Ac Conductivity Data Research Articles

An investigation of structural, electrical and optical properties of lead-free barium zirconium titanate (BZT)-based ceramic compounds

ABSTRACT The present work is a demonstration of improved electrical and optical properties of barium zirconium titanate ceramic modified by the addition of Europium, i.e. Ba(1–x)Eu2x/3Zr0.05Ti0.95O3 (x = 0.01, 0.02, 0.03, 0.04). The Rietveld refinement studies confirmed the formation of tetragonal phase in the samples. The scanning electron microscopy (SEM) images revealed a decrease in grain size with increasing Eu concentration. The dielectric constant, dielectric loss and TCC plots are drawn to study temperature and frequency dependence of the samples. The electric field-induced strain behavior has been studied for all the compositions of the synthesized ceramic at room temperature. Conduction mechanism in the samples as a function of frequency and temperature was studied with the help of AC conductivity data. Also, the effect of grain and grain boundaries are studied in term of Cole–Cole plots. Photoluminescence (PL) emission spectra were recorded upon excitation with a wavelength of 360 nm.

Investigation of optical and electrical conduction mechanism of AgYP2O7 prepared by solid state process

Diphosphate materials are promising materials for different applications where their properties need to be widely studied in order to optimize them. The AgYP2O7 compound was prepared following the solid-state reaction method. X-ray powder reveals that the title compound crystallizes in the triclinic system, while differential scanning calorimetry analysis discloses the existence of an endothermic peak around T = 480±10 K indicating the existence of a phase transition. As for optical properties, using reflectance spectroscopy and Kubelka– Munk's procedure, the deduced value of the direct energy gap of Eg =2.29±0.09 eV. The variation in conductivity with temperature confirms the presence of the phase transition evidenced by DSC measurements. The AC conductivity data are well described by Jonsher's law. The thermal behavior of the exponent parameter "s" reveals that the conduction mechanism changes from over large polaron tunneling to non-overlapping small polaron tunneling at the temperature of phase transition.

Investigation on Multiferroic Properties and Conduction Mechanism in Cobalt Doped Bi0.9Nd0.1FeO3 Solid Solutions

Bi0.9Nd0. 1Fe1–x Co x O3 (x = 0.025, 0.050, 0.075 and 0.1) solid solutions have been synthesized by doping of Co3+ at the Fe3+ site using solid-state reaction method. The prepared solid solutions have been investigated for their structural, magnetic, ferroelectric and magneto-dielectric properties and conduction mechanism. The XRD study reveals that all the solid solutions possess a rhombohedral symmetry. The vibrating sample magnetometer study reveals that all the samples possess magnetic orders and the remnant magnetization has been found to be increased from 0.2388 emu/g for x = 0.025 to 0.7112 emu/g for x = 0.1. The non-Debye type dielectric relaxation has been investigated for all the samples. The frequency dependent ac conductivity data follows Jonscher’s Power law. Variation of exponent n versus temperature follows the overlapping large polaron tunneling conduction model. The maximum value of remanent polarization (∼0.152 μC/cm2) was found for x = 0.1. All the samples exhibit positive magneto-dielectric response in the low-frequency region with the highest magneto-capacitance value of 13.54% at 500 Hz for sample x = 0.1.

Dielectric relaxation and small polaron hopping transport in sol-gel-derived NiCr2O4 spinel chromite

Herein, we have synthesized NiCr2O4 chromite by the sol-gel auto-combustion route. The refined X-ray powder diffraction pattern confirmed the single-phase formation of the material, which crystallized in a cubic normal spinel structure with space group Fd3m. The complex impedance study indicated the existence of relaxation phenomenon and predicted the semiconducting nature of the material. The frequency-dependent Nyquist plot modeled by (RGBCGB) (RGQG) equivalent circuit exhibited the effects of grain and grain boundary to the electrical response of the compound over the measured temperature range of 263-393 K. The experimental AC conductivity data followed Jonscher’s double power-law behavior, and the frequency exponent profile suggested small polaron hopping as the most probable transport mechanism for the sample. The complex modulus analysis showed the non-Debye type behavior of the material. In contrast, the dielectric constant exhibited dispersion in the low-frequency regime with a large tangent loss directly related to temperature.

