Dc Conductivity Data Research Articles

Crystal structure and dielectric properties of Ln2Ti2SiO9 (Ln = Pr and Nd)

Low loss and high dielectric constant materials are essentially desired for wide varieties of applications in electronics and communication technology. Herein the structure and dielectric properties of two titanosilicates, Ln2Ti2SiO9, for Ln = Pr3+ and Nd3+ are reported. Both materials are isostructural and have layered structure with layers of [LnTi2SiO9]3- and Ln3+ ions. Electrical properties of both have been analyzed by using the temperature and frequency dependent permittivity, loss, conductivity and modulus data. At room temperature, appreciable relative permittivity (35 for Nd2Ti2SiO9 and 22 for Pr2Ti2SiO9 over the frequency range of 100 Hz to 5 MHz) and low dielectric loss (like 0.007–0.03 at 100 Hz and 10−4-10−3 at 1 MHz). Analysis of dc-conductivity data of both compounds indicate that the conduction in both materials is due to the correlated barrier hopping (CBH) of polarons. The relaxation peak of modulus spectra indicates more non-Debye like relaxation in Pr2Ti2SiO9 than that in Nd2Ti2SiO9, and that is possibly due to increased correlation in the dynamics of hopping polarons in Pr2Ti2SiO9.

Structural, morphological, electrical, and dielectric properties of Na2Cu5(Si2O7)2 for ASSIBs.

Solid inorganic electrolyte materials are fundamental components for constructing all-solid-state sodium-ion batteries. These solid electrolytes offer considerable benefits related to safety, electrochemical performance, and mechanical stability in comparison to liquid organic electrolyte systems. This study investigates the sodium ion conduction mechanism and relaxation kinetics in the sorosilicate material Na2Cu5(Si2O7)2, a potential solid electrolyte, using impedance spectroscopy. Analysis of the DC conductivity data demonstrates that sodium ion mobility follows Arrhenius behavior with a thermal activation energy barrier of 1.21 eV. This work highlights the importance of carefully choosing an appropriate equivalent circuit model to extract DC conductivity parameters from impedance data, given the contributions from both grain and grain boundary effects. Analysis of the AC conductivity and dielectric constant as a function of frequency and temperature demonstrates that ionic conduction takes place in this material through a process in which charge carriers overcome correlated energy barriers, known as correlated barrier hopping. The neutron diffraction patterns were analyzed using soft bond valence sum (BVS) techniques to map the possible ionic conduction pathways within the unit cell. Examination of the data points to obstructions in the sodium ion diffusion routes along the a-axis and diagonal of the bc plane within the triclinic unit cell. These bottlenecks likely contribute to the high activation energy and correspondingly low ionic conductivity observed. Analysis of dielectric properties by modulus verified that the ionic conduction relaxation phenomena exhibit thermal activation and a distribution of relaxation times. In summary, this work elucidates the microscopic ionic conduction mechanism in Na2Cu5(Si2O7)2 through extensive analysis encompassing DC/AC conductivity, electric modulus, and dielectric constant measurements. The insights gained into the ionic conduction mechanism will aid in engineering optimized ionic conductor materials for battery technologies.

