Ac Conductivity Curves Research Articles

Rare-earth (Dy3+ and Pr3+) ratio variation effects on electrical properties of sodium fluoride alumino borate glass system

Inlaying two RE ions simultaneously in the glass network, greatly impacts its properties and therefore its study is paramount. A glass series with composition 60B2O3 + 30NaF + 10Al2O3 + (1 − x) Dy2O3 + (x/3)Pr6O11 (where x = 0, 0.2, 0.5, 0.7 and 1 mol%) was prepared by melt quenching technique. The influence of both composition, concentration of rare earth ions and temperature variation in wide frequency range on electrical properties were investigated. The DC and AC conductivity curves for all the prepared compositions obeyed Arrhenius relation and Jonscher’s Power law, respectively. The frequency exponent “s” parameter was obtained to study the conductivity mechanism. Dielectric parameters were observed to be decreasing with a rise in frequency and increasing with temperature. Electric Modulus and Nyquist Plots for all compositions were studied to examine the relaxation behavior in prepared glasses as Debye or non-Debye. Depressed semicircular Nyquist plots were observed.

Role of Crystal Structure on the Ionic Conduction and Electrical Properties of Germanate Compounds A2Cu3Ge4O12 (A = Na, K)

Crystal structure and electrical properties of A2Cu3Ge4O12 (where A = Na, K) have been investigated by neutron diffraction and electrical impedance spectroscopy (EIS). The real and imaginary parts of the impedance, dielectric constant, and electrical modulus have been studied as a function of frequency and temperature. The crystal structures of the compounds K2Cu3Ge4O12 (KCGO) and Na2Cu3Ge4O12 (NCGO) are made of perfect 2D and quasi-2D alkali metal ion layers, respectively. The dc conductivity occurs due to small polaron hopping for both compounds with single activation energy over the entire experimentally available temperature range. The values of activation energies are 0.90(3) and 1.22(6) eV for KCGO and NCGO, respectively, as determined from dc conductivity and relaxation time analysis. The frequency dependent ac conductivity curves for both compounds follow a universal Jonscher’s power law. Soft bond valence sum analysis of neutron diffraction data reveals that the conduction pathways are confined within a plane in KCGO, whereas they form a one-dimensional channel in NCGO. The bottlenecks for ionic conduction and the role of crystal structure on them are discussed. The scaling behavior of electrical modulus indicates that the relaxation process does not change with temperature; however, a sharp decrease in the time constant has been observed. The present comprehensive study facilitates the understanding of the role of crystal structure on the microscopic mechanism of ionic conduction in both battery materials, which would be useful in designing sodium and potassium based ionic conductors. Further, the constant value of activation energy over the kHz frequency range is suitable for potential applications of the studied materials in avalanche beacons and amateur and geophysical sensors.

Effects of the variation of doping content and heat treatment condition on the dielectric properties of Ga doped α-Fe2O3 system: A promising low loss magnetoelectric-semiconductor

The ac conductivity and dielectric properties of the α-Fe2-xGaxO3 samples have been studied in the frequency range 1 Hz–5 MHz and in the temperature range of 203 K–503 K. The samples are electrically semiconductor in nature and the dielectric properties are strongly affected by the transformation of magnetic spin order in the hematite structure. The acconductivity curves exhibited nearly constant loss (NCL) regime at the lower temperatures (where antiferromagnetic spin order dominates) and a charge hoping conduction regime dominates at the higher temperatures (where canted ferromagnetic spin order dominates). The samples showed higher electrical conductivity with the increase of Ga content in hematite structure. The features of electrical conductivity and dielectric properties are strongly dependent on the Ga content in hematite structure and also heat treatment condition of the chemical routed samples. The charge conduction mechanism in the α-Fe2-xGaxO3 system is largely controlled by the correlated barrier hopping of charge carriers, whereas the conduction mechanism in the samples with relatively higher Ga content follows the quantum mechanical tunnelling of charge carriers. The present work carried out a detailed analysis on the temperature and frequency dependent behaviour of the electrical conductivity, impedance spectra, electric modulus, dielectric constant and dielectric loss factor in order to extract the information of the contributions of dielectric parameters from grain and grain boundary of the samples and effect of the heat treatment conditions on dielectric properties.

