Electrical Transport Processes Research Articles

Complex impedance and electric modulus studies of magnetic ceramic Ni0.27Cu0.10Zn0.63Fe2O4

The electrical properties of Ni0.27Cu0.10Zn0.63Fe2O4 (NCZF) prepared from auto combustion synthesis of ferrite powders have been studied by impedance and modulus spectroscopy. We studied frequency and temperature dependencies of impedance and electric modulus of NCZF in a wide frequency range (20 Hz-5 MHz) at different measuring temperatures SM T (30-225 ℃). The complex impedance spectra clearly showed both grain and grain boundary effects on the electrical properties. The observed impedance spectra indicated that the magnitude of grain boundary resistance gb R becomes more prominent compared to grain resistance b R at room temperature, and with the increase in SM T , gb R decreases faster than the intrinsic b R. The frequency response of the imaginary part of impedance showed relaxation behavior at every SM T , and the relaxation frequency variation with SM T appeared to be of Arrhenius nature and the activation energy has been estimated to be 0.37 eV. A complex modulus spectrum was used to understand the mechanism of the electrical transport process, which indicated that a non-Debye type of conductivity relaxation characterizes this material.

Spectrophotometric and electrical properties of imperatorin: an organic molecule

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

Effect of Rare Earth Doping on Impedance, Modulus and Conductivity Properties of Multiferroic Composites: 0.5(BiLa x Fe1−x O3)–0.5(PbTiO3)

The Lanthanum-doped bismuth ferrite–lead titanate compositions of 0.5(BiLa x Fe1−x O3)–0.5(PbTiO3) (x = 0.05, 0.10, 0.15, 0.20) (BL x F1−x -PT) were prepared by mixed oxide method. Structural characterization was performed by X-ray diffraction and shows a tetragonal structure at room temperature. The lattice parameter c/a ratio decreases with increasing of La(x = 0.05–0.20) concentration of the composites. The effect of charge carrier/ion hopping mechanism, conductivity, relaxation process and impedance parameters was studied using an impedance analyzer in a wide frequency range (102–106 Hz) at different temperatures. The nature of Nyquist plot confirms the presence of bulk effects only, and non-Debye type of relaxation processes occurs in the composites. The electrical modulus exhibits an important role of the hopping mechanism in the electrical transport process of the materials. The ac conductivity and dc conductivity of the materials were studied, and the activation energy found to be 0.81, 0.77, 0.76 and 0.74 eV for all compositions of x = 0.05–0.20 at different temperatures (200–300 °C).

Study of dielectric, AC-impedance, modulus properties of 0.5Bi0.5Na0.5TiO3·0.5CaCu3Ti4O12 nano-composite synthesized by a modified solid state method

In the present research paper 0.5Bi0.5Na0.5TiO3·0.5CaCu3Ti4O12 nano-composite has been successfully synthesized by a simple, fast, and modified solid state method and shows improvement in both the dielectric constant (εr ~7007) and dielectric loss (tanδ~0.2) at 1kHz, at room temperature. X-ray diffraction analysis showed the existence of Bi0.5Na0.5TiO3 as a minor phase alongside the major phase of CaCu3Ti4O12. Average crystallite size calculated by XRD and particle size observed by transmission electron microscopy analysis were in good agreement. Energy dispersive X-ray analyses showed the presence of Ca, Cu, Bi, Na, Ti, O and demonstrated the purity and stoichiometry of the composite. The low frequency performance of the composite was estimated by measuring the frequency dispersion of the dielectric constant, dielectric loss, and AC electrical conductivity. The AC conductivity spectrum obeyed the Jonscher power law. Complex impedance spectroscopic studies reveal that the electrical relaxation process was temperature dependent and non-Debye type. The temperature dependence of the relaxation time was found to obey the Arrhenius law. The activation energy value (Ea~0.84eV) and relaxation nature of the modulus spectroscopic curve has been governed by the thermal motion and hopping mechanism of oxygen ion vacancies for electrical transport processes.

Piezo-phototronic Boolean logic and computation using photon and strain dual-gated nanowire transistors.

