Recrystallization of amorphous and nanocrystalline NdBa2Cu3O7-x and GdBa2Cu3O7-x

Using a novel melt-spinning technique, we have produced both amorphous and nanocrystalline NdBa2Cu3O7-x and GdBa2Cu3O7-x materials. Samples melt-spun in O2 consist of nanocrystals with the tetragonal 123 structure while those processed in N2 show an amorphous matrix with small amounts of crystalline BaCu2O2, as shown by XRD and TEM studies. The difference is due to the strong dependence of the phase relations on the O2 partial pressure. Superconductivity can be fully restored by heating above 1000C followed by a 450C anneal in O2. High temperature XRD studies show that the 123 phase crystallizes directly from the amorphous matrix below 800C. Poor superconducting properties for sample heated below 1000C are attributed to disorder on the heavy metal sites. 4 figs, 6 refs