S. K. Chattopadhyay

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.

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.

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.

An X-ray diffraction study of defect parameters in a Ti-base alloy

Detailed studies based on the well established method of Fourier line shape analysis have been made on the X-ray diffraction profile of hexagonal titanium alloy of nominal composition Ti-6.58% Al-3.16% Mo-1.81% Zr-008% Fe-0.012% N-0.0078% C. While deformation fault probability, α, has been found to be quite high compared to that of pure titanium, the deformation growth fault parameter, β, shows a negative value ruling out the presence of growth fault in this alloy in the deformed state.

Effect of alloying with zinc on SFE of aluminium by study of lattice imperfections in cold worked Al-Zn alloys

A detailed X-ray Fourier line shape analysis has been performed on three compositions of Al-Zn alloys viz. Al-3.55 wt% Zn, Al-14.7 wt% Zn and Al-19.3 wt% Zn infcc phase. It has been found that deformation stacking faults, both intrinsic ά and extrinsic α are absent in the cold worked state and twin fault β is found to be slightly present in the deformed lattice of the two initial compositions of the alloys. Similar to the effect of solute germanium and copper, respectively in Al-Ge and Al-Cu systems, hexagonal zinc also fails to impart faulting infcc Al-Zn system. This corroborates the fact that aluminium has high stacking fault energy.

Electrical resistivity and magnetoresistivity of protonic acid (H2SO4 and HCl)-doped polyaniline at low temperature

Electrical-transport properties of protonic acid (H2SO4 and HCl)-doped polyaniline (PANI) in an aqueous ethanol medium were investigated in the temperature range 1.8 K ≤ T ≤ 300 K and in a magnetic field up to 8 T. The room-temperature resistivity of HCl-doped PANI is larger than that of H2SO4-doped PANI. The resistivity ratios ρr = ρ(1.8 K)/ρ(300 K) of the samples are high. The samples in the insulating region show a crossover from a Mott to an Efros–Shklovskii variable range hopping conduction at T = 9.8 K for H2SO4-doped PANI and 8.5 K for HCl-doped PANI. The magnetoresistivity of these samples is also explained by the variable range hopping theory. The different physical parameters were calculated from the experimental data.

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.

Frequency Dependent Conductivity of Thin ZnO Films Prepared by R.F. Sputtering Technique

AC conductivity of different thin zinc oxide films measured in the frequency range of 10 Hz to 2 MHz in the temperature interval of 300 K to 575 K is reported. ZnO films were prepared by reactive r.f. magnetron sputtering from ZnO target. The experimental data reveal that a.c. conductivity is proportional to ωs. The value of s was found to be temperature dependent, decreases with increasing temperature. These observations suggest that correlated barrier hopping model is the most likely mechanism. The temperature dependence of a.c. Conductivity is expressed in power law form as σ(ω) ∝Tn. The temperature exponent n is found to be increasing with increasing temperature and decreasing frequency in accordance with the narrow band limit. At high temperature the conductivity variation with frequency is comparatively small. The polaron binding energy (Wm), the height of Coulomb barrier (W) and the characteristic relaxation time (τ0) have been calculated. The values of Wm and W increase as the thickness decreases whereas the values of τ0 decrease with decreasing thickness.

Low temperature electrical conductivity and magnetoconductivity of Fe39Ni39Mo4Si6B12 and Co58Ni10Fe5Si11B16 metallic glass alloys

A detailed study on the weak localization phenomenon vis-a-vis electron-electron interaction effects in magnetic metallic glasses has been carried out. We measured the electrical conductivity and magnetoconductivity within the temperature range 1.8≤T≤300K. A maximum on the conductivity versus temperature curve exists atT=Tm. The conductivity was observed to follow aT1/2 law forTTm. Magnetoconductivity data of these alloys indicate the prominence of electron-electron interaction at low temperatures. The authors have determined the inelastic scattering field and spin-orbit scattering field from the magnetoconductivity data. The inelastic scattering field obeys aTp law (p=2) at low temperatures.

Transport properties of Ti3Ir compound at low temperature

Electrical resistivity and magnetoresistivity of Ti3Ir compound have been measured in the temperature range 2.0 K ≤T ≤ 300 K in absence as well as in presence of magnetic field upto 7.7 T. The low temperature resistivity shows aT2 behaviour whereas the high temperature resistivity shows a linear behaviour. The magnetoresistivity is positive and cannot be explained by simple s-d scattering model. The enhancement of the coefficient A of theT2 term and the deviation from the quadratic field dependence of the resistivity may be due to the anisotropy in the compound.