분말 반응법에 의한 YBa2Cu3O7-y 합성과 벌크 초전도체의 제조

Abstract

YBa2Cu3O7-y (Y123) powders for the fabrication of bulk superconductors were synthesized by the powder reaction method using Y2O3 (99.9% purity), BaCO3 (99.75%) and CuO (99.9%) powders. The raw powders were weighed to the cation ratio of Y:Ba:Cu=1:2:3, mixed and calcined at 880oC-930oC in air with intermediate repeated crushing steps. It was found that the formation of Y123 powder was more sensitive to reaction temperature than reaction time. The calcined Y123 powder and a mixture of (Y123 + 0.25 mole Y2O3 + 1 wt.% CeO2, Y1.5Ba2Cu3Ox (Y1.5))were used as raw powders for the fabrication of poly-grain or single grain superconductors. The superconducting transition temperature (Tc,onset) of the sintered Y123 sample was 91 K and the transition width was as large as 11 K,whereas the Tc,onset of the melt-grown Y1.5 sample was 90.5 K and the transition width was 3.5 K. The critical current density (Jc) at 77 K and 0 T of the sintered Y123 was 700 A/cm2, whereas the Jc of the top-seeded melt growth (TSMG) processed Y1.5 sample was 3.2 × 104 A/cm2. The magnetic flux density (H) at 77 K of the TSMG-processed Y123 and Y1.5 sample showed the 0.53 kG and 2.45 kG, respectively, which are 15% and 71% of the applied magnetic field of 3.5 kG. The high H value of the TSMG-processed Y1.5 sample is attributed to the formation of the larger superconducting grain with fine Y211 dispersion.