Preparation of 94 K-superconducting NdBa2Cu3O7-delta without post-anneal in oxygen

The preparation of the polycrystalline NdBa2Cu3O7-delta superconductor using Ba2Cu3O5+x as a precursor has been studied. Ba2Cu3O5+x was prepared by the sol-gel process using metal acetates as starting materials, tartaric acid as an chelating reagent and water as solvent. The gel was heated at 780 degrees C for 60 h in O-2 to form the Ba2Cu3O5+x precursor. The value of x in Ba2Cu3O5+x was determined to be 0.5; that is, copper was in a highly oxidized state over +2. NdBa2Cu3O7-delta was obtained by the solid-state reaction between Nd2O3 and Ba2Cu3O5+x heated at 900 degrees C for 20 h in N-2. Although the sample did not undergo post-anneal in oxygen, it showed good superconducting properties; T-c of 94 K and the intragranular J(c) of 3.7 X 10(5) A/cm(2) under a field of 50 kOe at 20 K. The advantage of using Ba2Cu3O5+x is considered to be its sufficient amount of oxygen as well as prevention of the Nd3+/Ba2+ substitution.