Oriented grained Y-Ba-Cu-O superconductors having high critical currents and method for producing same

摘要

A superconductor material having a current density, J, of from about 30,000 to about 85,000 amps/cm.sup.2 at zero magnetic field and 77° K. is disclosed. The 123 superconductor, of the formula L.sub.1 Ba.sub.2 Cu.sub.3 O.sub.6 +&dgr; wherein L is preferably yttrium, is capable of entrapping sufficiently high magnetic fields and exhibits a low microwave surface resistance. The process of preparing the superconductor comprises compacting the bulk product, L.sub.1 Ba.sub.2 Cu. sub.3 O, and then sintering the reaction product at a temperature between about 40° C. to about 90° C. below its melting point, i.e., for Y. sub.1 Ba. sub.2 Cu.sub.3 O.sub.6 +&dgr; at a temperature of approximately 940. degree. C. The composition is then heated in a preheated chamber maintained at approximately 1090° C. to about 1,200° C. (approximately 1,100° C. for Y.sub.1 Ba.sub.2 Cu.sub.3 O.sub.6 +. delta.) until it has been decomposed, and is then rapidly cooled to a temperature between about 10° C. to about 30° C. above its melting point, i.e. for Y.sub.1 Ba.sub.2 Cu.sub.3 O.sub. 6 +&dgr; a temperature of 1030° C., and then is controlled cooled at a rate of 1° C./hr until it reaches a temperature of about 20° C. to about 40° C. below its melting point, i.e., for Y.sub.1 Ba.sub. 2 Cu.sub.3 O.sub.6 +&dgr; a temperature of 980° C. The composition is steadily held at this temperature for at least eight hours, and then cooled to a temperature of approximately 400° C. below its melting point (for Y. sub.1 Ba.sub.2 Cu.sub.3 O.sub.6 +&dgr; approximately a temperature of 600° C). The material is then slowly cooled by another 200° C. and is then annealed in oxygen.