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.

Electrical transport in lead-free Na0.5Bi0.5TiO3 ceramics

Lead-free Na0.5Bi0.5TiO3 (NBT) ceramics were prepared via a conventional oxide-mixed sintering route and their electrical transport properties were investigated. Direct current (DC, σDC) and alternating current (AC, σAC) electrical conductivity values, polarization current (first measurements) and depolarization current, current–voltage (I–U) characteristics (first measurements), and the Seebeck coefficient (α) were determined under various conditions. The mechanism of depolarization and the electrical conductivity phenomena observed for the investigated samples were found to be typical. For low voltages, the I–U characteristics were in good agreement with Ohm’s law; for higher voltages, the observed dependences were I–U2, I–U4, and then I–U6. The low-frequency σAC followed the formula σAC–ωs (ω is the angular frequency and s is the frequency exponent). The exponent s was equal to 0.18–0.77 and 0.73–0.99 in the low- and high-frequency regions, respectively, and decreased with temperature increasing. It was shown that conduction mechanisms involved the hopping of charge carriers at low temperatures, small polarons at intermediate temperatures, and oxygen vacancies at high temperatures. Based on AC conductivity data, the density of states at the Fermi-level, and the minimum hopping length were estimated. Electrical conduction was found to undergo p–n–p transitions with increasing temperature. These transitions occurred at depolarization temperature Td, 280 ℃, and temperature of the maximum of electric permittivity Tm is as typical of NBT materials.

Evaluation of Structural and Electrical Properties of Ball-milled NaNbO3 Ceramic

This work reports the effect of milling on the structural, microstructural, electrical, and piezoelectric properties of NaNbO₃ (NN) ceramics synthesized using a solid-state reaction method. X-ray diffraction studies exhibited that the lattice structure of milled and un-milled NN samples is orthorhombic with a space group <em>Pmc</em>21. The average particle size and lattice strain were found to 203 nm and 0.05 un-milled samples whereas they were 37 nm and 0.2 for 10 h milled samples. FTIR spectra indicated a shift in peak position with milling time. SEM image showed the formation of small grains ~1.2 µm for 10 h milled NN samples which is advantageous for dielectric applications in high density integrated circuits. An increase in the values of dielectric constant from 377 to 698, <em>d33</em> from 29 to 37, and a drop in critical temperature from 426°C to 352°C at 1 kHz were registered for un-milled and milled samples. A negative temperature coefficient of resistance behaviour was noticed from the impedance and ac conductivity analyses. The correlated barrier hopping model successfully explains the charge transport mechanism in the present ceramic system and ac conductivity data obeyed Jonscher’s universal power law. A marked increment in <em>d33</em> with smaller particle size was observed with the increasing milling hour that could make NN a promising lead-free piezoelectric material for piezo-sensing/detection and energy harvesting applications.

Enhanced electrical conductivity in Zr-Doped (La0.7Ba0.3)(Mn0.5Fe0.5)O3 solid solutions

The perovskite ([Formula: see text][Formula: see text]([Formula: see text][Formula: see text][Formula: see text]O3, where [Formula: see text] = 0.1, 0.2 and 0.3, ceramics were synthesized by solid-state reaction method. The introductory structural studies were followed through by X-ray diffraction technique and the results have disclosed that all the samples were crystallized into an isolated phase. The Zr substitution in the resulting solid solutions increases the electrical conductivity and the maximum value of ac conductivity has been found to be [Formula: see text]118.8 S [Formula: see text] cm[Formula: see text] for [Formula: see text] = 0.3 at 200[Formula: see text]C (at 1 MHz). The frequency dependence of ac conductivity data follows Jonscher’s power law. The variation of the exponent [Formula: see text] versus temperature follows the nonoverlapping small polaron tunneling (NSPT) model. The dielectric relaxation has been observed to be of non-Debye nature for all measuring temperatures (50–200[Formula: see text]C). The impedance spectroscopy reveals that all the samples exhibit negative temperature coefficient of resistance (NTCR) behavior. The prepared samples (for [Formula: see text] &gt; 1) are supposed to be suitable for cathode materials in SOFCs.

