FABRICATION AND CHARACTERIZATION OF LARGE-GRAIN YBA2CU3O7 SUPERCONDUCTORS BY SEEDED MELT TEXTURING

In this work, we investigate the fabrication and characterisation of Y BCO single grain monoliths using a seeding melt growth technique. It w as 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 remainin g inert to Y123 matrix by forming a Pt-containing secondary phase. Pel lets of diameter up to 3 cm were fabricated under isothermal slow cool ing 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 criti cal 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 levitati on forces in these pellets are oxygen inhomogeneities and cracks due t o oxygen diffusion induced stresses. (C) 1998 Elsevier Science B.V. Al l rights reserved.