ENHANCED I-C-B PERFORMANCE IN TL-BASE HIGH-T-C OXIDES PREPARED BY A DIFFUSION PROCESS

High-T-c Tl-base oxides can be synthesized by a diffusion reaction wit hin a short reaction time. The F addition apparently promotes the phas e transformation from 2223 to 1223. The scanning electron microscope o bservation reveals that the 1223 phase formed by the F addition shows a dense and homogeneous structure, resulting in an increase in transpo rt I-c at 77 K. Moreover, F addition significantly improves the I-c at 77 K under magnetic field, and shifts the irreversibility line to hig her temperature. Meanwhile, V addition was found to enhance the diffus ion reaction, resulting in the formation of 2223 layer of about 600 mu m in thickness after the reaction at 850 degrees C for 2 h. The V is pushed out from the diffusion layer and accumulates on the surface of the specimen. The V addition causes almost no degradation in T-c. I-c- B performance is appreciably improved by annealing in O-2 after the re action.