• K C Nagpal

      Articles written in Bulletin of Materials Science

    • Growth of highTc Bi-Sr-Ca-Cu-O thick films

      Sangeeta Chaudhry Neeraj Khare A K Gupta K C Nagpal V N Ojha G S N Reddy V S Tomar

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      Thick films of Bi-Sr-Ca-Cu-O were deposited on (100) MgO substrates by screen-printing technique with the starting composition 1112. To attain the superconducting state, the films were subjected to two-step heat-treatment. R-T and XRD have been studied for films annealed at different durations of the second step. InitiallyTc (R=0) increased from 77 to 103 K as the annealing duration was increased after whichTc decreased. Kinetics of the growth of highTc phase is discussed in the light of our results.

    • Interplay of low and highTc phases in Bi-Sr-Ca-Cu-O superconductor

      P L Upadhyay K C Nagpal R G Sharma

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      In the Bi-Sr-Ca-Cu-O system stringent conditions of heat-treatment lead to the formation of a mixture of both the low and highTc phases and obtaining a single-phase material becomes extremely difficult. This study reports preparation of samples with single superconducting transitions at ∼ 75 K and ∼ 108 K; the compositions of which correspond ton=2,3 in the series Bi2Sr2Can−1CunO4 + 2n. X-ray diffraction studies show that the lowerTc material is a relatively pure phase while the higherTc phase only co-exists with the lowerTc phase. The most obvious effect of doping the system with lead is to make the reaction take place faster and thereby increase the volume fraction of the 110K phase.

    • Study of Josephson effects in microbridges of Bi-Sr-Ca-Cu-O films made by spray pyrolysis

      D K Walia A K Gupta G S N Reddy V N Ojha V S Tomar Neeraj Khare N D Kataria K C Nagpal

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      Superconducting Bi-Sr-Ca-Cu-O (2212) films were prepared by spraying stoichiometric aqueous solutions of nitrates of bismuth, strontium, calcium and copper on heated MgO (100) substrates and subsequent annealing in air. TheR-T curves of the films show metallic behaviour above the superconducting transition temperature.Tc (R=0) is observed between 80 and 85 K. Annealing temperature has a profound effect onTc (R=0) and on the orientation of the film. Annealing in air in near-melting region yields highly oriented films withc-axis perpendicular to the substrate. These films show a sharp superconducting transition with zero resistance at 85 K. Microbridges of the dimensions of 50 µm × 50 µm have been patterned photolithographically followed with chemical etching. The 1 V characteristics of the microbridges show Josephson effects due to the presence of grain boundary weaklinks. The temperature dependence of the critical current for these microbridges suggest formation of superconductor-normal-superconductor type weaklinks.

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