Texture development in Bi2Sr2CaCu2Oy current leads

Isothermal melt processing has been used to partially texture bulk samples of Bi2Sr2CaCu2Oy (Bi-2212). Anisotropic growth of Bi-2212 occurs from the partial melt in the presence of an oxygen gradient. The orientational preference is for the c-axis of the Bi-2212 grains to align perpendicular to the oxygen gradient. However, the one-dimensional nature of the oxygen gradient does not result in uniaxial texture. Incorporation of a set of silver plates aligned parallel to the oxygen gradient was found to provide the second texturing mechanism needed to improve grain-to-grain alignment and start the development of uniaxial texture within bulk Bi-2212 bars. Texture within the bars was investigated by anisotropy measurements of the critical current in applied magnetic fields and compared to previously published results on Bi-2212 films. At liquid nitrogen temperatures, the presence of partial texture in the bulk Bi-2212 bars was found to increase the performance in applied fields by a factor of two relative to the untextured current leads. However, comparison of the bulk-textured bar to the Bi-2212 film revealed that the bar has a significantly larger spread in grain orientations than does the 50 mu m thick film. (C) 1998 Elsevier Science B.V.