Preparation of pure superconductors from polymer chelate YBa2Cu3O7-x precursors using poly[(N, N-dicarboxymethyl)allylamine

Abstract

Bulk Yba2Cu3O7-x (YBCO) was prepared by a polymer chelate precursor method using poly[(N,N-dicarboxymethyl)allylamine] (PDAA) as a chelating polymer. An aqueous solution containing PDAA and 1/2 or 1/4 equivalent 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-metal chelate precursor. The precursor containing 1/2 equivalent molar amount of metal ions was calcined at 880°C for 10 h, sintered at 920°C for 2 h, and annealed at 600°C for 5 h. The product exhibited a pure superconducting orthorhombic phase. However, the precursor containing 1/4 equivalent molar amount of metal ions gave a mixture of orthorhombic and tetragonal phases under the same conditions. The influence of a purification process for PDAA on the preparation of YBCO was also examined. The electrical resistance and susceptibility of the YBCO sample prepared by optimum conditions were measured. The sintered sample showed superconductivity with Tc (onset) at 93 K and Tc (end) at 91 K. The narrow superconducting transition demonstrated here is attributed to the high purity and homogeneity of the sample prepared from optimized polymer chelate precursor technique.