Ac Conductivity Data Research Articles

Structural and transport properties of Bi-substituted Co2MnO4

We report the structural and transport properties of the Bi-substituted Co2MnO4 multiferroic materials. Samples synthesized using the solid state reaction route with the composition BixCo2−xMnO4 (<0x<0.3) exhibit a single phase behavior with a cubic spinel structure (space group Fd3m). The lattice parameter was found to increase with the Bi substitution. The dc-conductivity studies reveal that all the samples possess a semiconducting behavior. The resistivity was found to decrease with the increase in the Bi substitution. The dc- as well as ac-conductivity data were analyzed in the light of various conduction models. The dc-conductivity data are explained using the variable range hopping model. The ac conductivity calculated from the dielectric data as a function of temperature and frequency demonstrates the cross over from small polaron tunneling to correlated barrier hopping type conduction in these materials.

Observation on Probability Function by Measuring Time Series of Electric Property in Gadolinium Nitrate Crystal at Low Temperature

The observation of the dynamics of fluctuation in a nonlinear nonequilibrium material system in a low-temperature region gives valuable information for developments in the physics of both nonlinear quantum dynamics and nonequilibrium thermodynamics. Rare-earth nitrate crystals have the same crystal habit and triclinic space group. The crystal structure is independent of temperature above 80K. Nonlinear and nonequilibrium phenomena have been observed in rare-earth nitrate crystals. Distinct intermittent nonperiodic oscillations (bursts) were observed in the measurement of the time series data for conductivity. The phenomena could be classified into a macroscopic chaos in a dissipative dynamical system. The effect of rare-earth elements on the fluctuation was found in the electric properties of the crystals. The characteristic properties of rare-earth nitrate crystals were observed in the electric measurement of the crystals in the lower-temperature region below 200K. We have measured the time series of ac conductivity, and clarified unknown properties of rare-earth nitrate crystals in the low-temperature region below 200K. A singularity in the probability distribution function was observed by measuring the time series of ac conductivity in the direction perpendicular to the c-axis of the gadolinium nitrate crystal at 11K. The result was given in the present note. A single crystal was grown in a gadolinium nitrate aqueous solution by evaporation at temperatures from 312 to 309K for 1994 h. The sample was 0:040 0:005 cm in thickness and 0:276 0:005 cm in area. The time series data of ac conductivity at 2 kHz were measured using a twophase digital lock-in amplifier (EG&G Princeton Applied Research 5210) and an analog memory recorder (Yokogawa AR1100). The experimental apparatus was controlled by a computer with a general-purpose interface bus (GPIB). The time series data of ac conductivity perpendicular to the c-axis (c2-axis) were measured at a sensitivity within 10 11 1 cm . The measurement was performed under isothermal condition controlled within 0:1K using a closed-cycle refrigerator system (Janis Research CCS-300). At 11K, with a sampling time of 50ms, 5000 data points were collected for the time series data. Figure 1 shows the time series of the fluctuation 0 for the real part 0 of the complex conductivity at 2 kHz for the electric field E applied in the direction perpendicular to the c-axis at 11K in a cooling cycle. The fluctuation 0 is defined by the relation 0 1⁄4 0 0, where 0 is the average derived from the data of the conductivity 0, given by 0 2:0298 10 6 1 cm 1 at 11K. Bursts occur randomly as nonperiodic unstable oscillations in the time series of 0 at the temperature. The probability distribution function of the time series data { 0} on the semilogarithm scale is given in Fig. 2. The probability function could not be classified into both standard Gaussian and Lorentzian line shapes. The functional form of the probability function is symmetrical and has a sharp peak as seen from Fig. 2. Figure 3 shows a log– log plot of the probability distribution function versus the fluctuation 0. The result indicates that the singularity of the probability function is proportional to ð 0Þ , where the exponent s of the power law is given by s 1⁄4 1:43 0:2. The temperature variation in the probability functions was observed in other rare-earth nitrate crystals, which were classified into the Gaussian one. 0 50 100 150 200 250 -10 -5 0 5 10

