Effect of heat treatment conditions on critical current of YBa2Cu3O7- delta /Ag powder-in-tube wires

Abstract

A systematic, statistically-designed study of the effect of heat-treatment conditions on critical currents in mono-filamentary silver wires having cores of sintered YBa2Cu3O7- delta , has been conducted. Powder was produced by aerosol pyrolysis of nitrates. Wires were made by inserting pressed pellets into silver billets and swaging and hydrostatically extruding to 0.06" (1.5 mm) OD. Samples from these were heat treated in flowing O2 at atmospheric pressure. Four conditions were varied to generate data for a factorial model for Jc: time at sintering temperature (920 degrees C), cooling rate from sintering temperature to reoxygenation temperature, temperature of reoxygenation anneal, and duration of anneal. Analysis showed large random variation in the data, but test heat treatments, using conditions which, according to the model, should yield improved critical currents, did show such improved currents. The highest critical current density achieved was about 500 A cm-2, based on metallographically measured core diameters. The factors limiting Jc and the likely sources of the random variation are discussed.