Ac Conductivity Studies Research Articles

Studies of AC conductivity and dielectric relaxation behavior of CdO‐doped nanometric polyaniline

AbstractThe Cadmium oxide doped in nanocrystalline polyaniline (CdO/PANI) composite were prepared with various weight percentages by in situ polymerization method using aniline, ammonium per sulfate, and CdO as starting materials. The frequency dependent conductivity and dielectric behavior of PANI/CdO composites have been studied. The formation of nano PANI and PANI/CdO composites with regards to the structural and microstructural properties of the materials were investigated by XRD, FTIR, and SEM techniques. The variation of σac with frequency obeys Jonscher power law except a small deviation in the low frequency region and is due to dipole polarization effect. The σac increases with increase in CdO concentration. Studies of dielectric properties at lower frequencies show that the relaxation behavior is superimposed by dipole polarization effect. The appearance of peak for each concentration in the loss tangent suggests the presence of relaxing dipoles in the PANI/CdO composite. On addition of CdO, the peak shifts toward higher frequency side indicating the speed up of the relaxation time. Analysis of frequency dependent dielectric suggests that the electronic and polymer segmental motions are strongly coupled. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

AC conductivity and dielectric studies of (C5H10N)2BiCl5 compound

The bis (3-dimethylammonium-1-propyne) pentachlorobismuthate (III) exhibits a structural phase transition at T1 = (337 ± 2 K), which has been characterized by differential scanning calorimetric, X-ray powder analysis, AC conductivity and dielectric measurements. The dielectric dispersion yielded the real and imaginary parts of impedance of (C5H10N)2BiCl5 in the form of a semicircle in a complex plane. Besides, a Cole–Cole plot was observed at frequencies ranging from 209 Hz to 5 MHz, whose result was found to fit the theoretical resistor–capacitor parallel circuit model. The temperature dependence of the electrical conductivity in the different phases follows the Arrhenius law. The frequency-dependent conductivity data were fitted in the modified power law: \( \sigma = {\sigma_{dc}} + {B_1}(T){\omega^{{s_1}}} + {B_2}(T){\omega^{{s_2}}} \). The imaginary part of the permittivity constant is analyzed with the Cole–Cole formalism. With regard to the modulus plot, it can be characterized by full width at half height or in terms of a non-exponential decay function \( \phi (t) = \exp {\left( {\frac{{ - t}}{{{\tau_\sigma }}}} \right)^\beta } \). Besides, the activation energy responsible for relaxation has been evaluated and found to be close the DC conductivity.

Ionic to Electronic Conductivity Studies of Lithium-Borate Ruby-Glass-Ceramics Containing Gold Nano Particles

Glass-ceramics containing Au nanoparticles have been synthesized in the glass composition 30Li2O-70B2O3 with HAuCl4.3H2O as dopant. The characteristic ruby colour has been observed which is attributed to the surface Plasmon resonance of the Au nanoparticles, uniformly embedded in the glass matrix. The imparted red colour due to the presence of gold nanoparticles has been confirmed by studying the optical absorption spectra using UV-VIS spectrometer in the visible range (400–1000 nm) which show a characteristic absorption peak at ∼560 nm. In order to check the crystallization/ amorphous nature, the samples were powdered and characterized using X-ray diffraction (XRD). The microstructural modifications in the samples due to the addition of Au have been recorded using scanning electron microscopy (SEM). Further, the electron spin resonance (ESR) studies reveal that the electronic state of gold is either Au0 or Au+. AC conductivity studies have been performed at room temperature over a frequency range 100 to 10 MHz. The ac conductivity data is fitted by Almond-West law with power exponent ‘s’. The dc conductivity is found to be increasing with the increase of temperature for a typical ruby glass, but almost constant with dopant concentration.

IMPEDANCE SPECTROSCOPY AND AC CONDUCTIVITY STUDIES OF FERROELECTRIC (K0.5Na0.5)NbO3 CERAMICS

Lead free (K0.5Na0.5)NbO3 (KNN) ceramics were prepared by conventional solid state reaction route. For single perovskite phase formation, calcination temperature was optimized at 850°C for 6 h, whereas for dense morphology the sintering of the ceramic was carried out at 1120°C for 4 h. X-ray diffraction XRD analysis confirmed the formation of single phase with orthorhombic structure at room temperature. Impedance analysis and AC conductivity studies of the KNN sample was carried out in the temperature range of 703–773 K. Impedance study showed the increase in conducting behavior at higher temperature. The temperature dependence of AC conductivity indicated that the conduction process is due to doubly ionized oxygen vacancies in the higher temperature region.