Nanocomposite Solid Electrolytes Based on Lithium Perchlorate

High-conductive composite solid electrolytes with the conductivity of 10-3-10-2 S/cm at 200oC were obtained by doping of lithium perchlorate with different oxide additives, such as nanocrystalline α-Al2O3, α-LiAlO2, γ-Al2O3, γ-LiAlO2, MgO and mesoporous SiO2 (MCM-41). It was experimentally shown that the crystal structure and chemical nature of the oxide influence upon electrical properties of the composites, primarily on the activation energy of connductivity. The composite 0.4LiClO4 - 0.6γ-Al2O3 was investigated by 7Li, 27Al and 1H nuclear magnetic resonance methods. It was shown that practically all lithium cations in the composite are mobile. The NMR data agree with ac-conductivity data at high temperatures, whereas there is a discrepancy at low temperatures.

Mixed cation effect on silver–lithium solid electrolyte (AgI) 0.5(LiPO 3) 0.5

On quenching the molten mixture (AgI) 0.5(LiPO 3) 0.5 two different components were obtained. The first type is the clear and transparent glass, named G-(AgI) 0.5(LiPO 3) 0.5 and the second is the yellowish-green opaque named C-(AgI) 0.5(LiPO 3) 0.5. The X-ray diffraction data confirmed that the G-(AgI) 0.5(LiPO 3) 0.5 is an amorphous phase, with a broad peak corresponds to original LiPO 3 glass, but its conductivity increases from 10 − 8 S/cm to 10 − 6 S/cm at ambient temperature, and the glass transition temperature decreases from 327 °C to 321 °C. The composite part, C-(AgI) 0.5(LiPO 3) 0.5 consists of a mixture of amorphous background and several Bragg peaks that correspond to the crystalline AgI, but its conductivity increases from 10 − 6 S/cm to 10 − 3 S/cm at ambient temperature. The AC conductivity data at various temperatures were fit to the Non Linear Least Square Equation containing three parameters, the DC conductivity ( σ DC), the onset frequency ( ω p) and the exponent factor ( n). The values of n were found to be larger than 1 for LiPO 3 and G-(AgI) 0.5(LiPO 3) 0.5 which are in agreement with earlier results, while for C-(AgI) 0.5(LiPO 3) 0.5 the n values are between 0.5 and 0.7. The n value really depends on the characteristic of the disorder materials and it may be due to more than one vibration that occur at the same time.

ELECTRIC MODULUS AND DIELECTRIC STUDIES OF ALIZARIN DOPED ANTHRAQUINONE

The electrical properties of alizarin doped anthraquinone were investigated using a complex impedance spectroscopy technique. Dielectric study revealed a phase transition from the semiconducting to the conducting state at 53°C. The dielectric relaxation was found to be of non-Debye type. Evidence of temperature-dependent electrical relaxation phenomena as well as a positive temperature coefficient of conductivity character were observed in the sample. The frequency dependence of AC conductivity data followed a power law. Electric modulus as well as AC conductivity analyses indicated the possibility of a hopping mechanism for electrical conduction in the system. The activation energy and minimum hopping distance were estimated from the AC conductivity data.

Low frequency divergence of the dielectric constant and signature of the Meyer–Neldel rule in the ac conductivity of PbS and PbS:Mn nanorods in polymer

We report here the temperature (130–296K) and frequency (100Hz–1MHz) dependent dielectric study for PbS and PbS:Mn nanorods of diameter ∼30nm grown in polymer matrix. The frequency dependent capacitance data show the divergence of capacitance in the low frequency regime below a cutoff frequency ∼20kHz, above which it is fairly constant or slowly varying with frequency. The temperature variation of ac conductivity data for such quasi-one-dimensional nanorods reveals the signature of correlated barrier hopping transport in the framework of the Meyer–Neldel rule. We also extend our discussion for Mn doped PbS nanorods to get insight into the effect of magnetic doping on the dielectric properties.

