Amita Chandra

Ion transport studies in PEO∶NH4I polymer electrolytes with dispersed Al2O3

Ion conducting polymer electrolyte films having high salt concentrations have been studied. The system studied is PEO∶NH4I, dispersed with α-Al2O3. Mechanically stable films with NH4+/EO ratio ≥0.13 have been obtained by dispersal of Al2O3. The films have been characterized using various techniques such as X-ray diffraction (XRD), differential thermal analysis (DTA), polarization and complex impedance spectroscopy. Intercorrelation between polymer matrix crystallite size, conductivity, and α-Al2O3 particle size is established.

Mixed-anion effect in polyethylene-oxide-based sodium-ion-conducting polymer electrolytes

Electrical conductivity, mobility, cationic and anionic transference numbers and numbers of respective mobile charge carriers have been measured for polyethylene-oxide-based polymer electrolytes complexed with mixed anion salts. The systems studied are (polyethylene oxide)15: ((1-x)NaI+xNaSCN) and (polyethylene oxide)15: ((1-x)NaI+xNaClO4). It is shown that the presence of mixed anions in the polymer salt complex electrolytes changes the relative number of mobile cations and anions together with their respective transference numbers as well as the crystallinity of the polymer matrix. A qualitative correlation has been established between the crystallinity, tcation, conductivity and the number of mobile anions/cations. The maximum change in the cationic (Na+) transference number was for polyethylene oxide: NaI for which tNa+ could be increased from 0.18 to about 0.6 in the mixed anion system (polyethylene oxide)15: (0.35NaI+0.65NaSCN) with comparable conductivity.

Semiconductor-dispersed polymer electrolyte composites

Composites of polyethylene oxide (PEO)/NH4I polymer electrolyte dispersed with semiconductors PbS, CdS and PbxCd1 � xS in different weight ratios have been prepared and characterised. Relevant amount of Pb and/or Cd acetates were added to a viscous solution of polymer PEO/NH4I complex. On sulfuration by bubbling H2S through it, the in situ formation and dispersal of PbS, CdS or PbxCd1 � xS resulted. Solution casting gave the ‘‘semiconductor-dispersed polymer electrolyte’’ (SPDE) membranes with 10–20% of electronic conductivity depending upon the preparatory conditions. D 2002 Published by Elsevier Science B.V.

Properties and morphology of highly conducting inorganic solid–liquid composites based on AgCl

Abstract Composites of a Frenkel disordered solid (AgCl) with Schottky disordered solids (KCl, RbCl and CsCl) have been prepared and characterised. Unlike two-phase mixtures of two Frenkel disordered solids, no significant conductivity enhancement has been observed in any of these composites studied. This is in full accordance with the two-phase model. The composites show interesting morphological behaviour. The eutectic composition (0.7AgCl/0.3KCl) of the composites exhibits a lamellar structure, which leads to a highly porous weblike AgCl network after removal of KCl from this structure by aqueous dissolution (normal and under ultrasonication). In addition to its possible use as NH 3 sensor material, it offers a solid framework in which liquid electrolytes such as AgNO 3 (aq) can be inserted. These inorganic solid–liquid composites show very favourable properties, in that they combine liquid-like ionic conductivities with the mechanical advantages of a soft solid.

Anion clustering and fractal pattern growth in ion conducting polymeric matrix

Abstract Mobile iodine anions are shown to cluster in large size isotropic fractal patterns (Diffusion Limited Aggregates, DLA) in ion conducting polymeric system PEO:NaI (and also PEO:NH 4 I). Anisotropic “tree-like” patterns have also been obtained by deliberately creating physical interface such that the aggregating species arrive only from one direction. The aggregating species is I 3 − which may thermally relax leading to the breaking up of the fractal arms. It is further shown that in the regions where I 2 (instead of I 3 − ) gets formed, a “strain-field” results forbidding further anion clustering.

Tempos structures with gold nanoclusters

Following the preparation of novel electronic MOS-like structures (TEMPOS, tunable electronic material with pores on semiconductors) with Ag-nanocluster (NC)-filled etched ion tracks, Au-nanocluster-filled TEMPOS (Au-NC-TEMPOS) structures are presented in this work. In spite of some similarities, the characteristics of both Ag- and Au-TEMPOS structures differ markedly. This is mainly attributed to the different distributions of the metallic nanoparticles. As in the case of Au-NC-TEMPOS, instabilities show up in their current/voltage characteristics that might be exploited for the construction of electronically active devices.

Transport studies on a new fast silver ion conducting system: 0.7[0.75AgI: 0.25AgCl]: 0.3[yAg2O:(1 − y)B2O3]

Abstract A silver borate system with the composition 0.7[0.75AgI: 0.25AgCl]: 0.3[ y Ag 2 O:(1 − y )B 2 O 3 ] has been prepared in which the host salt used is a “quenched [0.75AgI: 0.25AgCl] mixed system” instead of the commonly used host AgI. Three sample preparation procedures were adopted: (a) molten sample at ∼ 650°C dropped into neutral liquid bath at ∼ 10°C; (b) molten sample in silica ampule at ∼ 650°C left in air to cool by itself; (c) molten sample left in furnace and allowed to come to room temperature in ∼ 24 h. The highest room temperature conductivity σ ⋍ 2.23 × 10 −2 S cm −1 was obtained for the sample composition: 0.7[0.75AgI: 0.25AgCl]: 0.3[0.833Ag 2 O: 0.167B 2 O 3 ] prepared by procedure “a” and referred to as an “optimal composition”. The DTA, XRD (including linewidth measurement for determining Scherrer length/crystallite size), temperature dependence of σ (by Impedence Spectroscopy), mobility μ (by Transient Ionic Current technique), and number of charge carriers n are also reported. Solid state batteries with the cell configuration: Ag/ 0.7[0.75AgI: 0.25AgCl]: 0.3[0.833Ag 2 O: 0.167B 2 O 3 ]/ (C + I 2 ) were fabricated and the discharge characteristics were studied.

Ion Beam Modified Conducting Polymer Composites: Material for Gas Sensing

A polyaniline based conducting composite was prepared by oxidative polymerisation of aniline in presence of polyvinylchloride (PVC) matrix. The coherent free standing thin films of the composite were prepared by solution casting method. The PVC-polyaniline composite (90:10) of thickness 40 μm was irradiated with 90 MeV C 5+ ions at different ion fluence ranging 5× 10 11 -5× 10 13 ions/cm 2 . The changes in resistance of pristine and irradiated composite in presence of ammonia gas were studied. A general decrease in surface resistance is observed upon irradiation. The sensitivity, response time and recovery time were studied as a function of ion fluence on exposing the sensor material to ammonia gas at ambient condition. It is observed that irradiated composite films are more sensitive and fast in response to ammonia gas. The preliminary results observed are encouraging.