Voigt Profile is Suitable for Impedance Spectroscopic Analysis of BLSF Ceramics

Abstract: In our earlier studies, samarium-modified bismuth layer-structured ferroelectrics (BLSF), namely SmxBi3-x TiNbO9 (SBTN); (x=0, 0.2, 0.4, 0.6. 0.8, and 1.0), prepared by solid-state reaction method, have shown broad dielectric relaxations. Among all the compositions, Bi2.6Sm0.4TiNbO9 (BST-0.4) has shown a lower tolerance factor, high remnant polarization (Pr) value, and low stretching factor. In addition, the compound has shown interesting broad dielectric relaxation and non-Debye nature. The specific reasons for the broad relaxation remain unclear. To gain more insights, we synthesized multi rare earth ion substituted compounds, namely, Bi2.6La0.2Sm0.2TiNbO9 (sample A) and Bi2.6La0.2Gd0.2TiNbO9 (sample B), using the conventional solid-state reaction method. A single impedance spectroscopic approach alone may not be sufficient to explain the asymmetric or non-Debye behavior, therefore Lorentzian, Gaussian, and Voigt fitting were adopted in the present investigation. From the analysis, the Voigt profile (Vf and Vʹf) is found to be a valuable alternative tool to understand the broad impedance non-Debye relaxations. Finally, results were corroborated by dc-conductivity data. Keywords: BLSF, Modulus spectroscopy, Relaxation, Defect-mechanism, Gaussian, Lorentz and Voigt fitting, Dc conductivity.

The novel oxy-sulfide glassy ionic conductors Na4P2S7-xOx 0 ≤ x ≤ 7: Understanding the features of static and dynamic cations

We present a 23Na nuclear spin dynamics model for interpreting nuclear magnetic resonance (NMR) spin-lattice relaxation and central linewidth data in the invert glass system Na4P2S7-xOx, 0 ≤ x ≤ 7. The glassy nature of this material results in variations in local Na+ cation environments that may be described by a Gaussian distribution of activation energies. A consistent difference between the mean activation energies determined by NMR and DC conductivity measurements was observed, and interpreted using a percolation theory model. From this, the NaNa coordination number in the sodium cation sublattice was obtained. These values were consistent with jumps through tetrahedral faces of the sodium cages for the sulfur rich glasses, x < 5, consistent with proposed models of their short range order (SRO) structures. From NMR spin-echo measurements, we determined the NaNa second moment M2 resulting from the NaNa magnetic dipole interaction of nearest neighbors. Values of M2 obtained as a function of sodium number density N were in agreement with models for uniform sodium distribution, indicating that these invert glass systems form so as to maximize the average NaNa distance. A simple Coulombic attraction model between Na+ cation and X (=S−, O−) anion was applied to calculate the activation energy. In the range 1.5 ≤ x ≤ 7, an increase in activation energy with increasing oxygen content x occurred, and was consistent with the decrease in average anionic radius, and the increase in Coulombic attraction. For small oxygen additions, 0 ≤ x ≤ 1.5, the suggested minimum at low oxygen concentration seen in the activation energies obtained from DC conductivity data is not evident in the model.

Effect of DC bias on dipolar response of yttrium iron garnet

Yttrium iron garnet (YIG) is a prominent magnetic (ferrimagnetic) insulator and an excellent material for wide ranging microwave and millimeter-wave applications. In polycrystalline form it exhibits high dielectric loss due to contributions coming from grain & grain boundaries, and Fe heterovalency. We have investigated the effect of dc bias voltage on the dielectric properties of YIG in a wide range of temperature (100 - 600 K) and frequencies (100 Hz - 1 MHz). Consistent with previous observations, without bias a dominant frequency dispersion due to hopping of the Fe2＋ & Fe3＋ is observed in low temperature region and a wider frequency dispersion is observed at higher temperatures arising due to grain-grain boundary contributions. Application of a small dc bias voltage increases the dielectric constant and reduces the dielectric loss significantly at higher frequencies. The DC bias-induced improvements are much more dramatic at higher temperatures, where grain boundary contributions dominate. Our detailed analysis of dc and ac conductivity data show that the dc bias suppresses the grain boundary contributions significantly and at the same time it boosts the polarizability due to the Fe2＋/Fe3＋ hopping.