Mixed conductivity studies in silver oxide based barium vanado–tellurite glasses

The dc conductivity and frequency dependent ac conductivity of the quaternary glass system x(BaO:1.5 Ag 2O)–(95 − x)V 2O 5–5TeO 2, are reported in the frequency range 1 Hz to 32 MHz in the temperature range from room temperature to 433 K. The dc conductivity measured in high temperature range increased with transition metal oxide content while the activation range decreased. The conductivity arises mainly from polaron hopping between V 4+ and V 5+ ions. High temperature conductivity data satisfy Mott's small polaron hopping model. It is found that a mechanism of non-adiabatic hopping is the most appropriate conduction model for these glasses. A power law behavior σ( ω) = σ dc + Aω n (with 0 < n < 1) is well exhibited by the ac conductivity data of the glasses. The activation energy calculated from both the relaxation time and dc conductivity is found to be nearly same in both the cases. A scaling of the conductivity spectra with respect to temperature and composition is attempted and it is observed that the relaxation dynamics of charge carriers in the present glasses is independent of temperature and composition.

Electrical conduction in (Na0·5Bi0·5)TiO3 ceramic: impedance spectroscopy analysis

Polycrystalline sample of (Na0·5Bi0·5)TiO3 was prepared using a high temperature solid-state reaction synthesis at 1070°C and subsequent sintering at 1100°C in oxygen atmosphere. X-ray diffraction (XRD) analysis of (Na0·5Bi0·5)TiO3 powder indicated the formation of a single phase rhombohedral structure. Dielectric study revealed the diffuse phase transition at 340°C. The ac conductivity data were found to obey power law and showed negative temperature coefficient of resistance character. Complex electric modulus analysis indicated non-Debye type dielectric relaxation in the system. The ac conductivity data were used to evaluate the density of states at Fermi level, minimum hopping length and activation energy of the compound. The correlated barrier hopping model was found to successfully explain the mechanism of charge transport in (Na0·5Bi0·5)TiO3.

Synthesis, characterization, and electrochemical and electrical properties of a novel ball-type hexanuclear metallophthalo-cyanine, bridged by calix[4]arenes substituted with four hexyl-thiometallophthalocyanines through nitro coupling

In this study, the synthesis of a supramolecular hexaphthalocyaninato hexazinc(II) with hexylthio substituents is reported. Starting from 5,11,17,23-tetra-tert-butyl-25,27-dihydroxy-26,28-dimethoxycalix[4]arene, mononitro derivative of calix[4]arene 1 was obtained. Compound 1 was converted to phthalodinitrile derivative 2 by the reaction with 4-nitrophthalonitrile in dry dimethylsulfoxide by the method of nucleophilic substitution of an activated nitro group in an aromatic ring. The tetramerization of compound 2 with Zn ( OAc )2·2 H 2 O in 1-pentanol gave the novel ball-type binuclear zinc (II) phthalocyanine 3 which was reacted with unsymmetric zinc(II) phthalocyanine 4 to furnish a supramolecular assembly of a zinc(II) phthalocyanine of a ball type with four zinc(II) phthalocyanines through azo bridges, 5. Newly synthesized compounds were characterized by elemental analysis, UV-vis, IR, MALDI-TOF MS and 1 H NMR spectra. The electrochemical and spectroelectrochemical properties of 5 were also examined in nonaqueous media. The measurements showed the formation of various mixed-valence oxidation and reduction species, due to the strong intramolecular interactions between the Pc rings. Both DC and AC conductivity data were analyzed by the existing theory.