Effect of Fe substitution on the structural, microstructural and dielectric properties of sodium bismuth titanate

Lead free sodium bismuth titanate (NBT) is widely being studied as an emerging room temperature multiferroic and as a ferroelectric material with potential to replace toxic lead based ceramics. Various elements can be substituted in the A-site or B-site to improve its electrical and magnetic properties. In this work, pure and Fe substituted NBT having the chemical formula Na0.5Bi0.5Ti(1-x)FexO3 (x = 0.00, 0.02) were synthesized using sol gel auto ignition method to study the effect of Fe substitution on the properties of NBT. XRD analysis confirmed the rhombohedral symmetry of the synthesized samples and the crystallite size of the samples were calculated using Scherrer’s formula. The morphological property of the samples was studied from the SEM images. UV–Visible Spectroscopy method was employed to study the optical properties of the samples. The dielectric properties of the samples were measured as a function of frequency in the range 100 Hz to 1 MHz at room temperature and also as a function of temperature in the range of 298 K- 473 K using an Agilent HP4284 LCR meter. Usual dispersive behavior of dielectric constant was observed for both the samples at the studied temperature range. Study of frequency and temperature dependence of the AC conductivity suggested that the conduction process in the materials is thermally activated. Jonchers’ universal power law was used to fit the AC conductivity curves to describe the dynamics of charge carrier with suitable conduction mechanism.

Synthesis, structural and impedance response of (Ba-Sr)-Co-O nanoparticles

Barium strontium cobaltite (BSC) (Ba0.5Sr0.5CoO3−δ) samples were successfully produced through modified chemical synthesis procedures. The methods used are hydrothermal, without water and surfactant (WOWS) sol-gel and co-precipitation technique. The effect of different synthesis procedures on structure, morphology and electrical conduction behaviour of BSC samples was studied. X-Ray diffraction showed the development of orthorhombic phase pure perovskite structure. FTIR spectroscopy confirmed the synthesis of perovskite structure by revealing its fingerprint peaks. Morphological studies by SEM displayed evenly dispersed, agglomerated and micro porous like morphology. Nyquist plots as a function of frequency displayed single semi-circular arcs. These arcs are an indication of grain boundary contribution in the electrical conduction mechanism. Modulus study displayed the Debye type conductivity relaxation. AC conductivity curves agreed well with Jonscher's power rule. Hydrothermally synthesized samples have the least impedances at higher frequencies. That form them possible candidate for cathode material in (IT-SOFCs) applications.

A New Approach to Estimate Activation Energy of Oil-impregnated Pressboard Stressed under Switching Impulse at Different Temperatures

This paper presents an advanced technique for calculating activation energy of oil-impregnated pressboard through dielectric response current measurement under switching impulse voltage at different temperatures. The proposed technique analyzes the measured impulse voltage and current signals to formulate its equivalent circuit at different temperatures. The equivalent circuit parameters are utilized to determine the shifting of ac conductivity curve along frequency axis with variations in temperatures. Based on the shifted ac conductivity curves at different temperatures, the corresponding activation energy of the insulation is estimated. The effectiveness of the proposed technique is investigated through a few laboratory prepared test samples.

Investigation of low temperature dielectric properties of manganese doped-copper oxide nanoparticles by coprecipitation method

Mn-doped CuO nanoparticles were prepared by the co-precipitation method. X-ray diffraction patterns of pristine and Mn-doped CuO (5, 10 and 15%) nanoparticles confirm the formation of monoclinic structure. Scanning electron microscopy revealed that, the change in morphology with increasing Mn content. Dielectric permittivity value increases with increase in Mn concentration. AC conductivity curves depict improvement in conductivity with a low concentration of Mn content. DC conductivity and AC conductivity values are in accordance with Jonscher’s universal power law

Understanding the sodium-ion dynamics in NASICON (Na3Al2P3O12) glass containing NaF: Scaling of electrical conductivity spectra

