Ac Conductivity Studies Research Articles

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.

AC conductivity and dielectric spectra study of a blended solid polymer electrolyte

AC conductivity and dielectric spectra study of a blended solid polymer electrolyte

Effect of Multiple Substitutions (Pb, Ti, Zr) on Structural, Permittivity and Electrical Properties of BiFeO3 Ceramics

Three complex polycrystalline samples of Bi1-xPbxFe1-x Zrx-yTiyO3,with the combination of (i) x, y = 0.0 (BFO), (ii) x = 0.5 and y = 0.5 (BFPTO)and (iii) x = 0.5 and y = 0.25 (BFPZTO) were prepared by a standard mixed oxide (solid state reaction route) method at optimized calcinations (900oC) and sintering (930-950oC)temperatures. The effect of multiple (Pb, Ti and/or Zr) substitutions of different amount onthe permittivity, impedance and modulus characteristics of the materials has been investigated at different frequencies and temperature.Limitation associated with BiFeO3 (BFO) due to its semiconducting behavior acts as constraint in polling the material at room temperature leading to large dielectric loss. Attempts were made to minimizethe loss by substitution of Pb on the Bi site and Ti and/or Zr at the Fe site of BFO. The study indicates that the phase transition temperature of BFO is lowered,the degree of diffuse phase transition is enhanced and electrical parameters (dielectric constant, electrical resistivity, remnant polarization and maximum polarization) areincreased with a significant reduction in dielectric loss as a consequence of the substitution. Detailed studies of Nyquist plots with impedance and electric modulus data suggest that the existence of non-Debye type of relaxation phenomena in the materials. The ac conductivity study reveals that the conduction mechanism in the material obeys universal Jonscher’s power law.

Dielectric Relaxation Study of Multiferroic BiFe0.95(Ni0.5Ti0.5)0.05O3

The doping of BiFeO3 (BFO) with 5% of Ni and Ti to form the composition BiFe0.95(Ni0.5Ti0.5)0.05O3 (BFNT05) was prepared via a solid state reaction technique. X-ray diffraction (XRD) shows that the prepared ceramic has a pure-phase perovskite structure with rhombohedral symmetry. Thermal evolution of the permittivity reveals a large value of permittivity accompanied by a strong dispersion. This evolution indicates a dielectric anomaly at around 520 K near the Neel temperature (T N), which supports a strong magneto-dielectric coupling. The dielectric dispersion in BFNT05 was studied by the measurement of the permittivity over a wide frequency range from 20 Hz to 1 MHz at different temperatures 300–700 K. The experimental dielectric data was described by the Cole–Cole relaxation equation modified by introducing the conductivity. Modified impedance and modulus expressions were used successfully as tools to separate the contribution from grains and grain boundaries of BFNT05. The calculated bulk grain conductivity indicated an anomalous behavior near the temperature related to the antiferro-paramagnetic phase transition of the corresponding BFNT05 ceramic. In contrast, this ceramic exhibited a predominant grain boundaries behavior at the studied temperature and frequency range. In this case, they were the elements responsible for dielectric dispersion, and also they played an important role in the improvement of the dielectric behavior of this ceramic. The ac conductivity study confirmed the modified impedance and modulus expressions.

Structural, dielectric, magnetic and electromagnetic interference shielding investigations of polyaniline decorated Co0.5Ni0.5Fe2O4 nanoferrites

In the present work, we have investigated structural, dielectric, ac conductivity, magnetic and electromagnetic interference (EMI) shielding effectiveness (SE) performance of Co0.5Ni0.5Fe2O4 nanoparticles and Polyaniline (PANI)/Co0.5Ni0.5Fe2O4 nanocomposites for EMI shielding applications. The Co0.5Ni0.5Fe2O4 nanoparticles were synthesized by solution combustion method. PANI/Co0.5Ni0.5Fe2O4 nanocomposites were prepared by in-situ polymerization method. As-prepared samples were examined by using X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) spectroscopy. The microstructural and composition studies have been performed using Field emission scanning electron microscopy (FE-SEM) and Energy Dispersive X-ray (EDX) analysis. Thermal stability of the composite was analyzed using thermo gravimetric analysis (TGA). Frequency dependence of dielectric and ac conductivity (σac) studies have been undertaken on the Co0.5Ni0.5Fe2O4 nanoparticles and PANI/Co0.5Ni0.5Fe2O4 nanocomposites in the frequency range 50 Hz–5 MHz. The electrical conduction mechanism in the synthesized samples found to be in accordance with the electron hopping model. Present Co0.5Ni0.5Fe2O4 nanoparticles and PANI/Co0.5Ni0.5Fe2O4 nanocomposites exhibited hysteretic behavior under the applied magnetic field at room temperature. The maximum values 39.9 and 58.22 dB of SE at 50 Hz were obtained at room temperature for Co0.5Ni0.5Fe2O4 nanoparticles and PANI/Co0.5Ni0.5Fe2O4 nanocomposites respectively. Present Co0.5Ni0.5Fe2O4 nanoparticles decorated with PANI can be recognized as a promising functional material for the absorbing of electromagnetic (EM) waves due to large amount of dipole polarizations in the polymer backbone and at the interfaces of the Co–Ni ferrite nanoparticles and PANI matrix.