Electrical properties of some Y2O3 and/or Fe2O3-containing lithium silicate glasses and glass-ceramics

The ac electrical properties of some lithium silicate glasses and glass-ceramics containing varying proportions of Y2O3 and/or Fe2O3 were measured to investigate their electronic hopping mechanism. There is a clear variation of these properties with composition. The obtained results were related to the concentration and role of Y2O3 and/or Fe2O3 in the lithium silicate glass structure. In crystalline solids the electrical properties data obtained were correlated to the type and content of the mineral phases formed as indicated by X-ray diffraction analysis (XRD). The conductivity, dielectric constant and dielectric loss of the studied glasses were studied using the frequency response in the interval 30 Hz–100 KHz and the effect of compositional changes on the measured properties was investigated. The measurements revealed that the electrical responses of the samples were different and complex. The addition of Y2O3 generally, decreased the ac conductivity, dielectric constant and dielectric losses of the lithium silicate glasses. The addition of Fe2O3 in Y2O3-containing glasses increases the conductivity, while, the dielectric constant and dielectric losses were found to be decreased. However, the addition of Fe2O3 instead of Y2O3 led to decrease the ac conductivity and increased their dielectric constant and dielectric losses. The obtained data were argued to the internal structure of the lithium silicate glass and the nature or role-played by weakness or rigidity of the structure of the sample. Lithium disilicate-Li2Si2O5, lithium metasilicate-Li2SiO3, two forms of yttrium silicate Y2Si2O7 & Y2SiO5, iron yttrium oxide-YFeO3, lithium iron silicate-LiFeSi2O6 and α-quartz phases were mostly developed in the crystallized glasses. The conductivity of the crystalline materials was found to be relatively lower than those of the glass. At low frequency, as the Y2O3 content increased the ac conductivity, dielectric constant and dielectric loss data of the glass-ceramics decreased. However, the addition of Fe2O3 to the Y2O3 containing glass-ceramic led to increase the conductivity. The addition of high content of Fe2O3 instead of Y2O3 in the glass ceramic led to increase the ac conductivity.

Electrical properties of a lead-free perovskite ceramic: (Na0.5Sb0.5)TiO3

Polycrystalline (Na0.5Sb0.5)TiO3 was prepared using a high-temperature solid-state reaction method. An XRD analysis indicated the formation of a single-phase monoclinic structure. Complex impedance studies revealed the presence of grain boundary effects from 300 °C onwards. Also, the dielectric relaxation in the system was found to be of a non-Debye type. The ac conductivity data were used to evaluate the density of states at the Fermi level, the minimum hopping length and activation energy of the compound. The dc electrical and thermal conductivities of grain and grain boundary have been assessed. The correlated barrier hopping model was found to successfully explain the mechanism of charge transport in (Na0.5Sb0.5)TiO3.

Dielectric and impedance study of lead-free ceramic: (Na0.5Bi0.5)ZrO3

Polycrystalline sample of (Na0.5Bi0.5)ZrO3 was prepared using a high-temperature solid-state reaction technique. XRD analysis indicated the formation of a single-phase orthorhombic structure. Dielectric study revealed the diffuse phase transition at 425 °C. AC impedance plots were used as tools to analyse the electrical behaviour of the sample as a function of frequency at different temperatures. The ac impedance studies revealed the presence of grain boundary effect at and above 350 °C. Complex impedance analysis indicated non-Debye type dielectric relaxation and negative temperature coefficient of resistance (NTCR) character of (Na0.5Bi0.5)ZrO3. AC conductivity data were used to evaluate the density of states at Fermi level and activation energy of the compound. DC electrical and thermal conductivities of grain and grain boundary have been assessed.

Influence of TiO2 and ZnO on the conductivity and dielectric properties of copper-bismuth glasses

Influence of TiO2 and ZnO oxides has been investigated elaborately on the conductivity and dielectric properties of unconventional and technologically important 40CuO–40Bi2O3–20X (where X=TiO2 and ZnO) glasses. The dc electrical conductivity of ZnO containing glass is found to be higher than that of TiO2 containing one at all temperatures (300–600K). A change from adiabatic to nonadiabatic small polaron hopping conduction is observed due to the influence of TiO2 and ZnO oxides. It has been perceived that the ZnO doped glass shows relatively more ac conductivity compared to that of the TiO2 doped one, consistent with the dc conductivity data. Random-free-energy barrier model of Dyre [J. Appl. Phys. 64, 2456 (1988)] is suited to be the most appropriate one for explaining the frequency dependence of ac conductivity data and frequency exponent. The large dielectric constant in both the glasses can be explained by the response of Bi3+ ions to ac.