Temperature dependent AC-Conduction and relaxation mechanism of spinel MgCo2O4 system by impedance spectroscopy

MgCo2O4 a spinel ceramic was studied by complex impedance spectroscopy. The measurements were performed in the temperature and frequency ranges 83 to 323 K and 40 Hz to 1 MHz, respectively. The decreasing trend in Nyquist plots semicircles was observed as a function of temperature indicating the distribution of different relaxaion processes. Two equivalent circuit models (RgCg)(RgbQgb) below 173 K and above this temperature (Rg)(RgbQgb) were applied to fit the impedance data. The values obtained for Rgb and Rg from these model fitting displayed semiconducting like behavior in the material. The variable range hopping model was employed to explain electrical conduction mechanism of grains and grain-boundaries. The complex modulus analysis asserted the contribution of both bulk and grain boundaries in electrical conductivity at low temperatures. The frequency dependent ac-conductivity followed the universal Jonscher's power law. The frequency exponent n showed a decreasing trend with increasing temperature. The ac-conductivity data was further elaborated by Correlated Barrier Hopping Model (CBH).

Structural, impedance and electrical evaluation of complex perovskite: Ca(Mn1/3Ni1/3W1/3)O3

A complex perovskite Ca(Mn1/3Ni1/3W1/3)O3, abbreviated as CMNWO, is synthesized by adopting the solid-state ceramic procedure. The X-ray diffraction analysis of CMNWO shows that the present perovskite is acquiring a cubic crystal structure having the cell dimension of a = 3.8321 A. The obtained cell parameter is in good agreement with the theoretical cell parameter obtained from the SPuDS-V2.19.05.14 code. The micrograph describes the uniform grain distribution in the CMNWO sample. The average crystallite size of the sample was found to be 50.98 nm, which was calculated using the Scherrer relation. The dielectric and electrical properties like dielectric constant, dissipation factor, impedance, electrical modulus and conductivity of CMNWO were studied. The activation energies were determined from the AC-conductivity data in the temperature range of 200–350°C and 360–500°C. The dielectric spectra with temperature suggest that the present CMNWO is semiconducting in nature and follows the negative temperature coefficient of resistance kind of behaviour.

Impedance spectroscopic study of charge transport and relaxation mechanism in MnCr2O4 ceramic chromite

In the present report, MnCr2O4 ceramic oxide has been prepared via the solution based self-combustion sol-gel route sintered at 900 °C. The Rietveld refinement of X-ray powder diffraction profile revealed the single-phase normal spinel structure of the ceramic crystallized in a face-centered cubic unit cell with Fd3m space group symmetry. The field emission scanning electron microscopy exposed well distribution of grains separated by grain boundaries as micro-constituents of the sample. Complex impedance spectroscopy deduced the distribution of relaxation times and thermal activation of charge carriers in the frequency and temperature ranges of 70−4×106 Hz and 543−643 K, respectively. The depressed semicircular arcs of the Nyquist plot modeled by an equivalent circuit with configuration RG׀׀CG+RGB׀׀CGB confirmed the bulk and interface contribution to the electrical response of the material. The correlated barrier hopping conduction addressed the temperature dependence of frequency exponent after simulation of the AC conductivity data by the equation of Jonscher. The complex modulus study identified the electro-active components of the material and determined the dominant role of grains in the conduction mechanism. The analysis of dielectric constant and loss factor stated thermally activated hopping mechanism of charge carriers between Cr2+ and Cr3+ ions at the octahedral sites of the crystal structure.

