Sanat Kumar Chatterjee

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.

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...

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.

Structural characterization and observation of variable range hopping conduction mechanism at high temperature in CdSe quantum dot solids

We have used Rietveld refinement technique to extract the microstructural parameters of thioglycolic acid capped CdSe quantum dots. The quantum dot formation and its efficient capping are further confirmed by HR-TEM, UV-visible and FT-IR spectroscopy. Comparative study of the variation of dc conductivity with temperature (298 K ≤ T ≤ 460 K) is given considering Arrhenius formalism, small polaron hopping and Schnakenberg model. We observe that only Schnakenberg model provides good fit to the non-linear region of the variation of dc conductivity with temperature. Experimental variation of ac conductivity and dielectric parameters with temperature (298 K ≤ T ≤ 460 K) and frequency (80 Hz ≤ f ≤ 2 MHz) are discussed in the light of hopping theory and quantum confinement effect. We have elucidated the observed non-linearity in the I-V curves (measured within ±50 V), at dark and at ambient light, in view of tunneling mechanism. Tunnel exponents and non-linearity weight factors have also been evaluated in this re...

A study on the transport properties of Fe67Co18B14Si1 and Fe81B13.5Si3.5C2 metallic glass alloys at low temperatures

Abstract We report the results of a comprehensive study of localization and electron–electron interaction effects in Fe-base metallic glasses. We have measured the electrical conductivity and magnetoconductivity within the temperature range 1.8 K ≤T≤300 K . A maximum is observed in the conductivity versus temperature curve at temperature T=Tm. The conductivity obeys a T1/2 law for T Tm. Magnetoconductivity data indicate that the electron–electron interaction is most prominent in these alloys at low temperature. From the magneto-conductivity data we have calculated the inelastic scattering field and spin–orbit scattering field. The inelastic scattering field follows a Tp law (p=2) at low temperature.

Study of Microstructural Defect Parameters in Vanadium–Aluminium Alloys using Warren–Averbach Method and Modified Rietveld Technique

Detailed X-ray diffraction line profile analysis using Warren–Averbach method and modified Rietveld technique has been performed on the X-ray diffraction profile of body centered cubic vanadium-base aluminium alloys of nominal compositions in wt % as V–26% Al (Alloy I), V–24% Al (Alloy II), V–20% Al (Alloy III) and V–18% Al (Alloy IV). The microstructural parameters such as coherent domain size, microstrain within the domains and compound faults were evaluated in the alloys by applying Fourier line shape analysis. The Fourier analysis has been done taking silicon as standard. The growth fault parameter (β) has been observed to be either negligibly small or negative. This shows that growth faults are absent in this bcc system. It has also been observed that the spacing fault (αe) is totally absent in the system because the values are negative. The faulting parameter (1.5 α+ β) and deformation stacking fault α obtained from these analyses are however, not negligible.

Microstructural studies on variation of defect parameters in Zr-Sn alloys and their transition with interchange of solvent and solute in Zr-Ti and Ti-Zr alloy systems by modified Rietveld method and Warren-Averbach method

The effects of deformation and the transition of microstructural defect states with the interchange of solvent and solute in Ti-Zr and Zr-Ti alloys of six different compositions and Zr-Sn alloys in three different compositions have been investigated by X-ray diffraction line profile analysis. The detailed analysis of the X-ray powder diffraction line profiles was interpreted by Fourier line shape analysis using modified Rietveld method and Warren-Averbach method taking silicon as standard. Finally the microstructural parameters such as coherent domain size, microstrains within domains, faulting probability and dislocation density were evaluated from the analysis of X-ray powder diffraction data of Zr base Sn, Ti and Ti base Zr alloys by modified Rietveld powder structure refinement. This analysis confirms that the growth fault, β, is totally absent or negligibly present in Zr-Ti, Ti-Zr and Zr-Sn alloy systems, because the growth fault, β, has been observed to be either negative or very small for these alloy systems. This analysis also revealed that the deformation fault, α, has significant presence in titanium-base zirconium alloy systems but when zirconium content in the matrix goes on increasing beyond 50%, this faulting behaviour suffers a drastic transition and faulting tendency abruptly drops to a level of negligible presence or zero. This tendency has also been observed in Zr-Sn alloys signifying high stacking fault energy. Therefore, Zr and Zr-base alloys having high stacking fault energy can be used as hard alloys in nuclear technology at high temperature.

Synthesis and characterization of TbMnO 3 nanorods

We report the synthesis and characterization of multiferroic TbMnO3 nanorods by sol-gel route. From XRD analysis it was observed that annealing at 700°C for 2h is the most favorable condition for the fabrication of TbMnO3 nano rods. The TEM study revealed that the diameter of these rods varied from 12.6 – 38.1nm and the length of these nanorods varied from 88.6 – 292 nm. SAED pattern of the nano rods revealed single crystalline structure. Presence of TbMnO3 nano particles was also observed alongwith the nanorods. UV, PL, F.T.I.R study on the samples annealed at different calcination condition is also reported.

Electric modulus and impedance spectroscopy analysis on selenium nanoparticles at and above room temperature

Here we report the electric modulus and impedance spectroscopy study on selenium nanoparticles in the temperature (T) range of 298K ≤ T ≤ 364K and in the frequency (f) of range 20Hz ≤ f ≤ 2MHz. Variation of the imaginary part of the electric modulus (M”) with frequency yields well defined peaks (non–Debye type) which shift to higher frequency side with increasing temperature. From the response peaks of M” versus f graphs relaxation times (τ) are calculated which follows Arrhenius law with temperature with an activation energy of 0.27 eV. We observe that similar relaxation dynamics prevails at all temperatures with significant suppression of electrode effects. Role of grain and grain boundaries is also elucidated by the impedance spectroscopy analysis. We found that grain resistance varies from 0.07 MΩ to 0.48 MΩ whereas the grain boundary resistance varies in the range 0.09 MΩ to 0.82 MΩ. Both the grain and grain boundary resistances follow Arrhenius law with temperature having activation energies of 0.28...