Surface Morphology and Dielectric Behaviour of Gd-Doped Ba(Zr0.52Ti0.48)O3 Nanocrystalline Ceramics

Surface analysis, frequency dependent permittivity, impedance and ac conductivity studies of gadolinium (Gd) doped BZT perovskite ceramics having stoichiometry (Ba1–xGdx)(Zr0.52Ti0.48)O3 (x = 0.1 and 0.2) were reported. Surface morphology including grain distribution, histogram of area, volume, length and perimeter was examined through atomic force microscope. Surface morphological images showed non-uniform distribution of grains. These compounds exhibited abnormal dielectric losses in the frequency range of 10 kHz to 1 MHz. Anomalous variation in frequency dependent relative permittivity (ϵʹ) behaved as non linear dielectric materials with interesting properties. Substitution of Gd ion in BZT resulted in significant lattice distortion due to strain imported via doping. This distortion caused low impedance which in turn increased the magnitude of ac conductivity.

Synthesis, Characterization and Electrical Properties of Carbon Coated LiCoPO<SUB>4</SUB> Nanoparticles

Lithium cobalt phosphate (LiCoPO4) nanoparticles were synthesized using modified polyol process. Shape and size of LiCoPO4 nanoparticles were controlled by using poly (vinylpyrrolidone) (PVP) stabilizer. Coating of carbon over the LiCoPO4 nanoparticles was done using the resin coating process to enhance its conductivity. XRD and FTIR results respectively confirm the crystalline phase and structure of pure and carbon coated LiCoPO4 nanoparticles. SEM-EDX results confirm size and shape and also the presence of carbon over LiCoPO4 nanoparticles. Electrical conductivity of pure and carbon coated LiCoPO4 nanoparticles were evaluated by analyzing the measured impedance data using the win fit software. More than three orders of conductivity enhancement was observed in carbon coated LiCoPO4 nanoparticles when compared to pure ones. Further, transport properties like temperature dependence conductivity, AC conductivity, dielectric constant and electric modulus studies were made to find out the bulk and relaxation properties of LiCoPO4 nanoparticles.

Core‐shell method of synthesis, characterizations, and ac conductivity studies of polyaniline/n‐TiO2 composites

AbstractPolyaniline/nano‐titanium dioxide composites (PANI/n‐TiO2) were prepared using α‐dextrose as surfactant and ammonium per sulfate as oxidant. The PANI/n‐TiO2 composite is characterized by Fourier transform infrared spectra and confirmed the presence of benzenoid and qunoide ring structures and also formation of free ions. The transmission electron microscopy study reveals that the size of TiO2 is in the order of 7 nm where as the composite size is of the order of 13 nm; further, it is observed that the TiO2 particles are intercalated to form a core shell of PANI. The X‐ray diffraction (XRD) studies show that the monoclinic structure of the composites. ac Conductivity, permittivity, and tangent loss studies on these samples suggest that these composites may be well suited for gas sensor. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Impedance spectroscopy analysis of Ba0.7Sr03TiO3/La0.7Sr0.3MnO3 heterostructure

Impedance spectroscopy technique has been used to study the effect of grains and grain boundaries in a heterostructure constituted with ferromagnetic La0.7Sr0.3MnO3 (LSMO) and ferroelectric Ba0.7Sr0.3TiO3 (BST) layers grown by pulsed laser deposition technique on (1 0 0) oriented MgO substrate. Frequency and temperature dependence of the complex impedance and complex electric modulus were measured in (BST20u.c,/LSMO10u.c)25 over a temperature range of 360–500 K. Non-Debye relaxation was observed in the investigated system. An equivalent circuit and the modified constant phase element circuit were used to describe the impedance spectroscopy, and excellent agreement between the calculated and measured curves was obtained from each model. The activation energy (∼0.25 eV–0.48 eV) has been obtained from Arrhenius fitting of different relaxation processes present in the material, and its characteristic values support a model of Maxwell–Wagner relaxation in the heterostructured film at elevated temperatures and in the low frequency range. The electrical ac and dc conductivity studies showed that the heterostructure possesses negative temperature coefficient of resistance properties. It was found that the resistance of grain boundaries was larger than the resistance of intra-grains.