Using polarization charges created at the metal-cadmium sulfide interface under strain to gate/modulate electrical transport and optoelectronic processes of charge carriers, the piezo-phototronic effect is applied to process mechanical and optical stimuli into electronic controlling signals. The cascade nanowire networks are demonstrated for achieving logic gates, binary computations, and gated D latches to store information carried by these stimuli.

Investigation of complex impedance and modulus properties of Nd doped 0.5BiFeO3-0.5PbTiO3 multiferroic Composites

Abstract 0.5BiNdxFe1−x O 3 − 0.5PbTiO3 (BNxF1−x − PT)(x = 0.05, 0.10, 0.15, 0.20) composites were successfully synthesized by a solid state reaction technique. At room temperature, X-ray diffraction shows tetragonal structure for all concentrations of Nd doped 0.5BiFeO3 − 0.5PbTiO3 composites. The nature of Nyquist plot confirms the presence of bulk effects only for BNxF1−x − PT (x = 0.05, 0.10, 0.15, 0.20) composites. The bulk resistance is found to decreases with the increasing temperature as well as Nd concentration and exhibits a typical negative temperature coefficient of resistance (NTCR) behavior. Both the complex impedance and modulus studies have suggested the presence of non-Debye type of relaxation in the composites. Conductivity spectra reveal the presence of hopping mechanism in the electrical transport process of the composites. The activation energy calculated from impedance plot of the composite decreases with increasing Ndx concentration and found to be 0.89, 0.76, 0.71 and 0.70 eV for x=0.05, 0.10, 0.15 and 0.20 respectively.

Correlating the Resulting Internal Structures of Lithium-Ion Battery Electrodes to the Prior-to-Coating Suspension Properties

On the way to environmentally friendly and sustainable mobility lithium-ion batteries are in focus of various research works. Fundamental studies regarding the synthesis of new active materials or improvements of other important components, e.g. electrolytes or binders, are providing essential progress towards efficient e-mobility. In addition to all the material based developments, it is indispensable to gain a more detailed understanding of the main leverages which improve the electric and ionic transport processes inside the electrode and cell. One crucial property is the electrode’s inner structure. Since not only the materials but also the production processes have a considerable impact on the electrode structure, knowledge of the relationships between processes and structures is essential for a targeted electrode manufacturing.Electrode’s inner structure is basically predetermined by the chosen components, particularly by their particle size distributions and aggregation status (active material, additives) or molecular weight (binder). In addition, some process steps in the manufacturing chain for lithium-ion battery electrodes, such as dispersing and calendering, show crucial impact on the resulting electrode structure. The process modalities while dispersing the powdery materials in a solvent control the desagglomeration degree of the carbon blacks and thus significantly affect the structure in the subsequently produced electrode. Changes in pore diameter distribution (see figure 1), porosity and tortuosity of the pores can be achieved by a more/less intensive or longer/shorter dispersing of the components in the solvent. To predict these structural alterations it is necessary to learn more about the suspension properties, especially about its structure.Colloidal suspensions are commonly analyzed regarding their rheological characteristics in terms of flow behavior to estimate the properties for further processing steps like coating. In addition, rheological measurements can provide indirect structural information of battery suspensions, for instance concerning the fragmentation degree of the carbon black and the structural changes in the suspension while dispersing. Figure 2 exemplarily depicts the observed differences between suspensions with an aggregated particle-network (solid/gel like: phase angle 0°) to a more liquid-like (phase angle increasing up to 90°) suspension structure. A notable structural decrease can be identified after 45 minutes of dispersing compared to a shorter dispersing time of 10 minutes.The correlation between suspension structure, analyzed via rheological measurements, and the resulting electrode structure, characterized via mercury porosimetry, is in the focus of the presented work. Additional investigations on the interrelations between structures and electric or ionic transport processes as well as electrochemical cell performances provide a basis for targeted electrode manufacturing.

