Fabrication and characterisation of large-grain YBa2Cu3O7 superconductors by seeded melt texturing

In this work, we investigate the fabrication and characterisation of YBCO single grain monoliths using a seeding melt growth technique. It was found that there exits a narrow temperature-composition window for the stable growth of single grain monoliths. Addition of platinum has the beneficial role of refining the Y211 particles size while remaining inert to Y123 matrix by forming a Pt-containing secondary phase. Pellets of diameter up to 3 cm were fabricated under isothermal slow cooling condition. Neutron scattering and field mapping show their single grain nature, in spite of the existence of low-angle grain boundaries and slightly misoriented grains. Small size samples exhibit high critical current densities, either from magnetic measurement or from direct transport measurement, while J(c) are reduced three- to four- fold in large bulk pellets. It is believed that main limitations for levitation forces in these pellets are oxygen inhomogeneities and cracks due to oxygen diffusion induced stresses. (C) 1998 Elsevier Science B.V. All rights reserved.