Quest for high ion-conducting solid electrolyte materials for sodium-ion batteries has been tremendously increasing. Glass materials are a potential solid electrolyte for high-energy Na-ion batteries. Nevertheless, the effective research on glass materials for their applications in Na-ion batteries is dawdling due to its low ionic DC-conductivity and poor understanding of the dynamics of mobile cations. Herein, we have attempted to address the effect of substitution of NaF for Al2O3 on the conductivity of Na3Al2P3O12(NAP) glass (mol%: 37.5P2O5–25.0Al2O3–37.5 Na2O). Raman spectra reveal that the increase in the substituent NaF concentration significantly affects the coordination of Al3+ and the distribution of sodium cations in the network structure of NAP glass. Impedance spectra reveal that the change in conductivity of NAP glass with an increase in the NaF concentration is highly dependent on a specific temperature range. At a lower temperature range, (<150 °C), the conductivity increases initially with the increase in NaF concentration and it decreases with any further increase in the NaF concentration; whereas, at temperatures above 150 °C, the conductivity increases continuously with an increase in the NaF concentration. The frequency-dependent AC-conductivity has been analyzed using the time-temperature scaling principle (TTSP) based on Summerfield and Ghosh scaling procedures to probe the ion conduction mechanism. The NAP glass that contains low NaF concentrations (<7.5 mol%) obeys the AC-conductivity scaling, i.e., it satisfies the TTSP principle, with respect to temperature based on the Summerfield scaling procedure; this indicates that the sodium-ion dynamics are independent of the temperature. The scaled AC-conductivity curves for NAP glass containing high NaF concentrations (>10 mol%) have deviated from Summerfield scaling and further indicate that the fraction of sodium-ions responsible for the ionic conductivity is decreasing with an increase in the temperature. Scaling of AC-conductivity curves for all the glass samples using the Ghosh procedure suggests that the number density along with the hopping distance of sodium ions changes with increasing temperature. The Modified random network structural model has been further utilized to explain the variation in the NAP glass conductivity with an increase in the NaF concentrations. The outcome of this work will certainly aid in designing the chemical compositions of glasses for the development of solid electrolyte materials for their applications in Na-ion batteries.

Mn Doped CuO Nanoparticles Synthesized by Spray Pyrolysis: Structural, Optical and Magnetic Characterization

Pure and Mn (2.5 %, 5 % and 10 %) doped CuO nanoparticles were synthesized via chemical process of ultrasonic spray pyrolysis method. The crystal structure and grain size of the particles were determined using XRD. The optical properties of the samples were investigated using UV-Visible spectroscopy. The SEM micrographs revealed the surface morphology of sphere-shaped particles in all samples. The ZFC magnetization exhibits a sharp peak at 32 K and the FC magnetization saturated below this peak temperature. This is a characteristic feature of typical spin-glass behavior. In addition, the AC conductivity curves show an increasing conductivity value with increasing Mn content. The enhanced conductivity is due to the Mn doping in CuO induce defects in grain boundary.

Synthesis and investigation of oxygen deficiency effect on electric properties of La0.75Ba0.10Sr0.15FeO2.875-δ (δ = 0.00, 0.125 and 0.25) ferrites

In the present investigation, La0.75Ba0.10Sr0.15FeO2.875-δ oxygen-deficient ferrites with δ = 0.00, 0.125 and 0.25 were synthesized by sol–gel method. The physical characterization has been carried out by X-ray diffraction, scanning electron microscope SEM, Raman spectroscopy, and complex impedance. All samples are formed in orthorhombic crystal symmetry with Pnma space group. Synthesized compounds have nanocrystallite size of 32–46 nm. Raman spectrum shows the oxygen vacancy effect on the tilt and stretching phonon modes. Electric properties were investigated in the framework of impedance and electric conductivity. The complex impedance was measured over a wide range of temperatures (300–380 K) and frequencies (40 Hz–1 MHz). The electrical measurements indicate semiconductor behavior for the three compositions and emphasize the evidence of contribution of grain boundaries in the transport properties. The ac conductivity curves obey the Jonsher universal power law and are assigned to hopping conduction mechanism. It is found that the values of activation energy, estimated from the conductivity analysis, are in the same order with those deduced from relaxation process. Such result proves that both processes, conduction and relaxation, are related to the same defect.