Investigation of Structural and Dielectric Properties of Polycrystalline PbMg1∕3 Ti1∕3W1∕3O3 Tungsten Perovskite

Lead magnesium tungsten titanate PbMg[Formula: see text] Ti[Formula: see text]W[Formula: see text]O3 was prepared by adopting a high-temperature solid-state reaction method. The sample has tetragonal crystal structure having average crystallite size 45.1325[Formula: see text]nm calculated using Scherer’s relation and the average grain size is about 40[Formula: see text]nm from Scanning Electron Microscope (SEM) measurement. Measurements of dielectric permittivity ([Formula: see text]) and loss ([Formula: see text]) have been investigated, both as a function of frequency (1[Formula: see text]kHz to 5[Formula: see text]MHz) and temperature (25–[Formula: see text]C) and the results showed the presence of interfacial polarization of the material. The dielectric spectra with frequency and temperature suggest that the prepared sample is semiconducting in nature following the NTCR behavior. The complex impedance results showed the contribution of grain and grain boundaries in the conduction mechanism. The activation energies were determined from the ac conductivity data in the temperature ranges of 200–[Formula: see text]C and 360–[Formula: see text]C. It has been observed that with the rise of frequency and temperature, the activation energy increases in the sample. The greater value of the activation energy always supports the conduction mechanism due to hopping of the charge carriers. The semicircular arcs of Cole–Cole plots confirm that the sample is semiconducting in nature which supports our dielectric results.

Structural, Impedance, and Leakage Current Characteristics of Stannum Modified Bi0.5Na0.5TiO3 Ceramic

A perovskite ceramic oxide, stannum (Sn) modified bismuth sodium titanate (BNT) (i.e., Bi0.5Na0.5Ti0.80Sn0.20O3) was synthesized by using a mixed oxide powder reaction route. Analysis of the X-Ray diffraction spectrum supports the polycrystalline nature of the compound with tetragonal symmetry. A phase change from the ferroelectric to paraelectric transition is observed at around 315 °C. The temperature and frequency dependence of dielectric properties and AC conductivity data of the material are analyzed. The Nyquist plots explain the effect of the grain and grain boundary contribution on the polarization process of the material. The analysis of complex modulus spectroscopy exhibits the non-Debye relaxation in the compound. The doping of stannum at the titanium-site of BNT enhances the dielectric characteristics of the material.

Development of chemically synthesized lead-free double perovskite compound: BiBaFeCeO6

In this communication, preliminary structural and detailed electrical (impedance, and conductivity) along with multiferroic (ferroelectric and ferromagnetisc) characteristics of a cost effective chemically processed double perovskite compound, BiBaFeCeO6, have been reported. By analyzing the X-ray diffraction data, the orthorhombic crystal structure of the compound with a single-phase characteristic is obtained. Combining the two simple perovskite materials, BiFeO3 with BaCeO3, in equal ratio produces a new double perovskite compound BibaFeCeO6 with the enhanced dielectric constant (as compared to that of individual perovskite). The shift in the dielectric peak and increase of peak broadening with increase in frequency suggest the existence of relaxation process and relaxor characterizes in the studied compound. The variation of the characteristic of dc conductivity with temperature displays the presence of semiconductor (negative temperature coefficient of resistance) behavior in the compound. Analysis of frequency dependence of ac conductivity data shows that the studied compound obeys the Jonscher’s universal power law. The analysis of complex impedance and modulus spectroscopy data exhibits the non-Debye type of relaxation mechanisms in the compound. The multiferroicity in the compound has been confirmed from the P–E, M–H hysteresis loop and M–E coupling characteristics.