Impedance-spectroscopy analysis of oriented and mercerized bamboo fiber-reinforced epoxy composite

Bamboo fiber-reinforced epoxy composites were fabricated with untreated and alkali treated bamboo fibers. Dielectric, electric modulus, ac, and dc conductivity studies were carried out to rationalize the dielectric behavior of bamboo/epoxy composites. Composites of two fiber orientation parallel and perpendicular to the electric field were prepared. The dielectric behavior and electric modulus spectra of the composites were characterized using standard impedance analyzer. Dielectric properties were analyzed as a function of frequency (95 Hz–2 MHz) for temperatures in the range from 30 to 180 °C. Real part of dielectric constant (e′), conductivity, and dielectric dissipation factor (tan δ) of 0° oriented bamboo/epoxy composites were higher than that of 90° oriented composites. Conductivity activation energy, tan δ, e′, and volume resistivity decreased with increase in frequency at all the temperatures under study. Mercerization reduces the water absorption in bamboo fibers and thus improves corresponding dielectric properties of composites. Relaxation times 39.80 μs and 258.5 μs for 0° and 90° oriented bamboo/epoxy composites were calculated respectively from the relaxation peaks observed in electric modulus spectra at 180 °C.

Dielectric relaxation and ac conductivity study of Ba(Sr 1/3Nb 2/3)O 3

Single phase perovskite Ba(Sr 1/3Nb 2/3)O 3 ceramics was prepared using the columbite precursor method. X-ray diffraction (XRD) technique is used to verify the single phase formation. It stabilizes in hexagonal phase with lattice constants a=12.1243 Å and c=15.3747 Å. Impedance analysis shows distributed relaxation time. Single semicircular arc observed in complex impedance plot confirms that only semiconducting grains are contributing to the polarization. The scaling behavior of both Z″ and M″ infers that the dynamical processes are temperature independent. Comparison of the impedance and electrical modulus data shows that the bulk response has contributions from both localized, i.e. defect relaxation, and non-localized conduction, i.e. ionic or electronic conductivity. The ac conductivity of the ceramics at higher temperatures indicates NTCR (negative temperature coefficient of resistance) behavior like semiconductors. The ac conduction activation energies are estimated from Arrhenius plots and conduction is largely due to hopping process.

Electrical Properties of (1-x)Ba(Bi0.5Ta0.5)O3-xBaTiO3 Ceramic System

Lead-free perovskite (1-x)Ba(Bi0.5Ta0.5)O3-xBaTiO3; x = 0.25, 0.50, 0.75 were prepared by conventional ceramic fabrication technique at 1220-1290°C/4h in air atmosphere. X-ray, SEM, electric modulus, dielectric and ac conductivity studies was carried out for characterization. The SEM analysis shows the average grain size to be 0.12 to 0.45 m. Complex electric modulus analyses suggested the dielectric relaxation to be of non-Debye type. Dielectric studies indicated the relaxor behaviour of 0.25Ba(Bi0.5Ta0.5)O3-0.75BaTiO3. The correlated barrier hopping model was employed to successfully explain the mechanism of charge transport in the system. AC conductivity data indicated the negative temperature coefficient of resistance (NTCR) character of the samples like that of semiconductors.

Dielectric and impedance spectroscopy studies on sisal fibre-reinforced polyester composite

Frequency and temperature dependence of dielectric constant (er), dielectric loss (tanδ), ac conductivity (σac) and complex impedance spectroscopy studies on cured polyester matrix and sisal fibre-reinforced polyester composites (SFRPC) have been investigated in the frequency range from 180 Hz to 1 MHz and temperature range from room temperature to 200 °C. The experimental results showed that with the incorporation of sisal fibre, the values of er, tanδ and σac are increased. It is also found that the values of er and tanδ for both cured polyester matrix and SFRPC are decreased with increasing frequency, which indicates that the major contribution to the polarization may come from orientation polarization and interfacial polarization. The increasing value of er with increasing temperature at a particular frequency is due to free motion of the dipole molecular chains within the cured polyester matrix and SFRPC at higher temperature.

