Abstract

YBa_2Cu_3O_7-y (Y123) powders for the fabrication of bulk superconductors were synthesized by the powder reaction method using Y_2O_3 (99.9% purity), BaCO_3 (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 880°C-930°C 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 Y_2O_3 + 1 wt.% CeO_2, Y_1.5Ba_2Cu_3O_x (Y1.5)) were used as raw powders for the fabrication of poly-grain or single grain superconductors. The superconducting transition temperature (T_c,onset) of the sintered Y123 sample was 91 K and the transition width was as large as 11 K, whereas the T_c,onset of the melt-grown Y1.5 sample was 90.5 K and the transition width was 3.5 K. The critical current density (J_c) at 77 K and 0 T of the sintered Y123 was 700 A/cm2, whereas the J_c of the top-seeded melt growth (TSMG) processed Y1.5 sample was 3.2times104;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.

• Keywords: Oxide superconductors;Powder reaction;Bulk;Seed growth;Superconducting propert;