Electric Modulus Analysis of Carbon Black/Copolymer Composite Materials

We have investigated the electrical properties of carbon black (CB) loaded in ethylene butylacrylate copolymer composite (EBA) in the frequency range between 102 and 104 Hz and temperature range between 153 and 353 K. The frequency dependence of electrical data that have been analyzed in two frameworks: the electrical modulus formalism with the Kohlrausch-Williams-Watts stretched exponential function (KWW) and the electrical conductivity by using the Jonscher’s power law in the frequency domain. The stretching exponent βKWW and n are found to be temperature independent for all CB fractions and to be decreased when the CB volume concentrations loaded in copolymer matrix increases. It is found that the activation energy obtained by the modulus method is in good agreement with that obtained by the DC conductivity in the power law which is independent on the CB contents that exist in the copolymer matrix, suggesting that these particles do not interact significantly with the chain segments of the macromolecules in the EBA copolymer.

Complex impedance and electric modulus studies of magnetic ceramic Ni_(0.27)Cu_(0.10)Zn_(0.63)Fe_(2)O_(4)

The electrical properties of Ni_(0.27)Cu_(0.10)Zn_(0.63)Fe_(2)O_(4)(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 T_(SM)(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 R_(gb) becomes more prominent compared to grain resistance R_(b) at room temperature,and with the increase in T_(SM),R_(gb) decreases faster than the intrinsic R_(b).The frequency response of the imaginary part of impedance showed relaxation behavior at every T_(SM),and the relaxation frequency variation with T_(SM) 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.

The electrical impedance, AC conductivity and dielectric properties of phenol red compound investigated and modeled by an artificial neural network

The impedance spectroscopy,electrical conductivity and electric modulus of bulk phenol red were measured,as a function of both frequency and temperature.Artificial neural networks(ANNs)were used for modeling its electrical properties.The two parts(real and imaginary)of its complex impedance(Z^*)were analyzed and the activation energy related to the electrical relaxation process was evaluated.Nyquist curves were plotted showing semicircles for the different temperatures.The AC electrical conductivity follows a power lawσac(ω)αω^η.The maximum barrier height Bm was derived for specific temperatures.A plausible mechanism for the AC conduction of bulk phenol red was deduced from the temperature reliance of the frequency exponent.The dielectric data was analyzed using electric modulus as a tool.In addition,ANNs were used to model the impedance parts and the total electrical conductivity.Numerous runs were tried,to obtain the best performance.The training and prediction results were compared to the equivalent experimental results,with a good match obtained.An equation describing the experimental results was obtained mathematically,based on the use of ANNs.The outputs demonstrated that ANNs are an admirable tool for modeling experimental results.

Electrical conduction properties of the BZT-BST ceramics

0.5Ba(Zr_(0.2)Ti_(0.8))O3-0.5(Ba_(0.7)Sr_(0.3))TiO3(BZT-BST)has been explored in recent times for potential applications in energy harvesting,electrocaloric and energy storage.To this end,energy harvesting/conversion and storage applications require an understanding of the conduction and loss mechanisms.The conduction mechanism in BZT-BST ceramics is studied using impedance spectroscopy(IS)at 0.1 Hz−3 MHz and 100−600°C.Impedance study reveals the presence of two types of relaxation processes due to grain and grain boundary contributions.The relaxation time and dc conductivity activation energies are obtained as 1.12/1.3 eV and 1.05/1.2eV for bulk/grain boundary,respectively,and found that oxygen vacancies dominated electrical behavior.The relaxation mechanism follows non-Debye-type behavior.The high resistance of the grain(bulk)in the ferroelectric region does not contribute to the high losses;the losses probably result from the phase transition.Also,BZT-BST ceramics exhibit a negative temperature coefficient of resistance(NTCR)behaviour.From a practical application point of view in the temperature regime of 25-65°C,the loss’s contri-bution is low.The significant contributions of loss result from the response of phase-transition in this temperature range(25-65°C)。

