AC conductivity behavior of the compound has been analyzed by Jonscher's universal power law. The scaling behavior in the AC conductivity data has been studied by hopping frequency (ωh) and DC conductivity (σdc). The non-overlapping small polaron tunneling model (NSPT) has been proposed as a closely good model to describe the dominant conduction mechanism.

South Africa: Continental Compounders – plastics masterbatch & compounds

A series of composites of polycarbonate (PC) with 23 different contents of multiwalled carbon nanotubes (MWNT) was produced by melt mixing using the masterbatch dilution method. In dielectric measurements, AC conductivity and complex permittivity data obtained in the frequency range between 10−3 and 107 Hz at room temperature indicated the electrical percolation threshold at about 1.0 wt%.The dynamic mode melt rheological measurements for the same samples at eight temperatures between 170 and 280 °C showed a visible change in the frequency dependence of dynamic moduli and the absolute value of the complex viscosity |η*| particularly at low frequencies. In literature these changes are sometimes related to so called ‘percolation threshold concentration’. Applying this picture to our experimental data we have to assume that the percolation threshold is strongly dependent on the measurement temperature. It changes from about 5 to 0.5 wt% MWNT by increasing the measurement temperature from 170 to 280 °C, respectively. This temperature dependence cannot be explained by a classical liquid-solid transition but may be related to the existence of a combined nanotube-polymer network.

Spectrophotometric and electrical properties of imperatorin: an organic molecule

Imperatorin (molecular formula = C16H14O4, molecular mass = 270) an organic molecule was isolated from ethyl acetate extract of the root parts of the plant Prangos pabularia. The optical study was carried out by ultraviolet–visible spectroscopy, and this compound showed an indirect allowed transition. The optical band gap (E g ) was found around 3.75 eV. Photoluminescence shows various good emission bands. The frequency-dependent real part of the complex ac conductivity was found to follow the universal dielectric response: σ ac (ω) α ω s [where σ ac (ω) is the frequency-dependent total conductivity, ω is the frequency, and s is the frequency exponent]. From ac conductivity data analysis, correlated barrier hopping charge-transport mechanism is the dominant electrical transport process shown by this compound. The good emission, less absorption, wide band gap and good electrical properties shown by this compound project them as a bright choice for organic electronic devices.

Ac conductivity and ferroelectric phase transition of Bi0.7(Ba0.8Sr0.2)0.3Fe0.7Ti0.3O3 ceramic

The Bi0.7(Ba0.8Sr0.2)0.3Fe0.7Ti0.3O3 ceramic is synthesized by a solid state reaction method and characterized by X-ray diffraction (XRD), SEM, Raman spectra and impedance spectroscopy. Besides, the XRD pattern shows perovskite phase with rhombohedral structure (R3c space group) at room temperature. Furthermore, the ferroelectric-paraelectric phase transition (TC) and G-type antiferromagnetic Neel temperature (TN) is detected by Raman spectroscopy. Meanwhile, the electrical conductivity of the sample is investigated in the temperature and the frequency range 713–773K and 100–1000kHz respectively by means of impedance spectroscopy. The Nyquist plots (−Z″ versus Z′) frequency plots are well fitted to an equivalent circuit model. The ac conductivity data obey the universal power law. The nature of variation of dc conductivity suggests Arrhenius type of electrical conductivity. The temperature dependence of the alternative current conductivity (σg) and direct current conductivity (σdc) confirm the presence of the ferroelectric–paraelectric phase transition.

Study of electrical and ferroelectric properties of Bi3.4Ce0.6Ti2.4Zr0.6O12 ceramics

Polycrystalline samples of Bi3.4Ce0.6Ti2.4Zr0.6O12 (CeZrBIT) ceramics were synthesized using solution combustion route. X-ray diffraction study indicates the presence of pyrochlore phase due to Ce doping and orthorhombic distortion in the bismuth titanate lattice due to Zr addition. Improvement in dielectric and ferroelectric properties of CeZrBIT was observed in comparison with undoped bismuth titanate. Electrical behaviour of the sample was analyzed using the complex impedance plots as a function of frequency at different temperatures. Non-Debye type dielectric relaxation is shown by this lead free ceramic. The Nyquist plot demonstrates the negative temperature coefficient of resistance characteristic of CeZrBIT. Density of states at Fermi level and activation energy of the compound was also evaluated using the AC conductivity data.

