Decomposition of Y!3a,Cu408 into YBazCuaOr-s + CuO in the silver-sheathed tape form has been studied. In these tapes, the excess CuO is expected to provide additional flux pinning centres and consequently to increase the critical current density beyond that of an equivalent conventional YBa2Cu307-6. Silver-sheathed YBazCu408 tapes were produced by first using an oxalate solution method to coprecipitate (submicrometre to nanometre size) precursor powder that was then drawn into tapes by a powder in tube technique. From a series of investigations of the parameters for decomposition of YBa2Cu408, the optimal time and temperature for processing these tapes were found to be 25 min and 915"C, with oxygenation for 48 h at 450 "C. This procedure yielded the best J, of 2.2 x lo4 A in self-field at 5 K. This critical current value is an enhancement of two orders of magnitude from the value obtained in as-drawn tape.
Capacitance-Voltage (C-V) characteristics of Au/PrB2Cu3Oy/YBa2Cu3Ox structure were studied. YBa2Cu3Ox and PrBa2Cu3Oy were deposited by rf magnetron sputtering. Deposition temperatures were 700°C for YBa2Cu3Ox and 690°C for PrBa2Cu3Oy. Capacitance was measured at liquid-helium temperature. At this temperature PrBa2Cu3Oy behaves as an insulator, and C-V characteristics of Au/PrBa2Cu3Oy/YBa2Cu3Ox as a MIS diode can be measured. From analyses of C-V characteristics, a depletion layer was found to exist near the PrBa2Cu3Oy/YBa2Cu3Ox interface when DC bias was zero. The acceptor density of this layer was calculated to be about 1016/cm3 from C-V characteristics.
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