MORPHOTROPIC PHASE BOUNDARY AND DIELECTRIC RELAXATION STUDY OF(Bi_(0.5)Na_(0.5))TiO_(3)-BaTiO_(3)LEAD-FREE CERAMIC

We report the temperature and frequency dependence impedance spectroscopy of(1-x)(Bi_(0.5)Na_(0.5))TiO_(3-x)BaTiO_(3)(abbreviated as BNT-BT)ceramics with 0≤x≤0.07 prepared by conventional solid-state route.X-ray diffraction analysis indicated that a solid solution is formed when BaTiO_(3)diffuses into the(Bi_(0.5)Na_(0.5))TiO_(3)lattice and a morphotropic phase boundary between rhombohedral and tetragonal locates at x=0.07.The microstructure indicated that the grain size reduces and the shape changes from rectangular to quasi-spherical with increase in BaTiO_(3)content.Complex Impedance Spectroscopy analysis suggested the presence of temperature-dependent relaxation process in the materials.The modulus mechanism indicated the nonDebye type of conductivity relaxation in the materials,which is supported by impedance data.The activation energies have been calculated from impedance,electric modulus studies and dc conductivity which suggests that the conductions are ionic in nature.The activation energy increases with increase of BT content up to x=0.05 and decreases at x=0.07 which also indicates the presence of morphotropic phase boundary at x=0.07.

Structural and dielectric properties of prepared PbS and PbTe nanomaterials

In this work, PbS and PbTe nanomaterials with various morphologies were synthesized by a hydrothermal method. The structural properties were investigated by using X-ray diffraction(XRD) and corresponding scanning electron microscopy together with their EDX analysis. Both the PbS and PbTe nanomaterials possess good polycrystalline structure. The crystallite size, determined from the XRD data, of PbS is 5 nm whereas the corresponding value of PbTe is 2.69 nm. SEM micrographs reveal that the prepared PbS nanomaterial has starshaped structures, micro-flowers, some cubes, and semi-dendrites, whereas PbTe has semi-flower structures. Additionally, the dielectric properties have been studied in a broad frequency range from 0.1 Hz up to 1 MHz at temperatures from 298-423 K. The real and imaginary parts of the complex dielectric constant ε' and ε" of PbTe are comparatively higher than those of PbS. Moreover, the dielectric data were analyzed on the basis of the electric modulus.

Impedance Studies of La_2Mo_(2-x)Sn_xO(9-δ) Oxide Ion Conductors

A series of compounds La2Mo2-xSnxO9-6 （x=0-0.3） have been synthesized by solid-state reaction technique. Materials have been characterized by XRD, SEM, DSC and impedance study. In the temperature regime 520℃-590 ℃, the specimens with x〈0.05 have the conductivity higher than La2Mo2O9. Conductivity of Sn-doped compound decreases consistently with increasing Sn-doping, compared to the undoped compound both below and above phase transition, barring the specimens with x〈 0.05, where conductivity values remains almost same as that of undoped specimen in high temperature region. In the intermediate temperature regime （520℃-590℃）, the conductivity of doped compounds increases for x〈0.05 as compared to parent compound. Also, there is no indication of phase stabilization with Sn-doping in this compound even with the highest doping level, x=0.3. Electric modulus analysis suggests that thermally activated oxygen ion hopping mechanism is responsible for the conduction in Sn-doped compound.

AC Conductivity and Dielectric Relaxation Behavior of Sol-gel Ba_xSr_(1-x)TiO_3 Thin Films

BaxSr1-xTiO3 sol-gel thin films with x--0.5, 0.7 and 0.8 have been fabricated as AI/BST/Pt capacitor. The AC conductivity and dielectric properties over a frequency rang of 10 Hz and I MHz have been studied in order to explore the ion dynamics and relaxation mechanisms in the films. The frequency dependent conductivity plots show three regions of conduction processes. Dielectric results show that ε＇ at low frequencies increases as Sr content decreases, whereas at high frequencies, it shows opposite variation, which is attributed to the dipole dynamics. The electric modulus plots reveal the relaxation peaks which are not observed in the ε＂ plots and the contribution of the grains, grain boundaries and electrode to the relaxation mechanisms.