Ionization Difference between Weak and Strong Electrolytes as Perturbed by Conductivity Spectra Analysis

While the static structure of aqueous electrolytes has been studied for decades, their dynamic microscopic structure remains unresolved yet critical in many areas. We report a comparative study of dc and ac (1 Hz to 20 GHz) conductivity data of weak and strong electrolytes, highlighting previously missing differences and similarities. Based on these results, we introduce into consideration the intrinsic short-lived ions of water, namely, excess protons (H3O+) and proton holes (OH-). We show that the model accounting for the neutralization of these ions by the species of electrolyte explains the conductivity of aqueous solutions in the concentration range 10-7-10 M. Based on independent experimental data, we hypothesize that the aggregation of the species in weak electrolytes may determine the main difference between the conductivity of weak and strong electrolytes. Our results push forward the understanding of the dynamic structure of aqueous electrolyte solutions and are important to nanofluidic, biological, and electrochemical systems.

Structural, Optical and Electrical Conductivity Studies in Polycarbazole and its Metal Oxide Nano Composites

Polycarbazole (PCz) has been synthesized by chemical oxidation method using APS as an oxidizing agent and PCz/CuO and PCz/Fe2O3 nanocomposites by in situ polymerization method for different wt% of CuO and Fe2O3 at room temperature. XRD patterns confirmed crystalline nature of samples. FTIR indicated strong interaction between PCz and nano fillers. The morphological and optical absorption studies were carried out using SEM and UV–Vis respectively. Addition of CuO or Fe2O3 to PCz decreased its direct and indirect band gaps. However, band gap showed a small change with dopant contents up to 30%. Urbach energy decreased with the addition of dopants. But Urbach energy of the composites increased with increasing dopants content from 10 to 30%. DC conductivity of PCz and its nanocomposites has been measured by following two probe technique in the temperature range 300–423 K. The conductivity of both the nanocomposites is found to be less than the pure PCz and it is found to increase with wt% of CuO or Fe2O3 as the case may be. The activation energy has been determined by fitting Arrhenius expression to the dc conductivity data at high temperature. The activation energy of polycarbazole is determined to be less than that of the composites. In both the composites, activation energy decreased and conductivity increased with the increase of dopant content.

Dielectric relaxation of 1-butyl-3-methylimidazolium tetrafluoroborate/TX-100/toluene microemulsions: Structure transition, percolation mechanism, interfacial polarization and electrical properties of microdroplets

The dielectric relaxation spectra of the non-aqueous ionic liquid (IL) microemulsions composed of 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4])/p-(1,1,3,3-tetramethylbutyl)phenoxypolyoxyethyleneglycol (TX-100)/toluene were obtained, the measured frequency is between 1 MHz and 3 GHz. A unique dielectric relaxation located at 10–100 MHz was observed. The direct current (dc) conductivity data were obtained from the total dielectric loss. Near the percolation transition, weight fraction dependence of dc conductivity and static dielectric constant, frequency dependence of permittivity and loss angle all suggest that static percolation occurs in this hydrophilic IL microemulsion. Phase boundaries of IL-in-toluene (IL/O), bicontinuous (B.C.) and toluene-in-IL (O/IL) subregions were determined by the inflection points in the dependent curve of relaxation parameters varied with weight fraction. The mechanism of this dielectric relaxation is attributed to the interfacial polarization of droplets by analyzing relaxation time with Maxwell-Wagner theory. The phase parameters, which reflect the interior properties of the spherical dispersed particle, were calculated by Hanai theory. The dependence of phase parameters on the variation of sample composition was properly explained. For O/IL subregion, the continuous phase should be an IL/TX-100 binary solvent rather than the pure IL. For IL/O subregions, a certain amount of toluene was dissolved in the droplets.

Charge carrier transport and electrochemical stability of Li2O doped glassy ceramics

We study electrical conductivity of new Li2O doped glassy ceramics in wide frequency and temperature regime not only for their applicability in various fields like lithium ion conductors but also for academic interest. Here, we employ “Jonscher’s power law model and Almond-West formalism” to interpret mixed conduction process in the present system. We use “Mott’s variable range hopping” model to analyse low temperature DC conductivity data. It also points that the ratio of power law pre-factor to the exponent (–log10 A/S) indicates temperature independency and strong composition dependency of present conductors. Higher lithium content in the composition may disturb “electrochemical stability” of the present system. We do believe that these glassy ceramics are suitable candidates for lithium ion battery application with lower lithium content.

