EFFECT OF GRAIN ALIGNMENT AND PROCESSING TEMPERATURE ON CRITICAL CURRENTS IN YBA2CU3O7-DELTA SINTERED COMPACTS

Magnetically aligned YBa2Cu3O7_δ ceramics show resistivities approaching that of single crystals and improved transport critical currents in a magnetic field. Reduced microcracking and increased transport along the ab-plane are believed responsible for the improved performance over nonaligned ceramics. Aligned and nonaligned samples were prepared in parallel using a range of sintering and annealing temperatures. A rapid rise in density for samples sintered above 900 °C in oxygen is accompanied by rapid grain growth, improved alignment, a drop in the room temperature resistivity, and an increase in the critical current. The presence of low melting point (i.e., Ba-Cu-O-rich) phases at grain boundaries is believed responsible for the rapid densification. However, the presence of this phase does not appear to be the most important factor limiting Jc. A high temperature oxygen anneal at 900 °C improved performance as compared to anneals at 500 °C, possibly due to the removal of carbon. For aligned samples sintered at 980 °C, critical currents are over 200 A/cm2 at 77 K, 1/4 tesla, and room temperature resistivities are below 350 µΩ-cm. © 1990, Materials Research Society. All rights reserved.