Electrical Properties of Polypyrrole Conducting Polymer at Various Dopant Concentrations

Polypyrrole conducting polymer was prepared by chemical reaction method with various concentrations of iron (III) chloride (FeCl3) as dopant. The dc conductivity was obtained from current-voltage characteristic by using parallel-plate techniques in the temperature range of 100-300K. With the involvement of chloride, Cl- in the polymeric chain, the conductivity increased as temperature and the dopant concentration increased. To describe the electrical transport process, Mott’s 1-D, 2-D and 3-D variable range hopping (VRH) models have been considered. The result gives evidence of transport mechanism based on Mott’s 3-D VRH mechanism for all various dopant concentrations studied.

Electrical conductivity spectra of Sn doped BaTi0.95Zr0.05O3

The alternating current (ac) conductivity spectra of Sn doped BaTi0.95Zr0.05O3 prepared by solid state reaction have been studied in the temperature range of 373–473 K. Mixed valency of Sn atoms and the oxygen vacancy controls electrical transport process. The ac conductivity follows Jonscher type power law as a function of frequency. Derived dc conductivity and hopping frequency follow Arrhenius type temperature dependency and have same activation energy. Almost temperature independent nature of frequency exponent indicates that the electrical conduction in Zr and Sn co-doped BaTiO3 relaxor is quantum mechanical electron tunneling. The conductivity spectra are perfectly scaled using the scaling parameters as dc conductivity and hopping frequency.

Ag0.225Ge0.260S0.515-AgBr glasses

Homogeneous glasses have been obtained in the composition range 1.0–9.6 mol % AgBr by quenching molten mixtures of Ag0.225Ge0.260S0.515 and AgBr. The density, microhardness, glass transition temperature, and crystallization temperature of the glasses have been determined, and their electrical conductivity has been measured in the range 270–400 K by a dc probe technique. All of the glasses have purely ionic (Ag+ and Br−) conductivity. The mechanisms of electrical and mass transport processes in the alloys are discussed.

Electrical conductivity of 1 : 1 and 2 : 1 clay minerals

The A.C. impedance plots were used as tools to analyze the electrical response of two varieties of Tunisian halloysite 1: 1 and illitic samples 2: 1 as a function of frequency at different temperatures (80–800°C). The real and imaginary parts of the complex impedance trace semicircles in the complex plane. Except for the illite, It-1, the second sample analyzed in this study, these plots give evidence for the presence of both bulk and grain boundary effect, above 600°C onwards. The bulk resistance of the materials decreases with the rise in temperature. Impedance Spectroscopy data reveal a non-Debye type of dielectric relaxation. The Nyquist plots show the negative temperature coefficient of resistance of both pure Tunisian illite and halloysite samples. The results of bulk electrical conductivity and its activation energy are presented for the two mineral clay samples. For illite It-1, the activation energy values estimated from the AC conductivity pattern and modulus pattern are very similar and suggest a possibility of a long-range mobility of charge carriers (ions) via hopping mechanism of electrical transport processes at higher temperature. On the other hand, for the halloysite sample provided from kasserine, (Ha-Kass), the modulus analysis admit that the electrical transport processes of the material are very likely of electronic nature. Relaxation frequencies follow an Arrhenius behavior with the activation energy values not comparable to those found for the electrical conductivity.

