• A K Shukla

      Articles written in Bulletin of Materials Science

    • Electrical transport properties of La1−xSrxFeO3

      A K Shukla P K Basu

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      La1−xSrxFeO3 (0·1⩽x⩽0·4) samples exhibit nearly the same low resistivity value around the Neél temperatures. AboveTN, electrons seem to become itinerant as suggested by Mōssbauer data.

    • Thermopower of$$Ag_{2 + \delta } $$S across theα-β transitionacross theα-β transition

      H N Vasan A K Shukla

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      Thermopower data of$$Ag_{2 + \delta } $$S in both of itsα- andβ-phases are reported and the results are compared with the data on$$Ag_{2 + \delta } $$Se.

    • Electrochemical ways of tapping solar energy: an appraisal

      A K Shukla R Manoharan K V Ramesh

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      In recent years, solar cell technology has advanced significantly and is nearing commercial viability. Practical solar cells that are capable of converting the solar radiation directly into electricity are now available. It is, however, imperative to couple them with appropriate power storage systems. This article is a brief review of the current status of electrochemical power systems such as storage batteries and fuel-electrolysis cell hybrids which could be successfully utilized to this end.

    • MnO2 catalyzed carbon electrodes for dioxygen reduction in concentrated alkali

      R Manoharan A K Shukla

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      A process to depositγ-MnO2 catalytic oxide onto coconut-shell charcoal substrate is described. Current-potential curves for electroreduction of dioxygen with electrodes fabricated from this catalyzed substrate are obtained in 6M KOH under ambient conditions. The performance of these electrodes is competitive with platinized carbon electrodes.

    • Concept of thermodynamic capacity

      R Akila K T Jacob A K Shukla

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      The thermodynamic capacity of a species (Ci)in a homogeneous phase is defined as (∂ni/∂µiP, T, njwhereniis the total number of moles ofi per unit quantity of the system irrespective of the actual system chemistry andµiis its chemical potential. Based on this definition, the thermodynamic capacity of oxygen in non-reactive and reactive gas mixtures and in binary and ternary liquid solutions has been computed. For reactive gas mixtures containing stable chemical species which do not undergo significant dissociation such as CO + CO2, H2 + H2O and H2 + CO2, the capacity curves show a maximum at equimolar ratio and a minimum at higher oxygen potentials. If one of the chemical species partly dissociates as in the case of H2S in H2 + H2S mixtures or SO3 in SO2 + SO3 mixtures, capacity curves do not exhibit such maxima and minima, especially at high temperatures. It would be difficult to produce stable oxygen fugacities when the capacity has a low value, for example at compositions near the minimum. Oxygen capacities of non-ideal liquid solutions, Cu-O and Cu-O-Sn, and heterogeneous systems formed at saturation with the respective oxides are discussed.

    • Low-temperature synthesis and characterization of Ag2S1−xTex(0≤x≤1)

      H N Vasan A K Shukla

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      A low-temperature route for the synthesis of Ag2S, Ag2Te and their solid solutions Ag2S1 −xTex(0 ≤x ≤ 1) is reported. Ag2S is prepared by the direct addition of silver nitrate solution to thiourea, while Ag2 Te is prepared by reacting silver nitrate solution with tellurium in nitric acid and subsequently reducing it with hydrazine hydrate. The solid solutions of Ag2S and Ag2Te are obtained by the addition of nitrate solutions of silver and tellurium to thiourea followed by its reduction with hydrazine hydrate. The method enables the synthesis of low-temperature crystalline phase of Ag2S1 −xTex solid solutions. The powder X-ray diffraction studies suggest that the solid solutions of compositionsx 〈 0·3 have a phase akin toα-Ag2S and those with compositionsx 〉 0·6 are similar toα-Ag2 Te. In the intermediate range of compositions (x=0·4 and 0·5), the solid solutions are found to be mixtures ofα-Ag2S andα-Ag2 Te phases which transform totally toα-Ag2S phase on prolonged annealing at about 473 K.

    • Structural and dielectric properties of a novel Bi2O3-(1 −x)WO3-xCuO solid solution

      Vandana Sharma K B R Varma A K Shukla

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      A novel solid solution in the system Bi-W-Cu-O has been synthesized and its structural and dielectric properties studied. The solid solution Bi2O3-(1 −x)WO3-xCuO exists up tox=0·7; the solid solutions up tox=0·65 are orthorhombic but stabilize in tetragonal structure in a narrow range aroundx=0·7. The solid solutions are non-centrosymmetric and exhibit ferroelectric behaviour similar to their parent phase Bi2WO6. The Curie point of the solid solution is found to decrease with increase inx.

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