Synthesis, Electrical Conductivity, and Dielectric Behavior of Polyaniline/V 2

Conducting polymer composites of polyaniline/vanadium pentaoxide PANI/V2O5 (with different initial weight percentage of V2O5) has been synthesized by in situ polymerization method. DC conductivity of compressed pellets has been analyzed in the temperature range 300–550 K and was found to increase with V2O5 doping. This increase in conductivity is mainly due to band conduction. It has also been observed that the dielectric constant and dielectric loss increase with the level of doping of V2O5 but remain independent of the frequency (50 KHz–1 MHz). X-ray diffraction pattern shows some order of crystallinity of composites due to interaction of polyaniline with V2O5. UV-visible spectroscopy shows an increase in the optical band gap with doping

Dielectric properties of microwave flash combustion derived and spark plasma sintered CaCu3Ti4O12 ceramic: role of reduction in grain boundary activation energy

CaCu3Ti4O12 nanocrystals have been synthesized by the microwave flash combustion technique. The calcined powders were spark plasma sintered at 1050 degrees C for 10 min. The surface morphology of sintered samples was studied by SEM. The effects of grain boundary activation energy on dielectric properties of CCTO were investigated by collecting the dielectric data in the frequencies of 30 Hz-8 MHz at temperatures of 20-100 degrees C under dc bias of 0-6 V. The potential energy barrier at grain boundary has been examined by dc bias experiments. It is observed that, with an increase in dc bias from 0 to 6 V, the grain boundary activation energy decreases from 0.532 to 0.463 eV. The reduction in such grain boundary activation energy results in the decrease in dielectric constant. It is noticed that CCTO ceramic at room temperature under zero dc bias has a colossal dielectric constant of 20,000 (at 100 Hz). Using the cole-cole plot, grain and grain boundary resistance are calculated to be 13 and 52,100 Omega, respectively

Improved Performance of Organic LEDs with Modified Metal-Organic Interface

Incorporation of thin layers of strong acceptor tetrafluro-tetracyanoquinodi methane (F(4)TCNQ) over conducting substrate Indium-Tin-Oxide (ITO) modified its work function. The enhancement depended on the thickness of F(4)TCNQ film. These modified ITO substrates were used as hole injection contacts in OLEDs which show enhanced device current, lower operating voltages and enhanced current efficiency

Effect of Gamma Irradiation on Structural and optical properties of Thin Films of a-Cd5Se95-xZnx

We report the gamma irradiation effect on the structural and optical properties of a-Cd5Se95xZnx (x=0, 2, 4) thin films. Thin films were prepared by thermal evaporation technique at a base pressure of 10-5 torr. The investigated thin films of ~ 200 nm thickness are then irradiated by 25-100 kGy doses of 60co gamma rays. The elemental composition of as-deposited thin films of Cd5Se95-xZnx (x=0, 2, 4) were verified by RBS spectrometry shows good agreement with the actual elemental composition. XRD, PL and FT-IR study confirms the crystallinity of the investigated thin films increases after gamma irradiation. The optical parameters were estimated from optical absorption spectra data measured from UV-vis-spectrophotometer. It was found that the value of optical band gap of investigated thin films decreases and the corresponding absorption coefficient increases up to 75 kGy dose of gamma irradiation. This post irradiation change in the values of optical band gap and absorption coefficient were interpreted in terms of increase in crystallinity of the material after gamma irradiation

Photoconductivity of Se_90-xTe₁₀Zn_x thin films

53-59Photoconductive properties such as dark conductivity, steady state and transient photoconductivity of a-Se90-xTe10Znx thin films, prepared by thermal vacuum evaporation technique have been studied in temperature range 312-380 K. Analysis of data shows that activation energy of dark current is greater as compared to activation energy of photo current. Activation energy decreases with increase in Zn concentration which may be due to increase in defect density of states. Analysis of intensity dependent photoconductivity shows that bimolecular recombination is predominant. Photosensitivity is found to be maximum for Se88Te10Zn2 composition after that it decreases with increase in Zn concentration. Carrier lifetime decreases with increase in Zn concentration which also confirms that density of defect states increases. Transient photoconductivity shows that the carrier lifetime decreases with increase in Zn concentration. This decrease is due to transition trapping process