Effect of nickel doping on structural, optical and electrical properties of TiO 2 nanoparticles by sol–gel method

Nickel-doped anatase TiO 2 nanoparticles have been prepared by sol–gel method. The X-ray powder diffraction study reveals that all the prepared samples have pure anatase phase tetragonal system. The average crystallite size of the prepared sample is 14 nm, when found through transmission electron microscope. A strong frequency dependence of both dielectric constant ( ɛ′) and dielectric loss (tan δ) were observed for various dopant levels at room temperature in the frequency range of 42 Hz to 5 MHz. At low frequency, the piling up of mobile charge carriers at the grain boundary produces interfacial polarization giving rise to high dielectric constant. The asymmetric shape of frequency dependence of the dielectric loss for the primary relaxation process is observed for each concentration. From the ac conductivity studies, the reduction in conductivity may arise due to the decreasing particle with the increase in Ni-dopant level.

Structural and electrical properties of Ba 5− xCa xSmTi 3Nb 7O 30 ( x = 0–5) ferroelectric ceramics

Samples of the compositions Ba 5− x Ca x SmTi 3Nb 7O 30 ( x = 0–5), where Ba has been replaced by Ca in steps, were synthesized by solid state reaction method and studied for their structural, dielectric and electrical properties. X-ray diffraction analysis shows the formation of the compounds in an orthorhombic structure at room temperature. Scanning electron micrographs reveal that the average grain size of the compounds increases with increase in calcium content. Detailed studies of dielectric properties as a function of temperature at different frequencies suggest that the synthesized compounds undergo non-relaxor type ferroelectric–paraelectric phase transition of diffuse nature with a decrease in the value of dielectric constant as calcium content increases. When barium is completely replaced by calcium (i.e., Ca 5SmTi 3Nb 7O 30), the compound does not show any phase transition. The ferroelectric nature of the studied compounds was confirmed by recording the polarization–electric field ( P– E) hysteresis loops at room temperature. The remanent polarization value is observed to be highest in the sample with x = 1. The temperature variation of P– E loop in the Ca free compound has been reported. The dc and ac conductivity study over a wide temperature range suggests that the compounds have negative temperature coefficient of resistance (NTCR) behaviour.

Dielectric and ac conductivity studies in as‐grown Ga2Te3 crystals with the defect zinc‐blende structure

AbstractGa2Te3 crystallizes in the zinc‐blende structure where one‐third of the cation sites are vacant. The dielectric properties of as‐grown Ga2Te3 crystals have been studied in the frequency range from 102 to 109 Hz. Below room temperature, the dielectric constant is around 20 and almost independent of temperature. The ac conductivity is found to obey a power law σac ∼ ωs, with s ∼ 1 indicating that the conduction is due to hopping of localized charge carriers. Above room temperature the dielectric constant shows an S‐shaped step‐like increase up to a very large value around 104. The relaxation is found to be of thermal activated Debye type, the relaxation time changes as $\tau = \tau _0 \,{\rm exp}(E_\tau /kT)$ ($E_\tau \approx 0.27\,{\rm eV}$). The activation energy of the relaxation nearly coincides with that deduced from conductivity. These results are analyzed using the Maxwell Wagner model and the space charge model.

Impedance Spectroscopy, Electrical Relaxation and Ac Conductivity Studies of an Organic-Inorganic Hybrid Compound: C12H14N2CuCl4

The AC conductivity of the compound, C12H14N2CuCl4, in the temperature and frequency range from 373 to 423 K and 209 Hz – 5 MHz, respectively, is reported. The differential scanning calorimetry and thermogravimetric analysis indicate the presence of a phase transition at 400 K. The Z’ and Z’’ vs. frequency plots are found to be well fit by using the equivalent circuit model. The circuits consist of a parallel combination of bulk resistance Rp and constant phase element. Besides, the analysis of the experimental data based on the jump relaxation model shows that the translation motion of the charge carrier and reorientation hopping between the equivalent sites of the metal chloride anion and the cation groups are responsible for the observed AC conductivity in the temperature regions I (373–400 K) and II (400–423 K). The frequency dependence of the conductivity which follows the Arrhenius equation is interpreted in terms of Jonscher's law: σ (ω) = σdc +A ω S.