AC and DC conductivity study of LiH2PO4 compound using impedance spectroscopy

The lithium dihydrogen phosphate LiH2PO4 has been investigated by X-ray powder diffraction, scanning electron microscopy (SEM), and electrical impedance spectroscopy. The Rietveld refinements based on the XRD patterns show that the compound is crystallized in the orthorhombic system with Pna21 space group, and the refined unit cell parameters are a = 6.2428 A, b = 7.6445 A, and c = 6.873 A. The electrical properties were studied using complex impedance spectroscopy as a function of frequency (104–107 Hz) at various temperatures (300–400 K). The Nyquist plots are well fitted to an equivalent circuit consisting of a series of combination of grains and inhomogeneous electrode surface effect. The frequency dependence of the conductivity is interpreted in terms of Jonscher’s law. Moreover, the near value of the activation energies obtained from the equivalent circuit and analysis of M″ confirms that the transport is through ion hopping mechanism dominated by the motion of the proton in the structure of the investigated material.

Structural and ac conductivity studies of sodium tetralead triphosphate compound

Sodium tetralead triphosphate NaPb4(PO4)3 compound was synthesized by the solid-state reaction method, characterized through X-ray powder diffraction, Raman and electrical impedance spectroscopy. A Rietveld analysis of powder X-ray diffraction has shown that the title compound crystallizes in the hexagonal system at room temperature, space group P63/m. A pellet of 92% density was used for the electrical measurements. All electrical measurements of real and imaginary components of the impedance parameters were made over a wide range of temperature (598–720) K and frequency (209 Hz–1 MHz) using a Tegam 3550 impedance analyzer interfaced to a compatible computer. Ac conductivity data affirm that for high frequencies σac is proportional to ωs. The frequency exponent values increase with increasing temperature revealing that the non-overlapping small polaron tunneling is the appropriate conduction mechanism.

Structural, dielectric and AC-conductivity studies of Gd doped lead-free Bi0.5Na0.5TiO3 ceramics

ABSTRACTLead–free (Bi1-xGdx)0.5Na0.5TiO3 (BGNT; x = 0.00 to 0.06) ceramics synthesized by a solid state reaction method. The effect of Gd on the structural, microstructural and dielectric properties of BNT ceramics was reported. X-ray diffraction pattern shows the pure perovskite rhombohedral phase without any secondary phase. The microstructural analysis revealed that the reduction in the grain size observed with increasing the Gd concentration. The x = 0.06 sample exhibited the improved dielectric properties such as higher dielectric constant (ϵr = 809) and lower dielectric loss (tanδ = 0.201), measured at 1 MHz. The frequency dependent AC-conductivity (σac) of BGNT ceramics was analyzed using Jonscher's power law.

Facile hydrothermal synthesis and characterization of cesium-doped PbI2 nanostructures for optoelectronic, radiation detection and photocatalytic applications

