A.K. Meikap

Hopping transport in HCl doped conducting polyaniline

Abstract The present work includes a study on the transport property based on the measurement of the electrical conductivity of HCl doped conducting polyaniline in the presence as well as in the absence of a magnetic field in the temperature range 1.8 K≤ T ≤300 K. It has been observed that the conductivity of the samples increases with increasing temperature and the conductivity ratio [ r = σ (300 K)/ σ (1.8 K)] is large for the sample having higher dopant concentration. A crossover from Mott ( T −1/4 ) to Efros–Shklovskii (ES) ( T −1/2 ) in temperature dependent conductivity of the samples is observed at 10 K. In the presence of a magnetic field the electrical conductivity varies as T −3/4 . From the plot of conductivity versus temperature, different physical quantities like density of states, molecular vibrational frequency, hopping distance and localization length have been determined.

Electron transport properties of cobalt doped polyaniline

Electrical transport properties of cobalt doped polyaniline in an aqueous ethanol medium were investigated in the temperature range 77 ≤ T ≤ 300 K, applying magnetic fields up to 1 T in the frequency range 20 Hz–1 MHz. The room temperature dc resistivity increases with increase in Co content. The dc resistivity and magnetoresistivity of these samples have been interpreted in terms of the variable range hopping theory. The frequency dependence of conductivity has been described by a power law σ(ω) ∝ ωS. The value of s is found to be temperature dependent, which shows a decreasing trend with temperature. The correlated barrier hopping model is the most likely mechanism for the electron transport. The different physical parameters were calculated from the experimental data.

Dielectric relaxation and ac conductivity behaviour of polyvinyl alcohol–HgSe quantum dot hybrid films

Here we report a comparative study on the dielectric relaxation and ac conductivity behaviour of pure polyvinyl alcohol (PVA) and PVA?mercury selenide (HgSe) quantum dot hybrid films in the temperature range 298?K???T???420?K and in the frequency range 100?Hz???f???1?MHz. The prepared nanocomposite exhibits a larger dielectric constant as compared to the pure PVA. The real and imaginary parts of the dielectric constants were found to fit appreciably with the modified Cole?Cole equation, from which temperature-dependent values of the relaxation times, free charge carrier conductivity and space charge carrier conductivity were calculated. The relaxation time decreases with the quantum dots inclusion in the PVA matrix and with an increase in temperature, whereas free charge carrier conductivity and space charge carrier conductivity increases with an increase in temperature. An increase in ac conductivity for the nanocomposites has also been observed, while the charge transport mechanism was found to follow the correlated barrier hopping model in both cases. An easy-path model with a suitable electrical equivalent circuit has been employed to analyse the temperature-dependent impedance spectra. The imaginary part of the complex electric modulus spectra exhibit an asymmetric nature and a non-Debye type of behaviour, which has been elucidated considering a generalized susceptibility function. The electric modulus spectra of the nanocomposite demonstrate a smaller amplitude and broader width, as compared to the pure PVA sample.

Effect of multiwalled carbon nanotubes on electrical conductivity and magnetoconductivity of polyaniline

An in situ chemical polymerization method was applied in order to prepare polyaniline-multiwalled carbon nanotube (PANI-MWCNT) composites with different concentrations of MWCNT. X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, optical absorption and photoluminescence analyses of the composites were performed to investigate the structural, morphological and optical properties of the composites. Electrical transport properties of different PANI-MWCNT composites were investigated in the temperature range 77?K ? T??? 300?K in the presence and also in the absence of a magnetic field up to 1?T. The dc resistivity of the composites follows Motts variable range hopping theory. Two different slopes have been observed in temperature variation of resistivity, which occurs due to the presence of MWCNT in the polymer matrix. The magnetoconductivity of the samples at different temperatures is negative, which can be explained by the wavefunction shrinkage effect.

Semiconducting selenium nanoparticles: Structural, electrical characterization, and formation of a back-to-back Schottky diode device

Well crystalline selenium nanoparticles having an optical band gap of 2.95 eV have been synthesized using oxalic acid. Microstructural parameters such as crystallite size, lattice strain, cell parameters, and unit cell volume are estimated from X-ray diffraction line profile analysis by Rietveld refinement technique. dc and ac transport properties of the nanoparticles in the temperature range 300 K ≤ T ≤ 390 K and frequency range 20 Hz ≤ f ≤ 2 MHz have also been studied. The values of dc activation energies in the low and high temperature regions are found to be 0.083 eV and 0.382 eV, respectively. The charge transport mechanism of the sample follows correlated barrier hopping (CBH) model and the calculated value of barrier height and relaxation time is 0.786 eV and 2.023 × 10−11 s, respectively, while grain boundary contribution being greater than the grain contribution. Considering metal electrode-semiconductor contact as a back-to-back Schottky diode device, analysis of the current-voltage and capacita...