Low Frequency AC Conduction in Polyaniline/Zinc Tungstate (PANI/ZnWO4) Composites

In the present paper, we report low frequency ac conductivity and dielectric studies on the composites of conducting polyaniline (PANI) with crystalline zinc tungstate (ZnWO4) powder. These composites have been synthesized by single step in situ polymerization technique by placing fine grade powder of ZnWO4 during the polymerization of aniline. The composites thus formed were characterized by FTIR spectra and scanning electron microscopy (SEM), which conforms the presence of ZnWO4 in polyaniline matrix and the formation of the composite. AC conductivity and dielectric response of these composites were investigated in the frequency ranging from 50 Hz to 5 MHz. it was found that the ac conductivity obeyed the power law index, where the ac conductivity increases with frequency. PANI/ZnWO4 composites have shown high dielectric constant, which could be related to conductivity relaxation phenomenon. It is observed that both dielectric constant and dielectric loss have decreased with increase in frequency. Variations in measured parameters of AC response with increase frequency of the composites follow systematic trends that are similar to those observed with decreasing temperature and level of doping.

Studies on magnetic, dielectric and magnetoelectric behavior of ( x) NiFe 1.9Mn 0.1O 4 and (1 − x) BaZr 0.08Ti 0.92O 3 magnetoelectric composites

In the present research work, the magnetoelectric (ME) composites of ferrite and ferroelectric phases with ( x) NiFe 1.9Mn 0.1O 4 and (1 − x) BaZr 0.08Ti 0.92O 3 (where x = 0.10, 0.20 and 0.30) respectively were synthesized by the conventional ceramic method. The X-ray diffraction pattern of the composite reveals a spinel phase formation for the ferrite and perovskite phase formation for the ferroelectric phase without any other phase. The SEM micrographs of composites were taken to determine the average grain size and also to study the surface morphology. The effect of constituent phase variation on the B– H hysteresis behavior and the dielectric properties was examined. The dielectric constant shows usual dielectric dispersion behavior with increasing frequency which is due to the Maxwell–Wagner type surface interfacial polarization. From the ac conductivity study, it is confirmed that the conduction in the present composites is of small polaron type. The static magnetoelectric (ME) voltage coefficient developed on the surface of magnetoelectric material was measured as a function of applied dc magnetic field. The maximum ME conversion factor of 1.18 mV/cm Oe was observed for x = 0.10 composite. Such composites may be useful to fabricate the magnetic field sensors and applicable in many linear ME devices.

Structural, electrical conduction and magnetoelectric properties of y (Ni 0.3Cu 0.4Zn 0.3Fe 2o 4)+(1− y) [50% batio 3 +50% PZT] ME composites

The particulate composites containing NiCuZn ferrite, barium titanate (BaTiO 3) and lead zirconate titanate (PZT) as constituents having the general formula of the system y (Ni 0.3Cu 0.4Zn 0.3Fe 2O 4)+(1− y) (50% BaTiO 3+50% PZT) with y=0.15, 0.30, 0.45 were prepared by ceramic method. The spinel and tetragonal phase formation of ferrite and ferroelectrics, respectively, was confirmed by X-ray diffraction techniques. The dc resistivity measurements were made as a function of temperature. The variation of dielectric constant (έ) and tan δ with frequency was studied in the range 20 Hz–1 MHz. It shows dielectric dispersion in lower frequency region and remains almost constant at higher frequencies. The studies of ac conductivity indicate small polarons type conduction. The static magnetoelectric sensitivity factor was measured as a function of magnetic field. All the composites show decrease in ME (Magnetoelectric) coefficient with increase in magnetic field.

On the structural, magnetic and electrical properties of sol–gel derived nanosized cobalt ferrite

Nanoparticles of cobalt ferrite were synthesized by sol gel method. These particles were structurally characterized by using X-Ray Diffraction and Transmission Electron Microscopy, High Resolution Transmission Electron Microscopy, Energy Dispersive Spectrum and Inductively Coupled Plasma Analysis and the results confirmed the formation of spherically shaped nanoparticles of cobalt ferrite having a size lying in the range of 13–14 nm. The as prepared sample was sintered at 800 °C and the structural, magnetic and dielectric properties were measured. The dielectric properties were studied and analyzed as a function of temperature and frequency. The ac and dc conductivity studies were carried out to delve into the conduction mechanism. The existing models based on quantum mechanical tunneling were effectively employed to explain the frequency dependent conductivity.