Effects of atmosphere and heating rate during processing of a ceramic superconductor.

摘要

Properties of ceramic superconductors depend strongly on the temperature, heating rate, pressure, and atmosphere used during synthesis and fabrication. We have developed a process for synthesizing orthorhombic YBa(sub 2)Cu(sub 3)O(sub x) (123) superconducting powders by calcining the precursor powders under reduced total oxygen pressure. The resultant 123 powders are mixed with organics, and wires and coils are fabricated by extrusion. The wires and coils are fired at a reduced total pressure in flowing O(sub 2) to reduce the concentrations of CO(sub 2), CO, and H(sub 2)O and thus prevent decomposition of the 123. Transport critical current density of the superconductor decreases drastically with increasing concentrations of CO(sub 2) in the gas mixture. Transmission electron microscopy of materials sintered in O(sub 2) atmospheres containing various levels of CO(sub 2) clearly shows the extent of grain boundary degradation. 29 refs., 9 figs., 2 tabs.