PREPARATION OF PURE YBA2CU3O7-X SUPERCONDUCTORS FROM POLYMER CHELATE PRECURSORS USING POLY[(N,N-DICARBOXYMETHYL)ALLYLAMINE]

Bulk YBa2Cu3O7-x (YBCO) was prepared by a polymer chelate precursor me thod using poly[(N,N-dicarboxymethyl)allylamine] (PDAA) as a chelating polymer. An aqueous solution containing PDAA and 1/2 or 1/4 equivalen t molar amount of metal nitrates (Y:Ba:Cu=1:2:3) to the repeating unit of PDAA at pH 8 was poured into ethanol to precipitate the polymer-me tal chelate precursor. The precursor containing 1/2 equivalent molar a mount of metal ions was calcined at 880 degrees C for 10 h, sintered a t 920 degrees C for 2 h, and annealed at 600 degrees C for 5 h. The pr oduct exhibited a pure superconducting orthorhombic phase. However, th e precursor containing 1/4 equivalent molar amount of metal ions gave a mixture of orthorhombic and tetragonal phases under the same conditi ons. The influence of a purification process for PDAA on the preparati on of YBCO was also examined. The electrical resistance and susceptibi lity of the YBCO sample prepared by optimum conditions were measured. The sintered sample showed superconductivity with T-c (onset) at 93 K and T-c (end) at 91 K. The narrow superconducting transition demonstra ted here is attributed to the high purity and homogeneity of the sampl e prepared from optimized polymer chelate precursor technique.