• Y S Reddy

      Articles written in Bulletin of Materials Science

    • Low percolation concentration for zero thermoelectric power in Y1Ba2Cu3O7−x

      S R Jha Y S Reddy R G Sharma

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      Effect of oxygen deficiency on the thermoelectric power and the resistive transition is studied by changing the cooling rate of the sintered specimens of R1Ba2Cu3O7−x where R=Y, Gd and Sm. Slow-cooled (60°C/h) specimens are superconducting and show positive TEP with a broad peak aboveTc. It is a decreasing function of temperature at higher temperatures. Pair fluctuation aboveTc is thought to be responsible for this peak. Highly O2-deficient sample of Y123 has a finite resistivity atTc and yet shows a zero TEP. It is suggested that the percolation concentration of the superconducting phase for zero TEP should be much smaller than that required for the electrical conduction.

    • Critical current studies on metal clad R1Ba2Cu3O7−x wires

      S R Shukla Y S Reddy R G Sharma

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      Silver clad wires of R1Ba2Cu3O7−x (R=Y, Gd, Sm, Dy and Ho) have been fabricated following the powder-in-tube method and cold-rolling. The critical current densityJc at 77 K and zero magnetic field is restricted to 66 A.cm−2. In a separate experiment we have studied the effect of silver sheath thickness onJc of the Y1Ba2Cu3O7−x wires. Interestingly,Jc is higher for larger sheath thickness indicating that large sheath thickness prevents oxygen loss during sintering. Uniaxial pressing of the wires into flat tapes results in an increase of theJc. MaximumJx is, however, limited to 169 A.cm−2. No grain alignment is found in the core material of our wires which is essential for highJc. Several options are being tried.

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