Dielectric and multiferroic properties of 0.75BiFeO3–0.25BaTiO3 solid solution

Solid solution 0.75BiFeO3–0.25BaTiO3 (BFO–25 % BT) was prepared by solid state reaction method. Powder X-ray diffraction showed the morphotropic phase boundary (MPB) with the coexistence of both rhombohedral and cubic phases due to splitting in the line at 2θ = 39.7°. Scanning electron micrographs indicated that the ceramic has compact and uniform microstructure with average grain size <3 μm. The polarization vs applied electric field analysis showed an unsaturated hysteresis loop with the remnant polarization 12.95 μC/cm2 at 22 kV/cm for 0.75BiFeO3–0.25BaTiO3 ceramic. The calculations of diffuse parameter i.e. slope γ = 1.63 suggested a high degree of diffusion in BFO–BT lattice. The room temperature magnetic measurements confirmed the weak ferromagnetism of magnetization ~0.1 emu/gm at an applied magnetic field of H = 5 kOe for 0.75BiFeO3–0.25BaTiO3 ceramic. The high temperature magnetic and dielectric analysis suggested a coupling between ferroelectric and magnetic parameters near the antiferromagnetic–paramagnetic transition Tc ~ 310 °C, which was responsible for the broad frequency dependent dielectric maxima. The impedance spectroscopy and complex modulus analysis confirmed the conventional relaxor, NTCR (negative temperature coefficient of resistance), giant ferroelectricity and polydispersive non-Debye type dielectric relaxation behaviour for 0.75BiFeO3–0.25BaTiO3 ceramic at 170 °C on 1 kHz with activation energy 2.33 eV. The modulus analysis also confirmed the possibility of hopping mechanism for electrical transport process in material.

Structures, optical properties, and electrical transport processes of SnO2 films with oxygen deficiencies

The structures, optical and electrical transport properties of SnO2 films, fabricated by rf sputtering method at different oxygen partial pressures, were systematically investigated. It has been found that preferred growth orientation of SnO2 film is strongly related to the oxygen partial pressure during deposition, which provides an effective way to tune the surface texture of SnO2 film. All films reveal relatively high transparency in the visible range, and both the transmittance and optical band gap increase with increasing oxygen partial pressure. The temperature dependence of resisitivities was measured from 380 K down to liquid helium temperatures. At temperature above K, besides the nearest‐neighbor‐hopping process, thermal activation processes related to two donor levels ( and 100 meV below the conduction band minimum) of oxygen vacancies are responsible for the charge transport properties. Below K, Mott variable‐range hopping conduction process governs the charge transport properties at higher temperatures, while Efros–Shklovskii (ES) variable‐range‐hopping conduction process dominates the transport properties at lower temperatures. Distinct crossover from Mott type to ES type variable‐range‐hopping conduction process at several to a few tens kelvin are observed for all SnO2 films.

Synthesis, electrical and dielectric properties of (Na2O)0.5–(P2O5)0.5 glass

The electrical and dielectric properties of sodium phosphate glass in the system Na2O–P2O5 were studied at different temperatures from 100 to 230 °C as a function of frequency between 10 Hz and 13 MHz. The sample was prepared by the conventional melt quenching technique. The amorphous nature of the synthesized glassy material was confirmed through X-ray diffraction. Detailed studies on the electrical and dielectric properties of the compound were carried out by solid state impedance spectroscopy. A maximum dc conductivity of 5.39 × 10−5 S cm−1 was observed at 230 °C. The calculated activation energy from dc conductivity was found to be 0.65 eV. It was evident that the electrical transport process in the system was due to the hopping mechanism. Detailed dielectric studies were also carried out.

Electrical properties of Na2Pb2R2W2Ti4V4O30 (R = Dy, Pr) ceramics

The polycrystalline samples of complex tungsten bronze (TB) Na2Pb2R2W2Ti4V4O30 (R=Dy, Pr) compounds were prepared by solid-state reaction technique. Room- temperature preliminary structural studies confirm the formation of the compounds in the orthorhombic crystal system. Detailed studies of electrical properties of the materials using complex impedance spectroscopy technique exhibit that the impedance and related parameters are strongly dependent upon temperature and microstructure (bulk, grain boundary, etc). An observation of negative temperature coefficient of resistance (NTCR) suggests the materials have semiconducting properties. The variation of AC conductivity with temperature shows a typical Arrhenius behavior of the materials. Both the samples obey Jonscher’s universal power law. The existence of hopping mechanism in the electrical transport processes in the system with non-exponential type of conductivity relaxation is confirmed by electrical modulus analysis.

