Rapid consolidation of YBa₂Cu₃O₇ powder

Abstract

Electrical current in a powder transits particle contact points, whose high resistance localizesI ² R heating. The occurrence of sintering at particle contact points suggests an efficient means of consolidating the difficult-to-sinter ceramic superconductor YBa₂Cu₃O₇.

A specially fabricated apparatus for simultaneous application of pressure and passage of electrical current accomplished the consolidation. Computerized control continuously adjusted current levels for changes in specimen resistance, maintaining a constant level of power dissipation. Power dissipation of 55 W for one minute produced solid specimens, either cylinders 3 mm in diameter x 4 mm, or blocks 2 mm x 5 mm x 5 mm. The specimens were annealed in flowing oxygen, save for one control.

Annealed specimens exhibited Meissner effect, transition to zero resistivity near 90 K, andj _c ≈ 75 A/cm². The scanning electron microscope (SEM) showed porous microstructures for all but one specimen. The control had a similar microstructure, showing annealing added little consolidation. This work demonstrates the rapid consolidation of YBa₂Cu₃O₇ powder into a solid which upon oxygen annealing exhibits true superconductivity.