Low-temperature hydrothermal-assisted synthesis of pure and cesium (Cs) (1, 3, 5, 7 and 10 wt%) doped lead iodide (PbI2) nanorods and nanosheets have been achieved successfully for the first time. The structural and vibrational studies confirm the formation of a 2H-polytypic PbI2 predominantly. Scanning electron microscope analysis confirms the formation of well-aligned nanorods of average size ~ 100 nm at low concentration and nanosheets of average thicknesses in the range of ~ 20–40 nm at higher concentrations of Cs doping. The presence of Cs doping was confirmed by energy dispersive X-ray study. Ultra-violet-visible absorbance spectra were recorded, and energy gap was calculated in the range of 3.33 to 3.45 eV for pure and Cs-doped PbI2 nanostructures which is higher than the bulk value (i.e., ~ 2.27 eV) due to quantum confinement effect. Dielectric constant, loss, and AC conductivity studies have been done. Enhancement in Gamma linear absorption coefficient due to Cs doping confirms the suitability of prepared nanostructures for radiation detection applications. Furthermore, the photocatalytic performance of the synthesized nanostructures was evaluated in the decolorization of methyl green (MG) and methyl orange (MO) under the illumination of visible light (λ > 420 nm). The observed photocatalytic activity for 5 and 7 wt% Cs-doped PbI2 was observed to be more than pure PbI2 and also > 10 times higher than the commercially available photocatalysts. The results suggest that the prepared nanostructures are highly applicable in optoelectronic, radiation detection and many other applications.

Structural characterization, AC conductivity, optical properties and biochemical study of a new hybrid phosphate: Scavenger of free radicals

Single crystal of the hybrid compound [p-(F)C6H4NH3]6P6O18·2H2O has been grown with sizes up to 0.65 × 0.45 × 0.3 mm3 by the slow evaporation method. The crystal structure of this material was determined by single crystal X-ray diffraction. It crystallizes in the triclinic space group P 1¯ with the lattice parameters a = 10.16(3) Å, b = 15.87(3) Å, c = 16.36(4) Å, α = 80.93(2)°, β = 85.92(18)°, γ = 85.31(2)°, V = 2591.1(12) Å3 and Z = 2. Its crystal structure is a packing of alternated inorganic and organic layers parallel to (a, c) planes. The cohesion of the structure is essentially ensured by a hydrogen bonding network as well as electrostatic and Van Der Waals interactions and also F…F interactions so as to increase the stability of the 3D-network. The effect of the nature of the substituent in para-position with respect to amine group on obtained structures and on other studied properties was discussed. Crystal symmetry is confirmed by 31P MAS-NMR. Furthermore, IR characteristics and thermal analysis are given. The luminescent properties of this material have been carried out at room temperature based on UV absorption spectroscopy data. AC conductivity of this compound has been investigated by means of impedance spectroscopy measurements in the 303–383 K temperature range. The antioxidant study was determined, in vitro, using 1,1-diphenyl-2-picrylhydrazyl (DPPH), hydroxyl radical and reducing power and with ascorbic acid as a control. X-rays structural results are correlated with electrical and antioxidant findings.

AC and DC conductivity study of KPb4(PO4)3 compound using impedance spectroscopy

Orthophosphate KPb4(PO4)3 compound was synthesized by the conventional solid-state reaction. The phase formation of the compound was confirmed from the powder X-ray diffraction. Vibrational study confirms the existence of [PO4]3− group. The impedance spectroscopy measurements was realized with Compact disc, Φ = 8 mm diameter and 1.2 mm thickness in the range temperature (659–708)K and frequency (209 Hz–1 MHz), respectively. As well, the impedance spectra are well adjusted to an equivalent circuit formed by a serial combination of three cells. It was found that the non-overlapping small polaron tunneling (NSPT) model is suitable to describe the conduction mechanism in this compound.

Effect of aluminium substitution on the electrical properties of Ni-Zn nanoferrites

Nanoferrites of general formula Ni0.5 Zn0.5 Alx Fe2−x O4 (x=0.0, 0.2, 0.4, 0.6, 0.8, 1.0, 1.2, 1.4, 1.6, 1.8 and 2.0) synthesized by sol-gel auto combustion technique can be characterized by dielectric behaviour and AC conductivity studies with the help of LCR impedance meter. This paper gives an insight on variations in dielectric constant, dielectric loss with reference to frequency, temperature and Al3+ ion substitution and also the determination of DC resistivity, activation energy and Curie temperature by two probe experimental set-up.

Growth, morphology, optical, thermal, mechanical and electrical studies of a cesium chloride doped l-alanine single crystal

A cesium chloride doped l-alanine (LACC) nonlinear optical single crystal was grown successfully from an aqueous solution by employing the slow solvent evaporation method. The LACC single crystal appears as a square as viewed along the crystallographic a-direction. The crystal structure was determined by single and powder X-ray diffraction. The presence of the dopant was confirmed from an energy dispersive X-ray analysis. The UV-visible-NIR spectroscopic study of the crystal shows that the crystal has a good optical transparency over a wide spectral range 240–1083 nm. It has a lower wavelength cutoff at around 215 nm. The optical band gap of the crystal was calculated, and it is 5.64 eV. The optical parameters have also been calculated. The second harmonic generation (SHG) efficiency was measured by the Kurtz and Perry powder method. The SHG efficiency of LACC is 0.85 times that of potassium dihydrogen phosphate and 3.85 times that of l-alanine. The crystal is thermally stable up to 248 °C. The dielectric constant of the crystal is moderate. The low value of dielectric loss reveals the good quality of the crystal. Photoluminescence, mechanical, activation energy, and ac conductivity studies have also been presented.

