Artificial Hole Effect of YBa2Cu3O7–y Superconducting Bulk

Previous studies showed that the superconducting properties of YBCO bulk could be improved by providing a path for oxygen diffusion into the crystal, made by drilling artificial holes in the bulk. Proposed in this paper is a process to provide artificial holes by forming holes by molding. The gas formed from chemical reactions inside the superconducting bulk cannot escape because of highly viscose surrounding materials with high melting points. When holes are provided in the YBCO superconductor bulk, the holes can act as paths for the gas to escape, which would result in the reduction of porosity. The levitation force of the superconductor due to the Meisner Effect was measured in the cooled condition without magnetism. The number and size of pores in the superconductor decreased as the surface area provided by the artificial holes in the superconducting bulk increased. Both the magnetic levitation force and the trapped magnetic force measured at 77 K of the specimen with a 2.5 mm diameter hole were 135 N and 344 mT respectively, which were 16.8% higher than those of the specimen without a hole. The reasons for the higher magnetic levitation force of the specimen with a hole seem that the single crystalline grain does not get disconnected because the density of porosity decreased due to the larger surface area, and that the efficiency of annealing improved because the area for oxygen to diffuse increased during annealing.