Dielectric relaxation and charge conduction mechanism in mechanochemically synthesized methylammonium bismuth iodide

In this work, methylammonium bismuth iodide [(CH3NH3)3Bi2I9] has been synthesized through the mechanochemical process. Indeed, (CH3NH3)3Bi2I9 emerges as promising alternative to lead-based inorganic–organic perovskite due to low toxicity and better stability. X-ray diffraction spectra reveal monoclinic structure of (CH3NH3)Bi2I9 with space group C2/c. Kubelka–Munk method is conducted to compute the bandgap (2.16 eV). The impedance and dielectric properties of (CH3NH3)3Bi2I9 have been investigated within frequency range of 4 Hz to 1 MHz for several temperatures in between 333 to 453 K. The complex impedance spectroscopy has analyzed by fitting the Cole–Cole plot with suitable grain and grain boundary contributions (rg, rgb). Conductivity and electric modulus spectra have been analyzed to enlight the shaded portion of transportation properties. The scaled coordination of modulus spectrum merges in a single master curve which signifies that the distribution of relaxation time is temperature independent. To compute the DC conductivity, AC conductivity data have fitted using Jonscher’s power law. The activation energy calculated from Arrhenius plot is 0.477 eV.

High Temperature Dielectric Response and AC Conductivity Mechanism of (Nd, Ni) codoped BiFeO3

BiFeO3(BFO)and Bi0.9Nd0.1Fe0.9Ni0.1O3 (BNFNO) nanocrystalline samples have been synthesized through the sol-gel auto combustion process. Frequency and temperature dependent dielectric measurements have been performed in order to apprehend the influence of (Nd,Ni) co-doping on the conduction mechanism of pristine BFO.Thereal part of the dielectric constant is found to increase with the Nd and Ni doping, which is accredited to higher space charge polarization induced by the dopant ions.The dielectric constant measured as a function of frequency exhibits a dispersivebehaviour within low frequency region and attains a constant value at higher frequencies. A thermally activated relaxation peak is found at around 500K in the BNFNO samplewhich shifts towards lower temperatures at higher frequencies. The AC conductivity follows the Jonscher’s universal dynamic law, which has been utilized to evaluate the value of frequency exponent ‘s’. The decrease in the value of the ‘s’ parameter with the increase in temperature establishes that the conduction mechanism is governed by the correlated barrier hopping (CBH) model. The ac conductivity data has been utilized to evaluate the minimum hopping distance (Rmin) and the binding energies (Wm) of the electrons in BNFNO. Arrhenius equation has been used to fit the experimental data and activation energy has been evaluated at different temperatures. The Activation energy is found to increase with the increase in the temperatures, owing to the creation of more oxygen vacancies instigated by (Nd, Ni) co-doping.

Dielectric Properties, AC Conductivity, and Electric Modulus Analysis of Bulk Ethylcarbazole‐Terphenyl

Electrical and dielectric properties for bulk ethylcarbazole‐terphenyl (PEcbz‐Ter) have been studied over frequency range 1 kHz–2 MHz and temperature range (R.T –120°C). The copolymer PEcbz‐Ter was characterised by using X‐ray diffraction. The frequency dependence of the dielectric constant () and dielectric loss () has been investigated using the complex permittivity. of the copolymer decreases with increasing frequency and increases with temperature. AC conductivity (σac) data were analysed by the universal power law. The behaviour of σac increases with increasing temperature and frequency. The change of the frequency exponent (s) with temperature was analysed in terms of different conduction mechanisms, and it was found that the correlated barrier‐hopping model is the predominant conduction mechanism. The electric modulus was used to analyze the relaxation phenomenon in the material.

Transport phenomena of Cu-S-Te chalcogenide nanocomposites: frequency response and AC conductivity.