Dielectric and AC conductivity studies of novel porous armalcolite nanocomposite‐based humidity sensor

AbstractArmalcolite, a current motivated rare earth ceramic usually available in the moon, had been used for the first time, as dielectric‐type humidity sensors. The armalcolite nanocomposite was prepared using multistep solid‐state sintering under high pressure and a high‐sensitive dielectric sensor was developed for humidity controlling applications. Different concerning phases developed by the proper sintering were analyzed precisely by X‐ray diffraction (XRD) as well as scanning electron microscopy (SEM). At 100 Hz frequency, the obtained dielectric constant was 24 times greater at 95% relative humidity (RH) as compared to 33% RH. The armalcolite‐based sensor showed lower hysteresis (<3.5%), good stability, and faster response (~18 seconds) and recovery (~35 seconds) times compared to conventional humidity sensors. The sensing mechanism of the nanocomposite was categorically determined by the analyzed characteristics parameters such as dielectric constants, normalized loss tangent, and alternating current conductivity properties. This study also confirmed that the whole conduction mechanism was accomplished by electrons or ions and dipoles in the entire RH range. Therefore, the present armalcolite‐based porous nanocomposite would be a potential sensing material for novel humidity sensors.

Thickness-dependent Crack Propagation in Uniaxially Strained Conducting Graphene Oxide Films on Flexible Substrates

We demonstrate that crack propagation in uniaxially strained reduced graphene oxide (rGO) films is substantially dependent on the film thickness, for films in the sub-micron regime. rGO film on flexible polydimethylsiloxane (PDMS) substrate develop quasi-periodic cracks upon application of strain. The crack density and crack width follow contrasting trends as film thickness is increased and the results are described in terms of a sequential cracking model. Further, these cracks also have a tendency to relax when the strain is released. These features are also reflected in the strain-dependent electrical dc and ac conductivity studies. For an optimal thickness (3-coat), the films behave as strain-resistant, while for all other values it becomes strain-responsive, attributed to a favorable combination of crack density and width. This study of the film thickness dependent response and the crack propagation mechanism under strain is a significant step for rationalizing the application of layered graphene-like systems for flexible optoelectronic and strain sensing applications. When the thickness is tuned for enhanced extent of crack propagation, strain-sensors with gauge factor up to ∼470 are realized with the same material. When thickness is chosen to suppress the crack propagation, strain-resistive flexible TiO2- rGO UV photoconductor is realized.

Structural, impedance, dielectric and modulus analysis of LiNi 1-x-y-0.02 Mg 0.02 Co x Zn y O 2 cathode materials for lithium-ion batteries

Abstract Mg, Co and Zn co-substituted layer-structured cathode materials LiNiCoxZnyMg0.02O2 (x = y = 0.0, 0.02 and 0.04) were prepared by a solid-state reaction method. The materials were systematically characterized by X-ray diffraction (XRD), field effect scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FT-IR), and electrical impedance spectroscopy (EIS) techniques. XRD analyses revealed the formation of a rhombohedral structure in the prepared materials with a typical α-NaFeO2 layered structure within R 3 ¯ m space group. The grain size was determined by FESEM in the range from 3.19 to 3.85 μm for all materials synthesized. The site of the local cation (Li–O) and of the transition metal cations (M–O) in the materials were identified by FT-IR. The complex impedance and modulus studies suggested the presence of a non-Debye type of multiple relaxations in these materials. The dielectric constant was found to increase with increasing Co and Zn concentrations. The ac conductivity studies revealed a typical negative temperature coefficient of resistance (NTCR) behavior, and the conductivity values varied from 1.58 × 10−5 to 8.46 × 10−6 S cm−1. The activation energy determined from the Arrhenius plots at 50 Hz was in the range of 0.23–0.78 eV.

