Browsing by Author "Amreesh Chandra"

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Ionic noise measurement in polymer electrolytes
(2006) Amreesh Chandra; D.P. Singh; P.K. Singh; Neeraj Khare; S. Chandra
Electrical noise associated with ion transport (termed as "ionic noise") has been measured at different temperatures, using a lock-in amplifier and dynamic signal analyzer for a polymer electrolyte PEO:NH 4I and its CdS dispersed composite. The ionic noise suddenly increases as the polymer passes through its phase transition at T g and T m. The T g-peak in the noise measurement appears more clearly than what it does in DTA/DSC or conductivity measurements. Therefore, we suggest the noise technique as a good probe for studying phase transitions in ion conducting solid electrolytes. Further, the present noise measurements also confirm the known results of DTA/DSC studies that both T g and T m of polymer electrolytes shift on the formation of composites. © Springer-Verlag 2007.
Nanocrystalline ZnS dispersed in polymer electrolyte (PEO :NH4I): Preparation and electrical conductivity measurements
(2002) P.K. Singh; Rana Pratap; Amreesh Chandra
Nano-composites of a polymer electrolyte PEO:NH4I (80:20) have been prepared by dispersing nano-size ZnS crystallites in it. The measured band gap of dispersed ZnS is ∼3.9 eV and its particle size as estimated from the XRD linewidths is ∼ 11 nm. Detailed I-V and polarisation studies show that the composite polymer film is a mixed (ionic+electronic) conductor and that the dispersoid ZnS is n-type. The total electrical conductivity Vs composition studies show two peaks at the ZnS concentrations of 4 and 10 wt% which can be qualitatively explained on the basis of two-percolation threshold model.
On the correlation between the thermal and electrical transport in ionic conductors
(2006) S. Chandra; S.B. Rai; Pramod K. Singh; Kaushal Kumar; Amreesh Chandra
Simultaneous measurements of the thermal diffusivity and electrical conductivity of some 'ion conducting' polymer-solid and solid-solid composites have led us to establish, for the first time, a correlation between these quantities in ionic conductors similar to the Wiedmann-Franz law applicable to 'electron conducting' metals according to which the ratio of thermal to electrical conductivity is almost constant. However, the proportionality constants for the 'ionic conductors' are found to be different for systems with (a) different mobile species, namely H+, Li+ or Ag + and/or (b) different morphology, i.e. polymeric or polycrystalline. © 2006 IOP Publishing Ltd.
Role of the dielectric constant of ferroelectric ceramic in enhancing the ionic conductivity of a polymer electrolyte composite
(2003) Pramod Kumar Singh; Amreesh Chandra
The effect of dispersal of ferroelectric ceramic materials Ba0.70Sr0.30TiO3 (Tc ≈ 30°C) and Ba0.88Sr0.12TiO3 (Tc ≈ 90°C) on the ionic conductivity of an ion conducting polymer electrolyte (PEO:NH4I) is reported. The addition of 3 wt% of Ba1-xSrxTiO3 (x = 0.30 and 0.12) results in an increase in the conductivity by one to two orders of magnitude. Further, a study on the temperature dependence of conductivity of these composites shows that the conductivity enhancement 'peaks' as we approach the dielectric phase transition of the dispersed ferroelectric material where the ε changes rapidly from ∼2400 to 7500 (for x = 0.30) and from 1100 to 5500 (for x = 0.12). This establishes the role of dielectric constant of the dispersoid in enhancing the ionic conductivity of the polymeric composites.
Thermal diffusivity and electrical conductivity in fast ion conducting composites: A correlation
(2006) S. Chandra; S.B. Rai; Pramod K. Singh; Kaushal Kumar; Amreesh Chandra
The thermal diffusivity and electrical conductivity have been measured for two ion conducting polyethylene oxide (PEO) based polymer-ceramic composites viz. (PEO:NH4I) + xAl2O3, (PEO:LiBF4) + xBa0.70Sr0.30TiO3 and two solid-solid composites viz. AgI + xAl2O3, AgI +xBa0.70Sr0.30TiO3. The thermal diffusivity has been measured by the novel photoacoustic technique while the electrical conductivity has been measured by impedance spectroscopy technique using complex impedance plots. The pattern of variation in the electrical conductivity (σ) vs. composition plot and that in the thermal diffusivity (αs) vs. composition plot are similar. Interestingly, the correlation between αs and σ is not only qualitative but is quantitative as well in the sense that the ratio (αs / σ) remains constant for all the samples within the same system (though their conductivities are different) similar to Wiedmann-Franz law applicable to metallic conductors. © 2006 Elsevier B.V. All rights reserved.