In this work, the development and electrical characterization of several chalcogenide nanocomposites have been reported. X-ray diffraction (XRD) has been used to reveal their microstructures. Mott's variable range hopping model has been used to interpret the DC conductivity data of the nanocomposites at lower temperatures. The DC conductivity data at higher temperatures has been explained well using Greave's model. To explain the AC conductivity data, the Meyer-Neldel (MN) conduction rule has been employed. The AC conductivity spectra at different temperatures have been analyzed using Almond-West formalism. Different conduction models, namely, correlated barrier hopping (CBH) and modified non-overlapping small polaron tunneling (NSPT), have been used to interpret the conduction mechanism of the nanocomposites. Scaling of the AC conductivity spectra reveals that the electrical relaxation process is independent of temperature, but depends on the nanocomposite composition. The conductivity mechanism is explained using a schematic structural model.

Structural, dielectric and magnetic properties of Bi–Mn doped SmFeO3

We have studied the structural, magnetic, dielectric and impedance properties of the Sm1-xBixFe1-yMnyO3 [SmFeO3 (SFO), Sm0.9Bi0.1FeO3 (SBFO), Sm0.9Bi0.1Fe0.9Mn0.1O3 (SBFMO)] polycrystalline samples synthesized by solid-state reaction method. Rietveld refinement of room temperature (RT) powder x-ray diffraction pattern confirms the orthorhombic crystal structure with Pnma/Pbnm space group. The average particle size of Bi doped and co-doped (Bi–Mn) samples determined from SEM analysis are 5.6 μm and 5.2 μm, respectively. Room temperature field-dependent magnetization increases, suggesting the presence of magnetic contribution due to the Rare earth-Fe ion interaction which persists even at RT. However, with co-doping of Bi and Mn, a decrease in magnetization is observed, which corresponds to the dilution of Fe3+-Fe3+ interactions due to the presence of Mn3+ ions. The observed values of magnetization at 90 kOe for Bi doped sample is (2.87 emu/g) approximately two times and for codoped (0.7 emu/g) sample is nearly half of that of pristine sample (1.51 emu/g). Dielectric measurements as a function of frequency/temperature and impedance analysis using equivalent circuit model reveal grain and grain boundary contributions of SBFO (at high temperature) and SBFMO (for all temperature) samples towards the electrical properties indicating the electrically heterogeneous nature of these samples. However, for SFO sample grain contribution is dominant. Observed value of dielectric constant varies from ~103-104 with Bi–Mn doping. The conduction mechanism of the studied samples has been explained by considering Jonscher power law. Arrhenius law fitting of AC conductivity data manifests two types of conduction mechanisms in these samples. The depressing nature of the semicircular arc observed in the Nyquist plot of all the samples indicates the presence of a non-Debye type of relaxation.

Structural, magnetic and dielectric studies of siderite nano-particles synthesized by hydrothermal method

Siderite or ferrous carbonate [Formula: see text] is a well-known mineral and finds applications in various fields such as dietary supplement to treat anemia and in petroleum drilling fluids for [Formula: see text] removal. The FeCO3 nano-particles are synthesized by hydrothermal method using aqueous solutions of iron sulfate, ascorbic acid and ammonium carbonate with a molar ratio of 1:1:3, respectively, and heating at [Formula: see text]C for 1.5 h in Teflon-lined stainless steel autoclave. The recovered sample is characterized by several techniques. The powder XRD indicates the hexagonal crystal system and the average crystallite size of 17.32 nm are obtained from the Scherrer’s formula and 18.98 nm is obtained from the Williamson and Hall formula. The TEM images suggest the spherical nature of the nano-particles. The EDX confirms the elemental presence of iron, carbon and oxygen. The impedance and dielectric studies are carried out within 20 Hz–2 MHz range at room temperature. The complex impedance plot, i.e. the Nyquist plot, is composed of one semicircle indicating the contribution from the grain only. The Jonscher’s power-law is applied to AC conductivity data. The VSM data at room temperature and at low temperature, i.e. 20–300 K range, suggests a weak antiferromagnetic nature of the sample.