SILVER-SHEATHED YBA2CU4O8 TAPES - DECOMPOSITION, CHARACTERIZATION, AND CRITICAL-CURRENT ENHANCEMENT

Decomposition of YBa2Cu4O8 into YBa2Cu3O7-delta + CuO in the silver-sh eathed tape form has been studied. In these tapes, the excess CuO is e xpected to provide additional flux pinning centres and consequently to increase the critical current density beyond that of an equivalent co nventional YBa2Cu3O7-delta. Silver-sheathed YBa2Cu4O8 tapes were produ ced by first using an oxalate solution method to coprecipitate (submic rometre to nanometre size) precursor powder that was then drawn into t apes by a powder in tube technique. From a series of investigations of the parameters for decomposition of YBa2Cu4O8, the optimal time and t emperature for processing these tapes were found to be 25 min and 915- degrees-C, with oxygenation for 48 h at 450-degrees-C. This procedure yielded the best J(c) of 2.2 x 10(4) A cm-2 in self-field at 5 K. This critical current value is an enhancement of two orders of magnitude f rom the value obtained in as-drawn tape.