Electrical transport in paratoluene sulfonate doped polypyrrole films at low temperature

Transport data for paratoluene sulfonate dope polypyrrole films in the insulating regime and near the metal-insulator (M-I) boundary are presented and analyzed. Samples in the insulating region show a crossover from Mott to Efros–Shklovskii variable range hopping conduction at T=5 K and magnetoconductance of these samples is also explained by variable range hopping theory. The power law dependence of conductivity σ(T)∝Tβ is observed for the sample close to metallic side of the M-I transition with β=0.83 for 20 K<T<300 K and β=1/2 for 1.8 K⩽T⩽20 K. The magnetoconductance of this sample is analyzed by three dimensional electron-electron interaction and weak electron localization theory. The inelastic scattering length Lin obeys a power law temperature dependence, Lin∝T−p/2 with p=1.

Anomalous electrical transport properties of polyvinyl alcohol-multiwall carbon nanotubes composites below room temperature

The dc and ac electrical transport property of polyvinyl alcohol-multiwall carbon nanotubes composites has been investigated within a temperature range 77≤T≤300 K and in the frequency range 20 Hz–1 MHz in presence as well as in absence of a transverse magnetic field up to 1 T. The dc conductivity follows variable range hopping model. The magnetoconductivity of the samples changes a sign from positive to negative with an increase in temperature which can be interpreted by the dominancy of the quantum interference effect over the wave function shrinkage effect. The ac conductivity follows a power law whereas the temperature dependence of frequency exponent s can be explained by correlated barrier hopping model. The dielectric behavior of the samples has been governed by the grain and grain boundary resistance and capacitance. The ac conductivity reduces with the application of magnetic field. Although the theoretical model to explain it, is still lacking, we may conclude that this is due to the increase in ...

Alternate and direct current conductivity of conducting polyaniline dispersed with poly vinyl alcohol and blended with methyl cellulose

The electrical conductivity, both dc and ac, of conducting polyanilline dispersed with poly vinyl alcohol and blended with methyl cellulose has been investigated in the temperature range of 77⩽T⩽300K and in the frequency range 20 Hz to 1 MHz. The dc conductivity does not obey the standard variable range hopping model, but it satisfies hopping transport between the superlocalized states of polymer. The frequency dependence of conductivity has been described by the power law, σ(ω)αωs. The variation of “s” with temperature suggests that the ac conduction is due to the correlated barrier hopping. Temperature and frequency dependent dielectric constant indicates the Debye-type dispersion.

Dielectric relaxation in polyvinyl alcohol–polypyrrole–multiwall carbon nanotube composites below room temperature

Polyvinyl alcohol?polypyrrole?multiwall carbon nanotube composite polymer films have been synthesized by a chemical oxidative polymerization technique. Dielectric properties have been measured in the frequency range from 20?Hz to 1?MHz and in the temperature range 77???T??? 300?K. Electric modulus vector analysis gives the presence of dielectric relaxation peaks for different composites from which the activation energies have been calculated.

Synthesis of La0.67Sr0.33MnO3 and polyaniline nanocomposite with its electrical and magneto-transport properties

We have synthesized composite of polyaniline nanotubes with lanthanum strontium manganite (La0.67Sr0.33MnO3) (LSMO) nanoparticles. Scanning electron microscopy, x-ray diffraction, Fourier transform infrared, and thermogravimetric analysis scans are done for morphological, structural, and thermal characterization of polyaniline-LSMO nanocomposite. Room temperature hysteresis loop shows ferromagnetic behavior of polyaniline-LSMO nanocomposite but with very low saturation magnetization. Overall pattern of temperature dependence of resistivity for polyaniline has been best-fitted with the form ln[ρ(T)]∝T−1/2. This may be attributed to quasi-one dimensional hopping and also tunneling between mesoscopic ferromagnetic metallic islands. Total resistivity due to grain and grain boundary reduces by application of magnetic field. Remarkable increase (∼73%) in magnetoresistance (MR) is obtained in these polymer coated LSMO compared to the without coated counterpart (16%). The MR% is found to increase with the increas...