Existence of negative permittivity in carbon coated iron nanoparticle - PDMS composites

We prepared polydimethylsiloxane (PDMS)-carbon coated iron nanoparticle (CCFeNP) composites (varying filler content) to investigate the dielectric behaviour, in the frequency range 100 Hz–100 MHz. The sample structures were studied by means of Transmission Electron Microscopy (TEM), Scanning electron microscopy (SEM) and X-ray diffraction (XRD). The ac conductivity, impedance, permittivity and dielectric loss of PDMS-CCFeNP composites were analysed. The real part of permittivity/epsilon (εʹ) for the cured composites varied inversely with frequency and switched from positive to negative. The 10 wt% composites exhibit negative permittivity at higher frequency, whereas for 50 wt% permittivity switches from a highly positive to negative at very low frequency and remained negative thereafter. The shifting of switching frequency towards lower frequencies with increasing filler loading is attributed to the increased inductive nature of the composites. The unique frequency dispersion of permittivity is explained by interband transition and Drude model (multiband nature of the electronic excitations). The well dispersed filler particles in PDMS matrix gave the high permittivity of 833 for 30 wt% composite at 1 kHz. The frequency dependence of real part of ac conductivity (σacʹ) and impedance studies were carried out to elucidate the capacitive-inductive transition and dielectric resonance in the composites.

Optoelectronic properties of novel alkyl-substituted Triphenylamine derivatives

Hole transport characteristics in three new organic compounds based on triphenylamine (TPA) moiety are presented. The effect on electrical and optical properties of TPA, attached with methyl or tert-butyl side groups, has been investigated through measurement of current density versus voltage (J-V), capacitance versus voltage (C-V), frequency dependent capacitance, ac conductivity, Impedance spectroscopy, UV-Vis spectroscopy, Photoluminescence (PL) spectroscopy and X-Ray Diffraction (XRD) studies. These measurements reveal that, the attachment of methyl or tert-butyl group in the para-position of the TPA moiety leads to improved optoelectronic properties and greater molecular stability. XRD analysis of the samples indicates that the inter-molecular distance is the lowest for TPA with tert-butyl side group (3.43 Å) as compared to pure TPA (3.57 Å). This leads to stronger inter-molecular interaction as evidenced by the UV-Vis spectra. PL studies indicate significant Quantum Efficiency (∼30%) for alkyl attached TPA. In order to get a better understanding of the charge transport phenomena, the effect of molecular structure dynamics on charge transfer kinetics is analyzed by evaluating the charge carrier hopping rate coefficient and dynamic state factor. The dynamic state factor b has higher value for lower bias voltage, corresponding to dc conductivity, whereas, at higher bias, the value of b is smaller, indicating the dominance of ac conductivity. Hopping conductivity is seen to be highest for the device with tert-butyl substitution in TPA moiety. Our experiments indicate an order of magnitude enhancement in charge carrier mobility for alkyl-substituted TPA.

AC conductivity and dielectric behavior of poly (o-phenylenediamine)/TiO2 nanocomposites

Poly (o-phenylenediamine) and their nanocomposites with TiO2 nanoparticles were synthesized using oxidative polymerization technique and the polymer nanocomposites were characterized using spectral techniques like FT-IR, UV-VIS spectroscopy and the morphology have been analyzed by XRD, SEM and TEM. The stability of the prepared polymer nanocomposites was studied using TGA, DTA and found to have high thermal stability. The study of ac conductivity, dielectric property revealed that the formed nanocomposites are semiconducting in nature and can be widely used in the field of energy storage and semiconductor devices, in diodes, batteries etc.

AC and DC conductivity study of ceramic compound NaGd(WO4)2 using impedance spectroscopy

In this works, the NaGd(WO4)2 compound was obtained by the conventional solid-state reaction method at 923 K, has been investigated by X-ray diffraction, vibrational and impedance spectroscopy. The X-ray diffraction’s results indicate that the sample possess single crystalline phase in the tetragonal system with space group I41/a. The unit cell parameters are: a = 5.246(6) A, c = 11.380(1) A, and V = 313.257(8) A3. Thus, the impedance spectroscopy measurements were performed in the (209Hz–5 MHz) frequency and the (613–711 K) temperature ranges. Besides, the ac conductivity contribution is interpreted using the universal Jonscher’s power law and is thermally activated with an activation energy of grain, grain boundary and total were 0.91(4), 0.79(3) and 0.97(5) eV respectively. The mechanism of conduction is due to the displacement of Na+ ion that can be interpreted by the model NSPT (non-overlapping small polaron tunneling).