Carrier transport and dielectric permittivity of SiO2 films containing ion-beam synthesized InSb nanocrystals

The structural and electrical properties of the SiO2 layers containing ion-beam synthesized spherical InSb nanoparticles were studied. The I–V characteristics, low-frequency conductivity as well as capacity, phase shift angle and loss tangent at the frequencies from 50 Hz to 5 × 106 Hz were measured at the temperatures varied from 30 K to 375 K. The capacity and phase shift angle behaviour confirms the capacitive character of the examined structures. The AC conductivity curves show the transition from the carrier transport mechanism provided by Mott electron hopping to the zone-like transport at the increase of temperature above 200 K. Both real and imaginary parts of the dielectric permittivity have the exponential dependence on the frequency within the whole studied temperature range. The origin of the obtained effect is discussed in the frame of the SiO2 polarization at the InSb/SiO2 interface.

Structural, Dielectric and Electrical investigation of Zirconium and Tin modified 0.5BFO-0.5BST

The compounds (Bi1/2Ba1/4Sr1/4)(Ti1/2Fe1/2)O3 (BFBST-0), (Bi1/2Ba1/4Sr1/4)(Ti1/4R1/4Fe1/2)O3 (BFBST-1 for R = Zr and BFBST-2 for R = Sn) have successively been prepared through the high-temperature solid-state reaction route. The structural (XRD) analysis through the Rietveld refinement reveals the tetragonal (P4mm) phase of the compounds. The refined site occupancy and respective fractional coordinates support the stoichiometry of the compounds. The dielectric, electrical (impedance and conductivity) and ferroelectric properties are investigated. The materials are having a diffused type of dielectric behavior and a variety TC indicating the relaxation effect. The deviation from the very conventional Curie Weiss law is explained through the diffusion coefficient (1≪γ2). Zr and Sn substitution increased the resistivity, decreased the dielectric loss and the leakage current of the parent (BFBST-0) sample. The leakage behavior is analyzed through J ~ E plots. The findings include the decreased value of the leakage current as well as dielectric loss with the addition of Zr and Sn in B-site as compared to that of the parent BFBST-0. This may signify the pathway to enhance the applicability of the BFBST system. The grain and grain boundary effects are explained through the Nyquist plots. A negative temperature coefficient of resistance (NTCR)/semiconductor like behavior can be seen in the studied samples. The activation energy (Ea) is calculated from the Arrhenius fit of inverse temperature versus AC conductivity curves. The Ea is higher at the high temperature region as compared to that of the low temperature region.

Effect of particles size on magnetodielectric, magnetoimpedance and electrical properties of LaFeO3 nanoparticles

Effect of particles size on the behavior of magnetoimpedance, magnetodielectric and detailed electrical properties of structural characterized LaFeO3 nanoparticles prepared through chemical ‘pyrophoric reaction’ technique having particles size of ~ 21, 43 and 51 nm have investigated. Dielectric constant of these nanoparticles gives the evidence of space charge polarization in the sample at lower frequency regime. Maximum magnetodielectric effect is obtained to ~ 61% at room temperature for particle size of ~ 21 nm, which may be due to the large surface to volume ratio of this nanoparticles compared to other particles size attributing the enhancement of space charge polarization. The maximum value of magnetoimpedance is found to ~ 92% for ~ 21 nm nanoparticle at room temperature. Magnetic field and frequency dependence room temperature magnetoimpedance are decreased with particles size of the nanoparticles. This behaviour has been explained through the light of classical electrodynamics, which reveals that this effect is depending on the magnetic field and ac signal frequency. Impedance spectroscopy is employed to study the electrical transport properties of the samples considering an equivalent circuit model for the effect of nanometric grain size. The electrical relaxation process of these materials is temperature dependent. Furthermore, ac conductivity curves follow the Jonscher’s power law for electrical conduction process of the system through polaronic hopping.