Impedance spectroscopy of (Na0.5Bi0.5)(Zr0.25Ti0.75)O3 lead-free ceramic

Polycrystalline sample of (Na0.5Bi0.5)(Zr0.25Ti0.75)O3 was prepared using a high-temperature solid-state reaction technique. XRD analysis indicated the formation of a single-phase orthorhombic structure. AC impedance plots were used as tool to analyse the electrical behaviour of the sample as a function of frequency at different temperature. The AC impedance studies revealed the presence of grain boundary effect, from 350°C onward. Complex impedance analysis indicated non-Debye type dielectric relaxation. The Nyquist plot showed the negative temperature coefficient of resistance (NTCR) character of (Na0.5Bi0.5)(Zr0.25Ti0.75)O3. AC conductivity data were used to evaluate the density of states at Fermi level and activation energy of the compound. DC electrical and thermal conductivities of grain and grain boundary have been assessed.

Electrical characterisation of Pb2Bi3SmTi5O18 ceramic using impedance spectroscopy

Polycrystalline sample of Pb2Bi3SmTi5O18, a member of tungsten–bronze (TB) family, was prepared using a high temperature solid state reaction technique. X-ray diffraction (XRD) analysis indicated the formation of a single phase orthorhombic structure. AC impedance plots were used as a tool to analyse the electrical behaviour of the sample as a function of frequency at different temperatures. The ac impedance studies revealed the presence of grain boundary effect, from 350°C onward. Complex impedance analysis indicated non-Debye type dielectric relaxation. The Nyquist plot showed the negative temperature coefficient of resistance (NTCR) character of Pb2Bi3SmTi5O18. AC conductivity data were used to evaluate the density of states at Fermi level and activation energy of the compound.

Structural and lithium ion transport studies in borophosphate glasses

Lithium ion transport process and glass network modification upon the variation of network modifier (M) to former (F) ratio (M/F) in 30% LiBO 2–70% [(M Li 2O–F P 2O 5)] glasses have been investigated. The glasses with different M/F ratios (0.42–1.0) were prepared by melt quenching technique and characterized by X-ray diffraction (XRD), differential scanning calorimetry (DSC), Raman and impedance spectroscopy techniques. The glass transition temperature, T g increased with increasing M/F ratio suggesting an increase in overall connectivity of the network structure. Dc conductivity showed an enhancement of three orders of magnitude with increasing M/F. The observed increase in T g and dc conductivity with modifier concentration has been explained on the basis of the competition between network breaking/forming events, leading to an increase in overall connectivity of the network and the formation of continuous channels for ion migration. Ac conductivity data were analyzed by fitting the data to Almond-West type power law equation, σ′( ω) = σ(0) + Aω n . The power law exponent, n, was found to be temperature dependent and exhibited a minimum, n min. The observation of n min has been explained in the light of diffusion controlled relaxation (DCR) model. Furthermore, the scaling of both ac conductivity and electrical modulus data showed an excellent collapse on to a single master curve indicating that there is a good time–temperature superposition and that conduction mechanism remains unchanged in this glass system.

Dielectric, Impedance, Magnetic and Magnetoelectric Measurements on YMnO3

Polycrystalline hexagonal Yttrium Manganites (YMnO 3 ) were prepared by solid-state route. X-ray studies revealed the formation of homogenous and single phase material in hexagonal structure. Dielectric, impedance, electrical, magnetic and magnetoelectric measurements were performed on the YMnO 3 ceramics. Dielectric and impedance studies show relaxations near 200°C. Complex spectroscopic analysis, in the temperature range of 30–300°C from 1 kHz to 1 MHz, showed non-Debye relaxations. Ac and dc electrical measurements were extracted to understand the transport mechanism: Ac conductivity data is found to obey ‘Universal’ power law with exponent 0.8. Low temperature magnetization measurements were performed to understand the magnetic nature of the sample. Room temperature magnetoelectric (ME) measurements were also performed and corroborated with the magnetization data.

