V N Ojha
Articles written in Bulletin of Materials Science
Volume 14 Issue 2 April 1991 pp 461-467 International Conference On Superconductivity—I
Thin films of Y-Ba-Cu-O material have been prepared by rf diode sputtering using a single oxide target on strontium titanate substrates kept at an ambient temperature. It was found difficult to attain stoichiometry of the films identical to that of the target due to resputtering of the films. The influence of sputtering parameters such as target-substrate distance, rf power, gas pressure and substrate temperature in attaining a particular stoichiometry of the film has been studied. The I–V characteristics of the bridges show Shapiro steps when the bridges are irradiated with microwave radiations. The thin film bridges have the dimensions larger than coherence length; thus all the Josephson effect features are understood to arise due to intergranular junctions.
Volume 14 Issue 2 April 1991 pp 521-524 International Conference On Superconductivity—I
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. Initially
Volume 14 Issue 4 August 1991 pp 1119-1123 International Conference On Superconductivity—III
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. The
Volume 14 Issue 4 August 1991 pp 1125-1129 International Conference On Superconductivity—III
Break junctions of Y-Ba-Cu-O superconductor were realized by creating fresh crack in the bar shape bulk samples mounted in a specially designed probe kept in the liquid nitrogen bath. While the bulk sample was kept static, a sharp tip of a shaft was moved downward from the outside of the dewar in order to break the sample. It was possible to change the critical current of the break junctions by adjusting pressure on the tip of the shaft. The effects of magnetic field and microwave power on the I-V characteristic of the junction were studied. The junction was found to show periodic V-B behaviour and the microwave-induced Shapiro steps were clearly observed at 77 K. The flux noise spectrum of the junction was also studied.
Volume 14 Issue 4 August 1991 pp 1131-1134 International Conference On Superconductivity—III
A two-hole rf SQUID has been fabricated out of bulk YBCO by drilling two holes and careful erosion of the wall between the holes. Commercial SQUID electronics is inductively coupled to the SQUID through a copper coil glued in one of the holes. Periodic oscillations in V-B characteristic of the SQUID are observed at 77 K. The spectral density of the flux noise in the white noise region is 5·5 × 10−4Φ0 / √Hz. The flux noise is frequency-dependent below 200 Hz.
Volume 14 Issue 4 August 1991 pp 1163-1166 International Conference On Superconductivity—III
Galvanomagnetic effect has been studied at 77 K on Bi-Sr-Ca-Cu-O films as a function of d.c. bias current. These films were prepared by spray pyrolysis and screen-printing techniques, with
Volume 42 | Issue 3