CRITICAL-CURRENT DENSITY OF BI-2212 THICK-FILMS PROCESSED BY PARTIAL MELTING

Bi2Sr2CaCu2O8+delta (Bi-2212) thick films were produced via tape casti ng and partial melting. The aim of the study was to investigate the in fluence of the different heat treatment steps on the critical current density of the films. Five processing parameters were studied: maximum densification temperature, cooling rate during crystallization, annea ling time after crystallization, reduction treatment and processing at mosphere. It will also be demonstrated that the critical current densi ty strongly depends on the sample thickness. In 20 mu m thick films we achieved 20 000 A cm(-2) at 77 K-0 T and 300 000 A cm(-2) at 10 K-0 T . The critical current density at 77 K-O T dropped to 6200 A cm(-2) in 130 mu m thick films and levelled out at 3000 A cm(-2) in bulk sample s thicker than 500 mu m. These high critical current densities were re ached only using a narrow processing window. The maximum densification temperature had to be within 5-10 degrees C above the solidus tempera ture (875 degrees C). Cooling from the maximum temperature to an annea ling temperature of 850 degrees C had to be around 5 to 10 degrees C h (-1) and the final annealing step was prolonged up to 70 h to optimize the critical current density. All processing steps were carried out i n pure oxygen (1 atm) except the last step, reduction annealing at 500 degrees C for 20 h, that was performed in nitrogen (p(O-2) approximat e to 0.01 atm). Processing in air (p(O-2) = 0.21 atm) instead of oxyge n leads to strongly decreased critical current densities in the high-t emperature region above 30 K.