Microstructures and charge carrier transport of some Li2O doped glassy ceramics

We study electrical conductivity of new Li2O doped glassy ceramics in wide frequency and temperature regime not only for their applicability in various fields like lithium ion conductors but also for academic interest. Here, we employ “Mott’s variable range hopping” model to analyse low temperature DC conductivity data. The microstructures and electrical conductivity of them have been explored and correlated. We do believe that these glassy ceramics are suitable candidates for lithium ion battery application.

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 and electron transport properties of CaFe2O4 synthesized in air and in helium atmosphere

The samples with the CaFe2O4-type crystal structure were obtained by the solid-state reaction method at 1000 °C in the air and the helium atmosphere for the first time. We investigated the modification of the structural and electronic properties of the obtained samples. Mössbauer, XAFS-, XPS-spectroscopies, and dc-, ac-conductivity measurements were carried out. Mössbauer and XAFS-spectroscopies showed that the local environment of Fe and Ca cations does not change in the case of the inert atmosphere synthesis. Nevertheless, a sharp six-order increase in the electrical resistance observed at room temperature for the sample obtained in the in the helium atmosphere. Moreover, calculated from dc-conductivity data activation energy rises from 0.327 for the air-synthesized sample to 0.585 eV for helium-obtained one. This behavior indicates significant modification of in-band-gap energy structure, which correlated with thermally activated charge carriers. Our ac-conductivity measurements in the frequency range of 1 kHz–2 MHz for the CaFe2O4 obtained in the air showed the presence of defect levels in the energy band structure. Oxygen pressure reduction during the synthesis results in levels vanishing. Therefore, we suppose the key role of oxygen atoms in the transport properties of the material, which is indirectly confirmed by XPS data. In prospect, CaFe2O4 can be used in promising gas analyzers.

Structural, AC conductivity, conduction mechanism and dielectric properties of La0.62Eu0.05Ba0.33Mn0.85Fe0.15O3 ceramic compound

The new perovskite compound La0.62Eu0.05Ba0.33Mn0.85Fe0.15O3 was successfully synthesized via the sol–gel process. X-ray diffraction revealed that our sample is pure and crystallizes in the orthorhombic structure with Pbnm space group. Electrical properties were performed using the complex impedance spectroscopy technique in the range of frequency (40–10 MHz) and at various temperatures (80–400 K). AC-conductivity results are well described by the universal Jonsher’s power law at low temperatures and the DC-conductivity data are well fitted by the small polaron hopping model at high temperatures. Impedance results show a negative temperature coefficient of resistance (NTCR) which discloses the semiconductor behaviour of the studied sample. Nyquist plots were well fitted by an equivalent circuit involving the contribution of grain and grain boundaries in the conduction process. Giant dielectric values, useful in electronic devices, were obtained. Moreover, a relaxation diffuse phase transition is attributed to a strong heterogeneity in A and B sites of the studied perovskite.

Exploring disorder in the spin gapless semiconductor Mn2CoAl

Since the prediction of spin gapless semiconducting behaviour in the Heusler compound Mn2CoAl, evidence of spin gapless behaviour in thin films has typically been inferred from magnetotransport measurements. The spin gapless state is however fragile, and further, band structure calculations indicate that even a small amount of atomic disorder may destroy it. To explore the impact of disorder on the properties of Mn2CoAl, we have undertaken an experimental study of the structural, magnetotransport and optical properties from the far infrared to the UV, on DC magnetron sputtered Mn2CoAl thin films. A very short mean free path, of the order of a lattice spacing, is extracted from the DC transport data. A room temperature resistivity of 200 μΩcm along with a small and negative temperature coefficient of resistance between 4 and 400 K was measured. We note that parameters of this magnitude are often observed in disordered metals. We find this behaviour is well described by a weak localisation model, a result that is supported by a large Drude contribution to the optical response, where a high scattering rate is derived, which is equal to the value derived from the DC conductivity and Hall effect data. We also note the strong similarities between the magnetotransport behaviour reported for Mn2CoAl films in the literature, including ours. We conclude that, based on comparisons between the experimental data, and recent band structure calculations that explicitly include disorder, as-prepared Mn2CoAl films are best described as a disordered metal, rather than a spin gapless semiconductor.