Ion transport dynamics in ionic liquid incorporated CuBTC–metal-organic framework based composite polymer electrolyte

Cu based metal-organic framework (MOF), copper 1,3,5-benzenetricarboxylate (CuBTC) has been incorporated with ionic liquid (IL) 1-butyl-3 methylimidazolium bromide at different wt% to be used as composite nanofiller in poly (ethylene oxide) polymer electrolyte system. Shifting of carboxylate vibrational modes is observed from FTIR and significant changes of binding energies of Cu spin–orbit peaks are obtained from XPS spectra suggesting strong interaction between Cu metal cluster of MOF and Br− anions of the IL. Oscillation periodicity and local coordination structure of Cu K-edge are investigated in k-space and R-space from the scanning XANES and EXAFS spectra. Dielectric modulus spectra show non-Debye relaxation dynamics and optimum ionic conductivity of 5 × 10−3 S cm−1 is obtained for the nanocomposite containing 50 wt% IL at 380 K. The frequency dependent AC conductivity curves depict ion concentration and temperature independent scaling behavior by collapsing to a single curve. The electrochemical stability and cycling performance increases with increasing IL concentration and attains electrochemical stability of 6.1 V with discharge capacity of 152.5 mAh/g after 500 cycles at 50 wt% of IL.

Synthesis, optical and electrical properties of Mn doped ZnO nanoparticles

In this paper, we are interested to study the structural optical and electrical properties of Zn1−xMnxO ( $$0\le x\le 0.03$$ ) nanoparticles (Nps). The Nps were synthesized by the co-precipitation method. X-ray diffraction patterns reveal the formation of a single-phase hexagonal wurtzite-type ZnO structure for all samples. Moreover, the Photoluminescence emission spectra for the entire samples confirm the presence of various defect centers inside the doped ZnO wurtzite nanostructure. The electrical measurements were performed in the 40–10 MHz frequency range and 460–620 K temperature intervals. It is revealed that the DC conductivity increases with temperature which follows the Arrhenius law. Besides, The variation of DC conductivity with Mn content shows gradual decrease which is explained by formation of grain boundary defect barrier. It is noted that, the Ea values are found to increase with the increase in Mn concentration. The AC conductivity curves were analyzed by Jonscher power law. The obtained results are discussed in terms of the correlated barrier hopping model.

Study of enhancement in the dielectric and electrical properties of WO3-doped LiF nano-composite

We report the dielectric and electrical behavior of thermally evaporated lithium fluoride (LiF)–tungsten trioxide (WO3) (x wt% WO3-doped LiF; x = 0, 1, 3, 5, 7, 10) nano-composite thin films at room temperature over a wide range of frequencies from 0.1 Hz to 1 MHz. Among the various doping concentrations of WO3, the 5 wt% WO3-doped LiF nano-composite thin film reaches to the maximum dielectric constant ~ 25, compared with those of pure LiF ~ 9 thin film. The electrical studies of the films have been done by complex impedance spectroscopy and show the presence of grain and grain boundaries contribution in the films for all doping concentrations. The relaxation behavior in the nano-composite films has been observed in the dielectric curve at low frequencies which is superimposed by electrode polarization. The non-Debye type of relaxation in the films has been observed in the impedance and modulus curve. The peaks appearing at low frequencies for each doping concentration in loss tangent spectrum show the presence of relaxing dipoles in the films. An increment in the ac conductivity has been observed with doping concentration up to 5%. The ac conductivity curves obey the jump relaxation power law where an electrode polarization effect can be seen at low-frequency region.

XZn0.3Ni0.7Fe2O4–(1 − x)HoMnO3 (x = 0.1, 0.3 and 0.5) nanocomposites: magnetoelectric, magnetodielectric and AC electrical response

We have investigated room temperature magnetoelectric coupling, magnetic fields and temperatures dependent ac electrical properties of chemically synthesized xZn0.3Ni0.7Fe2O4–(1 − x)HoMnO3 (x = 0.1, 0.3 and 0.5) nanocomposites. The magnetoelectric voltage is measured in both longitudinal and transverse direction. The value of magnetodielectric effect and magnetoimpedance is found to ~18 and ~20% for magnetostriction property of the magnetostictive material of the samples. Nyquist plots have been fitted using parallel combinations of resistances-constant phase element circuits showing dominant role of grain boundaries and interface of two types of grains of the samples. We have estimated activation energy of those composite using Arrhenius relation from relaxation frequencies and further verified from dielectric measurement. AC conductivity curves follow a Jonscher’s double power law attributing the conduction mechanism for the small and large polaronic hopping in the system.