Investigations on electrical properties of PVP:KIO4 polymer electrolyte films

Solid polymer electrolytes based on poly(vinyl pyrrolidone) (PVP) complexed with potassium periodide (KIO4) salt at different weight percent ratios were prepared using solution-cast technique. X-ray diffraction (XRD) results revealed that the amorphous nature of PVP polymer matrix increased with the increase of KIO4 salt concentration. The complexation of the salt with the polymer was confirmed by Fourier transform infrared (FTIR) spectroscopy studies. The ionic conductivity was found to increase with the increase of temperature as well as dopant concentration. The maximum ionic conductivity (1.421 × 10−4 S cm−1) was obtained for 15 wt% KIO4 doped polymer electrolyte at room temperature. The variation of ac conductivity with frequency obeyed Jonscher power law. The dynamical aspects of electrical transport process in the electrolyte were analyzed using complex electrical modulus. The peaks found in the electric modulus plots have been characterized in terms of the stretched exponential parameter. Optical absorption studies were performed in the wavelength range 200–600 nm and the absorption band energies (direct band gap and indirect band gap) values were evaluated. Using these polymer electrolyte films electrochemical cells were fabricated and their discharge characteristics were studied.

Electrical Transport Properties of BaWO4 under High Pressure

An alternate current impedance spectrum was utilized to differentiate the electrical transport process, respectively, in the bulk and the grain boundary of barium tungstate microcrystallines under ...

Synthesis and characterization of cancrinite-type zeolite, and its ionic conductivity study by AC impedance analysis

The synthesis of cancrinite in the system NaOH-SiO2-Al2O3-NaHCO3-H2O was performed, according to methods described in the literature, in an autoclave under hydrothermal conditions at T = 473 K. The electrical properties of cancrinite-type zeolite pellets were investigated by complex impedance spectroscopy in the temperature range 465–800°C. The effect of temperature on impedance parameters was studied using an impedance analyzer in a wide frequency range (1 Hz to 13 MHz). The real and imaginary parts of complex impedance trace semicircles in the complex plane are plotted. The bulk resistance of the material decreases with rise in temperature. This exhibits a typical negative temperature coefficient of resistance (NTCR) behavior of the material. The results of bulk electrical conductivity and its activation energy are presented. The modulus analysis suggests that the electrical transport processes in the material are very likely to be of electronic nature. Relaxation frequencies follow an Arrhenius behavior with activation energy values not comparable to those found for the electrical conductivity.

Dielectric relaxation and alternating current conductivity of lanthanum, gadolinium, and erbium-polyvinyl alcohol doped films.

Fourier transform infrared (FTIR) spectrum dielectric constant, ε', loss tangent, tan(δ), electric modulus, M*, and ac conductivity, σ(ac), of pure polyvinyl alcohol (PVA) as well as La-, Gd-, and Er-PVA doped samples have been carried out. The dielectric properties have been studied in the temperature and frequency ranges; 300-450 K and 1 kHz-4 MHz, respectively. FTIR measurements reveal that La(3+), Gd(3+), and Er(3+) ions form complex configuration within PVA structure. Two relaxation processes, namely, ρ and α were observed in pure PVA sample. The first process is due to the interfacial or Maxwell-Wagner-Sillers polarization. The second one is related to the micro-Brownian motion of the main chains. For doped PVA samples, α-relaxation process splits into α(a) and α(c). This splitting is due to the segmental motion in the amorphous (α(a)) and crystalline (α(c)) phases of PVA matrix. Electric modulus analysis was discussed to understand the mechanism of the electrical transport process. The behavior of ac conductivity for all PVA samples indicates that the conduction mechanism is correlated barrier hopping.

Polarization fluctuation dominated electrical transport processes of polymer-based ferroelectric field effect transistors

Ferroelectric field effect transistors (FE-FETs) consisting of tunable dielectric layers are utilized to investigate interfacial transport processes. Large changes in the dielectric constant as a function of temperature are observed in FE-FETs in conjunction with the ferroelectric to paraelectric transition. The devices offer a test bed to evaluate specific effects of polarization on the electrical processes. FE-FETs have dominant contributions from polarization fluctuation rather than static dipolar disorder prevalent in high $k$ paraelectric dielectric-based FETs. Additionally, photo-excitation measurements in the depletion mode reveal clear features in the FET response at different temperatures, indicative of different transport regimes.