Effect of porosity on electrical conductivity of hot pressed AlN ceramic

Temperature dependence of electrical conductivity has been studied for hot pressed AlN ceramic having different volume percentage of porosity (0.2 to 15 %) in the temperature range (500 K to 950 K). It has been observed that electrical conductivity decreases by two orders of magnitude as the volume percentage of porosity increases from 0.2 to 15 %. The effect of moisture on electrical conductivity has also been studied on the same samples of AlN. Samples having small porosity (upto 4 volume %) did not show any appreciable effect of moisture on electrical conductivity. However, at higher concentration of porosity (15 volume %), the conductivity increases by three orders of magnitude after exposing to the moisture

Effect of Zinc additive on dielectric properties of Cd–Se glassy system

Cd5Se95–xZnx (x=0, 2, 4, 6) glassy alloy has been prepared by a melt-quenching technique. Thin films were deposited by thermal coating unit on ultraclean glass substrate under a vacuum of 10–6 Torr. The absence of any sharp peaks in the X-ray diffraction confirms the amorphous nature of thin films. The frequency and temperature dependence of dielectric constant and dielectric loss in the frequency range of 1 kHz to 1 MHz and in the temperature range of 290–370 K were studied. Dielectric dispersion was observed when Zinc (Zn) was incorporated into the Cd–Se system. The increase in dielectric parameter with Zn concentration may be due to increase in defect states. The DC conductivity has been reported to investigate the effect of Zn concentration on DC conduction loss. The results are interpreted in term of dipolar theory for Cd5Se95 and Cd5Se93Zn2 samples, while the remaining samples have been explained on the basis of DC conduction loss. It was also observed that the DC conductivity increased with the increase of Zinc concentration, which may be due to the decrease in the band gap near Fermi level

Ac Conductivity Measurement of Cd5Se95−xZnxCd_{5}Se_{95-x}Zn_{x} Chalcogenide Semiconductor Using Correlated Barrier Hopping Model

$Cd_{5}Se_{95-x}Zn_{x}$ (x=0, 2, 4, 6) chalcogenide semiconductors were prepared by conventional melt-quenching and were characterized by X-ray diffraction, scanning electron microscopy, and Fourier transform infrared studies. Ac conductivity of $Cd_{5}Se_{95-x}Zn_{x}$ chalcogenide semiconductor has been investigated in the frequency range of 1 kHz-1 MHz and in the temperature range of 290-370 K. The analysis of the experimental results indicates that the ac conductivity is temperature, frequency and concentration dependent. Ac conductivity is found to obey the power law $\omega^{s}$ where s < 1. A strong dependence of ac conductivity and exponent s can be well interpreted in terms of correlated barrier hopping model. The maximum barrier height W_{m} were calculated from the results of dielectric loss according to the Guintini equation that agree with the theory of hopping of charge carriers over potential barrier as suggested by Elliot in case of chalcogenide semiconductors

Synthesis, Characterization and Properties of MgB2 Doped Polyaniline

Present paper reports novel synthesis of MgB2 doped Polyaniline (PAni). PAni is synthesized through oxidative polymerization method using Ammonium Peroxodisulphate and doped by different compositions of MgB2. The DC conductivity of undoped and doped polymers is measured in the temperature range of 300 – 400 K and is found to increase with temperature. An increase in conductivity by five orders of magnitude has been observed after doping. Conduction mechanism was also studied in all of the samples. FT-IR (Fourier Transform Infrared spectroscopy) and Ultraviolet (UV)-Visible studies confirm the occurrence of PAni in conducting emeraldine salt form in the composites. The optical studies signify that absorption mechanism is due to direct allowed transition and the band gap decrease after doping. Thermal stability of all the composites has been explained on the basis of variation in Tc–Tg and ∆Hc by using DSC (Differential Scanning Calorimetery) measurements