Structural properties and impedance spectroscopy of excimer laser ablated Zr substituted BaTiO3 thin films

BaZr0.15Ti0.85O3 thin films were deposited on Pt-coated Si substrates using the pulsed excimer laser ablation technique. X-ray diffraction and atomic force microscope techniques were used to study the structural characteristics of the films. Films with good crystalline quality, with an average grain size of 0.5 µm were obtained, under various oxygen background pressures. Ferroelectric hysteresis loops recorded on the films deposited at 26.66 Pa oxygen pressure showed the best properties. To gain a further understanding of the electrical properties of these films, impedance spectroscopy was used and data acquired at several different temperatures. AC conductivity plots showed the presence of space charge conduction at low frequencies; however, at high frequencies, all the curves merged and expectedly showed an almost dc conduction behaviour. The activation energy obtained from ac conductivity data may be attributed to oxygen vacancy motion.

Effect of sintering on the ionic conductivity of garnet-related structure Li 5La 3Nb 2O 12 and In- and K-doped Li 5La 3Nb 2O 12

Garnet-structure related metal oxides with the nominal chemical composition of Li 5La 3Nb 2O 12, In-substituted Li 5.5La 3Nb 1.75In 0.25O 12 and K-substituted Li 5.5La 2.75K 0.25Nb 2O 12 were prepared by solid-state reactions at 900, 950, and 1000 °C using appropriate amounts of corresponding metal oxides, nitrates and carbonates. The powder XRD data reveal that the In- and K-doped compounds are isostructural with the parent compound Li 5La 3Nb 2O 12. The variation in the cubic lattice parameter was found to change with the size of the dopant ions, for example, substitution of larger In 3+( r CN6: 0.79 Å) for smaller Nb 5+ ( r CN6: 0.64 Å) shows an increase in the lattice parameter from 12.8005(9) to 12.826(1) Å at 1000 °C. Samples prepared at higher temperatures (950, 1000 °C) show mainly bulk lithium ion conductivity in contrast to those synthesized at lower temperatures (900 °C). The activation energies for the ionic conductivities are comparable for all samples. Partial substitution of K + for La 3+ and In 3+ for Nb 5+ in Li 5La 3Nb 2O 12 exhibits slightly higher ionic conductivity than that of the parent compound over the investigated temperature regime 25–300 °C. Among the compounds investigated, the In-substituted Li 5.5La 3Nb 1.75In 0.25O 12 exhibits the highest bulk lithium ion conductivity of 1.8×10 −4 S/cm at 50 °C with an activation energy of 0.51 eV. The diffusivity (“component diffusion coefficient”) obtained from the AC conductivity and powder XRD data falls in the range 10 −10–10 −7 cm 2/s over the temperature regime 50–200 °C, which is extraordinarily high and comparable with liquids. Substitution of Al, Co, and Ni for Nb in Li 5La 3Nb 2O 12 was found to be unsuccessful under the investigated conditions.

Estimation of charge-carrier concentration and ac conductivity scaling properties near theV−Iphase transition of polycrystallineNa2SO4

The conductivity spectra of polycrystalline ${\mathrm{Na}}_{2}\mathrm{S}{\mathrm{O}}_{4}$ have been investigated in the frequency range $42\phantom{\rule{0.3em}{0ex}}\mathrm{Hz}--1\phantom{\rule{0.3em}{0ex}}\mathrm{MHz}$ at different temperatures below and above the $V\text{\ensuremath{-}}I$ phase transition temperature. The conductivity data have been analyzed using Almond-West formalism. The dc conductivity, the hopping frequency of the charge carriers, and their respective activation energies have been obtained from the analysis of the ac conductivity data, and the concentration of charge carriers was calculated at different temperatures. The power-law exponent $n$ of the conductivity spectra has average values of 0.43 and 0.61 in phases $V$ and $I$, respectively, which indicates different conduction properties in the two phases. Moreover, scaling of the conductivity spectra at the low- and high-temperature phases was performed in accord with Ghosh's scaling approach. It is found that the scaling properties depend on the structure of the investigated material.