Investigating the effect of thickness on the structural, morphological, optical and electrical properties of AgBiSe2 thin films

Herein, a one-step thermal evaporation was used for fabrication of silver bismuth selenide (AgBiSe2) thin films of various thickness. The influence of thickness on the structural, optical and electrical properties of AgBiSe2 thin films has been studied. The X-ray diffraction confirmed single hexagonal structure of deposited AgBiSe2 thin films. The average grain sizes D and microstrain ε of deposited AgBiSe2 films were estimated by Williamson-Hall (W-H) relation. The grain size increases from 11.52 to 29.12 nm as the thickness was increased from 150 to 550 nm, whereas strain dislocation density (ξ) and the number of crystallites N tends to decrease with thickness. The selected area electron diffraction pattern (SAED) obtained by high resolution transmission electron microscopy (HRTEM) verified the polycrystalline nature of samples and it is found to nearly agree with X-ray diffraction data. The elemental composition measurement of the as-deposited AgBiSe2 thin film showed that the as-deposited film is near stoichiometric in compound. The influence of film thickness on the optical parameters of the AgBiSe2 thin films, such as refractive index n, extinction coefficient k, real dielectric ε1, imaginary dielectric constant ε2, skin depth and the optical band gap, Eg has been studied. It is found that the values of energy gap decrease from 1.88 to 1.68 eV with increasing thickness, while the values of Urbach energy follow an opposite trend. The electrical conductivity was measured by four-probe experiment in the range from 300 to 500 K. The analysis of dc conductivity data revealed the presence of two distinct regions with two various slopes confirming the transformation from hexagonal phase to rhombohedral phase at about 460 K.

Polaron conduction mechanisms in (B2O3)-(TeO2)-(MoO3)-(Er2O3) glasses

A set of borotellurite glasses in the compositions, (B2O3)0.1-(TeO2)0.5-x-(MoO3)0.4-(Er2O3)x; x = 0.01, 0.02, 0.03, 0.04, 0.05 have been synthesized and investigated for structure, density and dc conductivity as a function of temperature. Powder XRD patterns confirmed non-crystalline nature of glasses. Density and molar volume both varied arbitrarily with Er2O3 nano particle concentration revealing dynamic nature of the glass network. Some parameters associated with polarons have been determined. Semiconducting behavior of the glasses has been established by dc conductivity data. Mott’s small polaron hopping (SPH) model fit to the conductivity data enabled to determine Debye’s temperature and activation energy for conduction. Both Conductivity and activation energy decreased with Er2O3 nano particle concentration which infer that the structure of the glasses is changing in such a way that hindrance to the polaronic motion is developed in the increasing order with increase of Er2O3 concentration. The conductivity data deviated from SPH fit has been analyzed using Mott’s variable range hopping model and from it the density of states at Fermi level has been determined. For the first time, polaron conduction mechanisms have been probed in borotellurite glasses doped with MoO3 and Er2O3.

Structural, electrical, dielectric properties and conduction mechanism of sol-gel prepared Pr0.75Bi0.05Sr0.1Ba0.1Mn0.98Ti0.02O3 compound

A detailed investigation of structural, electrical and dielectric properties of Pr0.75Bi0.05Sr0.1Ba0.1Mn0.98Ti0.02O3 manganite prepared by the sol-gel method was undertaken. The Rietveld refinement of X-ray diffraction pattern reveals that this compound is indexed in the orthorhombic structure with Pbnm space group. Structural properties are also analyzed by scanning electron microscopy and energy dispersive X-ray spectroscopy at room temperature. DC conductivity (σDC) data show the presence of a semiconductor-metal transition at TSM = 360 K. σDC is described by small polaron hopping model at high temperatures and variable range hopping model at low temperatures. AC conductivity results follow the universal Jonsher's power law at relatively low temperatures and Drude's model at high temperatures. The impedance plots display the contribution of both intra- and inter-granular contributions. Dielectric measurements exhibit highly remarkable dielectric permittivities useful in electronic devices. Dielectric losses are shown to be governed by the DC conduction mechanism and described by the Giuntini theory.