Magnetoelectric coupling, dielectric and electrical properties of xLa0.7Sr0.3MnO3 – (1−x) Pb (Zr0.58Ti0.42)O3 (x = 0.05 and 0.1) multiferroic nanocomposites

We have investigated magnetoelectric coupling, dielectric and electrical properties of xLa0.7Sr0.3MnO3(LSMO)– (1-x) Pb(Zr0.58Ti0.42)O3 (x = 0.05 and 0.1) nanocomposites, prepared through low temperature pyrophoric reaction process. Magnetoelectric response has been detected in these multiferroic nanocomposites at room temperature attributing the presence of magnetostriction properties of piezomagnetic material. Noticeably, all nanocomposites are found to exhibit room temperature ferroelectric behavior. Studies of dielectric constant of those nanocomposites reveal the Maxwell Wagner interfacial polarization at low frequency regime. The ac electrical properties of nanocomposites have been studied employing impedance spectroscopy technique. The value of impedance has been found to decrease with increase in magnetic field attributing to the depinning of LSMO domain walls at the grain boundaries pinning centres and thereby enhancing the spin dependent transport mechanism in the composites. Impedance study at different temperatures shows temperature dependent electrical relaxation process in the system. The activation energy is estimated from Nyquist plots, dc and ac conductivity data using the Arrhenius relation. This is indicating that the same type of charge carrier is responsible for both the relaxation and the conduction processes in the system. Ac conductivity curves follow a Jonscher's double power law. The conduction mechanism in temperature is mainly due to the small and large polaronic hopping in the system.

Temperature and frequency dependence of AC electrical properties of Zn and Ni doped CoFe2O4 nanocrystals

We have investigated the structure and the electrical properties of CoFe2O4, Ni0.5Co0.5Fe2O4 and Zn0.5Co0.5Fe2O4 nanoparticles, prepared through a chemical pyrophoric reaction technique. The study of the dielectric constant reveals evidence of Rabinkin and Novikova polarisation in the system. The increased value of the dielectric constant at low frequency is attributed to the presence of interfacial and dipolar polarisation in the system. The impedance for Zn0.5Co0.5Fe2O4 nanoparticles is found to decrease with increase in temperature, indicating the presence of a temperature-dependent electrical relaxation process in the system. Nyquist plots have been fitted using parallel combinations of grain boundaries resistance and grain boundaries capacitance. The activation energy is estimated from Nyquist plots, dc and ac conductivity data using the Arrhenius relation. This is indicating that the same type of charge carrier is responsible for the relaxation and the conduction processes in the system. Ac conductivity curves follow a double power law, as proposed by Jonscher. The conduction mechanism with temperature is mainly due to the large polaronic hopping in the system.

Studies of temperature and frequency dependence of dielectric permittivities of two Schiff's base liquid crystal compounds

Abstract Effect of temperature and frequency on the dielectric permittivities of two Schiff's base liquid crystal compounds p-ethoxybenzylidine p-heptylaniline(EBHA) and p-butoxybenzylidine p-heptylaniline(BBHA) have been studied by using a digital LCR bridge (HIOKI 3532-50 LCR HiTESTER). Due to the changes of CH 2 groups at the oxygen containing flexible side chain between these two compounds, some changes occur in the behavior of their temperature dependent physical properties such as dielectric anisotropy, splay elastic constant, relaxation time, which has been studied extensively. The frequency dependent electrical conductivity of these two compounds has also been carried out. At the nematic mesophase the values of activation energy have been estimated from the temperature dependent DC and AC conductivity curves. The optical band gap of EBHA and BBHA has been calculated from UV spectra.