NANOCRYSTALLINE Y-BA-CU-O POWDER

Nanocrystalline Y-Ba-Cu-O precursor was prepared by wet high-energy ba ll milling. It was found that with an increase of milling time, the or thorhombic 123 phase changes to a metastable (Y0.33Ba0.66)CuO3-x disor dered cubic phase, and that the particle size distribution moves towar d smaller sizes. The median particle size of the YBCO powder milled fo r 90 h was found to be less than 20 nm. This metastable cubic phase de composes into a multi-phase mixture in the temperature range of 200-50 0 degrees C, and the mixture further tranforms to the pure tetragonal 123 phase at 800-900 degrees C. Furthermore, the temperature for nucle ation of 123 from this nanometer-sized precursor was found to be lower than that in micron-sized 123.