1 College of Mathematics and Physics, Shanghai University of Electric Power, Shanghai 201306, China 2 State Key Laboratory of Space Power Technology, Shanghai Institute of Space Power-Sources, Shanghai 200245, China 3 Laboratory of Applied Physics, Tokyo University of Marine Science and Technology, Tokyo 135-8533, Japan
Abstract: Alarge-sized GdBa2Cu3O7-δ (GdBCO) bulk superconductor with high performance, which is 32 mm in diameter and 13 mm in thickness, has been successfully fabricated by the top-hot-seeded melt-texture growth process in air. The YBa2Cu3O7-δ (Y123) is chosen as the liquid phase source, which can effectively avoid the leakage of the liquid phase during the crystal growth, ultimately leading to the performance improvement of the GdBCO bulk superconductor. Both superconducting properties and microstructure of the bulk have been investigated. It can be found that the superconducting transition temperature (TC) keeps above 94 K, and the maximum trapped magnetic flux density (Btrap) of the bulk is 0.29 T. The highest critical current density (JC) of 5.29×104 A/cm2 is obtained in the B2 specimen near the edge far from the surface of the bulk at 77 K in self field, which can be explained by the enrichment of the Gd2BaCuO5 (Gd211) particles. In the region close to the surface of the bulk, the pinning centers are mainly provided by the oxygen vacancies due to the insufficient liquid phase source. These oxygen vacancies highly aggregate under the seed and its diffusion rate decreases with the increase of the distance from the center during crystal growth, which results in a higher JC of the C1 specimen under the seed than JC of the B1 specimen near the edge. In comparison, in the region far from the surface of the bulk, the pinning centers are mainly provided by the Gd2BaCuO5 (Gd211) particles due to the sufficient liquid phase source. Owing to a large number of Gd211 particles as the effective pinning centers in the whole region far from the surface of the bulk, the JC of the C2 specimen under the seed is close to that of the B2 specimen near the edge. Moreover, the JC of both C2 and B2 specimens have been improved in intermediate and high fields because of the substitution of Ba2+ by Gd3+, which is vitally important for the engineering applications of the bulk superconductors.
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2022, Vol. 36 