Effect of oxygen-ion motion on dielectric properties of Ba0.6Sr0.4TiO3 thick films

The dielectric properties and electrical conductivity of porous Ba0.6Sr0.4TiO3 thick films prepared by screen printing were investigated. The thick films displayed several anomalous dielectric behaviors differing from dense Ba0.6Sr0.4TiO3 ceramics. The AC conductivity data obeyed the power-law relation of the universal dielectric response model, suggesting the existence of polarization resulting from hopping carriers in the thick films. Impedance spectroscopy analysis indicated two separate contributions for the thick films, both corresponding to the response of the grains. The activation energies of the two response processes were determined to be ∼1.0eV, manifesting that oxygen ions were the mobile carriers. The electrical heterogeneity of the grains was interpreted in relation to the porosity of the thick films. The dielectric anomalies of the thick films were linked to oxygen-ion motion. This work highlights an important effect of oxygen-ion hopping on the dielectric loss of the thick films in a wide frequency range.

Dielectric relaxation in YMnO3 single crystals

We have investigated the origin of the dielectric relaxation in YMnO3 single crystals. Two distinct dielectric relaxation features were observed at low (200⩽T⩽373K) and high (300⩽T⩽450K) temperatures. Analysis of our detailed frequency, electrode and thickness dependent dielectric measurements and ac conductivity data as well as the use of single crystals allow us to get a comprehensive picture of these relaxations. The low temperature relaxation is attributed to the Maxwell–Wagner type effects originating from the dipoles at the surface while the high temperature one is suggested to originate from hopping of charge carriers resulting from the second ionization of oxygen vacancies.

Green synthesis and characterization of Ag1/2Al1/2TiO3 nanoceramics

Abstract Single phase silver aluminum titanate (Ag1/2Al1/2)TiO3, later called AAT, nanoceramic powder (particle size 2 to 7.5 nm) was synthesized by a low-cost, green and reproducible tartaric acid gel process. X-ray, FT-IR, energy dispersive X-ray and high resolution transmission electron microscopy analyses were performed to ascertain the formation of AAT nanoceramics. X-ray diffraction data analysis indicated the formation of monoclinic structure having the space group P2/m(10). UV-Vis study revealed the surface plasmon resonance at 296 nm. Dielectric study revealed that AAT nanoceramics could be a suitable candidate for capacitor applications and meets the specifications for “Z7R” of Class I dielectrics of Electronic Industries Association. Complex impedance analyses suggested the dielectric relaxation to be of non-Debye type. To find a correlation between the response of the real system and idealized model circuit composed of discrete electrical components, the model fittings were performed using the impedance data. Electric modulus studies supported the hopping type of conduction in AAT. The correlated barrier hopping model was employed to successfully explain the mechanism of charge transport in AAT. The ac conductivity data were used to evaluate the density of states at Fermi level and minimum hopping length of the compound.

Electrical conductivity and dielectric relaxation in Pr2CoZrO6 double perovskite

Sample of Pr2CoZrO6 (PCZ) was synthesized through the standard solid state reaction method. X-ray diffraction experiments and least square-like analysis reveal that the material crystallizes in an orthorhombic structure. SEM image displayed well-defined regular shaped spherical grains with average grain-size 0.615μm. Frequency dependence of impedance and electric modulus properties are studied over a wide frequency range of 44Hz to 1MHz at various temperatures to confirm the contribution from grain and grain-boundary. Impedance data are presented in the Nyquist plot which is used to identify an equivalent circuit and fundamental circuit parameters. Scaling behavior of the impedance data suggests that the relaxation describes the same mechanism at various temperatures. The ac conductivity data has been analyzed by fitting the data into Jonscher power law and the conduction in this system is interpreted as due to small polaron hopping. Summerfield scaling plot is used to investigate Arrhenius temperature dependence of conductivity.