Tuning of the electrical and thermal properties of SnSb2S4 sulfosalt vacuum evaporated thin films subjected to a heat treatment for thermoelectric application

This work covers the results of annealing effect in air on the structural, electrical and thermal properties of SnSb2S4. These films were deposited on unheated glass substrates by vacuum thermal evaporation and then they were subjected to annealing process for one hour in air ambient at 300 °C. First, X-ray diffraction analysis revealed that annealed film corresponds to SnSb2S4 material which has polycrystalline nature and the cristallites have the preferential orientation towards 531 direction. Second, the electrical properties have been investigated by means of complex impedance spectroscopy technique in frequency range 40 Hz–107 Hz and in temperature range 300 K–540 K. The effect of frequency and temperature on dielectric constant and dielectric loss has been discussed in terms of hopping of charge carriers. Moreover, the activation energy was estimated from both temperature dependence of dc conductivity and relaxation time data. Finally, the electro-pyroelectric method has been recognized as a reliable and useful tool for the measurement of thermal properties of SnSb2S4. Using a new approach based on theoretical models of electro-pyroelectric method, thermal properties of SnSb2S4 have been deduced. Indeed, thermal conductivity of annealed film at 300 °C is about 80.4 Wm−1 K−1. These results may be of interest for thermoelectric application of such ternary material.

Temperature and frequency response of conductivity in Ag2S doped chalcogenide glassy semiconductor

The electric conductivity of chalcogenide glassy semiconductor xAg2S-(1-x)(0.5S-0.5Te) has been presented here as a function of temperature and frequency. Formation of different nanocrystallites has been confirmed from X-ray diffraction study. It is also noteworthy that average size of nanocrystallites decreases with the increase of dislocation density. Dc conductivity data have been interpreted using Mott's model and Greaves's model in low and high temperature regions respectively. Ac conductivity above the room temperature has been analyzed using Meyer-Neldel (MN) conduction rule. It is interestingly noted that Correlated Barrier Hopping (CBH) model is the most appropriate conduction mechanism for x = 0.35, where pairs of charge carrier are considered to hop over the potential barrier between the sites via thermal activation. To interpret experimental data for x = 0.45, modified non–overlapping small polaron tunnelling (NSPT) model is supposed to be appropriate model due to tunnelling through grain boundary. The conductivity spectra at various temperatures have been analyzed using Almond-West Formalism (power law model). Scaling of conductivity spectra reveals that electrical relaxation process of charge carriers (polaron) is temperature independent but depends upon the composition of the present chalcogenide glassy system.

AC Conductivity and Dielectric spectra study of a blended solid polymer electrolyte.

Conductivity and dielectric spectra of a polymer blend electrolyte have been investigated in the temperature range ±20°C. AC conductivity data has been fitted with Jonscher's power law to confirm the hopping nature of ions. Further, the dielectric property has been studied by using the modulus and loss tangent spectra. Activation energy has been calculated from DC conductivity and loss tangent data. A similarity between the activation energy from DC conductivity and dielectric data indicates identical conducting species was involved in ion migration. Almond-West formalism has been applied to calculate the effective carrier concentration in the sample. Temperature variation of cation concentration shows a systematic decrease at sub-ambient temperature. A systematic change in DC conductivity, hopping frequency, and cation concentration at sub-ambient temperature indicates trapping of effective cation within the polymer matrix at sub-ambient temperature.