K. Hariharan

Investigations on silver iodide silver oxysalt glass ceramics

Abstract Silver ion conductivity and microstructural changes during the crystallization process of the glass systems AgI-Ag 2 O-M x O y ( M = V , P , Mo , B ) have been investigated by impedance spectroscopy and high temperature X-ray diffraction. The observed anomalous increase of the conductivity depends sensitively on the variation of the glass crystal interface area, suggesting a high conductivity in the interface region. The involvement of silver ions with different co-ordination shells in the transport process is modelled by valence sum pseudo-potential maps for the vanadate system Ag 8 I 4 V 2 O 7 .

Ion transport studies in PbI2–Ag2O–V2O5 glassy system

Abstract New glasses in the system xPbI2–(100−x)(2Ag2O–1V2O5), 5≤x≤20, have been prepared and characterized by X-ray diffraction and differential scanning calorimetry. Variations of conductivity with composition, frequency, and temperature has been investigated. Conductivity of the glasses increases with increase in mole% of PbI2 and attains a value of 1.4×10−3 ohm−1 cm−1 at 300 K for x=20. IR spectroscopy studies on these glasses indicate that the oxyanion network is unaffected by the addition of PbI2. The transport number of Ag+ determined by the e.m.f. method is 0.99. The diffusion coefficient of Ag+ ions in x=10 mole% of PbI2 with Ag111 as the radioactive tracer was found to be 9.5×10−9 cm2 s−1 at 363 K. The frequency dependence of electrical conductivity for various glass compositions at different temperatures has been analysed in terms of Jonschers universal expression. The above studies along with the data on density, molar volume and carrier concentration of Ag+ and I−, indicate the formation of `AgI clusters due to co-ordinate exchange between Pb2+ and Ag+, contributing to high Ag+ ion conductivity.

Crystallization kinetics and phase transformation in superionic lithium metaphosphate (Li2O?P2O5) glass system

The ionic conductivity of mol% 50Li(2)O-50P(2)O(5) melt quenched glass shows an anomalous increase after its glass transition temperature (T(g)) around 590xa0K. On further increasing the temperature gradually, the conductivity decreases owing to the devitrification of Li(2)O-P(2)O(5) glass. The evolution of devitrified crystallites was evidenced by XRD patterns. To understand the devitrification process, isothermal and non-isothermal DSC studies have been carried out on mol% 50Li(2)O-50P(2)O(5) glass. T(g) as well as T(c) values are found to increase monotonically with increasing heating rates. Variation of T(g) as a function of heating rates has been investigated to evaluate the lower limiting temperature of T(g) and the activation energy for structural relaxation. Results of the DSC studies indicate (i)xa0single-stage bulk crystallization of the glass, with DSC traces exhibiting a single [Formula: see text] transition, (ii)xa0an order parameter (Avrami constant) of 2.8 ± 0.1, suggesting internal (bulk) crystallization of the glass, (iii)xa0an activation energy for crystallization equal to 121.7xa0kJxa0mol(-1) and (iv) the activation energy for structural relaxation, E(g), to be 558.8xa0kJxa0mol(-1). The crystallization mechanism is closely associated with the JMA model and the experimental dataset have been fitted to a non-isothermal Avrami expression and the obtained parameters confirm the experimental results.

Enhanced ionic conduction in NaNO3 by dispersed oxide inclusions

Abstract The composite solid electrolytes, NaNO 3 dispersed with Al 2 O 3 , CeO 2 , ZrO 2 and SiO 2 have been prepared by melt quenching method and investigated through XRD, DSC and electrical conductivity techniques. Typical increase in conductivity is about two orders of magnitude for 10xa0mol% of Al 2 O 3 at 200xa0°C. The electronic transference number evaluated through dc polarization method was found out to be 1×10 −2 at 200xa0°C. The dependence of conductivity on concentration of dispersoids and particle size is in accordance with the space charge theory of conduction. The enhanced conductivity of NaNO 3 homogenously doped by Ca(NO 3 ) 2 was further enhanced by heterogeneous doping of Al 2 O 3 . By the contribution of these doping processes, the conductivity is enhanced by three orders of magnitude at 200xa0°C. The experimental and theoretically calculated values of conductivity using Maiers space charge layer model are in reasonable agreement.

New solid electrolyte system: Polycrystalline CuI-Ag2O-MoO3

Abstract Preparation, characterization (X-ray and DSC), transport number and electrical conductivity studies on the systems x CuI- (100− x )(Ag 2 O-MoO 3 ) indicate that the above system acts as a fast silver ion conductor up to 50 mol% CuI. The composition 30CuI-35Ag 2 O-35MoO 3 has the highest conductivity with σ =1.96×10 −3 S cm −1 and E a=0.28 eV. Discharge characteristic s of the solid state battery with the above conducting composition as the electrolyte show that the cell could be discharged up to 100 μA/cm 2 without severe polarization.

Mixed mobile ion effect in copper and silver molybdate glasses

Abstract Electrical conductivity versus temperature and composition studies of copper and silver molybdate glasses show a minimum in conductivity and maximum in activation energy when AgI and CuI are added to CuI-Cu2O-MoO3 and AgI-Ag2O-MoO3 glasses respectively. Preliminary results have been explained on the basis of the weak electrolyte theory.

Influence of glass former to modifier ratio on the transport phenomena of glassy silver iodochromate solid electrolytes

Abstract Fast ionic conduction in the AgI-Ag 2 O-CrO 3 electrolyte system has been studied and the influence of glass former to glass modifier ratio on the conduction phenomena has been reported. These electrolytes have been characterised by X-ray diffraction, electrical and electronic conductivities, complex impedance, thermoelectric power and infrared absorption techniques. The possible structural changes occurring in the Ag 2 O-CrO 3 matrix on the variation of the glass former to modifier ratio have been discussed.

Characterisation of X(AgI) · (1−X)(Ag2CrO4) electrolytes by transport and structural properties

Abstract Fast ion conducting electrolytes in the system X(AgI) · (1− X)Ag2CrO4) for 0⩽x⩽100 mol% of AgI, have been characterised by X-ray diffraction, electrical and electronic conductivities, thermoelectric power and infrared absorption techniques. A high ionic conductivity of the order of 10−3 with low electronic conductivity has been observed for two electrolyte compositions for X=33.33 and 80 mol%. Infrared absorption studies have shown vibrational modes characteristic of CrO42− structural units.

Glass formation in AgI:Ag2O:V2O5 and AgI:Ag2O: (V2O5+B2O3) systems: Application to solid state battery

Transport properties of glasses in the system AgI:Ag 2 O:V 2 O 5 and AgI:Ag 2 O: (V 2 O 5 +B 2 O 3 ) have been investigated. It was found that, at high AgI concentrations, the addition of another glass former (B 2 O 3 ) did not improve the conduction characteristics of the pure vanadate glasses, the best conducting composition of which had ambient temperature, ionic conductivity comparable to that of conventional liquid electrolytes. The highest conducting composition was used as an electrolyte in the study of silver solid state cells. The discharge characteristics of different cells fabricated with the glassy electrolyte, have been compared with those having the best conducting polycrystalline ompositions as electrolytes.

Thermoelectric power of superionic conductor Ag7I4VO4

Abstract Thermoelectric power studies on Ag7I4VO4. superionic conductor have been carried out in the temperature range 25 to 60°C. Thermo-electric power is found to vary linearly with the inverse of the absolute temperature, and can be expressed by the equation −θ = [(0.182 × 103/T) + 0.276] mV/K. The heat of transport is nearly equal to the activation energy of Ag+ ion migration calculated from the conductivity plots indicating that the material has an average structure.