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pp.569-574
Large single grain Gd1.5Ba2Cu3O7-y (Gd1.5) bulk superconductors were fabricated by a top-seeded melt growth (TSMG) process using an NdBa2Cu3O7-y seed. The seeded Gd1.5 powder compacts with a diameter of 50 mm were subjected to the heating cycles of a TSMG process. After the TSMG process, the diameter of the single grain Gd1.5 compact was reduced to 43 mm owing to the volume contraction during the heat treatment. The superconducting transition temperature (Tc) of the top surface of the single grain Gd1.5 sample was as high as 93.5 K. The critical current densities (Jcs) at 77 K and 1T and 1.5 T were in ranges of 25,200-43,900 A/cm2 and 10,000-23,000 A/cm2, respectively. The maximum attractive force at 77 K of the sample field-cooled using an Nd-B-Fe permanent magnet (surface magnetic field of 0. 527 T) was 108.3 N; the maximum repulsive force of the zero field-cooled sample was 262 N. The magnetic flux density of the sample field-cooled at 77 K was 0.311T, which is approximately 85% of the applied magnetic field of 0.375 T. Microstructure investigation showed that many Gd2BaCuO5 (Gd211) particles of a few μm in size, which are flux pinning sites of Gd123, were trapped within the GdBa2Cu3O7-y (Gd123) grain; unreacted Ba3Cu5O8 liquid and Gd211 particles were present near the edge regions of the single grain Gd1.5 bulk compact.
