• Kalyan Adhikary

      Articles written in Bulletin of Materials Science

    • Effect of heat treatment and composition on the superconductivity in Pb-Sr-R-Ca-Cu-O oxide system

      N C Soni Ram Prasad Kalyan Adhikary A Gulnar C V Tomy S K Malik

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      The effect of compositions, sintering temperatures and furnace atmospheres on the superconducting transition temperatures of several members of the series Pb2Sr2R1−xCaxCu3Oz(0.0⩽x⩽0.7, R=Y, Gd) has been studied. The effect of partial replacement of Pb, Ca and Y by In has also been studied. The shapes of the resistivity-temperature curves and the zero resistance temperatures are found to be extremely sensitive to the synthesis parameters employed. Superconductivity is not observed in samples treated in oxidizing atmosphere or heated at very high temperatures. Samples sintered in flowing nitrogen showed incomplete transition in resistivity starting at about 75 K and extending down to 15 K. A new and comparatively simple synthesis procedure involving treatment of the samples in vacuum has been employed to obtain nearly single-phase materials showing metallic behaviour. Using this procedure, samples of the above composition, but containing no Ca(i.e. Pb2Sr2RCu3Oz, R=Y and Dy), are also found to be superconducting with zero resistance up to 48 K.

    • 151Eu Mössbauer studies on Zn-doped EuBa2Cu3O7−y

      C V Tomy R Nagarajan S K Malik Ram Prasad N C Soni Kalyan Adhikary

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      151Eu Mössbauer studies have been performed on the compounds EuBa2(Cu1−xZnx)3O7−y withx=0·0, 0·025, 0·05, 0·075 and 0·1. The parent compound, EuBa2Cu3O7−y is superconducting with a transition temperature (Tc) of 88 K.Tc is depressed as Zn is substituted for Cu in this system and the compounds withx>0·05 do not show superconductivity down to 12 K.151Eu Mössbauer studies at 295 K show a single Mössbauer line in all the compounds (whether superconducting or not) with isomer shift value typical of Eu3 + ion. Further, the isomer shift values are nearly independent ofx and the temperatures down to 10 K. These observations imply that the Cu-O network responsible for superconductivity is very weakly coupled to the Eu sublattice.

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