Papers by Keyword: AC Conductivity

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Authors: M. Singh, K.L. Bhatia, P. Singh, R.S. Kundu, N. Kishore
Authors: M.S. Jogad, V.K. Shrikhande, A.H. Dyama, L.A. Udachan, Govind P. Kothiyal
Abstract: AC and DC conductivities have been measured by using the real (e¢) and imaginary (e¢¢) parts of the dielectric constant data of glass and glass-ceramics (GC) at different temperatures in the rage 297-642K and in the frequency range 100 Hz to 10 MHz. Using Anderson –Stuart model, we have calculated the activation energy, which is observed to be lower than that of the DC conductivity. The analysis for glass/glass-ceramics indicates that the conductivity variation with frequency exhibits an initial linear region followed by nonlinear region with a maximum in the high-frequency region. The observed frequency dependence of ionic conductivity has been analyzed within the extended Anderson–Stuart model considering both the electrostatic and elastic strain terms. In glass/glassceramic the calculations based on the Anderson-Stuart model agree with the experimental observations in the low frequency region but at higher frequencies there is departure from measured data.
Authors: W. Huang, T. Khan, T. Paul Chow
Abstract: Both n-type and p-type GaN MOS capacitors with plasma-enhanced CVD-SiO2 as the gate oxide were characterized using both capacitance and conductance techniques. From a n type MOS capacitor, an interface state density of 3.8×1010/cm2-eV was estimated at 0.19eV near the conduction band and decreases deeper into the bandgap while from a p type MOS capacitor, an interface state density of 1.4×1011/cm2-eV 0.61eV above the valence band was estimated and decreases deeper into the bandgap. Unlike the symmetric interface state density distribution in Si, an asymmetric interface state density distribution with lower density near the conduction band and higher density near the valence band has been determined.
Authors: P.K. Mehta, Bhagwati Bishnoi, Ravi Kumar, R.J. Choudhary, D.M. Phase
Abstract: Study of Sr[(Mg0.32Co0.02) Nb0.66]O3 [SMCN] thin films prepared by Pulsed Laser Deposition Technique (PLD) were carried out in the temperature range of 150 to 450K and frequency range of 100KHz to 1.1MHz. X-ray diffraction of the thin film shows single phase formation with monoclinic symmetry. The dielectric properties show enhanced ε' values compared to bulk suggesting promising applications in alternative technologies. Due to simultaneous increase in dissipation factor with temperature the net ac conductivity is found to be decreasing. Technologically important two step activation energy is observed in the film. This property can be used in switching devices. In low temperature region the activation energy corresponds to shallow traps while the migration of oxygen vacancies contributes in high temperature region.
Authors: Zhong Yang Wang, Xin Yan Li, Run Hua Fan, Pei Tao Xie, Kai Sun, Guo Hua Fan, Chuan Xin Hou, Xiang Zhang
Abstract: Conductor–insulator composites have been extensive researched for high dielectric constant. Most of them concentrated on metal polymers or metal ceramics. Barium titanate–carbon fibers composites were prepared by using a solid state reaction process with carbon fibers contents ranging from7 vol% to 23 vol%. Due to the high-aspect-ratio of carbon fiber, it was easy to produce a conducting network at much lower volume fraction. FESEM images illustrated that the carbon fibers influenced the densification and microstructure of the ceramics. Besides, addition of carbon fibers led to increase in dielectric permittivity, also had effects on the dielectric loss and ac conductivity. The dielectric and conductivity properties as a function of carbon fibers volume fraction were explained by the percolation theory.
Authors: Shinde J. Tukaram, Gadkari B. Ashok, Vasambekar N. Pramod
Abstract: Nickel–zinc ferrites with chemical formula Ni1-xZnxFe2O4 (x = 0, 0.2, 0.4, 0.6, 0.8 and 1.0) were prepared by oxalate co-precipitation method. The dielectric constant (ε') dielectric loss (tanδ) and AC conductivity (σac) of all the samples were determined at room temperature in the frequency range 20Hz -1MHz. The dielectric constant and dielectric loss are much smaller than those for samples prepared by ceramic method. The dielectric behaviour is attributed to the Maxwell–Wagner type interfacial polarization. AC conductivity of all the samples lies in the range 1.20×10-8 to 54.7×10-8 Ω-1cm-1. Low dielectric loss and high resistivity suggest the suitability of these ferrites for high frequency applications.
Authors: Omed Ghareb Abdullah, Dana Abdull Tahir, Gelas Mukaram Jamal, Salah Raza Saeed
Abstract: Dielectric constant and ac conductivity of Polyester doped with carbon black are investigated in the frequency range (0.5-103) KHz and within the temperature range (26-80) oC. Dielectric permittivity and loss tangent reduced with increasing frequency and increase with increasing temperature. The ac conductivity σac for all samples were found to be weak frequency dependent at low frequency, however vary with frequency as a power law ωs at higher frequency range. The variation of frequency exponential factor s between 0.63 and 0.77, indicates a dominant hopping process at low temperatures. From the temperature dependence of dc conductivity, the increase of activation energy was observed with carbon black concentrations.
Authors: Tan Winie, Nur Syuhada Mohd Shahril, Nur Shazlinda Muhammad Hanif, Ri Hanum Yahaya Subban, Chin Han Chan
Abstract: Hexanoyl chitosan exhibited solubility in tetrahydrofuran (THF) was prepared by acyl modification of chitosan. Polystyrene with molecular weight 280,000 g mol-1 was chosen to blend with hexanoyl chitosan. LiCF3SO3 was employed as the doping salt. Untreated and H2SO4 treated TiO2 was added as the filler. Films of hexanoyl chitosan-polystyrene-LiCF3SO3-TiO2 polymer electrolyte were obtained by solution casting technique. The ac conductivity of the sample was calculated from the relation σac = εoεiω, where εo is the permittivity of the free space, the angular frequency, ω=2πf, and εi is the dielectric loss. The ac conductivity dispersion observed is analyzed using the Jonshers universal power law, σ (ω) = σdc + Aωn where A is a pre-exponential constant and n is the power law exponent with value in the range 0 < n < 1. The temperature dependence of exponent n will then be interpreted using the existing theoretical models.
Authors: Humaira Anwar, Ashari Maqsood
Abstract: Mn-Zn ferrite powders (Mn0.5Zn0.5Fe2O4) were prepared by the chemical co-precipitation method. The effect of sintering temperature on the crystalline phase formation and dielectric properties were investigated by X-ray diffraction and impedance analyzer respectively. The TGA/DTA analysis was carried out to know decomposition mechanism. Ferrites decomposed to Fe3O4 above 873 K sintering temperature. Crystallite size increased with increasing sintering temperature between 7-13 nm. The resistivity decreased with increase in temperature showing semiconducting like behaviour. Activation energy was in the range of 0.70 to 0.77eV for these samples. Dielectric constant decreased with increasing frequency. Relaxation peak occurred for loss tangent versus frequency curves. The ac conductivity explained using small polaron tunnelling (SPT) model.
Authors: Kameshwar Kumar, Vimal Sharma, Pankaj Sharma, Nagesh Thakur
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