Study of the heterogeneous nucleation of 211-particle by the addition of CeO/sub 2/ precursor with different sizes

The microstructure and superconducting properties of air-processed melt-textured grown Y-Ba-Cu-O samples with the addition of CeO/sub 2/ precursor of different sizes, e.g. micro-scale and nano-scale were studied. Samples with micro-scale CeO/sub 2/ addition exhibit an enhanced Jc, which were attributed to the refinement of 211-particles. The mechanism for refining the 211-particles was proposed to be the formation of new nuclei sites from the reaction of CeO/sub 2/ and Y2-1-1 matrix in the melt-grown process. By reducing the CeO/sub 2/ precursors to nano-scale from micro-scale, significantly more heterogeneous nucleation site will be introduced with the same amounts of CeO/sub 2/ additions. And the J/sub c/ will be enhanced with the refining of 211 particles. But in this study, it shows the opposite results. The higher J/sub c/ value is enhanced by doping micro-scale CeO/sub 2/. Pinning forces vs. magnetic field studies indicated that both the nano- and micro- CeO/sub 2/ samples have the same pinning mechanisms as compared with that of the un-doped sample.