Recrystallization of amorphous and nanocrystalline NdBa/sub 2/Cu/sub 3/O/sub 7-x/ and GdBa/sub 2/Cu/sub 3/O/sub 7-x/

Using a novel melt-spinning technique, the authors have produced both amorphous and nanocrystalline NdBa/sub 2/Cu/sub 3/O/sub 7-x/ and GdBa/sub 2/Cu/sub 3/O/sub 7-x/ materials. Samples melt-spun in O/sub 2/ consist of nanocrystals with the tetragonal 123 structure while those processed in N/sub 2/ show an amorphous matrix with small amounts of crystalline BaCu/sub 2/O/sub 2/, as shown by X-ray diffraction (XRD) and transmission electron microscopy (TEM) studies. The difference is due to the strong dependence of the phase relations on the O/sub 2/ partial pressure. Superconductivity can be fully restored by heating above 1000 degrees C followed by a 450 degrees C anneal in O/sub 2/. High-temperature XRD studies show that the 123 phase crystallizes directly from the amorphous matrix below 800 degrees C. Restoration of the orthorhombic 123 phase does not necessarily ensure good superconducting properties, a result attributed to disorder on the heavy metal sites.<>